Implementation for RFC #756

packages/@glimmer/integration-tests/test/managers/helper-manager-test.ts

@@ -32,6 +32,133 @@ class HelperManagerTest extends RenderTest {
     this.assertHTML('hello');
   }
 
+  @test '(Default Helper Manager) plain functions work as helpers'(assert: Assert) {
+    let count = 0;
+
+    const hello = () => {
+      count++;
+      return 'plain function';
+    };
+
+    const Main = defineComponent({ hello }, '{{hello}}');
+
+    this.renderComponent(Main);
+
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('plain function');
+
+    this.rerender();
+
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('plain function');
+  }
+
+  @test '(Default Helper Manager) plain functions track positional args'(assert: Assert) {
+    let count = 0;
+
+    let obj = (x: string) => {
+      count++;
+      return x;
+    };
+    let args = trackedObj({ value: 'hello', unused: 'unused' });
+
+    this.renderComponent(defineComponent({ obj }, '{{obj @value @unused}}'), args);
+
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('hello');
+
+    args.value = 'there';
+    this.rerender();
+
+    assert.equal(count, 2, 'rendered twice');
+    this.assertHTML('there');
+
+    args.unused = 'unused2';
+    this.rerender();
+
+    assert.equal(count, 3, 'rendered thrice');
+    this.assertHTML('there');
+  }
+
+  @test '(Default Helper Manager) plain functions do not track unused named args'(assert: Assert) {
+    let count = 0;
+
+    let obj = (x: string, _options: Record<string, unknown>) => {
+      count++;
+      return x;
+    };
+    let args = trackedObj({ value: 'hello', unused: 'unused' });
+
+    this.renderComponent(defineComponent({ obj }, '{{obj @value namedOpt=@unused}}'), args);
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('hello');
+
+    args.unused = 'unused2';
+    this.rerender();
+
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('hello');
+  }
+
+  @test '(Default Helper Manager) plain functions tracked used named args'(assert: Assert) {
+    let count = 0;
+
+    let obj = (_x: string, options: Record<string, unknown>) => {
+      count++;
+      return options.namedOpt;
+    };
+
+    let args = trackedObj({ value: 'hello', used: 'used' });
+
+    this.renderComponent(defineComponent({ obj }, '{{obj @value namedOpt=@used}}'), args);
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('used');
+
+    args.used = 'there';
+    this.rerender();
+
+    assert.equal(count, 2, 'rendered twice');
+    this.assertHTML('there');
+  }
+
+  @test '(Default Helper Manager) plain function helpers can have default values (missing data)'(
+    assert: Assert
+  ) {
+    let count = 0;
+    let obj = (x = 'default value') => {
+      count++;
+      return x;
+    };
+
+    let args = trackedObj({});
+
+    this.renderComponent(defineComponent({ obj }, 'result: {{obj}}'), args);
+    this.assertHTML('result: default value');
+    assert.equal(count, 1, 'rendered once');
+  }
+
+  @test '(Default Helper Manager) plain function helpers can have overwritten default values'(
+    assert: Assert
+  ) {
+    let count = 0;
+    let obj = (x = 'default value') => {
+      count++;
+      return x;
+    };
+
+    let args = trackedObj({ value: undefined });
+
+    this.renderComponent(defineComponent({ obj }, 'result: {{obj @value}}'), args);
+    this.assertHTML('result: default value');
+    assert.equal(count, 1, 'rendered once');
+
+    args.value = 'value';
+    this.rerender();
+
+    this.assertHTML('result: value');
+    assert.equal(count, 2, 'rendered twice');
+  }
+
   @test 'tracks changes to named arguments'(assert: Assert) {
     let count = 0;
 

packages/@glimmer/manager/lib/internal/defaults.ts

@@ -0,0 +1,50 @@
+import { buildCapabilities } from '../util/capabilities';
+
+import type { CapturedArguments as Arguments, HelperCapabilities } from '@glimmer/interfaces';
+
+type FnArgs<Args extends Arguments = Arguments> =
+  | [...Args['positional'], Args['named']]
+  | [...Args['positional'], {}];
+
+interface FunctionHelperState<Args extends Arguments = Arguments> {
+  fn: <Return>(...args: FnArgs<Args>) => Return;
+  args: Args;
+}
+
+export class FunctionHelperManager<State extends FunctionHelperState> {
+  capabilities = buildCapabilities({
+    hasValue: true,
+    hasDestroyable: false,
+    hasScheduledEffect: false,
+  }) as HelperCapabilities;
+
+  createHelper(fn: State['fn'], args: State['args']) {
+    return { fn, args };
+  }
+
+  getValue({ fn, args }: State) {
+    let namedKeys = Object.keys(args.named).length;
+
+    if (args.positional.length === 0 && namedKeys === 0) {
+      return fn();
+    }
+
+    // This consumes all positional args
+    let argsForFn: FnArgs<Arguments> = [...args.positional];
+
+    if (namedKeys > 0) {
+      // This consumes all named args
+      argsForFn.push(args.named);
+    }
+
+    return fn(...argsForFn);
+  }
+
+  getDebugName(fn: State['fn']) {
+    if (fn.name) {
+      return `(helper function ${fn.name})`;
+    }
+
+    return '(anonymous helper function)';
+  }
+}

packages/@glimmer/manager/lib/internal/index.ts

@@ -7,6 +7,7 @@ import {
   Owner,
 } from '@glimmer/interfaces';
 import { CustomHelperManager } from '../public/helper';
+import { FunctionHelperManager } from './defaults';
 
 type InternalManager =
   | InternalComponentManager
@@ -119,6 +120,8 @@ export function setInternalHelperManager<T extends object, O extends Owner>(
   return setManager(HELPER_MANAGERS, manager, definition);
 }
 
+const DEFAULT_MANAGER = new CustomHelperManager(() => new FunctionHelperManager());
+
 export function getInternalHelperManager(definition: object): CustomHelperManager | Helper;
 export function getInternalHelperManager(
   definition: object,
@@ -138,7 +141,13 @@ export function getInternalHelperManager(
     );
   }
 
-  const manager = getManager(HELPER_MANAGERS, definition);
+  let manager = getManager(HELPER_MANAGERS, definition);
+
+  // Functions are special-cased because functions are defined
+  // as the "default" helper, per: https://github.com/emberjs/rfcs/pull/756
+  if (manager === undefined && typeof definition === 'function') {
+    manager = DEFAULT_MANAGER;
+  }
 
   if (manager) {
     return manager;

packages/@glimmer/manager/test/managers-test.ts

@@ -183,11 +183,26 @@ module('Managers', () => {
       assert.ok(typeof instance === 'object', 'manager is an internal manager');
       assert.ok(
         typeof instance.getHelper({}) === 'function',
-        'manager can generatew helper function'
+        'manager can generate helper function'
       );
       assert.equal(instance['factory'], factory, 'manager has correct delegate factory');
     });
 
+    test('it determines the default manager', (assert) => {
+      let myTestHelper = () => 0;
+      let instance = getInternalHelperManager(myTestHelper) as CustomHelperManager<object>;
+
+      assert.ok(typeof instance === 'object', 'manager is an internal manager');
+      assert.ok(
+        typeof instance.getHelper({}) === 'function',
+        'manager can generate helper function'
+      );
+      assert.strictEqual(
+        instance['factory']({})?.getDebugName?.(myTestHelper),
+        '(helper function myTestHelper)'
+      );
+    });
+
     test('it works with internal helpers', (assert) => {
       let helper = () => {
         return UNDEFINED_REFERENCE;