When adding match arm, don't let the floating comma

crates/ra_assists/src/handlers/fill_match_arms.rs

@@ -1,15 +1,11 @@
-//! FIXME: write short doc here
-
 use std::iter;
 
 use hir::{Adt, HasSource, ModuleDef, Semantics};
 use itertools::Itertools;
 use ra_ide_db::RootDatabase;
+use ra_syntax::ast::{self, make, AstNode, MatchArm, NameOwner, Pat};
 
 use crate::{Assist, AssistCtx, AssistId};
-use ra_syntax::ast::{self, make, AstNode, NameOwner};
-
-use ast::{MatchArm, Pat};
 
 // Assist: fill_match_arms
 //
@@ -717,4 +713,28 @@ mod tests {
             "#,
         );
     }
+
+    #[test]
+    fn fill_match_arms_placeholder() {
+        check_assist(
+            fill_match_arms,
+            r#"
+            enum A { One, Two, }
+            fn foo(a: A) {
+                match a<|> {
+                    _ => (),
+                }
+            }
+            "#,
+            r#"
+            enum A { One, Two, }
+            fn foo(a: A) {
+                match <|>a {
+                    A::One => {}
+                    A::Two => {}
+                }
+            }
+            "#,
+        );
+    }
 }

crates/ra_syntax/src/ast/edit.rs

@@ -369,21 +369,32 @@ impl ast::MatchArmList {
 
     #[must_use]
     pub fn remove_placeholder(&self) -> ast::MatchArmList {
-        let placeholder = self.arms().find(|arm| {
-            if let Some(ast::Pat::PlaceholderPat(_)) = arm.pat() {
-                return true;
-            }
-            false
-        });
+        let placeholder =
+            self.arms().find(|arm| matches!(arm.pat(), Some(ast::Pat::PlaceholderPat(_))));
         if let Some(placeholder) = placeholder {
-            let s: SyntaxElement = placeholder.syntax().clone().into();
-            let e = s.clone();
-            self.replace_children(s..=e, &mut iter::empty())
+            self.remove_arm(&placeholder)
         } else {
             self.clone()
         }
     }
 
+    #[must_use]
+    fn remove_arm(&self, arm: &ast::MatchArm) -> ast::MatchArmList {
+        let start = arm.syntax().clone();
+        let end = if let Some(comma) = start
+            .siblings_with_tokens(Direction::Next)
+            .skip(1)
+            .skip_while(|it| it.kind().is_trivia())
+            .next()
+            .filter(|it| it.kind() == T![,])
+        {
+            comma
+        } else {
+            start.clone().into()
+        };
+        self.replace_children(start.into()..=end, None)
+    }
+
     #[must_use]
     pub fn append_arm(&self, item: ast::MatchArm) -> ast::MatchArmList {
         let r_curly = match self.syntax().children_with_tokens().find(|it| it.kind() == T!['}']) {