refactor(frontend-plugin,app-api): make app spec plugin required

Signed-off-by: Camila Belo <camilaibs@gmail.com>

.changeset/fluffy-otters-cry.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-app-api': minor
+---
+
+Use an empty root plugin for built-in extension app node specs.

.changeset/thirty-eagles-run.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-app-api': minor
+---
+
+**BREAKING:** The `AppNodeSpec.plugin` property is now required.

packages/frontend-app-api/src/tree/instantiateAppNodeTree.test.ts

@@ -24,6 +24,7 @@ import {
   createExtension,
   createExtensionDataRef,
   createExtensionInput,
+  createFrontendPlugin,
 } from '@backstage/frontend-plugin-api';
 import {
   createAppNodeInstance,
@@ -56,7 +57,7 @@ function makeSpec<TConfig, TConfigInput>(
     attachTo: extension.attachTo,
     disabled: extension.disabled,
     extension: extension as Extension<unknown, unknown>,
-    plugin: undefined,
+    plugin: createFrontendPlugin({ pluginId: 'root' }),
     ...spec,
   };
 }

packages/frontend-app-api/src/tree/resolveAppNodeSpecs.test.ts

@@ -20,7 +20,7 @@ import {
   Extension,
   ExtensionDefinition,
 } from '@backstage/frontend-plugin-api';
-import { resolveAppNodeSpecs } from './resolveAppNodeSpecs';
+import { resolveAppNodeSpecs, rootPlugin } from './resolveAppNodeSpecs';
 
 function makeExt(
   id: string,
@@ -62,12 +62,15 @@ describe('resolveAppNodeSpecs', () => {
         builtinExtensions: [a],
         parameters: [],
       }),
-    ).toEqual([
+    ).toStrictEqual([
       {
         id: 'a',
         extension: a,
         attachTo: { id: 'root', input: 'default' },
         disabled: true,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
     ]);
   });
@@ -87,12 +90,18 @@ describe('resolveAppNodeSpecs', () => {
         extension: a,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'b',
         extension: b,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
     ]);
   });
@@ -120,6 +129,9 @@ describe('resolveAppNodeSpecs', () => {
         extension: b,
         attachTo: { id: 'derp', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'test/a',
@@ -204,12 +216,18 @@ describe('resolveAppNodeSpecs', () => {
         extension: b,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'a',
         extension: a,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
     ]);
   });
@@ -238,42 +256,63 @@ describe('resolveAppNodeSpecs', () => {
         extension: e,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'd',
         extension: d,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'c',
         extension: c,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'a',
         extension: a,
         attachTo: { id: 'root', input: 'default' },
         disabled: true,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'b',
         extension: b,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'f',
         extension: f,
         attachTo: { id: 'root', input: 'default' },
         disabled: false,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
       {
         id: 'g',
         extension: g,
         attachTo: { id: 'root', input: 'default' },
         disabled: true,
+        config: undefined,
+        plugin: rootPlugin,
+        source: rootPlugin,
       },
     ]);
   });

packages/frontend-app-api/src/tree/resolveAppNodeSpecs.ts

@@ -14,7 +14,11 @@
  * limitations under the License.
  */
 
-import { Extension, FrontendFeature } from '@backstage/frontend-plugin-api';
+import {
+  createFrontendPlugin,
+  Extension,
+  FrontendFeature,
+} from '@backstage/frontend-plugin-api';
 import { ExtensionParameters } from './readAppExtensionsConfig';
 import { AppNodeSpec } from '@backstage/frontend-plugin-api';
 import { OpaqueFrontendPlugin } from '@internal/frontend';
@@ -26,6 +30,8 @@ import {
 // eslint-disable-next-line @backstage/no-relative-monorepo-imports
 import { toInternalExtension } from '../../../frontend-plugin-api/src/wiring/resolveExtensionDefinition';
 
+export const rootPlugin = createFrontendPlugin({ pluginId: 'root' });
+
 /** @internal */
 export function resolveAppNodeSpecs(options: {
   features?: FrontendFeature[];
@@ -106,8 +112,8 @@ export function resolveAppNodeSpecs(options: {
       return {
         extension: internalExtension,
         params: {
-          source: undefined,
-          plugin: undefined,
+          source: rootPlugin,
+          plugin: rootPlugin,
           attachTo: internalExtension.attachTo,
           disabled: internalExtension.disabled,
           config: undefined as unknown,

packages/frontend-app-api/src/tree/resolveAppTree.test.ts

@@ -18,6 +18,7 @@ import {
   coreExtensionData,
   createExtension,
   createExtensionInput,
+  createFrontendPlugin,
   Extension,
 } from '@backstage/frontend-plugin-api';
 import { resolveAppTree } from './resolveAppTree';
@@ -37,6 +38,7 @@ const baseSpec = {
   extension,
   attachTo: { id: 'nonexistent', input: 'nonexistent' },
   disabled: false,
+  plugin: createFrontendPlugin({ pluginId: 'root' }),
 };
 
 describe('buildAppTree', () => {
@@ -284,8 +286,20 @@ describe('buildAppTree', () => {
       ) as Extension<unknown, unknown>;
 
       const tree = resolveAppTree('a', [
-        { attachTo: e1.attachTo, id: 'a', extension: e1, disabled: false },
-        { attachTo: e2.attachTo, id: 'b', extension: e2, disabled: false },
+        {
+          attachTo: e1.attachTo,
+          id: 'a',
+          extension: e1,
+          disabled: false,
+          plugin: baseSpec.plugin,
+        },
+        {
+          attachTo: e2.attachTo,
+          id: 'b',
+          extension: e2,
+          disabled: false,
+          plugin: baseSpec.plugin,
+        },
       ]);
 
       expect(tree.root).toMatchInlineSnapshot(`
@@ -352,9 +366,27 @@ describe('buildAppTree', () => {
       ) as Extension<unknown, unknown>;
 
       const tree = resolveAppTree('test-2', [
-        { attachTo: e1.attachTo, id: e1.id, extension: e1, disabled: false },
-        { attachTo: e2.attachTo, id: e2.id, extension: e2, disabled: false },
-        { attachTo: e3.attachTo, id: e3.id, extension: e3, disabled: false },
+        {
+          attachTo: e1.attachTo,
+          id: e1.id,
+          extension: e1,
+          disabled: false,
+          plugin: baseSpec.plugin,
+        },
+        {
+          attachTo: e2.attachTo,
+          id: e2.id,
+          extension: e2,
+          disabled: false,
+          plugin: baseSpec.plugin,
+        },
+        {
+          attachTo: e3.attachTo,
+          id: e3.id,
+          extension: e3,
+          disabled: false,
+          plugin: baseSpec.plugin,
+        },
       ]);
 
       expect(tree.nodes.get('test-3')?.edges.attachedTo?.node).toBe(

packages/frontend-plugin-api/src/apis/definitions/AppTreeApi.ts

@@ -37,7 +37,7 @@ export interface AppNodeSpec {
   readonly extension: Extension<unknown, unknown>;
   readonly disabled: boolean;
   readonly config?: unknown;
-  readonly plugin?: FrontendPlugin;
+  readonly plugin: FrontendPlugin;
 }
 
 /**