[Bug c++/105061] New: [9/10 Regression] [c++2a+] anonymous bitfield templated offset rejected

[Bug c++/105061] New: [9/10 Regression] [c++2a+] anonymous bitfield templated offset rejected

[wjwray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

            Bug ID: 105061
           Summary: [9/10 Regression] [c++2a+] anonymous bitfield
                    templated offset rejected
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wjwray at gmail dot com
  Target Milestone: ---

A very specific regression: https://godbolt.org/z/dWxnvd93j

    template <typename alloc_unit, int width, int offset>
    struct offset_bitfield { alloc_unit : offset, field : width; };

 accepted forever  with -std=c++17-
 accepted in  9.4  with -std=c++2a
 rejected in 10.1+ with -std=c++20+
(accepted in Clang & MSVC, any std)

My guess as to the cause: the c++20 change to allow bitfield initializers.

    template <typename alloc_unit, int width, int offset>
    struct offset_bitfield { alloc_unit : offset, field : width; };
    //                                  ^       ^
    // error: found ':' in nested-name-specifier, expected '::'
    // error: expected unqualified-id before ',' token

The template is accepted if the typename parameter is removed:

    template <int width, int offset>
    struct uint_offset_bitfield { unsigned : offset, field : width; };

[Bug c++/105061] [9/10 Regression] [c++2a+] anonymous bitfield templated offset rejected

[wjwray at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

--- Comment #1 from Will Wray <wjwray at gmail dot com> ---
Hmm, the accepted simplified version ^^^ with typename parameter removed
is then rejected if 'unsigned' is replaced with 'uint32_t' from <cstdint>

    #include <cstdint>
    template <int width, int offset>
    struct uint_offset_bitfield { uint32_t : offset, field : width; };
    |                                      ^
    | error: found ':' in nested-name-specifier, expected '::'
    |                                      ::
    | error: invalid use of '::'

(and "error: invalid use of '::'" is just wrong - no use of '::' at all)

[Bug c++/105061] [10/11/12 Regression] [c++2a+] anonymous bitfield templated offset rejected

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |10.3.1
           Keywords|                            |needs-bisection
   Target Milestone|---                         |10.4
            Summary|[9/10 Regression] [c++2a+]  |[10/11/12 Regression]
                   |anonymous bitfield          |[c++2a+] anonymous bitfield
                   |templated offset rejected   |templated offset rejected
      Known to work|                            |9.4.1

[Bug c++/105061] [10/11/12 Regression] [c++2a+] anonymous bitfield templated offset rejected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org
           Keywords|needs-bisection             |
           Priority|P3                          |P2
   Last reconfirmed|                            |2022-03-28

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r10-3735-gcb57504a550158913258e5be8ddb991376475efb
P0683R1 was done already r8-3526-g603be0224edf653c1e38229e1d32ed449ffd23bd
template <typename T, int U, int V>
struct A { T : V, u : U; };
template <int U, int V>
struct B { unsigned : V, u : U; };
typedef unsigned uns;
template <int U, int V>
struct C { uns : V, u : U; };

[Bug c++/105061] [10/11/12 Regression] [c++2a+] anonymous bitfield templated offset rejected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Just a wild guess, should cp_parser_template_introduction temporarily clear
parser->colon_corrects_to_scope_p (perhaps only if member_p)?

[Bug c++/105061] [10/11/12 Regression] [c++2a+] anonymous bitfield templated offset rejected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 52701
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52701&action=edit
gcc12-pr105061.patch

After reading what template-introduction is I think that is the right fix.

[Bug c++/105061] [10/11/12 Regression] [c++2a+] anonymous bitfield templated offset rejected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:4f2795218a6ba6a7b7b9b18ca7a6e390661e1608

commit r12-7913-g4f2795218a6ba6a7b7b9b18ca7a6e390661e1608
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Mar 30 09:16:41 2022 +0200

    c++: Fox template-introduction tentative parsing in class bodies clear
colon_corrects_to_scope_p [PR105061]

    The concepts support (in particular template introductions from concepts
TS)
    broke the following testcase, valid unnamed bitfields with dependent
    types (or even just typedefs) were diagnosed as typos (: instead of correct
    ::) in template introduction during their tentative parsing.
    The following patch fixes that by not doing this : to :: correction when
    member_p is true.

    2022-03-30  Jakub Jelinek  <jakub@redhat.com>

            PR c++/105061
            * parser.cc (cp_parser_template_introduction): If member_p,
temporarily
            clear parser->colon_corrects_to_scope_p around tentative parsing of
            nested name specifier.

            * g++.dg/concepts/pr105061.C: New test.

[Bug c++/105061] [10/11/12 Regression] [c++2a+] anonymous bitfield templated offset rejected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:7b5a2b6e4f78395962835790c6d4a3e27ab8d378

commit r11-9738-g7b5a2b6e4f78395962835790c6d4a3e27ab8d378
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Mar 30 09:16:41 2022 +0200

    c++: Fox template-introduction tentative parsing in class bodies clear
colon_corrects_to_scope_p [PR105061]

    The concepts support (in particular template introductions from concepts
TS)
    broke the following testcase, valid unnamed bitfields with dependent
    types (or even just typedefs) were diagnosed as typos (: instead of correct
    ::) in template introduction during their tentative parsing.
    The following patch fixes that by not doing this : to :: correction when
    member_p is true.

    2022-03-30  Jakub Jelinek  <jakub@redhat.com>

            PR c++/105061
            * parser.c (cp_parser_template_introduction): If member_p,
temporarily
            clear parser->colon_corrects_to_scope_p around tentative parsing of
            nested name specifier.

            * g++.dg/concepts/pr105061.C: New test.

    (cherry picked from commit 4f2795218a6ba6a7b7b9b18ca7a6e390661e1608)

[Bug c++/105061] [10 Regression] [c++2a+] anonymous bitfield templated offset rejected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
            Summary|[10/11/12 Regression]       |[10 Regression] [c++2a+]
                   |[c++2a+] anonymous bitfield |anonymous bitfield
                   |templated offset rejected   |templated offset rejected
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 11.3+ and 12.1+.

[Bug c++/105061] [10 Regression] [c++2a+] anonymous bitfield templated offset rejected

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:3d8d22d7bd799fbdcddb4762a97c39d6107ee077

commit r10-10700-g3d8d22d7bd799fbdcddb4762a97c39d6107ee077
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Mar 30 09:16:41 2022 +0200

    c++: Fox template-introduction tentative parsing in class bodies clear
colon_corrects_to_scope_p [PR105061]

    The concepts support (in particular template introductions from concepts
TS)
    broke the following testcase, valid unnamed bitfields with dependent
    types (or even just typedefs) were diagnosed as typos (: instead of correct
    ::) in template introduction during their tentative parsing.
    The following patch fixes that by not doing this : to :: correction when
    member_p is true.

    2022-03-30  Jakub Jelinek  <jakub@redhat.com>

            PR c++/105061
            * parser.c (cp_parser_template_introduction): If member_p,
temporarily
            clear parser->colon_corrects_to_scope_p around tentative parsing of
            nested name specifier.

            * g++.dg/concepts/pr105061.C: New test.

    (cherry picked from commit 4f2795218a6ba6a7b7b9b18ca7a6e390661e1608)

[Bug c++/105061] [10 Regression] [c++2a+] anonymous bitfield templated offset rejected

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105061

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

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

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 10.4 too.