feat(datasource/cpan): populate latest tag

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

@@ -63,7 +63,16 @@ describe('modules/datasource/cpan/index', () => {
           (body) =>
             body.query.filtered.filter.and[0].term['module.name'] === 'Plack',
         )
-        .reply(200, Fixtures.get('Plack.json'));
+        .reply(200, Fixtures.get('Plack.json'))
+        .get('/v1/module/Plack')
+        .reply(200, {
+          module: [
+            {
+              name: 'Plack',
+              version: '1.0048',
+            },
+          ],
+        });
       const res = await getPkgReleases({
         datasource: CpanDatasource.id,
         packageName: 'Plack',
@@ -86,6 +95,7 @@ describe('modules/datasource/cpan/index', () => {
         releaseTimestamp: '2020-11-30T00:21:36.000Z',
         version: '1.0048',
       });
+      expect(res?.tags?.latest).toBe('1.0048');
     });
   });
 });

lib/modules/datasource/cpan/index.ts

@@ -1,3 +1,4 @@
+import { logger } from '../../../logger';
 import { cache } from '../../../util/cache/package/decorator';
 import { joinUrlParts } from '../../../util/url';
 import * as perlVersioning from '../../versioning/perl';
@@ -107,6 +108,25 @@
           changelogUrl: `https://metacpan.org/dist/${latestDistribution}/changes`,
           homepage: `https://metacpan.org/pod/${packageName}`,
         };
+
+        try {
+          const latestVersionUrl = joinUrlParts(
+            registryUrl,
+            'v1/module/',
+            packageName,
+          );
+          const latestVersionRes = (
+            await this.http.getJson<MetaCpanApiFile>(latestVersionUrl)
+          ).body;
+          const latestVersion = latestVersionRes?.module?.[0]?.version;
+
+          if (latestVersion) {
+            result.tags ??= {};
+            result.tags.latest ??= latestVersion;
+          }
+        } catch {
+          logger.debug(`Error while fetching latest tag for ${packageName}.`);
+        }
       }
     }
     return result;