[Bug c++/96363] New: bogus error with constrained partial specialization

[Bug c++/96363] New: bogus error with constrained partial specialization

[nathan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

            Bug ID: 96363
           Summary: bogus error with constrained partial specialization
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nathan at gcc dot gnu.org
  Target Milestone: ---

template <typename T> class TPL;

template <typename T> struct Trait;

template <typename T>
  requires (Trait<T>::val == 0)
class TPL<T>;  // #1

template <typename T>
  requires (Trait<T>::val == 1)
class TPL<T>;  // #2 error here

cc1plus -quiet -std=c++20 par.cc 
par.cc:11:7: error: ‘TPL<T>’ does not match original declaration
   11 | class TPL<T>;
      |       ^~~~~~
par.cc:1:29: note: original template declaration here
    1 | template <typename T> class TPL;
      |                             ^~~

ICBW, but if #2 is rejected, why is #1 accepted.  Aren't these just two partial
specializations with different constraints?

[Bug c++/96363] bogus error with constrained partial specialization

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

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

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
PR92944 looks related.

[Bug c++/96363] bogus error with constrained partial specialization

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-07-29
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=92944
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
             Blocks|                            |67491


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67491
[Bug 67491] [meta-bug] concepts issues

[Bug c++/96363] bogus error with constrained partial specialization

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mate.kelemen.12 at gmail dot com

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 105718 has been marked as a duplicate of this bug. ***

[Bug c++/96363] bogus error with constrained partial specialization

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

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

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 99501 has been marked as a duplicate of this bug. ***

[Bug c++/96363] bogus error with multiple constrained partial specialization forward declarations

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

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

[Bug c++/96363] bogus error with multiple constrained partial specialization forward declarations

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

--- Comment #4 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:97dc78d705a90c1ae83c78a7f2e24942cc3a6257

commit r13-779-g97dc78d705a90c1ae83c78a7f2e24942cc3a6257
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu May 26 09:43:14 2022 -0400

    c++: constrained partial spec forward decl [PR96363]

    Here during cp_parser_single_declaration for #2, we were calling
    associate_classtype_constraints for TPL<T> (the primary template type)
    before maybe_process_partial_specialization could get a chance to
    notice that we're in fact declaring a distinct constrained partial
    spec and not redeclaring the primary template.  This caused us to
    emit a bogus error about differing constraints b/t the primary template
    and #2's constraints.  This patch fixes this by moving the call to
    associate_classtype_constraints after the call to shadow_tag (which
    calls maybe_process_partial_specialization) and adjusting shadow_tag to
    use the return value of m_p_p_s.

    Moreover, if we later try to define a constrained partial specialization
    that's been declared earlier (as in the third testcase), then
    maybe_new_partial_specialization correctly notices it's a redeclaration
    and returns NULL_TREE.  But in this case we also need to update TYPE to
    point to the redeclared partial spec (it'll otherwise continue pointing
    to the primary template type, eventually leading to a bogus error).

            PR c++/96363

    gcc/cp/ChangeLog:

            * decl.cc (shadow_tag): Use the return value of
            maybe_process_partial_specialization.
            * parser.cc (cp_parser_single_declaration): Call shadow_tag
            before associate_classtype_constraints.
            * pt.cc (maybe_new_partial_specialization): Change return type
            to bool.  Take 'type' argument by mutable reference.  Set 'type'
            to point to the correct constrained specialization when
            appropriate.
            (maybe_process_partial_specialization): Adjust accordingly.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-partial-spec12.C: New test.
            * g++.dg/cpp2a/concepts-partial-spec12a.C: New test.
            * g++.dg/cpp2a/concepts-partial-spec13.C: New test.

[Bug c++/96363] bogus error with multiple constrained partial specialization forward declarations

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.2

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed on trunk so far.

[Bug c++/96363] bogus error with multiple constrained partial specialization forward declarations

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:12d8a4a0fb26729290a184c40956329bb614625f

commit r12-8600-g12d8a4a0fb26729290a184c40956329bb614625f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu May 26 09:43:14 2022 -0400

    c++: constrained partial spec forward decl [PR96363]

    Here during cp_parser_single_declaration for #2, we were calling
    associate_classtype_constraints for TPL<T> (the primary template type)
    before maybe_process_partial_specialization could get a chance to
    notice that we're in fact declaring a distinct constrained partial
    spec and not redeclaring the primary template.  This caused us to
    emit a bogus error about differing constraints b/t the primary template
    and #2's constraints.  This patch fixes this by moving the call to
    associate_classtype_constraints after the call to shadow_tag (which
    calls maybe_process_partial_specialization) and adjusting shadow_tag to
    use the return value of m_p_p_s.

    Moreover, if we later try to define a constrained partial specialization
    that's been declared earlier (as in the third testcase), then
    maybe_new_partial_specialization correctly notices it's a redeclaration
    and returns NULL_TREE.  But in this case we also need to update TYPE to
    point to the redeclared partial spec (it'll otherwise continue pointing
    to the primary template type, eventually leading to a bogus error).

            PR c++/96363

    gcc/cp/ChangeLog:

            * decl.cc (shadow_tag): Use the return value of
            maybe_process_partial_specialization.
            * parser.cc (cp_parser_single_declaration): Call shadow_tag
            before associate_classtype_constraints.
            * pt.cc (maybe_new_partial_specialization): Change return type
            to bool.  Take 'type' argument by mutable reference.  Set 'type'
            to point to the correct constrained specialization when
            appropriate.
            (maybe_process_partial_specialization): Adjust accordingly.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-partial-spec12.C: New test.
            * g++.dg/cpp2a/concepts-partial-spec12a.C: New test.
            * g++.dg/cpp2a/concepts-partial-spec13.C: New test.

    (cherry picked from commit 97dc78d705a90c1ae83c78a7f2e24942cc3a6257)

[Bug c++/96363] bogus error with multiple constrained partial specialization forward declarations

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96363

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

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

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12.2/13