Fix handling of spaces after for as

crates/compiler/parse/src/pattern.rs

@@ -63,9 +63,14 @@ pub fn loc_pattern_help<'a>() -> impl Parser<'a, Loc<Pattern<'a>>, EPattern<'a>>
             },
             Ok((_, pattern_as, state)) => {
                 let region = Region::span_across(&pattern.region, &pattern_as.identifier.region);
-                let pattern = arena
+
-                    .alloc(pattern.value)
+                let mut pattern = pattern;
-                    .with_spaces_after(pattern_spaces, pattern.region);
+                if !pattern_spaces.is_empty() {
+                    pattern = arena
+                        .alloc(pattern.value)
+                        .with_spaces_after(pattern_spaces, pattern.region)
+                }
+
                 let as_pattern = Pattern::As(arena.alloc(pattern), pattern_as);
 
                 Ok((MadeProgress, Loc::at(region, as_pattern), state))

crates/compiler/test_syntax/tests/snapshots/pass/pattern_as.expr.result-ast

@@ -7,11 +7,8 @@ When(
             patterns: [
                 @14-20 SpaceBefore(
                     As(
-                        @14-15 SpaceAfter(
+                        @14-15 Underscore(
-                            Underscore(
+                            "",
-                                "",
-                            ),
-                            [],
                         ),
                         PatternAs {
                             spaces_before: [],

crates/compiler/test_syntax/tests/test_fmt.rs

@@ -6113,6 +6113,31 @@ mod test_fmt {
         );
     }
 
+    #[test]
+    fn issue_6215() {
+        expr_formats_to(
+            indoc!(
+                r"
+                when list is
+                    [first as last]
+                    | [first, last]   ->
+                        first
+                    _->Not
+                "
+            ),
+            indoc!(
+                r"
+                when list is
+                    [first as last]
+                    | [first, last] ->
+                        first
+                
+                    _ -> Not
+                "
+            ),
+        );
+    }
+
     // this is a parse error atm
     //    #[test]
     //    fn multiline_apply() {