110 files changed, 3111 insertions, 1575 deletions

diff --git a/crates/ra_assists/src/assist_context.rs b/crates/ra_assists/src/assist_context.rs
new file mode 100644
index 000000000..3085c4330
--- /dev/null
+++ b/crates/ra_assists/src/assist_context.rs
@@ -0,0 +1,233 @@
+//! See `AssistContext`
+
+use algo::find_covering_element;
+use hir::Semantics;
+use ra_db::{FileId, FileRange};
+use ra_fmt::{leading_indent, reindent};
+use ra_ide_db::{
+    source_change::{SingleFileChange, SourceChange},
+    RootDatabase,
+};
+use ra_syntax::{
+    algo::{self, find_node_at_offset, SyntaxRewriter},
+    AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken, TextRange, TextSize,
+    TokenAtOffset,
+};
+use ra_text_edit::TextEditBuilder;
+
+use crate::{Assist, AssistId, GroupLabel, ResolvedAssist};
+
+/// `AssistContext` allows to apply an assist or check if it could be applied.
+///
+/// Assists use a somewhat over-engineered approach, given the current needs.
+/// The assists workflow consists of two phases. In the first phase, a user asks
+/// for the list of available assists. In the second phase, the user picks a
+/// particular assist and it gets applied.
+///
+/// There are two peculiarities here:
+///
+/// * first, we ideally avoid computing more things then necessary to answer "is
+///   assist applicable" in the first phase.
+/// * second, when we are applying assist, we don't have a guarantee that there
+///   weren't any changes between the point when user asked for assists and when
+///   they applied a particular assist. So, when applying assist, we need to do
+///   all the checks from scratch.
+///
+/// To avoid repeating the same code twice for both "check" and "apply"
+/// functions, we use an approach reminiscent of that of Django's function based
+/// views dealing with forms. Each assist receives a runtime parameter,
+/// `resolve`. It first check if an edit is applicable (potentially computing
+/// info required to compute the actual edit). If it is applicable, and
+/// `resolve` is `true`, it then computes the actual edit.
+///
+/// So, to implement the original assists workflow, we can first apply each edit
+/// with `resolve = false`, and then applying the selected edit again, with
+/// `resolve = true` this time.
+///
+/// Note, however, that we don't actually use such two-phase logic at the
+/// moment, because the LSP API is pretty awkward in this place, and it's much
+/// easier to just compute the edit eagerly :-)
+pub(crate) struct AssistContext<'a> {
+    pub(crate) sema: Semantics<'a, RootDatabase>,
+    pub(super) db: &'a RootDatabase,
+    pub(crate) frange: FileRange,
+    source_file: SourceFile,
+}
+
+impl<'a> AssistContext<'a> {
+    pub fn new(sema: Semantics<'a, RootDatabase>, frange: FileRange) -> AssistContext<'a> {
+        let source_file = sema.parse(frange.file_id);
+        let db = sema.db;
+        AssistContext { sema, db, frange, source_file }
+    }
+
+    // NB, this ignores active selection.
+    pub(crate) fn offset(&self) -> TextSize {
+        self.frange.range.start()
+    }
+
+    pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
+        self.source_file.syntax().token_at_offset(self.offset())
+    }
+    pub(crate) fn find_token_at_offset(&self, kind: SyntaxKind) -> Option<SyntaxToken> {
+        self.token_at_offset().find(|it| it.kind() == kind)
+    }
+    pub(crate) fn find_node_at_offset<N: AstNode>(&self) -> Option<N> {
+        find_node_at_offset(self.source_file.syntax(), self.offset())
+    }
+    pub(crate) fn find_node_at_offset_with_descend<N: AstNode>(&self) -> Option<N> {
+        self.sema.find_node_at_offset_with_descend(self.source_file.syntax(), self.offset())
+    }
+    pub(crate) fn covering_element(&self) -> SyntaxElement {
+        find_covering_element(self.source_file.syntax(), self.frange.range)
+    }
+    // FIXME: remove
+    pub(crate) fn covering_node_for_range(&self, range: TextRange) -> SyntaxElement {
+        find_covering_element(self.source_file.syntax(), range)
+    }
+}
+
+pub(crate) struct Assists {
+    resolve: bool,
+    file: FileId,
+    buf: Vec<(Assist, Option<SourceChange>)>,
+}
+
+impl Assists {
+    pub(crate) fn new_resolved(ctx: &AssistContext) -> Assists {
+        Assists { resolve: true, file: ctx.frange.file_id, buf: Vec::new() }
+    }
+    pub(crate) fn new_unresolved(ctx: &AssistContext) -> Assists {
+        Assists { resolve: false, file: ctx.frange.file_id, buf: Vec::new() }
+    }
+
+    pub(crate) fn finish_unresolved(self) -> Vec<Assist> {
+        assert!(!self.resolve);
+        self.finish()
+            .into_iter()
+            .map(|(label, edit)| {
+                assert!(edit.is_none());
+                label
+            })
+            .collect()
+    }
+
+    pub(crate) fn finish_resolved(self) -> Vec<ResolvedAssist> {
+        assert!(self.resolve);
+        self.finish()
+            .into_iter()
+            .map(|(label, edit)| ResolvedAssist { assist: label, source_change: edit.unwrap() })
+            .collect()
+    }
+
+    pub(crate) fn add(
+        &mut self,
+        id: AssistId,
+        label: impl Into<String>,
+        target: TextRange,
+        f: impl FnOnce(&mut AssistBuilder),
+    ) -> Option<()> {
+        let label = Assist::new(id, label.into(), None, target);
+        self.add_impl(label, f)
+    }
+    pub(crate) fn add_group(
+        &mut self,
+        group: &GroupLabel,
+        id: AssistId,
+        label: impl Into<String>,
+        target: TextRange,
+        f: impl FnOnce(&mut AssistBuilder),
+    ) -> Option<()> {
+        let label = Assist::new(id, label.into(), Some(group.clone()), target);
+        self.add_impl(label, f)
+    }
+    fn add_impl(&mut self, label: Assist, f: impl FnOnce(&mut AssistBuilder)) -> Option<()> {
+        let change_label = label.label.clone();
+        let source_change = if self.resolve {
+            let mut builder = AssistBuilder::new(self.file);
+            f(&mut builder);
+            Some(builder.finish(change_label))
+        } else {
+            None
+        };
+
+        self.buf.push((label, source_change));
+        Some(())
+    }
+
+    fn finish(mut self) -> Vec<(Assist, Option<SourceChange>)> {
+        self.buf.sort_by_key(|(label, _edit)| label.target.len());
+        self.buf
+    }
+}
+
+pub(crate) struct AssistBuilder {
+    edit: TextEditBuilder,
+    cursor_position: Option<TextSize>,
+    file: FileId,
+}
+
+impl AssistBuilder {
+    pub(crate) fn new(file: FileId) -> AssistBuilder {
+        AssistBuilder { edit: TextEditBuilder::default(), cursor_position: None, file }
+    }
+
+    /// Remove specified `range` of text.
+    pub(crate) fn delete(&mut self, range: TextRange) {
+        self.edit.delete(range)
+    }
+    /// Append specified `text` at the given `offset`
+    pub(crate) fn insert(&mut self, offset: TextSize, text: impl Into<String>) {
+        self.edit.insert(offset, text.into())
+    }
+    /// Replaces specified `range` of text with a given string.
+    pub(crate) fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
+        self.edit.replace(range, replace_with.into())
+    }
+    pub(crate) fn replace_ast<N: AstNode>(&mut self, old: N, new: N) {
+        algo::diff(old.syntax(), new.syntax()).into_text_edit(&mut self.edit)
+    }
+    /// Replaces specified `node` of text with a given string, reindenting the
+    /// string to maintain `node`'s existing indent.
+    // FIXME: remove in favor of ra_syntax::edit::IndentLevel::increase_indent
+    pub(crate) fn replace_node_and_indent(
+        &mut self,
+        node: &SyntaxNode,
+        replace_with: impl Into<String>,
+    ) {
+        let mut replace_with = replace_with.into();
+        if let Some(indent) = leading_indent(node) {
+            replace_with = reindent(&replace_with, &indent)
+        }
+        self.replace(node.text_range(), replace_with)
+    }
+    pub(crate) fn rewrite(&mut self, rewriter: SyntaxRewriter) {
+        let node = rewriter.rewrite_root().unwrap();
+        let new = rewriter.rewrite(&node);
+        algo::diff(&node, &new).into_text_edit(&mut self.edit)
+    }
+
+    /// Specify desired position of the cursor after the assist is applied.
+    pub(crate) fn set_cursor(&mut self, offset: TextSize) {
+        self.cursor_position = Some(offset)
+    }
+    // FIXME: better API
+    pub(crate) fn set_file(&mut self, assist_file: FileId) {
+        self.file = assist_file;
+    }
+
+    // FIXME: kill this API
+    /// Get access to the raw `TextEditBuilder`.
+    pub(crate) fn text_edit_builder(&mut self) -> &mut TextEditBuilder {
+        &mut self.edit
+    }
+
+    fn finish(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/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
deleted file mode 100644
index da2880037..000000000
--- a/crates/ra_assists/src/assist_ctx.rs
+++ /dev/null
@@ -1,277 +0,0 @@
-//! This module defines `AssistCtx` -- the API surface that is exposed to assists.
-use hir::Semantics;
-use ra_db::FileRange;
-use ra_fmt::{leading_indent, reindent};
-use ra_ide_db::RootDatabase;
-use ra_syntax::{
-    algo::{self, find_covering_element, find_node_at_offset},
-    AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken, TextRange, TextSize,
-    TokenAtOffset,
-};
-use ra_text_edit::TextEditBuilder;
-
-use crate::{AssistAction, AssistFile, AssistId, AssistLabel, GroupLabel, ResolvedAssist};
-use algo::SyntaxRewriter;
-
-#[derive(Clone, Debug)]
-pub(crate) struct Assist(pub(crate) Vec<AssistInfo>);
-
-#[derive(Clone, Debug)]
-pub(crate) struct AssistInfo {
-    pub(crate) label: AssistLabel,
-    pub(crate) group_label: Option<GroupLabel>,
-    pub(crate) action: Option<AssistAction>,
-}
-
-impl AssistInfo {
-    fn new(label: AssistLabel) -> AssistInfo {
-        AssistInfo { label, group_label: None, action: None }
-    }
-
-    fn resolved(self, action: AssistAction) -> AssistInfo {
-        AssistInfo { action: Some(action), ..self }
-    }
-
-    fn with_group(self, group_label: GroupLabel) -> AssistInfo {
-        AssistInfo { group_label: Some(group_label), ..self }
-    }
-
-    pub(crate) fn into_resolved(self) -> Option<ResolvedAssist> {
-        let label = self.label;
-        let group_label = self.group_label;
-        self.action.map(|action| ResolvedAssist { label, group_label, action })
-    }
-}
-
-pub(crate) type AssistHandler = fn(AssistCtx) -> Option<Assist>;
-
-/// `AssistCtx` allows to apply an assist or check if it could be applied.
-///
-/// Assists use a somewhat over-engineered approach, given the current needs. The
-/// assists workflow consists of two phases. In the first phase, a user asks for
-/// the list of available assists. In the second phase, the user picks a
-/// particular assist and it gets applied.
-///
-/// There are two peculiarities here:
-///
-/// * first, we ideally avoid computing more things then necessary to answer
-///   "is assist applicable" in the first phase.
-/// * second, when we are applying assist, we don't have a guarantee that there
-///   weren't any changes between the point when user asked for assists and when
-///   they applied a particular assist. So, when applying assist, we need to do
-///   all the checks from scratch.
-///
-/// To avoid repeating the same code twice for both "check" and "apply"
-/// functions, we use an approach reminiscent of that of Django's function based
-/// views dealing with forms. Each assist receives a runtime parameter,
-/// `should_compute_edit`. It first check if an edit is applicable (potentially
-/// computing info required to compute the actual edit). If it is applicable,
-/// and `should_compute_edit` is `true`, it then computes the actual edit.
-///
-/// So, to implement the original assists workflow, we can first apply each edit
-/// with `should_compute_edit = false`, and then applying the selected edit
-/// again, with `should_compute_edit = true` this time.
-///
-/// Note, however, that we don't actually use such two-phase logic at the
-/// moment, because the LSP API is pretty awkward in this place, and it's much
-/// easier to just compute the edit eagerly :-)
-#[derive(Clone)]
-pub(crate) struct AssistCtx<'a> {
-    pub(crate) sema: &'a Semantics<'a, RootDatabase>,
-    pub(crate) db: &'a RootDatabase,
-    pub(crate) frange: FileRange,
-    source_file: SourceFile,
-    should_compute_edit: bool,
-}
-
-impl<'a> AssistCtx<'a> {
-    pub fn new(
-        sema: &'a Semantics<'a, RootDatabase>,
-        frange: FileRange,
-        should_compute_edit: bool,
-    ) -> AssistCtx<'a> {
-        let source_file = sema.parse(frange.file_id);
-        AssistCtx { sema, db: sema.db, frange, source_file, should_compute_edit }
-    }
-
-    pub(crate) fn add_assist(
-        self,
-        id: AssistId,
-        label: impl Into<String>,
-        f: impl FnOnce(&mut ActionBuilder),
-    ) -> Option<Assist> {
-        let label = AssistLabel::new(label.into(), id);
-
-        let mut info = AssistInfo::new(label);
-        if self.should_compute_edit {
-            let action = {
-                let mut edit = ActionBuilder::new(&self);
-                f(&mut edit);
-                edit.build()
-            };
-            info = info.resolved(action)
-        };
-
-        Some(Assist(vec![info]))
-    }
-
-    pub(crate) fn add_assist_group(self, group_name: impl Into<String>) -> AssistGroup<'a> {
-        AssistGroup { ctx: self, group_name: group_name.into(), assists: Vec::new() }
-    }
-
-    pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
-        self.source_file.syntax().token_at_offset(self.frange.range.start())
-    }
-
-    pub(crate) fn find_token_at_offset(&self, kind: SyntaxKind) -> Option<SyntaxToken> {
-        self.token_at_offset().find(|it| it.kind() == kind)
-    }
-
-    pub(crate) fn find_node_at_offset<N: AstNode>(&self) -> Option<N> {
-        find_node_at_offset(self.source_file.syntax(), self.frange.range.start())
-    }
-
-    pub(crate) fn find_node_at_offset_with_descend<N: AstNode>(&self) -> Option<N> {
-        self.sema
-            .find_node_at_offset_with_descend(self.source_file.syntax(), self.frange.range.start())
-    }
-
-    pub(crate) fn covering_element(&self) -> SyntaxElement {
-        find_covering_element(self.source_file.syntax(), self.frange.range)
-    }
-    pub(crate) fn covering_node_for_range(&self, range: TextRange) -> SyntaxElement {
-        find_covering_element(self.source_file.syntax(), range)
-    }
-}
-
-pub(crate) struct AssistGroup<'a> {
-    ctx: AssistCtx<'a>,
-    group_name: String,
-    assists: Vec<AssistInfo>,
-}
-
-impl<'a> AssistGroup<'a> {
-    pub(crate) fn add_assist(
-        &mut self,
-        id: AssistId,
-        label: impl Into<String>,
-        f: impl FnOnce(&mut ActionBuilder),
-    ) {
-        let label = AssistLabel::new(label.into(), id);
-
-        let mut info = AssistInfo::new(label).with_group(GroupLabel(self.group_name.clone()));
-        if self.ctx.should_compute_edit {
-            let action = {
-                let mut edit = ActionBuilder::new(&self.ctx);
-                f(&mut edit);
-                edit.build()
-            };
-            info = info.resolved(action)
-        };
-
-        self.assists.push(info)
-    }
-
-    pub(crate) fn finish(self) -> Option<Assist> {
-        if self.assists.is_empty() {
-            None
-        } else {
-            Some(Assist(self.assists))
-        }
-    }
-}
-
-pub(crate) struct ActionBuilder<'a, 'b> {
-    edit: TextEditBuilder,
-    cursor_position: Option<TextSize>,
-    target: Option<TextRange>,
-    file: AssistFile,
-    ctx: &'a AssistCtx<'b>,
-}
-
-impl<'a, 'b> ActionBuilder<'a, 'b> {
-    fn new(ctx: &'a AssistCtx<'b>) -> Self {
-        Self {
-            edit: TextEditBuilder::default(),
-            cursor_position: None,
-            target: None,
-            file: AssistFile::default(),
-            ctx,
-        }
-    }
-
-    pub(crate) fn ctx(&self) -> &AssistCtx<'b> {
-        &self.ctx
-    }
-
-    /// Replaces specified `range` of text with a given string.
-    pub(crate) fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
-        self.edit.replace(range, replace_with.into())
-    }
-
-    /// Replaces specified `node` of text with a given string, reindenting the
-    /// string to maintain `node`'s existing indent.
-    // FIXME: remove in favor of ra_syntax::edit::IndentLevel::increase_indent
-    pub(crate) fn replace_node_and_indent(
-        &mut self,
-        node: &SyntaxNode,
-        replace_with: impl Into<String>,
-    ) {
-        let mut replace_with = replace_with.into();
-        if let Some(indent) = leading_indent(node) {
-            replace_with = reindent(&replace_with, &indent)
-        }
-        self.replace(node.text_range(), replace_with)
-    }
-
-    /// Remove specified `range` of text.
-    #[allow(unused)]
-    pub(crate) fn delete(&mut self, range: TextRange) {
-        self.edit.delete(range)
-    }
-
-    /// Append specified `text` at the given `offset`
-    pub(crate) fn insert(&mut self, offset: TextSize, text: impl Into<String>) {
-        self.edit.insert(offset, text.into())
-    }
-
-    /// Specify desired position of the cursor after the assist is applied.
-    pub(crate) fn set_cursor(&mut self, offset: TextSize) {
-        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
-    }
-
-    pub(crate) fn replace_ast<N: AstNode>(&mut self, old: N, new: N) {
-        algo::diff(old.syntax(), new.syntax()).into_text_edit(&mut self.edit)
-    }
-    pub(crate) fn rewrite(&mut self, rewriter: SyntaxRewriter) {
-        let node = rewriter.rewrite_root().unwrap();
-        let new = rewriter.rewrite(&node);
-        algo::diff(&node, &new).into_text_edit(&mut self.edit)
-    }
-
-    pub(crate) fn set_file(&mut self, assist_file: AssistFile) {
-        self.file = assist_file
-    }
-
-    fn build(self) -> AssistAction {
-        AssistAction {
-            edit: self.edit.finish(),
-            cursor_position: self.cursor_position,
-            target: self.target,
-            file: 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 c0f9bc1fb..000000000
--- a/crates/ra_assists/src/doc_tests.rs
+++ /dev/null
@@ -1,35 +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 = assist.action.edit.apply(&before);
-    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..795a225a4 100644
--- a/crates/ra_assists/src/handlers/add_custom_impl.rs
+++ b/crates/ra_assists/src/handlers/add_custom_impl.rs
@@ -6,7 +6,10 @@ use ra_syntax::{
 };
 use stdx::SepBy;
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId,
+};
 
 // Assist: add_custom_impl
 //
@@ -25,7 +28,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //
 // }
 // ```
-pub(crate) fn add_custom_impl(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_custom_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let input = ctx.find_node_at_offset::<ast::AttrInput>()?;
     let attr = input.syntax().parent().and_then(ast::Attr::cast)?;
 
@@ -48,9 +51,8 @@ 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();
+    acc.add(AssistId("add_custom_impl"), label, target, |edit| {
         let new_attr_input = input
             .syntax()
             .descendants_with_tokens()
@@ -95,7 +97,7 @@ 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..fb08c19e9 100644
--- a/crates/ra_assists/src/handlers/add_derive.rs
+++ b/crates/ra_assists/src/handlers/add_derive.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
     TextSize,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: add_derive
 //
@@ -24,10 +24,11 @@ use crate::{Assist, AssistCtx, AssistId};
 //     y: u32,
 // }
 // ```
-pub(crate) fn add_derive(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_derive(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     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();
+    acc.add(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)
     })
 }
@@ -57,8 +57,9 @@ fn derive_insertion_offset(nominal: &ast::NominalDef) -> Option<TextSize> {
 
 #[cfg(test)]
 mod tests {
+    use crate::tests::{check_assist, check_assist_target};
+
     use super::*;
-    use crate::helpers::{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..55409e501 100644
--- a/crates/ra_assists/src/handlers/add_explicit_type.rs
+++ b/crates/ra_assists/src/handlers/add_explicit_type.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
     TextRange,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: add_explicit_type
 //
@@ -21,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     let x: i32 = 92;
 // }
 // ```
-pub(crate) fn add_explicit_type(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let stmt = ctx.find_node_at_offset::<LetStmt>()?;
     let expr = stmt.initializer()?;
     let pat = stmt.pat()?;
@@ -59,11 +59,11 @@ pub(crate) fn add_explicit_type(ctx: AssistCtx) -> Option<Assist> {
 
     let db = ctx.db;
     let new_type_string = ty.display_truncated(db, None).to_string();
-    ctx.add_assist(
+    acc.add(
         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..275184e24 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
@@ -4,10 +4,10 @@ use ra_syntax::{
     TextSize,
 };
 use stdx::format_to;
-
-use crate::{utils::FamousDefs, Assist, AssistCtx, AssistId};
 use test_utils::tested_by;
 
+use crate::{utils::FamousDefs, AssistContext, AssistId, Assists};
+
 // Assist add_from_impl_for_enum
 //
 // Adds a From impl for an enum variant with one tuple field
@@ -25,7 +25,7 @@ use test_utils::tested_by;
 //     }
 // }
 // ```
-pub(crate) fn add_from_impl_for_enum(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_from_impl_for_enum(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let variant = ctx.find_node_at_offset::<ast::EnumVariant>()?;
     let variant_name = variant.name()?;
     let enum_name = variant.parent_enum().name()?;
@@ -42,14 +42,16 @@ pub(crate) fn add_from_impl_for_enum(ctx: AssistCtx) -> Option<Assist> {
         _ => return None,
     };
 
-    if existing_from_impl(ctx.sema, &variant).is_some() {
+    if existing_from_impl(&ctx.sema, &variant).is_some() {
         tested_by!(test_add_from_impl_already_exists);
         return None;
     }
 
-    ctx.add_assist(
+    let target = variant.syntax().text_range();
+    acc.add(
         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..6b5616aa9 100644
--- a/crates/ra_assists/src/handlers/add_function.rs
+++ b/crates/ra_assists/src/handlers/add_function.rs
@@ -1,13 +1,13 @@
+use hir::HirDisplay;
+use ra_db::FileId;
 use ra_syntax::{
-    ast::{self, AstNode},
+    ast::{self, edit::IndentLevel, ArgListOwner, AstNode, ModuleItemOwner},
     SyntaxKind, SyntaxNode, TextSize,
 };
-
-use crate::{Assist, AssistCtx, AssistFile, AssistId};
-use ast::{edit::IndentLevel, ArgListOwner, ModuleItemOwner};
-use hir::HirDisplay;
 use rustc_hash::{FxHashMap, FxHashSet};
 
+use crate::{AssistContext, AssistId, Assists};
+
 // Assist: add_function
 //
 // Adds a stub function with a signature matching the function under the cursor.
@@ -33,7 +33,7 @@ use rustc_hash::{FxHashMap, FxHashSet};
 // }
 //
 // ```
-pub(crate) fn add_function(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_function(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let path_expr: ast::PathExpr = ctx.find_node_at_offset()?;
     let call = path_expr.syntax().parent().and_then(ast::CallExpr::cast)?;
     let path = path_expr.path()?;
@@ -57,14 +57,12 @@ 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();
+    acc.add(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 +70,7 @@ struct FunctionTemplate {
     insert_offset: TextSize,
     cursor_offset: TextSize,
     fn_def: ast::SourceFile,
-    file: AssistFile,
+    file: FileId,
 }
 
 struct FunctionBuilder {
@@ -80,7 +78,7 @@ struct FunctionBuilder {
     fn_name: ast::Name,
     type_params: Option<ast::TypeParamList>,
     params: ast::ParamList,
-    file: AssistFile,
+    file: FileId,
     needs_pub: bool,
 }
 
@@ -88,13 +86,13 @@ impl FunctionBuilder {
     /// Prepares a generated function that matches `call` in `generate_in`
     /// (or as close to `call` as possible, if `generate_in` is `None`)
     fn from_call(
-        ctx: &AssistCtx,
+        ctx: &AssistContext,
         call: &ast::CallExpr,
         path: &ast::Path,
         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 +105,7 @@ 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 +131,11 @@ 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 }
     }
 }
 
@@ -157,7 +151,7 @@ fn fn_name(call: &ast::Path) -> Option<ast::Name> {
 
 /// Computes the type variables and arguments required for the generated function
 fn fn_args(
-    ctx: &AssistCtx,
+    ctx: &AssistContext,
     call: &ast::CallExpr,
 ) -> Option<(Option<ast::TypeParamList>, ast::ParamList)> {
     let mut arg_names = Vec::new();
@@ -224,7 +218,7 @@ fn fn_arg_name(fn_arg: &ast::Expr) -> Option<String> {
     }
 }
 
-fn fn_arg_type(ctx: &AssistCtx, fn_arg: &ast::Expr) -> Option<String> {
+fn fn_arg_type(ctx: &AssistContext, fn_arg: &ast::Expr) -> Option<String> {
     let ty = ctx.sema.type_of_expr(fn_arg)?;
     if ty.is_unknown() {
         return None;
@@ -259,9 +253,8 @@ 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 +271,12 @@ 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..df114a0d8 100644
--- a/crates/ra_assists/src/handlers/add_impl.rs
+++ b/crates/ra_assists/src/handlers/add_impl.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
 };
 use stdx::{format_to, SepBy};
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: add_impl
 //
@@ -25,11 +25,11 @@ use crate::{Assist, AssistCtx, AssistId};
 //
 // }
 // ```
-pub(crate) fn add_impl(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_impl(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     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 target = nominal.syntax().text_range();
+    acc.add(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();
@@ -60,7 +60,7 @@ pub(crate) fn add_impl(ctx: AssistCtx) -> Option<Assist> {
 #[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 e466c9a86..3482a75bf 100644
--- a/crates/ra_assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/handlers/add_missing_impl_members.rs
@@ -9,9 +9,10 @@ use ra_syntax::{
 };
 
 use crate::{
+    assist_context::{AssistContext, Assists},
     ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
-    utils::{get_missing_impl_items, resolve_target_trait},
-    Assist, AssistCtx, AssistId,
+    utils::{get_missing_assoc_items, resolve_target_trait},
+    AssistId,
 };
 
 #[derive(PartialEq)]
@@ -50,8 +51,9 @@ enum AddMissingImplMembersMode {
 //
 // }
 // ```
-pub(crate) fn add_missing_impl_members(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_missing_impl_members(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     add_missing_impl_members_inner(
+        acc,
         ctx,
         AddMissingImplMembersMode::NoDefaultMethods,
         "add_impl_missing_members",
@@ -91,8 +93,9 @@ pub(crate) fn add_missing_impl_members(ctx: AssistCtx) -> Option<Assist> {
 //
 // }
 // ```
-pub(crate) fn add_missing_default_members(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_missing_default_members(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     add_missing_impl_members_inner(
+        acc,
         ctx,
         AddMissingImplMembersMode::DefaultMethodsOnly,
         "add_impl_default_members",
@@ -101,36 +104,37 @@ pub(crate) fn add_missing_default_members(ctx: AssistCtx) -> Option<Assist> {
 }
 
 fn add_missing_impl_members_inner(
-    ctx: AssistCtx,
+    acc: &mut Assists,
+    ctx: &AssistContext,
     mode: AddMissingImplMembersMode,
     assist_id: &'static str,
     label: &'static str,
-) -> Option<Assist> {
+) -> Option<()> {
     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::ImplItem| -> Option<SmolStr> {
+    let def_name = |item: &ast::AssocItem| -> Option<SmolStr> {
         match item {
-            ast::ImplItem::FnDef(def) => def.name(),
-            ast::ImplItem::TypeAliasDef(def) => def.name(),
-            ast::ImplItem::ConstDef(def) => def.name(),
+            ast::AssocItem::FnDef(def) => def.name(),
+            ast::AssocItem::TypeAliasDef(def) => def.name(),
+            ast::AssocItem::ConstDef(def) => def.name(),
         }
         .map(|it| it.text().clone())
     };
 
-    let missing_items = get_missing_impl_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::ImplItem::FnDef(i.source(ctx.db).value),
-            hir::AssocItem::TypeAlias(i) => ast::ImplItem::TypeAliasDef(i.source(ctx.db).value),
-            hir::AssocItem::Const(i) => ast::ImplItem::ConstDef(i.source(ctx.db).value),
+            hir::AssocItem::Function(i) => ast::AssocItem::FnDef(i.source(ctx.db).value),
+            hir::AssocItem::TypeAlias(i) => ast::AssocItem::TypeAliasDef(i.source(ctx.db).value),
+            hir::AssocItem::Const(i) => ast::AssocItem::ConstDef(i.source(ctx.db).value),
         })
         .filter(|t| def_name(&t).is_some())
         .filter(|t| match t {
-            ast::ImplItem::FnDef(def) => match mode {
+            ast::AssocItem::FnDef(def) => match mode {
                 AddMissingImplMembersMode::DefaultMethodsOnly => def.body().is_some(),
                 AddMissingImplMembersMode::NoDefaultMethods => def.body().is_none(),
             },
@@ -142,25 +146,24 @@ fn add_missing_impl_members_inner(
         return None;
     }
 
-    let sema = ctx.sema;
-
-    ctx.add_assist(AssistId(assist_id), label, |edit| {
-        let n_existing_items = impl_item_list.impl_items().count();
-        let source_scope = sema.scope_for_def(trait_);
-        let target_scope = sema.scope(impl_item_list.syntax());
+    let target = impl_def.syntax().text_range();
+    acc.add(AssistId(assist_id), label, target, |edit| {
+        let n_existing_items = impl_item_list.assoc_items().count();
+        let source_scope = ctx.sema.scope_for_def(trait_);
+        let target_scope = ctx.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))
             .map(|it| match it {
-                ast::ImplItem::FnDef(def) => ast::ImplItem::FnDef(add_body(def)),
+                ast::AssocItem::FnDef(def) => ast::AssocItem::FnDef(add_body(def)),
                 _ => it,
             })
             .map(|it| edit::remove_attrs_and_docs(&it));
         let new_impl_item_list = impl_item_list.append_items(items);
         let cursor_position = {
-            let first_new_item = new_impl_item_list.impl_items().nth(n_existing_items).unwrap();
+            let first_new_item = new_impl_item_list.assoc_items().nth(n_existing_items).unwrap();
             first_new_item.syntax().text_range().start()
         };
 
@@ -170,18 +173,17 @@ fn add_missing_impl_members_inner(
 }
 
 fn add_body(fn_def: ast::FnDef) -> ast::FnDef {
-    if fn_def.body().is_none() {
-        let body = make::block_expr(None, Some(make::expr_todo()));
-        let body = IndentLevel(1).increase_indent(body);
-        fn_def.with_body(body)
-    } else {
-        fn_def
+    if fn_def.body().is_some() {
+        return fn_def;
     }
+    let body = make::block_expr(None, Some(make::expr_todo()));
+    let body = IndentLevel(1).increase_indent(body);
+    fn_def.with_body(body)
 }
 
 #[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 0f9174a29..fe7451dcf 100644
--- a/crates/ra_assists/src/handlers/add_new.rs
+++ b/crates/ra_assists/src/handlers/add_new.rs
@@ -7,7 +7,7 @@ use ra_syntax::{
 };
 use stdx::{format_to, SepBy};
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: add_new
 //
@@ -29,7 +29,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // }
 //
 // ```
-pub(crate) fn add_new(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_new(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let strukt = ctx.find_node_at_offset::<ast::StructDef>()?;
 
     // We want to only apply this to non-union structs with named fields
@@ -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();
+    acc.add(AssistId("add_new"), "Add default constructor", target, |edit| {
         let mut buf = String::with_capacity(512);
 
         if impl_def.is_some() {
@@ -124,7 +123,7 @@ fn generate_impl_text(strukt: &ast::StructDef, code: &str) -> String {
 //
 // FIXME: change the new fn checking to a more semantic approach when that's more
 // viable (e.g. we process proc macros, etc)
-fn find_struct_impl(ctx: &AssistCtx, strukt: &ast::StructDef) -> Option<Option<ast::ImplDef>> {
+fn find_struct_impl(ctx: &AssistContext, strukt: &ast::StructDef) -> Option<Option<ast::ImplDef>> {
     let db = ctx.db;
     let module = strukt.syntax().ancestors().find(|node| {
         ast::Module::can_cast(node.kind()) || ast::SourceFile::can_cast(node.kind())
@@ -162,8 +161,8 @@ fn find_struct_impl(ctx: &AssistCtx, strukt: &ast::StructDef) -> Option<Option<a
 
 fn has_new_fn(imp: &ast::ImplDef) -> bool {
     if let Some(il) = imp.item_list() {
-        for item in il.impl_items() {
-            if let ast::ImplItem::FnDef(f) = item {
+        for item in il.assoc_items() {
+            if let ast::AssocItem::FnDef(f) = item {
                 if let Some(name) = f.name() {
                     if name.text().eq_ignore_ascii_case("new") {
                         return true;
@@ -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..0feba5e11 100644
--- a/crates/ra_assists/src/handlers/apply_demorgan.rs
+++ b/crates/ra_assists/src/handlers/apply_demorgan.rs
@@ -1,6 +1,6 @@
 use ra_syntax::ast::{self, AstNode};
 
-use crate::{utils::invert_boolean_expression, Assist, AssistCtx, AssistId};
+use crate::{utils::invert_boolean_expression, AssistContext, AssistId, Assists};
 
 // Assist: apply_demorgan
 //
@@ -21,7 +21,7 @@ use crate::{utils::invert_boolean_expression, Assist, AssistCtx, AssistId};
 //     if !(x == 4 && y) {}
 // }
 // ```
-pub(crate) fn apply_demorgan(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn apply_demorgan(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let expr = ctx.find_node_at_offset::<ast::BinExpr>()?;
     let op = expr.op_kind()?;
     let op_range = expr.op_token()?.text_range();
@@ -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);
+    acc.add(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..78d23150d 100644
--- a/crates/ra_assists/src/handlers/auto_import.rs
+++ b/crates/ra_assists/src/handlers/auto_import.rs
@@ -1,5 +1,6 @@
 use std::collections::BTreeSet;
 
+use either::Either;
 use hir::{
     AsAssocItem, AssocItemContainer, ModPath, Module, ModuleDef, PathResolution, Semantics, Trait,
     Type,
@@ -12,12 +13,7 @@ use ra_syntax::{
 };
 use rustc_hash::FxHashSet;
 
-use crate::{
-    assist_ctx::{Assist, AssistCtx},
-    utils::insert_use_statement,
-    AssistId,
-};
-use either::Either;
+use crate::{utils::insert_use_statement, AssistContext, AssistId, Assists, GroupLabel};
 
 // Assist: auto_import
 //
@@ -38,7 +34,7 @@ use either::Either;
 // }
 // # pub mod std { pub mod collections { pub struct HashMap { } } }
 // ```
-pub(crate) fn auto_import(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn auto_import(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let auto_import_assets = AutoImportAssets::new(&ctx)?;
     let proposed_imports = auto_import_assets.search_for_imports(ctx.db);
     if proposed_imports.is_empty() {
@@ -46,14 +42,19 @@ 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());
+    let 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);
-            insert_use_statement(&auto_import_assets.syntax_under_caret, &import, edit);
-        });
+        acc.add_group(
+            &group,
+            AssistId("auto_import"),
+            format!("Import `{}`", &import),
+            range,
+            |builder| {
+                insert_use_statement(&auto_import_assets.syntax_under_caret, &import, ctx, builder);
+            },
+        );
     }
-    group.finish()
+    Some(())
 }
 
 #[derive(Debug)]
@@ -64,7 +65,7 @@ struct AutoImportAssets {
 }
 
 impl AutoImportAssets {
-    fn new(ctx: &AssistCtx) -> Option<Self> {
+    fn new(ctx: &AssistContext) -> Option<Self> {
         if let Some(path_under_caret) = ctx.find_node_at_offset_with_descend::<ast::Path>() {
             Self::for_regular_path(path_under_caret, &ctx)
         } else {
@@ -72,7 +73,7 @@ impl AutoImportAssets {
         }
     }
 
-    fn for_method_call(method_call: ast::MethodCallExpr, ctx: &AssistCtx) -> Option<Self> {
+    fn for_method_call(method_call: ast::MethodCallExpr, ctx: &AssistContext) -> Option<Self> {
         let syntax_under_caret = method_call.syntax().to_owned();
         let module_with_name_to_import = ctx.sema.scope(&syntax_under_caret).module()?;
         Some(Self {
@@ -82,7 +83,7 @@ impl AutoImportAssets {
         })
     }
 
-    fn for_regular_path(path_under_caret: ast::Path, ctx: &AssistCtx) -> Option<Self> {
+    fn for_regular_path(path_under_caret: ast::Path, ctx: &AssistContext) -> Option<Self> {
         let syntax_under_caret = path_under_caret.syntax().to_owned();
         if syntax_under_caret.ancestors().find_map(ast::UseItem::cast).is_some() {
             return None;
@@ -105,8 +106,8 @@ impl AutoImportAssets {
         }
     }
 
-    fn get_import_group_message(&self) -> String {
-        match &self.import_candidate {
+    fn get_import_group_message(&self) -> GroupLabel {
+        let name = match &self.import_candidate {
             ImportCandidate::UnqualifiedName(name) => format!("Import {}", name),
             ImportCandidate::QualifierStart(qualifier_start) => {
                 format!("Import {}", qualifier_start)
@@ -117,7 +118,8 @@ impl AutoImportAssets {
             ImportCandidate::TraitMethod(_, trait_method_name) => {
                 format!("Import a trait for method {}", trait_method_name)
             }
-        }
+        };
+        GroupLabel(name)
     }
 
     fn search_for_imports(&self, db: &RootDatabase) -> BTreeSet<ModPath> {
@@ -277,7 +279,7 @@ 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() {
@@ -384,7 +386,7 @@ mod tests {
             }
             ",
             r"
-            use PubMod1::PubStruct;
+            use PubMod3::PubStruct;
 
             PubSt<|>ruct
 
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..5c907097e
--- /dev/null
+++ b/crates/ra_assists/src/handlers/change_return_type_to_result.rs
@@ -0,0 +1,971 @@
+use ra_syntax::{
+    ast::{self, BlockExpr, Expr, LoopBodyOwner},
+    AstNode,
+    SyntaxKind::{COMMENT, WHITESPACE},
+    SyntaxNode, TextSize,
+};
+
+use crate::{AssistContext, AssistId, Assists};
+
+// 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(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    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;
+    }
+
+    acc.add(
+        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 44f6a1dae..e631766ef 100644
--- a/crates/ra_assists/src/handlers/change_visibility.rs
+++ b/crates/ra_assists/src/handlers/change_visibility.rs
@@ -7,10 +7,10 @@ use ra_syntax::{
     },
     SyntaxNode, TextSize, T,
 };
-
-use crate::{Assist, AssistCtx, AssistId};
 use test_utils::tested_by;
 
+use crate::{AssistContext, AssistId, Assists};
+
 // Assist: change_visibility
 //
 // Adds or changes existing visibility specifier.
@@ -22,14 +22,14 @@ use test_utils::tested_by;
 // ```
 // pub(crate) fn frobnicate() {}
 // ```
-pub(crate) fn change_visibility(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn change_visibility(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     if let Some(vis) = ctx.find_node_at_offset::<ast::Visibility>() {
-        return change_vis(ctx, vis);
+        return change_vis(acc, vis);
     }
-    add_vis(ctx)
+    add_vis(acc, ctx)
 }
 
-fn add_vis(ctx: AssistCtx) -> Option<Assist> {
+fn add_vis(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let item_keyword = ctx.token_at_offset().find(|leaf| match leaf.kind() {
         T![const] | T![fn] | T![mod] | T![struct] | T![enum] | T![trait] => true,
         _ => false,
@@ -47,8 +47,7 @@ fn add_vis(ctx: AssistCtx) -> Option<Assist> {
             return None;
         }
         (vis_offset(&parent), keyword.text_range())
-    } else {
-        let field_name: ast::Name = ctx.find_node_at_offset()?;
+    } else if let Some(field_name) = ctx.find_node_at_offset::<ast::Name>() {
         let field = field_name.syntax().ancestors().find_map(ast::RecordFieldDef::cast)?;
         if field.name()? != field_name {
             tested_by!(change_visibility_field_false_positive);
@@ -58,10 +57,16 @@ fn add_vis(ctx: AssistCtx) -> Option<Assist> {
             return None;
         }
         (vis_offset(field.syntax()), field_name.syntax().text_range())
+    } else if let Some(field) = ctx.find_node_at_offset::<ast::TupleFieldDef>() {
+        if field.visibility().is_some() {
+            return None;
+        }
+        (vis_offset(field.syntax()), field.syntax().text_range())
+    } else {
+        return None;
     };
 
-    ctx.add_assist(AssistId("change_visibility"), "Change visibility to pub(crate)", |edit| {
-        edit.target(target);
+    acc.add(AssistId("change_visibility"), "Change visibility to pub(crate)", target, |edit| {
         edit.insert(offset, "pub(crate) ");
         edit.set_cursor(offset);
     })
@@ -78,24 +83,30 @@ fn vis_offset(node: &SyntaxNode) -> TextSize {
         .unwrap_or_else(|| node.text_range().start())
 }
 
-fn change_vis(ctx: AssistCtx, vis: ast::Visibility) -> Option<Assist> {
+fn change_vis(acc: &mut Assists, vis: ast::Visibility) -> Option<()> {
     if vis.syntax().text() == "pub" {
-        return ctx.add_assist(
+        let target = vis.syntax().text_range();
+        return acc.add(
             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 acc.add(
+            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
 }
@@ -104,7 +115,7 @@ 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::*;
 
@@ -129,7 +140,8 @@ mod tests {
             change_visibility,
             r"struct S { <|>field: u32 }",
             r"struct S { <|>pub(crate) field: u32 }",
-        )
+        );
+        check_assist(change_visibility, r"struct S ( <|>u32 )", r"struct S ( <|>pub(crate) u32 )");
     }
 
     #[test]
diff --git a/crates/ra_assists/src/handlers/early_return.rs b/crates/ra_assists/src/handlers/early_return.rs
index eede2fe91..810784ad5 100644
--- a/crates/ra_assists/src/handlers/early_return.rs
+++ b/crates/ra_assists/src/handlers/early_return.rs
@@ -9,7 +9,7 @@ use ra_syntax::{
 };
 
 use crate::{
-    assist_ctx::{Assist, AssistCtx},
+    assist_context::{AssistContext, Assists},
     utils::invert_boolean_expression,
     AssistId,
 };
@@ -36,7 +36,7 @@ use crate::{
 //     bar();
 // }
 // ```
-pub(crate) fn convert_to_guarded_return(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn convert_to_guarded_return(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
     if if_expr.else_branch().is_some() {
         return None;
@@ -93,9 +93,10 @@ 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();
+    let cursor_position = ctx.offset();
 
-    ctx.add_assist(AssistId("convert_to_guarded_return"), "Convert to guarded return", |edit| {
+    let target = if_expr.syntax().text_range();
+    acc.add(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 => {
@@ -143,7 +144,6 @@ pub(crate) fn convert_to_guarded_return(ctx: AssistCtx) -> Option<Assist> {
                 replace(let_stmt.syntax(), &then_block, &parent_block, &if_expr)
             }
         };
-        edit.target(if_expr.syntax().text_range());
         edit.replace_ast(parent_block, ast::BlockExpr::cast(new_block).unwrap());
         edit.set_cursor(cursor_position);
 
@@ -182,7 +182,7 @@ pub(crate) fn convert_to_guarded_return(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/fill_match_arms.rs b/crates/ra_assists/src/handlers/fill_match_arms.rs
index 8d1af9933..13c1e7e80 100644
--- a/crates/ra_assists/src/handlers/fill_match_arms.rs
+++ b/crates/ra_assists/src/handlers/fill_match_arms.rs
@@ -5,7 +5,7 @@ use itertools::Itertools;
 use ra_ide_db::RootDatabase;
 use ra_syntax::ast::{self, make, AstNode, MatchArm, NameOwner, Pat};
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: fill_match_arms
 //
@@ -31,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn fill_match_arms(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn fill_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let match_expr = ctx.find_node_at_offset::<ast::MatchExpr>()?;
     let match_arm_list = match_expr.match_arm_list()?;
 
@@ -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();
+    acc.add(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..692ba4895 100644
--- a/crates/ra_assists/src/handlers/flip_binexpr.rs
+++ b/crates/ra_assists/src/handlers/flip_binexpr.rs
@@ -1,6 +1,6 @@
 use ra_syntax::ast::{AstNode, BinExpr, BinOp};
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: flip_binexpr
 //
@@ -17,7 +17,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     let _ = 2 + 90;
 // }
 // ```
-pub(crate) fn flip_binexpr(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn flip_binexpr(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let expr = ctx.find_node_at_offset::<BinExpr>()?;
     let lhs = expr.lhs()?.syntax().clone();
     let rhs = expr.rhs()?.syntax().clone();
@@ -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);
+    acc.add(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..dfe2a7fed 100644
--- a/crates/ra_assists/src/handlers/flip_comma.rs
+++ b/crates/ra_assists/src/handlers/flip_comma.rs
@@ -1,6 +1,6 @@
 use ra_syntax::{algo::non_trivia_sibling, Direction, T};
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: flip_comma
 //
@@ -17,7 +17,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     ((3, 4), (1, 2));
 // }
 // ```
-pub(crate) fn flip_comma(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn flip_comma(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let comma = ctx.find_token_at_offset(T![,])?;
     let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
     let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;
@@ -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());
+    acc.add(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..8a08702ab 100644
--- a/crates/ra_assists/src/handlers/flip_trait_bound.rs
+++ b/crates/ra_assists/src/handlers/flip_trait_bound.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
     Direction, T,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: flip_trait_bound
 //
@@ -17,7 +17,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // fn foo<T: Copy + Clone>() { }
 // ```
-pub(crate) fn flip_trait_bound(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn flip_trait_bound(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     // We want to replicate the behavior of `flip_binexpr` by only suggesting
     // the assist when the cursor is on a `+`
     let plus = ctx.find_token_at_offset(T![+])?;
@@ -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();
+    acc.add(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..5b26814d3 100644
--- a/crates/ra_assists/src/handlers/inline_local_variable.rs
+++ b/crates/ra_assists/src/handlers/inline_local_variable.rs
@@ -5,7 +5,10 @@ use ra_syntax::{
 };
 use test_utils::tested_by;
 
-use crate::{assist_ctx::ActionBuilder, Assist, AssistCtx, AssistId};
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId,
+};
 
 // Assist: inline_local_variable
 //
@@ -23,7 +26,7 @@ use crate::{assist_ctx::ActionBuilder, Assist, AssistCtx, AssistId};
 //     (1 + 2) * 4;
 // }
 // ```
-pub(crate) fn inline_local_variable(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn inline_local_variable(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let let_stmt = ctx.find_node_at_offset::<ast::LetStmt>()?;
     let bind_pat = match let_stmt.pat()? {
         ast::Pat::BindPat(pat) => pat,
@@ -33,7 +36,7 @@ pub(crate) fn inline_local_variable(ctx: AssistCtx) -> Option<Assist> {
         tested_by!(test_not_inline_mut_variable);
         return None;
     }
-    if !bind_pat.syntax().text_range().contains_inclusive(ctx.frange.range.start()) {
+    if !bind_pat.syntax().text_range().contains_inclusive(ctx.offset()) {
         tested_by!(not_applicable_outside_of_bind_pat);
         return None;
     }
@@ -106,26 +109,22 @@ 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);
 
-    ctx.add_assist(
-        AssistId("inline_local_variable"),
-        "Inline variable",
-        move |edit: &mut ActionBuilder| {
-            edit.delete(delete_range);
-            for (desc, should_wrap) in refs.iter().zip(wrap_in_parens) {
-                let replacement =
-                    if should_wrap { init_in_paren.clone() } else { init_str.clone() };
-                edit.replace(desc.file_range.range, replacement)
-            }
-            edit.set_cursor(delete_range.start())
-        },
-    )
+    let target = bind_pat.syntax().text_range();
+    acc.add(AssistId("inline_local_variable"), "Inline variable", target, move |builder| {
+        builder.delete(delete_range);
+        for (desc, should_wrap) in refs.iter().zip(wrap_in_parens) {
+            let replacement = if should_wrap { init_in_paren.clone() } else { init_str.clone() };
+            builder.replace(desc.file_range.range, replacement)
+        }
+        builder.set_cursor(delete_range.start())
+    })
 }
 
 #[cfg(test)]
 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..fdf3ada0d 100644
--- a/crates/ra_assists/src/handlers/introduce_variable.rs
+++ b/crates/ra_assists/src/handlers/introduce_variable.rs
@@ -9,7 +9,7 @@ use ra_syntax::{
 use stdx::format_to;
 use test_utils::tested_by;
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: introduce_variable
 //
@@ -27,7 +27,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     var_name * 4;
 // }
 // ```
-pub(crate) fn introduce_variable(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn introduce_variable(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     if ctx.frange.range.is_empty() {
         return None;
     }
@@ -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();
+    acc.add(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..527c7caef 100644
--- a/crates/ra_assists/src/handlers/invert_if.rs
+++ b/crates/ra_assists/src/handlers/invert_if.rs
@@ -3,7 +3,11 @@ use ra_syntax::{
     T,
 };
 
-use crate::{utils::invert_boolean_expression, Assist, AssistCtx, AssistId};
+use crate::{
+    assist_context::{AssistContext, Assists},
+    utils::invert_boolean_expression,
+    AssistId,
+};
 
 // Assist: invert_if
 //
@@ -24,7 +28,7 @@ use crate::{utils::invert_boolean_expression, Assist, AssistCtx, AssistId};
 // }
 // ```
 
-pub(crate) fn invert_if(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn invert_if(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let if_keyword = ctx.find_token_at_offset(T![if])?;
     let expr = ast::IfExpr::cast(if_keyword.parent())?;
     let if_range = if_keyword.text_range();
@@ -40,29 +44,28 @@ pub(crate) fn invert_if(ctx: AssistCtx) -> Option<Assist> {
 
     let cond = expr.condition()?.expr()?;
     let then_node = expr.then_branch()?.syntax().clone();
+    let else_block = match expr.else_branch()? {
+        ast::ElseBranch::Block(it) => it,
+        ast::ElseBranch::IfExpr(_) => return None,
+    };
 
-    if let ast::ElseBranch::Block(else_block) = expr.else_branch()? {
-        let cond_range = cond.syntax().text_range();
-        let flip_cond = invert_boolean_expression(cond);
-        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);
-            edit.replace(cond_range, flip_cond.syntax().text());
-            edit.replace(else_range, then_node.text());
-            edit.replace(then_range, else_node.text());
-        });
-    }
-
-    None
+    let cond_range = cond.syntax().text_range();
+    let flip_cond = invert_boolean_expression(cond);
+    let else_node = else_block.syntax();
+    let else_range = else_node.text_range();
+    let then_range = then_node.text_range();
+    acc.add(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());
+    })
 }
 
 #[cfg(test)]
 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..ac3e53c27 100644
--- a/crates/ra_assists/src/handlers/merge_imports.rs
+++ b/crates/ra_assists/src/handlers/merge_imports.rs
@@ -6,7 +6,10 @@ use ra_syntax::{
     AstNode, Direction, InsertPosition, SyntaxElement, T,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{
+    assist_context::{AssistContext, Assists},
+    AssistId,
+};
 
 // Assist: merge_imports
 //
@@ -20,10 +23,10 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // use std::{fmt::Formatter, io};
 // ```
-pub(crate) fn merge_imports(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn merge_imports(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let tree: ast::UseTree = ctx.find_node_at_offset()?;
     let mut rewriter = SyntaxRewriter::default();
-    let mut offset = ctx.frange.range.start();
+    let mut offset = ctx.offset();
 
     if let Some(use_item) = tree.syntax().parent().and_then(ast::UseItem::cast) {
         let (merged, to_delete) = next_prev()
@@ -52,10 +55,11 @@ pub(crate) fn merge_imports(ctx: AssistCtx) -> Option<Assist> {
         }
     };
 
-    ctx.add_assist(AssistId("merge_imports"), "Merge imports", |edit| {
-        edit.rewrite(rewriter);
+    let target = tree.syntax().text_range();
+    acc.add(AssistId("merge_imports"), "Merge imports", target, |builder| {
+        builder.rewrite(rewriter);
         // FIXME: we only need because our diff is imprecise
-        edit.set_cursor(offset);
+        builder.set_cursor(offset);
     })
 }
 
@@ -125,7 +129,7 @@ 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..d4e38aa6a 100644
--- a/crates/ra_assists/src/handlers/merge_match_arms.rs
+++ b/crates/ra_assists/src/handlers/merge_match_arms.rs
@@ -6,7 +6,7 @@ use ra_syntax::{
     Direction, TextSize,
 };
 
-use crate::{Assist, AssistCtx, AssistId, TextRange};
+use crate::{AssistContext, AssistId, Assists, TextRange};
 
 // Assist: merge_match_arms
 //
@@ -32,7 +32,7 @@ use crate::{Assist, AssistCtx, AssistId, TextRange};
 //     }
 // }
 // ```
-pub(crate) fn merge_match_arms(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn merge_match_arms(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let current_arm = ctx.find_node_at_offset::<ast::MatchArm>()?;
     // Don't try to handle arms with guards for now - can add support for this later
     if current_arm.guard().is_some() {
@@ -45,7 +45,7 @@ pub(crate) fn merge_match_arms(ctx: AssistCtx) -> Option<Assist> {
         InExpr(TextSize),
         InPat(TextSize),
     }
-    let cursor_pos = ctx.frange.range.start();
+    let cursor_pos = ctx.offset();
     let cursor_pos = if current_expr.syntax().text_range().contains(cursor_pos) {
         CursorPos::InExpr(current_text_range.end() - cursor_pos)
     } else {
@@ -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| {
+    acc.add(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..a41aacfc3 100644
--- a/crates/ra_assists/src/handlers/move_bounds.rs
+++ b/crates/ra_assists/src/handlers/move_bounds.rs
@@ -5,7 +5,7 @@ use ra_syntax::{
     T,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: move_bounds_to_where_clause
 //
@@ -22,7 +22,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     f(x)
 // }
 // ```
-pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn move_bounds_to_where_clause(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let type_param_list = ctx.find_node_at_offset::<ast::TypeParamList>()?;
 
     let mut type_params = type_param_list.type_params();
@@ -49,7 +49,8 @@ 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 target = type_param_list.syntax().text_range();
+    acc.add(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())
@@ -71,7 +72,6 @@ pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx) -> Option<Assist> {
             _ => format!(" {}", where_clause.syntax()),
         };
         edit.insert(anchor.text_range().start(), to_insert);
-        edit.target(type_param_list.syntax().text_range());
     })
 }
 
@@ -89,7 +89,7 @@ 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..fc0335b57 100644
--- a/crates/ra_assists/src/handlers/move_guard.rs
+++ b/crates/ra_assists/src/handlers/move_guard.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
     TextSize,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: move_guard_to_arm_body
 //
@@ -31,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn move_guard_to_arm_body(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let match_arm = ctx.find_node_at_offset::<MatchArm>()?;
     let guard = match_arm.guard()?;
     let space_before_guard = guard.syntax().prev_sibling_or_token();
@@ -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();
+    acc.add(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() {
@@ -88,7 +88,7 @@ pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx) -> Option<Assist> {
 //     }
 // }
 // ```
-pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn move_arm_cond_to_match_guard(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let match_arm: MatchArm = ctx.find_node_at_offset::<MatchArm>()?;
     let match_pat = match_arm.pat()?;
 
@@ -108,11 +108,12 @@ pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx) -> Option<Assist> {
 
     let buf = format!(" if {}", cond.syntax().text());
 
-    ctx.add_assist(
+    let target = if_expr.syntax().text_range();
+    acc.add(
         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..c20ffe0b3 100644
--- a/crates/ra_assists/src/handlers/raw_string.rs
+++ b/crates/ra_assists/src/handlers/raw_string.rs
@@ -5,7 +5,7 @@ use ra_syntax::{
     TextSize,
 };
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{AssistContext, AssistId, Assists};
 
 // Assist: make_raw_string
 //
@@ -22,11 +22,11 @@ use crate::{Assist, AssistCtx, AssistId};
 //     r#"Hello, World!"#;
 // }
 // ```
-pub(crate) fn make_raw_string(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn make_raw_string(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     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();
+    acc.add(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() {
@@ -51,11 +51,11 @@ pub(crate) fn make_raw_string(ctx: AssistCtx) -> Option<Assist> {
 //     "Hello, \"World!\"";
 // }
 // ```
-pub(crate) fn make_usual_string(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn make_usual_string(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     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();
+    acc.add(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));
@@ -77,10 +77,10 @@ pub(crate) fn make_usual_string(ctx: AssistCtx) -> Option<Assist> {
 //     r##"Hello, World!"##;
 // }
 // ```
-pub(crate) fn add_hash(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn add_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     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();
+    acc.add(AssistId("add_hash"), "Add # to raw string", target, |edit| {
         edit.insert(token.text_range().start() + TextSize::of('r'), "#");
         edit.insert(token.text_range().end(), "#");
     })
@@ -101,15 +101,15 @@ pub(crate) fn add_hash(ctx: AssistCtx) -> Option<Assist> {
 //     r"Hello, World!";
 // }
 // ```
-pub(crate) fn remove_hash(ctx: AssistCtx) -> Option<Assist> {
+pub(crate) fn remove_hash(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
     let text = token.text().as_str();
     if text.starts_with("r\"") {
         // 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();
+    acc.add(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::*;