[clang] [C++20] [Modules] Instantiate pending instantiations when GMF ends (PR #126842)

[Matheus Izvekov via cfe-commits]

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@@ -1104,9 +1104,13 @@ void Sema::ActOnStartOfTranslationUnit() {
 }
 
 void Sema::ActOnEndOfTranslationUnitFragment(TUFragmentKind Kind) {
-  // No explicit actions are required at the end of the global module fragment.
-  if (Kind == TUFragmentKind::Global)
+  if (Kind == TUFragmentKind::Global) {
+    // Perform Pending Instantiations at the end of global module fragment so
+    // that the module ownership of TU-level decls won't get messed.
+    llvm::TimeTraceScope TimeScope("PerformPendingInstantiations");
+    PerformPendingInstantiations();
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mizvekov wrote:

The distinction lexical vs semantic context does not matter here, they are both properties of the pattern and of the instantiation, and they do not depend on the template parameters, so we shouldn't change them when instantiating.

Well you say it works fine, but surely it does not work fine in this case. And I remember someone on discord was recently complaining about our inconsistencies in this area.

https://github.com/llvm/llvm-project/pull/126842