C23 constexpr should not have external linkage

[gustedt]

Hi,
thanks for implementing constexpr for clang-19!

The following code

constexpr int category_width = 5;
int const w = 5;
int const* a = &category_width;

compiles, but produces an external symbol for category_width and then multiple defined symbol errors on linkage. So I cannot use constexpr in header files, or I'd have to prefix it with static, which defeats the purpose of constexpr ...

C23 has in 6.2.2 p3

If the declaration of a file scope identifier for:
— an object contains any of the storage-class specifiers static or constexpr;
— or, a function contains the storage-class specifier static,
then the identifier has internal linkage.

Thanks
Jens

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Jens Gustedt (gustedt)

Hi, thanks for implementing `constexpr` for clang-19!

The following code

constexpr int category_width = 5;
int const w = 5;
int const* a = &category_width;

compiles, but produces an external symbol for category_width and then multiple defined symbol errors on linkage. So I cannot use constexpr in header files, or I'd have to prefix it with static, which defeats the purpose of constexpr ...

C23 has in 6.2.2 p3

> If the declaration of a file scope identifier for:
> — an object contains any of the storage-class specifiers static or constexpr;
> — or, a function contains the storage-class specifier static,
> then the identifier has internal linkage.

Thanks
Jens

[chestnykh]

Can i assign this issue to myself?