Add access to computed attributes that are not AttributeType

Sources/JSONAPI/Resource/Entity.swift

@@ -407,8 +407,19 @@ public extension EntityProxy {
 	/// allows you to write `entity[\.propertyName]` instead
 	/// of `entity.relationships.propertyName`.
 	subscript<T, TFRM: Transformer, U>(_ path: KeyPath<Description.Attributes, TransformedAttribute<T, TFRM>?>) -> U? where TFRM.To == U? {
+		// Implementation Note: Handles Transform that returns optional
+		// type.
 		return attributes[keyPath: path].flatMap { $0.value }
 	}
+
+	/// Access the computed attribute at the given keypath. This just
+	/// allows you to write `entity[\.propertyName]` instead
+	/// of `entity.relationships.propertyName`.
+	subscript<T>(_ path: KeyPath<Description.Attributes, T>) -> T {
+		// Implementation Note: Handles attributes that are not
+		// AttributeType. These should only exist as computed properties.
+		return attributes[keyPath: path]
+	}
 }
 
 // MARK: Relationship Access

Tests/JSONAPITests/Computed Properties/ComputedPropertiesTests.swift

@@ -29,6 +29,12 @@ class ComputedPropertiesTests: XCTestCase {
 		XCTAssertEqual(entity[\.computed], "Sarah2")
 	}
 
+	func test_ComputedNonAttributeAccess() {
+		let entity = decoded(type: TestType.self, data: computed_property_attribute)
+
+		XCTAssertEqual(entity[\.computed2], "Sarah2")
+	}
+
 	func test_ComputedRelationshipAccess() {
 		let entity = decoded(type: TestType.self, data: computed_property_attribute)
 
@@ -46,6 +52,10 @@ extension ComputedPropertiesTests {
 			public var computed: Attribute<String> {
 				return name.map { $0 + "2" }
 			}
+
+			public var computed2: String {
+				return computed.value
+			}
 		}
 
 		public struct Relationships: JSONAPI.Relationships {