Auto merge of #52397 - estebank:println-comma, r=oli-obk

Suggest comma when writing `println!("{}" a);`

Fix #49370.

src/test/ui/codemap_tests/bad-format-args.stderr

@@ -7,20 +7,16 @@ LL |     format!(); //~ ERROR requires at least a format string argument
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: expected token: `,`
-  --> $DIR/bad-format-args.rs:13:5
+  --> $DIR/bad-format-args.rs:13:16
    |
 LL |     format!("" 1); //~ ERROR expected token: `,`
-   |     ^^^^^^^^^^^^^^
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |                ^
 
 error: expected token: `,`
-  --> $DIR/bad-format-args.rs:14:5
+  --> $DIR/bad-format-args.rs:14:19
    |
 LL |     format!("", 1 1); //~ ERROR expected token: `,`
-   |     ^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+   |                   ^
 
 error: aborting due to 3 previous errors
 

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

@@ -0,0 +1,20 @@
+// 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.
+
+macro_rules! foo {
+    ($a:ident, $b:ident) => ()
+}
+
+fn main() {
+    println!("{}" a);
+    //~^ ERROR expected token: `,`
+    foo!(a b);
+    //~^ ERROR no rules expected the token `b`
+}

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

@@ -0,0 +1,16 @@
+error: expected token: `,`
+  --> $DIR/missing-comma.rs:16:19
+   |
+LL |     println!("{}" a);
+   |                   ^
+
+error: no rules expected the token `b`
+  --> $DIR/missing-comma.rs:18:12
+   |
+LL |     foo!(a b);
+   |           -^
+   |           |
+   |           help: missing comma here
+
+error: aborting due to 2 previous errors
+