[Bug c++/97202] New: GCC reports an error: expected unqualified-id before ‘short’

[Bug c++/97202] New: GCC reports an error: expected unqualified-id before ‘short’

[tangyixuan at mail dot dlut.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

            Bug ID: 97202
           Summary: GCC reports an error: expected unqualified-id before
                    ‘short’
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tangyixuan at mail dot dlut.edu.cn
  Target Milestone: ---

Hi, GCC 11 rejects the following code when the class 'A' is instantiated.  When
I fed it into GCC 1O, it is accepted. Also, clang accepts it. I guess maybe it
is valid.

$ cat s.cpp

template <class T> class A { 
  public:
    A(short,short a=0) {}
    A<T>(short b) {}
};

$ g++ -c s.cpp
s.cpp:4:10: error: expected unqualified-id before ‘short’
    4 |     A<T>(short b) {}
      |          ^~~~~
s.cpp:4:10: error: expected ‘)’ before ‘short’
    4 |     A<T>(short b) {}
      |         ~^~~~~
      |          )


$ g++ -v
Using built-in specs.
COLLECT_GCC=/usr/local/gcc-20200920/bin/g++
COLLECT_LTO_WRAPPER=/usr/local/gcc-20200920/libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-11-20200920/configure --prefix=/usr/local/gcc-20200920
--enable-checking=release --enable-languages=c,c++ --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.0.0 20200920 (experimental) (GCC)

[Bug c++/97202] [11 Regression] GCC reports an error: expected unqualified-id before ‘short’

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|GCC reports an error:       |[11 Regression] GCC reports
                   |expected unqualified-id     |an error: expected
                   |before ‘short’              |unqualified-id before
                   |                            |‘short’
           Keywords|                            |rejects-valid
   Target Milestone|---                         |11.0

[Bug c++/97202] [11 Regression] GCC reports an error: expected unqualified-id before ‘short’

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Could this be a c++17 difference?

[Bug c++/97202] [11 Regression] GCC reports an error: expected unqualified-id before ‘short’

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
This is C++20 DR 2237, disallow simple-template-id in cdtor: see 
[diff.cpp17.class]p2.  Just the diagnostic we give is horrible ;(.

Remove <T> to make this work.

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|rejects-valid               |diagnostic
             Status|RESOLVED                    |ASSIGNED
   Last reconfirmed|                            |2020-09-25
            Summary|[11 Regression] GCC reports |GCC reports an error:
                   |an error: expected          |expected unqualified-id
                   |unqualified-id before       |before ‘short’
                   |‘short’                     |
         Resolution|INVALID                     |---
     Ever confirmed|0                           |1

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Actually, let me reopen this to improve the diagnostic.

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|11.0                        |---

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |felix.morgner at gmail dot com

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
*** Bug 100997 has been marked as a duplicate of this bug. ***

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kevin.c.eady at gmail dot com

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 101032 has been marked as a duplicate of this bug. ***

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If the invalid special member is defined out of the class body, you get another
error:

template<typename T>
struct F
{
  F<T>();
};

template<typename T>
inline F<T>::F() { }


101032.C:4:8: error: expected unqualified-id before ‘)’ token
    4 |   F<T>();
      |        ^
101032.C:8:8: error: no declaration matches ‘F<T>::F()’
    8 | inline F<T>::F() { }
      |        ^~~~
101032.C:8:8: note: no functions named ‘F<T>::F()’
101032.C:2:8: note: ‘struct F<T>’ defined here
    2 | struct F
      |        ^

As well as improving the first error (which is the subject of this bug) maybe
the constructor could be parsed as though it had been written correctly, so
that the "no declaration matches" error doesn't happen. Compilation is already
going to fail, we don't need to also complain about the valid function
definition not matching anything.

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jengelh at inai dot de

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
*** Bug 104437 has been marked as a duplicate of this bug. ***

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
PR 104437 pointed out that the invalid constructor is accepted if it has a
redundant inline specifier:

template<typename Base> struct S : Base {
        inline S<Base>() {}
};

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

--- Comment #9 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:cff174fabd6c980c09aee95db1d9d5c22421761f

commit r14-8915-gcff174fabd6c980c09aee95db1d9d5c22421761f
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Feb 2 14:53:01 2024 -0500

    c++: DR2237, cdtor and template-id tweaks [PR107126]

    Since my r11-532 changes to implement DR2237, for this test:

      template<typename T>
      struct S {
        S<T>();
      };

    in C++20 we emit the ugly:

    q.C:3:8: error: expected unqualified-id before ')' token
        3 |   S<T>();

    which doesn't explain what the problem is.  This patch improves that
    diagnostic, reduces the error to a pedwarn, and adds a -Wc++20-compat
    diagnostic.  We now say:

    q.C:3:7: warning: template-id not allowed for constructor in C++20
[-Wtemplate-id-cdtor]
        3 |   S<T>();
    q.C:3:7: note: remove the '< >'

    This patch also fixes
    <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202#c8>
    where the C++20 diagnostic was missing altogether:  The problem was that I
checked
    for CPP_TEMPLATE_ID too early, at a point at which cp_parser_template_id
may not
    have been called yet.  So let's check for it at the end of the function,
after
    the tentative parse and rollback.

    -Wc++20-compat triggered in libitm/; I sent a patch for that.

            DR 2237
            PR c++/107126
            PR c++/97202

    gcc/c-family/ChangeLog:

            * c-opts.cc (c_common_post_options): In C++20 or with
-Wc++20-compat,
            turn on -Wtemplate-id-cdtor.
            * c.opt (Wtemplate-id-cdtor): New.

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_unqualified_id): Downgrade the DR2237 error
to
            a pedwarn.
            (cp_parser_constructor_declarator_p): Likewise.

    gcc/ChangeLog:

            * doc/invoke.texi: Document -Wtemplate-id-cdtor.

    gcc/testsuite/ChangeLog:

            * g++.dg/DRs/dr2237.C: Adjust dg-error.
            * g++.dg/parse/constructor2.C: Likewise.
            * g++.dg/template/error34.C: Likewise.
            * g++.old-deja/g++.pt/ctor2.C: Likewise.
            * g++.dg/DRs/dr2237-2.C: New test.
            * g++.dg/DRs/dr2237-3.C: New test.
            * g++.dg/DRs/dr2237-4.C: New test.
            * g++.dg/DRs/dr2237-5.C: New test.
            * g++.dg/warn/Wtemplate-id-cdtor-1.C: New test.
            * g++.dg/warn/Wtemplate-id-cdtor-2.C: New test.
            * g++.dg/warn/Wtemplate-id-cdtor-3.C: New test.
            * g++.dg/warn/Wtemplate-id-cdtor-4.C: New test.

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #10 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Should be all fixed now.

[Bug c++/97202] GCC reports an error: expected unqualified-id before ‘short’

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97202

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0