[llvm-branch-commits] [clang] [serialization] No transitive type change (PR #92511)

[Ilya Biryukov via llvm-branch-commits]

================
@@ -6659,13 +6655,22 @@ void ASTWriter::MacroRead(serialization::MacroID ID, MacroInfo *MI) {
 }
 
 void ASTWriter::TypeRead(TypeIdx Idx, QualType T) {
-  // Always take the highest-numbered type index. This copes with an interesting
+  // Always take the type index that comes in later module files.
+  // This copes with an interesting
   // case for chained AST writing where we schedule writing the type and then,
   // later, deserialize the type from another AST. In this case, we want to
-  // keep the higher-numbered entry so that we can properly write it out to
+  // keep the just writing entry so that we can properly write it out to
   // the AST file.
   TypeIdx &StoredIdx = TypeIdxs[T];
-  if (Idx.getIndex() >= StoredIdx.getIndex())
+
+  // Ignore it if the type comes from the current being written module file.
+  unsigned ModuleFileIndex = StoredIdx.getModuleFileIndex();
+  if (ModuleFileIndex == 0 && StoredIdx.getValue())
+    return;
+
+  // Otherwise, keep the highest ID since the module file comes later has
+  // higher module file indexes.
+  if (Idx.getValue() >= StoredIdx.getValue())
----------------
ilya-biryukov wrote:

```suggestion 
  if (Idx.getModuleFileIndex() >= StoredIdx.getModuleFileIndex())
```
This seems to align better with what the comment for the code are saying. If this does not work, I might be missing something.

https://github.com/llvm/llvm-project/pull/92511