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

[Jan Svoboda via cfe-commits]

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@@ -372,6 +381,10 @@ class HeaderSearch {
   /// map their keys to the SearchDir index of their header map.
   void indexInitialHeaderMaps();
 
+  /// Build the header cache for a directory's module map.
+  void buildHeaderCache(DirectoryEntryRef Dir,
+                        ModuleMapDirectoryState &MMState);
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jansvoboda11 wrote:

What's the header cache? Do you mean the new members of `ModuleMapDirectoryState`? Some clarification here would be useful.

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