forbid empty identifiers from concat_idents

diff --git a/src/libsyntax_ext/concat_idents.rs b/src/libsyntax_ext/concat_idents.rs
index 544b1410d3d912135d8550c01d5345635ebb40d6..b8345e7cf40c109431a740ab8aea7b19efb46a24 100644 (file)
--- a/src/libsyntax_ext/concat_idents.rs
+++ b/src/libsyntax_ext/concat_idents.rs
@@ -31,6 +31,11 @@ pub fn expand_syntax_ext<'cx>(cx: &'cx mut ExtCtxt,
         return base::DummyResult::expr(sp);
     }
 
+    if tts.is_empty() {
+        cx.span_err(sp, "concat_idents! takes 1 or more arguments.");
+        return DummyResult::expr(sp);
+    }
+
     let mut res_str = String::new();
     for (i, e) in tts.iter().enumerate() {
         if i & 1 == 1 {

diff --git a/src/test/ui/issue-50403.rs b/src/test/ui/issue-50403.rs
new file mode 100644 (file)
index 0000000..8d4c6c5
--- /dev/null
+++ b/src/test/ui/issue-50403.rs
@@ -0,0 +1,15 @@
+// Copyright 2016 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.
+
+#![feature(concat_idents)]
+
+fn main() {
+    let x = concat_idents!(); //~ ERROR concat_idents! takes 1 or more arguments
+}