feat(datasource/custom): Support digest in custom datasource

lib/modules/datasource/custom/index.spec.ts

@@ -697,4 +697,13 @@ describe('modules/datasource/custom/index', () => {
       expect(result).toEqual(expected);
     });
   });
+
+  describe('getDigest', () => {
+    it('returns null as digest should be provided in releases', async () => {
+      const digest = await new CustomDatasource().getDigest({
+        packageName: 'my-package',
+      });
+      expect(digest).toBeNull();
+    });
+  });
 });

lib/modules/datasource/custom/index.ts

@@ -2,7 +2,7 @@ import is from '@sindresorhus/is';
 import jsonata from 'jsonata';
 import { logger } from '../../../logger';
 import { Datasource } from '../datasource';
-import type { GetReleasesConfig, ReleaseResult } from '../types';
+import type { DigestConfig, GetReleasesConfig, ReleaseResult } from '../types';
 import { fetchers } from './formats';
 import { ReleaseResultZodSchema } from './schema';
 import { getCustomConfig } from './utils';
@@ -57,4 +57,12 @@ export class CustomDatasource extends Datasource {
       return null;
     }
   }
+
+  override getDigest(
+    { packageName }: DigestConfig,
+    newValue?: string,
+  ): Promise<string | null> {
+    // Return null here to support setting a digest: value can be provided digest in getReleases
+    return Promise.resolve(null);
+  }
 }

lib/workers/repository/process/lookup/index.spec.ts

@@ -5,6 +5,7 @@ import * as httpMock from '../../../../../test/http-mock';
 import { partial } from '../../../../../test/util';
 import { getConfig } from '../../../../config/defaults';
 import { CONFIG_VALIDATION } from '../../../../constants/error-messages';
+import { CustomDatasource } from '../../../../modules/datasource/custom';
 import { DockerDatasource } from '../../../../modules/datasource/docker';
 import { GitRefsDatasource } from '../../../../modules/datasource/git-refs';
 import { GithubReleasesDatasource } from '../../../../modules/datasource/github-releases';
@@ -62,6 +63,11 @@ describe('workers/repository/process/lookup/index', () => {
 
   const getMavenReleases = jest.spyOn(MavenDatasource.prototype, 'getReleases');
 
+  const getCustomDatasourceReleases = jest.spyOn(
+    CustomDatasource.prototype,
+    'getReleases',
+  );
+
   const getDockerDigest = jest.spyOn(DockerDatasource.prototype, 'getDigest');
 
   beforeEach(() => {
@@ -3849,6 +3855,33 @@ describe('workers/repository/process/lookup/index', () => {
       });
     });
 
+    it('handles digest update for custom datasource', async () => {
+      config.currentValue = '1.0.0';
+      config.packageName = 'my-package';
+      config.datasource = CustomDatasource.id;
+      config.currentDigest = 'zzzzzzzzzzzzzzz';
+      getCustomDatasourceReleases.mockResolvedValueOnce({
+        releases: [
+          {
+            version: '1.0.0',
+            newDigest: '0123456789abcdef',
+          },
+        ],
+      });
+
+      const { updates } = await Result.wrap(
+        lookup.lookupUpdates(config),
+      ).unwrapOrThrow();
+
+      expect(updates).toEqual([
+        {
+          newDigest: '0123456789abcdef',
+          newValue: '1.0.0',
+          updateType: 'digest',
+        },
+      ]);
+    });
+
     it('handles digest update for non-version', async () => {
       config.currentValue = 'alpine';
       config.packageName = 'node';