[Bug c++/105741] New: Wrong preprocessor parameter substitution with ##__VA_ARGS__.

[Bug c++/105741] New: Wrong preprocessor parameter substitution with ##__VA_ARGS__.

[gcc.gnu.org_bugzilla at jfa dot knudsen.ovh]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105741

            Bug ID: 105741
           Summary: Wrong preprocessor parameter substitution with
                    ##__VA_ARGS__.
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc.gnu.org_bugzilla at jfa dot knudsen.ovh
  Target Milestone: ---

This code :

#define CALL2(dummy, p1, ...) "dummy"=dummy, "p1"=p1, "va"=__VA_ARGS__

#define CALL(dummy, ...) CALL2(dummy, ##__VA_ARGS__)
#define CALL_WITHOPT(dummy, ...) CALL2(dummy __VA_OPT__(,) __VA_ARGS__)


#define CALL_ARGS "param1", "param2"

CALL("dum", "param1", "param2");
CALL_WITHOPT("dum", CALL_ARGS);
CALL("dum", CALL_ARGS);


preprocessed gives :

"dummy"="dum", "p1"="param1", "va"="param2";
"dummy"="dum", "p1"="param1", "va"="param2";
"dummy"="dum", "p1"="param1", "param2", "va"=;

We can see that, at the third line, parameter p1 = "param1", "param2" and
__VA_ARGS__ is empty.
It seems that CALL_ARGS expands to "param1", "param2" but is still only one
parameter in the variable list.

Is that the way it is supposed to be ?
Any workaround before it's fixed ?

[Bug c++/105741] Wrong preprocessor parameter substitution with ##__VA_ARGS__.

[gcc.gnu.org_bugzilla at jfa dot knudsen.ovh]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105741

--- Comment #1 from JFK <gcc.gnu.org_bugzilla at jfa dot knudsen.ovh> ---
Same problem with 10.2.0

[Bug c++/105741] Wrong preprocessor parameter substitution with ##__VA_ARGS__.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105741

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Even gcc 3.2 behaves this way.  It is a GNU extension, so there is no standard
that would cover this except for GCC documentation (and implementation).  And
clang behaves the same.
So I think it would only cause harm to change this.
Especially when the extension is there only for backwards compatibility, new
code should use __VA_OPT__ which is standard.

[Bug c++/105741] Wrong preprocessor parameter substitution with ##__VA_ARGS__.

[gcc.gnu.org_bugzilla at jfa dot knudsen.ovh]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105741

--- Comment #3 from JFK <gcc.gnu.org_bugzilla at jfa dot knudsen.ovh> ---
Any idea about how to work around this without the use of VA_OPT ?