[Bug plugins/98059] New: [11 regression] Plugins don't compile with c++20

[Bug plugins/98059] New: [11 regression] Plugins don't compile with c++20

[sss@li-snyder.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

            Bug ID: 98059
           Summary: [11 regression] Plugins don't compile with c++20
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: plugins
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sss@li-snyder.org
  Target Milestone: ---

The following example fails with gcc 11 (20201128):

$ echo '#include "gcc-plugin.h"' | g++  -x c++ -std=c++20 -c -o x.o - -I`g++
-print-file-name=plugin`/include
In file included from
/usr/local/gcc/lib/gcc/x86_64-pc-linux-gnu/11.0.0/plugin/include/config.h:8,
                 from
/usr/local/gcc/lib/gcc/x86_64-pc-linux-gnu/11.0.0/plugin/include/gcc-plugin.h:27,
                 from <stdin>:1:
/usr/local/gcc/lib/gcc/x86_64-pc-linux-gnu/11.0.0/plugin/include/ansidecl.h:424:9:
error: expected unqualified-id before ‘const’
  424 |   TYPE (const TYPE&) = delete;                  \
      |         ^~~~~
/usr/local/gcc/lib/gcc/x86_64-pc-linux-gnu/11.0.0/plugin/include/vec.h:1605:3:
note: in expansion of macro ‘DISABLE_COPY_AND_ASSIGN’
 1605 |   DISABLE_COPY_AND_ASSIGN(auto_delete_vec<T>);
      |   ^~~~~~~~~~~~~~~~~~~~~~~
/usr/local/gcc/lib/gcc/x86_64-pc-linux-gnu/11.0.0/plugin/include/ansidecl.h:424:9:
error: expected ‘)’ before ‘const’
  424 |   TYPE (const TYPE&) = delete;                  \
      |        ~^~~~~
/usr/local/gcc/lib/gcc/x86_64-pc-linux-gnu/11.0.0/plugin/include/vec.h:1605:3:
note: in expansion of macro ‘DISABLE_COPY_AND_ASSIGN’
 1605 |   DISABLE_COPY_AND_ASSIGN(auto_delete_vec<T>);
      |   ^~~~~~~~~~~~~~~~~~~~~~~


Can be fixed with this patch:

diff --git a/gcc/vec.h b/gcc/vec.h
index 14d77e87342..90904515ea0 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -1602,7 +1602,7 @@ class auto_delete_vec : public auto_vec <T *>
   ~auto_delete_vec ();

 private:
-  DISABLE_COPY_AND_ASSIGN(auto_delete_vec<T>);
+  DISABLE_COPY_AND_ASSIGN(auto_delete_vec);
 };

 /* Conditionally allocate heap memory for VEC and its internal vector.  */

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

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

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

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

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

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

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Indeed, C++20 rejects this since
r11-532-g4b38d56dbac6742b038551a36ec80200313123a1
DR2237 http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#2237
change.

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- Comment #2 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:bad800c03d00a57fc21718c160459d9a1e8d747a

commit r11-5660-gbad800c03d00a57fc21718c160459d9a1e8d747a
Author: Scott Snyder <sss@li-snyder.org>
Date:   Wed Dec 2 15:42:56 2020 +0100

    vec.h: Fix GCC build with -std=gnu++20 [PR98059]

    Apparently vec.h doesn't build with -std=c++20/gnu++20, since the
    DR2237 r11-532 change.
    template <typename T>
    class auto_delete_vec
    {
    private:
      auto_vec_delete<T> (const auto_delete_vec<T> &) = delete;
    };
    which vec.h uses is invalid C++20, one needs to use
      auto_vec_delete (const auto_delete_vec &) = delete;
    instead which is valid all the way back to C++11 (and without = delete
    to C++98).

    2020-12-02  Scott Snyder  <sss@li-snyder.org>

            PR plugins/98059
            * vec.h (auto_delete_vec): Use
            DISABLE_COPY_AND_ASSIGN(auto_delete_vec) instead of
            DISABLE_COPY_AND_ASSIGN(auto_delete_vec<T>) to make it valid C++20
            after DR2237.

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This change is incorrect, r11-532-g4b38d56dbac6742b038551a36ec80200313123a1 is
wrong to reject that assignment operator. The declarator-id is "operator=" and
so doesn't contain a template-id at all.

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Well, strictly speaking the change isn't wrong, and arguably it's an
improvement. But it's incorrect for GCC to require it in C++20 mode.

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
We were using:
template <typename T>
struct S {
private:
  S<T> (const S<T> &) = delete;
  S<T> operator = (const S<T> &) = delete;
};
With the change we are using:
template <typename T>
struct S {
private:
  S (const S &) = delete;
  S operator = (const S &) = delete;
};
We could be using also:
template <typename T>
struct S {
private:
  S (const S<T> &) = delete;
  S<T> operator = (const S<T> &) = delete;
};
and it would be still valid C++20 (and is accepted), just the first form is
not, because after DR2237 one can't use S<T> () for the constructor.

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to CVS Commits from comment #2)
>     Apparently vec.h doesn't build with -std=c++20/gnu++20, since the
>     DR2237 r11-532 change.
>     template <typename T>
>     class auto_delete_vec
>     {
>     private:
>       auto_vec_delete<T> (const auto_delete_vec<T> &) = delete;


Ugh, I misread this as an assignment operator despite there being no operator=
there at all.

It's a copy ctor, and yes, it's invalid. Sorry.

>     };
>     which vec.h uses is invalid C++20, one needs to use
>       auto_vec_delete (const auto_delete_vec &) = delete;

The <T> is allowed on the parameter, it's only disallowed on the first one, so
this would be OK too:

     auto_vec_delete (const auto_delete_vec<T> &) = delete;

But the macro can't generate that, and there's no reason to prefer it.

Sorry for the noise  :-(

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

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

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

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Anyway, fixed now.

[Bug plugins/98059] [11 regression] Plugins don't compile with c++20

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98059

--- 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:45a5aa80240d2033fb490f974756b947f8d0db40

commit r10-9213-g45a5aa80240d2033fb490f974756b947f8d0db40
Author: Scott Snyder <sss@li-snyder.org>
Date:   Wed Dec 2 15:42:56 2020 +0100

    vec.h: Fix GCC build with -std=gnu++20 [PR98059]

    Apparently vec.h doesn't build with -std=c++20/gnu++20, since the
    DR2237 r11-532 change.
    template <typename T>
    class auto_delete_vec
    {
    private:
      auto_vec_delete<T> (const auto_delete_vec<T> &) = delete;
    };
    which vec.h uses is invalid C++20, one needs to use
      auto_vec_delete (const auto_delete_vec &) = delete;
    instead which is valid all the way back to C++11 (and without = delete
    to C++98).

    2020-12-02  Scott Snyder  <sss@li-snyder.org>

            PR plugins/98059
            * vec.h (auto_delete_vec): Use
            DISABLE_COPY_AND_ASSIGN(auto_delete_vec) instead of
            DISABLE_COPY_AND_ASSIGN(auto_delete_vec<T>) to make it valid C++20
            after DR2237.

    (cherry picked from commit bad800c03d00a57fc21718c160459d9a1e8d747a)