* [Bug c++/100396] [11.1 regression] The template function overload is not selected correctly
2021-05-03 14:41 [Bug c++/100396] New: [11.1 regression] The template function overload is not selected correctly vopl at bk dot ru
@ 2021-05-03 15:14 ` ppalka at gcc dot gnu.org
2021-05-03 16:07 ` vopl at bk dot ru
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-05-03 15:14 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100396
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
CC| |ppalka at gcc dot gnu.org
--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Thanks for the bug report. It looks like we started rejecting this after
r11-2774.
The testcase is invalid, I think. You need to declare 'valid' as a concept
instead of a constexpr variable so that substitution failure during constraint
checking of the first overload of 'ovr' is a SFINAE error.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug c++/100396] [11.1 regression] The template function overload is not selected correctly
2021-05-03 14:41 [Bug c++/100396] New: [11.1 regression] The template function overload is not selected correctly vopl at bk dot ru
2021-05-03 15:14 ` [Bug c++/100396] " ppalka at gcc dot gnu.org
@ 2021-05-03 16:07 ` vopl at bk dot ru
2021-05-03 17:59 ` ppalka at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: vopl at bk dot ru @ 2021-05-03 16:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100396
--- Comment #2 from vopl at bk dot ru ---
Please, try this, also failed
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
template<class F, class... Args> struct Checker
{
using Some = decltype(F{}(Args{}...));
};
template<class F, class... Args> concept valid =
requires { typename Checker<F, Args...>::Some; };
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
template<class F, class... Args> auto ovr(F f, Args... args)
requires valid<F, Args...>
{
return ovr<F, Args...>(int{}, f, args...); // a second ovr is expected to
be called, but the compiler tries to call this ovr again. Collision between
'int' and 'F' is ignored, extra Args provided to call
}
template<class F, class... Args> auto ovr(int, F f, Args... args)
{
return f(args...);
}
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
void use()
{
ovr([]{});
}
$ g++-11.1.0 -std=c++20 -c src.cpp
src.cpp: In instantiation of 'struct Checker<use()::<lambda()>,
use()::<lambda()> >':
src.cpp:8:25: required by substitution of 'template<class F, class ... Args>
auto ovr(F, Args ...) requires valid<F, Args ...> [with F = use()::<lambda()>;
Args = {use()::<lambda()>}]'
src.cpp:14:27: required from 'auto ovr(F, Args ...) requires valid<F, Args
...> [with F = use()::<lambda()>; Args = {}]'
src.cpp:25:8: required from here
src.cpp:4:30: error: no match for call to '(use()::<lambda()>)
(use()::<lambda()>)'
4 | using Some = decltype(F{}(Args{}...));
| ~~~^~~~~~~~~~~
src.cpp:4:30: note: candidate: 'void (*)()' (conversion)
src.cpp:4:30: note: candidate expects 1 argument, 2 provided
src.cpp:25:9: note: candidate: 'use()::<lambda()>'
25 | ovr([]{});
| ^
src.cpp:25:9: note: candidate expects 0 arguments, 1 provided
----------
IMHO, the problem is not caused by concepts, but caused by corrupted
overloading selection mechanic. Please, take a look at the collision between
argument 'int{}' and first template parameter specified as 'F'. Next, no SFINAE
expected in this case due to correct overloading, but overloading failed and
SFINAE happens. Thanks.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug c++/100396] [11.1 regression] The template function overload is not selected correctly
2021-05-03 14:41 [Bug c++/100396] New: [11.1 regression] The template function overload is not selected correctly vopl at bk dot ru
2021-05-03 15:14 ` [Bug c++/100396] " ppalka at gcc dot gnu.org
2021-05-03 16:07 ` vopl at bk dot ru
@ 2021-05-03 17:59 ` ppalka at gcc dot gnu.org
2021-05-04 10:08 ` vopl at bk dot ru
2021-05-04 14:29 ` [Bug c++/100396] [11 " ppalka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-05-03 17:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100396
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to vopl from comment #2)
> Please, try this, also failed
>
> /////////0/////////1/////////2/////////3/////////4/////////5/////////6///////
> //7
> template<class F, class... Args> struct Checker
> {
> using Some = decltype(F{}(Args{}...));
> };
>
> template<class F, class... Args> concept valid =
> requires { typename Checker<F, Args...>::Some; };
>
> /////////0/////////1/////////2/////////3/////////4/////////5/////////6///////
> //7
> template<class F, class... Args> auto ovr(F f, Args... args)
> requires valid<F, Args...>
> {
> return ovr<F, Args...>(int{}, f, args...); // a second ovr is expected
> to be called, but the compiler tries to call this ovr again. Collision
> between 'int' and 'F' is ignored, extra Args provided to call
> }
>
> template<class F, class... Args> auto ovr(int, F f, Args... args)
> {
> return f(args...);
> }
>
> /////////0/////////1/////////2/////////3/////////4/////////5/////////6///////
> //7
> void use()
> {
> ovr([]{});
> }
>
>
> $ g++-11.1.0 -std=c++20 -c src.cpp
> src.cpp: In instantiation of 'struct Checker<use()::<lambda()>,
> use()::<lambda()> >':
> src.cpp:8:25: required by substitution of 'template<class F, class ...
> Args> auto ovr(F, Args ...) requires valid<F, Args ...> [with F =
> use()::<lambda()>; Args = {use()::<lambda()>}]'
> src.cpp:14:27: required from 'auto ovr(F, Args ...) requires valid<F,
> Args ...> [with F = use()::<lambda()>; Args = {}]'
> src.cpp:25:8: required from here
> src.cpp:4:30: error: no match for call to '(use()::<lambda()>)
> (use()::<lambda()>)'
> 4 | using Some = decltype(F{}(Args{}...));
> | ~~~^~~~~~~~~~~
> src.cpp:4:30: note: candidate: 'void (*)()' (conversion)
> src.cpp:4:30: note: candidate expects 1 argument, 2 provided
> src.cpp:25:9: note: candidate: 'use()::<lambda()>'
> 25 | ovr([]{});
> | ^
> src.cpp:25:9: note: candidate expects 0 arguments, 1 provided
>
> ----------
> IMHO, the problem is not caused by concepts, but caused by corrupted
> overloading selection mechanic. Please, take a look at the collision between
> argument 'int{}' and first template parameter specified as 'F'. Next, no
> SFINAE expected in this case due to correct overloading, but overloading
> failed and SFINAE happens. Thanks.
Although the collision between 'int{}' and the template argument for 'F' does
mean that the first overload ultimately isn't viable, the compiler as per
CWG2369 first needs to check the overload's constraints (using the
provided/deduced template arguments) _before_ checking whether 'int' is
convertible to 'F', and it's during this constraint checking we hit the hard
error. So as far as I can tell, the compiler is behaving as specified. See
also PR99599 and its related PRs.
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug c++/100396] [11.1 regression] The template function overload is not selected correctly
2021-05-03 14:41 [Bug c++/100396] New: [11.1 regression] The template function overload is not selected correctly vopl at bk dot ru
` (2 preceding siblings ...)
2021-05-03 17:59 ` ppalka at gcc dot gnu.org
@ 2021-05-04 10:08 ` vopl at bk dot ru
2021-05-04 14:29 ` [Bug c++/100396] [11 " ppalka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: vopl at bk dot ru @ 2021-05-04 10:08 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100396
--- Comment #4 from vopl at bk dot ru ---
I understand what you're saying. But, apparently, there is still corruption in
the calculus of the substituted Args, please look at this code (thanks to
johny5):
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
template<class F, class... Args> struct Checker
{
using Some = decltype(F{}(Args{}...));
};
template<class F, class... Args> concept valid =
requires { typename Checker<F, Args...>::Some; };
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
template<class F, class... Args> auto ovr(F f, Args... args)
requires valid<F, Args...>
{
return ovr<F, Args...>(int{}, f, args...);
}
template<class F, class... Args> auto ovr(int, F f, Args... args)
{
return f(args...);
}
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
void use()
{
ovr([](double){}, 2.);
}
-----------------------
<source>: In instantiation of 'struct Checker<use()::<lambda(double)>, double,
double>':
<source>:8:25: required by substitution of 'template<class F, class ... Args>
auto ovr(F, Args ...) requires valid<F, Args ...> [with F =
use()::<lambda(double)>; Args = {double, double}]'
<source>:14:27: required from 'auto ovr(F, Args ...) requires valid<F, Args
...> [with F = use()::<lambda(double)>; Args = {double}]'
<source>:25:8: required from here
<source>:4:30: error: no match for call to '(use()::<lambda(double)>) (double,
double)'
4 | using Some = decltype(F{}(Args{}...));
| ~~~^~~~~~~~~~~
<source>:4:30: note: candidate: 'void (*)(double)' (conversion)
<source>:4:30: note: candidate expects 2 arguments, 3 provided
<source>:25:9: note: candidate: 'use()::<lambda(double)>'
25 | ovr([](double){}, 2.);
| ^
<source>:25:9: note: candidate expects 1 argument, 2 provided
Take attention at 'Args' - it was {double} initially, but becomes {double,
double} for second ovr call
^ permalink raw reply [flat|nested] 6+ messages in thread* [Bug c++/100396] [11 regression] The template function overload is not selected correctly
2021-05-03 14:41 [Bug c++/100396] New: [11.1 regression] The template function overload is not selected correctly vopl at bk dot ru
` (3 preceding siblings ...)
2021-05-04 10:08 ` vopl at bk dot ru
@ 2021-05-04 14:29 ` ppalka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-05-04 14:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100396
--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to vopl from comment #4)
> Take attention at 'Args' - it was {double} initially, but becomes {double,
> double} for second ovr call.
That seems correct to me. The second ovr call has three function arguments,
and two explicit template arguments. The first double in Args={double,double}
comes from the second explicit template argument. The second double is deduced
from the third function argument.
^ permalink raw reply [flat|nested] 6+ messages in thread