Add test for issue 48941

A broken test to be fixed in the next commit.

src/test/compile-fail-fulldeps/auxiliary/macro_crate_test.rs

@@ -37,6 +37,9 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_syntax_extension(
         Symbol::intern("into_multi_foo"),
         MultiModifier(Box::new(expand_into_foo_multi)));
+    reg.register_syntax_extension(
+        Symbol::intern("noop_attribute"),
+        MultiModifier(Box::new(expand_noop_attribute)));
     reg.register_syntax_extension(
         Symbol::intern("duplicate"),
         MultiDecorator(Box::new(expand_duplicate)));
@@ -93,6 +96,13 @@ fn expand_into_foo_multi(cx: &mut ExtCtxt,
     }
 }
 
+fn expand_noop_attribute(_cx: &mut ExtCtxt,
+                         _sp: Span,
+                         _attr: &MetaItem,
+                         it: Annotatable) -> Annotatable {
+    it
+}
+
 // Create a duplicate of the annotatable, based on the MetaItem
 fn expand_duplicate(cx: &mut ExtCtxt,
                     _sp: Span,

src/test/compile-fail-fulldeps/issue-48941.rs

@@ -0,0 +1,29 @@
+// Copyright 2013-2014 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.
+
+// This is a regression test against an ICE that used to occur
+// on malformed attributes for a custom MultiModifier.
+
+// aux-build:macro_crate_test.rs
+// ignore-stage1
+
+#![feature(plugin)]
+#![plugin(macro_crate_test)]
+
+#[noop_attribute"x"] //~ ERROR expected one of
+fn night() { }
+
+#[noop_attribute("hi"), rank = 2] //~ ERROR unexpected token
+fn knight() { }
+
+#[noop_attribute("/user", data= = "<user")] //~ ERROR literal or identifier
+fn nite() { }
+
+fn main() {}