[ConstraintSystem] Mark member result type as a potential hole if base was incorrect

If it has been established that member found via static member
lookup on protocol metatype doesn't have correct result type,
chain's result type the should be treated as a hole.

Author: xedin

lib/Sema/CSBindings.cpp

@@ -432,6 +432,32 @@ void PotentialBindings::finalize(
         FullyBound = true;
       }
     }
+
+    if (cs.shouldAttemptFixes() &&
+        locator->isLastElement<LocatorPathElt::UnresolvedMemberChainResult>()) {
+      // Let's see whether this chain is valid, is it isn't then to avoid
+      // diagnosing the same issue multiple different ways, let's infer
+      // result of the chain to be a hole.
+      auto *resultExpr =
+          castToExpr<UnresolvedMemberChainResultExpr>(locator->getAnchor());
+      auto *baseLocator = cs.getConstraintLocator(
+          resultExpr->getChainBase(), ConstraintLocator::UnresolvedMember);
+
+      if (cs.hasFixFor(
+              baseLocator,
+              FixKind::AllowInvalidStaticMemberRefOnProtocolMetatype)) {
+        cs.recordPotentialHole(TypeVar);
+        // Clear all of the previously inferred bindings which are inferred
+        // from inside of a member chain.
+        Bindings.erase(
+            llvm::remove_if(
+                Bindings,
+                [](const ConstraintSystem::PotentialBinding &binding) {
+                  return binding.Kind == AllowedBindingKind::Supertypes;
+                }),
+            Bindings.end());
+      }
+    }
   }
 }
 

lib/Sema/CSSimplify.cpp

@@ -4556,6 +4556,10 @@ bool ConstraintSystem::repairFailures(
   }
 
   case ConstraintLocator::UnresolvedMemberChainResult: {
+    // Ignore this mismatch if result is already a hole.
+    if (rhs->isHole())
+      return true;
+
     if (repairViaOptionalUnwrap(*this, lhs, rhs, matchKind, conversionsOrFixes,
                                 locator))
       break;