https://github.com/ChuanqiXu9 created https://github.com/llvm/llvm-project/pull/102572
Motivated by https://github.com/llvm/llvm-project/issues/101348 Although I don't want the tool's doc to explain the standard's wording, the wording itself has some unspecified thing. So I feel it will be helpful to make it clear. At least it may help us receive less invalid issue reports. >From c5766b29042cd5109c22f7c399ebc33ffd0f6b3b Mon Sep 17 00:00:00 2001 From: Chuanqi Xu <yedeng...@linux.alibaba.com> Date: Fri, 9 Aug 2024 13:48:35 +0800 Subject: [PATCH] [Doc] [C++20] [Modules] Clarify the reachability of internal partition units --- clang/docs/StandardCPlusPlusModules.rst | 51 +++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/clang/docs/StandardCPlusPlusModules.rst b/clang/docs/StandardCPlusPlusModules.rst index 2478a77e7640c5..bf076d74ca41e4 100644 --- a/clang/docs/StandardCPlusPlusModules.rst +++ b/clang/docs/StandardCPlusPlusModules.rst @@ -1230,6 +1230,57 @@ parsing their headers, those should be included after the import. If the imported modules don't provide such a header, one can be made manually for improved compile time performance. +Reachability of internal partition units +---------------------------------------- + +The internal partition units are called as implementation partition unit somewhere else. +But the name may be confusing since implementation partition units are not implementation +units. + +According to [module.reach]p1,2: + + A translation unit U is necessarily reachable from a point P if U is a module + interface unit on which the translation unit containing P has an interface + dependency, or the translation unit containing P imports U, in either case + prior to P. + + All translation units that are necessarily reachable are reachable. Additional + translation units on which the point within the program has an interface + dependency may be considered reachable, but it is unspecified which are and + under what circumstances. + +For example, + +.. code-block:: c++ + + // a.cpp + import B; + int main() + { + g<void>(); + } + + // b.cppm + export module B; + import :C; + export template <typename T> inline void g() noexcept + { + return f<T>(); + } + + // c.cppm + module B:C; + template<typename> inline void f() noexcept {} + +The internal partition units ``c.cppm`` is not necessarily reachable to +``a.cpp`` since ``c.cppm`` is not a module interface unit and ``a.cpp`` +doesn't import ``c.cppm``. Then it is up to the compiler to decide if +``c.cppm`` is reachable to ``a.cpp`` or not. Clang's decision is the +non-directly imported internal partition units are not reachable. + +The suggestion to use internal partition units is, only import them in +the implementation units unless we understand the codebases very well. + Known Issues ------------ _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
