[Sema] InitAccessors: Make sure that init accessor default subsumes initialization of stored properties

Default expression associated with an init accessor property
should always subsume that of any property listed in "initializes".

Author: xedin

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2483,6 +2483,20 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
         }
       }
     }
+
+    // If this is an init accessor property with a default initializer,
+    // make sure that it subsumes initializers of all of its "initializes"
+    // stored properties.
+    if (auto *var = PBD->getSingleVar()) {
+      auto *initAccessor = var->getAccessor(AccessorKind::Init);
+      if (initAccessor && PBD->isInitialized(0)) {
+        for (auto *property : initAccessor->getInitializedProperties()) {
+          auto *propertyBinding = property->getParentPatternBinding();
+          if (propertyBinding->isInitialized(0))
+            propertyBinding->setInitializerSubsumed(0);
+        }
+      }
+    }
   }
 
   void visitSubscriptDecl(SubscriptDecl *SD) {

test/Interpreter/init_accessors.swift

@@ -479,9 +479,9 @@ func test_memberwise_with_default_args() {
 test_memberwise_with_default_args()
 // CHECK: test-memberwise_with_default-1: TestWithoutDefault(_a: -1, _b: 42)
 // CHECK-NEXT: test-memberwise_with_default-2: TestWithoutDefault(_a: 42, _b: -1)
-// CHECK-NEXT: test-defaulted-1: TestDefaulted(_a: 0, _b: 0)
+// CHECK-NEXT: test-defaulted-1: TestDefaulted(_a: 1, _b: 2)
 // CHECK-NEXT: test-defaulted-2: TestDefaulted(_a: 3, _b: 4)
-// CHECK-NEXT: test-defaulted-class: ("<<default>>", 1)
+// CHECK-NEXT: test-defaulted-class: ("", 42)
 
 func test_init_accessors_without_setters() {
   struct TestStruct<T> {

test/SILOptimizer/init_accessor_raw_sil_lowering.swift

@@ -206,4 +206,31 @@ func test_default_inits() {
       self.x = x
     }
   }
+
+  class Test3 {
+    var _x: Int = 42
+    var x: Int = 42 {
+      @storageRestrictions(initializes: _x)
+      init {
+        _x = newValue
+      }
+      get { _x }
+    }
+
+    var _y: String = ""
+    var y: String = "" {
+      @storageRestrictions(initializes: _y)
+      init {
+        _y = newValue
+      }
+      get { _y }
+    }
+
+    // CHECK-LABEL: sil private [ossa] @$s23assign_or_init_lowering18test_default_initsyyF5Test3L_CADycfc : $@convention(method) (@owned Test3) -> @owned Test3
+    // CHECK: function_ref variable initialization expression of x in Test3 #1 in test_default_inits()
+    // CHECK-NOT: function_ref variable initialization expression of _x in Test3 #1 in test_default_inits()
+    //
+    // CHECK: function_ref variable initialization expression of y in Test3 #1 in test_default_inits()
+    // CHECK-NOT: function_ref variable initialization expression of _y in Test3 #1 in test_default_inits()
+  }
 }