1 files changed, 33 insertions, 0 deletions

diff --git a/crates/ra_assists/src/flip_comma.rs b/crates/ra_assists/src/flip_comma.rs
new file mode 100644
index 000000000..a49820c29
--- /dev/null
+++ b/crates/ra_assists/src/flip_comma.rs
@@ -0,0 +1,33 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    Direction,
+    SyntaxKind::COMMA,
+};
+
+use crate::{AssistCtx, Assist, non_trivia_sibling};
+
+pub(crate) fn flip_comma(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+    let comma = ctx.leaf_at_offset().find(|leaf| leaf.kind() == COMMA)?;
+    let prev = non_trivia_sibling(comma, Direction::Prev)?;
+    let next = non_trivia_sibling(comma, Direction::Next)?;
+    ctx.build("flip comma", |edit| {
+        edit.replace(prev.range(), next.text());
+        edit.replace(next.range(), prev.text());
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::helpers::check_assist;
+
+    #[test]
+    fn flip_comma_works_for_function_parameters() {
+        check_assist(
+            flip_comma,
+            "fn foo(x: i32,<|> y: Result<(), ()>) {}",
+            "fn foo(y: Result<(), ()>,<|> x: i32) {}",
+        )
+    }
+}