2 files changed, 58 insertions, 11 deletions

diff --git a/crates/libeditor/src/lib.rs b/crates/libeditor/src/lib.rs
index 9e44f5d92..28da457d1 100644
--- a/crates/libeditor/src/lib.rs
+++ b/crates/libeditor/src/lib.rs
@@ -12,8 +12,8 @@ mod code_actions;
 use libsyntax2::{
     ast::{self, NameOwner},
     AstNode,
-    algo::walk,
-    SyntaxKind::*,
+    algo::{walk, find_leaf_at_offset},
+    SyntaxKind::{self, *},
 };
 pub use libsyntax2::{File, TextRange, TextUnit};
 pub use self::{
@@ -52,6 +52,28 @@ pub fn parse(text: &str) -> ast::File {
     ast::File::parse(text)
 }
 
+pub fn matching_brace(file: &ast::File, offset: TextUnit) -> Option<TextUnit> {
+    const BRACES: &[SyntaxKind] = &[
+        L_CURLY, R_CURLY,
+        L_BRACK, R_BRACK,
+        L_PAREN, R_PAREN,
+        L_ANGLE, R_ANGLE,
+    ];
+    let syntax = file.syntax();
+    let syntax = syntax.as_ref();
+    let (brace_node, brace_idx) = find_leaf_at_offset(syntax, offset)
+        .filter_map(|node| {
+            let idx = BRACES.iter().position(|&brace| brace == node.kind())?;
+            Some((node, idx))
+        })
+        .next()?;
+    let parent = brace_node.parent()?;
+    let matching_kind = BRACES[brace_idx ^ 1];
+    let matching_node = parent.children()
+        .find(|node| node.kind() == matching_kind)?;
+    Some(matching_node.range().start())
+}
+
 pub fn highlight(file: &ast::File) -> Vec<HighlightedRange> {
     let syntax = file.syntax();
     let mut res = Vec::new();
diff --git a/crates/libeditor/tests/test.rs b/crates/libeditor/tests/test.rs
index 7063425ce..d5df9d0cc 100644
--- a/crates/libeditor/tests/test.rs
+++ b/crates/libeditor/tests/test.rs
@@ -9,7 +9,7 @@ use itertools::Itertools;
 use libeditor::{
     File, TextUnit, TextRange, ActionResult, CursorPosition,
     highlight, runnables, extend_selection, file_structure,
-    flip_comma, add_derive,
+    flip_comma, add_derive, matching_brace,
 };
 
 #[test]
@@ -119,6 +119,25 @@ fn test_add_derive() {
     )
 }
 
+#[test]
+fn test_matching_brace() {
+    fn do_check(before: &str, after: &str) {
+        let (pos, before) = extract_cursor(before);
+        let file = file(&before);
+        let new_pos = match matching_brace(&file, pos) {
+            None => pos,
+            Some(pos) => pos,
+        };
+        let actual = add_cursor(&before, new_pos);
+        assert_eq_text!(after, &actual);
+    }
+
+    do_check(
+        "struct Foo { a: i32, }<|>",
+        "struct Foo <|>{ a: i32, }",
+    );
+}
+
 fn file(text: &str) -> File {
     File::parse(text)
 }
@@ -138,16 +157,12 @@ fn check_action<F: Fn(&File, TextUnit) -> Option<ActionResult>>(
     let file = file(&before);
     let result = f(&file, before_cursor_pos).expect("code action is not applicable");
     let actual = result.edit.apply(&before);
-    let actual_cursor_pos: u32 = match result.cursor_position {
+    let actual_cursor_pos = match result.cursor_position {
         CursorPosition::Same => result.edit.apply_to_offset(before_cursor_pos).unwrap(),
         CursorPosition::Offset(off) => off,
-    }.into();
-    let actual_cursor_pos = actual_cursor_pos as usize;
-    let mut actual_with_cursor = String::new();
-    actual_with_cursor.push_str(&actual[..actual_cursor_pos]);
-    actual_with_cursor.push_str("<|>");
-    actual_with_cursor.push_str(&actual[actual_cursor_pos..]);
-    assert_eq_text!(after, &actual_with_cursor);
+    };
+    let actual = add_cursor(&actual, actual_cursor_pos);
+    assert_eq_text!(after, &actual);
 }
 
 fn extract_cursor(text: &str) -> (TextUnit, String) {
@@ -162,3 +177,13 @@ fn extract_cursor(text: &str) -> (TextUnit, String) {
     let cursor_pos = TextUnit::from(cursor_pos as u32);
     (cursor_pos, new_text)
 }
+
+fn add_cursor(text: &str, offset: TextUnit) -> String {
+    let offset: u32 = offset.into();
+    let offset: usize = offset as usize;
+    let mut res = String::new();
+    res.push_str(&text[..offset]);
+    res.push_str("<|>");
+    res.push_str(&text[offset..]);
+    res
+}