Implementation for RFC #756

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

@@ -0,0 +1,36 @@
+import { CAPABILITIES, CapturedArguments as Arguments } 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 = {
+    [CAPABILITIES]: true,
+    hasValue: true,
+    hasDestroyable: false,
+    hasScheduledEffect: false,
+  } as const;
+
+  createHelper(fn: State['fn'], args: State['args']) {
+    return { fn, args };
+  }
+
+  getValue({ fn, args }: State) {
+    let argsForFn: FnArgs<Arguments> = [
+      ...args.positional,
+      Object.keys(args.named).length > 0 ? args.named : {},
+    ];
+
+    return fn(...argsForFn);
+  }
+
+  getDebugName(fn: State['fn']) {
+    return fn.name || '(anonymous function)';
+  }
+}

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

@@ -8,6 +8,7 @@ import {
 import { CustomComponentManager } from './component';
 import { CustomModifierManager } from './modifier';
 import { CustomHelperManager } from './helper';
+import { FunctionHelperManager } from '../internal/defaults';
 
 type Manager = ComponentManager<unknown> | ModifierManager<unknown> | HelperManager<unknown>;
 
@@ -33,3 +34,5 @@ export function setHelperManager<O extends Owner, T extends object>(
 ): T {
   return setInternalHelperManager(new CustomHelperManager(factory), obj);
 }
+
+setHelperManager(() => new FunctionHelperManager(), Function.prototype);