[clang] [clang][modules] Headers meant to be included multiple times can be completely invisible in clang module builds (PR #83660)

[Ian Anderson via cfe-commits]

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@@ -1403,94 +1421,146 @@ bool HeaderSearch::isFileMultipleIncludeGuarded(FileEntryRef File) const {
 void HeaderSearch::MarkFileModuleHeader(FileEntryRef FE,
                                         ModuleMap::ModuleHeaderRole Role,
                                         bool isCompilingModuleHeader) {
-  bool isModularHeader = ModuleMap::isModular(Role);
-
   // Don't mark the file info as non-external if there's nothing to change.
   if (!isCompilingModuleHeader) {
-    if (!isModularHeader)
+    if ((Role & ModuleMap::ExcludedHeader))
       return;
     auto *HFI = getExistingFileInfo(FE);
     if (HFI && HFI->isModuleHeader)
       return;
   }
 
   auto &HFI = getFileInfo(FE);
-  HFI.isModuleHeader |= isModularHeader;
+  HFI.mergeModuleMembership(Role);
   HFI.isCompilingModuleHeader |= isCompilingModuleHeader;
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ian-twilightcoder wrote:

Ohhh. So I need to be checking the `getExistingFileInfo` to see if `isModuleHeader` and `isTextualModuleHeader` match the given `ModuleHeaderRole`?

https://github.com/llvm/llvm-project/pull/83660