fix: only update lock files if necessary

lib/workers/branch/get-updated.spec.ts

@@ -345,6 +345,33 @@ describe('workers/branch/get-updated', () => {
         ],
       });
     });
+
+    it('reuse branch when update artifacts on update-lockfile strategy with no updateLockedDependency', async () => {
+      config.upgrades.push({
+        packageFile: 'pyproject.toml',
+        manager: 'poetry',
+        branchName: undefined,
+        isLockfileUpdate: true,
+      });
+      poetry.updateArtifacts.mockResolvedValueOnce([
+        {
+          file: {
+            type: 'addition',
+            path: 'poetry.lock',
+            contents: 'some contents',
+          },
+        },
+      ]);
+      git.getFile.mockResolvedValueOnce('some contents');
+      const res = await getUpdatedPackageFiles(config);
+      expect(res).toEqual({
+        artifactErrors: [],
+        reuseExistingBranch: undefined,
+        updatedArtifacts: [],
+        updatedPackageFiles: [],
+      });
+    });
+
     it('attempts updateLockedDependency and handles unsupported', async () => {
       config.upgrades.push({
         packageFile: 'package.json',

lib/workers/branch/get-updated.ts

@@ -264,16 +264,27 @@ export async function getUpdatedPackageFiles(
         config,
       });
       if (is.nonEmptyArray(results)) {
-        updatedPackageFiles.push(packageFile);
+        let updated = false;
         for (const res of results) {
           const { file, artifactError } = res;
           // istanbul ignore else
-          if (file) {
+          if (
+            file?.type === 'addition' &&
+            file.contents !== '' && // only check if artifact is non-empty --> ignore git-submodule artifacts
+            (await getFile(
+              file.path,
+              reuseExistingBranch ? config.branchName : config.baseBranch
+            )) !== file.contents.toString() // convert to string if defined as buffer
+          ) {
             updatedArtifacts.push(file);
+            updated = true;
           } else if (artifactError) {
             artifactErrors.push(artifactError);
           }
         }
+        if (updated) {
+          updatedPackageFiles.push(packageFile);
+        }
       }
     }
   }