fix: ignore empty stash

Ignore "No stash entries found." when stashing
is enabled but no files were actually stashed.

Resolves: #55

Author: saitho

src/perform-backmerge.test.ts

@@ -247,6 +247,49 @@ describe("perform-backmerge", () => {
         verify(mockedGit.unstash()).calledAfter(pushAction);
     });
 
+    it("stash and unstash with empty stash", async () => {
+        const mockedGit = mock(Git);
+        const mockedLogger = mock(NullLogger);
+        when(mockedGit.checkout(anyString())).thenResolve();
+        when(mockedGit.configFetchAllRemotes()).thenResolve();
+        when(mockedGit.getModifiedFiles())
+            .thenReturn(new Promise<string[]>(resolve => resolve([])));
+        when(mockedGit.fetch()).thenResolve();
+        when(mockedGit.commit(anyString())).thenResolve();
+        when(mockedGit.rebase(anyString())).thenResolve();
+        const makeError = require('execa/lib/error')
+        when(mockedGit.unstash()).thenThrow(makeError({
+            stderr: 'No stash entries found.',
+            parsed: {options:{timeout: 0}}
+        }));
+        when(mockedGit.push(anyString(), anyString(), anything())).thenResolve();
+
+        const context = {logger: instance(mockedLogger), branch: {name: 'master'}, options: {repositoryUrl: 'my-repo'}} as Context;
+
+        await performBackmerge(
+            instance(mockedGit),
+            {
+                backmergeBranches: ['develop'],
+                clearWorkspace: true,
+                restoreWorkspace: true
+            },
+            context
+        );
+        verify(mockedLogger.log('Performing back-merge into develop branch "develop".')).once();
+        verify(mockedGit.checkout('master')).once();
+        verify(mockedGit.configFetchAllRemotes()).once();
+        verify(mockedGit.fetch(context.options!.repositoryUrl)).once();
+
+        const checkoutDevelopAction = mockedGit.checkout('develop');
+        verify(mockedGit.stash()).calledBefore(checkoutDevelopAction);
+        verify(checkoutDevelopAction).once();
+        verify(mockedGit.rebase('master')).once();
+
+        const pushAction = mockedGit.push('my-repo', 'develop', false)
+        verify(pushAction).once();
+        verify(mockedGit.unstash()).calledAfter(pushAction);
+    });
+
     it("merge as backmerge strategy", async () => {
         const mockedGit = mock(Git);
         const mockedLogger = mock(NullLogger);

src/perform-backmerge.ts

@@ -130,7 +130,13 @@ export async function performBackmerge(git: Git, pluginConfig: Partial<Config>,
 
     if (options.restoreWorkspace) {
         context.logger.log('Restoring stashed files to Git workspace.');
-        await git.unstash();
+        try {
+            await git.unstash();
+        } catch (error: any) {
+            if (error?.stderr !== 'No stash entries found.') {
+                throw error;
+            }
+        }
     }
 }