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* [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays
@ 2020-03-11 18:41 redi at gcc dot gnu.org
2020-03-11 18:47 ` [Bug c++/94149] " redi at gcc dot gnu.org
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: redi at gcc dot gnu.org @ 2020-03-11 18:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
Bug ID: 94149
Summary: __is_constructible doesn't know about C++20
parenthesized init for arrays
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
In C++20 this is well-formed:
using T = int[2];
T t(1, 2);
which means that std::is_constructible_v<int[2], int, int> should be true.
The FE intrinsic gives the wrong answer, and the std::is_nothrow_constructible
library trait isn't going to work even if the intrinsic starts to give the
right answer.
i.e. this should compile with -std=gnu++2a
#include <type_traits>
int main()
{
using T = int[2];
T t(1, 2);
static_assert(__is_constructible(T, int, int));
static_assert(std::is_constructible_v<T, int, int>);
static_assert(std::is_nothrow_constructible_v<T, int, int>);
return t[0];
}
a.cc: In function 'int main()':
a.cc:8:17: error: static assertion failed
8 | static_assert(__is_constructible(T, int, int));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:9:22: error: static assertion failed
9 | static_assert(std::is_constructible_v<T, int, int>);
| ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
a.cc:10:22: error: static assertion failed
10 | static_assert(std::is_nothrow_constructible_v<T, int, int>);
| ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
@ 2020-03-11 18:47 ` redi at gcc dot gnu.org
2020-03-11 19:58 ` mpolacek at gcc dot gnu.org
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: redi at gcc dot gnu.org @ 2020-03-11 18:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-03-11
Ever confirmed|0 |1
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And of course __is_constructible(int[3], int, int) should work too.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
2020-03-11 18:47 ` [Bug c++/94149] " redi at gcc dot gnu.org
@ 2020-03-11 19:58 ` mpolacek at gcc dot gnu.org
2020-03-11 20:29 ` ville.voutilainen at gmail dot com
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-03-11 19:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mpolacek at gcc dot gnu.org
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |mpolacek at gcc dot gnu.org
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
C++20 paren-init -> mine.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
2020-03-11 18:47 ` [Bug c++/94149] " redi at gcc dot gnu.org
2020-03-11 19:58 ` mpolacek at gcc dot gnu.org
@ 2020-03-11 20:29 ` ville.voutilainen at gmail dot com
2020-04-09 21:03 ` mpolacek at gcc dot gnu.org
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: ville.voutilainen at gmail dot com @ 2020-03-11 20:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
Ville Voutilainen <ville.voutilainen at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ville.voutilainen at gmail dot com
--- Comment #3 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
(In reply to Marek Polacek from comment #2)
> C++20 paren-init -> mine.
This goes from constructible_expr into
perform_direct_initialization_if_possible, which then goes into
implicit_conversion, which fails to build a conversion.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
` (2 preceding siblings ...)
2020-03-11 20:29 ` ville.voutilainen at gmail dot com
@ 2020-04-09 21:03 ` mpolacek at gcc dot gnu.org
2020-04-10 17:55 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-04-09 21:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |patch, rejects-valid
--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Patch posted:
<https://gcc.gnu.org/pipermail/gcc-patches/2020-April/543670.html>
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
` (3 preceding siblings ...)
2020-04-09 21:03 ` mpolacek at gcc dot gnu.org
@ 2020-04-10 17:55 ` cvs-commit at gcc dot gnu.org
2020-04-10 17:56 ` mpolacek at gcc dot gnu.org
2020-04-21 21:19 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2020-04-10 17:55 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:
https://gcc.gnu.org/g:62c25d7adb1a5664982449dda0e7f9ca63cf4735
commit r10-7681-g62c25d7adb1a5664982449dda0e7f9ca63cf4735
Author: Marek Polacek <polacek@redhat.com>
Date: Thu Apr 9 16:31:59 2020 -0400
c++: make __is_constructible work with paren-init of aggrs [PR94149]
In C++20 this is well-formed:
using T = int[2];
T t(1, 2);
which means that std::is_constructible_v<int[2], int, int> should be true.
But constructible_expr immediately returned the error_mark_node when it
saw a list with more than one element. To give accurate results in
C++20, we have to try initializing the aggregate from a parenthesized list
of
values.
To not repeat the same mistake as in c++/93790, if there's only one
element, I'm trying {} only when () didn't succeed. is_constructible5.C
verifies this.
In paren-init24.C std::is_nothrow_constructible_v doesn't work due to
error: invalid 'static_cast' from type 'int' to type 'int [1]'
and
error: functional cast to array type 'int [2]'
This needs to be fixed in libstdc++.
PR c++/94149
* method.c (constructible_expr): In C++20, try using parenthesized
initialization of aggregates to determine the result of
__is_constructible.
* g++.dg/cpp2a/paren-init24.C: New test.
* g++.dg/cpp2a/paren-init25.C: New test.
* g++.dg/ext/is_constructible5.C: New test.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
` (4 preceding siblings ...)
2020-04-10 17:55 ` cvs-commit at gcc dot gnu.org
@ 2020-04-10 17:56 ` mpolacek at gcc dot gnu.org
2020-04-21 21:19 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-04-10 17:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug c++/94149] __is_constructible doesn't know about C++20 parenthesized init for arrays
2020-03-11 18:41 [Bug c++/94149] New: __is_constructible doesn't know about C++20 parenthesized init for arrays redi at gcc dot gnu.org
` (5 preceding siblings ...)
2020-04-10 17:56 ` mpolacek at gcc dot gnu.org
@ 2020-04-21 21:19 ` cvs-commit at gcc dot gnu.org
6 siblings, 0 replies; 8+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2020-04-21 21:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94149
--- Comment #7 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:d76925e46fad09fc9be6759cbf1f23c9a8344dbf
commit r10-7856-gd76925e46fad09fc9be6759cbf1f23c9a8344dbf
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Apr 21 22:18:51 2020 +0100
libstdc++: Support arrays in std::is_nothrow_constructible (PR 94149)
The front end now supports parenthesized initialization for arrays in
C++20, so extend std::is_nothrow_constructible to support them too.
gcc/testsuite:
PR c++/94149
* g++.dg/cpp2a/paren-init24.C: Fix FIXMEs.
libstdc++-v3:
PR c++/94149
* include/std/type_traits (__is_nt_constructible_impl): Add partial
specializations for bounded arrays with non-empty initializers.
* testsuite/20_util/is_nothrow_constructible/value_c++20.cc: New
test.
^ permalink raw reply [flat|nested] 8+ messages in thread
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2020-03-11 18:47 ` [Bug c++/94149] " redi at gcc dot gnu.org
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