1 files changed, 43 insertions, 0 deletions

diff --git a/crates/ra_ide/src/matching_brace.rs b/crates/ra_ide/src/matching_brace.rs
new file mode 100644
index 000000000..d1204fac0
--- /dev/null
+++ b/crates/ra_ide/src/matching_brace.rs
@@ -0,0 +1,43 @@
+//! FIXME: write short doc here
+
+use ra_syntax::{ast::AstNode, SourceFile, SyntaxKind, TextUnit, T};
+
+pub fn matching_brace(file: &SourceFile, offset: TextUnit) -> Option<TextUnit> {
+    const BRACES: &[SyntaxKind] =
+        &[T!['{'], T!['}'], T!['['], T![']'], T!['('], T![')'], T![<], T![>]];
+    let (brace_node, brace_idx) = file
+        .syntax()
+        .token_at_offset(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_with_tokens().find(|node| node.kind() == matching_kind)?;
+    Some(matching_node.text_range().start())
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::{add_cursor, assert_eq_text, extract_offset};
+
+    use super::*;
+
+    #[test]
+    fn test_matching_brace() {
+        fn do_check(before: &str, after: &str) {
+            let (pos, before) = extract_offset(before);
+            let parse = SourceFile::parse(&before);
+            let new_pos = match matching_brace(&parse.tree(), 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, }");
+    }
+}