[clang] [BoundsSafety][Sema] Allow counted_by and counted_by_or_null on pointers where the pointee type is incomplete but potentially completable (PR #106321)

[Dan Liew via cfe-commits]

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@@ -13559,6 +13562,27 @@ QualType Sema::CheckAssignmentOperands(Expr *LHSExpr, ExprResult &RHS,
   QualType LHSType = LHSExpr->getType();
   QualType RHSType = CompoundType.isNull() ? RHS.get()->getType() :
                                              CompoundType;
+
+  if (RHS.isUsable()) {
+    // Even if this check fails don't return early to allow the best
+    // possible error recovery and to allow any subsequent diagnostics to
+    // work.
+    (void)BoundsSafetyCheckAssignmentToCountAttrPtr(
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delcypher wrote:

@AaronBallman The return value isn't always ignored in our fork. See [here](https://github.com/swiftlang/llvm-project/blob/b0bbd7e8a003990aff9ce373bc6b83407630b5f5/clang/lib/Sema/SemaBoundsSafety.cpp#L645)

https://github.com/llvm/llvm-project/pull/106321