[clang] [clang][modulemap] Lazily load module maps by header name (PR #181916)

[Jan Svoboda via cfe-commits]

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@@ -6316,6 +6316,15 @@ llvm::Error ASTReader::ReadSubmoduleBlock(ModuleFile &F,
       CurrentModule->ConfigMacrosExhaustive = ConfigMacrosExhaustive;
       CurrentModule->ModuleMapIsPrivate = ModuleMapIsPrivate;
       CurrentModule->NamedModuleHasInit = NamedModuleHasInit;
+
+      if (!ParentModule && !F.BaseDirectory.empty()) {
+        if (auto Dir = FileMgr.getOptionalDirectoryRef(F.BaseDirectory))
+          CurrentModule->Directory = *Dir;
+      } else if (ParentModule && ParentModule->Directory) {
+        // Submodules inherit the directory from their parent.
+        CurrentModule->Directory = ParentModule->Directory;
+      }
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jansvoboda11 wrote:

This technically doesn't depend on the rest of this patch, right? Could we extract it into a separate commit? And add a test for this specifically?

https://github.com/llvm/llvm-project/pull/181916