[Bug c++/88128] G++ should implement CWG 330

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

Marek Polacek  changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution|--- |FIXED

--- Comment #8 from Marek Polacek  ---
Implemented for GCC 10.

[Bug c++/88128] G++ should implement CWG 330

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

--- Comment #7 from Marek Polacek  ---
Author: mpolacek
Date: Wed Oct  9 20:58:00 2019
New Revision: 276771

URL: https://gcc.gnu.org/viewcvs?rev=276771&root=gcc&view=rev
Log:
Implement C++20 P0388R4, DR 1307, and DR 330.

This patch implements P0388R4, Permit conversions to arrays of unknown bound,
.  CWG 393 allowed references to arrays of unknown
bound and this C++20 feature allows conversions like

  void f(int(&)[]);
  int arr[1];

  void g() { f(arr); }
  int(&r)[] = arr;

The proposal seemed fairly straightforward but it turned out to be quite
shifty.  I found out that I needed to implement DR 2352 (done), and also
DR 1307 (done in this patch).  The latter DR added wording for
list-initialization ranking of references to arrays which this proposal
extends.  DR 330 was also implemented in this patch.

PR c++/91364 - P0388R4: Permit conversions to arrays of unknown bound.
PR c++/69531 - DR 1307: Differently bounded array parameters.
PR c++/88128 - DR 330: Qual convs and pointers to arrays of pointers.
* call.c (build_array_conv): Build ck_identity at the beginning
of the conversion.
(standard_conversion): Pass bounds_none to comp_ptr_ttypes_const.
(maybe_warn_array_conv): New.
(convert_like_real): Call it.  Add an error message about converting
from arrays of unknown bounds.
(conv_get_original_expr): New.
(nelts_initialized_by_list_init): New.
(conv_binds_to_array_of_unknown_bound): New.
(compare_ics): Implement list-initialization ranking based on
array sizes, as specified in DR 1307 and P0388R.
* cp-tree.h (comp_ptr_ttypes_const): Adjust declaration.
(compare_bounds_t): New enum.
* typeck.c (comp_array_types): New bool and compare_bounds_t
parameters.  Use them.
(structural_comptypes): Adjust the call to comp_array_types.
(similar_type_p): Handle ARRAY_TYPE.
(build_const_cast_1): Pass bounds_none to comp_ptr_ttypes_const.
(comp_ptr_ttypes_real): Don't check cv-quals of ARRAY_TYPEs.  Use
comp_array_types to compare array types.  Look through arrays as per
DR 330.
(comp_ptr_ttypes_const): Use comp_array_types to compare array types.
Look through arrays as per DR 330.

* g++.dg/conversion/qual1.C: New test.
* g++.dg/conversion/qual2.C: New test.
* g++.dg/conversion/qual3.C: New test.
* g++.dg/conversion/ref2.C: New test.
* g++.dg/conversion/ref3.C: New test.
* g++.dg/cpp0x/initlist-array3.C: Remove dg-error.
* g++.dg/cpp0x/initlist-array7.C: New test.
* g++.dg/cpp0x/initlist-array8.C: New test.
* g++.dg/cpp2a/array-conv1.C: New test.
* g++.dg/cpp2a/array-conv10.C: New test.
* g++.dg/cpp2a/array-conv11.C: New test.
* g++.dg/cpp2a/array-conv12.C: New test.
* g++.dg/cpp2a/array-conv13.C: New test.
* g++.dg/cpp2a/array-conv14.C: New test.
* g++.dg/cpp2a/array-conv15.C: New test.
* g++.dg/cpp2a/array-conv16.C: New test.
* g++.dg/cpp2a/array-conv17.C: New test.
* g++.dg/cpp2a/array-conv2.C: New test.
* g++.dg/cpp2a/array-conv3.C: New test.
* g++.dg/cpp2a/array-conv4.C: New test.
* g++.dg/cpp2a/array-conv5.C: New test.
* g++.dg/cpp2a/array-conv6.C: New test.
* g++.dg/cpp2a/array-conv7.C: New test.
* g++.dg/cpp2a/array-conv8.C: New test.
* g++.dg/cpp2a/array-conv9.C: New test.
* g++.old-deja/g++.bugs/900321_01.C: Adjust dg-error.

* testsuite/23_containers/span/lwg3255.cc: Adjust test to match the
post-P0388R4 behavior.


Added:
trunk/gcc/testsuite/g++.dg/conversion/qual1.C
trunk/gcc/testsuite/g++.dg/conversion/qual2.C
trunk/gcc/testsuite/g++.dg/conversion/qual3.C
trunk/gcc/testsuite/g++.dg/conversion/ref2.C
trunk/gcc/testsuite/g++.dg/conversion/ref3.C
trunk/gcc/testsuite/g++.dg/cpp0x/initlist-array7.C
trunk/gcc/testsuite/g++.dg/cpp0x/initlist-array8.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv1.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv10.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv11.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv12.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv13.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv14.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv15.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv16.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv17.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv2.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv3.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv4.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv5.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv6.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv7.C
trunk/gcc/testsuite/g++.dg/cpp2a/array-conv8.C
trunk/gcc/testsuit

[Bug c++/88128] G++ should implement CWG 330

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

Marek Polacek  changed:

   What|Removed |Added

 Status|NEW |ASSIGNED
   Assignee|unassigned at gcc dot gnu.org  |mpolacek at gcc dot 
gnu.org

--- Comment #6 from Marek Polacek  ---
I think I have a patch; e.g. this now compiles:

double *const (*d)[3];
double const *const (*e)[3] = d;
int *(*f)[3];
const int *const (*g)[3] = f;

int main()
{
 double *array2D[2][3];

 double   *   (*array2DPtr1)[3] = array2D; // Legal
 double   * const (*array2DPtr2)[3] = array2DPtr1; // Legal
 double const * const (*array2DPtr3)[3] = array2DPtr2; // Illegal
}

[Bug c++/88128] G++ should implement CWG 330

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

--- Comment #5 from Jonathan Wakely  ---
(In reply to Jonathan Wakely from comment #4)
> (In reply to Viktor Ostashevskyi from comment #3)
> > Is it possible to make std::span from std::vector?
> 
> Yes, that works with current trunk.

Although that could be a bug: the constraints use declval<_Container&>() but
should be using declval().

[Bug c++/88128] G++ should implement CWG 330

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

--- Comment #4 from Jonathan Wakely  ---
(In reply to Viktor Ostashevskyi from comment #3)
> Was this bug fixed for implenting it?

No.

> Is it possible to make std::span from std::vector?

Yes, that works with current trunk.

[Bug c++/88128] G++ should implement CWG 330

[ostash at ostash dot kiev.ua]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

--- Comment #3 from Viktor Ostashevskyi  ---
I see that std::span implementation was proposed in
https://gcc.gnu.org/ml/libstdc++/2019-08/msg00068.html.

Was this bug fixed for implenting it?

Is it possible to make std::span from std::vector?

[Bug c++/88128] G++ should implement CWG 330

[ostash at ostash dot kiev.ua]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

--- Comment #2 from Viktor Ostashevskyi  ---
Actually, even current C++17 unique_ptr::reset for array objects is defined in
terms of pointer to array convertibility ([unique.ptr.runtime.modifiers]).

[Bug c++/88128] G++ should implement CWG 330

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88128

Jonathan Wakely  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2018-11-21
 Ever confirmed|0   |1

--- Comment #1 from Jonathan Wakely  ---
Confirmed.

[Moved to DR as N4261 at the November, 2014 meeting.]

The resolution is in https://wg21.link/n4261