[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".

(cherry picked from commit fd2a7d5)

Author: xedin

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2448,6 +2448,20 @@ 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()
+  }
 }