[Sema] TypeWrappers: Allow let properties to be managed by a type wrapper

Author: xedin

lib/Sema/TypeCheckStorage.cpp

@@ -3306,7 +3306,8 @@ static void finishStorageImplInfo(AbstractStorageDecl *storage,
     } else if (var->hasAttachedPropertyWrapper()) {
       finishPropertyWrapperImplInfo(var, info);
     } else if (var->isAccessedViaTypeWrapper()) {
-      info = StorageImplInfo::getMutableComputed();
+      info = var->isLet() ? StorageImplInfo::getImmutableComputed()
+                          : StorageImplInfo::getMutableComputed();
     }
   }
 

lib/Sema/TypeCheckTypeWrapper.cpp

@@ -325,7 +325,7 @@ bool IsPropertyAccessedViaTypeWrapper::evaluate(Evaluator &evaluator,
   if (!(parent && parent->hasTypeWrapper()))
     return false;
 
-  if (property->isStatic() || property->isLet())
+  if (property->isStatic())
     return false;
 
   // If this property has `@typeWrapperIgnored` attribute

test/Interpreter/Inputs/type_wrapper_defs.swift

@@ -7,6 +7,13 @@ public struct Wrapper<S> {
     self.underlying = memberwise
   }
 
+  public subscript<V>(storageKeyPath path: KeyPath<S, V>) -> V {
+    get {
+      print("in read-only getter")
+      return underlying[keyPath: path]
+    }
+  }
+
   public subscript<V>(storageKeyPath path: WritableKeyPath<S, V>) -> V {
     get {
       print("in getter")

test/Interpreter/type_wrappers.swift

@@ -358,10 +358,11 @@ testPropertyWrappers()
 
 do {
   var person = PersonWithUnmanagedTest(name: "Arthur Dent")
-  // CHECK: Wrapper.init($Storage(_favoredColor: type_wrapper_defs.PropWrapper<Swift.String>(value: "red")))
+  // CHECK: Wrapper.init($Storage(name: "Arthur Dent", _favoredColor: type_wrapper_defs.PropWrapper<Swift.String>(value: "red")))
 
   print(person.name)
-  // CHECK: Arthur Dent
+  // CHECK: in read-only getter
+  // CHECK-NEXT: Arthur Dent
 
   print(person.age)
   // CHECK: 30

test/type/type_wrapper.swift

@@ -351,7 +351,7 @@ func testDeclarationsWithUnmanagedProperties() {
   }
 
   _ = WithDefaultedLet(age: 32) // Ok
-  _ = WithDefaultedLet(name: "", age: 0) // expected-error {{extra argument 'name' in call}}
+  _ = WithDefaultedLet(name: "", age: 0) // Ok
 
   @NoopWrapper
   struct WithLazy {