[ConstraintSystem] Default generic parameters associated with missing member to Any

As part of the `DefineBasedOnUse` fix introduced in places where
there is a reference to non-existent member, let's also add
constraints which allow to default any generic parameters found
in base type to `Any`.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -4751,6 +4751,19 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
     // Since member with given base and name doesn't exist, let's try to
     // fake its presence based on use, that makes it possible to diagnose
     // problems related to member lookup more precisely.
+
+    origBaseTy.transform([&](Type type) -> Type {
+      if (auto *typeVar = type->getAs<TypeVariableType>()) {
+        if (typeVar->getImpl().hasRepresentativeOrFixed())
+          return type;
+        // Default all of the generic parameters found in base to `Any`.
+        addConstraint(ConstraintKind::Defaultable, typeVar,
+                      getASTContext().TheAnyType,
+                      typeVar->getImpl().getLocator());
+      }
+      return type;
+    });
+
     auto *fix =
         DefineMemberBasedOnUse::create(*this, origBaseTy, member, locator);
     if (recordFix(fix))