PR c++/64235 - missing syntax error with invalid alignas.

	* parser.c (cp_parser_std_attribute_spec): Commit to tentative parse
	if there's a missing close paren.

	* g++.dg/parse/alignas1.C: New test.

From-SVN: r272570

gcc/cp/ChangeLog

 2019-06-21  Marek Polacek  <polacek@redhat.com>
 
+	PR c++/64235 - missing syntax error with invalid alignas.
+	* parser.c (cp_parser_std_attribute_spec): Commit to tentative parse
+	if there's a missing close paren.
+
 	PR c++/90490 - fix decltype issues in noexcept-specifier.
 	* except.c (build_noexcept_spec): Call
 	instantiate_non_dependent_expr_sfinae before

gcc/cp/parser.c

@@ -26371,6 +26371,12 @@ cp_parser_std_attribute_spec (cp_parser *parser)
       if (alignas_expr == error_mark_node)
 	return error_mark_node;
 
+      /* Missing ')' means the code cannot possibly be valid; go ahead
+	 and commit to make sure we issue a hard error.  */
+      if (cp_parser_uncommitted_to_tentative_parse_p (parser)
+	  && cp_lexer_next_token_is_not (parser->lexer, CPP_CLOSE_PAREN))
+	cp_parser_commit_to_tentative_parse (parser);
+
       if (!parens.require_close (parser))
 	return error_mark_node;
 

gcc/testsuite/ChangeLog

+2019-06-19  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/64235 - missing syntax error with invalid alignas.
+	* g++.dg/parse/alignas1.C: New test.
+
 2019-06-21  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	PR fortran/67884

gcc/testsuite/g++.dg/parse/alignas1.C

+// PR c++/64235
+// { dg-do compile { target c++11 } }
+
+struct S {
+  double d;
+};
+
+struct alignas(sizeof(S) S1 { }; // { dg-error "expected '\\)' before 'S1'" }
+struct alignas(16 S2 { }; // { dg-error "expected '\\)' before 'S2'" }
+struct alignas(int S3 { }; // { dg-error "expected '\\)' before 'S3'" }