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The headers that include_next compiler and OS headers need to be in different top level modules in order to avoid module cycles. e.g. libc++'s stdlib.h will #include_next stdlib.h from the compiler and then the C library. Either of those are likely to include stddef.h, which will come back up to the libc++ module map and create a module cycle. Putting stdlib.h and stddef.h (and the rest of the C standard library headers) in top level modules resolves this by letting the order go cxx_stdlib_h -> os_stdlib_h -> cxx_stddef_h -> os_stddef_h. All of those headers' dependencies then need to be moved into top level modules themselves to avoid module cycles between the new top level level cstd modules. This starts to get complicated, as the libc++ C headers, by standard, have to include many of the C++ headers, which include the private detail headers, which are intertwined. e.g. some `__algorithm` headers include `__memory` headers and vice versa. Make top level modules for all of the libc++ headers to easily guarantee that the modules aren't cyclic. Add enough module exports to fix `check-cxx` and `run-buildbot generic-modules`. `__stop_token/intrusive_shared_ptr.h` uses `__atomic/atomic.h` but has no include path to it. Add that include. `math.h` absorbs `bits/atomic_wide_counter.h` on some platforms that don't have modules, work around that by including `math.h` in `__threading_support`. <mutex> doesn't actually require threads, there are a few pieces like once_flag that work without threads. Remove the requirement from its module. AIX is no longer able to support modular builds. Reviewed By: ldionne, #libc Differential Revision: https://reviews.llvm.org/D144322
libc++ Documentation ==================== The libc++ documentation is written using the Sphinx documentation generator. It is currently tested with Sphinx 1.1.3. To build the documents into html configure libc++ with the following cmake options: * -DLLVM_ENABLE_SPHINX=ON * -DLIBCXX_INCLUDE_DOCS=ON After configuring libc++ with these options the make rule `docs-libcxx-html` should be available. The documentation in this directory is published at https://libcxx.llvm.org. It is kept up-to-date by a build bot: https://lab.llvm.org/buildbot/#/builders/publish-sphinx-docs. If you notice that the documentation is not updating anymore, please contact one of the maintainers.