[CSSimplify] If bound type var is more optional

than a binding type var, attempt to match
types and solve.

Author: Amritpan Kaur

lib/Sema/CSSimplify.cpp

@@ -4628,6 +4628,13 @@ repairViaBridgingCast(ConstraintSystem &cs, Type fromType, Type toType,
   return true;
 }
 
+/// Return tuple of type and number of optionals on that type.
+static std::pair<Type, unsigned> getObjectTypeAndNumUnwraps(Type type) {
+  SmallVector<Type, 2> optionals;
+  Type objType = type->lookThroughAllOptionalTypes(optionals);
+  return std::make_pair(objType, optionals.size());
+}
+
 static bool
 repairViaOptionalUnwrap(ConstraintSystem &cs, Type fromType, Type toType,
                         ConstraintKind matchKind,
@@ -4745,17 +4752,11 @@ repairViaOptionalUnwrap(ConstraintSystem &cs, Type fromType, Type toType,
     }
   }
 
-  auto getObjectTypeAndUnwraps = [](Type type) -> std::pair<Type, unsigned> {
-    SmallVector<Type, 2> optionals;
-    Type objType = type->lookThroughAllOptionalTypes(optionals);
-    return std::make_pair(objType, optionals.size());
-  };
-
   Type fromObjectType, toObjectType;
   unsigned fromUnwraps, toUnwraps;
 
-  std::tie(fromObjectType, fromUnwraps) = getObjectTypeAndUnwraps(fromType);
-  std::tie(toObjectType, toUnwraps) = getObjectTypeAndUnwraps(toType);
+  std::tie(fromObjectType, fromUnwraps) = getObjectTypeAndNumUnwraps(fromType);
+  std::tie(toObjectType, toUnwraps) = getObjectTypeAndNumUnwraps(toType);
 
   // Since equality is symmetric and it decays into a `Bind`, eagerly
   // unwrapping optionals from either side might be incorrect since
@@ -6484,6 +6485,19 @@ bool ConstraintSystem::repairFailures(
     if (!fromType || !toType)
       break;
 
+    Type fromObjectType, toObjectType;
+    unsigned fromUnwraps, toUnwraps;
+
+    std::tie(fromObjectType, fromUnwraps) = getObjectTypeAndNumUnwraps(lhs);
+    std::tie(toObjectType, toUnwraps) = getObjectTypeAndNumUnwraps(rhs);
+
+    // If the bound contextual type is more optional than the binding type, then
+    // propogate binding type to contextual type and attempt to solve.
+    if (fromUnwraps < toUnwraps) {
+      (void)matchTypes(fromObjectType, toObjectType, ConstraintKind::Bind,
+                       TMF_ApplyingFix, locator);
+    }
+
     // Drop both `GenericType` elements.
     path.pop_back();
     path.pop_back();