feat: add custom processor module to add ScaffoldedFrom relation

plugins/catalog-backend-module-scaffolder-relation-processor/.eslintrc.js

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+module.exports = require('@backstage/cli/config/eslint-factory')(__dirname);

plugins/catalog-backend-module-scaffolder-relation-processor/README.md

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+# Catalog Backend Module for Scaffolder Relation Catalog Processor
+
+This is an extension module to the catalog-backend plugin, providing an additional catalog entity processor that adds a new relation that depends on the `spec.scaffoldedFrom` field to link scaffolder templates and the catalog entities they generated.
+
+## Getting Started
+
+1. Install the scaffolder relation catalog processor module using the following command:
+
+   ```console
+   yarn workspace backend add @janus-idp/backstage-plugin-catalog-backend-module-scaffolder-relation-processor
+   ```
+
+### Installing on the new backend system
+
+To install this module into the [new backend system](https://backstage.io/docs/backend-system/), add the following into the `packages/backend/src/index.ts` file:
+
+```ts title="packages/backend/src/index.ts
+const backend = createBackend();
+
+// highlight-add-start
+backend.add(
+  import(
+    '@janus-idp/backstage-plugin-catalog-backend-module-scaffolder-relation-processor/alpha'
+  ),
+);
+// highlight-add-end
+
+backend.start();
+```
+
+### Installing on the legacy backend system
+
+To install this module into the legacy backend system, add the following to the `packages/backend/src/plugins/catalog.ts` file:
+
+```ts title=packages/backend/src/plugins/catalog.ts
+// highlight-add-start
+import { ScaffolderRelationEntityProcessor } from '@janus-idp/backstage-plugin-catalog-backend-module-scaffolder-relation-processor';
+
+// highlight-add-end
+
+export default async function createPlugin(
+  env: PluginEnvironment,
+): Promise<Router> {
+  const builder = await CatalogBuilder.create(env);
+
+  /* ... other processors and/or providers ... */
+  // highlight-add-start
+  builder.addProcessor(new ScaffolderRelationEntityProcessor());
+  // highlight-add-end
+
+  const { processingEngine, router } = await builder.build();
+  await processingEngine.start();
+
+  return router;
+}
+```
+
+### Usage
+
+Catalog entities containing the `spec.scaffoldedFrom` field will have a relation link be formed between it and the `template` corresponding to the entity ref in the `spec.scaffoldedFrom` field.
+
+This link can be viewed in the `relations` field of the Raw YAML view of a catalog entity when inspecting an entity. In the entity with the `spec.scaffoldedFrom` field, the relation type is `scaffoldedFrom` with a target pointing to the value of the `spec.scaffoldedFrom` field. Conversely, for the target template, it will have a relation type of `ScaffolderOf` with a target pointing to the entity with the `spec.scaffoldedFrom` field.
+
+These relations should also appear on the `EntityCatalogGraphView` component from the `@backstage/plugin-catalog-graph` package (only if the entity corresponding to the entity ref exists in the catalog).
+
+#### Example graph view
+
+![scaffoldedFrom Relation Graph View](./docs/example-images/scaffoldedFromGraphView.png)
+![scaffolderOf Relation Graph View](./docs/example-images/scaffolderOfGraphView.png)
+
+#### Example Raw YAML view
+
+![scaffoldedFrom Relation YAML View](./docs/example-images/scaffoldedFromYAMLView.png)
+![scaffoldedOf Relation YAML View](./docs/example-images/scaffolderOfYAMLView.png)

plugins/catalog-backend-module-scaffolder-relation-processor/config.d.ts

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+export interface Config {}

plugins/catalog-backend-module-scaffolder-relation-processor/dist-dynamic/package.json

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+{
+  "name": "@janus-idp/backstage-plugin-catalog-backend-module-scaffolder-relation-processor-dynamic",
+  "description": "The scaffolder-relation-processor backend module for the catalog plugin.",
+  "version": "0.1.0",
+  "main": "dist/index.cjs.js",
+  "types": "dist/index.d.ts",
+  "license": "Apache-2.0",
+  "publishConfig": {
+    "access": "public",
+    "main": "dist/index.cjs.js",
+    "types": "dist/index.d.ts"
+  },
+  "backstage": {
+    "role": "backend-plugin-module"
+  },
+  "exports": {
+    ".": {
+      "require": "./dist/index.cjs.js",
+      "default": "./dist/index.cjs.js"
+    },
+    "./alpha": {
+      "require": "./dist/alpha.cjs.js",
+      "default": "./dist/alpha.cjs.js"
+    },
+    "./package.json": "./package.json"
+  },
+  "scripts": {},
+  "dependencies": {},
+  "devDependencies": {},
+  "files": [
+    "dist",
+    "config.d.ts",
+    "app-config.janus-idp.yaml",
+    "alpha"
+  ],
+  "configSchema": "config.d.ts",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/janus-idp/backstage-plugins",
+    "directory": "plugins/catalog"
+  },
+  "keywords": [
+    "backstage",
+    "plugin"
+  ],
+  "homepage": "https://janus-idp.io/",
+  "bugs": "https://github.com/janus-idp/backstage-plugins/issues",
+  "bundleDependencies": true,
+  "peerDependencies": {
+    "@backstage/backend-common": "^0.21.6",
+    "@backstage/backend-dynamic-feature-service": "^0.2.8",
+    "@backstage/backend-plugin-api": "^0.6.16",
+    "@backstage/catalog-model": "^1.4.5",
+    "@backstage/plugin-catalog-common": "^1.0.22",
+    "@backstage/plugin-catalog-node": "^1.11.1"
+  },
+  "overrides": {
+    "@aws-sdk/util-utf8-browser": {
+      "@smithy/util-utf8": "^2.0.0"
+    }
+  },
+  "resolutions": {
+    "@aws-sdk/util-utf8-browser": "npm:@smithy/util-utf8@~2"
+  }
+}

plugins/catalog-backend-module-scaffolder-relation-processor/dist-dynamic/yarn.lock

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+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+"@aws-sdk/util-utf8-browser@npm:@smithy/util-utf8@~2":
+  version "2.3.0"
+  resolved "https://registry.yarnpkg.com/@smithy/util-utf8/-/util-utf8-2.3.0.tgz#dd96d7640363259924a214313c3cf16e7dd329c5"
+  integrity sha512-R8Rdn8Hy72KKcebgLiv8jQcQkXoLMOGGv5uI1/k0l+snqkOzQ1R0ChUBCxWMlBsFMekWjq0wRudIweFs7sKT5A==
+  dependencies:
+    "@smithy/util-buffer-from" "^2.2.0"
+    tslib "^2.6.2"
+
+"@smithy/is-array-buffer@^2.2.0":
+  version "2.2.0"
+  resolved "https://registry.yarnpkg.com/@smithy/is-array-buffer/-/is-array-buffer-2.2.0.tgz#f84f0d9f9a36601a9ca9381688bd1b726fd39111"
+  integrity sha512-GGP3O9QFD24uGeAXYUjwSTXARoqpZykHadOmA8G5vfJPK0/DC67qa//0qvqrJzL1xc8WQWX7/yc7fwudjPHPhA==
+  dependencies:
+    tslib "^2.6.2"
+
+"@smithy/util-buffer-from@^2.2.0":
+  version "2.2.0"
+  resolved "https://registry.yarnpkg.com/@smithy/util-buffer-from/-/util-buffer-from-2.2.0.tgz#6fc88585165ec73f8681d426d96de5d402021e4b"
+  integrity sha512-IJdWBbTcMQ6DA0gdNhh/BwrLkDR+ADW5Kr1aZmd4k3DIF6ezMV4R2NIAmT08wQJ3yUK82thHWmC/TnK/wpMMIA==
+  dependencies:
+    "@smithy/is-array-buffer" "^2.2.0"
+    tslib "^2.6.2"
+
+tslib@^2.6.2:
+  version "2.6.2"
+  resolved "https://registry.yarnpkg.com/tslib/-/tslib-2.6.2.tgz#703ac29425e7b37cd6fd456e92404d46d1f3e4ae"
+  integrity sha512-AEYxH93jGFPn/a2iVAwW87VuUIkR1FVUKB77NwMF7nBTDkDrrT/Hpt/IrCJ0QXhW27jTBDcf5ZY7w6RiqTMw2Q==

plugins/catalog-backend-module-scaffolder-relation-processor/package.json

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+{
+  "name": "@janus-idp/backstage-plugin-catalog-backend-module-scaffolder-relation-processor",
+  "description": "The scaffolder-relation-processor backend module for the catalog plugin.",
+  "version": "0.1.0",
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "license": "Apache-2.0",
+  "publishConfig": {
+    "access": "public",
+    "main": "dist/index.cjs.js",
+    "types": "dist/index.d.ts"
+  },
+  "backstage": {
+    "role": "backend-plugin-module"
+  },
+  "exports": {
+    ".": "./src/index.ts",
+    "./alpha": "./src/alpha.ts",
+    "./package.json": "./package.json"
+  },
+  "typesVersions": {
+    "*": {
+      "alpha": [
+        "src/alpha.ts"
+      ],
+      "package.json": [
+        "package.json"
+      ]
+    }
+  },
+  "scripts": {
+    "build": "backstage-cli package build",
+    "clean": "backstage-cli package clean",
+    "export-dynamic": "janus-cli package export-dynamic-plugin",
+    "lint": "backstage-cli package lint",
+    "postpack": "backstage-cli package postpack",
+    "postversion": "yarn run export-dynamic",
+    "prepack": "backstage-cli package prepack",
+    "start": "backstage-cli package start",
+    "test": "backstage-cli package test --passWithNoTests --coverage",
+    "tsc": "tsc"
+  },
+  "dependencies": {
+    "@backstage/backend-common": "^0.21.6",
+    "@backstage/backend-dynamic-feature-service": "^0.2.8",
+    "@backstage/backend-plugin-api": "^0.6.16",
+    "@backstage/catalog-model": "^1.4.5",
+    "@backstage/plugin-catalog-common": "^1.0.22",
+    "@backstage/plugin-catalog-node": "^1.11.1"
+  },
+  "devDependencies": {
+    "@backstage/backend-test-utils": "0.3.6",
+    "@backstage/cli": "0.26.2",
+    "@janus-idp/cli": "1.8.2"
+  },
+  "files": [
+    "dist",
+    "config.d.ts",
+    "dist-dynamic/*.*",
+    "dist-dynamic/dist/**",
+    "dist-dynamic/alpha/*",
+    "app-config.janus-idp.yaml"
+  ],
+  "configSchema": "config.d.ts",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/janus-idp/backstage-plugins",
+    "directory": "plugins/catalog"
+  },
+  "keywords": [
+    "backstage",
+    "plugin"
+  ],
+  "homepage": "https://janus-idp.io/",
+  "bugs": "https://github.com/janus-idp/backstage-plugins/issues"
+}

plugins/catalog-backend-module-scaffolder-relation-processor/src/ScaffolderRelationEntityProcessor.test.ts

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+import { Entity } from '@backstage/catalog-model';
+
+import { ScaffolderRelationEntityProcessor } from './ScaffolderRelationEntityProcessor';
+
+describe('ScaffolderRelationEntityProcessor', () => {
+  describe('postProcessEntity', () => {
+    const processor = new ScaffolderRelationEntityProcessor();
+    const location = { type: 'url', target: 'test-url' };
+    const emit = jest.fn();
+
+    afterEach(() => jest.resetAllMocks());
+
+    it('generates relations for any arbitrary entity', async () => {
+      const entity: Entity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'Component',
+        metadata: { name: 'test-entity' },
+        spec: {
+          scaffoldedFrom: 'test-template',
+        },
+      };
+
+      await processor.postProcessEntity(entity, location, emit);
+      expect(emit).toHaveBeenCalledTimes(2);
+      expect(emit).toHaveBeenCalledWith({
+        type: 'relation',
+        relation: {
+          source: {
+            kind: 'Template',
+            namespace: 'default',
+            name: 'test-template',
+          },
+          type: 'scaffolderOf',
+          target: {
+            kind: 'Component',
+            namespace: 'default',
+            name: 'test-entity',
+          },
+        },
+      });
+      expect(emit).toHaveBeenCalledWith({
+        type: 'relation',
+        relation: {
+          source: {
+            kind: 'Component',
+            namespace: 'default',
+            name: 'test-entity',
+          },
+          type: 'scaffoldedFrom',
+          target: {
+            kind: 'Template',
+            namespace: 'default',
+            name: 'test-template',
+          },
+        },
+      });
+    });
+    it('generates no relations if the `spec.scaffoldedFrom` field is empty or does not exist', async () => {
+      const entity: Entity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'Component',
+        metadata: { name: 'n' },
+        spec: {
+          type: 'service',
+        },
+      };
+      await processor.postProcessEntity(entity, location, emit);
+      expect(emit).toHaveBeenCalledTimes(0);
+
+      const entity2: Entity = {
+        apiVersion: 'backstage.io/v1alpha1',
+        kind: 'Component',
+        metadata: { name: 'n' },
+        spec: {
+          scaffoldedFrom: '',
+        },
+      };
+      await processor.postProcessEntity(entity2, location, emit);
+      expect(emit).toHaveBeenCalledTimes(0);
+    });
+  });
+});