[Bug c++/94422] New: static_cast from std::array to enum class

[Bug c++/94422] New: static_cast from std::array to enum class

[vincent.hamp at higaski dot at]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

            Bug ID: 94422
           Summary: static_cast from std::array to enum class
           Product: gcc
           Version: 9.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincent.hamp at higaski dot at
  Target Milestone: ---

static_cast from std::array operator[] to an enum class inside a template class
produces an unexpected expression error. It seems that error is only present in
9.3, 9.2 and trunk work.

#include <array>
#include <cstdint>

enum class EnumC : int8_t { Forward = 1, Backward = -1 };

std::array<uint8_t, sizeof(EnumC)> buf;

template <typename T>
struct S {
  void foo() { auto const cast_to_enum{static_cast<EnumC>(buf[0])}; }
};

S<int> s;

[Bug c++/94422] [9 Regression] static_cast from std::array operator[] to enum class

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-03-31
      Known to work|                            |9.2.0
            Summary|static_cast from std::array |[9 Regression] static_cast
                   |operator[] to enum class    |from std::array operator[]
                   |                            |to enum class
      Known to fail|                            |9.3.0
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
You didn't say what gcc options you're using, and since this only happens with
C++17 or C++20 (not the default options) that's not very helpful.

Confirmed for -std=gnu++17

[Bug c++/94422] [9/10 Regression] static_cast from std::array operator[] to enum class

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[9 Regression] static_cast  |[9/10 Regression]
                   |from std::array operator[]  |static_cast from std::array
                   |to enum class               |operator[] to enum class
      Known to fail|                            |10.0

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:

// { dg-options "-std=gnu++17" }
template<typename T, unsigned N>
struct array
{
  T data[N];

  constexpr T& operator[](unsigned n) { return data[n]; }
};

enum class EnumC : signed char { Forward = 1, Backward = -1 };

array<unsigned char, sizeof(EnumC)> buf;

template <typename T>
struct S {
  void foo() { auto const cast_to_enum{static_cast<EnumC>(buf[0])}; }
};

S<int> s;

[Bug c++/94422] [9 Regression] static_cast from std::array operator[] to enum class

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |9.4
           Priority|P3                          |P2

[Bug c++/94422] [9 Regression] static_cast from std::array operator[] to enum class

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Started with r9-8323-gb4e53e9b3c963b1c0fe9637618dec8042764f599

[Bug c++/94422] [9 Regression] static_cast from std::array operator[] to enum class

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|9.4                         |9.5

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 9.4 is being released, retargeting bugs to GCC 9.5.

[Bug c++/94422] [9 Regression] static_cast from std::array operator[] to enum class

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94422

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|9.5                         |10.0

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed in GCC 10.