[libcxx-commits] [libcxx] [libc++] Avoid including vector in <functional> (PR #144310)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Summarizing our live discussion just now.

The breaking change contained in this patch is that we don't provide the declaration for `std::vector` anymore in C++23/C++26. It's not about including the `<vector>` public header from `<functional>` specifically, it's about the set of declarations that we provide from a header. The set of public headers we transitively include is just a proxy to that, and it's a proxy that used to work better than it does nowadays (since everything is granularized). But still, I think we agree on the intent of providing a somewhat stable set of declarations from `<functional>` and other public headers.

Hence, I think we agreed that this patch can move forward if it includes `<__vector/vector.h>` from `<functional>` for backwards compatibility.

https://github.com/llvm/llvm-project/pull/144310