Component signature

package.json

@@ -22,7 +22,7 @@
     "test:babel-plugins": "yarn workspace @glimmer/babel-preset test",
     "test:browsers": "testem ci",
     "test:ember": "yarn workspace @glimmer/component ember try:one",
-    "test:types": "dtslint test/types",
+    "test:types": "tsc --noEmit --project test/types && dtslint test/types",
     "test:watch": "testem"
   },
   "browserslist": {
@@ -53,6 +53,7 @@
     "@typescript-eslint/parser": "^4.18.0",
     "babel-loader": "^8.1.0",
     "dtslint": "^3.4.1",
+    "expect-type": "~0.13.0",
     "eslint": "^6.8.0",
     "eslint-config-prettier": "^6.10.1",
     "eslint-plugin-prettier": "^3.1.2",

packages/@glimmer/component/addon/-private/component.ts

@@ -10,12 +10,66 @@ export function setDestroyed(component: GlimmerComponent<object>): void {
   DESTROYED.set(component, true);
 }
 
-export let ARGS_SET: WeakMap<object, boolean>;
+// This provides a type-safe `WeakMap`: the getter and setter link the key to a
+// specific value. This is how `WeakMap`s actually behave, but the TS type
+// system does not (yet!) have a good way to capture that for types like
+// `WeakMap` where the type is generic over another generic type (here, `Args`).
+interface ArgsSetMap extends WeakMap<Args<unknown>, boolean> {
+  get<S>(key: Args<S>): boolean | undefined;
+  set<S>(key: Args<S>, value: boolean): this;
+}
+
+// SAFETY: this only holds because we *only* acces this when `DEBUG` is `true`.
+// There is not a great way to connect that data in TS at present.
+export let ARGS_SET: ArgsSetMap;
 
 if (DEBUG) {
-  ARGS_SET = new WeakMap();
+  ARGS_SET = new WeakMap() as ArgsSetMap;
 }
 
+// --- Type utilities for component signatures --- //
+
+// This provides us a way to have a "fallback" which represents an empty object,
+// without the downsides of how TS treats `{}`. Specifically: this will
+// correctly leverage "excess property checking" so that, given a component
+// which has no named args, if someone invokes it with any named args, they will
+// get a type error.
+declare const Empty: unique symbol;
+type EmptyObject = { [Empty]?: true };
+
+type GetOrElse<Obj, K, Fallback> = K extends keyof Obj ? Obj[K] : Fallback;
+
+/** Given a signature `S`, get back the `Args` type. */
+type ArgsFor<S> = 'Args' extends keyof S
+  ? S['Args'] extends { Named?: object; Positional?: unknown[] } // Are they longhand already?
+    ? {
+        Named: GetOrElse<S['Args'], 'Named', EmptyObject>;
+        Positional: GetOrElse<S['Args'], 'Positional', []>;
+      }
+    : { Named: S['Args']; Positional: [] }
+  : { Named: EmptyObject; Positional: [] };
+
+/** Given any allowed shorthand form of a signature, desugars it to its full expanded type */
+type ExpandSignature<T> = {
+  Element: GetOrElse<T, 'Element', null>;
+  Args: keyof T extends 'Args' | 'Element' | 'Blocks' // Is this a `Signature`?
+    ? ArgsFor<T> // Then use `Signature` args
+    : { Named: T; Positional: [] }; // Otherwise fall back to classic `Args`.
+  Blocks: 'Blocks' extends keyof T
+    ? {
+        [Block in keyof T['Blocks']]: T['Blocks'][Block] extends unknown[]
+          ? { Positional: T['Blocks'][Block] }
+          : T['Blocks'][Block];
+      }
+    : EmptyObject;
+};
+
+/**
+ * @internal we use this type for convenience internally; inference means users
+ *   should not normally need to name it
+ */
+export type Args<S> = ExpandSignature<S>['Args']['Named'];
+
 /**
  * The `Component` class defines an encapsulated UI element that is rendered to
  * the DOM. A component is made up of a template and, optionally, this component
@@ -139,7 +193,7 @@ if (DEBUG) {
  * `args` property. For example, if `{{@firstName}}` is `Tom` in the template,
  * inside the component `this.args.firstName` would also be `Tom`.
  */
-export default class GlimmerComponent<Args extends {} = {}> {
+export default class GlimmerComponent<S = unknown> {
   /**
    * Constructs a new component and assigns itself the passed properties. You
    * should not construct new components yourself. Instead, Glimmer will
@@ -148,7 +202,7 @@ export default class GlimmerComponent<Args extends {} = {}> {
    * @param owner
    * @param args
    */
-  constructor(_owner: unknown, args: Args) {
+  constructor(_owner: unknown, args: Args<S>) {
     if (DEBUG && !ARGS_SET.has(args)) {
       throw new Error(
         `You must pass both the owner and args to super() in your component: ${this.constructor.name}. You can pass them directly, or use ...arguments to pass all arguments through.`
@@ -185,7 +239,7 @@ export default class GlimmerComponent<Args extends {} = {}> {
    * <p>Welcome, {{@firstName}} {{@lastName}}!</p>
    * ```
    */
-  args: Readonly<Args>;
+  readonly args: Readonly<Args<S>>;
 
   get isDestroying(): boolean {
     return DESTROYING.get(this) || false;

packages/@glimmer/component/addon/index.ts

@@ -12,11 +12,11 @@ declare module '@ember/component' {
 import { setComponentManager } from '@ember/component';
 
 import GlimmerComponentManager from './-private/ember-component-manager';
-import _GlimmerComponent from './-private/component';
+import _GlimmerComponent, { Args } from './-private/component';
 import { setOwner } from '@ember/application';
 
-export default class GlimmerComponent extends _GlimmerComponent {
-  constructor(owner, args) {
+export default class GlimmerComponent<S> extends _GlimmerComponent<S> {
+  constructor(owner: object, args: Args<S>) {
     super(owner, args);
 
     if (DEBUG && !(owner !== null && typeof owner === 'object')) {

packages/@glimmer/component/src/component.ts

@@ -1,10 +1,10 @@
 import { setComponentManager, setOwner } from '@glimmer/core';
 import GlimmerComponentManager from './component-manager';
-import _GlimmerComponent from '../addon/-private/component';
+import _GlimmerComponent, { Args } from '../addon/-private/component';
 import { DEBUG } from '@glimmer/env';
 
-export default class GlimmerComponent<Args extends {} = {}> extends _GlimmerComponent<Args> {
-  constructor(owner: object, args: Args) {
+export default class GlimmerComponent<S> extends _GlimmerComponent<S> {
+  constructor(owner: object, args: Args<S>) {
     super(owner, args);
 
     if (DEBUG && !(owner !== null && typeof owner === 'object')) {

packages/@glimmer/tracking/src/tracked.ts

@@ -121,7 +121,9 @@ function descriptorForField<T extends object, K extends keyof T>(
 ): PropertyDescriptor {
   if (DEBUG && desc && (desc.value || desc.get || desc.set)) {
     throw new Error(
-      `You attempted to use @tracked on ${key}, but that element is not a class field. @tracked is only usable on class fields. Native getters and setters will autotrack add any tracked fields they encounter, so there is no need mark getters and setters with @tracked.`
+      `You attempted to use @tracked on ${String(
+        key
+      )}, but that element is not a class field. @tracked is only usable on class fields. Native getters and setters will autotrack add any tracked fields they encounter, so there is no need mark getters and setters with @tracked.`
     );
   }
 

test/types/component-test.ts

@@ -1,39 +1,96 @@
+import { expectTypeOf } from 'expect-type';
 import * as gc from '@glimmer/component';
-import { hasExactKeys } from './utils';
 
 const Component = gc.default;
 
-hasExactKeys<{
-  default: unknown;
-}>()(gc);
-
-// $ExpectType typeof GlimmerComponent
-gc.default;
+expectTypeOf(gc).toHaveProperty('default');
+expectTypeOf(gc.default).toEqualTypeOf<typeof Component>();
 
 type Args = {
   foo: number;
 };
 
-const component = new Component<Args>({}, { foo: 123 });
+const componentWithLegacyArgs = new Component<Args>({}, { foo: 123 });
+expectTypeOf(componentWithLegacyArgs).toHaveProperty('args');
+expectTypeOf(componentWithLegacyArgs).toHaveProperty('isDestroying');
+expectTypeOf(componentWithLegacyArgs).toHaveProperty('isDestroyed');
+expectTypeOf(componentWithLegacyArgs).toHaveProperty('willDestroy');
+expectTypeOf(componentWithLegacyArgs.args).toEqualTypeOf<Readonly<Args>>();
+expectTypeOf(componentWithLegacyArgs.isDestroying).toEqualTypeOf<boolean>();
+expectTypeOf(componentWithLegacyArgs.isDestroyed).toEqualTypeOf<boolean>();
+expectTypeOf(componentWithLegacyArgs.willDestroy).toEqualTypeOf<() => void>();
+
+interface ArgsOnly {
+  Args: Args;
+}
+
+const componentWithArgsOnly = new Component<ArgsOnly>({}, { foo: 123 });
+expectTypeOf(componentWithArgsOnly.args).toEqualTypeOf<Readonly<Args>>();
+
+interface ElementOnly {
+  Element: HTMLParagraphElement;
+}
+
+const componentWithElOnly = new Component<ElementOnly>({}, {});
+
+// We cannot check on toEqualTypeOf here b/c EmptyObject is intentionally not
+// public.
+expectTypeOf(componentWithElOnly.args).toMatchTypeOf<Readonly<{}>>();
+
+interface Blocks {
+  default: [name: string];
+  inverse: [];
+}
+
+interface BlockOnlySig {
+  Blocks: Blocks;
+}
+
+const componentWithBlockOnly = new Component<BlockOnlySig>({}, {});
+
+// We cannot check on toEqualTypeOf here b/c EmptyObject is intentionally not
+// public.
+expectTypeOf(componentWithBlockOnly.args).toMatchTypeOf<Readonly<{}>>();
+
+interface ArgsAndBlocks {
+  Args: Args;
+  Blocks: Blocks;
+}
+
+const componentwithArgsAndBlocks = new Component<ArgsAndBlocks>({}, { foo: 123 });
+expectTypeOf(componentwithArgsAndBlocks.args).toEqualTypeOf<Readonly<Args>>();
 
-hasExactKeys<{
-  args: unknown;
-  isDestroying: unknown;
-  isDestroyed: unknown;
-  willDestroy: unknown;
-}>()(component);
+interface ArgsAndEl {
+  Args: Args;
+  Element: HTMLParagraphElement;
+}
 
-// $ExpectType Readonly<Args>
-component.args;
+const componentwithArgsAndEl = new Component<ArgsAndEl>({}, { foo: 123 });
+expectTypeOf(componentwithArgsAndEl.args).toEqualTypeOf<Readonly<Args>>();
 
-// $ExpectType boolean
-component.isDestroying;
+interface FullShortSig {
+  Args: Args;
+  Element: HTMLParagraphElement;
+  Blocks: Blocks;
+}
 
-// $ExpectType boolean
-component.isDestroyed;
+const componentWithFullShortSig = new Component<FullShortSig>({}, { foo: 123 });
+expectTypeOf(componentWithFullShortSig.args).toEqualTypeOf<Readonly<Args>>();
 
-// $ExpectType () => void
-component.willDestroy;
+interface FullLongSig {
+  Args: {
+    Named: Args;
+    Positional: [];
+  };
+  Element: HTMLParagraphElement;
+  Blocks: {
+    default: {
+      Params: {
+        Positional: [name: string];
+      };
+    };
+  };
+}
 
-// $ExpectError
-component.args.bar = 123;
+const componentWithFullSig = new Component<FullLongSig>({}, { foo: 123 });
+expectTypeOf(componentWithFullSig.args).toEqualTypeOf<Readonly<Args>>();

yarn.lock

@@ -6898,6 +6898,11 @@ expand-tilde@^2.0.0, expand-tilde@^2.0.2:
   dependencies:
     homedir-polyfill "^1.0.1"
 
+expect-type@~0.13.0:
+  version "0.13.0"
+  resolved "https://registry.yarnpkg.com/expect-type/-/expect-type-0.13.0.tgz#916646a7a73f3ee77039a634ee9035efe1876eb2"
+  integrity sha512-CclevazQfrqo8EvbLPmP7osnb1SZXkw47XPPvUUpeMz4HuGzDltE7CaIt3RLyT9UQrwVK/LDn+KVcC0hcgjgDg==
+
 express@^4.10.7, express@^4.17.1:
   version "4.17.2"
   resolved "https://registry.npmjs.org/express/-/express-4.17.2.tgz#c18369f265297319beed4e5558753cc8c1364cb3"