From 040f1c06bc7c1c5fa37477513227114d343b3ec3 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Wed, 18 Sep 2013 13:51:07 -0700
Subject: [PATCH] Allow trailing commas in format!

This is more consistent with other parts of the language and it also makes it
easier to use in situations where format string is massive.
---
 src/libsyntax/ext/format.rs | 1 +
 src/test/run-pass/ifmt.rs   | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index 9f4e55b1a92..cace4648df2 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -76,6 +76,7 @@ impl Context {
                 self.ecx.span_err(sp, "expected token: `,`");
                 return (extra, None);
             }
+            if *p.token == token::EOF { break } // accept trailing commas
             if named || (token::is_ident(p.token) &&
                          p.look_ahead(1, |t| *t == token::EQ)) {
                 named = true;
diff --git a/src/test/run-pass/ifmt.rs b/src/test/run-pass/ifmt.rs
index 351bad193da..6ca21c6c5a1 100644
--- a/src/test/run-pass/ifmt.rs
+++ b/src/test/run-pass/ifmt.rs
@@ -243,6 +243,10 @@ pub fn main() {
     }
 
     test_format_args();
+
+    // test that trailing commas are acceptable
+    format!("{}", "test",);
+    format!("{foo}", foo="test",);
 }
 
 // Basic test to make sure that we can invoke the `write!` macro with an