12 files changed, 744 insertions, 430 deletions

diff --git a/crates/ra_editor/src/assists.rs b/crates/ra_editor/src/assists.rs
new file mode 100644
index 000000000..57b78342a
--- /dev/null
+++ b/crates/ra_editor/src/assists.rs
@@ -0,0 +1,188 @@
+//! This modules contains various "assits": suggestions for source code edits
+//! which are likely to occur at a given cursor positon. For example, if the
+//! cursor is on the `,`, a possible assist is swapping the elments around the
+//! comma.
+
+mod flip_comma;
+mod add_derive;
+mod add_impl;
+mod introduce_variable;
+mod change_visibility;
+mod split_import;
+
+use ra_text_edit::{TextEdit, TextEditBuilder};
+use ra_syntax::{
+    Direction, SyntaxNodeRef, TextUnit, TextRange,SourceFileNode, AstNode,
+    algo::{find_leaf_at_offset, find_covering_node, LeafAtOffset},
+};
+
+use crate::find_node_at_offset;
+
+pub use self::{
+    flip_comma::flip_comma,
+    add_derive::add_derive,
+    add_impl::add_impl,
+    introduce_variable::introduce_variable,
+    change_visibility::change_visibility,
+    split_import::split_import,
+};
+
+/// Return all the assists applicable at the given position.
+pub fn assists(file: &SourceFileNode, range: TextRange) -> Vec<LocalEdit> {
+    let ctx = AssistCtx::new(file, range);
+    [
+        flip_comma,
+        add_derive,
+        add_impl,
+        introduce_variable,
+        change_visibility,
+        split_import,
+    ]
+    .iter()
+    .filter_map(|&assist| ctx.clone().apply(assist))
+    .collect()
+}
+
+#[derive(Debug)]
+pub struct LocalEdit {
+    pub label: String,
+    pub edit: TextEdit,
+    pub cursor_position: Option<TextUnit>,
+}
+
+fn non_trivia_sibling(node: SyntaxNodeRef, direction: Direction) -> Option<SyntaxNodeRef> {
+    node.siblings(direction)
+        .skip(1)
+        .find(|node| !node.kind().is_trivia())
+}
+
+/// `AssistCtx` allows to apply an assist or check if it could be applied.
+///
+/// Assists use a somewhat overengeneered 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 neccessary to answer
+///   "is assist applicable" in the first phase.
+/// * second, when we are appling assist, we don't have a gurantee 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 remeniscent 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 eagarly :-)
+#[derive(Debug, Clone)]
+pub struct AssistCtx<'a> {
+    source_file: &'a SourceFileNode,
+    range: TextRange,
+    should_compute_edit: bool,
+}
+
+#[derive(Debug)]
+pub enum Assist {
+    Applicable,
+    Edit(LocalEdit),
+}
+
+#[derive(Default)]
+struct AssistBuilder {
+    edit: TextEditBuilder,
+    cursor_position: Option<TextUnit>,
+}
+
+impl<'a> AssistCtx<'a> {
+    pub fn new(source_file: &'a SourceFileNode, range: TextRange) -> AssistCtx {
+        AssistCtx {
+            source_file,
+            range,
+            should_compute_edit: false,
+        }
+    }
+
+    pub fn apply(mut self, assist: fn(AssistCtx) -> Option<Assist>) -> Option<LocalEdit> {
+        self.should_compute_edit = true;
+        match assist(self) {
+            None => None,
+            Some(Assist::Edit(e)) => Some(e),
+            Some(Assist::Applicable) => unreachable!(),
+        }
+    }
+
+    pub fn check(mut self, assist: fn(AssistCtx) -> Option<Assist>) -> bool {
+        self.should_compute_edit = false;
+        match assist(self) {
+            None => false,
+            Some(Assist::Edit(_)) => unreachable!(),
+            Some(Assist::Applicable) => true,
+        }
+    }
+
+    fn build(self, label: impl Into<String>, f: impl FnOnce(&mut AssistBuilder)) -> Option<Assist> {
+        if !self.should_compute_edit {
+            return Some(Assist::Applicable);
+        }
+        let mut edit = AssistBuilder::default();
+        f(&mut edit);
+        Some(Assist::Edit(LocalEdit {
+            label: label.into(),
+            edit: edit.edit.finish(),
+            cursor_position: edit.cursor_position,
+        }))
+    }
+
+    pub(crate) fn leaf_at_offset(&self) -> LeafAtOffset<SyntaxNodeRef<'a>> {
+        find_leaf_at_offset(self.source_file.syntax(), self.range.start())
+    }
+    pub(crate) fn node_at_offset<N: AstNode<'a>>(&self) -> Option<N> {
+        find_node_at_offset(self.source_file.syntax(), self.range.start())
+    }
+    pub(crate) fn covering_node(&self) -> SyntaxNodeRef<'a> {
+        find_covering_node(self.source_file.syntax(), self.range)
+    }
+}
+
+impl AssistBuilder {
+    fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
+        self.edit.replace(range, replace_with.into())
+    }
+    #[allow(unused)]
+    fn delete(&mut self, range: TextRange) {
+        self.edit.delete(range)
+    }
+    fn insert(&mut self, offset: TextUnit, text: impl Into<String>) {
+        self.edit.insert(offset, text.into())
+    }
+    fn set_cursor(&mut self, offset: TextUnit) {
+        self.cursor_position = Some(offset)
+    }
+}
+
+#[cfg(test)]
+fn check_assist(assist: fn(AssistCtx) -> Option<Assist>, before: &str, after: &str) {
+    crate::test_utils::check_action(before, after, |file, off| {
+        let range = TextRange::offset_len(off, 0.into());
+        AssistCtx::new(file, range).apply(assist)
+    })
+}
+
+#[cfg(test)]
+fn check_assist_range(assist: fn(AssistCtx) -> Option<Assist>, before: &str, after: &str) {
+    crate::test_utils::check_action_range(before, after, |file, range| {
+        AssistCtx::new(file, range).apply(assist)
+    })
+}
diff --git a/crates/ra_editor/src/assists/add_derive.rs b/crates/ra_editor/src/assists/add_derive.rs
new file mode 100644
index 000000000..1e2cd4f30
--- /dev/null
+++ b/crates/ra_editor/src/assists/add_derive.rs
@@ -0,0 +1,84 @@
+use ra_syntax::{
+    ast::{self, AstNode, AttrsOwner},
+    SyntaxKind::{WHITESPACE, COMMENT},
+    TextUnit,
+};
+
+use crate::assists::{AssistCtx, Assist};
+
+pub fn add_derive(ctx: AssistCtx) -> Option<Assist> {
+    let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
+    let node_start = derive_insertion_offset(nominal)?;
+    ctx.build("add `#[derive]`", |edit| {
+        let derive_attr = nominal
+            .attrs()
+            .filter_map(|x| x.as_call())
+            .filter(|(name, _arg)| name == "derive")
+            .map(|(_name, arg)| arg)
+            .next();
+        let offset = match derive_attr {
+            None => {
+                edit.insert(node_start, "#[derive()]\n");
+                node_start + TextUnit::of_str("#[derive(")
+            }
+            Some(tt) => tt.syntax().range().end() - TextUnit::of_char(')'),
+        };
+        edit.set_cursor(offset)
+    })
+}
+
+// Insert `derive` after doc comments.
+fn derive_insertion_offset(nominal: ast::NominalDef) -> Option<TextUnit> {
+    let non_ws_child = nominal
+        .syntax()
+        .children()
+        .find(|it| it.kind() != COMMENT && it.kind() != WHITESPACE)?;
+    Some(non_ws_child.range().start())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist;
+
+    #[test]
+    fn add_derive_new() {
+        check_assist(
+            add_derive,
+            "struct Foo { a: i32, <|>}",
+            "#[derive(<|>)]\nstruct Foo { a: i32, }",
+        );
+        check_assist(
+            add_derive,
+            "struct Foo { <|> a: i32, }",
+            "#[derive(<|>)]\nstruct Foo {  a: i32, }",
+        );
+    }
+
+    #[test]
+    fn add_derive_existing() {
+        check_assist(
+            add_derive,
+            "#[derive(Clone)]\nstruct Foo { a: i32<|>, }",
+            "#[derive(Clone<|>)]\nstruct Foo { a: i32, }",
+        );
+    }
+
+    #[test]
+    fn add_derive_new_with_doc_comment() {
+        check_assist(
+            add_derive,
+            "
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+struct Foo { a: i32<|>, }
+            ",
+            "
+/// `Foo` is a pretty important struct.
+/// It does stuff.
+#[derive(<|>)]
+struct Foo { a: i32, }
+            ",
+        );
+    }
+}
diff --git a/crates/ra_editor/src/assists/add_impl.rs b/crates/ra_editor/src/assists/add_impl.rs
new file mode 100644
index 000000000..9353e2717
--- /dev/null
+++ b/crates/ra_editor/src/assists/add_impl.rs
@@ -0,0 +1,66 @@
+use join_to_string::join;
+use ra_syntax::{
+    ast::{self, AstNode, NameOwner, TypeParamsOwner},
+    TextUnit,
+};
+
+use crate::assists::{AssistCtx, Assist};
+
+pub fn add_impl(ctx: AssistCtx) -> Option<Assist> {
+    let nominal = ctx.node_at_offset::<ast::NominalDef>()?;
+    let name = nominal.name()?;
+    ctx.build("add impl", |edit| {
+        let type_params = nominal.type_param_list();
+        let start_offset = nominal.syntax().range().end();
+        let mut buf = String::new();
+        buf.push_str("\n\nimpl");
+        if let Some(type_params) = type_params {
+            type_params.syntax().text().push_to(&mut buf);
+        }
+        buf.push_str(" ");
+        buf.push_str(name.text().as_str());
+        if let Some(type_params) = type_params {
+            let lifetime_params = type_params
+                .lifetime_params()
+                .filter_map(|it| it.lifetime())
+                .map(|it| it.text());
+            let type_params = type_params
+                .type_params()
+                .filter_map(|it| it.name())
+                .map(|it| it.text());
+            join(lifetime_params.chain(type_params))
+                .surround_with("<", ">")
+                .to_buf(&mut buf);
+        }
+        buf.push_str(" {\n");
+        edit.set_cursor(start_offset + TextUnit::of_str(&buf));
+        buf.push_str("\n}");
+        edit.insert(start_offset, buf);
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist;
+
+    #[test]
+    fn test_add_impl() {
+        check_assist(
+            add_impl,
+            "struct Foo {<|>}\n",
+            "struct Foo {}\n\nimpl Foo {\n<|>\n}\n",
+        );
+        check_assist(
+            add_impl,
+            "struct Foo<T: Clone> {<|>}",
+            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n<|>\n}",
+        );
+        check_assist(
+            add_impl,
+            "struct Foo<'a, T: Foo<'a>> {<|>}",
+            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n<|>\n}",
+        );
+    }
+
+}
diff --git a/crates/ra_editor/src/assists/change_visibility.rs b/crates/ra_editor/src/assists/change_visibility.rs
new file mode 100644
index 000000000..6c8466394
--- /dev/null
+++ b/crates/ra_editor/src/assists/change_visibility.rs
@@ -0,0 +1,116 @@
+use ra_syntax::{
+    AstNode,
+    ast::{self, VisibilityOwner, NameOwner},
+    SyntaxKind::{VISIBILITY, FN_KW, MOD_KW, STRUCT_KW, ENUM_KW, TRAIT_KW, FN_DEF, MODULE, STRUCT_DEF, ENUM_DEF, TRAIT_DEF, IDENT},
+};
+
+use crate::assists::{AssistCtx, Assist};
+
+pub fn change_visibility(ctx: AssistCtx) -> Option<Assist> {
+    if let Some(vis) = ctx.node_at_offset::<ast::Visibility>() {
+        return change_vis(ctx, vis);
+    }
+    add_vis(ctx)
+}
+
+fn add_vis(ctx: AssistCtx) -> Option<Assist> {
+    let item_keyword = ctx.leaf_at_offset().find(|leaf| match leaf.kind() {
+        FN_KW | MOD_KW | STRUCT_KW | ENUM_KW | TRAIT_KW => true,
+        _ => false,
+    });
+
+    let offset = if let Some(keyword) = item_keyword {
+        let parent = keyword.parent()?;
+        let def_kws = vec![FN_DEF, MODULE, STRUCT_DEF, ENUM_DEF, TRAIT_DEF];
+        // Parent is not a definition, can't add visibility
+        if !def_kws.iter().any(|&def_kw| def_kw == parent.kind()) {
+            return None;
+        }
+        // Already have visibility, do nothing
+        if parent.children().any(|child| child.kind() == VISIBILITY) {
+            return None;
+        }
+        parent.range().start()
+    } else {
+        let ident = ctx.leaf_at_offset().find(|leaf| leaf.kind() == IDENT)?;
+        let field = ident.ancestors().find_map(ast::NamedFieldDef::cast)?;
+        if field.name()?.syntax().range() != ident.range() && field.visibility().is_some() {
+            return None;
+        }
+        field.syntax().range().start()
+    };
+
+    ctx.build("make pub(crate)", |edit| {
+        edit.insert(offset, "pub(crate) ");
+        edit.set_cursor(offset);
+    })
+}
+
+fn change_vis(ctx: AssistCtx, vis: ast::Visibility) -> Option<Assist> {
+    if vis.syntax().text() != "pub" {
+        return None;
+    }
+    ctx.build("chage to pub(crate)", |edit| {
+        edit.replace(vis.syntax().range(), "pub(crate)");
+        edit.set_cursor(vis.syntax().range().start());
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist;
+
+    #[test]
+    fn change_visibility_adds_pub_crate_to_items() {
+        check_assist(
+            change_visibility,
+            "<|>fn foo() {}",
+            "<|>pub(crate) fn foo() {}",
+        );
+        check_assist(
+            change_visibility,
+            "f<|>n foo() {}",
+            "<|>pub(crate) fn foo() {}",
+        );
+        check_assist(
+            change_visibility,
+            "<|>struct Foo {}",
+            "<|>pub(crate) struct Foo {}",
+        );
+        check_assist(
+            change_visibility,
+            "<|>mod foo {}",
+            "<|>pub(crate) mod foo {}",
+        );
+        check_assist(
+            change_visibility,
+            "<|>trait Foo {}",
+            "<|>pub(crate) trait Foo {}",
+        );
+        check_assist(change_visibility, "m<|>od {}", "<|>pub(crate) mod {}");
+        check_assist(
+            change_visibility,
+            "unsafe f<|>n foo() {}",
+            "<|>pub(crate) unsafe fn foo() {}",
+        );
+    }
+
+    #[test]
+    fn change_visibility_works_with_struct_fields() {
+        check_assist(
+            change_visibility,
+            "struct S { <|>field: u32 }",
+            "struct S { <|>pub(crate) field: u32 }",
+        )
+    }
+
+    #[test]
+    fn change_visibility_pub_to_pub_crate() {
+        check_assist(
+            change_visibility,
+            "<|>pub fn foo() {}",
+            "<|>pub(crate) fn foo() {}",
+        )
+    }
+}
diff --git a/crates/ra_editor/src/assists/flip_comma.rs b/crates/ra_editor/src/assists/flip_comma.rs
new file mode 100644
index 000000000..a343413cc
--- /dev/null
+++ b/crates/ra_editor/src/assists/flip_comma.rs
@@ -0,0 +1,31 @@
+use ra_syntax::{
+    Direction,
+    SyntaxKind::COMMA,
+};
+
+use crate::assists::{non_trivia_sibling, AssistCtx, Assist};
+
+pub fn flip_comma(ctx: AssistCtx) -> Option<Assist> {
+    let comma = ctx.leaf_at_offset().find(|leaf| leaf.kind() == COMMA)?;
+    let prev = non_trivia_sibling(comma, Direction::Prev)?;
+    let next = non_trivia_sibling(comma, Direction::Next)?;
+    ctx.build("flip comma", |edit| {
+        edit.replace(prev.range(), next.text());
+        edit.replace(next.range(), prev.text());
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist;
+
+    #[test]
+    fn flip_comma_works_for_function_parameters() {
+        check_assist(
+            flip_comma,
+            "fn foo(x: i32,<|> y: Result<(), ()>) {}",
+            "fn foo(y: Result<(), ()>,<|> x: i32) {}",
+        )
+    }
+}
diff --git a/crates/ra_editor/src/assists/introduce_variable.rs b/crates/ra_editor/src/assists/introduce_variable.rs
new file mode 100644
index 000000000..782861023
--- /dev/null
+++ b/crates/ra_editor/src/assists/introduce_variable.rs
@@ -0,0 +1,144 @@
+use ra_syntax::{
+    ast::{self, AstNode},
+    SyntaxKind::WHITESPACE,
+    SyntaxNodeRef, TextUnit,
+};
+
+use crate::assists::{AssistCtx, Assist};
+
+pub fn introduce_variable<'a>(ctx: AssistCtx) -> Option<Assist> {
+    let node = ctx.covering_node();
+    let expr = node.ancestors().filter_map(ast::Expr::cast).next()?;
+
+    let anchor_stmt = anchor_stmt(expr)?;
+    let indent = anchor_stmt.prev_sibling()?;
+    if indent.kind() != WHITESPACE {
+        return None;
+    }
+    ctx.build("introduce variable", move |edit| {
+        let mut buf = String::new();
+
+        buf.push_str("let var_name = ");
+        expr.syntax().text().push_to(&mut buf);
+        let is_full_stmt = if let Some(expr_stmt) = ast::ExprStmt::cast(anchor_stmt) {
+            Some(expr.syntax()) == expr_stmt.expr().map(|e| e.syntax())
+        } else {
+            false
+        };
+        if is_full_stmt {
+            edit.replace(expr.syntax().range(), buf);
+        } else {
+            buf.push_str(";");
+            indent.text().push_to(&mut buf);
+            edit.replace(expr.syntax().range(), "var_name".to_string());
+            edit.insert(anchor_stmt.range().start(), buf);
+        }
+        edit.set_cursor(anchor_stmt.range().start() + TextUnit::of_str("let "));
+    })
+}
+
+/// Statement or last in the block expression, which will follow
+/// the freshly introduced var.
+fn anchor_stmt(expr: ast::Expr) -> Option<SyntaxNodeRef> {
+    expr.syntax().ancestors().find(|&node| {
+        if ast::Stmt::cast(node).is_some() {
+            return true;
+        }
+        if let Some(expr) = node
+            .parent()
+            .and_then(ast::Block::cast)
+            .and_then(|it| it.expr())
+        {
+            if expr.syntax() == node {
+                return true;
+            }
+        }
+        false
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist_range;
+
+    #[test]
+    fn test_introduce_var_simple() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    foo(<|>1 + 1<|>);
+}",
+            "
+fn foo() {
+    let <|>var_name = 1 + 1;
+    foo(var_name);
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_expr_stmt() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>1 + 1<|>;
+}",
+            "
+fn foo() {
+    let <|>var_name = 1 + 1;
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_part_of_expr_stmt() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>1<|> + 1;
+}",
+            "
+fn foo() {
+    let <|>var_name = 1;
+    var_name + 1;
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_last_expr() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    bar(<|>1 + 1<|>)
+}",
+            "
+fn foo() {
+    let <|>var_name = 1 + 1;
+    bar(var_name)
+}",
+        );
+    }
+
+    #[test]
+    fn test_introduce_var_last_full_expr() {
+        check_assist_range(
+            introduce_variable,
+            "
+fn foo() {
+    <|>bar(1 + 1)<|>
+}",
+            "
+fn foo() {
+    let <|>var_name = bar(1 + 1);
+    var_name
+}",
+        );
+    }
+
+}
diff --git a/crates/ra_editor/src/assists/split_import.rs b/crates/ra_editor/src/assists/split_import.rs
new file mode 100644
index 000000000..75f9e8dfb
--- /dev/null
+++ b/crates/ra_editor/src/assists/split_import.rs
@@ -0,0 +1,44 @@
+use ra_syntax::{
+    TextUnit, AstNode, SyntaxKind::COLONCOLON,
+    ast,
+    algo::generate,
+};
+
+use crate::assists::{AssistCtx, Assist};
+
+pub fn split_import(ctx: AssistCtx) -> Option<Assist> {
+    let colon_colon = ctx
+        .leaf_at_offset()
+        .find(|leaf| leaf.kind() == COLONCOLON)?;
+    let path = colon_colon.parent().and_then(ast::Path::cast)?;
+    let top_path = generate(Some(path), |it| it.parent_path()).last()?;
+
+    let use_tree = top_path.syntax().ancestors().find_map(ast::UseTree::cast);
+    if use_tree.is_none() {
+        return None;
+    }
+
+    let l_curly = colon_colon.range().end();
+    let r_curly = top_path.syntax().range().end();
+
+    ctx.build("split import", |edit| {
+        edit.insert(l_curly, "{");
+        edit.insert(r_curly, "}");
+        edit.set_cursor(l_curly + TextUnit::of_str("{"));
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist;
+
+    #[test]
+    fn test_split_import() {
+        check_assist(
+            split_import,
+            "use crate::<|>db::RootDatabase;",
+            "use crate::{<|>db::RootDatabase};",
+        )
+    }
+}
diff --git a/crates/ra_editor/src/code_actions.rs b/crates/ra_editor/src/code_actions.rs
deleted file mode 100644
index 7615f37a6..000000000
--- a/crates/ra_editor/src/code_actions.rs
+++ /dev/null
@@ -1,415 +0,0 @@
-use join_to_string::join;
-
-use ra_syntax::{
-    algo::{find_covering_node, find_leaf_at_offset},
-    ast::{self, AstNode, AttrsOwner, NameOwner, TypeParamsOwner},
-    Direction, SourceFileNode,
-    SyntaxKind::{COMMA, WHITESPACE, COMMENT, VISIBILITY, FN_KW, MOD_KW, STRUCT_KW, ENUM_KW, TRAIT_KW, FN_DEF, MODULE, STRUCT_DEF, ENUM_DEF, TRAIT_DEF},
-    SyntaxNodeRef, TextRange, TextUnit,
-};
-
-use crate::{find_node_at_offset, TextEdit, TextEditBuilder};
-
-#[derive(Debug)]
-pub struct LocalEdit {
-    pub label: String,
-    pub edit: TextEdit,
-    pub cursor_position: Option<TextUnit>,
-}
-
-pub fn flip_comma<'a>(
-    file: &'a SourceFileNode,
-    offset: TextUnit,
-) -> Option<impl FnOnce() -> LocalEdit + 'a> {
-    let syntax = file.syntax();
-
-    let comma = find_leaf_at_offset(syntax, offset).find(|leaf| leaf.kind() == COMMA)?;
-    let prev = non_trivia_sibling(comma, Direction::Prev)?;
-    let next = non_trivia_sibling(comma, Direction::Next)?;
-    Some(move || {
-        let mut edit = TextEditBuilder::new();
-        edit.replace(prev.range(), next.text().to_string());
-        edit.replace(next.range(), prev.text().to_string());
-        LocalEdit {
-            label: "flip comma".to_string(),
-            edit: edit.finish(),
-            cursor_position: None,
-        }
-    })
-}
-
-pub fn add_derive<'a>(
-    file: &'a SourceFileNode,
-    offset: TextUnit,
-) -> Option<impl FnOnce() -> LocalEdit + 'a> {
-    let nominal = find_node_at_offset::<ast::NominalDef>(file.syntax(), offset)?;
-    let node_start = derive_insertion_offset(nominal)?;
-    return Some(move || {
-        let derive_attr = nominal
-            .attrs()
-            .filter_map(|x| x.as_call())
-            .filter(|(name, _arg)| name == "derive")
-            .map(|(_name, arg)| arg)
-            .next();
-        let mut edit = TextEditBuilder::new();
-        let offset = match derive_attr {
-            None => {
-                edit.insert(node_start, "#[derive()]\n".to_string());
-                node_start + TextUnit::of_str("#[derive(")
-            }
-            Some(tt) => tt.syntax().range().end() - TextUnit::of_char(')'),
-        };
-        LocalEdit {
-            label: "add `#[derive]`".to_string(),
-            edit: edit.finish(),
-            cursor_position: Some(offset),
-        }
-    });
-
-    // Insert `derive` after doc comments.
-    fn derive_insertion_offset(nominal: ast::NominalDef) -> Option<TextUnit> {
-        let non_ws_child = nominal
-            .syntax()
-            .children()
-            .find(|it| it.kind() != COMMENT && it.kind() != WHITESPACE)?;
-        Some(non_ws_child.range().start())
-    }
-}
-
-pub fn add_impl<'a>(
-    file: &'a SourceFileNode,
-    offset: TextUnit,
-) -> Option<impl FnOnce() -> LocalEdit + 'a> {
-    let nominal = find_node_at_offset::<ast::NominalDef>(file.syntax(), offset)?;
-    let name = nominal.name()?;
-
-    Some(move || {
-        let type_params = nominal.type_param_list();
-        let mut edit = TextEditBuilder::new();
-        let start_offset = nominal.syntax().range().end();
-        let mut buf = String::new();
-        buf.push_str("\n\nimpl");
-        if let Some(type_params) = type_params {
-            type_params.syntax().text().push_to(&mut buf);
-        }
-        buf.push_str(" ");
-        buf.push_str(name.text().as_str());
-        if let Some(type_params) = type_params {
-            let lifetime_params = type_params
-                .lifetime_params()
-                .filter_map(|it| it.lifetime())
-                .map(|it| it.text());
-            let type_params = type_params
-                .type_params()
-                .filter_map(|it| it.name())
-                .map(|it| it.text());
-            join(lifetime_params.chain(type_params))
-                .surround_with("<", ">")
-                .to_buf(&mut buf);
-        }
-        buf.push_str(" {\n");
-        let offset = start_offset + TextUnit::of_str(&buf);
-        buf.push_str("\n}");
-        edit.insert(start_offset, buf);
-        LocalEdit {
-            label: "add impl".to_string(),
-            edit: edit.finish(),
-            cursor_position: Some(offset),
-        }
-    })
-}
-
-pub fn introduce_variable<'a>(
-    file: &'a SourceFileNode,
-    range: TextRange,
-) -> Option<impl FnOnce() -> LocalEdit + 'a> {
-    let node = find_covering_node(file.syntax(), range);
-    let expr = node.ancestors().filter_map(ast::Expr::cast).next()?;
-
-    let anchor_stmt = anchor_stmt(expr)?;
-    let indent = anchor_stmt.prev_sibling()?;
-    if indent.kind() != WHITESPACE {
-        return None;
-    }
-    return Some(move || {
-        let mut buf = String::new();
-        let mut edit = TextEditBuilder::new();
-
-        buf.push_str("let var_name = ");
-        expr.syntax().text().push_to(&mut buf);
-        let is_full_stmt = if let Some(expr_stmt) = ast::ExprStmt::cast(anchor_stmt) {
-            Some(expr.syntax()) == expr_stmt.expr().map(|e| e.syntax())
-        } else {
-            false
-        };
-        if is_full_stmt {
-            edit.replace(expr.syntax().range(), buf);
-        } else {
-            buf.push_str(";");
-            indent.text().push_to(&mut buf);
-            edit.replace(expr.syntax().range(), "var_name".to_string());
-            edit.insert(anchor_stmt.range().start(), buf);
-        }
-        let cursor_position = anchor_stmt.range().start() + TextUnit::of_str("let ");
-        LocalEdit {
-            label: "introduce variable".to_string(),
-            edit: edit.finish(),
-            cursor_position: Some(cursor_position),
-        }
-    });
-
-    /// Statement or last in the block expression, which will follow
-    /// the freshly introduced var.
-    fn anchor_stmt(expr: ast::Expr) -> Option<SyntaxNodeRef> {
-        expr.syntax().ancestors().find(|&node| {
-            if ast::Stmt::cast(node).is_some() {
-                return true;
-            }
-            if let Some(expr) = node
-                .parent()
-                .and_then(ast::Block::cast)
-                .and_then(|it| it.expr())
-            {
-                if expr.syntax() == node {
-                    return true;
-                }
-            }
-            false
-        })
-    }
-}
-
-pub fn make_pub_crate<'a>(
-    file: &'a SourceFileNode,
-    offset: TextUnit,
-) -> Option<impl FnOnce() -> LocalEdit + 'a> {
-    let syntax = file.syntax();
-
-    let keyword = find_leaf_at_offset(syntax, offset).find(|leaf| match leaf.kind() {
-        FN_KW | MOD_KW | STRUCT_KW | ENUM_KW | TRAIT_KW => true,
-        _ => false,
-    })?;
-    let parent = keyword.parent()?;
-    let def_kws = vec![FN_DEF, MODULE, STRUCT_DEF, ENUM_DEF, TRAIT_DEF];
-    let node_start = parent.range().start();
-    Some(move || {
-        let mut edit = TextEditBuilder::new();
-
-        if !def_kws.iter().any(|&def_kw| def_kw == parent.kind())
-            || parent.children().any(|child| child.kind() == VISIBILITY)
-        {
-            return LocalEdit {
-                label: "make pub crate".to_string(),
-                edit: edit.finish(),
-                cursor_position: Some(offset),
-            };
-        }
-
-        edit.insert(node_start, "pub(crate) ".to_string());
-        LocalEdit {
-            label: "make pub crate".to_string(),
-            edit: edit.finish(),
-            cursor_position: Some(node_start),
-        }
-    })
-}
-
-fn non_trivia_sibling(node: SyntaxNodeRef, direction: Direction) -> Option<SyntaxNodeRef> {
-    node.siblings(direction)
-        .skip(1)
-        .find(|node| !node.kind().is_trivia())
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::test_utils::{check_action, check_action_range};
-
-    #[test]
-    fn test_swap_comma() {
-        check_action(
-            "fn foo(x: i32,<|> y: Result<(), ()>) {}",
-            "fn foo(y: Result<(), ()>,<|> x: i32) {}",
-            |file, off| flip_comma(file, off).map(|f| f()),
-        )
-    }
-
-    #[test]
-    fn add_derive_new() {
-        check_action(
-            "struct Foo { a: i32, <|>}",
-            "#[derive(<|>)]\nstruct Foo { a: i32, }",
-            |file, off| add_derive(file, off).map(|f| f()),
-        );
-        check_action(
-            "struct Foo { <|> a: i32, }",
-            "#[derive(<|>)]\nstruct Foo {  a: i32, }",
-            |file, off| add_derive(file, off).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn add_derive_existing() {
-        check_action(
-            "#[derive(Clone)]\nstruct Foo { a: i32<|>, }",
-            "#[derive(Clone<|>)]\nstruct Foo { a: i32, }",
-            |file, off| add_derive(file, off).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn add_derive_new_with_doc_comment() {
-        check_action(
-            "
-/// `Foo` is a pretty important struct.
-/// It does stuff.
-struct Foo { a: i32<|>, }
-            ",
-            "
-/// `Foo` is a pretty important struct.
-/// It does stuff.
-#[derive(<|>)]
-struct Foo { a: i32, }
-            ",
-            |file, off| add_derive(file, off).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_add_impl() {
-        check_action(
-            "struct Foo {<|>}\n",
-            "struct Foo {}\n\nimpl Foo {\n<|>\n}\n",
-            |file, off| add_impl(file, off).map(|f| f()),
-        );
-        check_action(
-            "struct Foo<T: Clone> {<|>}",
-            "struct Foo<T: Clone> {}\n\nimpl<T: Clone> Foo<T> {\n<|>\n}",
-            |file, off| add_impl(file, off).map(|f| f()),
-        );
-        check_action(
-            "struct Foo<'a, T: Foo<'a>> {<|>}",
-            "struct Foo<'a, T: Foo<'a>> {}\n\nimpl<'a, T: Foo<'a>> Foo<'a, T> {\n<|>\n}",
-            |file, off| add_impl(file, off).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_introduce_var_simple() {
-        check_action_range(
-            "
-fn foo() {
-    foo(<|>1 + 1<|>);
-}",
-            "
-fn foo() {
-    let <|>var_name = 1 + 1;
-    foo(var_name);
-}",
-            |file, range| introduce_variable(file, range).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_introduce_var_expr_stmt() {
-        check_action_range(
-            "
-fn foo() {
-    <|>1 + 1<|>;
-}",
-            "
-fn foo() {
-    let <|>var_name = 1 + 1;
-}",
-            |file, range| introduce_variable(file, range).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_introduce_var_part_of_expr_stmt() {
-        check_action_range(
-            "
-fn foo() {
-    <|>1<|> + 1;
-}",
-            "
-fn foo() {
-    let <|>var_name = 1;
-    var_name + 1;
-}",
-            |file, range| introduce_variable(file, range).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_introduce_var_last_expr() {
-        check_action_range(
-            "
-fn foo() {
-    bar(<|>1 + 1<|>)
-}",
-            "
-fn foo() {
-    let <|>var_name = 1 + 1;
-    bar(var_name)
-}",
-            |file, range| introduce_variable(file, range).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_introduce_var_last_full_expr() {
-        check_action_range(
-            "
-fn foo() {
-    <|>bar(1 + 1)<|>
-}",
-            "
-fn foo() {
-    let <|>var_name = bar(1 + 1);
-    var_name
-}",
-            |file, range| introduce_variable(file, range).map(|f| f()),
-        );
-    }
-
-    #[test]
-    fn test_make_pub_crate() {
-        check_action(
-            "<|>fn foo() {}",
-            "<|>pub(crate) fn foo() {}",
-            |file, off| make_pub_crate(file, off).map(|f| f()),
-        );
-        check_action(
-            "f<|>n foo() {}",
-            "<|>pub(crate) fn foo() {}",
-            |file, off| make_pub_crate(file, off).map(|f| f()),
-        );
-        check_action(
-            "<|>struct Foo {}",
-            "<|>pub(crate) struct Foo {}",
-            |file, off| make_pub_crate(file, off).map(|f| f()),
-        );
-        check_action("<|>mod foo {}", "<|>pub(crate) mod foo {}", |file, off| {
-            make_pub_crate(file, off).map(|f| f())
-        });
-        check_action(
-            "<|>trait Foo {}",
-            "<|>pub(crate) trait Foo {}",
-            |file, off| make_pub_crate(file, off).map(|f| f()),
-        );
-        check_action("m<|>od {}", "<|>pub(crate) mod {}", |file, off| {
-            make_pub_crate(file, off).map(|f| f())
-        });
-        check_action(
-            "pub(crate) f<|>n foo() {}",
-            "pub(crate) f<|>n foo() {}",
-            |file, off| make_pub_crate(file, off).map(|f| f()),
-        );
-        check_action(
-            "unsafe f<|>n foo() {}",
-            "<|>pub(crate) unsafe fn foo() {}",
-            |file, off| make_pub_crate(file, off).map(|f| f()),
-        );
-    }
-}
diff --git a/crates/ra_editor/src/diagnostics.rs b/crates/ra_editor/src/diagnostics.rs
index 1b336cfe2..199b0e502 100644
--- a/crates/ra_editor/src/diagnostics.rs
+++ b/crates/ra_editor/src/diagnostics.rs
@@ -57,7 +57,7 @@ fn check_unnecessary_braces_in_use_statement(
             text_edit_for_remove_unnecessary_braces_with_self_in_use_statement(single_use_tree)
                 .unwrap_or_else(|| {
                     let to_replace = single_use_tree.syntax().text().to_string();
-                    let mut edit_builder = TextEditBuilder::new();
+                    let mut edit_builder = TextEditBuilder::default();
                     edit_builder.delete(range);
                     edit_builder.insert(range.start(), to_replace);
                     edit_builder.finish()
@@ -93,7 +93,7 @@ fn text_edit_for_remove_unnecessary_braces_with_self_in_use_statement(
         let start = use_tree_list_node.prev_sibling()?.range().start();
         let end = use_tree_list_node.range().end();
         let range = TextRange::from_to(start, end);
-        let mut edit_builder = TextEditBuilder::new();
+        let mut edit_builder = TextEditBuilder::default();
         edit_builder.delete(range);
         return Some(edit_builder.finish());
     }
@@ -111,7 +111,7 @@ fn check_struct_shorthand_initialization(
             let field_name = name_ref.syntax().text().to_string();
             let field_expr = expr.syntax().text().to_string();
             if field_name == field_expr {
-                let mut edit_builder = TextEditBuilder::new();
+                let mut edit_builder = TextEditBuilder::default();
                 edit_builder.delete(named_field.syntax().range());
                 edit_builder.insert(named_field.syntax().range().start(), field_name);
                 let edit = edit_builder.finish();
diff --git a/crates/ra_editor/src/lib.rs b/crates/ra_editor/src/lib.rs
index bfc745e58..ac283e2e0 100644
--- a/crates/ra_editor/src/lib.rs
+++ b/crates/ra_editor/src/lib.rs
@@ -1,4 +1,4 @@
-mod code_actions;
+pub mod assists;
 mod extend_selection;
 mod folding_ranges;
 mod line_index;
@@ -10,7 +10,7 @@ mod typing;
 mod diagnostics;
 
 pub use self::{
-    code_actions::{add_derive, add_impl, flip_comma, introduce_variable, make_pub_crate, LocalEdit},
+    assists::LocalEdit,
     extend_selection::extend_selection,
     folding_ranges::{folding_ranges, Fold, FoldKind},
     line_index::{LineCol, LineIndex},
@@ -19,7 +19,7 @@ pub use self::{
     typing::{join_lines, on_enter, on_eq_typed},
     diagnostics::diagnostics
 };
-use ra_text_edit::{TextEdit, TextEditBuilder};
+use ra_text_edit::TextEditBuilder;
 use ra_syntax::{
     algo::find_leaf_at_offset,
     ast::{self, AstNode},
diff --git a/crates/ra_editor/src/structure.rs b/crates/ra_editor/src/structure.rs
index 2292b1ddf..32d59e335 100644
--- a/crates/ra_editor/src/structure.rs
+++ b/crates/ra_editor/src/structure.rs
@@ -60,7 +60,7 @@ fn structure_node(node: SyntaxNodeRef) -> Option<StructureNode> {
         .visit(decl::<ast::TypeDef>)
         .visit(decl::<ast::ConstDef>)
         .visit(decl::<ast::StaticDef>)
-        .visit(|im: ast::ImplItem| {
+        .visit(|im: ast::ImplBlock| {
             let target_type = im.target_type()?;
             let target_trait = im.target_trait();
             let label = match target_trait {
@@ -121,8 +121,8 @@ impl fmt::Debug for E {}
                 StructureNode { parent: None, label: "T", navigation_range: [81; 82), node_range: [76; 88), kind: TYPE_DEF },
                 StructureNode { parent: None, label: "S", navigation_range: [96; 97), node_range: [89; 108), kind: STATIC_DEF },
                 StructureNode { parent: None, label: "C", navigation_range: [115; 116), node_range: [109; 127), kind: CONST_DEF },
-                StructureNode { parent: None, label: "impl E", navigation_range: [134; 135), node_range: [129; 138), kind: IMPL_ITEM },
-                StructureNode { parent: None, label: "impl fmt::Debug for E", navigation_range: [160; 161), node_range: [140; 164), kind: IMPL_ITEM }]"#,
+                StructureNode { parent: None, label: "impl E", navigation_range: [134; 135), node_range: [129; 138), kind: IMPL_BLOCK },
+                StructureNode { parent: None, label: "impl fmt::Debug for E", navigation_range: [160; 161), node_range: [140; 164), kind: IMPL_BLOCK }]"#,
             &structure,
         )
     }
diff --git a/crates/ra_editor/src/typing.rs b/crates/ra_editor/src/typing.rs
index 21d068a7b..1b568e96c 100644
--- a/crates/ra_editor/src/typing.rs
+++ b/crates/ra_editor/src/typing.rs
@@ -21,7 +21,7 @@ pub fn join_lines(file: &SourceFileNode, range: TextRange) -> LocalEdit {
             None => {
                 return LocalEdit {
                     label: "join lines".to_string(),
-                    edit: TextEditBuilder::new().finish(),
+                    edit: TextEditBuilder::default().finish(),
                     cursor_position: None,
                 };
             }
@@ -33,7 +33,7 @@ pub fn join_lines(file: &SourceFileNode, range: TextRange) -> LocalEdit {
     };
 
     let node = find_covering_node(file.syntax(), range);
-    let mut edit = TextEditBuilder::new();
+    let mut edit = TextEditBuilder::default();
     for node in node.descendants() {
         let text = match node.leaf_text() {
             Some(text) => text,
@@ -76,7 +76,7 @@ pub fn on_enter(file: &SourceFileNode, offset: TextUnit) -> Option<LocalEdit> {
     let indent = node_indent(file, comment.syntax())?;
     let inserted = format!("\n{}{} ", indent, prefix);
     let cursor_position = offset + TextUnit::of_str(&inserted);
-    let mut edit = TextEditBuilder::new();
+    let mut edit = TextEditBuilder::default();
     edit.insert(offset, inserted);
     Some(LocalEdit {
         label: "on enter".to_string(),
@@ -127,7 +127,7 @@ pub fn on_eq_typed(file: &SourceFileNode, offset: TextUnit) -> Option<LocalEdit>
         return None;
     }
     let offset = let_stmt.syntax().range().end();
-    let mut edit = TextEditBuilder::new();
+    let mut edit = TextEditBuilder::default();
     edit.insert(offset, ";".to_string());
     Some(LocalEdit {
         label: "add semicolon".to_string(),
@@ -188,10 +188,14 @@ fn remove_newline(
         edit.delete(TextRange::from_to(prev.range().start(), node.range().end()));
     } else if prev.kind() == COMMA && next.kind() == R_CURLY {
         // Removes: comma, newline (incl. surrounding whitespace)
-        // Adds: a single whitespace
+        let space = if let Some(left) = prev.prev_sibling() {
+            compute_ws(left, next)
+        } else {
+            " "
+        };
         edit.replace(
             TextRange::from_to(prev.range().start(), node.range().end()),
-            " ".to_string(),
+            space.to_string(),
         );
     } else if let (Some(_), Some(next)) = (ast::Comment::cast(prev), ast::Comment::cast(next)) {
         // Removes: newline (incl. surrounding whitespace), start of the next comment
@@ -256,10 +260,20 @@ fn join_single_use_tree(edit: &mut TextEditBuilder, node: SyntaxNodeRef) -> Opti
 fn compute_ws(left: SyntaxNodeRef, right: SyntaxNodeRef) -> &'static str {
     match left.kind() {
         L_PAREN | L_BRACK => return "",
+        L_CURLY => {
+            if let USE_TREE = right.kind() {
+                return "";
+            }
+        }
         _ => (),
     }
     match right.kind() {
         R_PAREN | R_BRACK => return "",
+        R_CURLY => {
+            if let USE_TREE = left.kind() {
+                return "";
+            }
+        }
         DOT => return "",
         _ => (),
     }
@@ -331,6 +345,48 @@ fn foo() {
     }
 
     #[test]
+    fn test_join_lines_use_items_left() {
+        // No space after the '{'
+        check_join_lines(
+            r"
+<|>use ra_syntax::{
+    TextUnit, TextRange,
+};",
+            r"
+<|>use ra_syntax::{TextUnit, TextRange,
+};",
+        );
+    }
+
+    #[test]
+    fn test_join_lines_use_items_right() {
+        // No space after the '}'
+        check_join_lines(
+            r"
+use ra_syntax::{
+<|>    TextUnit, TextRange
+};",
+            r"
+use ra_syntax::{
+<|>    TextUnit, TextRange};",
+        );
+    }
+
+    #[test]
+    fn test_join_lines_use_items_right_comma() {
+        // No space after the '}'
+        check_join_lines(
+            r"
+use ra_syntax::{
+<|>    TextUnit, TextRange,
+};",
+            r"
+use ra_syntax::{
+<|>    TextUnit, TextRange};",
+        );
+    }
+
+    #[test]
     fn test_join_lines_use_tree() {
         check_join_lines(
             r"