Sema: Fix handling of Solution::typeBindings in replaySolution()

Author: slavapestov

lib/Sema/CSRanking.cpp

@@ -1350,6 +1350,9 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
   const auto &bindings2 = solutions[idx2].typeBindings;
 
   for (const auto &binding1 : bindings1) {
+    if (!binding1.second)
+      continue;
+
     auto *typeVar = binding1.first;
     auto *loc = typeVar->getImpl().getLocator();
 
@@ -1375,6 +1378,9 @@ SolutionCompareResult ConstraintSystem::compareSolutions(
     if (binding2 == bindings2.end())
       continue;
 
+    if (!binding2->second)
+      continue;
+
     TypeBindingsToCompare typesToCompare(binding1.second, binding2->second);
 
     // For short-form and self-delegating init calls, we want to prefer

lib/Sema/CSSolver.cpp

@@ -103,8 +103,10 @@ Solution ConstraintSystem::finalize() {
     // This type variable has no binding. Allowed only
     // when `FreeTypeVariableBinding::Allow` is set,
     // which is checked above.
-    if (!getFixedType(tv))
+    if (!getFixedType(tv)) {
+      solution.typeBindings[tv] = Type();
       continue;
+    }
 
     solution.typeBindings[tv] = simplifyType(tv)->reconstituteSugar(false);
   }
@@ -274,10 +276,15 @@ void ConstraintSystem::replaySolution(const Solution &solution,
   if (shouldIncreaseScore)
     replayScore(solution.getFixedScore());
 
-  // Assign fixed types to the type variables solved by this solution.
   for (auto binding : solution.typeBindings) {
     // If we haven't seen this type variable before, record it now.
     addTypeVariable(binding.first);
+  }
+
+  // Assign fixed types to the type variables solved by this solution.
+  for (auto binding : solution.typeBindings) {
+    if (!binding.second)
+      continue;
 
     // If we don't already have a fixed type for this type variable,
     // assign the fixed type from the solution.

test/Constraints/ranking.swift

@@ -440,3 +440,13 @@ extension SignalProtocol where Element: SignalProtocol, Error == Never {
 func no_ambiguity_error_vs_never<Element, Error>(_ signals: [Signal<Element, Error>]) -> Signal<Element, Error> {
   return Signal(sequence: signals).flatten() // Ok
 }
+
+// Regression test for a crash I reduced from the stdlib that wasn't covered
+// by tests
+struct HasIntInit {
+  init(_: Int) {}
+}
+
+func compare_solutions_with_bindings(x: UInt8, y: UInt8) -> HasIntInit {
+  return .init(Int(x / numericCast(y)))
+}