[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[herring at lanl dot gov]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

S. Davis Herring <herring at lanl dot gov> changed:

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

--- Comment #7 from S. Davis Herring <herring at lanl dot gov> ---
My example in Comment #5 works in 9.2 but not in (Compiler Explorer's) trunk.

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[ma.noack.pr at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

Matthias Noack <ma.noack.pr at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ma.noack.pr at gmail dot com

--- Comment #8 from Matthias Noack <ma.noack.pr at gmail dot com> ---
Still failing in 10.2 (original reproducer).

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

Johel Ernesto Guerrero Peña <johelegp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |johelegp at gmail dot com

--- Comment #9 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
I think Bug 97700 is also a duplicate of this.

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

--- Comment #10 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Another workaround, extended from Bug 92320's example. See
https://godbolt.org/z/69onWf.
You can wrap the closure object in a template function which itself invokes the
closure object and converts to a function pointer that GCC accepts.
```C++
template<auto V>
void templ() {}

void dummy(){}

template<auto F>
void fn(){F();}

void foo() {
    constexpr int a = 7 + 3;
    templ<a>();

    templ<dummy>();

    typedef void(FPtr)();
    constexpr FPtr * b = &dummy;
    templ<b>();

    constexpr auto l = []{};
    constexpr void (*d)()=fn<l>;
    templ<d>();

    constexpr FPtr * c = [](){};
    templ<c>();
}

```

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

--- Comment #11 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #4)
> Testcase from Bug 85589:
> 
> template<auto& v> struct foo {};
> 
>     int main() {
>         static auto v = "str";
>         (void) foo<v> {};
>     }

Note comment #4 is already fixed (I reopened PR 85589 to close it was fixed [or
as a dup if I can find one]).

The rest of the testcases still fail on the trunk.

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=97700

--- Comment #12 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Johel Ernesto Guerrero Peña from comment #9)
> I think Bug 97700 is also a duplicate of this.

Well, it seems related enough, at least...

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

--- Comment #13 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:c3afdb8ba8f1839544c414f57e41a58c8fda5349

commit r14-708-gc3afdb8ba8f1839544c414f57e41a58c8fda5349
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu May 11 10:04:25 2023 -0400

    c++: converted lambda as template argument [PR83258, ...]

    r8-1253-g3d2e25a240c711 removed the template argument linkage requirement
    in convert_nontype_argument for C++17 (which r9-3836-g4be5c72cf3ea3e later
    factored out into invalid_tparm_referent_p), but we need to also remove
    the one in convert_nontype_argument_function for benefit of the first and
    third testcase which we currently reject even in C++17/20 mode.

    And in invalid_tparm_referent_p we're inadvertendly returning false for
    the address of a lambda's static op() since it's DECL_ARTIFICIAL, which
    currently causes us to reject the second (C++20) testcase.  But this
    DECL_ARTIFICIAL check seems to be relevant only for VAR_DECL, and in fact
    this code path was originally reachable only for VAR_DECL until recently
    (r13-6970-gb5e38b1c166357).  So this patch restricts the check to VAR_DECL.

    Co-authored-by: Jonathan Wakely <jwakely@redhat.com>

            PR c++/83258
            PR c++/80488
            PR c++/97700

    gcc/cp/ChangeLog:

            * pt.cc (convert_nontype_argument_function): Remove linkage
            requirement for C++17 and later.
            (invalid_tparm_referent_p) <case ADDR_EXPR>: Restrict
            DECL_ARTIFICIAL rejection test to VAR_DECL.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/visibility/anon8.C: Don't expect a "no linkage"
            error for the template argument &B2:fn in C++17 mode.
            * g++.dg/cpp0x/lambda/lambda-conv15.C: New test.
            * g++.dg/cpp2a/nontype-class56.C: New test.
            * g++.dg/template/function2.C: New test.

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.2
                 CC|                            |ppalka at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #14 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed on trunk so far.

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

--- Comment #15 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:10098788ff61467f5a499f01c5443fb53ff564dd

commit r14-787-g10098788ff61467f5a499f01c5443fb53ff564dd
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri May 12 08:37:54 2023 -0400

    c++: remove redundant testcase [PR83258]

    I noticed only after the fact that the new testcase template/function2.C
    (from r14-708-gc3afdb8ba8f183) is just a subset of ext/visibility/anon8.C,
    so let's get rid of it.

            PR c++/83258

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/visibility/anon8.C: Mention PR83258.
            * g++.dg/template/function2.C: Removed.

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

--- Comment #16 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:42f9b481be3527b336b800128247d053fd18d121

commit r13-7324-g42f9b481be3527b336b800128247d053fd18d121
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu May 11 10:04:25 2023 -0400

    c++: converted lambda as template argument [PR83258, ...]

    r8-1253-g3d2e25a240c711 removed the template argument linkage requirement
    in convert_nontype_argument for C++17 (which r9-3836-g4be5c72cf3ea3e later
    factored out into invalid_tparm_referent_p), but we need to also remove
    the one in convert_nontype_argument_function for benefit of the first and
    third testcase which we currently reject even in C++17/20 mode.

    And in invalid_tparm_referent_p we're inadvertendly returning false for
    the address of a lambda's static op() since it's DECL_ARTIFICIAL, which
    currently causes us to reject the second (C++20) testcase.  But this
    DECL_ARTIFICIAL check seems to be relevant only for VAR_DECL, and in fact
    this code path was originally reachable only for VAR_DECL until recently
    (r13-6970-gb5e38b1c166357).  So this patch restricts the check to VAR_DECL.

    Co-authored-by: Jonathan Wakely <jwakely@redhat.com>

            PR c++/83258
            PR c++/80488
            PR c++/97700

    gcc/cp/ChangeLog:

            * pt.cc (convert_nontype_argument_function): Remove linkage
            requirement for C++17 and later.
            (invalid_tparm_referent_p) <case ADDR_EXPR>: Restrict
            DECL_ARTIFICIAL rejection test to VAR_DECL.

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/visibility/anon8.C: Don't expect a "no linkage"
            error for the template argument &B2:fn in C++17 mode.
            * g++.dg/cpp0x/lambda/lambda-conv15.C: New test.
            * g++.dg/cpp2a/nontype-class56.C: New test.
            * g++.dg/template/function2.C: New test.

    (cherry picked from commit c3afdb8ba8f1839544c414f57e41a58c8fda5349)

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:20b1e1d8a79356e03f50f53e2fa02b376d56d7d7

commit r13-7327-g20b1e1d8a79356e03f50f53e2fa02b376d56d7d7
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri May 12 08:37:54 2023 -0400

    c++: remove redundant testcase [PR83258]

    I noticed only after the fact that the new testcase template/function2.C
    (from r14-708-gc3afdb8ba8f183) is just a subset of ext/visibility/anon8.C,
    so let's get rid of it.

            PR c++/83258

    gcc/testsuite/ChangeLog:

            * g++.dg/ext/visibility/anon8.C: Mention PR83258.
            * g++.dg/template/function2.C: Removed.

    (cherry picked from commit 10098788ff61467f5a499f01c5443fb53ff564dd)

[Bug c++/83258] Rejecting function pointer non-type template parameter without linkage

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83258

Patrick Palka <ppalka at gcc dot gnu.org> changed:

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

--- Comment #18 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13.2