[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:

The name is not explicit. I prefer  something like `IsCXX20ModuleOrHeaderUnit`

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