From 4dec571ec69e14673b4e185e9881e4b71cd42aaa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sun, 1 Sep 2019 15:09:05 -0700
Subject: [PATCH] Be accurate on `format!` parse error expectations

---
 src/libsyntax_ext/format.rs                      | 16 ++++++++++++----
 src/test/ui/codemap_tests/bad-format-args.rs     |  2 +-
 src/test/ui/codemap_tests/bad-format-args.stderr |  4 ++--
 src/test/ui/type/ascription/issue-54516.rs       |  2 +-
 src/test/ui/type/ascription/issue-54516.stderr   |  4 ++--
 5 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/src/libsyntax_ext/format.rs b/src/libsyntax_ext/format.rs
index 47394c02b4186..d9ca693aca504 100644
--- a/src/libsyntax_ext/format.rs
+++ b/src/libsyntax_ext/format.rs
@@ -138,15 +138,23 @@ fn parse_args<'a>(
     }
 
     let fmtstr = p.parse_expr()?;
+    let mut first = true;
     let mut named = false;
 
     while p.token != token::Eof {
         if !p.eat(&token::Comma) {
-            let mut err = ecx.struct_span_err(p.token.span, "expected token: `,`");
-            err.span_label(p.token.span, "expected `,`");
-            p.maybe_annotate_with_ascription(&mut err, false);
-            return Err(err);
+            if first {
+                // After `format!(""` we always expect *only* a comma...
+                let mut err = ecx.struct_span_err(p.token.span, "expected token: `,`");
+                err.span_label(p.token.span, "expected `,`");
+                p.maybe_annotate_with_ascription(&mut err, false);
+                return Err(err);
+            } else {
+                // ...after that delegate to `expect` to also include the other expected tokens.
+                return Err(p.expect(&token::Comma).err().unwrap());
+            }
         }
+        first = false;
         if p.token == token::Eof {
             break;
         } // accept trailing commas
diff --git a/src/test/ui/codemap_tests/bad-format-args.rs b/src/test/ui/codemap_tests/bad-format-args.rs
index 9f90185774467..dff248344a53d 100644
--- a/src/test/ui/codemap_tests/bad-format-args.rs
+++ b/src/test/ui/codemap_tests/bad-format-args.rs
@@ -1,5 +1,5 @@
 fn main() {
     format!(); //~ ERROR requires at least a format string argument
     format!("" 1); //~ ERROR expected token: `,`
-    format!("", 1 1); //~ ERROR expected token: `,`
+    format!("", 1 1); //~ ERROR expected one of
 }
diff --git a/src/test/ui/codemap_tests/bad-format-args.stderr b/src/test/ui/codemap_tests/bad-format-args.stderr
index 5b01314d8ad4f..3372ef6dea1fc 100644
--- a/src/test/ui/codemap_tests/bad-format-args.stderr
+++ b/src/test/ui/codemap_tests/bad-format-args.stderr
@@ -12,11 +12,11 @@ error: expected token: `,`
 LL |     format!("" 1);
    |                ^ expected `,`
 
-error: expected token: `,`
+error: expected one of `,`, `.`, `?`, or an operator, found `1`
   --> $DIR/bad-format-args.rs:4:19
    |
 LL |     format!("", 1 1);
-   |                   ^ expected `,`
+   |                   ^ expected one of `,`, `.`, `?`, or an operator here
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/type/ascription/issue-54516.rs b/src/test/ui/type/ascription/issue-54516.rs
index 6d65760e299b5..b53bfe5df03f3 100644
--- a/src/test/ui/type/ascription/issue-54516.rs
+++ b/src/test/ui/type/ascription/issue-54516.rs
@@ -2,5 +2,5 @@ use std::collections::BTreeMap;
 
 fn main() {
     println!("{}", std::mem:size_of::<BTreeMap<u32, u32>>());
-    //~^ ERROR expected token: `,`
+    //~^ ERROR expected one of
 }
diff --git a/src/test/ui/type/ascription/issue-54516.stderr b/src/test/ui/type/ascription/issue-54516.stderr
index a846f3bc320e6..97942904a0ffa 100644
--- a/src/test/ui/type/ascription/issue-54516.stderr
+++ b/src/test/ui/type/ascription/issue-54516.stderr
@@ -1,8 +1,8 @@
-error: expected token: `,`
+error: expected one of `!`, `,`, or `::`, found `(`
   --> $DIR/issue-54516.rs:4:58
    |
 LL |     println!("{}", std::mem:size_of::<BTreeMap<u32, u32>>());
-   |                            -                             ^ expected `,`
+   |                            -                             ^ expected one of `!`, `,`, or `::` here
    |                            |
    |                            help: maybe write a path separator here: `::`
    |