57 files changed, 1834 insertions, 719 deletions

diff --git a/crates/ra_assists/src/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
index 83dd270c6..871671de2 100644
--- a/crates/ra_assists/src/assist_ctx.rs
+++ b/crates/ra_assists/src/assist_ctx.rs
@@ -1,8 +1,11 @@
 //! This module defines `AssistCtx` -- the API surface that is exposed to assists.
 use hir::Semantics;
-use ra_db::FileRange;
+use ra_db::{FileId, FileRange};
 use ra_fmt::{leading_indent, reindent};
-use ra_ide_db::RootDatabase;
+use ra_ide_db::{
+    source_change::{SingleFileChange, SourceChange},
+    RootDatabase,
+};
 use ra_syntax::{
     algo::{self, find_covering_element, find_node_at_offset, SyntaxRewriter},
     AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken, TextRange, TextSize,
@@ -10,7 +13,7 @@ use ra_syntax::{
 };
 use ra_text_edit::TextEditBuilder;
 
-use crate::{AssistAction, AssistFile, AssistId, AssistLabel, GroupLabel, ResolvedAssist};
+use crate::{AssistId, AssistLabel, GroupLabel, ResolvedAssist};
 
 #[derive(Clone, Debug)]
 pub(crate) struct Assist(pub(crate) Vec<AssistInfo>);
@@ -19,16 +22,16 @@ pub(crate) struct Assist(pub(crate) Vec<AssistInfo>);
 pub(crate) struct AssistInfo {
     pub(crate) label: AssistLabel,
     pub(crate) group_label: Option<GroupLabel>,
-    pub(crate) action: Option<AssistAction>,
+    pub(crate) source_change: Option<SourceChange>,
 }
 
 impl AssistInfo {
     fn new(label: AssistLabel) -> AssistInfo {
-        AssistInfo { label, group_label: None, action: None }
+        AssistInfo { label, group_label: None, source_change: None }
     }
 
-    fn resolved(self, action: AssistAction) -> AssistInfo {
-        AssistInfo { action: Some(action), ..self }
+    fn resolved(self, source_change: SourceChange) -> AssistInfo {
+        AssistInfo { source_change: Some(source_change), ..self }
     }
 
     fn with_group(self, group_label: GroupLabel) -> AssistInfo {
@@ -37,7 +40,7 @@ impl AssistInfo {
 
     pub(crate) fn into_resolved(self) -> Option<ResolvedAssist> {
         let label = self.label;
-        self.action.map(|action| ResolvedAssist { label, action })
+        self.source_change.map(|source_change| ResolvedAssist { label, source_change })
     }
 }
 
@@ -94,18 +97,19 @@ impl<'a> AssistCtx<'a> {
         self,
         id: AssistId,
         label: impl Into<String>,
+        target: TextRange,
         f: impl FnOnce(&mut ActionBuilder),
     ) -> Option<Assist> {
-        let label = AssistLabel::new(id, label.into(), None);
-
+        let label = AssistLabel::new(id, label.into(), None, target);
+        let change_label = label.label.clone();
         let mut info = AssistInfo::new(label);
         if self.should_compute_edit {
-            let action = {
+            let source_change = {
                 let mut edit = ActionBuilder::new(&self);
                 f(&mut edit);
-                edit.build()
+                edit.build(change_label)
             };
-            info = info.resolved(action)
+            info = info.resolved(source_change)
         };
 
         Some(Assist(vec![info]))
@@ -152,18 +156,19 @@ impl<'a> AssistGroup<'a> {
         &mut self,
         id: AssistId,
         label: impl Into<String>,
+        target: TextRange,
         f: impl FnOnce(&mut ActionBuilder),
     ) {
-        let label = AssistLabel::new(id, label.into(), Some(self.group.clone()));
-
+        let label = AssistLabel::new(id, label.into(), Some(self.group.clone()), target);
+        let change_label = label.label.clone();
         let mut info = AssistInfo::new(label).with_group(self.group.clone());
         if self.ctx.should_compute_edit {
-            let action = {
+            let source_change = {
                 let mut edit = ActionBuilder::new(&self.ctx);
                 f(&mut edit);
-                edit.build()
+                edit.build(change_label)
             };
-            info = info.resolved(action)
+            info = info.resolved(source_change)
         };
 
         self.assists.push(info)
@@ -181,8 +186,7 @@ impl<'a> AssistGroup<'a> {
 pub(crate) struct ActionBuilder<'a, 'b> {
     edit: TextEditBuilder,
     cursor_position: Option<TextSize>,
-    target: Option<TextRange>,
-    file: AssistFile,
+    file: FileId,
     ctx: &'a AssistCtx<'b>,
 }
 
@@ -191,8 +195,7 @@ impl<'a, 'b> ActionBuilder<'a, 'b> {
         Self {
             edit: TextEditBuilder::default(),
             cursor_position: None,
-            target: None,
-            file: AssistFile::default(),
+            file: ctx.frange.file_id,
             ctx,
         }
     }
@@ -237,14 +240,6 @@ impl<'a, 'b> ActionBuilder<'a, 'b> {
         self.cursor_position = Some(offset)
     }
 
-    /// Specify that the assist should be active withing the `target` range.
-    ///
-    /// Target ranges are used to sort assists: the smaller the target range,
-    /// the more specific assist is, and so it should be sorted first.
-    pub(crate) fn target(&mut self, target: TextRange) {
-        self.target = Some(target)
-    }
-
     /// Get access to the raw `TextEditBuilder`.
     pub(crate) fn text_edit_builder(&mut self) -> &mut TextEditBuilder {
         &mut self.edit
@@ -259,16 +254,16 @@ impl<'a, 'b> ActionBuilder<'a, 'b> {
         algo::diff(&node, &new).into_text_edit(&mut self.edit)
     }
 
-    pub(crate) fn set_file(&mut self, assist_file: AssistFile) {
-        self.file = assist_file
+    pub(crate) fn set_file(&mut self, assist_file: FileId) {
+        self.file = assist_file;
     }
 
-    fn build(self) -> AssistAction {
-        AssistAction {
-            edit: self.edit.finish(),
-            cursor_position: self.cursor_position,
-            target: self.target,
-            file: self.file,
+    fn build(self, change_label: String) -> SourceChange {
+        let edit = self.edit.finish();
+        if edit.is_empty() && self.cursor_position.is_none() {
+            panic!("Only call `add_assist` if the assist can be applied")
         }
+        SingleFileChange { label: change_label, edit, cursor_position: self.cursor_position }
+            .into_source_change(self.file)
     }
 }
diff --git a/crates/ra_assists/src/doc_tests.rs b/crates/ra_assists/src/doc_tests.rs
deleted file mode 100644
index f627f31dc..000000000
--- a/crates/ra_assists/src/doc_tests.rs
+++ /dev/null
@@ -1,39 +0,0 @@
-//! Each assist definition has a special comment, which specifies docs and
-//! example.
-//!
-//! We collect all the example and write the as tests in this module.
-
-mod generated;
-
-use ra_db::FileRange;
-use test_utils::{assert_eq_text, extract_range_or_offset};
-
-use crate::resolved_assists;
-
-fn check(assist_id: &str, before: &str, after: &str) {
-    let (selection, before) = extract_range_or_offset(before);
-    let (db, file_id) = crate::helpers::with_single_file(&before);
-    let frange = FileRange { file_id, range: selection.into() };
-
-    let assist = resolved_assists(&db, frange)
-        .into_iter()
-        .find(|assist| assist.label.id.0 == assist_id)
-        .unwrap_or_else(|| {
-            panic!(
-                "\n\nAssist is not applicable: {}\nAvailable assists: {}",
-                assist_id,
-                resolved_assists(&db, frange)
-                    .into_iter()
-                    .map(|assist| assist.label.id.0)
-                    .collect::<Vec<_>>()
-                    .join(", ")
-            )
-        });
-
-    let actual = {
-        let mut actual = before.clone();
-        assist.action.edit.apply(&mut actual);
-        actual
-    };
-    assert_eq_text!(after, &actual);
-}
diff --git a/crates/ra_assists/src/handlers/add_custom_impl.rs b/crates/ra_assists/src/handlers/add_custom_impl.rs
index 4ea26a550..869d4dc04 100644
--- a/crates/ra_assists/src/handlers/add_custom_impl.rs
+++ b/crates/ra_assists/src/handlers/add_custom_impl.rs
@@ -48,9 +48,8 @@ pub(crate) fn add_custom_impl(ctx: AssistCtx) -> Option<Assist> {
     let label =
         format!("Add custom impl '{}' for '{}'", trait_token.text().as_str(), annotated_name);
 
-    ctx.add_assist(AssistId("add_custom_impl"), label, |edit| {
-        edit.target(attr.syntax().text_range());
-
+    let target = attr.syntax().text_range();
+    ctx.add_assist(AssistId("add_custom_impl"), label, target, |edit| {
         let new_attr_input = input
             .syntax()
             .descendants_with_tokens()
@@ -95,7 +94,7 @@ pub(crate) fn add_custom_impl(ctx: AssistCtx) -> Option<Assist> {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/add_derive.rs b/crates/ra_assists/src/handlers/add_derive.rs
index 6254eb7c4..2a6bb1cae 100644
--- a/crates/ra_assists/src/handlers/add_derive.rs
+++ b/crates/ra_assists/src/handlers/add_derive.rs
@@ -27,7 +27,8 @@ use crate::{Assist, AssistCtx, AssistId};
 pub(crate) fn add_derive(ctx: AssistCtx) -> Option<Assist> {
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let node_start = derive_insertion_offset(&nominal)?;
-    ctx.add_assist(AssistId("add_derive"), "Add `#[derive]`", |edit| {
+    let target = nominal.syntax().text_range();
+    ctx.add_assist(AssistId("add_derive"), "Add `#[derive]`", target, |edit| {
         let derive_attr = nominal
             .attrs()
             .filter_map(|x| x.as_simple_call())
@@ -41,7 +42,6 @@ pub(crate) fn add_derive(ctx: AssistCtx) -> Option<Assist> {
             }
             Some(tt) => tt.syntax().text_range().end() - TextSize::of(')'),
         };
-        edit.target(nominal.syntax().text_range());
         edit.set_cursor(offset)
     })
 }
@@ -58,7 +58,7 @@ fn derive_insertion_offset(nominal: &ast::NominalDef) -> Option<TextSize> {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::helpers::{check_assist, check_assist_target};
+    use crate::tests::{check_assist, check_assist_target};
 
     #[test]
     fn add_derive_new() {
diff --git a/crates/ra_assists/src/handlers/add_explicit_type.rs b/crates/ra_assists/src/handlers/add_explicit_type.rs
index bc313782b..a59ec16b2 100644
--- a/crates/ra_assists/src/handlers/add_explicit_type.rs
+++ b/crates/ra_assists/src/handlers/add_explicit_type.rs
@@ -62,8 +62,8 @@ pub(crate) fn add_explicit_type(ctx: AssistCtx) -> Option<Assist> {
     ctx.add_assist(
         AssistId("add_explicit_type"),
         format!("Insert explicit type '{}'", new_type_string),
+        pat_range,
         |edit| {
-            edit.target(pat_range);
             if let Some(ascribed_ty) = ascribed_ty {
                 edit.replace(ascribed_ty.syntax().text_range(), new_type_string);
             } else {
@@ -77,7 +77,7 @@ pub(crate) fn add_explicit_type(ctx: AssistCtx) -> Option<Assist> {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn add_explicit_type_target() {
diff --git a/crates/ra_assists/src/handlers/add_from_impl_for_enum.rs b/crates/ra_assists/src/handlers/add_from_impl_for_enum.rs
index 49deb6701..81deb3dfa 100644
--- a/crates/ra_assists/src/handlers/add_from_impl_for_enum.rs
+++ b/crates/ra_assists/src/handlers/add_from_impl_for_enum.rs
@@ -47,9 +47,11 @@ pub(crate) fn add_from_impl_for_enum(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
+    let target = variant.syntax().text_range();
     ctx.add_assist(
         AssistId("add_from_impl_for_enum"),
         "Add From impl for this enum variant",
+        target,
         |edit| {
             let start_offset = variant.parent_enum().syntax().text_range().end();
             let mut buf = String::new();
@@ -97,7 +99,7 @@ fn existing_from_impl(
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
     use test_utils::covers;
 
     #[test]
diff --git a/crates/ra_assists/src/handlers/add_function.rs b/crates/ra_assists/src/handlers/add_function.rs
index 6c7456579..278079665 100644
--- a/crates/ra_assists/src/handlers/add_function.rs
+++ b/crates/ra_assists/src/handlers/add_function.rs
@@ -3,9 +3,10 @@ use ra_syntax::{
     SyntaxKind, SyntaxNode, TextSize,
 };
 
-use crate::{Assist, AssistCtx, AssistFile, AssistId};
+use crate::{Assist, AssistCtx, AssistId};
 use ast::{edit::IndentLevel, ArgListOwner, ModuleItemOwner};
 use hir::HirDisplay;
+use ra_db::FileId;
 use rustc_hash::{FxHashMap, FxHashSet};
 
 // Assist: add_function
@@ -57,14 +58,12 @@ pub(crate) fn add_function(ctx: AssistCtx) -> Option<Assist> {
 
     let function_builder = FunctionBuilder::from_call(&ctx, &call, &path, target_module)?;
 
-    ctx.add_assist(AssistId("add_function"), "Add function", |edit| {
-        edit.target(call.syntax().text_range());
-
-        if let Some(function_template) = function_builder.render() {
-            edit.set_file(function_template.file);
-            edit.set_cursor(function_template.cursor_offset);
-            edit.insert(function_template.insert_offset, function_template.fn_def.to_string());
-        }
+    let target = call.syntax().text_range();
+    ctx.add_assist(AssistId("add_function"), "Add function", target, |edit| {
+        let function_template = function_builder.render();
+        edit.set_file(function_template.file);
+        edit.set_cursor(function_template.cursor_offset);
+        edit.insert(function_template.insert_offset, function_template.fn_def.to_string());
     })
 }
 
@@ -72,7 +71,7 @@ struct FunctionTemplate {
     insert_offset: TextSize,
     cursor_offset: TextSize,
     fn_def: ast::SourceFile,
-    file: AssistFile,
+    file: FileId,
 }
 
 struct FunctionBuilder {
@@ -80,7 +79,7 @@ struct FunctionBuilder {
     fn_name: ast::Name,
     type_params: Option<ast::TypeParamList>,
     params: ast::ParamList,
-    file: AssistFile,
+    file: FileId,
     needs_pub: bool,
 }
 
@@ -94,7 +93,7 @@ impl FunctionBuilder {
         target_module: Option<hir::InFile<hir::ModuleSource>>,
     ) -> Option<Self> {
         let needs_pub = target_module.is_some();
-        let mut file = AssistFile::default();
+        let mut file = ctx.frange.file_id;
         let target = if let Some(target_module) = target_module {
             let (in_file, target) = next_space_for_fn_in_module(ctx.sema.db, target_module)?;
             file = in_file;
@@ -107,7 +106,7 @@ impl FunctionBuilder {
         Some(Self { target, fn_name, type_params, params, file, needs_pub })
     }
 
-    fn render(self) -> Option<FunctionTemplate> {
+    fn render(self) -> FunctionTemplate {
         let placeholder_expr = ast::make::expr_todo();
         let fn_body = ast::make::block_expr(vec![], Some(placeholder_expr));
         let mut fn_def = ast::make::fn_def(self.fn_name, self.type_params, self.params, fn_body);
@@ -133,15 +132,11 @@ impl FunctionBuilder {
             }
         };
 
-        let cursor_offset_from_fn_start = fn_def
-            .syntax()
-            .descendants()
-            .find_map(ast::MacroCall::cast)?
-            .syntax()
-            .text_range()
-            .start();
+        let placeholder_expr =
+            fn_def.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
+        let cursor_offset_from_fn_start = placeholder_expr.syntax().text_range().start();
         let cursor_offset = insert_offset + cursor_offset_from_fn_start;
-        Some(FunctionTemplate { insert_offset, cursor_offset, fn_def, file: self.file })
+        FunctionTemplate { insert_offset, cursor_offset, fn_def, file: self.file }
     }
 }
 
@@ -259,9 +254,8 @@ fn next_space_for_fn_after_call_site(expr: &ast::CallExpr) -> Option<GeneratedFu
 fn next_space_for_fn_in_module(
     db: &dyn hir::db::AstDatabase,
     module: hir::InFile<hir::ModuleSource>,
-) -> Option<(AssistFile, GeneratedFunctionTarget)> {
+) -> Option<(FileId, GeneratedFunctionTarget)> {
     let file = module.file_id.original_file(db);
-    let assist_file = AssistFile::TargetFile(file);
     let assist_item = match module.value {
         hir::ModuleSource::SourceFile(it) => {
             if let Some(last_item) = it.items().last() {
@@ -278,12 +272,12 @@ fn next_space_for_fn_in_module(
             }
         }
     };
-    Some((assist_file, assist_item))
+    Some((file, assist_item))
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/add_impl.rs b/crates/ra_assists/src/handlers/add_impl.rs
index d26f8b93d..557344ebb 100644
--- a/crates/ra_assists/src/handlers/add_impl.rs
+++ b/crates/ra_assists/src/handlers/add_impl.rs
@@ -28,39 +28,46 @@ use crate::{Assist, AssistCtx, AssistId};
 pub(crate) fn add_impl(ctx: AssistCtx) -> Option<Assist> {
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let name = nominal.name()?;
-    ctx.add_assist(AssistId("add_impl"), format!("Implement {}", name.text().as_str()), |edit| {
-        edit.target(nominal.syntax().text_range());
-        let type_params = nominal.type_param_list();
-        let start_offset = nominal.syntax().text_range().end();
-        let mut buf = String::new();
-        buf.push_str("\n\nimpl");
-        if let Some(type_params) = &type_params {
-            format_to!(buf, "{}", type_params.syntax());
-        }
-        buf.push_str(" ");
-        buf.push_str(name.text().as_str());
-        if let Some(type_params) = type_params {
-            let lifetime_params = type_params
-                .lifetime_params()
-                .filter_map(|it| it.lifetime_token())
-                .map(|it| it.text().clone());
-            let type_params =
-                type_params.type_params().filter_map(|it| it.name()).map(|it| it.text().clone());
+    let target = nominal.syntax().text_range();
+    ctx.add_assist(
+        AssistId("add_impl"),
+        format!("Implement {}", name.text().as_str()),
+        target,
+        |edit| {
+            let type_params = nominal.type_param_list();
+            let start_offset = nominal.syntax().text_range().end();
+            let mut buf = String::new();
+            buf.push_str("\n\nimpl");
+            if let Some(type_params) = &type_params {
+                format_to!(buf, "{}", type_params.syntax());
+            }
+            buf.push_str(" ");
+            buf.push_str(name.text().as_str());
+            if let Some(type_params) = type_params {
+                let lifetime_params = type_params
+                    .lifetime_params()
+                    .filter_map(|it| it.lifetime_token())
+                    .map(|it| it.text().clone());
+                let type_params = type_params
+                    .type_params()
+                    .filter_map(|it| it.name())
+                    .map(|it| it.text().clone());
 
-            let generic_params = lifetime_params.chain(type_params).sep_by(", ");
-            format_to!(buf, "<{}>", generic_params)
-        }
-        buf.push_str(" {\n");
-        edit.set_cursor(start_offset + TextSize::of(&buf));
-        buf.push_str("\n}");
-        edit.insert(start_offset, buf);
-    })
+                let generic_params = lifetime_params.chain(type_params).sep_by(", ");
+                format_to!(buf, "<{}>", generic_params)
+            }
+            buf.push_str(" {\n");
+            edit.set_cursor(start_offset + TextSize::of(&buf));
+            buf.push_str("\n}");
+            edit.insert(start_offset, buf);
+        },
+    )
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::helpers::{check_assist, check_assist_target};
+    use crate::tests::{check_assist, check_assist_target};
 
     #[test]
     fn test_add_impl() {
diff --git a/crates/ra_assists/src/handlers/add_missing_impl_members.rs b/crates/ra_assists/src/handlers/add_missing_impl_members.rs
index e47feda71..7df786590 100644
--- a/crates/ra_assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/handlers/add_missing_impl_members.rs
@@ -107,10 +107,10 @@ fn add_missing_impl_members_inner(
     label: &'static str,
 ) -> Option<Assist> {
     let _p = ra_prof::profile("add_missing_impl_members_inner");
-    let impl_node = ctx.find_node_at_offset::<ast::ImplDef>()?;
-    let impl_item_list = impl_node.item_list()?;
+    let impl_def = ctx.find_node_at_offset::<ast::ImplDef>()?;
+    let impl_item_list = impl_def.item_list()?;
 
-    let trait_ = resolve_target_trait(&ctx.sema, &impl_node)?;
+    let trait_ = resolve_target_trait(&ctx.sema, &impl_def)?;
 
     let def_name = |item: &ast::AssocItem| -> Option<SmolStr> {
         match item {
@@ -121,7 +121,7 @@ fn add_missing_impl_members_inner(
         .map(|it| it.text().clone())
     };
 
-    let missing_items = get_missing_assoc_items(&ctx.sema, &impl_node)
+    let missing_items = get_missing_assoc_items(&ctx.sema, &impl_def)
         .iter()
         .map(|i| match i {
             hir::AssocItem::Function(i) => ast::AssocItem::FnDef(i.source(ctx.db).value),
@@ -143,13 +143,13 @@ fn add_missing_impl_members_inner(
     }
 
     let sema = ctx.sema;
-
-    ctx.add_assist(AssistId(assist_id), label, |edit| {
+    let target = impl_def.syntax().text_range();
+    ctx.add_assist(AssistId(assist_id), label, target, |edit| {
         let n_existing_items = impl_item_list.assoc_items().count();
         let source_scope = sema.scope_for_def(trait_);
         let target_scope = sema.scope(impl_item_list.syntax());
         let ast_transform = QualifyPaths::new(&target_scope, &source_scope)
-            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_node));
+            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def));
         let items = missing_items
             .into_iter()
             .map(|it| ast_transform::apply(&*ast_transform, it))
@@ -181,7 +181,7 @@ fn add_body(fn_def: ast::FnDef) -> ast::FnDef {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/add_new.rs b/crates/ra_assists/src/handlers/add_new.rs
index e8a36c7de..1c3f8435a 100644
--- a/crates/ra_assists/src/handlers/add_new.rs
+++ b/crates/ra_assists/src/handlers/add_new.rs
@@ -41,9 +41,8 @@ pub(crate) fn add_new(ctx: AssistCtx) -> Option<Assist> {
     // Return early if we've found an existing new fn
     let impl_def = find_struct_impl(&ctx, &strukt)?;
 
-    ctx.add_assist(AssistId("add_new"), "Add default constructor", |edit| {
-        edit.target(strukt.syntax().text_range());
-
+    let target = strukt.syntax().text_range();
+    ctx.add_assist(AssistId("add_new"), "Add default constructor", target, |edit| {
         let mut buf = String::with_capacity(512);
 
         if impl_def.is_some() {
@@ -178,7 +177,7 @@ fn has_new_fn(imp: &ast::ImplDef) -> bool {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/apply_demorgan.rs b/crates/ra_assists/src/handlers/apply_demorgan.rs
index 260b9e073..a5b26e5b9 100644
--- a/crates/ra_assists/src/handlers/apply_demorgan.rs
+++ b/crates/ra_assists/src/handlers/apply_demorgan.rs
@@ -39,8 +39,7 @@ pub(crate) fn apply_demorgan(ctx: AssistCtx) -> Option<Assist> {
     let rhs_range = rhs.syntax().text_range();
     let not_rhs = invert_boolean_expression(rhs);
 
-    ctx.add_assist(AssistId("apply_demorgan"), "Apply De Morgan's law", |edit| {
-        edit.target(op_range);
+    ctx.add_assist(AssistId("apply_demorgan"), "Apply De Morgan's law", op_range, |edit| {
         edit.replace(op_range, opposite_op);
         edit.replace(lhs_range, format!("!({}", not_lhs.syntax().text()));
         edit.replace(rhs_range, format!("{})", not_rhs.syntax().text()));
@@ -60,7 +59,7 @@ fn opposite_logic_op(kind: ast::BinOp) -> Option<&'static str> {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     #[test]
     fn demorgan_turns_and_into_or() {
diff --git a/crates/ra_assists/src/handlers/auto_import.rs b/crates/ra_assists/src/handlers/auto_import.rs
index db6c4d2fa..2224b9714 100644
--- a/crates/ra_assists/src/handlers/auto_import.rs
+++ b/crates/ra_assists/src/handlers/auto_import.rs
@@ -48,8 +48,7 @@ pub(crate) fn auto_import(ctx: AssistCtx) -> Option<Assist> {
     let range = ctx.sema.original_range(&auto_import_assets.syntax_under_caret).range;
     let mut group = ctx.add_assist_group(auto_import_assets.get_import_group_message());
     for import in proposed_imports {
-        group.add_assist(AssistId("auto_import"), format!("Import `{}`", &import), |edit| {
-            edit.target(range);
+        group.add_assist(AssistId("auto_import"), format!("Import `{}`", &import), range, |edit| {
             insert_use_statement(&auto_import_assets.syntax_under_caret, &import, edit);
         });
     }
@@ -277,7 +276,7 @@ impl ImportCandidate {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn applicable_when_found_an_import() {
diff --git a/crates/ra_assists/src/handlers/change_return_type_to_result.rs b/crates/ra_assists/src/handlers/change_return_type_to_result.rs
new file mode 100644
index 000000000..1e8d986cd
--- /dev/null
+++ b/crates/ra_assists/src/handlers/change_return_type_to_result.rs
@@ -0,0 +1,971 @@
+use ra_syntax::{
+    ast, AstNode,
+    SyntaxKind::{COMMENT, WHITESPACE},
+    SyntaxNode, TextSize,
+};
+
+use crate::{Assist, AssistCtx, AssistId};
+use ast::{BlockExpr, Expr, LoopBodyOwner};
+
+// Assist: change_return_type_to_result
+//
+// Change the function's return type to Result.
+//
+// ```
+// fn foo() -> i32<|> { 42i32 }
+// ```
+// ->
+// ```
+// fn foo() -> Result<i32, > { Ok(42i32) }
+// ```
+pub(crate) fn change_return_type_to_result(ctx: AssistCtx) -> Option<Assist> {
+    let fn_def = ctx.find_node_at_offset::<ast::FnDef>();
+    let fn_def = &mut fn_def?;
+    let ret_type = &fn_def.ret_type()?.type_ref()?;
+    if ret_type.syntax().text().to_string().starts_with("Result<") {
+        return None;
+    }
+
+    let block_expr = &fn_def.body()?;
+    let cursor_in_ret_type =
+        fn_def.ret_type()?.syntax().text_range().contains_range(ctx.frange.range);
+    if !cursor_in_ret_type {
+        return None;
+    }
+
+    ctx.add_assist(
+        AssistId("change_return_type_to_result"),
+        "Change return type to Result",
+        ret_type.syntax().text_range(),
+        |edit| {
+            let mut tail_return_expr_collector = TailReturnCollector::new();
+            tail_return_expr_collector.collect_jump_exprs(block_expr, false);
+            tail_return_expr_collector.collect_tail_exprs(block_expr);
+
+            for ret_expr_arg in tail_return_expr_collector.exprs_to_wrap {
+                edit.replace_node_and_indent(&ret_expr_arg, format!("Ok({})", ret_expr_arg));
+            }
+            edit.replace_node_and_indent(ret_type.syntax(), format!("Result<{}, >", ret_type));
+
+            if let Some(node_start) = result_insertion_offset(&ret_type) {
+                edit.set_cursor(node_start + TextSize::of(&format!("Result<{}, ", ret_type)));
+            }
+        },
+    )
+}
+
+struct TailReturnCollector {
+    exprs_to_wrap: Vec<SyntaxNode>,
+}
+
+impl TailReturnCollector {
+    fn new() -> Self {
+        Self { exprs_to_wrap: vec![] }
+    }
+    /// Collect all`return` expression
+    fn collect_jump_exprs(&mut self, block_expr: &BlockExpr, collect_break: bool) {
+        let statements = block_expr.statements();
+        for stmt in statements {
+            let expr = match &stmt {
+                ast::Stmt::ExprStmt(stmt) => stmt.expr(),
+                ast::Stmt::LetStmt(stmt) => stmt.initializer(),
+            };
+            if let Some(expr) = &expr {
+                self.handle_exprs(expr, collect_break);
+            }
+        }
+
+        // Browse tail expressions for each block
+        if let Some(expr) = block_expr.expr() {
+            if let Some(last_exprs) = get_tail_expr_from_block(&expr) {
+                for last_expr in last_exprs {
+                    let last_expr = match last_expr {
+                        NodeType::Node(expr) | NodeType::Leaf(expr) => expr,
+                    };
+
+                    if let Some(last_expr) = Expr::cast(last_expr.clone()) {
+                        self.handle_exprs(&last_expr, collect_break);
+                    } else if let Some(expr_stmt) = ast::Stmt::cast(last_expr) {
+                        let expr_stmt = match &expr_stmt {
+                            ast::Stmt::ExprStmt(stmt) => stmt.expr(),
+                            ast::Stmt::LetStmt(stmt) => stmt.initializer(),
+                        };
+                        if let Some(expr) = &expr_stmt {
+                            self.handle_exprs(expr, collect_break);
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn handle_exprs(&mut self, expr: &Expr, collect_break: bool) {
+        match expr {
+            Expr::BlockExpr(block_expr) => {
+                self.collect_jump_exprs(&block_expr, collect_break);
+            }
+            Expr::ReturnExpr(ret_expr) => {
+                if let Some(ret_expr_arg) = &ret_expr.expr() {
+                    self.exprs_to_wrap.push(ret_expr_arg.syntax().clone());
+                }
+            }
+            Expr::BreakExpr(break_expr) if collect_break => {
+                if let Some(break_expr_arg) = &break_expr.expr() {
+                    self.exprs_to_wrap.push(break_expr_arg.syntax().clone());
+                }
+            }
+            Expr::IfExpr(if_expr) => {
+                for block in if_expr.blocks() {
+                    self.collect_jump_exprs(&block, collect_break);
+                }
+            }
+            Expr::LoopExpr(loop_expr) => {
+                if let Some(block_expr) = loop_expr.loop_body() {
+                    self.collect_jump_exprs(&block_expr, collect_break);
+                }
+            }
+            Expr::ForExpr(for_expr) => {
+                if let Some(block_expr) = for_expr.loop_body() {
+                    self.collect_jump_exprs(&block_expr, collect_break);
+                }
+            }
+            Expr::WhileExpr(while_expr) => {
+                if let Some(block_expr) = while_expr.loop_body() {
+                    self.collect_jump_exprs(&block_expr, collect_break);
+                }
+            }
+            Expr::MatchExpr(match_expr) => {
+                if let Some(arm_list) = match_expr.match_arm_list() {
+                    arm_list.arms().filter_map(|match_arm| match_arm.expr()).for_each(|expr| {
+                        self.handle_exprs(&expr, collect_break);
+                    });
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn collect_tail_exprs(&mut self, block: &BlockExpr) {
+        if let Some(expr) = block.expr() {
+            self.handle_exprs(&expr, true);
+            self.fetch_tail_exprs(&expr);
+        }
+    }
+
+    fn fetch_tail_exprs(&mut self, expr: &Expr) {
+        if let Some(exprs) = get_tail_expr_from_block(expr) {
+            for node_type in &exprs {
+                match node_type {
+                    NodeType::Leaf(expr) => {
+                        self.exprs_to_wrap.push(expr.clone());
+                    }
+                    NodeType::Node(expr) => match &Expr::cast(expr.clone()) {
+                        Some(last_expr) => {
+                            self.fetch_tail_exprs(last_expr);
+                        }
+                        None => {
+                            self.exprs_to_wrap.push(expr.clone());
+                        }
+                    },
+                }
+            }
+        }
+    }
+}
+
+#[derive(Debug)]
+enum NodeType {
+    Leaf(SyntaxNode),
+    Node(SyntaxNode),
+}
+
+/// Get a tail expression inside a block
+fn get_tail_expr_from_block(expr: &Expr) -> Option<Vec<NodeType>> {
+    match expr {
+        Expr::IfExpr(if_expr) => {
+            let mut nodes = vec![];
+            for block in if_expr.blocks() {
+                if let Some(block_expr) = block.expr() {
+                    if let Some(tail_exprs) = get_tail_expr_from_block(&block_expr) {
+                        nodes.extend(tail_exprs);
+                    }
+                } else if let Some(last_expr) = block.syntax().last_child() {
+                    nodes.push(NodeType::Node(last_expr));
+                } else {
+                    nodes.push(NodeType::Node(block.syntax().clone()));
+                }
+            }
+            Some(nodes)
+        }
+        Expr::LoopExpr(loop_expr) => {
+            loop_expr.syntax().last_child().map(|lc| vec![NodeType::Node(lc)])
+        }
+        Expr::ForExpr(for_expr) => {
+            for_expr.syntax().last_child().map(|lc| vec![NodeType::Node(lc)])
+        }
+        Expr::WhileExpr(while_expr) => {
+            while_expr.syntax().last_child().map(|lc| vec![NodeType::Node(lc)])
+        }
+        Expr::BlockExpr(block_expr) => {
+            block_expr.expr().map(|lc| vec![NodeType::Node(lc.syntax().clone())])
+        }
+        Expr::MatchExpr(match_expr) => {
+            let arm_list = match_expr.match_arm_list()?;
+            let arms: Vec<NodeType> = arm_list
+                .arms()
+                .filter_map(|match_arm| match_arm.expr())
+                .map(|expr| match expr {
+                    Expr::ReturnExpr(ret_expr) => NodeType::Node(ret_expr.syntax().clone()),
+                    Expr::BreakExpr(break_expr) => NodeType::Node(break_expr.syntax().clone()),
+                    _ => match expr.syntax().last_child() {
+                        Some(last_expr) => NodeType::Node(last_expr),
+                        None => NodeType::Node(expr.syntax().clone()),
+                    },
+                })
+                .collect();
+
+            Some(arms)
+        }
+        Expr::BreakExpr(expr) => expr.expr().map(|e| vec![NodeType::Leaf(e.syntax().clone())]),
+        Expr::ReturnExpr(ret_expr) => Some(vec![NodeType::Node(ret_expr.syntax().clone())]),
+        Expr::CallExpr(call_expr) => Some(vec![NodeType::Leaf(call_expr.syntax().clone())]),
+        Expr::Literal(lit_expr) => Some(vec![NodeType::Leaf(lit_expr.syntax().clone())]),
+        Expr::TupleExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::ArrayExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::ParenExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::PathExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::Label(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::RecordLit(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::IndexExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::MethodCallExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::AwaitExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::CastExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::RefExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::PrefixExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::RangeExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::BinExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::MacroCall(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        Expr::BoxExpr(expr) => Some(vec![NodeType::Leaf(expr.syntax().clone())]),
+        _ => None,
+    }
+}
+
+fn result_insertion_offset(ret_type: &ast::TypeRef) -> Option<TextSize> {
+    let non_ws_child = ret_type
+        .syntax()
+        .children_with_tokens()
+        .find(|it| it.kind() != COMMENT && it.kind() != WHITESPACE)?;
+    Some(non_ws_child.text_range().start())
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    #[test]
+    fn change_return_type_to_result_simple() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i3<|>2 {
+                let test = "test";
+                return 42i32;
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                return Ok(42i32);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_return_type() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let test = "test";
+                return 42i32;
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                return Ok(42i32);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_return_type_bad_cursor() {
+        check_assist_not_applicable(
+            change_return_type_to_result,
+            r#"fn foo() -> i32 {
+                let test = "test";<|>
+                return 42i32;
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_cursor() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> <|>i32 {
+                let test = "test";
+                return 42i32;
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                return Ok(42i32);
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -><|> i32 {
+                let test = "test";
+                42i32
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                Ok(42i32)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_only() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                42i32
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                Ok(42i32)
+            }"#,
+        );
+    }
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                if true {
+                    42i32
+                } else {
+                    24i32
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                if true {
+                    Ok(42i32)
+                } else {
+                    Ok(24i32)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_nested_if() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                if true {
+                    if false {
+                        1
+                    } else {
+                        2
+                    }
+                } else {
+                    24i32
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                if true {
+                    if false {
+                        Ok(1)
+                    } else {
+                        Ok(2)
+                    }
+                } else {
+                    Ok(24i32)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_await() {
+        check_assist(
+            change_return_type_to_result,
+            r#"async fn foo() -> i<|>32 {
+                if true {
+                    if false {
+                        1.await
+                    } else {
+                        2.await
+                    }
+                } else {
+                    24i32.await
+                }
+            }"#,
+            r#"async fn foo() -> Result<i32, <|>> {
+                if true {
+                    if false {
+                        Ok(1.await)
+                    } else {
+                        Ok(2.await)
+                    }
+                } else {
+                    Ok(24i32.await)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_array() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> [i32;<|> 3] {
+                [1, 2, 3]
+            }"#,
+            r#"fn foo() -> Result<[i32; 3], <|>> {
+                Ok([1, 2, 3])
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_cast() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -<|>> i32 {
+                if true {
+                    if false {
+                        1 as i32
+                    } else {
+                        2 as i32
+                    }
+                } else {
+                    24 as i32
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                if true {
+                    if false {
+                        Ok(1 as i32)
+                    } else {
+                        Ok(2 as i32)
+                    }
+                } else {
+                    Ok(24 as i32)
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_match() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                match my_var {
+                    5 => 42i32,
+                    _ => 24i32,
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let my_var = 5;
+                match my_var {
+                    5 => Ok(42i32),
+                    _ => Ok(24i32),
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_loop_with_tail() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                loop {
+                    println!("test");
+                    5
+                }
+
+                my_var
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let my_var = 5;
+                loop {
+                    println!("test");
+                    5
+                }
+
+                Ok(my_var)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_loop_in_let_stmt() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = let x = loop {
+                    break 1;
+                };
+
+                my_var
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let my_var = let x = loop {
+                    break 1;
+                };
+
+                Ok(my_var)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_match_return_expr() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                let res = match my_var {
+                    5 => 42i32,
+                    _ => return 24i32,
+                };
+
+                res
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let my_var = 5;
+                let res = match my_var {
+                    5 => 42i32,
+                    _ => return Ok(24i32),
+                };
+
+                Ok(res)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                let res = if my_var == 5 {
+                    42i32
+                } else {
+                    return 24i32;
+                };
+
+                res
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let my_var = 5;
+                let res = if my_var == 5 {
+                    42i32
+                } else {
+                    return Ok(24i32);
+                };
+
+                Ok(res)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_match_deeper() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let my_var = 5;
+                match my_var {
+                    5 => {
+                        if true {
+                            42i32
+                        } else {
+                            25i32
+                        }
+                    },
+                    _ => {
+                        let test = "test";
+                        if test == "test" {
+                            return bar();
+                        }
+                        53i32
+                    },
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let my_var = 5;
+                match my_var {
+                    5 => {
+                        if true {
+                            Ok(42i32)
+                        } else {
+                            Ok(25i32)
+                        }
+                    },
+                    _ => {
+                        let test = "test";
+                        if test == "test" {
+                            return Ok(bar());
+                        }
+                        Ok(53i32)
+                    },
+                }
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_tail_block_like_early_return() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i<|>32 {
+                let test = "test";
+                if test == "test" {
+                    return 24i32;
+                }
+                53i32
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                if test == "test" {
+                    return Ok(24i32);
+                }
+                Ok(53i32)
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_closure() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -><|> u32 {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return 99;
+                    } else {
+                        return 0;
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, <|>> {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return Ok(99);
+                    } else {
+                        return Ok(0);
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u32<|> {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return 99;
+                    } else {
+                        return 0;
+                    }
+                }
+                let t = None;
+
+                t.unwrap_or_else(|| the_field)
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, <|>> {
+                let true_closure = || {
+                    return true;
+                };
+                if the_field < 5 {
+                    let mut i = 0;
+
+
+                    if true_closure() {
+                        return Ok(99);
+                    } else {
+                        return Ok(0);
+                    }
+                }
+                let t = None;
+
+                Ok(t.unwrap_or_else(|| the_field))
+            }"#,
+        );
+    }
+
+    #[test]
+    fn change_return_type_to_result_simple_with_weird_forms() {
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let test = "test";
+                if test == "test" {
+                    return 24i32;
+                }
+                let mut i = 0;
+                loop {
+                    if i == 1 {
+                        break 55;
+                    }
+                    i += 1;
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                if test == "test" {
+                    return Ok(24i32);
+                }
+                let mut i = 0;
+                loop {
+                    if i == 1 {
+                        break Ok(55);
+                    }
+                    i += 1;
+                }
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i32<|> {
+                let test = "test";
+                if test == "test" {
+                    return 24i32;
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break 55;
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                if test == "test" {
+                    return Ok(24i32);
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break Ok(55);
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo() -> i3<|>2 {
+                let test = "test";
+                let other = 5;
+                if test == "test" {
+                    let res = match other {
+                        5 => 43,
+                        _ => return 56,
+                    };
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break 55;
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+            r#"fn foo() -> Result<i32, <|>> {
+                let test = "test";
+                let other = 5;
+                if test == "test" {
+                    let res = match other {
+                        5 => 43,
+                        _ => return Ok(56),
+                    };
+                }
+                let mut i = 0;
+                loop {
+                    loop {
+                        if i == 1 {
+                            break Ok(55);
+                        }
+                        i += 1;
+                    }
+                }
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u32<|> {
+                if the_field < 5 {
+                    let mut i = 0;
+                    loop {
+                        if i > 5 {
+                            return 55u32;
+                        }
+                        i += 3;
+                    }
+
+                    match i {
+                        5 => return 99,
+                        _ => return 0,
+                    };
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, <|>> {
+                if the_field < 5 {
+                    let mut i = 0;
+                    loop {
+                        if i > 5 {
+                            return Ok(55u32);
+                        }
+                        i += 3;
+                    }
+
+                    match i {
+                        5 => return Ok(99),
+                        _ => return Ok(0),
+                    };
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u3<|>2 {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    match i {
+                        5 => return 99,
+                        _ => return 0,
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, <|>> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    match i {
+                        5 => return Ok(99),
+                        _ => return Ok(0),
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> u32<|> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return 99
+                    } else {
+                        return 0
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, <|>> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return Ok(99)
+                    } else {
+                        return Ok(0)
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+
+        check_assist(
+            change_return_type_to_result,
+            r#"fn foo(the_field: u32) -> <|>u32 {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return 99;
+                    } else {
+                        return 0;
+                    }
+                }
+
+                the_field
+            }"#,
+            r#"fn foo(the_field: u32) -> Result<u32, <|>> {
+                if the_field < 5 {
+                    let mut i = 0;
+
+                    if i == 5 {
+                        return Ok(99);
+                    } else {
+                        return Ok(0);
+                    }
+                }
+
+                Ok(the_field)
+            }"#,
+        );
+    }
+}
diff --git a/crates/ra_assists/src/handlers/change_visibility.rs b/crates/ra_assists/src/handlers/change_visibility.rs
index 1cd532e80..489db83e6 100644
--- a/crates/ra_assists/src/handlers/change_visibility.rs
+++ b/crates/ra_assists/src/handlers/change_visibility.rs
@@ -66,11 +66,15 @@ fn add_vis(ctx: AssistCtx) -> Option<Assist> {
         return None;
     };
 
-    ctx.add_assist(AssistId("change_visibility"), "Change visibility to pub(crate)", |edit| {
-        edit.target(target);
-        edit.insert(offset, "pub(crate) ");
-        edit.set_cursor(offset);
-    })
+    ctx.add_assist(
+        AssistId("change_visibility"),
+        "Change visibility to pub(crate)",
+        target,
+        |edit| {
+            edit.insert(offset, "pub(crate) ");
+            edit.set_cursor(offset);
+        },
+    )
 }
 
 fn vis_offset(node: &SyntaxNode) -> TextSize {
@@ -86,22 +90,28 @@ fn vis_offset(node: &SyntaxNode) -> TextSize {
 
 fn change_vis(ctx: AssistCtx, vis: ast::Visibility) -> Option<Assist> {
     if vis.syntax().text() == "pub" {
+        let target = vis.syntax().text_range();
         return ctx.add_assist(
             AssistId("change_visibility"),
             "Change Visibility to pub(crate)",
+            target,
             |edit| {
-                edit.target(vis.syntax().text_range());
                 edit.replace(vis.syntax().text_range(), "pub(crate)");
                 edit.set_cursor(vis.syntax().text_range().start())
             },
         );
     }
     if vis.syntax().text() == "pub(crate)" {
-        return ctx.add_assist(AssistId("change_visibility"), "Change visibility to pub", |edit| {
-            edit.target(vis.syntax().text_range());
-            edit.replace(vis.syntax().text_range(), "pub");
-            edit.set_cursor(vis.syntax().text_range().start());
-        });
+        let target = vis.syntax().text_range();
+        return ctx.add_assist(
+            AssistId("change_visibility"),
+            "Change visibility to pub",
+            target,
+            |edit| {
+                edit.replace(vis.syntax().text_range(), "pub");
+                edit.set_cursor(vis.syntax().text_range().start());
+            },
+        );
     }
     None
 }
@@ -110,7 +120,7 @@ fn change_vis(ctx: AssistCtx, vis: ast::Visibility) -> Option<Assist> {
 mod tests {
     use test_utils::covers;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/early_return.rs b/crates/ra_assists/src/handlers/early_return.rs
index eede2fe91..4bd6040b2 100644
--- a/crates/ra_assists/src/handlers/early_return.rs
+++ b/crates/ra_assists/src/handlers/early_return.rs
@@ -95,94 +95,99 @@ pub(crate) fn convert_to_guarded_return(ctx: AssistCtx) -> Option<Assist> {
     then_block.syntax().last_child_or_token().filter(|t| t.kind() == R_CURLY)?;
     let cursor_position = ctx.frange.range.start();
 
-    ctx.add_assist(AssistId("convert_to_guarded_return"), "Convert to guarded return", |edit| {
-        let if_indent_level = IndentLevel::from_node(&if_expr.syntax());
-        let new_block = match if_let_pat {
-            None => {
-                // If.
-                let new_expr = {
-                    let then_branch =
-                        make::block_expr(once(make::expr_stmt(early_expression).into()), None);
-                    let cond = invert_boolean_expression(cond_expr);
-                    let e = make::expr_if(make::condition(cond, None), then_branch);
-                    if_indent_level.increase_indent(e)
-                };
-                replace(new_expr.syntax(), &then_block, &parent_block, &if_expr)
-            }
-            Some((path, bound_ident)) => {
-                // If-let.
-                let match_expr = {
-                    let happy_arm = {
-                        let pat = make::tuple_struct_pat(
-                            path,
-                            once(make::bind_pat(make::name("it")).into()),
-                        );
-                        let expr = {
-                            let name_ref = make::name_ref("it");
-                            let segment = make::path_segment(name_ref);
-                            let path = make::path_unqualified(segment);
-                            make::expr_path(path)
-                        };
-                        make::match_arm(once(pat.into()), expr)
+    let target = if_expr.syntax().text_range();
+    ctx.add_assist(
+        AssistId("convert_to_guarded_return"),
+        "Convert to guarded return",
+        target,
+        |edit| {
+            let if_indent_level = IndentLevel::from_node(&if_expr.syntax());
+            let new_block = match if_let_pat {
+                None => {
+                    // If.
+                    let new_expr = {
+                        let then_branch =
+                            make::block_expr(once(make::expr_stmt(early_expression).into()), None);
+                        let cond = invert_boolean_expression(cond_expr);
+                        let e = make::expr_if(make::condition(cond, None), then_branch);
+                        if_indent_level.increase_indent(e)
                     };
+                    replace(new_expr.syntax(), &then_block, &parent_block, &if_expr)
+                }
+                Some((path, bound_ident)) => {
+                    // If-let.
+                    let match_expr = {
+                        let happy_arm = {
+                            let pat = make::tuple_struct_pat(
+                                path,
+                                once(make::bind_pat(make::name("it")).into()),
+                            );
+                            let expr = {
+                                let name_ref = make::name_ref("it");
+                                let segment = make::path_segment(name_ref);
+                                let path = make::path_unqualified(segment);
+                                make::expr_path(path)
+                            };
+                            make::match_arm(once(pat.into()), expr)
+                        };
 
-                    let sad_arm = make::match_arm(
-                        // FIXME: would be cool to use `None` or `Err(_)` if appropriate
-                        once(make::placeholder_pat().into()),
-                        early_expression,
-                    );
+                        let sad_arm = make::match_arm(
+                            // FIXME: would be cool to use `None` or `Err(_)` if appropriate
+                            once(make::placeholder_pat().into()),
+                            early_expression,
+                        );
 
-                    make::expr_match(cond_expr, make::match_arm_list(vec![happy_arm, sad_arm]))
-                };
+                        make::expr_match(cond_expr, make::match_arm_list(vec![happy_arm, sad_arm]))
+                    };
 
-                let let_stmt = make::let_stmt(
-                    make::bind_pat(make::name(&bound_ident.syntax().to_string())).into(),
-                    Some(match_expr),
+                    let let_stmt = make::let_stmt(
+                        make::bind_pat(make::name(&bound_ident.syntax().to_string())).into(),
+                        Some(match_expr),
+                    );
+                    let let_stmt = if_indent_level.increase_indent(let_stmt);
+                    replace(let_stmt.syntax(), &then_block, &parent_block, &if_expr)
+                }
+            };
+            edit.replace_ast(parent_block, ast::BlockExpr::cast(new_block).unwrap());
+            edit.set_cursor(cursor_position);
+
+            fn replace(
+                new_expr: &SyntaxNode,
+                then_block: &ast::BlockExpr,
+                parent_block: &ast::BlockExpr,
+                if_expr: &ast::IfExpr,
+            ) -> SyntaxNode {
+                let then_block_items = IndentLevel::from(1).decrease_indent(then_block.clone());
+                let end_of_then = then_block_items.syntax().last_child_or_token().unwrap();
+                let end_of_then =
+                    if end_of_then.prev_sibling_or_token().map(|n| n.kind()) == Some(WHITESPACE) {
+                        end_of_then.prev_sibling_or_token().unwrap()
+                    } else {
+                        end_of_then
+                    };
+                let mut then_statements = new_expr.children_with_tokens().chain(
+                    then_block_items
+                        .syntax()
+                        .children_with_tokens()
+                        .skip(1)
+                        .take_while(|i| *i != end_of_then),
                 );
-                let let_stmt = if_indent_level.increase_indent(let_stmt);
-                replace(let_stmt.syntax(), &then_block, &parent_block, &if_expr)
+                replace_children(
+                    &parent_block.syntax(),
+                    RangeInclusive::new(
+                        if_expr.clone().syntax().clone().into(),
+                        if_expr.syntax().clone().into(),
+                    ),
+                    &mut then_statements,
+                )
             }
-        };
-        edit.target(if_expr.syntax().text_range());
-        edit.replace_ast(parent_block, ast::BlockExpr::cast(new_block).unwrap());
-        edit.set_cursor(cursor_position);
-
-        fn replace(
-            new_expr: &SyntaxNode,
-            then_block: &ast::BlockExpr,
-            parent_block: &ast::BlockExpr,
-            if_expr: &ast::IfExpr,
-        ) -> SyntaxNode {
-            let then_block_items = IndentLevel::from(1).decrease_indent(then_block.clone());
-            let end_of_then = then_block_items.syntax().last_child_or_token().unwrap();
-            let end_of_then =
-                if end_of_then.prev_sibling_or_token().map(|n| n.kind()) == Some(WHITESPACE) {
-                    end_of_then.prev_sibling_or_token().unwrap()
-                } else {
-                    end_of_then
-                };
-            let mut then_statements = new_expr.children_with_tokens().chain(
-                then_block_items
-                    .syntax()
-                    .children_with_tokens()
-                    .skip(1)
-                    .take_while(|i| *i != end_of_then),
-            );
-            replace_children(
-                &parent_block.syntax(),
-                RangeInclusive::new(
-                    if_expr.clone().syntax().clone().into(),
-                    if_expr.syntax().clone().into(),
-                ),
-                &mut then_statements,
-            )
-        }
-    })
+        },
+    )
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/fill_match_arms.rs b/crates/ra_assists/src/handlers/fill_match_arms.rs
index 8d1af9933..7c8f8bdf2 100644
--- a/crates/ra_assists/src/handlers/fill_match_arms.rs
+++ b/crates/ra_assists/src/handlers/fill_match_arms.rs
@@ -92,10 +92,9 @@ pub(crate) fn fill_match_arms(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
-    ctx.add_assist(AssistId("fill_match_arms"), "Fill match arms", |edit| {
+    let target = match_expr.syntax().text_range();
+    ctx.add_assist(AssistId("fill_match_arms"), "Fill match arms", target, |edit| {
         let new_arm_list = match_arm_list.remove_placeholder().append_arms(missing_arms);
-
-        edit.target(match_expr.syntax().text_range());
         edit.set_cursor(expr.syntax().text_range().start());
         edit.replace_ast(match_arm_list, new_arm_list);
     })
@@ -168,7 +167,7 @@ fn build_pat(db: &RootDatabase, module: hir::Module, var: hir::EnumVariant) -> O
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::fill_match_arms;
 
diff --git a/crates/ra_assists/src/handlers/flip_binexpr.rs b/crates/ra_assists/src/handlers/flip_binexpr.rs
index 8030efb35..cb7264d7b 100644
--- a/crates/ra_assists/src/handlers/flip_binexpr.rs
+++ b/crates/ra_assists/src/handlers/flip_binexpr.rs
@@ -33,8 +33,7 @@ pub(crate) fn flip_binexpr(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
-    ctx.add_assist(AssistId("flip_binexpr"), "Flip binary expression", |edit| {
-        edit.target(op_range);
+    ctx.add_assist(AssistId("flip_binexpr"), "Flip binary expression", op_range, |edit| {
         if let FlipAction::FlipAndReplaceOp(new_op) = action {
             edit.replace(op_range, new_op);
         }
@@ -69,7 +68,7 @@ impl From<BinOp> for FlipAction {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn flip_binexpr_target_is_the_op() {
diff --git a/crates/ra_assists/src/handlers/flip_comma.rs b/crates/ra_assists/src/handlers/flip_comma.rs
index 1dacf29f8..24982ae22 100644
--- a/crates/ra_assists/src/handlers/flip_comma.rs
+++ b/crates/ra_assists/src/handlers/flip_comma.rs
@@ -28,8 +28,7 @@ pub(crate) fn flip_comma(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
-    ctx.add_assist(AssistId("flip_comma"), "Flip comma", |edit| {
-        edit.target(comma.text_range());
+    ctx.add_assist(AssistId("flip_comma"), "Flip comma", comma.text_range(), |edit| {
         edit.replace(prev.text_range(), next.to_string());
         edit.replace(next.text_range(), prev.to_string());
     })
@@ -39,7 +38,7 @@ pub(crate) fn flip_comma(ctx: AssistCtx) -> Option<Assist> {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_target};
+    use crate::tests::{check_assist, check_assist_target};
 
     #[test]
     fn flip_comma_works_for_function_parameters() {
diff --git a/crates/ra_assists/src/handlers/flip_trait_bound.rs b/crates/ra_assists/src/handlers/flip_trait_bound.rs
index f56769624..6a3b2df67 100644
--- a/crates/ra_assists/src/handlers/flip_trait_bound.rs
+++ b/crates/ra_assists/src/handlers/flip_trait_bound.rs
@@ -32,8 +32,8 @@ pub(crate) fn flip_trait_bound(ctx: AssistCtx) -> Option<Assist> {
         non_trivia_sibling(plus.clone().into(), Direction::Next)?,
     );
 
-    ctx.add_assist(AssistId("flip_trait_bound"), "Flip trait bounds", |edit| {
-        edit.target(plus.text_range());
+    let target = plus.text_range();
+    ctx.add_assist(AssistId("flip_trait_bound"), "Flip trait bounds", target, |edit| {
         edit.replace(before.text_range(), after.to_string());
         edit.replace(after.text_range(), before.to_string());
     })
@@ -43,7 +43,7 @@ pub(crate) fn flip_trait_bound(ctx: AssistCtx) -> Option<Assist> {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn flip_trait_bound_assist_available() {
diff --git a/crates/ra_assists/src/handlers/inline_local_variable.rs b/crates/ra_assists/src/handlers/inline_local_variable.rs
index 60ec536a7..e5765c845 100644
--- a/crates/ra_assists/src/handlers/inline_local_variable.rs
+++ b/crates/ra_assists/src/handlers/inline_local_variable.rs
@@ -106,9 +106,11 @@ pub(crate) fn inline_local_variable(ctx: AssistCtx) -> Option<Assist> {
     let init_str = initializer_expr.syntax().text().to_string();
     let init_in_paren = format!("({})", &init_str);
 
+    let target = bind_pat.syntax().text_range();
     ctx.add_assist(
         AssistId("inline_local_variable"),
         "Inline variable",
+        target,
         move |edit: &mut ActionBuilder| {
             edit.delete(delete_range);
             for (desc, should_wrap) in refs.iter().zip(wrap_in_parens) {
@@ -125,7 +127,7 @@ pub(crate) fn inline_local_variable(ctx: AssistCtx) -> Option<Assist> {
 mod tests {
     use test_utils::covers;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/introduce_variable.rs b/crates/ra_assists/src/handlers/introduce_variable.rs
index 39c656305..3c340ff3b 100644
--- a/crates/ra_assists/src/handlers/introduce_variable.rs
+++ b/crates/ra_assists/src/handlers/introduce_variable.rs
@@ -42,7 +42,8 @@ pub(crate) fn introduce_variable(ctx: AssistCtx) -> Option<Assist> {
     if indent.kind() != WHITESPACE {
         return None;
     }
-    ctx.add_assist(AssistId("introduce_variable"), "Extract into variable", move |edit| {
+    let target = expr.syntax().text_range();
+    ctx.add_assist(AssistId("introduce_variable"), "Extract into variable", target, move |edit| {
         let mut buf = String::new();
 
         let cursor_offset = if wrap_in_block {
@@ -79,7 +80,6 @@ pub(crate) fn introduce_variable(ctx: AssistCtx) -> Option<Assist> {
                 buf.push_str(text);
             }
 
-            edit.target(expr.syntax().text_range());
             edit.replace(expr.syntax().text_range(), "var_name".to_string());
             edit.insert(anchor_stmt.text_range().start(), buf);
             if wrap_in_block {
@@ -136,7 +136,7 @@ fn anchor_stmt(expr: ast::Expr) -> Option<(SyntaxNode, bool)> {
 mod tests {
     use test_utils::covers;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/invert_if.rs b/crates/ra_assists/src/handlers/invert_if.rs
index 682e08512..b16271443 100644
--- a/crates/ra_assists/src/handlers/invert_if.rs
+++ b/crates/ra_assists/src/handlers/invert_if.rs
@@ -47,8 +47,7 @@ pub(crate) fn invert_if(ctx: AssistCtx) -> Option<Assist> {
         let else_node = else_block.syntax();
         let else_range = else_node.text_range();
         let then_range = then_node.text_range();
-        return ctx.add_assist(AssistId("invert_if"), "Invert if", |edit| {
-            edit.target(if_range);
+        return ctx.add_assist(AssistId("invert_if"), "Invert if", if_range, |edit| {
             edit.replace(cond_range, flip_cond.syntax().text());
             edit.replace(else_range, then_node.text());
             edit.replace(then_range, else_node.text());
@@ -62,7 +61,7 @@ pub(crate) fn invert_if(ctx: AssistCtx) -> Option<Assist> {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     #[test]
     fn invert_if_remove_inequality() {
diff --git a/crates/ra_assists/src/handlers/merge_imports.rs b/crates/ra_assists/src/handlers/merge_imports.rs
index 4be1238f1..de74d83d8 100644
--- a/crates/ra_assists/src/handlers/merge_imports.rs
+++ b/crates/ra_assists/src/handlers/merge_imports.rs
@@ -52,7 +52,8 @@ pub(crate) fn merge_imports(ctx: AssistCtx) -> Option<Assist> {
         }
     };
 
-    ctx.add_assist(AssistId("merge_imports"), "Merge imports", |edit| {
+    let target = tree.syntax().text_range();
+    ctx.add_assist(AssistId("merge_imports"), "Merge imports", target, |edit| {
         edit.rewrite(rewriter);
         // FIXME: we only need because our diff is imprecise
         edit.set_cursor(offset);
@@ -125,7 +126,7 @@ fn first_path(path: &ast::Path) -> ast::Path {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::check_assist;
+    use crate::tests::check_assist;
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/merge_match_arms.rs b/crates/ra_assists/src/handlers/merge_match_arms.rs
index 5a77d3dbc..7c4d9d55d 100644
--- a/crates/ra_assists/src/handlers/merge_match_arms.rs
+++ b/crates/ra_assists/src/handlers/merge_match_arms.rs
@@ -70,7 +70,7 @@ pub(crate) fn merge_match_arms(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
-    ctx.add_assist(AssistId("merge_match_arms"), "Merge match arms", |edit| {
+    ctx.add_assist(AssistId("merge_match_arms"), "Merge match arms", current_text_range, |edit| {
         let pats = if arms_to_merge.iter().any(contains_placeholder) {
             "_".into()
         } else {
@@ -87,7 +87,6 @@ pub(crate) fn merge_match_arms(ctx: AssistCtx) -> Option<Assist> {
         let start = arms_to_merge.first().unwrap().syntax().text_range().start();
         let end = arms_to_merge.last().unwrap().syntax().text_range().end();
 
-        edit.target(current_text_range);
         edit.set_cursor(match cursor_pos {
             CursorPos::InExpr(back_offset) => start + TextSize::of(&arm) - back_offset,
             CursorPos::InPat(offset) => offset,
@@ -105,7 +104,7 @@ fn contains_placeholder(a: &ast::MatchArm) -> bool {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/move_bounds.rs b/crates/ra_assists/src/handlers/move_bounds.rs
index 0f26884dc..44e50cb6e 100644
--- a/crates/ra_assists/src/handlers/move_bounds.rs
+++ b/crates/ra_assists/src/handlers/move_bounds.rs
@@ -49,30 +49,37 @@ pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx) -> Option<Assist> {
         }
     };
 
-    ctx.add_assist(AssistId("move_bounds_to_where_clause"), "Move to where clause", |edit| {
-        let new_params = type_param_list
-            .type_params()
-            .filter(|it| it.type_bound_list().is_some())
-            .map(|type_param| {
-                let without_bounds = type_param.remove_bounds();
-                (type_param, without_bounds)
-            });
-
-        let new_type_param_list = type_param_list.replace_descendants(new_params);
-        edit.replace_ast(type_param_list.clone(), new_type_param_list);
-
-        let where_clause = {
-            let predicates = type_param_list.type_params().filter_map(build_predicate);
-            make::where_clause(predicates)
-        };
-
-        let to_insert = match anchor.prev_sibling_or_token() {
-            Some(ref elem) if elem.kind() == WHITESPACE => format!("{} ", where_clause.syntax()),
-            _ => format!(" {}", where_clause.syntax()),
-        };
-        edit.insert(anchor.text_range().start(), to_insert);
-        edit.target(type_param_list.syntax().text_range());
-    })
+    let target = type_param_list.syntax().text_range();
+    ctx.add_assist(
+        AssistId("move_bounds_to_where_clause"),
+        "Move to where clause",
+        target,
+        |edit| {
+            let new_params = type_param_list
+                .type_params()
+                .filter(|it| it.type_bound_list().is_some())
+                .map(|type_param| {
+                    let without_bounds = type_param.remove_bounds();
+                    (type_param, without_bounds)
+                });
+
+            let new_type_param_list = type_param_list.replace_descendants(new_params);
+            edit.replace_ast(type_param_list.clone(), new_type_param_list);
+
+            let where_clause = {
+                let predicates = type_param_list.type_params().filter_map(build_predicate);
+                make::where_clause(predicates)
+            };
+
+            let to_insert = match anchor.prev_sibling_or_token() {
+                Some(ref elem) if elem.kind() == WHITESPACE => {
+                    format!("{} ", where_clause.syntax())
+                }
+                _ => format!(" {}", where_clause.syntax()),
+            };
+            edit.insert(anchor.text_range().start(), to_insert);
+        },
+    )
 }
 
 fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
@@ -89,7 +96,7 @@ fn build_predicate(param: ast::TypeParam) -> Option<ast::WherePred> {
 mod tests {
     use super::*;
 
-    use crate::helpers::check_assist;
+    use crate::tests::check_assist;
 
     #[test]
     fn move_bounds_to_where_clause_fn() {
diff --git a/crates/ra_assists/src/handlers/move_guard.rs b/crates/ra_assists/src/handlers/move_guard.rs
index b084dd9ee..29bc9a9ff 100644
--- a/crates/ra_assists/src/handlers/move_guard.rs
+++ b/crates/ra_assists/src/handlers/move_guard.rs
@@ -40,8 +40,8 @@ pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx) -> Option<Assist> {
     let arm_expr = match_arm.expr()?;
     let buf = format!("if {} {{ {} }}", guard_conditions.syntax().text(), arm_expr.syntax().text());
 
-    ctx.add_assist(AssistId("move_guard_to_arm_body"), "Move guard to arm body", |edit| {
-        edit.target(guard.syntax().text_range());
+    let target = guard.syntax().text_range();
+    ctx.add_assist(AssistId("move_guard_to_arm_body"), "Move guard to arm body", target, |edit| {
         let offseting_amount = match space_before_guard.and_then(|it| it.into_token()) {
             Some(tok) => {
                 if ast::Whitespace::cast(tok.clone()).is_some() {
@@ -108,11 +108,12 @@ pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx) -> Option<Assist> {
 
     let buf = format!(" if {}", cond.syntax().text());
 
+    let target = if_expr.syntax().text_range();
     ctx.add_assist(
         AssistId("move_arm_cond_to_match_guard"),
         "Move condition to match guard",
+        target,
         |edit| {
-            edit.target(if_expr.syntax().text_range());
             let then_only_expr = then_block.statements().next().is_none();
 
             match &then_block.expr() {
@@ -132,7 +133,7 @@ pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx) -> Option<Assist> {
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn move_guard_to_arm_body_target() {
diff --git a/crates/ra_assists/src/handlers/raw_string.rs b/crates/ra_assists/src/handlers/raw_string.rs
index 567400b9c..155c679b4 100644
--- a/crates/ra_assists/src/handlers/raw_string.rs
+++ b/crates/ra_assists/src/handlers/raw_string.rs
@@ -25,8 +25,8 @@ use crate::{Assist, AssistCtx, AssistId};
 pub(crate) fn make_raw_string(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(STRING).and_then(ast::String::cast)?;
     let value = token.value()?;
-    ctx.add_assist(AssistId("make_raw_string"), "Rewrite as raw string", |edit| {
-        edit.target(token.syntax().text_range());
+    let target = token.syntax().text_range();
+    ctx.add_assist(AssistId("make_raw_string"), "Rewrite as raw string", target, |edit| {
         let max_hash_streak = count_hashes(&value);
         let mut hashes = String::with_capacity(max_hash_streak + 1);
         for _ in 0..hashes.capacity() {
@@ -54,8 +54,8 @@ pub(crate) fn make_raw_string(ctx: AssistCtx) -> Option<Assist> {
 pub(crate) fn make_usual_string(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING).and_then(ast::RawString::cast)?;
     let value = token.value()?;
-    ctx.add_assist(AssistId("make_usual_string"), "Rewrite as regular string", |edit| {
-        edit.target(token.syntax().text_range());
+    let target = token.syntax().text_range();
+    ctx.add_assist(AssistId("make_usual_string"), "Rewrite as regular string", target, |edit| {
         // parse inside string to escape `"`
         let escaped = value.escape_default().to_string();
         edit.replace(token.syntax().text_range(), format!("\"{}\"", escaped));
@@ -79,8 +79,8 @@ pub(crate) fn make_usual_string(ctx: AssistCtx) -> Option<Assist> {
 // ```
 pub(crate) fn add_hash(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
-    ctx.add_assist(AssistId("add_hash"), "Add # to raw string", |edit| {
-        edit.target(token.text_range());
+    let target = token.text_range();
+    ctx.add_assist(AssistId("add_hash"), "Add # to raw string", target, |edit| {
         edit.insert(token.text_range().start() + TextSize::of('r'), "#");
         edit.insert(token.text_range().end(), "#");
     })
@@ -108,8 +108,8 @@ pub(crate) fn remove_hash(ctx: AssistCtx) -> Option<Assist> {
         // no hash to remove
         return None;
     }
-    ctx.add_assist(AssistId("remove_hash"), "Remove hash from raw string", |edit| {
-        edit.target(token.text_range());
+    let target = token.text_range();
+    ctx.add_assist(AssistId("remove_hash"), "Remove hash from raw string", target, |edit| {
         let result = &text[2..text.len() - 1];
         let result = if result.starts_with('\"') {
             // FIXME: this logic is wrong, not only the last has has to handled specially
@@ -138,7 +138,7 @@ fn count_hashes(s: &str) -> usize {
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn make_raw_string_target() {
diff --git a/crates/ra_assists/src/handlers/remove_dbg.rs b/crates/ra_assists/src/handlers/remove_dbg.rs
index 4e5eb4350..e6e02f2ae 100644
--- a/crates/ra_assists/src/handlers/remove_dbg.rs
+++ b/crates/ra_assists/src/handlers/remove_dbg.rs
@@ -57,8 +57,8 @@ pub(crate) fn remove_dbg(ctx: AssistCtx) -> Option<Assist> {
         text.slice(without_parens).to_string()
     };
 
-    ctx.add_assist(AssistId("remove_dbg"), "Remove dbg!()", |edit| {
-        edit.target(macro_call.syntax().text_range());
+    let target = macro_call.syntax().text_range();
+    ctx.add_assist(AssistId("remove_dbg"), "Remove dbg!()", target, |edit| {
         edit.replace(macro_range, macro_content);
         edit.set_cursor(cursor_pos);
     })
@@ -90,7 +90,7 @@ fn is_valid_macrocall(macro_call: &ast::MacroCall, macro_name: &str) -> Option<b
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
     fn test_remove_dbg() {
diff --git a/crates/ra_assists/src/handlers/remove_mut.rs b/crates/ra_assists/src/handlers/remove_mut.rs
index e598023b2..9f72f879d 100644
--- a/crates/ra_assists/src/handlers/remove_mut.rs
+++ b/crates/ra_assists/src/handlers/remove_mut.rs
@@ -25,7 +25,8 @@ pub(crate) fn remove_mut(ctx: AssistCtx) -> Option<Assist> {
         _ => mut_token.text_range().end(),
     };
 
-    ctx.add_assist(AssistId("remove_mut"), "Remove `mut` keyword", |edit| {
+    let target = mut_token.text_range();
+    ctx.add_assist(AssistId("remove_mut"), "Remove `mut` keyword", target, |edit| {
         edit.set_cursor(delete_from);
         edit.delete(TextRange::new(delete_from, delete_to));
     })
diff --git a/crates/ra_assists/src/handlers/reorder_fields.rs b/crates/ra_assists/src/handlers/reorder_fields.rs
index 5cbb98d73..0b930dea2 100644
--- a/crates/ra_assists/src/handlers/reorder_fields.rs
+++ b/crates/ra_assists/src/handlers/reorder_fields.rs
@@ -50,11 +50,11 @@ fn reorder<R: AstNode>(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
-    ctx.add_assist(AssistId("reorder_fields"), "Reorder record fields", |edit| {
+    let target = record.syntax().text_range();
+    ctx.add_assist(AssistId("reorder_fields"), "Reorder record fields", target, |edit| {
         for (old, new) in fields.iter().zip(&sorted_fields) {
             algo::diff(old, new).into_text_edit(edit.text_edit_builder());
         }
-        edit.target(record.syntax().text_range())
     })
 }
 
@@ -109,7 +109,7 @@ fn compute_fields_ranks(path: &Path, ctx: &AssistCtx) -> Option<HashMap<String,
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/replace_if_let_with_match.rs b/crates/ra_assists/src/handlers/replace_if_let_with_match.rs
index 9841f6980..2eb8348f8 100644
--- a/crates/ra_assists/src/handlers/replace_if_let_with_match.rs
+++ b/crates/ra_assists/src/handlers/replace_if_let_with_match.rs
@@ -44,37 +44,42 @@ pub(crate) fn replace_if_let_with_match(ctx: AssistCtx) -> Option<Assist> {
     };
 
     let sema = ctx.sema;
-    ctx.add_assist(AssistId("replace_if_let_with_match"), "Replace with match", move |edit| {
-        let match_expr = {
-            let then_arm = {
-                let then_expr = unwrap_trivial_block(then_block);
-                make::match_arm(vec![pat.clone()], then_expr)
+    let target = if_expr.syntax().text_range();
+    ctx.add_assist(
+        AssistId("replace_if_let_with_match"),
+        "Replace with match",
+        target,
+        move |edit| {
+            let match_expr = {
+                let then_arm = {
+                    let then_expr = unwrap_trivial_block(then_block);
+                    make::match_arm(vec![pat.clone()], then_expr)
+                };
+                let else_arm = {
+                    let pattern = sema
+                        .type_of_pat(&pat)
+                        .and_then(|ty| TryEnum::from_ty(sema, &ty))
+                        .map(|it| it.sad_pattern())
+                        .unwrap_or_else(|| make::placeholder_pat().into());
+                    let else_expr = unwrap_trivial_block(else_block);
+                    make::match_arm(vec![pattern], else_expr)
+                };
+                make::expr_match(expr, make::match_arm_list(vec![then_arm, else_arm]))
             };
-            let else_arm = {
-                let pattern = sema
-                    .type_of_pat(&pat)
-                    .and_then(|ty| TryEnum::from_ty(sema, &ty))
-                    .map(|it| it.sad_pattern())
-                    .unwrap_or_else(|| make::placeholder_pat().into());
-                let else_expr = unwrap_trivial_block(else_block);
-                make::match_arm(vec![pattern], else_expr)
-            };
-            make::expr_match(expr, make::match_arm_list(vec![then_arm, else_arm]))
-        };
 
-        let match_expr = IndentLevel::from_node(if_expr.syntax()).increase_indent(match_expr);
+            let match_expr = IndentLevel::from_node(if_expr.syntax()).increase_indent(match_expr);
 
-        edit.target(if_expr.syntax().text_range());
-        edit.set_cursor(if_expr.syntax().text_range().start());
-        edit.replace_ast::<ast::Expr>(if_expr.into(), match_expr);
-    })
+            edit.set_cursor(if_expr.syntax().text_range().start());
+            edit.replace_ast::<ast::Expr>(if_expr.into(), match_expr);
+        },
+    )
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
-    use crate::helpers::{check_assist, check_assist_target};
+    use crate::tests::{check_assist, check_assist_target};
 
     #[test]
     fn test_replace_if_let_with_match_unwraps_simple_expressions() {
diff --git a/crates/ra_assists/src/handlers/replace_let_with_if_let.rs b/crates/ra_assists/src/handlers/replace_let_with_if_let.rs
index 0cf23b754..a5509a567 100644
--- a/crates/ra_assists/src/handlers/replace_let_with_if_let.rs
+++ b/crates/ra_assists/src/handlers/replace_let_with_if_let.rs
@@ -47,7 +47,8 @@ pub(crate) fn replace_let_with_if_let(ctx: AssistCtx) -> Option<Assist> {
     let ty = ctx.sema.type_of_expr(&init)?;
     let happy_variant = TryEnum::from_ty(ctx.sema, &ty).map(|it| it.happy_case());
 
-    ctx.add_assist(AssistId("replace_let_with_if_let"), "Replace with if-let", |edit| {
+    let target = let_kw.text_range();
+    ctx.add_assist(AssistId("replace_let_with_if_let"), "Replace with if-let", target, |edit| {
         let with_placeholder: ast::Pat = match happy_variant {
             None => make::placeholder_pat().into(),
             Some(var_name) => make::tuple_struct_pat(
@@ -67,14 +68,13 @@ pub(crate) fn replace_let_with_if_let(ctx: AssistCtx) -> Option<Assist> {
         let stmt = stmt.replace_descendant(placeholder.into(), original_pat);
 
         edit.replace_ast(ast::Stmt::from(let_stmt), ast::Stmt::from(stmt));
-        edit.target(let_kw.text_range());
         edit.set_cursor(target_offset);
     })
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::check_assist;
+    use crate::tests::check_assist;
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs b/crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs
index ff2463c77..fd41da64b 100644
--- a/crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs
+++ b/crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs
@@ -33,9 +33,11 @@ pub(crate) fn replace_qualified_name_with_use(ctx: AssistCtx) -> Option<Assist>
         return None;
     }
 
+    let target = path.syntax().text_range();
     ctx.add_assist(
         AssistId("replace_qualified_name_with_use"),
         "Replace qualified path with use",
+        target,
         |edit| {
             let path_to_import = hir_path.mod_path().clone();
             insert_use_statement(path.syntax(), &path_to_import, edit);
@@ -74,7 +76,7 @@ fn collect_hir_path_segments(path: &hir::Path) -> Option<Vec<SmolStr>> {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs b/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs
index 62d4ea522..c6b73da67 100644
--- a/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs
+++ b/crates/ra_assists/src/handlers/replace_unwrap_with_match.rs
@@ -38,32 +38,38 @@ pub(crate) fn replace_unwrap_with_match(ctx: AssistCtx) -> Option<Assist> {
     let caller = method_call.expr()?;
     let ty = ctx.sema.type_of_expr(&caller)?;
     let happy_variant = TryEnum::from_ty(ctx.sema, &ty)?.happy_case();
+    let target = method_call.syntax().text_range();
+    ctx.add_assist(
+        AssistId("replace_unwrap_with_match"),
+        "Replace unwrap with match",
+        target,
+        |edit| {
+            let ok_path = make::path_unqualified(make::path_segment(make::name_ref(happy_variant)));
+            let it = make::bind_pat(make::name("a")).into();
+            let ok_tuple = make::tuple_struct_pat(ok_path, iter::once(it)).into();
 
-    ctx.add_assist(AssistId("replace_unwrap_with_match"), "Replace unwrap with match", |edit| {
-        let ok_path = make::path_unqualified(make::path_segment(make::name_ref(happy_variant)));
-        let it = make::bind_pat(make::name("a")).into();
-        let ok_tuple = make::tuple_struct_pat(ok_path, iter::once(it)).into();
+            let bind_path = make::path_unqualified(make::path_segment(make::name_ref("a")));
+            let ok_arm = make::match_arm(iter::once(ok_tuple), make::expr_path(bind_path));
 
-        let bind_path = make::path_unqualified(make::path_segment(make::name_ref("a")));
-        let ok_arm = make::match_arm(iter::once(ok_tuple), make::expr_path(bind_path));
+            let unreachable_call = make::unreachable_macro_call().into();
+            let err_arm =
+                make::match_arm(iter::once(make::placeholder_pat().into()), unreachable_call);
 
-        let unreachable_call = make::unreachable_macro_call().into();
-        let err_arm = make::match_arm(iter::once(make::placeholder_pat().into()), unreachable_call);
+            let match_arm_list = make::match_arm_list(vec![ok_arm, err_arm]);
+            let match_expr = make::expr_match(caller.clone(), match_arm_list);
+            let match_expr =
+                IndentLevel::from_node(method_call.syntax()).increase_indent(match_expr);
 
-        let match_arm_list = make::match_arm_list(vec![ok_arm, err_arm]);
-        let match_expr = make::expr_match(caller.clone(), match_arm_list);
-        let match_expr = IndentLevel::from_node(method_call.syntax()).increase_indent(match_expr);
-
-        edit.target(method_call.syntax().text_range());
-        edit.set_cursor(caller.syntax().text_range().start());
-        edit.replace_ast::<ast::Expr>(method_call.into(), match_expr);
-    })
+            edit.set_cursor(caller.syntax().text_range().start());
+            edit.replace_ast::<ast::Expr>(method_call.into(), match_expr);
+        },
+    )
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::helpers::{check_assist, check_assist_target};
+    use crate::tests::{check_assist, check_assist_target};
 
     #[test]
     fn test_replace_result_unwrap_with_match() {
diff --git a/crates/ra_assists/src/handlers/split_import.rs b/crates/ra_assists/src/handlers/split_import.rs
index f25826796..d49563974 100644
--- a/crates/ra_assists/src/handlers/split_import.rs
+++ b/crates/ra_assists/src/handlers/split_import.rs
@@ -28,8 +28,8 @@ pub(crate) fn split_import(ctx: AssistCtx) -> Option<Assist> {
     }
     let cursor = ctx.frange.range.start();
 
-    ctx.add_assist(AssistId("split_import"), "Split import", |edit| {
-        edit.target(colon_colon.text_range());
+    let target = colon_colon.text_range();
+    ctx.add_assist(AssistId("split_import"), "Split import", target, |edit| {
         edit.replace_ast(use_tree, new_tree);
         edit.set_cursor(cursor);
     })
@@ -37,7 +37,7 @@ pub(crate) fn split_import(ctx: AssistCtx) -> Option<Assist> {
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+    use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/handlers/unwrap_block.rs b/crates/ra_assists/src/handlers/unwrap_block.rs
index 859c70ad8..6df927abb 100644
--- a/crates/ra_assists/src/handlers/unwrap_block.rs
+++ b/crates/ra_assists/src/handlers/unwrap_block.rs
@@ -57,9 +57,9 @@ pub(crate) fn unwrap_block(ctx: AssistCtx) -> Option<Assist> {
         }
     };
 
-    ctx.add_assist(AssistId("unwrap_block"), "Unwrap block", |edit| {
+    let target = expr_to_unwrap.syntax().text_range();
+    ctx.add_assist(AssistId("unwrap_block"), "Unwrap block", target, |edit| {
         edit.set_cursor(expr.syntax().text_range().start());
-        edit.target(expr_to_unwrap.syntax().text_range());
 
         let pat_start: &[_] = &[' ', '{', '\n'];
         let expr_to_unwrap = expr_to_unwrap.to_string();
@@ -89,7 +89,7 @@ fn extract_expr(cursor_range: TextRange, block: ast::BlockExpr) -> Option<ast::E
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
 
diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index 0f94f5ee8..0473fd8c2 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -13,15 +13,14 @@ macro_rules! eprintln {
 mod assist_ctx;
 mod marks;
 #[cfg(test)]
-mod doc_tests;
+mod tests;
 pub mod utils;
 pub mod ast_transform;
 
 use hir::Semantics;
-use ra_db::{FileId, FileRange};
-use ra_ide_db::RootDatabase;
-use ra_syntax::{TextRange, TextSize};
-use ra_text_edit::TextEdit;
+use ra_db::FileRange;
+use ra_ide_db::{source_change::SourceChange, RootDatabase};
+use ra_syntax::TextRange;
 
 pub(crate) use crate::assist_ctx::{Assist, AssistCtx};
 
@@ -36,44 +35,31 @@ pub struct AssistLabel {
     /// Short description of the assist, as shown in the UI.
     pub label: String,
     pub group: Option<GroupLabel>,
+    /// Target ranges are used to sort assists: the smaller the target range,
+    /// the more specific assist is, and so it should be sorted first.
+    pub target: TextRange,
 }
 
 #[derive(Clone, Debug)]
 pub struct GroupLabel(pub String);
 
 impl AssistLabel {
-    pub(crate) fn new(id: AssistId, label: String, group: Option<GroupLabel>) -> AssistLabel {
+    pub(crate) fn new(
+        id: AssistId,
+        label: String,
+        group: Option<GroupLabel>,
+        target: TextRange,
+    ) -> AssistLabel {
         // FIXME: make fields private, so that this invariant can't be broken
         assert!(label.starts_with(|c: char| c.is_uppercase()));
-        AssistLabel { id, label, group }
+        AssistLabel { id, label, group, target }
     }
 }
 
 #[derive(Debug, Clone)]
-pub struct AssistAction {
-    pub edit: TextEdit,
-    pub cursor_position: Option<TextSize>,
-    // FIXME: This belongs to `AssistLabel`
-    pub target: Option<TextRange>,
-    pub file: AssistFile,
-}
-
-#[derive(Debug, Clone)]
 pub struct ResolvedAssist {
     pub label: AssistLabel,
-    pub action: AssistAction,
-}
-
-#[derive(Debug, Clone, Copy)]
-pub enum AssistFile {
-    CurrentFile,
-    TargetFile(FileId),
-}
-
-impl Default for AssistFile {
-    fn default() -> Self {
-        Self::CurrentFile
-    }
+    pub source_change: SourceChange,
 }
 
 /// Return all the assists applicable at the given position.
@@ -104,7 +90,7 @@ pub fn resolved_assists(db: &RootDatabase, range: FileRange) -> Vec<ResolvedAssi
         .flat_map(|it| it.0)
         .map(|it| it.into_resolved().unwrap())
         .collect::<Vec<_>>();
-    a.sort_by_key(|it| it.action.target.map_or(TextSize::from(!0u32), |it| it.len()));
+    a.sort_by_key(|it| it.label.target.len());
     a
 }
 
@@ -143,6 +129,7 @@ mod handlers {
     mod replace_qualified_name_with_use;
     mod replace_unwrap_with_match;
     mod split_import;
+    mod change_return_type_to_result;
     mod add_from_impl_for_enum;
     mod reorder_fields;
     mod unwrap_block;
@@ -159,6 +146,7 @@ mod handlers {
             add_new::add_new,
             apply_demorgan::apply_demorgan,
             auto_import::auto_import,
+            change_return_type_to_result::change_return_type_to_result,
             change_visibility::change_visibility,
             early_return::convert_to_guarded_return,
             fill_match_arms::fill_match_arms,
@@ -194,150 +182,3 @@ mod handlers {
         ]
     }
 }
-
-#[cfg(test)]
-mod helpers {
-    use std::sync::Arc;
-
-    use hir::Semantics;
-    use ra_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt};
-    use ra_ide_db::{symbol_index::SymbolsDatabase, RootDatabase};
-    use test_utils::{add_cursor, assert_eq_text, extract_range_or_offset, RangeOrOffset};
-
-    use crate::{handlers::Handler, AssistCtx, AssistFile};
-
-    pub(crate) fn with_single_file(text: &str) -> (RootDatabase, FileId) {
-        let (mut db, file_id) = RootDatabase::with_single_file(text);
-        // FIXME: ideally, this should be done by the above `RootDatabase::with_single_file`,
-        // but it looks like this might need specialization? :(
-        db.set_local_roots(Arc::new(vec![db.file_source_root(file_id)]));
-        (db, file_id)
-    }
-
-    pub(crate) fn check_assist(assist: Handler, ra_fixture_before: &str, ra_fixture_after: &str) {
-        check(assist, ra_fixture_before, ExpectedResult::After(ra_fixture_after));
-    }
-
-    // FIXME: instead of having a separate function here, maybe use
-    // `extract_ranges` and mark the target as `<target> </target>` in the
-    // fixuture?
-    pub(crate) fn check_assist_target(assist: Handler, ra_fixture: &str, target: &str) {
-        check(assist, ra_fixture, ExpectedResult::Target(target));
-    }
-
-    pub(crate) fn check_assist_not_applicable(assist: Handler, ra_fixture: &str) {
-        check(assist, ra_fixture, ExpectedResult::NotApplicable);
-    }
-
-    enum ExpectedResult<'a> {
-        NotApplicable,
-        After(&'a str),
-        Target(&'a str),
-    }
-
-    fn check(assist: Handler, before: &str, expected: ExpectedResult) {
-        let (text_without_caret, file_with_caret_id, range_or_offset, db) =
-            if before.contains("//-") {
-                let (mut db, position) = RootDatabase::with_position(before);
-                db.set_local_roots(Arc::new(vec![db.file_source_root(position.file_id)]));
-                (
-                    db.file_text(position.file_id).as_ref().to_owned(),
-                    position.file_id,
-                    RangeOrOffset::Offset(position.offset),
-                    db,
-                )
-            } else {
-                let (range_or_offset, text_without_caret) = extract_range_or_offset(before);
-                let (db, file_id) = with_single_file(&text_without_caret);
-                (text_without_caret, file_id, range_or_offset, db)
-            };
-
-        let frange = FileRange { file_id: file_with_caret_id, range: range_or_offset.into() };
-
-        let sema = Semantics::new(&db);
-        let assist_ctx = AssistCtx::new(&sema, frange, true);
-
-        match (assist(assist_ctx), expected) {
-            (Some(assist), ExpectedResult::After(after)) => {
-                let action = assist.0[0].action.clone().unwrap();
-
-                let mut actual = if let AssistFile::TargetFile(file_id) = action.file {
-                    db.file_text(file_id).as_ref().to_owned()
-                } else {
-                    text_without_caret
-                };
-                action.edit.apply(&mut actual);
-
-                match action.cursor_position {
-                    None => {
-                        if let RangeOrOffset::Offset(before_cursor_pos) = range_or_offset {
-                            let off = action
-                                .edit
-                                .apply_to_offset(before_cursor_pos)
-                                .expect("cursor position is affected by the edit");
-                            actual = add_cursor(&actual, off)
-                        }
-                    }
-                    Some(off) => actual = add_cursor(&actual, off),
-                };
-
-                assert_eq_text!(after, &actual);
-            }
-            (Some(assist), ExpectedResult::Target(target)) => {
-                let action = assist.0[0].action.clone().unwrap();
-                let range = action.target.expect("expected target on action");
-                assert_eq_text!(&text_without_caret[range], target);
-            }
-            (Some(_), ExpectedResult::NotApplicable) => panic!("assist should not be applicable!"),
-            (None, ExpectedResult::After(_)) | (None, ExpectedResult::Target(_)) => {
-                panic!("code action is not applicable")
-            }
-            (None, ExpectedResult::NotApplicable) => (),
-        };
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use ra_db::FileRange;
-    use ra_syntax::TextRange;
-    use test_utils::{extract_offset, extract_range};
-
-    use crate::{helpers, resolved_assists};
-
-    #[test]
-    fn assist_order_field_struct() {
-        let before = "struct Foo { <|>bar: u32 }";
-        let (before_cursor_pos, before) = extract_offset(before);
-        let (db, file_id) = helpers::with_single_file(&before);
-        let frange = FileRange { file_id, range: TextRange::empty(before_cursor_pos) };
-        let assists = resolved_assists(&db, frange);
-        let mut assists = assists.iter();
-
-        assert_eq!(
-            assists.next().expect("expected assist").label.label,
-            "Change visibility to pub(crate)"
-        );
-        assert_eq!(assists.next().expect("expected assist").label.label, "Add `#[derive]`");
-    }
-
-    #[test]
-    fn assist_order_if_expr() {
-        let before = "
-        pub fn test_some_range(a: int) -> bool {
-            if let 2..6 = <|>5<|> {
-                true
-            } else {
-                false
-            }
-        }";
-        let (range, before) = extract_range(before);
-        let (db, file_id) = helpers::with_single_file(&before);
-        let frange = FileRange { file_id, range };
-        let assists = resolved_assists(&db, frange);
-        let mut assists = assists.iter();
-
-        assert_eq!(assists.next().expect("expected assist").label.label, "Extract into variable");
-        assert_eq!(assists.next().expect("expected assist").label.label, "Replace with match");
-    }
-}
diff --git a/crates/ra_assists/src/tests.rs b/crates/ra_assists/src/tests.rs
new file mode 100644
index 000000000..17e3ece9f
--- /dev/null
+++ b/crates/ra_assists/src/tests.rs
@@ -0,0 +1,164 @@
+mod generated;
+
+use std::sync::Arc;
+
+use hir::Semantics;
+use ra_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt};
+use ra_ide_db::{symbol_index::SymbolsDatabase, RootDatabase};
+use ra_syntax::TextRange;
+use test_utils::{
+    add_cursor, assert_eq_text, extract_offset, extract_range, extract_range_or_offset,
+    RangeOrOffset,
+};
+
+use crate::{handlers::Handler, resolved_assists, AssistCtx};
+
+pub(crate) fn with_single_file(text: &str) -> (RootDatabase, FileId) {
+    let (mut db, file_id) = RootDatabase::with_single_file(text);
+    // FIXME: ideally, this should be done by the above `RootDatabase::with_single_file`,
+    // but it looks like this might need specialization? :(
+    db.set_local_roots(Arc::new(vec![db.file_source_root(file_id)]));
+    (db, file_id)
+}
+
+pub(crate) fn check_assist(assist: Handler, ra_fixture_before: &str, ra_fixture_after: &str) {
+    check(assist, ra_fixture_before, ExpectedResult::After(ra_fixture_after));
+}
+
+// FIXME: instead of having a separate function here, maybe use
+// `extract_ranges` and mark the target as `<target> </target>` in the
+// fixuture?
+pub(crate) fn check_assist_target(assist: Handler, ra_fixture: &str, target: &str) {
+    check(assist, ra_fixture, ExpectedResult::Target(target));
+}
+
+pub(crate) fn check_assist_not_applicable(assist: Handler, ra_fixture: &str) {
+    check(assist, ra_fixture, ExpectedResult::NotApplicable);
+}
+
+fn check_doc_test(assist_id: &str, before: &str, after: &str) {
+    let (selection, before) = extract_range_or_offset(before);
+    let (db, file_id) = crate::tests::with_single_file(&before);
+    let frange = FileRange { file_id, range: selection.into() };
+
+    let mut assist = resolved_assists(&db, frange)
+        .into_iter()
+        .find(|assist| assist.label.id.0 == assist_id)
+        .unwrap_or_else(|| {
+            panic!(
+                "\n\nAssist is not applicable: {}\nAvailable assists: {}",
+                assist_id,
+                resolved_assists(&db, frange)
+                    .into_iter()
+                    .map(|assist| assist.label.id.0)
+                    .collect::<Vec<_>>()
+                    .join(", ")
+            )
+        });
+
+    let actual = {
+        let change = assist.source_change.source_file_edits.pop().unwrap();
+        let mut actual = before.clone();
+        change.edit.apply(&mut actual);
+        actual
+    };
+    assert_eq_text!(after, &actual);
+}
+
+enum ExpectedResult<'a> {
+    NotApplicable,
+    After(&'a str),
+    Target(&'a str),
+}
+
+fn check(assist: Handler, before: &str, expected: ExpectedResult) {
+    let (text_without_caret, file_with_caret_id, range_or_offset, db) = if before.contains("//-") {
+        let (mut db, position) = RootDatabase::with_position(before);
+        db.set_local_roots(Arc::new(vec![db.file_source_root(position.file_id)]));
+        (
+            db.file_text(position.file_id).as_ref().to_owned(),
+            position.file_id,
+            RangeOrOffset::Offset(position.offset),
+            db,
+        )
+    } else {
+        let (range_or_offset, text_without_caret) = extract_range_or_offset(before);
+        let (db, file_id) = with_single_file(&text_without_caret);
+        (text_without_caret, file_id, range_or_offset, db)
+    };
+
+    let frange = FileRange { file_id: file_with_caret_id, range: range_or_offset.into() };
+
+    let sema = Semantics::new(&db);
+    let assist_ctx = AssistCtx::new(&sema, frange, true);
+
+    match (assist(assist_ctx), expected) {
+        (Some(assist), ExpectedResult::After(after)) => {
+            let mut action = assist.0[0].source_change.clone().unwrap();
+            let change = action.source_file_edits.pop().unwrap();
+
+            let mut actual = db.file_text(change.file_id).as_ref().to_owned();
+            change.edit.apply(&mut actual);
+
+            match action.cursor_position {
+                None => {
+                    if let RangeOrOffset::Offset(before_cursor_pos) = range_or_offset {
+                        let off = change
+                            .edit
+                            .apply_to_offset(before_cursor_pos)
+                            .expect("cursor position is affected by the edit");
+                        actual = add_cursor(&actual, off)
+                    }
+                }
+                Some(off) => actual = add_cursor(&actual, off.offset),
+            };
+
+            assert_eq_text!(after, &actual);
+        }
+        (Some(assist), ExpectedResult::Target(target)) => {
+            let range = assist.0[0].label.target;
+            assert_eq_text!(&text_without_caret[range], target);
+        }
+        (Some(_), ExpectedResult::NotApplicable) => panic!("assist should not be applicable!"),
+        (None, ExpectedResult::After(_)) | (None, ExpectedResult::Target(_)) => {
+            panic!("code action is not applicable")
+        }
+        (None, ExpectedResult::NotApplicable) => (),
+    };
+}
+
+#[test]
+fn assist_order_field_struct() {
+    let before = "struct Foo { <|>bar: u32 }";
+    let (before_cursor_pos, before) = extract_offset(before);
+    let (db, file_id) = with_single_file(&before);
+    let frange = FileRange { file_id, range: TextRange::empty(before_cursor_pos) };
+    let assists = resolved_assists(&db, frange);
+    let mut assists = assists.iter();
+
+    assert_eq!(
+        assists.next().expect("expected assist").label.label,
+        "Change visibility to pub(crate)"
+    );
+    assert_eq!(assists.next().expect("expected assist").label.label, "Add `#[derive]`");
+}
+
+#[test]
+fn assist_order_if_expr() {
+    let before = "
+    pub fn test_some_range(a: int) -> bool {
+        if let 2..6 = <|>5<|> {
+            true
+        } else {
+            false
+        }
+    }";
+    let (range, before) = extract_range(before);
+    let (db, file_id) = with_single_file(&before);
+    let frange = FileRange { file_id, range };
+    let assists = resolved_assists(&db, frange);
+    let mut assists = assists.iter();
+
+    assert_eq!(assists.next().expect("expected assist").label.label, "Extract into variable");
+    assert_eq!(assists.next().expect("expected assist").label.label, "Replace with match");
+}
diff --git a/crates/ra_assists/src/doc_tests/generated.rs b/crates/ra_assists/src/tests/generated.rs
index 6696cc832..972dbd251 100644
--- a/crates/ra_assists/src/doc_tests/generated.rs
+++ b/crates/ra_assists/src/tests/generated.rs
@@ -1,10 +1,10 @@
 //! Generated file, do not edit by hand, see `xtask/src/codegen`
 
-use super::check;
+use super::check_doc_test;
 
 #[test]
 fn doctest_add_custom_impl() {
-    check(
+    check_doc_test(
         "add_custom_impl",
         r#####"
 #[derive(Deb<|>ug, Display)]
@@ -23,7 +23,7 @@ impl Debug for S {
 
 #[test]
 fn doctest_add_derive() {
-    check(
+    check_doc_test(
         "add_derive",
         r#####"
 struct Point {
@@ -43,7 +43,7 @@ struct Point {
 
 #[test]
 fn doctest_add_explicit_type() {
-    check(
+    check_doc_test(
         "add_explicit_type",
         r#####"
 fn main() {
@@ -60,7 +60,7 @@ fn main() {
 
 #[test]
 fn doctest_add_function() {
-    check(
+    check_doc_test(
         "add_function",
         r#####"
 struct Baz;
@@ -87,7 +87,7 @@ fn bar(arg: &str, baz: Baz) {
 
 #[test]
 fn doctest_add_hash() {
-    check(
+    check_doc_test(
         "add_hash",
         r#####"
 fn main() {
@@ -104,7 +104,7 @@ fn main() {
 
 #[test]
 fn doctest_add_impl() {
-    check(
+    check_doc_test(
         "add_impl",
         r#####"
 struct Ctx<T: Clone> {
@@ -125,7 +125,7 @@ impl<T: Clone> Ctx<T> {
 
 #[test]
 fn doctest_add_impl_default_members() {
-    check(
+    check_doc_test(
         "add_impl_default_members",
         r#####"
 trait Trait {
@@ -159,7 +159,7 @@ impl Trait for () {
 
 #[test]
 fn doctest_add_impl_missing_members() {
-    check(
+    check_doc_test(
         "add_impl_missing_members",
         r#####"
 trait Trait<T> {
@@ -191,7 +191,7 @@ impl Trait<u32> for () {
 
 #[test]
 fn doctest_add_new() {
-    check(
+    check_doc_test(
         "add_new",
         r#####"
 struct Ctx<T: Clone> {
@@ -213,7 +213,7 @@ impl<T: Clone> Ctx<T> {
 
 #[test]
 fn doctest_apply_demorgan() {
-    check(
+    check_doc_test(
         "apply_demorgan",
         r#####"
 fn main() {
@@ -230,7 +230,7 @@ fn main() {
 
 #[test]
 fn doctest_auto_import() {
-    check(
+    check_doc_test(
         "auto_import",
         r#####"
 fn main() {
@@ -250,8 +250,21 @@ pub mod std { pub mod collections { pub struct HashMap { } } }
 }
 
 #[test]
+fn doctest_change_return_type_to_result() {
+    check_doc_test(
+        "change_return_type_to_result",
+        r#####"
+fn foo() -> i32<|> { 42i32 }
+"#####,
+        r#####"
+fn foo() -> Result<i32, > { Ok(42i32) }
+"#####,
+    )
+}
+
+#[test]
 fn doctest_change_visibility() {
-    check(
+    check_doc_test(
         "change_visibility",
         r#####"
 <|>fn frobnicate() {}
@@ -264,7 +277,7 @@ pub(crate) fn frobnicate() {}
 
 #[test]
 fn doctest_convert_to_guarded_return() {
-    check(
+    check_doc_test(
         "convert_to_guarded_return",
         r#####"
 fn main() {
@@ -288,7 +301,7 @@ fn main() {
 
 #[test]
 fn doctest_fill_match_arms() {
-    check(
+    check_doc_test(
         "fill_match_arms",
         r#####"
 enum Action { Move { distance: u32 }, Stop }
@@ -314,7 +327,7 @@ fn handle(action: Action) {
 
 #[test]
 fn doctest_flip_binexpr() {
-    check(
+    check_doc_test(
         "flip_binexpr",
         r#####"
 fn main() {
@@ -331,7 +344,7 @@ fn main() {
 
 #[test]
 fn doctest_flip_comma() {
-    check(
+    check_doc_test(
         "flip_comma",
         r#####"
 fn main() {
@@ -348,7 +361,7 @@ fn main() {
 
 #[test]
 fn doctest_flip_trait_bound() {
-    check(
+    check_doc_test(
         "flip_trait_bound",
         r#####"
 fn foo<T: Clone +<|> Copy>() { }
@@ -361,7 +374,7 @@ fn foo<T: Copy + Clone>() { }
 
 #[test]
 fn doctest_inline_local_variable() {
-    check(
+    check_doc_test(
         "inline_local_variable",
         r#####"
 fn main() {
@@ -379,7 +392,7 @@ fn main() {
 
 #[test]
 fn doctest_introduce_variable() {
-    check(
+    check_doc_test(
         "introduce_variable",
         r#####"
 fn main() {
@@ -397,7 +410,7 @@ fn main() {
 
 #[test]
 fn doctest_invert_if() {
-    check(
+    check_doc_test(
         "invert_if",
         r#####"
 fn main() {
@@ -414,7 +427,7 @@ fn main() {
 
 #[test]
 fn doctest_make_raw_string() {
-    check(
+    check_doc_test(
         "make_raw_string",
         r#####"
 fn main() {
@@ -431,7 +444,7 @@ fn main() {
 
 #[test]
 fn doctest_make_usual_string() {
-    check(
+    check_doc_test(
         "make_usual_string",
         r#####"
 fn main() {
@@ -448,7 +461,7 @@ fn main() {
 
 #[test]
 fn doctest_merge_imports() {
-    check(
+    check_doc_test(
         "merge_imports",
         r#####"
 use std::<|>fmt::Formatter;
@@ -462,7 +475,7 @@ use std::{fmt::Formatter, io};
 
 #[test]
 fn doctest_merge_match_arms() {
-    check(
+    check_doc_test(
         "merge_match_arms",
         r#####"
 enum Action { Move { distance: u32 }, Stop }
@@ -488,7 +501,7 @@ fn handle(action: Action) {
 
 #[test]
 fn doctest_move_arm_cond_to_match_guard() {
-    check(
+    check_doc_test(
         "move_arm_cond_to_match_guard",
         r#####"
 enum Action { Move { distance: u32 }, Stop }
@@ -515,7 +528,7 @@ fn handle(action: Action) {
 
 #[test]
 fn doctest_move_bounds_to_where_clause() {
-    check(
+    check_doc_test(
         "move_bounds_to_where_clause",
         r#####"
 fn apply<T, U, <|>F: FnOnce(T) -> U>(f: F, x: T) -> U {
@@ -532,7 +545,7 @@ fn apply<T, U, F>(f: F, x: T) -> U where F: FnOnce(T) -> U {
 
 #[test]
 fn doctest_move_guard_to_arm_body() {
-    check(
+    check_doc_test(
         "move_guard_to_arm_body",
         r#####"
 enum Action { Move { distance: u32 }, Stop }
@@ -559,7 +572,7 @@ fn handle(action: Action) {
 
 #[test]
 fn doctest_remove_dbg() {
-    check(
+    check_doc_test(
         "remove_dbg",
         r#####"
 fn main() {
@@ -576,7 +589,7 @@ fn main() {
 
 #[test]
 fn doctest_remove_hash() {
-    check(
+    check_doc_test(
         "remove_hash",
         r#####"
 fn main() {
@@ -593,7 +606,7 @@ fn main() {
 
 #[test]
 fn doctest_remove_mut() {
-    check(
+    check_doc_test(
         "remove_mut",
         r#####"
 impl Walrus {
@@ -610,7 +623,7 @@ impl Walrus {
 
 #[test]
 fn doctest_reorder_fields() {
-    check(
+    check_doc_test(
         "reorder_fields",
         r#####"
 struct Foo {foo: i32, bar: i32};
@@ -625,7 +638,7 @@ const test: Foo = Foo {foo: 1, bar: 0}
 
 #[test]
 fn doctest_replace_if_let_with_match() {
-    check(
+    check_doc_test(
         "replace_if_let_with_match",
         r#####"
 enum Action { Move { distance: u32 }, Stop }
@@ -653,7 +666,7 @@ fn handle(action: Action) {
 
 #[test]
 fn doctest_replace_let_with_if_let() {
-    check(
+    check_doc_test(
         "replace_let_with_if_let",
         r#####"
 enum Option<T> { Some(T), None }
@@ -679,7 +692,7 @@ fn compute() -> Option<i32> { None }
 
 #[test]
 fn doctest_replace_qualified_name_with_use() {
-    check(
+    check_doc_test(
         "replace_qualified_name_with_use",
         r#####"
 fn process(map: std::collections::<|>HashMap<String, String>) {}
@@ -694,7 +707,7 @@ fn process(map: HashMap<String, String>) {}
 
 #[test]
 fn doctest_replace_unwrap_with_match() {
-    check(
+    check_doc_test(
         "replace_unwrap_with_match",
         r#####"
 enum Result<T, E> { Ok(T), Err(E) }
@@ -718,7 +731,7 @@ fn main() {
 
 #[test]
 fn doctest_split_import() {
-    check(
+    check_doc_test(
         "split_import",
         r#####"
 use std::<|>collections::HashMap;
@@ -731,7 +744,7 @@ use std::{collections::HashMap};
 
 #[test]
 fn doctest_unwrap_block() {
-    check(
+    check_doc_test(
         "unwrap_block",
         r#####"
 fn foo() {
diff --git a/crates/ra_db/src/fixture.rs b/crates/ra_db/src/fixture.rs
index 8248684ee..51d4c493e 100644
--- a/crates/ra_db/src/fixture.rs
+++ b/crates/ra_db/src/fixture.rs
@@ -1,4 +1,48 @@
-//! FIXME: write short doc here
+//! Fixtures are strings containing rust source code with optional metadata.
+//! A fixture without metadata is parsed into a single source file.
+//! Use this to test functionality local to one file.
+//!
+//! Example:
+//! ```
+//! r#"
+//! fn main() {
+//!     println!("Hello World")
+//! }
+//! "#
+//! ```
+//!
+//! Metadata can be added to a fixture after a `//-` comment.
+//! The basic form is specifying filenames,
+//! which is also how to define multiple files in a single test fixture
+//!
+//! Example:
+//! ```
+//! "
+//! //- /main.rs
+//! mod foo;
+//! fn main() {
+//!     foo::bar();
+//! }
+//!
+//! //- /foo.rs
+//! pub fn bar() {}
+//! "
+//! ```
+//!
+//! Metadata allows specifying all settings and variables
+//! that are available in a real rust project:
+//! - crate names via `crate:cratename`
+//! - dependencies via `deps:dep1,dep2`
+//! - configuration settings via `cfg:dbg=false,opt_level=2`
+//! - environment variables via `env:PATH=/bin,RUST_LOG=debug`
+//!
+//! Example:
+//! ```
+//! "
+//! //- /lib.rs crate:foo deps:bar,baz cfg:foo=a,bar=b env:OUTDIR=path/to,OTHER=foo
+//! fn insert_source_code_here() {}
+//! "
+//! ```
 
 use std::str::FromStr;
 use std::sync::Arc;
diff --git a/crates/ra_hir_ty/src/_match.rs b/crates/ra_hir_ty/src/_match.rs
index 779e78574..149f65042 100644
--- a/crates/ra_hir_ty/src/_match.rs
+++ b/crates/ra_hir_ty/src/_match.rs
@@ -573,14 +573,20 @@ pub(crate) fn is_useful(
     matrix: &Matrix,
     v: &PatStack,
 ) -> MatchCheckResult<Usefulness> {
-    // Handle the special case of enums with no variants. In that case, no match
-    // arm is useful.
-    if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) =
-        cx.infer[cx.match_expr].strip_references()
-    {
-        if cx.db.enum_data(*enum_id).variants.is_empty() {
+    // Handle two special cases:
+    // - enum with no variants
+    // - `!` type
+    // In those cases, no match arm is useful.
+    match cx.infer[cx.match_expr].strip_references() {
+        Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) => {
+            if cx.db.enum_data(*enum_id).variants.is_empty() {
+                return Ok(Usefulness::NotUseful);
+            }
+        }
+        Ty::Apply(ApplicationTy { ctor: TypeCtor::Never, .. }) => {
             return Ok(Usefulness::NotUseful);
         }
+        _ => (),
     }
 
     if v.is_empty() {
@@ -1918,6 +1924,17 @@ mod tests {
     }
 
     #[test]
+    fn type_never() {
+        let content = r"
+            fn test_fn(never: !) {
+                match never {}
+            }
+        ";
+
+        check_no_diagnostic(content);
+    }
+
+    #[test]
     fn enum_never_ref() {
         let content = r"
             enum Never {}
diff --git a/crates/ra_ide/src/assists.rs b/crates/ra_ide/src/assists.rs
deleted file mode 100644
index 389339a03..000000000
--- a/crates/ra_ide/src/assists.rs
+++ /dev/null
@@ -1,42 +0,0 @@
-//! FIXME: write short doc here
-
-use ra_assists::{resolved_assists, AssistAction};
-use ra_db::{FilePosition, FileRange};
-use ra_ide_db::RootDatabase;
-
-use crate::{FileId, SourceChange, SourceFileEdit};
-
-pub use ra_assists::AssistId;
-
-#[derive(Debug)]
-pub struct Assist {
-    pub id: AssistId,
-    pub label: String,
-    pub group_label: Option<String>,
-    pub source_change: SourceChange,
-}
-
-pub(crate) fn assists(db: &RootDatabase, frange: FileRange) -> Vec<Assist> {
-    resolved_assists(db, frange)
-        .into_iter()
-        .map(|assist| {
-            let file_id = frange.file_id;
-            Assist {
-                id: assist.label.id,
-                label: assist.label.label.clone(),
-                group_label: assist.label.group.map(|it| it.0),
-                source_change: action_to_edit(assist.action, file_id, assist.label.label.clone()),
-            }
-        })
-        .collect()
-}
-
-fn action_to_edit(action: AssistAction, file_id: FileId, label: String) -> SourceChange {
-    let file_id = match action.file {
-        ra_assists::AssistFile::TargetFile(it) => it,
-        _ => file_id,
-    };
-    let file_edit = SourceFileEdit { file_id, edit: action.edit };
-    SourceChange::source_file_edit(label, file_edit)
-        .with_cursor_opt(action.cursor_position.map(|offset| FilePosition { offset, file_id }))
-}
diff --git a/crates/ra_ide/src/completion/completion_item.rs b/crates/ra_ide/src/completion/completion_item.rs
index 383b23ac4..6021f7279 100644
--- a/crates/ra_ide/src/completion/completion_item.rs
+++ b/crates/ra_ide/src/completion/completion_item.rs
@@ -2,11 +2,12 @@
 
 use std::fmt;
 
-use super::completion_config::SnippetCap;
 use hir::Documentation;
 use ra_syntax::TextRange;
 use ra_text_edit::TextEdit;
 
+use crate::completion::completion_config::SnippetCap;
+
 /// `CompletionItem` describes a single completion variant in the editor pop-up.
 /// It is basically a POD with various properties. To construct a
 /// `CompletionItem`, use `new` method and the `Builder` struct.
diff --git a/crates/ra_ide/src/lib.rs b/crates/ra_ide/src/lib.rs
index 09f602fe1..737f87109 100644
--- a/crates/ra_ide/src/lib.rs
+++ b/crates/ra_ide/src/lib.rs
@@ -16,7 +16,6 @@ macro_rules! eprintln {
 }
 
 pub mod mock_analysis;
-mod source_change;
 
 mod prime_caches;
 mod status;
@@ -32,7 +31,6 @@ mod syntax_highlighting;
 mod parent_module;
 mod references;
 mod impls;
-mod assists;
 mod diagnostics;
 mod syntax_tree;
 mod folding_ranges;
@@ -65,7 +63,6 @@ use ra_syntax::{SourceFile, TextRange, TextSize};
 use crate::display::ToNav;
 
 pub use crate::{
-    assists::{Assist, AssistId},
     call_hierarchy::CallItem,
     completion::{
         CompletionConfig, CompletionItem, CompletionItemKind, CompletionScore, InsertTextFormat,
@@ -78,7 +75,6 @@ pub use crate::{
     inlay_hints::{InlayHint, InlayHintsConfig, InlayKind},
     references::{Declaration, Reference, ReferenceAccess, ReferenceKind, ReferenceSearchResult},
     runnables::{Runnable, RunnableKind, TestId},
-    source_change::{FileSystemEdit, SourceChange, SourceFileEdit},
     ssr::SsrError,
     syntax_highlighting::{
         Highlight, HighlightModifier, HighlightModifiers, HighlightTag, HighlightedRange,
@@ -86,6 +82,7 @@ pub use crate::{
 };
 
 pub use hir::Documentation;
+pub use ra_assists::AssistId;
 pub use ra_db::{
     Canceled, CrateGraph, CrateId, Edition, FileId, FilePosition, FileRange, SourceRootId,
 };
@@ -94,6 +91,7 @@ pub use ra_ide_db::{
     line_index::{LineCol, LineIndex},
     line_index_utils::translate_offset_with_edit,
     search::SearchScope,
+    source_change::{FileSystemEdit, SourceChange, SourceFileEdit},
     symbol_index::Query,
     RootDatabase,
 };
@@ -135,10 +133,12 @@ pub struct AnalysisHost {
     db: RootDatabase,
 }
 
-impl Default for AnalysisHost {
-    fn default() -> AnalysisHost {
-        AnalysisHost::new(None)
-    }
+#[derive(Debug)]
+pub struct Assist {
+    pub id: AssistId,
+    pub label: String,
+    pub group_label: Option<String>,
+    pub source_change: SourceChange,
 }
 
 impl AnalysisHost {
@@ -188,6 +188,12 @@ impl AnalysisHost {
     }
 }
 
+impl Default for AnalysisHost {
+    fn default() -> AnalysisHost {
+        AnalysisHost::new(None)
+    }
+}
+
 /// Analysis is a snapshot of a world state at a moment in time. It is the main
 /// entry point for asking semantic information about the world. When the world
 /// state is advanced using `AnalysisHost::apply_change` method, all existing
@@ -296,7 +302,7 @@ impl Analysis {
                 file_id: frange.file_id,
                 edit: join_lines::join_lines(&parse.tree(), frange.range),
             };
-            SourceChange::source_file_edit("join lines", file_edit)
+            SourceChange::source_file_edit("Join lines", file_edit)
         })
     }
 
@@ -465,7 +471,17 @@ impl Analysis {
     /// Computes assists (aka code actions aka intentions) for the given
     /// position.
     pub fn assists(&self, frange: FileRange) -> Cancelable<Vec<Assist>> {
-        self.with_db(|db| assists::assists(db, frange))
+        self.with_db(|db| {
+            ra_assists::resolved_assists(db, frange)
+                .into_iter()
+                .map(|assist| Assist {
+                    id: assist.label.id,
+                    label: assist.label.label,
+                    group_label: assist.label.group.map(|it| it.0),
+                    source_change: assist.source_change,
+                })
+                .collect()
+        })
     }
 
     /// Computes the set of diagnostics for the given file.
@@ -490,7 +506,7 @@ impl Analysis {
     ) -> Cancelable<Result<SourceChange, SsrError>> {
         self.with_db(|db| {
             let edits = ssr::parse_search_replace(query, parse_only, db)?;
-            Ok(SourceChange::source_file_edits("ssr", edits))
+            Ok(SourceChange::source_file_edits("Structural Search Replace", edits))
         })
     }
 
diff --git a/crates/ra_ide/src/ssr.rs b/crates/ra_ide/src/ssr.rs
index 8bf52d0fa..1873d1d0d 100644
--- a/crates/ra_ide/src/ssr.rs
+++ b/crates/ra_ide/src/ssr.rs
@@ -1,18 +1,18 @@
 //!  structural search replace
 
-use crate::source_change::SourceFileEdit;
+use std::{collections::HashMap, iter::once, str::FromStr};
+
 use ra_db::{SourceDatabase, SourceDatabaseExt};
-use ra_ide_db::symbol_index::SymbolsDatabase;
-use ra_ide_db::RootDatabase;
-use ra_syntax::ast::make::try_expr_from_text;
+use ra_ide_db::{symbol_index::SymbolsDatabase, RootDatabase};
 use ra_syntax::ast::{
-    ArgList, AstToken, CallExpr, Comment, Expr, MethodCallExpr, RecordField, RecordLit,
+    make::try_expr_from_text, ArgList, AstToken, CallExpr, Comment, Expr, MethodCallExpr,
+    RecordField, RecordLit,
 };
 use ra_syntax::{AstNode, SyntaxElement, SyntaxKind, SyntaxNode};
 use ra_text_edit::{TextEdit, TextEditBuilder};
 use rustc_hash::FxHashMap;
-use std::collections::HashMap;
-use std::{iter::once, str::FromStr};
+
+use crate::SourceFileEdit;
 
 #[derive(Debug, PartialEq)]
 pub struct SsrError(String);
diff --git a/crates/ra_ide/src/typing.rs b/crates/ra_ide/src/typing.rs
index a03da4693..6f04f0be4 100644
--- a/crates/ra_ide/src/typing.rs
+++ b/crates/ra_ide/src/typing.rs
@@ -17,15 +17,16 @@ mod on_enter;
 
 use ra_db::{FilePosition, SourceDatabase};
 use ra_fmt::leading_indent;
-use ra_ide_db::RootDatabase;
+use ra_ide_db::{source_change::SingleFileChange, RootDatabase};
 use ra_syntax::{
     algo::find_node_at_offset,
     ast::{self, AstToken},
     AstNode, SourceFile, TextRange, TextSize,
 };
+
 use ra_text_edit::TextEdit;
 
-use crate::{source_change::SingleFileChange, SourceChange};
+use crate::SourceChange;
 
 pub(crate) use on_enter::on_enter;
 
diff --git a/crates/ra_ide_db/src/lib.rs b/crates/ra_ide_db/src/lib.rs
index e6f2d36e9..52fcd7b6f 100644
--- a/crates/ra_ide_db/src/lib.rs
+++ b/crates/ra_ide_db/src/lib.rs
@@ -10,6 +10,7 @@ pub mod change;
 pub mod defs;
 pub mod search;
 pub mod imports_locator;
+pub mod source_change;
 mod wasm_shims;
 
 use std::sync::Arc;
diff --git a/crates/ra_ide/src/source_change.rs b/crates/ra_ide_db/src/source_change.rs
index 10afd7825..af81a91a4 100644
--- a/crates/ra_ide/src/source_change.rs
+++ b/crates/ra_ide_db/src/source_change.rs
@@ -3,13 +3,12 @@
 //!
 //! It can be viewed as a dual for `AnalysisChange`.
 
-use ra_db::RelativePathBuf;
-use ra_text_edit::TextEdit;
+use ra_db::{FileId, FilePosition, RelativePathBuf, SourceRootId};
+use ra_text_edit::{TextEdit, TextSize};
 
-use crate::{FileId, FilePosition, SourceRootId, TextSize};
-
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct SourceChange {
+    /// For display in the undo log in the editor
     pub label: String,
     pub source_file_edits: Vec<SourceFileEdit>,
     pub file_system_edits: Vec<FileSystemEdit>,
@@ -19,7 +18,7 @@ pub struct SourceChange {
 impl SourceChange {
     /// Creates a new SourceChange with the given label
     /// from the edits.
-    pub(crate) fn from_edits<L: Into<String>>(
+    pub fn from_edits<L: Into<String>>(
         label: L,
         source_file_edits: Vec<SourceFileEdit>,
         file_system_edits: Vec<FileSystemEdit>,
@@ -34,7 +33,7 @@ impl SourceChange {
 
     /// Creates a new SourceChange with the given label,
     /// containing only the given `SourceFileEdits`.
-    pub(crate) fn source_file_edits<L: Into<String>>(label: L, edits: Vec<SourceFileEdit>) -> Self {
+    pub fn source_file_edits<L: Into<String>>(label: L, edits: Vec<SourceFileEdit>) -> Self {
         let label = label.into();
         assert!(label.starts_with(char::is_uppercase));
         SourceChange {
@@ -58,13 +57,13 @@ impl SourceChange {
 
     /// Creates a new SourceChange with the given label,
     /// containing only a single `SourceFileEdit`.
-    pub(crate) fn source_file_edit<L: Into<String>>(label: L, edit: SourceFileEdit) -> Self {
+    pub fn source_file_edit<L: Into<String>>(label: L, edit: SourceFileEdit) -> Self {
         SourceChange::source_file_edits(label, vec![edit])
     }
 
     /// Creates a new SourceChange with the given label
     /// from the given `FileId` and `TextEdit`
-    pub(crate) fn source_file_edit_from<L: Into<String>>(
+    pub fn source_file_edit_from<L: Into<String>>(
         label: L,
         file_id: FileId,
         edit: TextEdit,
@@ -74,43 +73,43 @@ impl SourceChange {
 
     /// Creates a new SourceChange with the given label
     /// from the given `FileId` and `TextEdit`
-    pub(crate) fn file_system_edit<L: Into<String>>(label: L, edit: FileSystemEdit) -> Self {
+    pub fn file_system_edit<L: Into<String>>(label: L, edit: FileSystemEdit) -> Self {
         SourceChange::file_system_edits(label, vec![edit])
     }
 
     /// Sets the cursor position to the given `FilePosition`
-    pub(crate) fn with_cursor(mut self, cursor_position: FilePosition) -> Self {
+    pub fn with_cursor(mut self, cursor_position: FilePosition) -> Self {
         self.cursor_position = Some(cursor_position);
         self
     }
 
     /// Sets the cursor position to the given `FilePosition`
-    pub(crate) fn with_cursor_opt(mut self, cursor_position: Option<FilePosition>) -> Self {
+    pub fn with_cursor_opt(mut self, cursor_position: Option<FilePosition>) -> Self {
         self.cursor_position = cursor_position;
         self
     }
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct SourceFileEdit {
     pub file_id: FileId,
     pub edit: TextEdit,
 }
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum FileSystemEdit {
     CreateFile { source_root: SourceRootId, path: RelativePathBuf },
     MoveFile { src: FileId, dst_source_root: SourceRootId, dst_path: RelativePathBuf },
 }
 
-pub(crate) struct SingleFileChange {
+pub struct SingleFileChange {
     pub label: String,
     pub edit: TextEdit,
     pub cursor_position: Option<TextSize>,
 }
 
 impl SingleFileChange {
-    pub(crate) fn into_source_change(self, file_id: FileId) -> SourceChange {
+    pub fn into_source_change(self, file_id: FileId) -> SourceChange {
         SourceChange {
             label: self.label,
             source_file_edits: vec![SourceFileEdit { file_id, edit: self.edit }],
diff --git a/crates/ra_text_edit/src/lib.rs b/crates/ra_text_edit/src/lib.rs
index 7138bbc65..3409713ff 100644
--- a/crates/ra_text_edit/src/lib.rs
+++ b/crates/ra_text_edit/src/lib.rs
@@ -4,7 +4,7 @@
 //! so `TextEdit` is the ultimate representation of the work done by
 //! rust-analyzer.
 
-use text_size::{TextRange, TextSize};
+pub use text_size::{TextRange, TextSize};
 
 /// `InsertDelete` -- a single "atomic" change to text
 ///
@@ -71,6 +71,10 @@ impl TextEdit {
         TextEdit { indels }
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.indels.is_empty()
+    }
+
     pub fn as_indels(&self) -> &[Indel] {
         &self.indels
     }
diff --git a/crates/test_utils/src/lib.rs b/crates/test_utils/src/lib.rs
index b1365444a..b13e13af2 100644
--- a/crates/test_utils/src/lib.rs
+++ b/crates/test_utils/src/lib.rs
@@ -155,7 +155,7 @@ pub fn add_cursor(text: &str, offset: TextSize) -> String {
     res
 }
 
-#[derive(Debug)]
+#[derive(Debug, Eq, PartialEq)]
 pub struct FixtureEntry {
     pub meta: String,
     pub text: String,
@@ -170,19 +170,26 @@ pub struct FixtureEntry {
 ///  // - other meta
 ///  ```
 pub fn parse_fixture(fixture: &str) -> Vec<FixtureEntry> {
-    let margin = fixture
-        .lines()
-        .filter(|it| it.trim_start().starts_with("//-"))
-        .map(|it| it.len() - it.trim_start().len())
-        .next()
-        .expect("empty fixture");
+    let fixture = indent_first_line(fixture);
+    let margin = fixture_margin(&fixture);
 
     let mut lines = fixture
         .split('\n') // don't use `.lines` to not drop `\r\n`
-        .filter_map(|line| {
+        .enumerate()
+        .filter_map(|(ix, line)| {
             if line.len() >= margin {
                 assert!(line[..margin].trim().is_empty());
-                Some(&line[margin..])
+                let line_content = &line[margin..];
+                if !line_content.starts_with("//-") {
+                    assert!(
+                        !line_content.contains("//-"),
+                        r#"Metadata line {} has invalid indentation. All metadata lines need to have the same indentation.
+The offending line: {:?}"#,
+                        ix,
+                        line
+                    );
+                }
+                Some(line_content)
             } else {
                 assert!(line.trim().is_empty());
                 None
@@ -202,6 +209,85 @@ pub fn parse_fixture(fixture: &str) -> Vec<FixtureEntry> {
     res
 }
 
+/// Adjusts the indentation of the first line to the minimum indentation of the rest of the lines.
+/// This allows fixtures to start off in a different indentation, e.g. to align the first line with
+/// the other lines visually:
+/// ```
+/// let fixture = "//- /lib.rs
+///                mod foo;
+///                //- /foo.rs
+///                fn bar() {}
+/// ";
+/// assert_eq!(fixture_margin(fixture),
+/// "               //- /lib.rs
+///                mod foo;
+///                //- /foo.rs
+///                fn bar() {}
+/// ")
+/// ```
+fn indent_first_line(fixture: &str) -> String {
+    if fixture.is_empty() {
+        return String::new();
+    }
+    let mut lines = fixture.lines();
+    let first_line = lines.next().unwrap();
+    if first_line.contains("//-") {
+        let rest = lines.collect::<Vec<_>>().join("\n");
+        let fixed_margin = fixture_margin(&rest);
+        let fixed_indent = fixed_margin - indent_len(first_line);
+        format!("\n{}{}\n{}", " ".repeat(fixed_indent), first_line, rest)
+    } else {
+        fixture.to_owned()
+    }
+}
+
+fn fixture_margin(fixture: &str) -> usize {
+    fixture
+        .lines()
+        .filter(|it| it.trim_start().starts_with("//-"))
+        .map(indent_len)
+        .next()
+        .expect("empty fixture")
+}
+
+fn indent_len(s: &str) -> usize {
+    s.len() - s.trim_start().len()
+}
+
+#[test]
+#[should_panic]
+fn parse_fixture_checks_further_indented_metadata() {
+    parse_fixture(
+        r"
+        //- /lib.rs
+          mod bar;
+
+          fn foo() {}
+          //- /bar.rs
+          pub fn baz() {}
+          ",
+    );
+}
+
+#[test]
+fn parse_fixture_can_handle_unindented_first_line() {
+    let fixture = "//- /lib.rs
+                   mod foo;
+                   //- /foo.rs
+                   struct Bar;
+";
+    assert_eq!(
+        parse_fixture(fixture),
+        parse_fixture(
+            "//- /lib.rs
+mod foo;
+//- /foo.rs
+struct Bar;
+"
+        )
+    )
+}
+
 /// Same as `parse_fixture`, except it allow empty fixture
 pub fn parse_single_fixture(fixture: &str) -> Option<FixtureEntry> {
     if !fixture.lines().any(|it| it.trim_start().starts_with("//-")) {
diff --git a/docs/user/assists.md b/docs/user/assists.md
index ee515949e..692fd4f52 100644
--- a/docs/user/assists.md
+++ b/docs/user/assists.md
@@ -241,6 +241,18 @@ fn main() {
 }
 ```
 
+## `change_return_type_to_result`
+
+Change the function's return type to Result.
+
+```rust
+// BEFORE
+fn foo() -> i32┃ { 42i32 }
+
+// AFTER
+fn foo() -> Result<i32, > { Ok(42i32) }
+```
+
 ## `change_visibility`
 
 Adds or changes existing visibility specifier.
diff --git a/docs/user/readme.adoc b/docs/user/readme.adoc
index 69f5b13d6..301e9a49c 100644
--- a/docs/user/readme.adoc
+++ b/docs/user/readme.adoc
@@ -61,7 +61,7 @@ The server binary is stored in:
 
 * Linux: `~/.config/Code/User/globalStorage/matklad.rust-analyzer`
 * macOS: `~/Library/Application Support/Code/User/globalStorage/matklad.rust-analyzer`
-* Windows: `%APPDATA%\Code\User\globalStorage`
+* Windows: `%APPDATA%\Code\User\globalStorage\matklad.rust-analyzer`
 
 Note that we only support the latest version of VS Code.
 
diff --git a/editors/code/package.json b/editors/code/package.json
index eeb3d3513..8849615c8 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -405,7 +405,7 @@
                         "ms-vscode.cpptools"
                     ],
                     "default": "auto",
-                    "description": "Preffered debug engine.",
+                    "description": "Preferred debug engine.",
                     "markdownEnumDescriptions": [
                         "First try to use [CodeLLDB](https://marketplace.visualstudio.com/items?itemName=vadimcn.vscode-lldb), if it's not installed try to use [MS C++ tools](https://marketplace.visualstudio.com/items?itemName=ms-vscode.cpptools).",
                         "Use [CodeLLDB](https://marketplace.visualstudio.com/items?itemName=vadimcn.vscode-lldb)",
diff --git a/xtask/src/codegen.rs b/xtask/src/codegen.rs
index 0e4dcb95a..b4907f4b2 100644
--- a/xtask/src/codegen.rs
+++ b/xtask/src/codegen.rs
@@ -27,7 +27,7 @@ const AST_NODES: &str = "crates/ra_syntax/src/ast/generated/nodes.rs";
 const AST_TOKENS: &str = "crates/ra_syntax/src/ast/generated/tokens.rs";
 
 const ASSISTS_DIR: &str = "crates/ra_assists/src/handlers";
-const ASSISTS_TESTS: &str = "crates/ra_assists/src/doc_tests/generated.rs";
+const ASSISTS_TESTS: &str = "crates/ra_assists/src/tests/generated.rs";
 const ASSISTS_DOCS: &str = "docs/user/assists.md";
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
diff --git a/xtask/src/codegen/gen_assists_docs.rs b/xtask/src/codegen/gen_assists_docs.rs
index 31d606535..4bd6b5f0c 100644
--- a/xtask/src/codegen/gen_assists_docs.rs
+++ b/xtask/src/codegen/gen_assists_docs.rs
@@ -101,14 +101,14 @@ fn collect_assists() -> Result<Vec<Assist>> {
 }
 
 fn generate_tests(assists: &[Assist], mode: Mode) -> Result<()> {
-    let mut buf = String::from("use super::check;\n");
+    let mut buf = String::from("use super::check_doc_test;\n");
 
     for assist in assists.iter() {
         let test = format!(
             r######"
 #[test]
 fn doctest_{}() {{
-    check(
+    check_doc_test(
         "{}",
 r#####"
 {}"#####, r#####"
diff --git a/xtask/tests/tidy-tests/cli.rs b/xtask/tests/tidy-tests/cli.rs
deleted file mode 100644
index f5b00a8b8..000000000
--- a/xtask/tests/tidy-tests/cli.rs
+++ /dev/null
@@ -1,32 +0,0 @@
-use xtask::{
-    codegen::{self, Mode},
-    run_rustfmt,
-};
-
-#[test]
-fn generated_grammar_is_fresh() {
-    if let Err(error) = codegen::generate_syntax(Mode::Verify) {
-        panic!("{}. Please update it by running `cargo xtask codegen`", error);
-    }
-}
-
-#[test]
-fn generated_tests_are_fresh() {
-    if let Err(error) = codegen::generate_parser_tests(Mode::Verify) {
-        panic!("{}. Please update tests by running `cargo xtask codegen`", error);
-    }
-}
-
-#[test]
-fn generated_assists_are_fresh() {
-    if let Err(error) = codegen::generate_assists_docs(Mode::Verify) {
-        panic!("{}. Please update assists by running `cargo xtask codegen`", error);
-    }
-}
-
-#[test]
-fn check_code_formatting() {
-    if let Err(error) = run_rustfmt(Mode::Verify) {
-        panic!("{}. Please format the code by running `cargo format`", error);
-    }
-}
diff --git a/xtask/tests/tidy-tests/main.rs b/xtask/tests/tidy.rs
index 3213c4dfa..b8e8860ba 100644
--- a/xtask/tests/tidy-tests/main.rs
+++ b/xtask/tests/tidy.rs
@@ -1,11 +1,41 @@
-mod cli;
-
 use std::{
     collections::HashMap,
     path::{Path, PathBuf},
 };
 
-use xtask::{not_bash::fs2, project_root, rust_files};
+use xtask::{
+    codegen::{self, Mode},
+    not_bash::fs2,
+    project_root, run_rustfmt, rust_files,
+};
+
+#[test]
+fn generated_grammar_is_fresh() {
+    if let Err(error) = codegen::generate_syntax(Mode::Verify) {
+        panic!("{}. Please update it by running `cargo xtask codegen`", error);
+    }
+}
+
+#[test]
+fn generated_tests_are_fresh() {
+    if let Err(error) = codegen::generate_parser_tests(Mode::Verify) {
+        panic!("{}. Please update tests by running `cargo xtask codegen`", error);
+    }
+}
+
+#[test]
+fn generated_assists_are_fresh() {
+    if let Err(error) = codegen::generate_assists_docs(Mode::Verify) {
+        panic!("{}. Please update assists by running `cargo xtask codegen`", error);
+    }
+}
+
+#[test]
+fn check_code_formatting() {
+    if let Err(error) = run_rustfmt(Mode::Verify) {
+        panic!("{}. Please format the code by running `cargo format`", error);
+    }
+}
 
 #[test]
 fn rust_files_are_tidy() {
@@ -24,7 +54,7 @@ fn check_todo(path: &Path, text: &str) {
         // This file itself is whitelisted since this test itself contains matches.
         "tests/cli.rs",
         // Some of our assists generate `todo!()` so those files are whitelisted.
-        "doc_tests/generated.rs",
+        "tests/generated.rs",
         "handlers/add_missing_impl_members.rs",
         "handlers/add_function.rs",
         // To support generating `todo!()` in assists, we have `expr_todo()` in ast::make.
@@ -106,7 +136,6 @@ impl TidyDocs {
         }
 
         let whitelist = [
-            "ra_db",
             "ra_hir",
             "ra_hir_expand",
             "ra_ide",