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* [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
@ 2021-06-18 13:33 redi at gcc dot gnu.org
2021-06-21 6:15 ` [Bug libstdc++/101124] " rguenth at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-06-18 13:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
Bug ID: 101124
Summary: [12 Regression] pair<T*, int>(0, 0) was intended to be
deprecated, but is rejected now
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
r12-220-gd96db15967e78d7cecea3b1cf3169ceb924678ac intended to deprecate the
non-standard constructors allowing this:
#include <utility>
std::pair<long*, int> p(0, 0);
However, as reported in PR 100375 the hack doesn't work, and it triggers a
warning (which is an error with -Wpedantic):
pair.C:2:29: warning: ISO C++ says that these are ambiguous, even though the
worst conversion for the first is better than the worst conversion for the
second:
2 | std::pair<long*, int> p(0, 0);
| ^
In file included from /home/jwakely/gcc/12/include/c++/12.0.0/utility:70,
from pair.C:1:
/home/jwakely/gcc/12/include/c++/12.0.0/bits/stl_pair.h:426:17: note: candidate
1: 'constexpr std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _U1 =
long int*; _U2 = int; typename std::enable_if<(std::_PCC<true, _T1,
_T2>::_ConstructiblePair<_U1, _U2>() && std::_PCC<true, _T1,
_T2>::_ImplicitlyConvertiblePair<_U1, _U2>()), bool>::type <anonymous> = true;
_T1 = long int*; _T2 = int]'
426 | constexpr pair(const _T1& __a, const _T2& __b)
| ^~~~
/home/jwakely/gcc/12/include/c++/12.0.0/bits/stl_pair.h:511:18: note: candidate
2: 'constexpr std::pair<_T1, _T2>::pair(std::pair<_T1,
_T2>::__null_ptr_constant, _U2&&) [with _U2 = int; typename std::enable_if<((!
std::__or_<std::is_same<_U2, const _T2&>, std::is_same<_U2, _T2&> >::value) &&
std::_PCC<true, _T1, _T2>::_DeprConsPair<true, std::nullptr_t, _U2>()),
bool>::type <anonymous> = true; _T1 = long int*; _T2 = int]'
511 | constexpr pair(__null_ptr_constant, _U2&& __y)
| ^~~~
Maybe this is OK, because it's a non-standard feature and so rejecting it with
-Wpedantic might be OK. But my intention was to accept it with a deprecation
warning for GCC 12, and only make it ill-formed for GCC 13.
I need to see if it's possible to make it work as intended, and if not then
just remove the hack and make it ill-formed for GCC 12.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/101124] [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
@ 2021-06-21 6:15 ` rguenth at gcc dot gnu.org
2021-09-25 20:08 ` redi at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2021-06-21 6:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |rejects-valid
Target Milestone|--- |12.0
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/101124] [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
2021-06-21 6:15 ` [Bug libstdc++/101124] " rguenth at gcc dot gnu.org
@ 2021-09-25 20:08 ` redi at gcc dot gnu.org
2022-01-17 14:26 ` rguenth at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-09-25 20:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2021-09-25
Status|UNCONFIRMED |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/101124] [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
2021-06-21 6:15 ` [Bug libstdc++/101124] " rguenth at gcc dot gnu.org
2021-09-25 20:08 ` redi at gcc dot gnu.org
@ 2022-01-17 14:26 ` rguenth at gcc dot gnu.org
2022-01-18 11:11 ` redi at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: rguenth at gcc dot gnu.org @ 2022-01-17 14:26 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P1
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/101124] [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
` (2 preceding siblings ...)
2022-01-17 14:26 ` rguenth at gcc dot gnu.org
@ 2022-01-18 11:11 ` redi at gcc dot gnu.org
2022-01-18 16:32 ` cvs-commit at gcc dot gnu.org
2022-01-18 16:37 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2022-01-18 11:11 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Another example that now fails:
#include <utility>
struct X { } x;
std::pair<const X, void*> p(x, 0);
This selects the pair<T1,T2>::pair<U1,U2>(U1&&, U2&&) constructor, because x is
non-const and the pair<T1,T2>::first_type type is const. U2 gets deduced as
int, and int cannot convert to a pointer.
This code is just wrong and the standard says it should not compile, it should
be fixed to use p(x, nullptr).
p(std::as_const(x), 0) would also work, but is gross. Just use nullptr.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/101124] [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
` (3 preceding siblings ...)
2022-01-18 11:11 ` redi at gcc dot gnu.org
@ 2022-01-18 16:32 ` cvs-commit at gcc dot gnu.org
2022-01-18 16:37 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2022-01-18 16:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:
https://gcc.gnu.org/g:302343d8dd30e34516f74a61ec758d80a6c4d1db
commit r12-6691-g302343d8dd30e34516f74a61ec758d80a6c4d1db
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Jan 18 15:10:06 2022 +0000
libstdc++: Fix ambiguous std::pair constructors [PR101124]
The deprecated non-standard std::pair constructors that allow
constructing std::pair<move-only-type, pointer-type> from an rvalue and
a literal zero where not sufficiently constrained. They were viable when
constructing std::pair<copyable-type, pointer-type>, and that case
should work fine using the standard constructors.
Replace the constraints on the non-standard constructors so they are
only viable in cases that should actually be ill-formed according to the
standard.
Also rename __null_ptr_constant to __zero_as_null_pointer_constant so it
matches the name of the -Wzero-as-null-pointer-constant warning. Also
make the text of the deprecated warning describe the problem in more
detail.
libstdc++-v3/ChangeLog:
PR libstdc++/101124
* include/bits/stl_pair.h (pair): Adjust constraints on
deprecated constructors accepting literal zero as null pointer
constant. Improve wording of deprecated attribute.
* testsuite/20_util/pair/cons/99957.cc: Check that deprecated
constructors do not cause ambiguities for copyable types.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/101124] [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now
2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
` (4 preceding siblings ...)
2022-01-18 16:32 ` cvs-commit at gcc dot gnu.org
@ 2022-01-18 16:37 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2022-01-18 16:37 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101124
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed
^ permalink raw reply [flat|nested] 7+ messages in thread
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2021-06-18 13:33 [Bug libstdc++/101124] New: [12 Regression] pair<T*, int>(0, 0) was intended to be deprecated, but is rejected now redi at gcc dot gnu.org
2021-06-21 6:15 ` [Bug libstdc++/101124] " rguenth at gcc dot gnu.org
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