[clang] [C++20][Modules][Serialization] Delay marking pending incomplete decl chains until the end of `finishPendingActions`. (PR #121245)

[Michael Park via cfe-commits]

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@@ -10483,6 +10476,13 @@ void ASTReader::finishPendingActions() {
   for (auto *ND : PendingMergedDefinitionsToDeduplicate)
     getContext().deduplicateMergedDefinitonsFor(ND);
   PendingMergedDefinitionsToDeduplicate.clear();
+
+  // For each decl chain that we wanted to complete while deserializing, mark
+  // it as "still needs to be completed".
+  for (unsigned I = 0; I != PendingIncompleteDeclChains.size(); ++I) {
+    markIncompleteDeclChain(PendingIncompleteDeclChains[I]);
+  }
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mpark wrote:

Yeah, why not

https://github.com/llvm/llvm-project/pull/121245