improve span of erroneous empty macro invocation

The ideas is to use the span of the complete macro invocation if the span of a
macro error is `DUMMY_SP`.

fixes rust-lang#7970

src/libsyntax/ext/tt/macro_parser.rs

@@ -249,22 +249,6 @@ pub enum ParseResult<T> {
 pub type NamedParseResult = ParseResult<HashMap<Ident, Rc<NamedMatch>>>;
 pub type PositionalParseResult = ParseResult<Vec<Rc<NamedMatch>>>;
 
-pub fn parse_or_else(sess: &ParseSess,
-                     cfg: ast::CrateConfig,
-                     rdr: TtReader,
-                     ms: Vec<TokenTree> )
-                     -> HashMap<Ident, Rc<NamedMatch>> {
-    match parse(sess, cfg, rdr, &ms[..]) {
-        Success(m) => m,
-        Failure(sp, str) => {
-            panic!(sess.span_diagnostic.span_fatal(sp, &str[..]))
-        }
-        Error(sp, str) => {
-            panic!(sess.span_diagnostic.span_fatal(sp, &str[..]))
-        }
-    }
-}
-
 /// Perform a token equality check, ignoring syntax context (that is, an
 /// unhygienic comparison)
 pub fn token_name_eq(t1 : &Token, t2 : &Token) -> bool {

src/libsyntax/ext/tt/macro_rules.rs

@@ -14,7 +14,7 @@ use ext::base::{ExtCtxt, MacResult, SyntaxExtension};
 use ext::base::{NormalTT, TTMacroExpander};
 use ext::tt::macro_parser::{Success, Error, Failure};
 use ext::tt::macro_parser::{NamedMatch, MatchedSeq, MatchedNonterminal};
-use ext::tt::macro_parser::{parse, parse_or_else};
+use ext::tt::macro_parser::parse;
 use parse::lexer::new_tt_reader;
 use parse::parser::Parser;
 use parse::token::{self, special_idents, gensym_ident, NtTT, Token};
@@ -211,12 +211,23 @@ fn generic_extension<'cx>(cx: &'cx ExtCtxt,
                 best_fail_spot = sp;
                 best_fail_msg = (*msg).clone();
               },
-              Error(sp, ref msg) => panic!(cx.span_fatal(sp, &msg[..]))
+              Error(mut spp, ref msg) => {
+                if spp == DUMMY_SP {
+                    spp = sp;
+                }
+
+                panic!(cx.span_fatal(spp, &msg[..]))
+              }
             }
           }
           _ => cx.bug("non-matcher found in parsed lhses")
         }
     }
+
+    if best_fail_spot == DUMMY_SP {
+        best_fail_spot = sp;
+    }
+
     panic!(cx.span_fatal(best_fail_spot, &best_fail_msg[..]));
 }
 
@@ -266,10 +277,20 @@ pub fn compile<'cx>(cx: &'cx mut ExtCtxt,
                                    None,
                                    None,
                                    def.body.clone());
-    let argument_map = parse_or_else(cx.parse_sess(),
-                                     cx.cfg(),
-                                     arg_reader,
-                                     argument_gram);
+
+    let argument_map = match parse(cx.parse_sess(),
+                                   cx.cfg(),
+                                   arg_reader,
+                                   &argument_gram) {
+        Success(m) => m,
+        Failure(mut sp, str) | Error(mut sp, str) => {
+            if sp == DUMMY_SP {
+                sp = def.span;
+            }
+
+            panic!(cx.parse_sess().span_diagnostic.span_fatal(sp, &str[..]));
+        }
+    };
 
     // Extract the arguments:
     let lhses = match **argument_map.get(&lhs_nm).unwrap() {

src/test/compile-fail/issue-7970a.rs

@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+fn main() {
+    println!();
+    //~^ ERROR unexpected end of macro invocation
+}

src/test/compile-fail/issue-7970b.rs

@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+fn main() {}
+
+macro_rules! test {}
+//~^ ERROR unexpected end of macro invocation