It seems that some C code likes to use static inline to indicate that a function should be inlined, but this is inconsistent with C++ conventions. In C++, namespace-scope static inline is useless, and it also hinders the adoption of modules in two different aspects:

When an external library declares a function as static inline, you cannot wrap that function as a module because functions with internal linkage cannot be declared as exported.

When an external library declares a function as static inline, you cannot call that function from an exported inline function within your own module, because doing so would expose TU-local entities.

I believe this is not an isolated case, because Windows' UCRT made this mistake, which blocked the STL for more than five years, and LLVM also made this mistake, causing many SIMD intrinsic functions to be unavailable. In my own experience,  I have found that some Windows headers still have this problem, even though these headers only support C++, and the problem also exists in other codebases. Therefore, I propose deprecating namespace-scope declarations that are declared both static and inline, and encouraging compilers to issue warnings in older standard modes. This will help existing code migrate to modules. Any such issue can seriously block C++'s progress toward modularization. If the standard deprecates them and implementations issue appropriate warnings, they can be recognized more quickly and addressed individually.