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Address PR review comments

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- Make ExtensionPointFactoryMiddleware an opaque type via new
  @internal/backend package using OpaqueType from @internal/opaque
- Use options object for createExtensionPointFactoryMiddleware
- Make middleware function async (returns Promise<T>)
- Remove extensionPointFactoryMiddleware from createBackend, keep only
  on createSpecializedBackend
- Export defaultServiceFactories from @backstage/backend-defaults

Signed-off-by: Jack Palmer <jackpalmer@spotify.com>
This commit is contained in:
Jack Palmer
2026-04-09 15:59:44 +01:00
parent 3595c974f6
commit e782afcb3b
16 changed files with 181 additions and 66 deletions
Download Patch File Download Diff File Expand all files Collapse all files
.changeset/extension-point-middleware-backend-defaults.md
+1 -1
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@@ -2,4 +2,4 @@
'@backstage/backend-defaults': patch
---
Added `extensionPointFactoryMiddleware` option to `createBackend()` to reimplement extension point outputs at backend initialization time. Also re-exports `ExtensionPointFactoryMiddleware` type and `createExtensionPointFactoryMiddleware` helper from `@backstage/backend-app-api`.
Exported `defaultServiceFactories` to allow use with `createSpecializedBackend` for advanced configuration like `extensionPointFactoryMiddleware`.
packages/backend-app-api/report.api.md
+6 -8
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@@ -44,10 +44,10 @@ export interface BackendStartupResult {
}
// @public
export function createExtensionPointFactoryMiddleware<T>(
extensionPoint: ExtensionPoint<T>,
middleware: (original: T) => T,
): ExtensionPointFactoryMiddleware;
export function createExtensionPointFactoryMiddleware<T>(options: {
extensionPoint: ExtensionPoint<T>;
middleware: (original: T) => Promise<T>;
}): ExtensionPointFactoryMiddleware<T>;
// @public (undocumented)
export function createSpecializedBackend(
@@ -63,11 +63,9 @@ export interface CreateSpecializedBackendOptions {
}
// @public
export interface ExtensionPointFactoryMiddleware<T = unknown> {
export interface ExtensionPointFactoryMiddleware<_T = unknown> {
// (undocumented)
extensionPoint: ExtensionPoint<T>;
// (undocumented)
middleware: (original: T) => T;
$$type: '@backstage/ExtensionPointFactoryMiddleware';
}
// @public
packages/backend-app-api/src/wiring/BackendInitializer.test.ts
+32 -20
View File
@@ -2122,10 +2122,13 @@ describe('BackendInitializer', () => {
});
const init = new BackendInitializer(baseFactories, [
createExtensionPointFactoryMiddleware(extensionPoint, original => ({
...original,
values: [...original.values, 'from-middleware'],
})),
createExtensionPointFactoryMiddleware({
extensionPoint,
middleware: async original => ({
...original,
values: [...original.values, 'from-middleware'],
}),
}),
]);
init.add(testPlugin);
@@ -2170,10 +2173,13 @@ describe('BackendInitializer', () => {
});
const init = new BackendInitializer(baseFactories, [
createExtensionPointFactoryMiddleware(extensionPointA, original => ({
...original,
values: [...original.values, 'wrapped'],
})),
createExtensionPointFactoryMiddleware({
extensionPoint: extensionPointA,
middleware: async original => ({
...original,
values: [...original.values, 'wrapped'],
}),
}),
]);
init.add(testPlugin);
@@ -2215,14 +2221,20 @@ describe('BackendInitializer', () => {
});
const init = new BackendInitializer(baseFactories, [
createExtensionPointFactoryMiddleware(extensionPoint, original => ({
...original,
values: [...original.values, 'first'],
})),
createExtensionPointFactoryMiddleware(extensionPoint, original => ({
...original,
values: [...original.values, 'second'],
})),
createExtensionPointFactoryMiddleware({
extensionPoint,
middleware: async original => ({
...original,
values: [...original.values, 'first'],
}),
}),
createExtensionPointFactoryMiddleware({
extensionPoint,
middleware: async original => ({
...original,
values: [...original.values, 'second'],
}),
}),
]);
init.add(testPlugin);
@@ -2262,13 +2274,13 @@ describe('BackendInitializer', () => {
});
const init = new BackendInitializer(baseFactories, [
createExtensionPointFactoryMiddleware(
unregisteredExtensionPoint,
original => ({
createExtensionPointFactoryMiddleware({
extensionPoint: unregisteredExtensionPoint,
middleware: async original => ({
...original,
values: [...original.values, 'never-applied'],
}),
),
}),
]);
init.add(testPlugin);
packages/backend-app-api/src/wiring/BackendInitializer.ts
+4 -2
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@@ -29,6 +29,7 @@ import {
ExtensionPointFactoryMiddleware,
ServiceOrExtensionPoint,
} from './types';
import { OpaqueExtensionPointFactoryMiddleware } from '@internal/backend';
// Direct internal import to avoid duplication
// eslint-disable-next-line @backstage/no-relative-monorepo-imports
import type {
@@ -210,8 +211,9 @@ export class BackendInitializer {
},
});
for (const mw of this.#extensionPointFactoryMiddleware) {
if (mw.extensionPoint.id === ref.id) {
epImpl = (mw.middleware as (original: unknown) => unknown)(epImpl);
const internal = OpaqueExtensionPointFactoryMiddleware.toInternal(mw);
if (internal.extensionPointId === ref.id) {
epImpl = await internal.middleware(epImpl);
}
}
result.set(name, epImpl);
packages/backend-app-api/src/wiring/types.ts
+11 -11
View File
@@ -20,6 +20,7 @@ import {
ServiceRef,
ServiceFactory,
} from '@backstage/backend-plugin-api';
import { OpaqueExtensionPointFactoryMiddleware } from '@internal/backend';
/**
* A middleware entry that reimplements a specific extension point's output.
@@ -28,9 +29,8 @@ import {
*
* @public
*/
export interface ExtensionPointFactoryMiddleware<T = unknown> {
extensionPoint: ExtensionPoint<T>;
middleware: (original: T) => T;
export interface ExtensionPointFactoryMiddleware<_T = unknown> {
$$type: '@backstage/ExtensionPointFactoryMiddleware';
}
/**
@@ -39,14 +39,14 @@ export interface ExtensionPointFactoryMiddleware<T = unknown> {
*
* @public
*/
export function createExtensionPointFactoryMiddleware<T>(
extensionPoint: ExtensionPoint<T>,
middleware: (original: T) => T,
): ExtensionPointFactoryMiddleware {
return {
extensionPoint: extensionPoint as ExtensionPoint<unknown>,
middleware: middleware as (original: unknown) => unknown,
};
export function createExtensionPointFactoryMiddleware<T>(options: {
extensionPoint: ExtensionPoint<T>;
middleware: (original: T) => Promise<T>;
}): ExtensionPointFactoryMiddleware<T> {
return OpaqueExtensionPointFactoryMiddleware.createInstance('v1', {
extensionPointId: options.extensionPoint.id,
middleware: options.middleware as (original: unknown) => Promise<unknown>,
});
}
/**
packages/backend-defaults/report.api.md
+4 -8
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@@ -5,18 +5,14 @@
```ts
import { Backend } from '@backstage/backend-app-api';
import { BackendFeature } from '@backstage/backend-plugin-api';
import { createExtensionPointFactoryMiddleware } from '@backstage/backend-app-api';
import { ExtensionPointFactoryMiddleware } from '@backstage/backend-app-api';
import { ServiceFactory } from '@backstage/backend-plugin-api';
// @public (undocumented)
export function createBackend(options?: {
extensionPointFactoryMiddleware?: ExtensionPointFactoryMiddleware[];
}): Backend;
export function createBackend(): Backend;
export { createExtensionPointFactoryMiddleware };
// @public (undocumented)
export const defaultServiceFactories: ServiceFactory[];
// @public
export const discoveryFeatureLoader: BackendFeature;
export { ExtensionPointFactoryMiddleware };
```
packages/backend-defaults/src/CreateBackend.ts
+6 -13
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@@ -14,11 +14,8 @@
* limitations under the License.
*/
import {
Backend,
createSpecializedBackend,
ExtensionPointFactoryMiddleware,
} from '@backstage/backend-app-api';
import { Backend, createSpecializedBackend } from '@backstage/backend-app-api';
import { ServiceFactory } from '@backstage/backend-plugin-api';
import { auditorServiceFactory } from '@backstage/backend-defaults/auditor';
import { authServiceFactory } from '@backstage/backend-defaults/auth';
import { cacheServiceFactory } from '@backstage/backend-defaults/cache';
@@ -46,7 +43,8 @@ import {
} from '@backstage/backend-defaults/alpha';
import { instanceMetadataServiceFactory } from './alpha/entrypoints/instanceMetadata/instanceMetadataServiceFactory';
export const defaultServiceFactories = [
/** @public */
export const defaultServiceFactories: ServiceFactory[] = [
auditorServiceFactory,
authServiceFactory,
cacheServiceFactory,
@@ -80,11 +78,6 @@ export const defaultServiceFactories = [
/**
* @public
*/
export function createBackend(options?: {
extensionPointFactoryMiddleware?: ExtensionPointFactoryMiddleware[];
}): Backend {
return createSpecializedBackend({
defaultServiceFactories,
extensionPointFactoryMiddleware: options?.extensionPointFactoryMiddleware,
});
export function createBackend(): Backend {
return createSpecializedBackend({ defaultServiceFactories });
}
packages/backend-defaults/src/index.ts
+1 -3
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@@ -20,7 +20,5 @@
* @packageDocumentation
*/
export { createBackend } from './CreateBackend';
export type { ExtensionPointFactoryMiddleware } from '@backstage/backend-app-api';
export { createExtensionPointFactoryMiddleware } from '@backstage/backend-app-api';
export { createBackend, defaultServiceFactories } from './CreateBackend';
export { discoveryFeatureLoader } from './discoveryFeatureLoader';
packages/backend-internal/.eslintrc.js
+5
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@@ -0,0 +1,5 @@
module.exports = require('@backstage/cli/config/eslint-factory')(__dirname, {
rules: {
'@backstage/no-top-level-material-ui-4-imports': 'error',
},
});
packages/backend-internal/README.md
+3
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@@ -0,0 +1,3 @@
# @internal/backend
This is an internal package used by the other backend packages. It does not get published to NPM, but instead inlined into consuming packages due to the `backstage.inline` flag in `package.json`.
packages/backend-internal/catalog-info.yaml
+9
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@@ -0,0 +1,9 @@
apiVersion: backstage.io/v1alpha1
kind: Component
metadata:
name: internal-backend
title: '@internal/backend'
spec:
lifecycle: experimental
type: backstage-node-library
owner: framework-maintainers
packages/backend-internal/package.json
+28
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@@ -0,0 +1,28 @@
{
"name": "@internal/backend",
"version": "0.0.1",
"backstage": {
"role": "node-library",
"inline": true
},
"private": true,
"repository": {
"type": "git",
"url": "https://github.com/backstage/backstage",
"directory": "packages/backend-internal"
},
"license": "Apache-2.0",
"sideEffects": false,
"main": "src/index.ts",
"types": "src/index.ts",
"files": [
"dist"
],
"scripts": {
"lint": "backstage-cli package lint",
"test": "backstage-cli package test"
},
"devDependencies": {
"@backstage/cli": "workspace:^"
}
}
packages/backend-internal/src/index.ts
+17
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@@ -0,0 +1,17 @@
/*
* Copyright 2026 The Backstage Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
export { OpaqueExtensionPointFactoryMiddleware } from './wiring';
packages/backend-internal/src/wiring/OpaqueExtensionPointFactoryMiddleware.ts
+29
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@@ -0,0 +1,29 @@
/*
* Copyright 2026 The Backstage Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import { OpaqueType } from '@internal/opaque';
export const OpaqueExtensionPointFactoryMiddleware = OpaqueType.create<{
public: { $$type: '@backstage/ExtensionPointFactoryMiddleware' };
versions: {
readonly version: 'v1';
readonly extensionPointId: string;
readonly middleware: (original: unknown) => Promise<unknown>;
};
}>({
type: '@backstage/ExtensionPointFactoryMiddleware',
versions: ['v1'],
});
packages/backend-internal/src/wiring/index.ts
+17
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@@ -0,0 +1,17 @@
/*
* Copyright 2026 The Backstage Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
export { OpaqueExtensionPointFactoryMiddleware } from './OpaqueExtensionPointFactoryMiddleware';
yarn.lock
+8
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@@ -9977,6 +9977,14 @@ __metadata:
languageName: node
linkType: hard
"@internal/backend@workspace:packages/backend-internal":
version: 0.0.0-use.local
resolution: "@internal/backend@workspace:packages/backend-internal"
dependencies:
"@backstage/cli": "workspace:^"
languageName: unknown
linkType: soft
"@internal/cli@workspace:packages/cli-internal":
version: 0.0.0-use.local
resolution: "@internal/cli@workspace:packages/cli-internal"