[clang] [C++20][Modules] Implement P1857R3 Modules Dependency Discovery (PR #107168)

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yronglin wrote:

> I see that CWG2947 test is unusual, because it take 9 RUN lines to test C++20 mode. I suggest you to group tests cases in fewer files, which should reduce the number of RUN lines. Then I'd like to see C++23 and C++26 modes tested.

>  Then I'd like to see C++23 and C++26 modes tested.

Done.

> I suggest you to group tests cases in fewer files, which should reduce the number of RUN lines.

Hmm, I kept 9 RUN lines and repeat it for C++23/26, because module/import directive lexical errors may cut-off lexing stage, so multiple module directive in the same file may impact the diagnostics, What do you think?


https://github.com/llvm/llvm-project/pull/107168