[clang] [clang][modules] Preserve the module map that allowed inferring (PR #113389)

[Ben Langmuir via cfe-commits]

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@@ -3018,13 +3019,19 @@ void ASTWriter::WriteSubmodules(Module *WritingModule) {
     SourceLocationEncoding::RawLocEncoding DefinitionLoc =
         getRawSourceLocationEncoding(getAdjustedLocation(Mod->DefinitionLoc));
 
+    ModuleMap &ModMap = PP->getHeaderSearchInfo().getModuleMap();
+    FileID InferredFID =
+        Mod->IsInferred ? ModMap.getModuleMapFileIDForUniquing(Mod) : FileID();
+    int Inferred = getAdjustedFileID(InferredFID).getOpaqueValue();
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benlangmuir wrote:

Nit: I would name this something less generic like "InferredAdjustedFID"

https://github.com/llvm/llvm-project/pull/113389