fix(pip-compile): Correctly report errors when a lock file is unchanged

lib/modules/manager/pip-compile/artifacts.spec.ts

@@ -1,7 +1,11 @@
 import { codeBlock } from 'common-tags';
 import { mockDeep } from 'jest-mock-extended';
 import { join } from 'upath';
-import { envMock, mockExecAll } from '../../../../test/exec-util';
+import {
+  envMock,
+  mockExecAll,
+  mockExecSequence,
+} from '../../../../test/exec-util';
 import { Fixtures } from '../../../../test/fixtures';
 import { env, fs, git, mocked, partial } from '../../../../test/util';
 import { GlobalConfig } from '../../../config/global';
@@ -80,7 +84,7 @@ describe('modules/manager/pip-compile/artifacts', () => {
     expect(execSnapshots).toEqual([]);
   });
 
-  it('returns null if unchanged', async () => {
+  it('returns null if all unchanged', async () => {
     fs.readLocalFile.mockResolvedValueOnce(simpleHeader);
     const execSnapshots = mockExecAll();
     fs.readLocalFile.mockResolvedValueOnce('new lock');
@@ -615,5 +619,32 @@ describe('modules/manager/pip-compile/artifacts', () => {
         'pip-compile --output-file=requirements.txt requirements.in --upgrade-package=foo==1.0.2 --upgrade-package=bar==2.0.0',
       );
     });
+
+    it('reports errors when a lock file is unchanged', async () => {
+      fs.readLocalFile.mockResolvedValue(simpleHeader);
+      mockExecSequence([
+        new Error('Oh noes!'),
+        { stdout: 'This one worked', stderr: '' },
+      ]);
+      git.getRepoStatus.mockResolvedValue(
+        partial<StatusResult>({
+          modified: [],
+        }),
+      );
+      const results = await updateArtifacts({
+        packageFileName: 'requirements.in',
+        updatedDeps: [],
+        newPackageFileContent: 'some new content',
+        config: {
+          ...config,
+          lockFiles: ['requirements1.txt', 'requirements2.txt'],
+        },
+      });
+      expect(results).toMatchObject([
+        {
+          artifactError: { lockFile: 'requirements1.txt', stderr: 'Oh noes!' },
+        },
+      ]);
+    });
   });
 });

lib/modules/manager/pip-compile/artifacts.ts

@@ -125,16 +125,15 @@ export async function updateArtifacts({
       logger.trace({ env: execOptions.extraEnv }, 'pip-compile extra env vars');
       await exec(cmd, execOptions);
       const status = await getRepoStatus();
-      if (!status?.modified.includes(outputFileName)) {
-        return null;
+      if (status?.modified.includes(outputFileName)) {
+        result.push({
+          file: {
+            type: 'addition',
+            path: outputFileName,
+            contents: await readLocalFile(outputFileName, 'utf8'),
+          },
+        });
       }
-      result.push({
-        file: {
-          type: 'addition',
-          path: outputFileName,
-          contents: await readLocalFile(outputFileName, 'utf8'),
-        },
-      });
     } catch (err) {
       // istanbul ignore if
       if (err.message === TEMPORARY_ERROR) {
@@ -150,5 +149,5 @@ export async function updateArtifacts({
     }
   }
   logger.debug('pip-compile: Returning updated output file(s)');
-  return result;
+  return result.length === 0 ? null : result;
 }