[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:

I was worried about making more widespread changes, but I'll give that a shot - certainly it seems reasonable to consider invalid as being incomplete.

I had a comment for Corentin asking if there's an existing function that basically answers the "is this a complete, valid, and fully instantiated type" (rather than these local helpers), but I'm not sure if such a query has any value beyond this specific case. Certainly if we were to use some bits in the type/decl and evaluate this logic eagerly in future this logic disappears and the query would become unnecessary so if there's no other need for such a general there would be no reason to add it globally.

Anyway, that last paragraph is independent of isIncomplete also testing for isInvalid. I have a suspicion that we may get some issues with diagnostics - at least the diagnostic messages themselves changing, I can't imagine it impacting actual correctness, but lets find out :D

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