Fix flip comma assist

crates/ra_assists/src/flip_comma.rs

@@ -7,6 +7,13 @@ pub(crate) fn flip_comma(mut ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
     let comma = ctx.token_at_offset().find(|leaf| leaf.kind() == T![,])?;
     let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
     let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;
+
+    // Don't apply a "flip" in case of a last comma
+    // that typically comes before punctuation
+    if next.kind().is_punct() {
+        return None;
+    }
+
     ctx.add_action(AssistId("flip_comma"), "flip comma", |edit| {
         edit.target(comma.text_range());
         edit.replace(prev.text_range(), next.to_string());
@@ -35,4 +42,22 @@ mod tests {
     fn flip_comma_target() {
         check_assist_target(flip_comma, "fn foo(x: i32,<|> y: Result<(), ()>) {}", ",")
     }
+
+    #[test]
+    #[should_panic]
+    fn flip_comma_before_punct() {
+        // See https://github.com/rust-analyzer/rust-analyzer/issues/1619
+        // "Flip comma" assist shouldn't be applicable to the last comma in enum or struct
+        // declaration body.
+        check_assist_target(flip_comma, 
+                            "pub enum Test { \
+                                A,<|> \
+                            }", ",");
+
+        
+        check_assist_target(flip_comma, 
+                            "pub struct Test { \
+                                foo: usize,<|> \
+                            }", ",");
+    }
 }