[all-commits] [llvm/llvm-project] 226409: [libc++] Only include_next C library headers when ...

[Louis Dionne via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 226409c62879bf5ff9928cd23a4255cd7c614fe0
      https://github.com/llvm/llvm-project/commit/226409c62879bf5ff9928cd23a4255cd7c614fe0
  Author: Louis Dionne <ldionne.2 at gmail.com>
  Date:   2022-11-15 (Tue, 15 Nov 2022)

  Changed paths:
    M libcxx/include/complex.h
    M libcxx/include/ctype.h
    M libcxx/include/errno.h
    M libcxx/include/fenv.h
    M libcxx/include/float.h
    M libcxx/include/inttypes.h
    M libcxx/include/limits.h
    M libcxx/include/locale.h
    M libcxx/include/math.h
    M libcxx/include/setjmp.h
    M libcxx/include/stdbool.h
    M libcxx/include/stddef.h
    M libcxx/include/stdint.h
    M libcxx/include/stdio.h
    M libcxx/include/stdlib.h
    M libcxx/include/string.h
    M libcxx/include/tgmath.h
    M libcxx/include/wchar.h

  Log Message:
  -----------
  [libc++] Only include_next C library headers when they exist

Some platforms don't provide all C library headers. In practice, libc++
only requires a few C library headers to exist, and only a few functions
on those headers. Missing functions that libc++ doesn't need for its own
implementation are handled properly by the using_if_exists attribute,
however a missing header is currently a hard error when we try to
do #include_next.

This patch should make libc++ more flexible on platforms that do not
provide C headers that libc++ doesn't actually require for its own
implementation. The only downside is that it may move some errors from
the #include_next point to later in the compilation if we actually try
to use something that isn't provided, which could be somewhat confusing.
However, these errors should be caught by folks trying to port libc++
over to a new platform (when running the libc++ test suite), not by end
users.

Differential Revision: https://reviews.llvm.org/D136683