From cfd94f29edc9aeb0178e1c23c3e3df03616b2386 Mon Sep 17 00:00:00 2001
From: Camila Belo <camilaibs@gmail.com>
Date: Wed, 20 Sep 2023 15:11:05 +0200
Subject: [PATCH] test(frontend-app-api): cover more levels of cyclical
 dependencies

Signed-off-by: Camila Belo <camilaibs@gmail.com>
---
 .../src/wiring/createApp.test.tsx             | 176 +++++++++++++++++-
 1 file changed, 175 insertions(+), 1 deletion(-)

diff --git a/packages/frontend-app-api/src/wiring/createApp.test.tsx b/packages/frontend-app-api/src/wiring/createApp.test.tsx
index 339948eec1..dcbd996f15 100644
--- a/packages/frontend-app-api/src/wiring/createApp.test.tsx
+++ b/packages/frontend-app-api/src/wiring/createApp.test.tsx
@@ -14,10 +14,18 @@
  * limitations under the License.
  */
 
-import { createExtension, createPlugin } from '@backstage/frontend-plugin-api';
+import {
+  createExtension,
+  createExtensionDataRef,
+  createExtensionInput,
+  createPageExtension,
+  createPlugin,
+} from '@backstage/frontend-plugin-api';
 import { createInstances } from './createApp';
 
 import { MockConfigApi } from '@backstage/test-utils';
+import React from 'react';
+import { createRouteRef } from '@backstage/core-plugin-api';
 
 describe('createInstances', () => {
   it('throws an error when a root extension is parametrized', () => {
@@ -63,4 +71,170 @@ describe('createInstances', () => {
       'The following plugins are overriding root extensions and root extensions cannot be overridden: plugin',
     );
   });
+
+  describe('throws an error when immediate cyclical dependencies are found', () => {
+    it('in an immediate level (e.g., A(plugin.page) -> A(plugin.page))', () => {
+      const config = new MockConfigApi({});
+
+      const addonExtensionData =
+        createExtensionDataRef<JSX.Element>('plugin.page.addon');
+
+      const addon = createExtension({
+        id: 'plugin.page', // cyclical
+        at: 'plugin.page/addons',
+        inputs: {},
+        output: {
+          element: addonExtensionData,
+        },
+        factory({ bind }) {
+          bind({
+            element: <div key="addon">Addon</div>,
+          });
+        },
+      });
+
+      const page = createPageExtension({
+        id: 'plugin.page',
+        defaultPath: '/',
+        routeRef: createRouteRef({ id: 'plugins.page.addon' }),
+        inputs: {
+          addons: createExtensionInput({
+            element: addonExtensionData,
+          }),
+        },
+        loader: async ({ inputs }) => (
+          <div>Page {inputs.addons.map(({ element }) => element)}</div>
+        ),
+      });
+
+      const plugins = [
+        createPlugin({
+          id: 'plugin',
+          extensions: [page, addon],
+        }),
+      ];
+
+      expect(() => createInstances({ config, plugins })).toThrow(
+        'There is a cyclical dependency with the extension "plugin.page": core.layout → core.routes → plugin.page → plugin.page',
+      );
+    });
+
+    it('in an intermediate level (e.g., A(core.routes) -> B(plugin.page) -> A(core.routes))', () => {
+      const config = new MockConfigApi({});
+
+      const addonExtensionData =
+        createExtensionDataRef<JSX.Element>('plugin.page.addon');
+
+      const addon = createExtension({
+        id: 'core.routes', // cyclical
+        at: 'plugin.page/addons',
+        inputs: {},
+        output: {
+          element: addonExtensionData,
+        },
+        factory({ bind }) {
+          bind({
+            element: <div key="addon">Addon</div>,
+          });
+        },
+      });
+
+      const page = createPageExtension({
+        id: 'plugin.page',
+        defaultPath: '/',
+        routeRef: createRouteRef({ id: 'plugins.page.addon' }),
+        inputs: {
+          addons: createExtensionInput({
+            element: addonExtensionData,
+          }),
+        },
+        loader: async ({ inputs }) => (
+          <div>Page {inputs.addons.map(({ element }) => element)}</div>
+        ),
+      });
+
+      const plugins = [
+        createPlugin({
+          id: 'plugin',
+          extensions: [page, addon],
+        }),
+      ];
+
+      expect(() => createInstances({ config, plugins })).toThrow(
+        'There is a cyclical dependency with the extension "core.routes": core.layout → core.routes → plugin.page → core.routes',
+      );
+    });
+
+    it('in an deep level (e.g., A(core.layout) -> B(core.routes) -> C(plugin.page) -> D(plugin.page.addon) -> B(core.routes))', () => {
+      const config = new MockConfigApi({});
+
+      const addonRendererInput = createExtensionDataRef<() => JSX.Element>(
+        'plugin.page.addon.renderer',
+      );
+
+      const renderer = createExtension({
+        id: 'core.routes', // cyclical
+        at: 'plugin.page.addon/renderer',
+        inputs: {},
+        output: {
+          renderer: addonRendererInput,
+        },
+        factory({ bind }) {
+          bind({
+            renderer: () => <div key="addon">Addon</div>,
+          });
+        },
+      });
+
+      const addonElementInput = createExtensionDataRef<JSX.Element>(
+        'plugin.page.addon.element',
+      );
+
+      const addon = createExtension({
+        id: 'plugin.page.addon',
+        at: 'plugin.page/addons',
+        inputs: {
+          renderer: createExtensionInput(
+            {
+              element: addonRendererInput,
+            },
+            { singleton: true, required: false },
+          ),
+        },
+        output: {
+          element: addonElementInput,
+        },
+        factory({ bind, inputs }) {
+          bind({
+            element: inputs.renderer?.element() ?? <div key="addon">Addon</div>,
+          });
+        },
+      });
+
+      const page = createPageExtension({
+        id: 'plugin.page',
+        defaultPath: '/',
+        routeRef: createRouteRef({ id: 'plugins.page.addon' }),
+        inputs: {
+          addons: createExtensionInput({
+            element: addonElementInput,
+          }),
+        },
+        loader: async ({ inputs }) => (
+          <div>Page {inputs.addons.map(({ element }) => element)}</div>
+        ),
+      });
+
+      const plugins = [
+        createPlugin({
+          id: 'plugin',
+          extensions: [page, addon, renderer],
+        }),
+      ];
+
+      expect(() => createInstances({ config, plugins })).toThrow(
+        'There is a cyclical dependency with the extension "core.routes": core.layout → core.routes → plugin.page → plugin.page.addon → core.routes',
+      );
+    });
+  });
 });