3 files changed, 33 insertions, 10 deletions

diff --git a/crates/syntax/Cargo.toml b/crates/syntax/Cargo.toml
index 1fe907753..c6a6f11e1 100644
--- a/crates/syntax/Cargo.toml
+++ b/crates/syntax/Cargo.toml
@@ -13,7 +13,7 @@ doctest = false
 [dependencies]
 itertools = "0.9.0"
 rowan = "0.10.0"
-rustc_lexer = { version = "688.0.0", package = "rustc-ap-rustc_lexer" }
+rustc_lexer = { version = "691.0.0", package = "rustc-ap-rustc_lexer" }
 rustc-hash = "1.1.0"
 arrayvec = "0.5.1"
 once_cell = "1.3.1"
@@ -28,6 +28,7 @@ stdx = { path = "../stdx", version = "0.0.0" }
 text_edit = { path = "../text_edit", version = "0.0.0" }
 parser = { path = "../parser", version = "0.0.0" }
 test_utils = { path = "../test_utils", version = "0.0.0" }
+profile = { path = "../profile", version = "0.0.0" }
 
 [dev-dependencies]
 walkdir = "2.3.1"
diff --git a/crates/syntax/src/algo.rs b/crates/syntax/src/algo.rs
index 320c430c9..ee89d9867 100644
--- a/crates/syntax/src/algo.rs
+++ b/crates/syntax/src/algo.rs
@@ -127,6 +127,8 @@ pub struct TreeDiff {
 
 impl TreeDiff {
     pub fn into_text_edit(&self, builder: &mut TextEditBuilder) {
+        let _p = profile::span("into_text_edit");
+
         for (anchor, to) in self.insertions.iter() {
             let offset = match anchor {
                 TreeDiffInsertPos::After(it) => it.text_range().end(),
@@ -154,6 +156,8 @@ impl TreeDiff {
 ///
 /// This function tries to find a fine-grained diff.
 pub fn diff(from: &SyntaxNode, to: &SyntaxNode) -> TreeDiff {
+    let _p = profile::span("diff");
+
     let mut diff = TreeDiff {
         replacements: FxHashMap::default(),
         insertions: FxIndexMap::default(),
@@ -467,6 +471,8 @@ impl<'a> SyntaxRewriter<'a> {
     }
 
     pub fn rewrite(&self, node: &SyntaxNode) -> SyntaxNode {
+        let _p = profile::span("rewrite");
+
         if self.f.is_none() && self.replacements.is_empty() && self.insertions.is_empty() {
             return node.clone();
         }
@@ -483,6 +489,7 @@ impl<'a> SyntaxRewriter<'a> {
     ///
     /// Returns `None` when there are no replacements.
     pub fn rewrite_root(&self) -> Option<SyntaxNode> {
+        let _p = profile::span("rewrite_root");
         fn element_to_node_or_parent(element: &SyntaxElement) -> SyntaxNode {
             match element {
                 SyntaxElement::Node(it) => it.clone(),
@@ -517,6 +524,8 @@ impl<'a> SyntaxRewriter<'a> {
     }
 
     fn rewrite_children(&self, node: &SyntaxNode) -> SyntaxNode {
+        let _p = profile::span("rewrite_children");
+
         //  FIXME: this could be made much faster.
         let mut new_children = Vec::new();
         if let Some(elements) = self.insertions(&InsertPos::FirstChildOf(node.clone())) {
@@ -533,6 +542,8 @@ impl<'a> SyntaxRewriter<'a> {
         acc: &mut Vec<NodeOrToken<rowan::GreenNode, rowan::GreenToken>>,
         element: &SyntaxElement,
     ) {
+        let _p = profile::span("rewrite_self");
+
         if let Some(replacement) = self.replacement(&element) {
             match replacement {
                 Replacement::Single(element) => acc.push(element_to_green(element)),
@@ -588,6 +599,8 @@ fn with_children(
     parent: &SyntaxNode,
     new_children: Vec<NodeOrToken<rowan::GreenNode, rowan::GreenToken>>,
 ) -> SyntaxNode {
+    let _p = profile::span("with_children");
+
     let len = new_children.iter().map(|it| it.text_len()).sum::<TextSize>();
     let new_node = rowan::GreenNode::new(rowan::SyntaxKind(parent.kind() as u16), new_children);
     let new_root_node = parent.replace_with(new_node);
diff --git a/crates/syntax/src/ast/token_ext.rs b/crates/syntax/src/ast/token_ext.rs
index 0c178039e..fa40e64e8 100644
--- a/crates/syntax/src/ast/token_ext.rs
+++ b/crates/syntax/src/ast/token_ext.rs
@@ -130,19 +130,28 @@ impl ast::String {
         let text = self.text().as_str();
         let text = &text[self.text_range_between_quotes()? - self.syntax().text_range().start()];
 
-        let mut buf = String::with_capacity(text.len());
+        let mut buf = String::new();
+        let mut text_iter = text.chars();
         let mut has_error = false;
-        unescape_literal(text, Mode::Str, &mut |_, unescaped_char| match unescaped_char {
-            Ok(c) => buf.push(c),
-            Err(_) => has_error = true,
+        unescape_literal(text, Mode::Str, &mut |char_range, unescaped_char| match (
+            unescaped_char,
+            buf.capacity() == 0,
+        ) {
+            (Ok(c), false) => buf.push(c),
+            (Ok(c), true) if Some(c) == text_iter.next() => (),
+            (Ok(c), true) => {
+                buf.reserve_exact(text.len());
+                buf.push_str(&text[..char_range.start]);
+                buf.push(c);
+            }
+            (Err(_), _) => has_error = true,
         });
 
-        if has_error {
-            return None;
+        match (has_error, buf.capacity() == 0) {
+            (true, _) => None,
+            (false, true) => Some(Cow::Borrowed(text)),
+            (false, false) => Some(Cow::Owned(buf)),
         }
-        // FIXME: don't actually allocate for borrowed case
-        let res = if buf == text { Cow::Borrowed(text) } else { Cow::Owned(buf) };
-        Some(res)
     }
 
     pub fn quote_offsets(&self) -> Option<QuoteOffsets> {