[Bug c++/87999] Constexpr eval. in static_assert makes string_view comparison non constexpr

[wieichdashasse at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87999

Justin Meyer  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |FIXED

--- Comment #2 from Justin Meyer  ---
This seems to be fixed in trunk. can't seem to find the commit that fixed it
though.

[Bug c++/87999] New: Constexpr eval. in static_assert makes string_view comparison non constexpr

[wieichdashasse at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87999

Bug ID: 87999
   Summary: Constexpr eval. in static_assert makes string_view
comparison non constexpr
   Product: gcc
   Version: 9.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: wieichdashasse at gmail dot com
  Target Milestone: ---

Hey,

I see an inconsistency when using gcc compared to other compilers when using a
constexpr return directly in a (constexpr) static_assert


Minimal repro:

#include 

constexpr bool IsValid_impl
(std::string_view name)
{
return name == "Steve";
}

template
constexpr void IsValid(F func)
{
// Using it via intermediate will make it work
// constexpr auto tmp = IsValid_impl(func());
// static_assert(tmp);
static_assert(IsValid_impl(func()));
}

int main()
{
IsValid([]{ return "Steve";});
}

(as featured in 
https://godbolt.org/z/YCVMRp)


Output:
test.cpp: In instantiation of 'constexpr void IsValid(F) [with F =
main()::]':

prog.cpp: In instantiation of 'constexpr void IsValid(F) [with F =
main()::]':
prog.cpp:20:46:   required from here
prog.cpp:15:31: error: non-constant condition for static assertion
   15 | static_assert(IsValid_impl(func()));
  |   ^~~~


Adding the intermediate makes it work, hence i think it is a bug.
I've tested this on 8.2.0, 9.0, 7.3.0 and 7.2.0

Cheers,
Justin Meyer