1 files changed, 30 insertions, 15 deletions
diff --git a/src/libsyntax_ext/cfg.rs b/src/libsyntax_ext/cfg.rs
index 2384b6a796e..3b47b03cbe8 100644
--- a/src/libsyntax_ext/cfg.rs
+++ b/src/libsyntax_ext/cfg.rs
@@ -1,17 +1,9 @@
-// Copyright 2013 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.
-
 /// The compiler code necessary to support the cfg! extension, which expands to
 /// a literal `true` or `false` based on whether the given cfg matches the
 /// current compilation environment.
 
+use errors::DiagnosticBuilder;
+use syntax::ast;
 use syntax::ext::base::*;
 use syntax::ext::base;
 use syntax::ext::build::AstBuilder;
@@ -25,16 +17,39 @@ pub fn expand_cfg<'cx>(cx: &mut ExtCtxt,
                        tts: &[tokenstream::TokenTree])
                        -> Box<dyn base::MacResult + 'static> {
     let sp = sp.apply_mark(cx.current_expansion.mark);
+
+    match parse_cfg(cx, sp, tts) {
+        Ok(cfg) => {
+            let matches_cfg = attr::cfg_matches(&cfg, cx.parse_sess, cx.ecfg.features);
+            MacEager::expr(cx.expr_bool(sp, matches_cfg))
+        }
+        Err(mut err) => {
+            err.emit();
+            DummyResult::expr(sp)
+        }
+    }
+}
+
+fn parse_cfg<'a>(
+    cx: &mut ExtCtxt<'a>,
+    sp: Span,
+    tts: &[tokenstream::TokenTree],
+) -> Result<ast::MetaItem, DiagnosticBuilder<'a>> {
     let mut p = cx.new_parser_from_tts(tts);
-    let cfg = panictry!(p.parse_meta_item());
+
+    if p.token == token::Eof {
+        let mut err = cx.struct_span_err(sp, "macro requires a cfg-pattern as an argument");
+        err.span_label(sp, "cfg-pattern required");
+        return Err(err);
+    }
+
+    let cfg = p.parse_meta_item()?;
 
     let _ = p.eat(&token::Comma);
 
     if !p.eat(&token::Eof) {
-        cx.span_err(sp, "expected 1 cfg-pattern");
-        return DummyResult::expr(sp);
+        return Err(cx.struct_span_err(sp, "expected 1 cfg-pattern"));
     }
 
-    let matches_cfg = attr::cfg_matches(&cfg, cx.parse_sess, cx.ecfg.features);
-    MacEager::expr(cx.expr_bool(sp, matches_cfg))
+    Ok(cfg)
 }