4 files changed, 109 insertions, 80 deletions

diff --git a/crates/ra_assists/src/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
index c45262efa..cbe12e908 100644
--- a/crates/ra_assists/src/assist_ctx.rs
+++ b/crates/ra_assists/src/assist_ctx.rs
@@ -2,7 +2,7 @@ use hir::db::HirDatabase;
 use ra_db::FileRange;
 use ra_fmt::{leading_indent, reindent};
 use ra_syntax::{
-    algo::{find_covering_element, find_node_at_offset},
+    algo::{self, find_covering_element, find_node_at_offset},
     AstNode, SourceFile, SyntaxElement, SyntaxNode, SyntaxToken, TextRange, TextUnit,
     TokenAtOffset,
 };
@@ -177,6 +177,12 @@ impl AssistBuilder {
         &mut self.edit
     }
 
+    pub(crate) fn replace_ast<N: AstNode>(&mut self, old: N, new: N) {
+        for (from, to) in algo::diff(old.syntax(), new.syntax()) {
+            self.edit.replace(from.text_range(), to.to_string())
+        }
+    }
+
     fn build(self) -> AssistAction {
         AssistAction {
             edit: self.edit.finish(),
diff --git a/crates/ra_assists/src/assists/add_missing_impl_members.rs b/crates/ra_assists/src/assists/add_missing_impl_members.rs
index 3fce4a5b7..c2e3eb06b 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -4,7 +4,7 @@ use ra_syntax::{
     SmolStr,
 };
 
-use crate::{ast_editor::AstEditor, Assist, AssistCtx, AssistId};
+use crate::{Assist, AssistCtx, AssistId};
 
 #[derive(PartialEq)]
 enum AddMissingImplMembersMode {
@@ -79,14 +79,13 @@ fn add_missing_impl_members_inner(
             ast::ImplItem::FnDef(def) => edit::strip_attrs_and_docs(add_body(def).into()),
             _ => edit::strip_attrs_and_docs(it),
         });
-        let mut ast_editor = AstEditor::new(impl_item_list);
-
-        ast_editor.append_items(items);
-
-        let first_new_item = ast_editor.ast().impl_items().nth(n_existing_items).unwrap();
-        let cursor_position = first_new_item.syntax().text_range().start();
-        ast_editor.into_text_edit(edit.text_edit_builder());
+        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();
+            first_new_item.syntax().text_range().start()
+        };
 
+        edit.replace_ast(impl_item_list, new_impl_item_list);
         edit.set_cursor(cursor_position);
     });
 
diff --git a/crates/ra_assists/src/ast_editor.rs b/crates/ra_assists/src/ast_editor.rs
index 60b8923e1..262e2fcf4 100644
--- a/crates/ra_assists/src/ast_editor.rs
+++ b/crates/ra_assists/src/ast_editor.rs
@@ -7,9 +7,7 @@ use ra_fmt::leading_indent;
 use ra_syntax::{
     algo,
     ast::{self, make::tokens, TypeBoundsOwner},
-    AstNode, Direction, InsertPosition, SyntaxElement,
-    SyntaxKind::*,
-    T,
+    AstNode, Direction, InsertPosition, SyntaxElement, T,
 };
 use ra_text_edit::TextEditBuilder;
 
@@ -67,38 +65,6 @@ impl<N: AstNode> AstEditor<N> {
         let new_syntax = algo::replace_children(self.ast().syntax(), to_delete, &mut to_insert);
         N::cast(new_syntax).unwrap()
     }
-
-    fn do_make_multiline(&mut self) {
-        let l_curly =
-            match self.ast().syntax().children_with_tokens().find(|it| it.kind() == T!['{']) {
-                Some(it) => it,
-                None => return,
-            };
-        let sibling = match l_curly.next_sibling_or_token() {
-            Some(it) => it,
-            None => return,
-        };
-        let existing_ws = match sibling.as_token() {
-            None => None,
-            Some(tok) if tok.kind() != WHITESPACE => None,
-            Some(ws) => {
-                if ws.text().contains('\n') {
-                    return;
-                }
-                Some(ws.clone())
-            }
-        };
-
-        let indent = leading_indent(self.ast().syntax()).unwrap_or("".into());
-        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
-        let to_insert = iter::once(ws.ws().into());
-        self.ast = match existing_ws {
-            None => self.insert_children(InsertPosition::After(l_curly), to_insert),
-            Some(ws) => {
-                self.replace_children(RangeInclusive::new(ws.clone().into(), ws.into()), to_insert)
-            }
-        };
-    }
 }
 
 impl AstEditor<ast::RecordFieldList> {
@@ -179,39 +145,6 @@ impl AstEditor<ast::RecordFieldList> {
     }
 }
 
-impl AstEditor<ast::ItemList> {
-    pub fn append_items(&mut self, items: impl Iterator<Item = ast::ImplItem>) {
-        if !self.ast().syntax().text().contains_char('\n') {
-            self.do_make_multiline();
-        }
-        items.for_each(|it| self.append_item(it));
-    }
-
-    pub fn append_item(&mut self, item: ast::ImplItem) {
-        let (indent, position) = match self.ast().impl_items().last() {
-            Some(it) => (
-                leading_indent(it.syntax()).unwrap_or_default().to_string(),
-                InsertPosition::After(it.syntax().clone().into()),
-            ),
-            None => match self.l_curly() {
-                Some(it) => (
-                    "    ".to_string() + &leading_indent(self.ast().syntax()).unwrap_or_default(),
-                    InsertPosition::After(it),
-                ),
-                None => return,
-            },
-        };
-        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
-        let to_insert: ArrayVec<[SyntaxElement; 2]> =
-            [ws.ws().into(), item.syntax().clone().into()].into();
-        self.ast = self.insert_children(position, to_insert.into_iter());
-    }
-
-    fn l_curly(&self) -> Option<SyntaxElement> {
-        self.ast().syntax().children_with_tokens().find(|it| it.kind() == T!['{'])
-    }
-}
-
 impl AstEditor<ast::TypeParam> {
     pub fn remove_bounds(&mut self) -> &mut Self {
         let colon = match self.ast.colon_token() {
diff --git a/crates/ra_syntax/src/ast/edit.rs b/crates/ra_syntax/src/ast/edit.rs
index 7013cc9b5..2af6f573e 100644
--- a/crates/ra_syntax/src/ast/edit.rs
+++ b/crates/ra_syntax/src/ast/edit.rs
@@ -7,10 +7,14 @@ use arrayvec::ArrayVec;
 
 use crate::{
     algo,
-    ast::{self, make, AstNode},
-    InsertPosition, SyntaxElement,
+    ast::{
+        self,
+        make::{self, tokens},
+        AstNode,
+    },
+    AstToken, InsertPosition, SmolStr, SyntaxElement,
     SyntaxKind::{ATTR, COMMENT, WHITESPACE},
-    SyntaxNode,
+    SyntaxNode, T,
 };
 
 impl ast::FnDef {
@@ -33,6 +37,74 @@ impl ast::FnDef {
     }
 }
 
+impl ast::ItemList {
+    #[must_use]
+    pub fn append_items(&self, items: impl Iterator<Item = ast::ImplItem>) -> ast::ItemList {
+        let mut res = self.clone();
+        if !self.syntax().text().contains_char('\n') {
+            res = res.make_multiline();
+        }
+        items.for_each(|it| res = res.append_item(it));
+        res
+    }
+
+    #[must_use]
+    pub fn append_item(&self, item: ast::ImplItem) -> ast::ItemList {
+        let (indent, position) = match self.impl_items().last() {
+            Some(it) => (
+                leading_indent(it.syntax()).unwrap_or_default().to_string(),
+                InsertPosition::After(it.syntax().clone().into()),
+            ),
+            None => match self.l_curly() {
+                Some(it) => (
+                    "    ".to_string() + &leading_indent(self.syntax()).unwrap_or_default(),
+                    InsertPosition::After(it),
+                ),
+                None => return self.clone(),
+            },
+        };
+        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
+        let to_insert: ArrayVec<[SyntaxElement; 2]> =
+            [ws.ws().into(), item.syntax().clone().into()].into();
+        insert_children(self, position, to_insert.into_iter())
+    }
+
+    fn l_curly(&self) -> Option<SyntaxElement> {
+        self.syntax().children_with_tokens().find(|it| it.kind() == T!['{'])
+    }
+
+    fn make_multiline(&self) -> ast::ItemList {
+        let l_curly = match self.syntax().children_with_tokens().find(|it| it.kind() == T!['{']) {
+            Some(it) => it,
+            None => return self.clone(),
+        };
+        let sibling = match l_curly.next_sibling_or_token() {
+            Some(it) => it,
+            None => return self.clone(),
+        };
+        let existing_ws = match sibling.as_token() {
+            None => None,
+            Some(tok) if tok.kind() != WHITESPACE => None,
+            Some(ws) => {
+                if ws.text().contains('\n') {
+                    return self.clone();
+                }
+                Some(ws.clone())
+            }
+        };
+
+        let indent = leading_indent(self.syntax()).unwrap_or("".into());
+        let ws = tokens::WsBuilder::new(&format!("\n{}", indent));
+        let to_insert = iter::once(ws.ws().into());
+        match existing_ws {
+            None => insert_children(self, InsertPosition::After(l_curly), to_insert),
+            Some(ws) => {
+                replace_children(self, RangeInclusive::new(ws.clone().into(), ws.into()), to_insert)
+            }
+        }
+    }
+}
+
 pub fn strip_attrs_and_docs<N: ast::AttrsOwner>(node: N) -> N {
     N::cast(strip_attrs_and_docs_inner(node.syntax().clone())).unwrap()
 }
@@ -50,6 +122,25 @@ fn strip_attrs_and_docs_inner(mut node: SyntaxNode) -> SyntaxNode {
     node
 }
 
+// Note this is copy-pasted from fmt. It seems like fmt should be a separate
+// crate, but basic tree building should be this crate. However, tree building
+// might want to call into fmt...
+fn leading_indent(node: &SyntaxNode) -> Option<SmolStr> {
+    let prev_tokens = std::iter::successors(node.first_token(), |token| token.prev_token());
+    for token in prev_tokens {
+        if let Some(ws) = ast::Whitespace::cast(token.clone()) {
+            let ws_text = ws.text();
+            if let Some(pos) = ws_text.rfind('\n') {
+                return Some(ws_text[pos + 1..].into());
+            }
+        }
+        if token.text().contains('\n') {
+            break;
+        }
+    }
+    None
+}
+
 #[must_use]
 fn insert_children<N: AstNode>(
     parent: &N,