Merge pull request #14584 from rudkx/rdar37073401

Fix an issue with the constraint favoring code in the constraint opti…

Author: rudkx

lib/Sema/CSGen.cpp

@@ -828,7 +828,20 @@ namespace {
 
     Type firstArgTy = argTupleTy->getElement(0).getType()->getWithoutParens();
     Type secondArgTy = argTupleTy->getElement(1).getType()->getWithoutParens();
-    
+
+    auto isOptionalWithMatchingObjectType = [](Type optional,
+                                               Type object) -> bool {
+      if (auto objTy = optional->getRValueType()->getOptionalObjectType())
+        return objTy->getRValueType()->isEqual(object->getRValueType());
+
+      return false;
+    };
+
+    auto isPotentialForcingOpportunity = [&](Type first, Type second) -> bool {
+      return isOptionalWithMatchingObjectType(first, second) ||
+             isOptionalWithMatchingObjectType(second, first);
+    };
+
     // Determine whether the given declaration is favored.
     auto isFavoredDecl = [&](ValueDecl *value) -> bool {
       auto valueTy = value->getInterfaceType();
@@ -882,14 +895,14 @@ namespace {
 
       auto resultTy = fnTy->getResult();
       auto contextualTy = CS.getContextualType(expr);
-      
-      return
-        (isFavoredParamAndArg(CS, firstParamTy, firstArg, firstArgTy,
-                              secondArgTy) ||
-         isFavoredParamAndArg(CS, secondParamTy, secondArg, secondArgTy,
-                              firstArgTy)) &&
-         firstParamTy->isEqual(secondParamTy) &&
-        (!contextualTy || contextualTy->isEqual(resultTy));
+
+      return (isFavoredParamAndArg(CS, firstParamTy, firstArg, firstArgTy,
+                                   secondArgTy) ||
+              isFavoredParamAndArg(CS, secondParamTy, secondArg, secondArgTy,
+                                   firstArgTy)) &&
+             firstParamTy->isEqual(secondParamTy) &&
+             !isPotentialForcingOpportunity(firstArgTy, secondArgTy) &&
+             (!contextualTy || contextualTy->isEqual(resultTy));
     };
 
     favorCallOverloads(expr, CS, isFavoredDecl);

test/stdlib/ImplicitlyUnwrappedOptional.swift

@@ -57,5 +57,18 @@ ImplicitlyUnwrappedOptionalTests.test("flatMap") {
   // expectNil((3 as Int!).flatMap(half))
 }
 
-runAllTests()
+infix operator *^* : ComparisonPrecedence
+
+func *^*(lhs: Int?, rhs: Int?) -> Bool { return true }
+func *^*(lhs: Int, rhs: Int) -> Bool { return true }
+
+ImplicitlyUnwrappedOptionalTests.test("preferOptional") {
+  let i: Int! = nil
+  let j: Int = 1
+  if i != j {} // we should choose != for Optionals rather than forcing i
+  if i == j {} // we should choose == for Optionals rather than forcing i
+  // FIXME: https://bugs.swift.org/browse/SR-6988
+  //  if i *^* j {} // we should choose *^* for Optionals rather than forcing i
+}
 
+runAllTests()