[libc-commits] [libc] [libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration (PR #98075)

[Joseph Huber via libc-commits]

jhuber6 wrote:

> > So, this replaces every single namespace declaration with the following?
> > ```c
> > #define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] LIBC_NAMESPACE
> > ```
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> > Before that we need to identify all the entrypoints and make sure they retain default visibility. @frobtech suggested that we split that up into introducing a macro for exporting global variables, then we'd need to make sure that `LIBC_FUNCTION_ATTRS` includes default visibility.
> > However, that's if we want non-hidden visibility at all. The main effect of everything being hidden is that if someone does `clang -shared foo.c -lc` with our `libc` the symbols won't be visible from the shared library. Maybe that's the desired behavior? The GPU doesn't care because we have no shared libraries.
> 
> Correct, although it's currently incomplete. Specifically because `LIBC_NAMESPACE_DECL` is declared in `libc/src/__support/macros/config.h`, any file that uses it needs an additional `#include`. I'm trying to see if I can automate this using `clang-include-fixer` rather than doing this manually. Similarly, we also need need to update the CMake files to introduce the additional dependency which I don't yet have a solution for.

Alright, so this is basically the effect of compiling with `-fvisibility=hidden` by manually putting every single declaration into the namespace. Though we also need to fix the clang-tidy rule or else it will be really annoying.

https://github.com/llvm/llvm-project/pull/98075