Account for comma in suggestion

Author: estebank

src/libsyntax/parse/parser.rs

@@ -3868,7 +3868,7 @@ impl<'a> Parser<'a> {
                     "move the `..` to the end of the field list",
                     vec![
                         (etc_span, "".into()),
-                        (self.span, ", .. }".into()),
+                        (self.span, format!("{}.. }}", if ate_comma { "" } else { ", " })),
                     ],
                 );
             }

src/test/parse-fail/bind-struct-early-modifiers.rs

@@ -13,7 +13,7 @@
 fn main() {
     struct Foo { x: isize }
     match (Foo { x: 10 }) {
-        Foo { ref x: ref x } => {}, //~ ERROR expected `,`, found `:`
+        Foo { ref x: ref x } => {}, //~ ERROR expected `,`
         _ => {}
     }
 }

src/test/ui/issue-49257.stderr

@@ -8,8 +8,8 @@ LL |     let Point { .., y, } = p; //~ ERROR expected `}`, found `,`
    |                 `..` must be at the end and cannot have a trailing comma
 help: move the `..` to the end of the field list
    |
-LL |     let Point {  y, , .. } = p; //~ ERROR expected `}`, found `,`
-   |                --   ^^^^^^
+LL |     let Point {  y, .. } = p; //~ ERROR expected `}`, found `,`
+   |                --   ^^^^
 
 error: expected `}`, found `,`
   --> $DIR/issue-49257.rs:21:19