[clang] [C++20][Modules] Omit imported PCM file info for explicitly mapped header units (PR #235597)

[Chuanqi Xu via cfe-commits]

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@@ -1607,9 +1609,19 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, StringRef isysroot) {
       AddStringBlob(M.ModuleName, Record, Blob);
       Record.push_back(M.StandardCXXModule);
 
-      // We don't want to hard code the information about imported modules
-      // in the C++20 named modules.
-      if (M.StandardCXXModule) {
+      // We don't want to hard code file information for C++20 Modules
+      // (including explicitly mapped header units).
+      const Module *ImportedModule =
+          PP.getHeaderSearchInfo().getModuleMap().findModule(M.ModuleName);
+      bool IsPrebuiltHeaderUnit =
+          ImportedModule && ImportedModule->isHeaderUnit() &&
+          M.Kind == MK_PrebuiltModule &&
+          HSOpts.PrebuiltModuleFiles.count(M.ModuleName);
+
+      bool HasFileInfo = !M.StandardCXXModule && !IsPrebuiltHeaderUnit;
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ChuanqiXu9 wrote:

Yeah, when I read the PR I was wondering what is "HasFileInfo" until I read the current position. If the name is `IsCXX20ModuleOrHeaderUnit ` or anything like that , I think I can understand this more easily as a code reader. The reason why I want it is, the major reason we did that (omit the PCM file info for C++20 modules) is because we decide it in the high level. It is not because other reasons so that we have to do it. It is just our decision for C++20 modules. So I want it.

So I prefer a name like `IsCXX20ModuleOrHeaderUnit`

https://github.com/llvm/llvm-project/pull/235597