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

[Jan Svoboda via cfe-commits]

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@@ -1360,6 +1370,26 @@ bool ModuleMap::parseModuleMapFile(FileEntryRef File, bool IsSystem,
       std::make_unique<modulemap::ModuleMapFile>(std::move(*MaybeMMF)));
   const modulemap::ModuleMapFile &MMF = *ParsedModuleMaps.back();
   std::vector<const modulemap::ExternModuleDecl *> PendingExternalModuleMaps;
+  std::function<void(const modulemap::ModuleDecl &)> CollectExternDecls =
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jansvoboda11 wrote:

Did we not recurse into extern module maps prior to this patch?

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