feat(go): Use type registry to find the correct target type for JSII Proxy (#3354)

With this PR, the type that is instantiated as JSII Proxy is looked up from the type registry using the TypeFQDN in the ref. If that type is registered in the type registry AND that type is assignable to the targeted value type, than that type is used to instantiate the JSII proxy. 

Fixes #3353 and relates to #2819.

Author: arnogeurts-sqills

packages/@jsii/go-runtime/jsii-runtime-go/cast.go

@@ -43,7 +43,7 @@ func UnsafeCast(from interface{}, into interface{}) {
 	client := kernel.GetClient()
 	if objID, found := client.FindObjectRef(rfrom); found {
 		// Ensures the value is initialized properly. Panics if the target value is not a jsii interface type.
-		client.Types().InitJsiiProxy(rinto)
+		client.Types().InitJsiiProxy(rinto, rinto.Type())
 
 		// If the target type is a behavioral interface, add it to the ObjectRef.Interfaces list.
 		if fqn, found := client.Types().InterfaceFQN(rinto.Type()); found {

packages/@jsii/go-runtime/jsii-runtime-go/internal/kernel/conversions.go

@@ -63,14 +63,20 @@ func (c *Client) castAndSetToPtr(ptr reflect.Value, data reflect.Value) {
 			return
 		}
 
+		targetType := ptr.Type()
+		if typ, ok := c.Types().FindType(ref.TypeFQN()); ok && typ.AssignableTo(ptr.Type()) {
+            // Specialize the return type to be the dynamic value type
+			targetType = typ
+		}
+
 		// If it's currently tracked, return the current instance
-		if object, ok := c.objects.GetObjectAs(ref.InstanceID, ptr.Type()); ok {
+		if object, ok := c.objects.GetObjectAs(ref.InstanceID, targetType); ok {
 			ptr.Set(object)
 			return
 		}
 
 		// If return data is jsii object references, add to objects table.
-		if err := c.Types().InitJsiiProxy(ptr); err == nil {
+		if err := c.Types().InitJsiiProxy(ptr, targetType); err == nil {
 			if err = c.RegisterInstance(ptr, ref); err != nil {
 				panic(err)
 			}

packages/@jsii/go-runtime/jsii-runtime-go/internal/typeregistry/typeregistry.go

@@ -89,9 +89,7 @@ func (t *TypeRegistry) FindType(fqn api.FQN) (typ reflect.Type, ok bool) {
 // InitJsiiProxy initializes a jsii proxy value at the provided pointer. It
 // returns an error if the pointer does not have a value of a registered
 // proxyable type (that is, a class or interface type).
-func (t *TypeRegistry) InitJsiiProxy(val reflect.Value) error {
-	valType := val.Type()
-
+func (t *TypeRegistry) InitJsiiProxy(val reflect.Value, valType reflect.Type) error {
 	switch valType.Kind() {
 	case reflect.Interface:
 		if maker, ok := t.proxyMakers[valType]; ok {
@@ -115,7 +113,7 @@ func (t *TypeRegistry) InitJsiiProxy(val reflect.Value) error {
 			if !field.Anonymous {
 				return fmt.Errorf("refusing to initialize non-anonymous field %s of %v", field.Name, val)
 			}
-			if err := t.InitJsiiProxy(val.Field(i)); err != nil {
+			if err := t.InitJsiiProxy(val.Field(i), field.Type); err != nil {
 				return err
 			}
 		}

packages/@jsii/go-runtime/jsii-runtime-go/runtime/runtime.go

@@ -102,7 +102,7 @@ func RegisterStruct(fqn FQN, strct reflect.Type) {
 // element of it is not a registered jsii interface or class type).
 func InitJsiiProxy(ptr interface{}) {
 	ptrVal := reflect.ValueOf(ptr).Elem()
-	if err := kernel.GetClient().Types().InitJsiiProxy(ptrVal); err != nil {
+	if err := kernel.GetClient().Types().InitJsiiProxy(ptrVal, ptrVal.Type()); err != nil {
 		panic(err)
 	}
 }
@@ -127,7 +127,7 @@ func Create(fqn FQN, args []interface{}, inst interface{}) {
 			if !fieldVal.IsNil() {
 				continue
 			}
-			if err := client.Types().InitJsiiProxy(fieldVal); err != nil {
+			if err := client.Types().InitJsiiProxy(fieldVal, fieldVal.Type()); err != nil {
 				panic(err)
 			}
 
@@ -136,7 +136,7 @@ func Create(fqn FQN, args []interface{}, inst interface{}) {
 			if !fieldVal.IsZero() {
 				continue
 			}
-			if err := client.Types().InitJsiiProxy(fieldVal); err != nil {
+			if err := client.Types().InitJsiiProxy(fieldVal, fieldVal.Type()); err != nil {
 				panic(err)
 			}
 		}