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* [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const
@ 2021-03-17 17:38 johelegp at gmail dot com
2021-03-18 13:20 ` [Bug c++/99631] " redi at gcc dot gnu.org
` (13 more replies)
0 siblings, 14 replies; 15+ messages in thread
From: johelegp at gmail dot com @ 2021-03-17 17:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Bug ID: 99631
Summary: decltype of non-type template-parameter shouldn't be
const
Product: gcc
Version: 11.0
URL: https://godbolt.org/z/4YY5r3
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: johelegp at gmail dot com
CC: johelegp at gmail dot com
Target Milestone: ---
See https://godbolt.org/z/4YY5r3.
```C++
#include<type_traits>
template<auto V>constexpr bool is_const=std::is_const_v<decltype(V)>;
struct A{};
static_assert(!is_const<A{}>);
```
```
<source>:4:15: error: static assertion failed
4 | static_assert(!is_const<A{}>);
| ^~~~~~~~~~~~~~
Compiler returned: 1
```
See https://bugs.llvm.org/show_bug.cgi?id=49609#c1 for an explanation.
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
@ 2021-03-18 13:20 ` redi at gcc dot gnu.org
2021-03-18 13:48 ` jakub at gcc dot gnu.org
` (12 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: redi at gcc dot gnu.org @ 2021-03-18 13:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2021-03-18
Status|UNCONFIRMED |NEW
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I'm not sure "rejects-valid" is appropriate, as it only fails to compile
because of the static assert (i.e. you've asked for it).
But wrong-code isn't really right either, because this is before any codegen
happens. Every bug in metaprogramming results can be turned into
accepts-invalid or rejects-valid or wrong-code, but none of those keywords is
really specific to the actual form of the bug. Maybe we need a new keyword (and
no, meta-bug is it either ;-).
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
2021-03-18 13:20 ` [Bug c++/99631] " redi at gcc dot gnu.org
@ 2021-03-18 13:48 ` jakub at gcc dot gnu.org
2021-03-18 23:44 ` johelegp at gmail dot com
` (11 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-03-18 13:48 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So, do we implement the http://eel.is/c++draft/dcl.type#decltype-1.2 point
anywhere?
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
2021-03-18 13:20 ` [Bug c++/99631] " redi at gcc dot gnu.org
2021-03-18 13:48 ` jakub at gcc dot gnu.org
@ 2021-03-18 23:44 ` johelegp at gmail dot com
2021-11-09 17:23 ` n60wb42d2 at relay dot firefox.com
` (10 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: johelegp at gmail dot com @ 2021-03-18 23:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
--- Comment #3 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Good point. How about 'conformance' for a keyword?
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (2 preceding siblings ...)
2021-03-18 23:44 ` johelegp at gmail dot com
@ 2021-11-09 17:23 ` n60wb42d2 at relay dot firefox.com
2022-09-26 1:46 ` johelegp at gmail dot com
` (9 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: n60wb42d2 at relay dot firefox.com @ 2021-11-09 17:23 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
n60wb42d2 at relay dot firefox.com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |n60wb42d2 at relay dot firefox.com
--- Comment #4 from n60wb42d2 at relay dot firefox.com ---
(In reply to Jonathan Wakely from comment #1)
> I'm not sure "rejects-valid" is appropriate, as it only fails to compile
> because of the static assert (i.e. you've asked for it).
Here it `rejects-valid`:
```c++
struct param{};
template<typename>
struct t;
template<>
struct t<param>{};
template<param... p>
auto test()
{
(void)t<decltype(p)...>{};
}
int main()
{
test<param{}>();
}
```
```
<source>:11:5: error: invalid use of incomplete type 'struct t<const param>'
11 | (void)t<decltype(p)...>{};
```
https://godbolt.org/z/MKxx1dobT
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (3 preceding siblings ...)
2021-11-09 17:23 ` n60wb42d2 at relay dot firefox.com
@ 2022-09-26 1:46 ` johelegp at gmail dot com
2022-09-26 1:47 ` johelegp at gmail dot com
` (8 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: johelegp at gmail dot com @ 2022-09-26 1:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
--- Comment #5 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Would the existing 'wrong-code' work?
> Generates incorrect code. Has to be able to compile and link.
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (4 preceding siblings ...)
2022-09-26 1:46 ` johelegp at gmail dot com
@ 2022-09-26 1:47 ` johelegp at gmail dot com
2022-12-26 17:10 ` pinskia at gcc dot gnu.org
` (7 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: johelegp at gmail dot com @ 2022-09-26 1:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
--- Comment #6 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
> But wrong-code isn't really right either [...]
Oh, you already mentioned them. I suggest 'non-conforming-result', or something
more appropriate than "result" to indicate the metaprogrammingness of it.
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (5 preceding siblings ...)
2022-09-26 1:47 ` johelegp at gmail dot com
@ 2022-12-26 17:10 ` pinskia at gcc dot gnu.org
2023-09-15 17:38 ` ppalka at gcc dot gnu.org
` (6 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-12-26 17:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |danakj at orodu dot net
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 108169 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (6 preceding siblings ...)
2022-12-26 17:10 ` pinskia at gcc dot gnu.org
@ 2023-09-15 17:38 ` ppalka at gcc dot gnu.org
2023-09-15 17:39 ` ppalka at gcc dot gnu.org
` (5 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-09-15 17:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
Resolution|--- |DUPLICATE
Status|NEW |RESOLVED
--- Comment #8 from Patrick Palka <ppalka at gcc dot gnu.org> ---
dup of PR98820
*** This bug has been marked as a duplicate of bug 98820 ***
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (7 preceding siblings ...)
2023-09-15 17:38 ` ppalka at gcc dot gnu.org
@ 2023-09-15 17:39 ` ppalka at gcc dot gnu.org
2023-09-15 17:41 ` ppalka at gcc dot gnu.org
` (4 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-09-15 17:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |ASSIGNED
Resolution|DUPLICATE |---
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
--- Comment #9 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Actually it's probably better to mark PR98820 as the dup
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (8 preceding siblings ...)
2023-09-15 17:39 ` ppalka at gcc dot gnu.org
@ 2023-09-15 17:41 ` ppalka at gcc dot gnu.org
2023-09-19 12:21 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-09-15 17:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |davveston at gmail dot com
--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 98820 has been marked as a duplicate of this bug. ***
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (9 preceding siblings ...)
2023-09-15 17:41 ` ppalka at gcc dot gnu.org
@ 2023-09-19 12:21 ` cvs-commit at gcc dot gnu.org
2023-09-24 18:42 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
13 siblings, 0 replies; 15+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-09-19 12:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
--- Comment #11 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:ddd064e3571c4a9e6258c75eba65585a07367712
commit r14-4137-gddd064e3571c4a9e6258c75eba65585a07367712
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Sep 19 08:21:05 2023 -0400
c++: constness of decltype of NTTP object [PR99631]
This corrects resolving decltype of a (class) NTTP object as per
[dcl.type.decltype]/1.2 and [temp.param]/6 in the type-dependent case.
Note that in the non-dependent case we resolve the decltype ahead of
time, in which case finish_decltype_type drops the const VIEW_CONVERT_EXPR
wrapper around the TEMPLATE_PARM_INDEX, and the latter has the desired
non-const type.
In the type-dependent case, at instantiation time tsubst drops the
VIEW_CONVERT_EXPR since the substituted NTTP is the already-const object
created by get_template_parm_object. So in this case finish_decltype_type
sees the const object, which this patch now adds special handling for.
PR c++/99631
gcc/cp/ChangeLog:
* semantics.cc (finish_decltype_type): For an NTTP object,
return its type modulo cv-quals.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/nontype-class60.C: New test.
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (10 preceding siblings ...)
2023-09-19 12:21 ` cvs-commit at gcc dot gnu.org
@ 2023-09-24 18:42 ` cvs-commit at gcc dot gnu.org
2023-09-24 18:44 ` ppalka at gcc dot gnu.org
2023-09-24 19:13 ` danakj at orodu dot net
13 siblings, 0 replies; 15+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-09-24 18:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:b9e02590f7d35f1f8e8e95ab1f2e30f24113f551
commit r13-7835-gb9e02590f7d35f1f8e8e95ab1f2e30f24113f551
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue Sep 19 08:21:05 2023 -0400
c++: constness of decltype of NTTP object [PR99631]
This corrects resolving decltype of a (class) NTTP object as per
[dcl.type.decltype]/1.2 and [temp.param]/6 in the type-dependent case.
Note that in the non-dependent case we resolve the decltype ahead of
time, in which case finish_decltype_type drops the const VIEW_CONVERT_EXPR
wrapper around the TEMPLATE_PARM_INDEX, and the latter has the desired
non-const type.
In the type-dependent case, at instantiation time tsubst drops the
VIEW_CONVERT_EXPR since the substituted NTTP is the already-const object
created by get_template_parm_object. So in this case finish_decltype_type
sees the const object, which this patch now adds special handling for.
PR c++/99631
gcc/cp/ChangeLog:
* semantics.cc (finish_decltype_type): For an NTTP object,
return its type modulo cv-quals.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/nontype-class60.C: New test.
(cherry picked from commit ddd064e3571c4a9e6258c75eba65585a07367712)
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (11 preceding siblings ...)
2023-09-24 18:42 ` cvs-commit at gcc dot gnu.org
@ 2023-09-24 18:44 ` ppalka at gcc dot gnu.org
2023-09-24 19:13 ` danakj at orodu dot net
13 siblings, 0 replies; 15+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-09-24 18:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Target Milestone|--- |13.3
Resolution|--- |FIXED
--- Comment #13 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13.3 / 14.
^ permalink raw reply [flat|nested] 15+ messages in thread
* [Bug c++/99631] decltype of non-type template-parameter shouldn't be const
2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
` (12 preceding siblings ...)
2023-09-24 18:44 ` ppalka at gcc dot gnu.org
@ 2023-09-24 19:13 ` danakj at orodu dot net
13 siblings, 0 replies; 15+ messages in thread
From: danakj at orodu dot net @ 2023-09-24 19:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99631
--- Comment #14 from danakj at orodu dot net ---
Thank you =)
^ permalink raw reply [flat|nested] 15+ messages in thread
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2021-03-17 17:38 [Bug c++/99631] New: decltype of non-type template-parameter shouldn't be const johelegp at gmail dot com
2021-03-18 13:20 ` [Bug c++/99631] " redi at gcc dot gnu.org
2021-03-18 13:48 ` jakub at gcc dot gnu.org
2021-03-18 23:44 ` johelegp at gmail dot com
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2022-09-26 1:46 ` johelegp at gmail dot com
2022-09-26 1:47 ` johelegp at gmail dot com
2022-12-26 17:10 ` pinskia at gcc dot gnu.org
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