Issue #50636: Improve error diagnostic with missing commas after struct fields.

src/test/ui/struct-missing-comma.rs

@@ -0,0 +1,23 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+// Issue #50636
+
+struct S {
+    foo: u32 //~ expected `,`, or `}`, found `bar`
+    //     ~^ HELP try adding a comma: ','
+    bar: u32
+}
+
+fn main() {
+    let s = S { foo: 5, bar: 6 };
+}

src/test/ui/struct-missing-comma.stderr

@@ -0,0 +1,8 @@
+error: expected `,`, or `}`, found `bar`
+  --> $DIR/struct-missing-comma.rs:16:13
+   |
+LL |     foo: u32 //~ expected `,`, or `}`, found `bar`
+   |             ^ help: try adding a comma: `,`
+
+error: aborting due to previous error
+