Re: [PATCH] c++: wrong parse with functors [PR64679]

[Jason Merrill via Gcc-patches]

On 5/2/22 12:18, Marek Polacek wrote:

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.

How vexing!

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.
I don't know how to fix it though, maybe move the pushdecl call to
grokparms?  Tricky :(.

Can we pop the parm decls when the tentative parse fails?

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

        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.
---
  gcc/cp/parser.cc                      | 25 ++++++++++++++++++++++++-
  gcc/testsuite/g++.dg/parse/functor1.C | 22 ++++++++++++++++++++++
  2 files changed, 46 insertions(+), 1 deletion(-)
  create mode 100644 gcc/testsuite/g++.dg/parse/functor1.C

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index a5cbb3e896f..6e2936b68ef 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);
+}

base-commit: 1cb220498e1f59021dab36c39c5d726e9f070c6a