Merge pull request swiftlang#66579 from xedin/allow-holes-in-diagnostic-mode-only

[ConstraintSystem] Allow generic parameters to bind to holes only in …

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -1868,11 +1868,14 @@ TypeVariableType *ConstraintSystem::openGenericParameter(
   auto *paramLocator = getConstraintLocator(
       locator.withPathElement(LocatorPathElt::GenericParameter(parameter)));
 
-  unsigned options = (TVO_PrefersSubtypeBinding |
-                      TVO_CanBindToHole);
+  unsigned options = TVO_PrefersSubtypeBinding;
+
   if (parameter->isParameterPack())
     options |= TVO_CanBindToPack;
 
+  if (shouldAttemptFixes())
+    options |= TVO_CanBindToHole;
+
   auto typeVar = createTypeVariable(paramLocator, options);
   auto result = replacements.insert(std::make_pair(
       cast<GenericTypeParamType>(parameter->getCanonicalType()), typeVar));