[clang] [PAC][clang] Correct handling of ptrauth queries of incomplete types (PR #164528)

[Oliver Hunt via cfe-commits]

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@@ -1618,8 +1618,26 @@ void ASTContext::setRelocationInfoForCXXRecord(
   RelocatableClasses.insert({D, Info});
 }
 
+// In future we may want to distinguish the presence or absence of address
+// discrimination, from the inability to determine the presence. For now we rely
+// on all source facing interfaces (type trait queries, etc) diagnosing and
+// reporting an error before reaching these paths.
+static bool canDeterminePointerAuthContent(QualType Type) {
+  if (Type->isIncompleteType() || Type->isDependentType())
+    return false;
+  const TagDecl *Decl = Type->getAsTagDecl();
+  return !Decl || !Decl->getDefinition()->isInvalidDecl();
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ojhunt wrote:

@mizvekov Changing the behavior of isIncompleteType, or changing RequireCompleteType as Corentin tried break all kinds of things everywhere. A lot of it seems to be diagnostics (significant regressions), but there are so many failures I can't be sure there are also actual correctness errors.

https://github.com/llvm/llvm-project/pull/164528