[PATCH] Fix PR c++/69139 (deduction failure with trailing return type)

[Patrick Palka <patrick at parcs dot ath dot cx>]

This patch makes the parser more robust in determining whether an 'auto'
specifier that appears in a parameter declaration corresponds to a
placeholder for a late return type, or corresponds to an implicit
template parameter as for an abbreviated function template.

Bootstrap + regtest in progress on x86_64-pc-linux-gnu, will also test
this change against Boost.  OK to commit if testing succeeds?  What
about for GCC 4.9/5?

gcc/cp/ChangeLog:

	PR c++/69139
	* parser.c (cp_parser_simple_type_specifier): Make the check
	for disambiguating between an 'auto' placeholder and an implicit
	template parameter more robust.

gcc/testsuite/ChangeLog:

	PR c++/69139
	* g++.dg/cpp0x/auto47.C: New test.
---
 gcc/cp/parser.c                     | 33 +++++++++++++++++++++++----------
 gcc/testsuite/g++.dg/cpp0x/auto47.C | 20 ++++++++++++++++++++
 2 files changed, 43 insertions(+), 10 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/auto47.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index d03b0c9..56c834f 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -16032,20 +16032,33 @@ cp_parser_simple_type_specifier (cp_parser* parser,
 	  /* The 'auto' might be the placeholder return type for a function decl
 	     with trailing return type.  */
 	  bool have_trailing_return_fn_decl = false;
-	  if (cp_lexer_peek_nth_token (parser->lexer, 2)->type
-	      == CPP_OPEN_PAREN)
+
+	  cp_parser_parse_tentatively (parser);
+	  cp_lexer_consume_token (parser->lexer);
+	  while (cp_lexer_next_token_is_not (parser->lexer, CPP_EQ)
+		 && cp_lexer_next_token_is_not (parser->lexer, CPP_COMMA)
+		 && cp_lexer_next_token_is_not (parser->lexer, CPP_CLOSE_PAREN)
+		 && cp_lexer_next_token_is_not (parser->lexer, CPP_EOF))
 	    {
-	      cp_parser_parse_tentatively (parser);
-	      cp_lexer_consume_token (parser->lexer);
-	      cp_lexer_consume_token (parser->lexer);
-	      if (cp_parser_skip_to_closing_parenthesis (parser,
+	      if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_PAREN))
+		{
+		  cp_lexer_consume_token (parser->lexer);
+		  cp_parser_skip_to_closing_parenthesis (parser,
 							 /*recovering*/false,
 							 /*or_comma*/false,
-							 /*consume_paren*/true))
-		have_trailing_return_fn_decl
-		  = cp_lexer_next_token_is (parser->lexer, CPP_DEREF);
-	      cp_parser_abort_tentative_parse (parser);
+							 /*consume_paren*/true);
+		  continue;
+		}
+
+	      if (cp_lexer_next_token_is (parser->lexer, CPP_DEREF))
+		{
+		  have_trailing_return_fn_decl = true;
+		  break;
+		}
+
+	      cp_lexer_consume_token (parser->lexer);
 	    }
+	  cp_parser_abort_tentative_parse (parser);
 
 	  if (have_trailing_return_fn_decl)
 	    {
diff --git a/gcc/testsuite/g++.dg/cpp0x/auto47.C b/gcc/testsuite/g++.dg/cpp0x/auto47.C
new file mode 100644
index 0000000..08adf31
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/auto47.C
@@ -0,0 +1,20 @@
+// PR c++/69139
+// { dg-do compile { target c++11 } }
+
+auto get(int) -> int { return {}; }
+template <class R> int f(auto (*)(int) -> R) { return {}; }
+int i = f(get);
+
+int foo1 (auto (int) -> char);
+
+int foo2 (auto f(int) -> char);
+
+int foo2 (auto (f)(int) -> char);
+
+int foo3 (auto (*f)(int) -> char);
+
+int foo4 (auto (*const **&f)(int) -> char);
+
+int foo5 (auto (*const **&f)(int, int *) -> char);
+
+int foo6 (auto (int) const -> char); // { dg-error "const" }
-- 
2.7.0.134.gf5046bd.dirty