[Sema] TypeWrappers: convert variable init expr into initializer default

All of the stored properties are wrapped which means that their
initializers are subsummed and moved to the synthesized `init`
as default arguments.

lib/Sema/CodeSynthesis.cpp

@@ -188,6 +188,28 @@ static void maybeAddMemberwiseDefaultArg(ParamDecl *arg, VarDecl *var,
   arg->setDefaultArgumentKind(DefaultArgumentKind::StoredProperty);
 }
 
+static void maybeAddTypeWrapperDefaultArg(ParamDecl *arg, VarDecl *var,
+                                          ASTContext &ctx) {
+  assert(var->isAccessedViaTypeWrapper());
+
+  if (!var->getParentPattern()->getSingleVar())
+    return;
+
+  auto *PBD = var->getParentPatternBinding();
+
+  auto *initExpr = PBD->getInit(/*index=*/0);
+  if (!initExpr)
+    return;
+
+  // Type wrapper variables are never initialized directly,
+  // initialization expression (if any) becomes an default
+  // argument of the initializer synthesized by the type wrapper.
+  PBD->setInitializerSubsumed(/*index=*/0);
+
+  arg->setDefaultExpr(initExpr, /*isTypeChecked=*/false);
+  arg->setDefaultArgumentKind(DefaultArgumentKind::Normal);
+}
+
 /// Describes the kind of implicit constructor that will be
 /// generated.
 enum class ImplicitConstructorKind {
@@ -339,6 +361,8 @@ static ConstructorDecl *createImplicitConstructor(NominalTypeDecl *decl,
       arg->setInterfaceType(var->getValueInterfaceType());
       arg->setImplicit();
 
+      maybeAddTypeWrapperDefaultArg(arg, var, ctx);
+
       params.push_back(arg);
     }
   }

test/Interpreter/Inputs/type_wrapper_defs.swift

@@ -24,3 +24,9 @@ public class Person<T> {
   public var name: String
   public var projects: [T]
 }
+
+@Wrapper
+public struct PersonWithDefaults {
+  public var name: String = "<no name>"
+  public var age: Int = 99
+}

test/Interpreter/type_wrappers.swift

@@ -37,3 +37,48 @@ print(p.name)
 print(p.projects)
 // CHECK: in getter
 // CHECK-NEXT: ["A", "B", "C", "D"]
+
+var pDefaults = PersonWithDefaults()
+// CHECK: Wrapper.init($Storage(name: "<no name>", age: 99))
+
+print(pDefaults.name)
+// CHECK: in getter
+// CHECK: <no name>
+
+print(pDefaults.age)
+// CHECK: in getter
+// CHECK: 99
+
+pDefaults.name = "Actual Name"
+// CHECK-NEXT: in setter => Actual Name
+
+pDefaults.age = 0
+// CHECK-NEXT: in setter => 0
+
+print(pDefaults.name)
+// CHECK: in getter
+// CHECK: Actual Name
+
+print(pDefaults.age)
+// CHECK: in getter
+// CHECK: 0
+
+let pDefaultsAge = PersonWithDefaults(name: "Actual Name")
+
+print(pDefaultsAge.name)
+// CHECK: in getter
+// CHECK: Actual Name
+
+print(pDefaultsAge.age)
+// CHECK: in getter
+// CHECK: 99
+
+let pDefaultsName = PersonWithDefaults(age: 31337)
+
+print(pDefaultsName.name)
+// CHECK: in getter
+// CHECK: <no name>
+
+print(pDefaultsName.age)
+// CHECK: in getter
+// CHECK: 31337

test/type/type_wrapper.swift

@@ -147,3 +147,18 @@ func testLocalWithNestedWrapper() {
   _ = t.test // Ok
   _ = t.computed // Ok
 }
+
+func testTypeWrapperWithDefaults() {
+  @NoopWrapper
+  struct A {
+    var question: String = "Ultimate Question"
+    var answer: Int = 42
+  }
+
+  let a = A()
+  _ = a.question
+  _ = a.answer
+
+  _ = A(question: "")
+  _ = A(answer: 0)
+}