a few undefined behaviour casting enums

[gulafaran]

found a few enum casting out of range i got no idea how to solve cleanly. thought id atleast make a bugreport about them.

https://github.com/hyprwm/aquamarine/blob/890d6177b2e008b79ef037c676d39b957f1f463d/src/backend/Wayland.cpp#L684 https://github.com/hyprwm/aquamarine/blob/890d6177b2e008b79ef037c676d39b957f1f463d/src/backend/Wayland.cpp#L751

casting to 0, while generated enum is

enum zwpLinuxBufferParamsV1Flags : uint32_t {
    ZWP_LINUX_BUFFER_PARAMS_V1_FLAGS_Y_INVERT = 1,
    ZWP_LINUX_BUFFER_PARAMS_V1_FLAGS_INTERLACED = 2,
    ZWP_LINUX_BUFFER_PARAMS_V1_FLAGS_BOTTOM_FIRST = 4,
};

[vaxerski]

don't think we can escape the protocol ones.

[Ferdi265]

According to C++ standard [expr.static.cast] p.9, it's only UB if the enum doesn't have an underlying type. The flags enum has an underlying type, so the cast is fine.

GCC doesn't enforce this, but Clang seems to consider casts to enums without an underlying type to be UB if the value is one bit bigger than the largest enum member:

enum foo {
  FOO = 200
};

enum bar : int {
  BAR = 200
};

constexpr foo f1 = foo(0);
constexpr foo f2 = foo(100);
constexpr foo f3 = foo(256); // error on Clang "256 is outside the valid range of values for the enumeration type"
constexpr bar b1 = bar(0);
constexpr bar b2 = bar(100);
constexpr bar b3 = bar(256);

[gulafaran]

According to C++ standard [expr.static.cast] p.9, it's only UB if the enum doesn't have an underlying type. The flags enum has an underlying type, so the cast is fine.

GCC doesn't enforce this, but Clang seems to consider casts to enums without an underlying type to be UB if the value is one bit bigger than the largest enum member:

enum foo {
  FOO = 200
};

enum bar : int {
  BAR = 200
};

constexpr foo f1 = foo(0);
constexpr foo f2 = foo(100);
constexpr foo f3 = foo(256); // error on Clang "256 is outside the valid range of values for the enumeration type"
constexpr bar b1 = bar(0);
constexpr bar b2 = bar(100);
constexpr bar b3 = bar(256);

yeah we figured that out in a hyprpaper PR just yesterday, heh so im closing this one. thanks tho :)