Bug 91364 - Implement P0388R4: Permit conversions to arrays of unknown bound
Summary: Implement P0388R4: Permit conversions to arrays of unknown bound
Status: RESOLVED FIXED
Alias: None
Product: gcc
Classification: Unclassified
Component: c++ (show other bugs)
Version: 10.0
: P3 normal
Target Milestone: ---
Assignee: Marek Polacek
URL:
Keywords: patch
Depends on: 69531 88128 91844
Blocks: 88323
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Reported: 2019-08-05 16:35 UTC by Marek Polacek
Modified: 2019-10-09 21:01 UTC (History)
2 users (show)

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Target:
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Known to work:
Known to fail:
Last reconfirmed: 2019-08-05 00:00:00


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Description Marek Polacek 2019-08-05 16:35:22 UTC
As per <http://wg21.link/p0388r4>.
Comment 1 Marek Polacek 2019-09-20 13:43:15 UTC
Sort of depends on CWG 2352 Similar types and reference binding which changed the definition of "reference-related".
Comment 2 Marek Polacek 2019-09-30 17:28:49 UTC
Workin' on it.
Comment 4 Marek Polacek 2019-10-05 16:08:39 UTC
Note to myself: while messing with this, perhaps implement DR 330 too for good measure.  Bug 88128.
Comment 5 Marek Polacek 2019-10-09 20:58:31 UTC
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,
<http://wg21.link/p0388r4>.  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/testsuite/g++.dg/cpp2a/array-conv9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/call.c
    trunk/gcc/cp/cp-tree.h
    trunk/gcc/cp/typeck.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/g++.dg/cpp0x/initlist-array3.C
    trunk/gcc/testsuite/g++.old-deja/g++.bugs/900321_01.C
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/testsuite/23_containers/span/lwg3255.cc
Comment 6 Marek Polacek 2019-10-09 21:01:35 UTC
Implemented for GCC 10.