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

[Hubert Tong via cfe-commits]

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@@ -986,6 +989,14 @@ def warn_module_conflict : Warning<
   InGroup<ModuleConflict>;
 
 // C++20 modules
+def err_pp_module_name_is_macro : Error<
+  "%select{module|partition}0 name component %1 cannot be a object-like macro">;
+def err_pp_module_expected_ident : Error<
+  "expected %select{identifier after '.' in |}0module name">;
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hubert-reinterpretcast wrote:

> We have a utility function `isNextPPTokenOneOf`, let me try. but it's disabled macro expansion.

If you mean that it determines what the next token is without trying to expand that token (if it is a macro name), then that's exactly what we want for the `(` restriction. It's the `;`/`[` check that needs to be done after macro expansion.

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