Add this as a self type (#1708)

stdlib/base.pkl

@@ -46,7 +46,7 @@ import "pkl:yaml"
 /// ```
 abstract external class Any {
   /// Returns the class of [this].
-  external function getClass(): Class
+  external function getClass(): Class<this>
 
   /// Returns a string representation of [this].
   ///
@@ -57,7 +57,7 @@ abstract external class Any {
   ///
   /// This method is the complement of the `??` operator and the equivalent of an `Option` type's
   /// `map` and `flatMap` methods.
-  external function ifNonNull<Result>(transform: (NonNull) -> Result): Result?
+  external function ifNonNull<Result>(transform: (this) -> Result): Result?
 }
 
 /// The type of [null] and null values created with [Null()].

stdlib/ref.pkl

@@ -210,7 +210,7 @@ external class Reference<out D, out T> {
 abstract class Domain {
   /// Determines how [Reference] instances are transformed to strings by [Reference.toString()] and
   /// string interpolation.
-  abstract function renderReference(reference: Reference<Domain, Any>): String
+  abstract function renderReference(reference: Reference<this, Any>): String
 }
 
 /// A property or subscript access as part of a [Reference]'s path.

stdlib/reflect.pkl

@@ -107,6 +107,9 @@ const bytesType: DeclaredType = DeclaredType(Class(Bytes))
 /// A mirror for the `module` type.
 external const moduleType: ModuleType
 
+/// A mirror for the `this` type.
+external const thisType: ThisType
+
 /// A mirror for the `unknown` type.
 external const unknownType: UnknownType
 
@@ -431,6 +434,11 @@ external class FunctionType extends Type {
 /// [moduleType] is an instance of this class.
 class ModuleType extends Type
 
+/// The `this` type.
+///
+/// [thisType] is an instance of this class.
+class ThisType extends Type
+
 /// The `unknown` type.
 ///
 /// [unknownType] is an instance of this class.