| Issue |
125180
|
| Summary |
Underlying type of unscoped and unfixed member enumerations of class templates
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
thebrandre
|
If compatibility with MSVC is enabled, Clang correctly uses `int` as the underlying type of an unscoped enumeration even if the assigned integer causes an overflow - at least at namespace scope. This is correct in the sense of compatibility, which is officially documented by Microsoft [here](https://learn.microsoft.com/en-us/cpp/build/reference/zc-enumtypes?view=msvc-170).
However, if the same declaration appears inside a class template, `-fms-compatibility` is not honored.
```cpp
template <typename T>
struct S {
enum E { X, Y = 0xFFFFFFFF };
};
enum E { X, Y = 0xFFFFFFFF };
constexpr bool check(int) { return true; }
constexpr bool check(unsigned int) { return false; }
static_assert(check(E::X), ""); // succeeds
static_assert(check(S<char>::E::X), ""); // fails
```
See here on Compiler Explorer: https://godbolt.org/z/Ge8qehE5P
I am aware that there are a lot of open issues on the underlying type of enumerations when using `-fms-compatibility` (#120759 #122032 #1883 to name a few) but this one should be orthogonal.
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