Merge pull request #68317 from xedin/delay-default-inference

[CSBindings] Delay default binding production until inference is exhausted

Author: xedin

lib/Sema/CSBindings.cpp

@@ -2052,7 +2052,7 @@ bool TypeVarBindingProducer::computeNext() {
     }
   }
 
-  if (NumTries == 0) {
+  if (newBindings.empty()) {
     // Add defaultable constraints (if any).
     for (auto *constraint : DelayedDefaults) {
       if (constraint->getKind() == ConstraintKind::FallbackType) {
@@ -2065,6 +2065,9 @@ bool TypeVarBindingProducer::computeNext() {
 
       addNewBinding(getDefaultBinding(constraint));
     }
+
+    // Drop all of the default since we have converted them into bindings.
+    DelayedDefaults.clear();
   }
 
   if (newBindings.empty())

unittests/Sema/BindingInferenceTests.cpp

@@ -395,3 +395,43 @@ TEST_F(SemaTest, TestNoDoubleVoidClosureResultInference) {
 
   verifyInference(closureResultWithoutVoid, 3);
 }
+
+TEST_F(SemaTest, TestSupertypeInferenceWithDefaults) {
+  ConstraintSystemOptions options;
+  ConstraintSystem cs(DC, options);
+
+  auto *genericArg = cs.createTypeVariable(
+      cs.getConstraintLocator({}, ConstraintLocator::GenericArgument),
+      /*options=*/0);
+
+  // KeyPath<String, Int> i.e. \.utf8.count or something similar
+  auto keyPath =
+      BoundGenericType::get(Context.getKeyPathDecl(), /*parent=*/Type(),
+                            {getStdlibType("String"), getStdlibType("Int")});
+
+  cs.addConstraint(ConstraintKind::Conversion, keyPath, genericArg,
+                   cs.getConstraintLocator({}));
+
+  cs.addConstraint(ConstraintKind::Defaultable, genericArg, Context.TheAnyType,
+                   cs.getConstraintLocator({}));
+
+  auto bindings = cs.getBindingsFor(genericArg);
+  TypeVarBindingProducer producer(bindings);
+
+  llvm::SmallVector<Type, 4> inferredTypes;
+  while (auto binding = producer()) {
+    ASSERT_TRUE(binding.has_value());
+    inferredTypes.push_back(binding->getType());
+  }
+
+  // The inference should produce 4 types: KeyPath<String, Int>,
+  // PartialKeyPath<String>, AnyKeyPath and Any - in that order.
+
+  ASSERT_EQ(inferredTypes.size(), 4);
+  ASSERT_TRUE(inferredTypes[0]->isEqual(keyPath));
+  ASSERT_TRUE(inferredTypes[1]->isEqual(
+      BoundGenericType::get(Context.getPartialKeyPathDecl(),
+                            /*parent=*/Type(), {getStdlibType("String")})));
+  ASSERT_TRUE(inferredTypes[2]->isEqual(getStdlibType("AnyKeyPath")));
+  ASSERT_TRUE(inferredTypes[3]->isEqual(Context.TheAnyType));
+}