[CS] Make CSRanking change slightly less risky for 6.2

Check for `isSolverAllocated` rather than
`hasTypeVariableOrPlaceholder`, and downgrade an `ASSERT` to
`CONDITIONAL_ASSERT`.

Author: hamishknight

lib/Sema/CSRanking.cpp

@@ -1413,10 +1413,9 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
     auto type1 = types.Type1;
     auto type2 = types.Type2;
 
-    // If either of the types have holes or unresolved type variables, we can't
-    // compare them. `isSubtypeOf` cannot be used with solver-allocated types.
-    if (type1->hasTypeVariableOrPlaceholder() ||
-        type2->hasTypeVariableOrPlaceholder()) {
+    // `isSubtypeOf` cannot be used with solver-allocated types.
+    if (type1->getRecursiveProperties().isSolverAllocated() ||
+        type2->getRecursiveProperties().isSolverAllocated()) {
       identical = false;
       continue;
     }
@@ -1468,12 +1467,15 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
     // The systems are not considered equivalent.
     identical = false;
 
-    // Archetypes are worse than concrete types
+    // Archetypes are worse than concrete types (i.e. non-placeholder and
+    // non-archetype)
     // FIXME: Total hack.
-    if (type1->is<ArchetypeType>() && !type2->is<ArchetypeType>()) {
+    if (type1->is<ArchetypeType>() && !type2->is<ArchetypeType>() &&
+        !type2->is<PlaceholderType>()) {
       ++score2;
       continue;
-    } else if (type2->is<ArchetypeType>() && !type1->is<ArchetypeType>()) {
+    } else if (type2->is<ArchetypeType>() && !type1->is<ArchetypeType>() &&
+               !type1->is<PlaceholderType>()) {
       ++score1;
       continue;
     }

lib/Sema/TypeCheckConstraints.cpp

@@ -1060,9 +1060,10 @@ bool TypeChecker::typesSatisfyConstraint(Type type1, Type type2,
   // avoid lifetime issues for e.g cases where we lazily populate the
   // `ContextSubMap` on `NominalOrBoundGenericNominalType` in the nested arena,
   // since it will be destroyed on leaving.
-  ASSERT(!type1->getRecursiveProperties().isSolverAllocated() &&
-         !type2->getRecursiveProperties().isSolverAllocated() &&
-         "Cannot escape solver-allocated types into a nested ConstraintSystem");
+  CONDITIONAL_ASSERT(
+      !type1->getRecursiveProperties().isSolverAllocated() &&
+      !type2->getRecursiveProperties().isSolverAllocated() &&
+      "Cannot escape solver-allocated types into a nested ConstraintSystem");
 
   ConstraintSystem cs(dc, ConstraintSystemOptions());
   if (openArchetypes) {