1 files changed, 78 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide/src/matching_brace.rs b/src/tools/rust-analyzer/crates/ide/src/matching_brace.rs
new file mode 100644
index 000000000..da70cecdd
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide/src/matching_brace.rs
@@ -0,0 +1,78 @@
+use syntax::{
+    ast::{self, AstNode},
+    SourceFile, SyntaxKind, TextSize, T,
+};
+
+// Feature: Matching Brace
+//
+// If the cursor is on any brace (`<>(){}[]||`) which is a part of a brace-pair,
+// moves cursor to the matching brace. It uses the actual parser to determine
+// braces, so it won't confuse generics with comparisons.
+//
+// |===
+// | Editor  | Action Name
+//
+// | VS Code | **Rust Analyzer: Find matching brace**
+// |===
+//
+// image::https://user-images.githubusercontent.com/48062697/113065573-04298180-91b1-11eb-8dec-d4e2a202f304.gif[]
+pub(crate) fn matching_brace(file: &SourceFile, offset: TextSize) -> Option<TextSize> {
+    const BRACES: &[SyntaxKind] =
+        &[T!['{'], T!['}'], T!['['], T![']'], T!['('], T![')'], T![<], T![>], T![|], T![|]];
+    let (brace_token, brace_idx) = file
+        .syntax()
+        .token_at_offset(offset)
+        .filter_map(|node| {
+            let idx = BRACES.iter().position(|&brace| brace == node.kind())?;
+            Some((node, idx))
+        })
+        .last()?;
+    let parent = brace_token.parent()?;
+    if brace_token.kind() == T![|] && !ast::ParamList::can_cast(parent.kind()) {
+        cov_mark::hit!(pipes_not_braces);
+        return None;
+    }
+    let matching_kind = BRACES[brace_idx ^ 1];
+    let matching_node = parent
+        .children_with_tokens()
+        .filter_map(|it| it.into_token())
+        .find(|node| node.kind() == matching_kind && node != &brace_token)?;
+    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, }$0", "struct Foo $0{ a: i32, }");
+        do_check("fn main() { |x: i32|$0 x * 2;}", "fn main() { $0|x: i32| x * 2;}");
+        do_check("fn main() { $0|x: i32| x * 2;}", "fn main() { |x: i32$0| x * 2;}");
+        do_check(
+            "fn func(x) { return (2 * (x + 3)$0) + 5;}",
+            "fn func(x) { return $0(2 * (x + 3)) + 5;}",
+        );
+
+        {
+            cov_mark::check!(pipes_not_braces);
+            do_check(
+                "fn main() { match 92 { 1 | 2 |$0 3 => 92 } }",
+                "fn main() { match 92 { 1 | 2 |$0 3 => 92 } }",
+            );
+        }
+    }
+}