[gcc r13-121] c++: wrong parse with functors [PR64679]

[gcc r13-121] c++: wrong parse with functors [PR64679]

[Marek Polacek]

https://gcc.gnu.org/g:a733dea9e7c39352ce9f72059938833eaa819467

commit r13-121-ga733dea9e7c39352ce9f72059938833eaa819467
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Apr 29 15:01:12 2022 -0400

    c++: wrong parse with functors [PR64679]
    
    Consider
    
      struct F {
        F(int) {}
        F operator()(int) const { return *this; }
      };
    
    and
    
      F(i)(0)(0);
    
    where we're supposed to first call the constructor and then invoke
    the operator() twice.  However, we parse this as an init-declarator:
    "(i)" looks like a perfectly valid declarator, then we see an '(' and
    think it must be an initializer, so we commit and we're toast.  My
    fix is to look a little bit farther before deciding we've seen an
    initializer.
    
    This is only a half of c++/64679, the other part of the PR is unrelated:
    there the problem is that we are calling pushdecl while parsing
    tentatively (in cp_parser_parameter_declaration_list), which is bad.
    
            PR c++/64679
    
    gcc/cp/ChangeLog:
    
            * parser.cc (cp_parser_init_declarator): Properly handle a series of
            operator() calls, they are not part of an init-declarator.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/parse/functor1.C: New test.

Diff:
---
 gcc/cp/parser.cc                      | 25 ++++++++++++++++++++++++-
 gcc/testsuite/g++.dg/parse/functor1.C | 22 ++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 5fa743b5a8e..b52cbe18b9a 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -22636,11 +22636,34 @@ cp_parser_init_declarator (cp_parser* parser,
       return error_mark_node;
     }
 
-  /* An `=' or an `(', or an '{' in C++0x, indicates an initializer.  */
+  /* An `=' or an '{' in C++11, indicate an initializer.  An '(' may indicate
+     an initializer as well. */
   if (token->type == CPP_EQ
       || token->type == CPP_OPEN_PAREN
       || token->type == CPP_OPEN_BRACE)
     {
+      /* Don't get fooled into thinking that F(i)(1)(2) is an initializer.
+	 It isn't; it's an expression.  (Here '(i)' would have already been
+	 parsed as a declarator.)   */
+      if (token->type == CPP_OPEN_PAREN
+	  && cp_parser_uncommitted_to_tentative_parse_p (parser))
+	{
+	  cp_lexer_save_tokens (parser->lexer);
+	  cp_lexer_consume_token (parser->lexer);
+	  cp_parser_skip_to_closing_parenthesis (parser,
+						 /*recovering*/false,
+						 /*or_comma*/false,
+						 /*consume_paren*/true);
+	  /* If this is an initializer, only a ',' or ';' can follow: either
+	     we have another init-declarator, or we're at the end of an
+	     init-declarator-list which can only be followed by a ';'.  */
+	  bool ok = (cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON)
+		     || cp_lexer_next_token_is (parser->lexer, CPP_COMMA));
+	  cp_lexer_rollback_tokens (parser->lexer);
+	  if (__builtin_expect (!ok, 0))
+	    /* Not an init-declarator.  */
+	    return error_mark_node;
+	}
       is_initialized = SD_INITIALIZED;
       initialization_kind = token->type;
       declarator->init_loc = token->location;
diff --git a/gcc/testsuite/g++.dg/parse/functor1.C b/gcc/testsuite/g++.dg/parse/functor1.C
new file mode 100644
index 00000000000..c014114c098
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/functor1.C
@@ -0,0 +1,22 @@
+// PR c++/64679
+// { dg-do run }
+
+struct F {
+  F(int) { }
+  F(int, int) { }
+  F operator()(int) const { return *this; }
+  F operator()(int, int) const { return *this; }
+};
+
+int main()
+{
+  // Init-declarators.
+  int i = 0;
+  int (j)(1);
+  // None of these is an init-declarator.
+  F(i)(1)(2);
+  F(i)(1, 2)(3);
+  F(i)(1)(2, 3);
+  F(i)(2)(3)(4)(5);
+  F(i, j)(1)(2)(3)(4)(5)(6);
+}