Fix a problem where plain functions can't be used as helper if they a…

…re not passed through the strict mode context object

It seems functions passed as strict mode context values follow a different code path than component arguments and class properties so the error wasn't shown there.

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

@@ -3,6 +3,7 @@ import {
   RenderTest,
   test,
   jitSuite,
+  GlimmerishComponent,
   tracked,
   defineComponent,
   trackedObj,
@@ -57,6 +58,58 @@ class HelperManagerTest extends RenderTest {
     this.assertHTML('plain function');
   }
 
+  @test({ skip: SKIP_DEFAULT_HELPER_MANAGER_TESTS })
+  '(Default Helper Manager) plain functions passed as component arguments work as helpers'(
+    assert: Assert
+  ) {
+    let count = 0;
+
+    const hello = () => {
+      count++;
+      return 'plain function';
+    };
+
+    const Main = defineComponent({}, '{{(@hello)}}');
+
+    this.renderComponent(Main, {
+      hello,
+    });
+
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('plain function');
+
+    this.rerender();
+
+    assert.equal(count, 1, 'rendered once');
+    this.assertHTML('plain function');
+  }
+
+  @test({ skip: SKIP_DEFAULT_HELPER_MANAGER_TESTS })
+  '(Default Helper Manager) plain functions stored on component class properties work as helpers'(
+    assert: Assert
+  ) {
+    let count = 0;
+
+    const Main = defineComponent({}, '{{(this.hello)}}', {
+      definition: class extends GlimmerishComponent {
+        hello = () => {
+          count++;
+          return 'plain function';
+        };
+      },
+    });
+
+    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({ skip: SKIP_DEFAULT_HELPER_MANAGER_TESTS })
   '(Default Helper Manager) plain functions track positional args'(assert: Assert) {
     let count = 0;

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

@@ -213,13 +213,36 @@ export function getInternalComponentManager(
 ///////////
 
 export function hasInternalComponentManager(definition: object): boolean {
-  return getManager(COMPONENT_MANAGERS, definition) !== undefined;
+  return (
+    hasDefaultComponentManager(definition) ||
+    getManager(COMPONENT_MANAGERS, definition) !== undefined
+  );
 }
 
 export function hasInternalHelperManager(definition: object): boolean {
-  return getManager(HELPER_MANAGERS, definition) !== undefined;
+  return (
+    hasDefaultHelperManager(definition) || getManager(HELPER_MANAGERS, definition) !== undefined
+  );
 }
 
 export function hasInternalModifierManager(definition: object): boolean {
-  return getManager(MODIFIER_MANAGERS, definition) !== undefined;
+  return (
+    hasDefaultModifierManager(definition) || getManager(MODIFIER_MANAGERS, definition) !== undefined
+  );
+}
+
+function hasDefaultComponentManager(_definition: object): boolean {
+  return false;
+}
+
+function hasDefaultHelperManager(definition: object): boolean {
+  if (FEATURE_DEFAULT_HELPER_MANAGER) {
+    return typeof definition === 'function';
+  }
+
+  return false;
+}
+
+function hasDefaultModifierManager(_definition: object): boolean {
+  return false;
 }