Merge pull request #5373 from DougGregor/iuo-infer-28621624

Author: swift-ci

lib/Sema/CSSolver.cpp

@@ -966,6 +966,7 @@ static PotentialBindings getPotentialBindings(ConstraintSystem &cs,
 
     // Don't deduce IUO types.
     Type alternateType;
+    bool adjustedIUO = false;
     if (kind == AllowedBindingKind::Supertypes &&
         constraint->getKind() >= ConstraintKind::Conversion &&
         constraint->getKind() <= ConstraintKind::OperatorArgumentConversion) {
@@ -974,6 +975,7 @@ static PotentialBindings getPotentialBindings(ConstraintSystem &cs,
           cs.lookThroughImplicitlyUnwrappedOptionalType(innerType)) {
         type = OptionalType::get(objectType);
         alternateType = objectType;
+        adjustedIUO = true;
       }
     }
 
@@ -1000,7 +1002,7 @@ static PotentialBindings getPotentialBindings(ConstraintSystem &cs,
     }
 
     if (exactTypes.insert(type->getCanonicalType()).second)
-      addPotentialBinding({type, kind, None});
+      addPotentialBinding({type, kind, None}, /*allowJoinMeet=*/!adjustedIUO);
     if (alternateType &&
         exactTypes.insert(alternateType->getCanonicalType()).second)
       addPotentialBinding({alternateType, kind, None}, /*allowJoinMeet=*/false);

test/Constraints/optional.swift

@@ -130,3 +130,14 @@ func testTernaryWithNil(b: Bool, s: String, i: Int) {
   let t4 = b ? nil : 1
   let _: Double = t4 // expected-error{{value of type 'Int?'}}
 }
+
+// inference with IUOs
+infix operator ++++
+
+protocol PPPP {
+  static func ++++(x: Self, y: Self) -> Bool
+}
+
+func compare<T: PPPP>(v: T, u: T!) -> Bool {
+  return v ++++ u
+}