Fix issue with wrong commit being checked out when local branch exists

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/github/pullRequestGitHelper.ts

@@ -91,20 +91,38 @@ export class PullRequestGitHelper {
 		const remoteName = remote.remoteName;
 		let branch: Branch;
 
+		// Always fetch the remote branch first to ensure we have the latest commits
+		const trackedBranchName = `refs/remotes/${remoteName}/${branchName}`;
+		Logger.appendLine(`Fetch tracked branch ${trackedBranchName}`, PullRequestGitHelper.ID);
+		progress.report({ message: vscode.l10n.t('Fetching branch {0}', branchName) });
+		await repository.fetch(remoteName, branchName);
+		const trackedBranch = await repository.getBranch(trackedBranchName);
+
 		try {
 			branch = await repository.getBranch(branchName);
 			// Make sure we aren't already on this branch
 			if (repository.state.HEAD?.name === branch.name) {
 				Logger.appendLine(`Tried to checkout ${branchName}, but branch is already checked out.`, PullRequestGitHelper.ID);
 				return;
 			}
+
+			// Check if local branch is pointing to the same commit as the remote
+			if (branch.commit !== trackedBranch.commit) {
+				Logger.debug(`Local branch ${branchName} commit ${branch.commit} differs from remote commit ${trackedBranch.commit}. Updating local branch.`, PullRequestGitHelper.ID);
+				progress.report({ message: vscode.l10n.t('Updating branch {0} to match remote', branchName) });
+				// Delete and recreate the local branch to point to the remote commit
+				await repository.deleteBranch(branchName, true);
+				await repository.createBranch(branchName, false, trackedBranch.commit);
+				// Get the updated branch reference
+				branch = await repository.getBranch(branchName);
+			}
+
 			Logger.debug(`Checkout ${branchName}`, PullRequestGitHelper.ID);
 			progress.report({ message: vscode.l10n.t('Checking out {0}', branchName) });
 			await repository.checkout(branchName);
 
 			if (!branch.upstream) {
 				// this branch is not associated with upstream yet
-				const trackedBranchName = `refs/remotes/${remoteName}/${branchName}`;
 				await repository.setBranchUpstream(branchName, trackedBranchName);
 			}
 
@@ -114,16 +132,11 @@ export class PullRequestGitHelper {
 				await repository.pull();
 			}
 		} catch (err) {
-			// there is no local branch with the same name, so we are good to fetch, create and checkout the remote branch.
+			// there is no local branch with the same name, so we are good to create and checkout the remote branch.
 			Logger.appendLine(
-				`Branch ${remoteName}/${branchName} doesn't exist on local disk yet.`,
+				`Branch ${branchName} doesn't exist on local disk yet. Creating from remote.`,
 				PullRequestGitHelper.ID,
 			);
-			const trackedBranchName = `refs/remotes/${remoteName}/${branchName}`;
-			Logger.appendLine(`Fetch tracked branch ${trackedBranchName}`, PullRequestGitHelper.ID);
-			progress.report({ message: vscode.l10n.t('Fetching branch {0}', branchName) });
-			await repository.fetch(remoteName, branchName);
-			const trackedBranch = await repository.getBranch(trackedBranchName);
 			// create branch
 			progress.report({ message: vscode.l10n.t('Creating and checking out branch {0}', branchName) });
 			await repository.createBranch(branchName, true, trackedBranch.commit);

src/test/github/pullRequestGitHelper.test.ts

@@ -44,6 +44,62 @@ describe('PullRequestGitHelper', function () {
 		sinon.restore();
 	});
 
+	describe('fetchAndCheckout', function () {
+		it('fetches remote and updates local branch when local branch exists with different commit', async function () {
+			const url = 'git@github.com:owner/name.git';
+			const remote = new GitHubRemote('origin', url, new Protocol(url), GitHubServerType.GitHubDotCom);
+			const gitHubRepository = new MockGitHubRepository(remote, credentialStore, telemetry, sinon);
+
+			const prItem = convertRESTPullRequestToRawPullRequest(
+				new PullRequestBuilder()
+					.number(100)
+					.user(u => u.login('me'))
+					.base(b => {
+						(b.repo)(r => (<RepositoryBuilder>r).clone_url('git@github.com:owner/name.git'));
+					})
+					.head(h => {
+						h.repo(r => (<RepositoryBuilder>r).clone_url('git@github.com:owner/name.git'));
+						h.ref('my-branch');
+					})
+					.build(),
+				gitHubRepository,
+			);
+
+			const pullRequest = new PullRequestModel(credentialStore, telemetry, gitHubRepository, remote, prItem);
+
+			// Setup: local branch exists with different commit than remote
+			const localBranch = {
+				type: RefType.Head,
+				name: 'my-branch',
+				commit: 'local-commit-hash',
+				upstream: undefined,
+			};
+			repository.state.refs.push(localBranch);
+			repository._branches.push(localBranch);
+
+			// Setup: remote branch has different commit
+			const remoteBranch = {
+				type: RefType.RemoteHead,
+				name: 'refs/remotes/origin/my-branch',
+				commit: 'remote-commit-hash',
+			};
+			repository.state.refs.push(remoteBranch);
+			repository._branches.push(remoteBranch);
+
+			const remotes = [remote];
+
+			// Expect fetch to be called
+			repository.expectFetch('origin', 'my-branch');
+
+			await PullRequestGitHelper.fetchAndCheckout(repository, remotes, pullRequest, { report: () => undefined });
+
+			// Verify that the local branch was updated to point to the remote commit
+			const updatedBranch = repository._branches.find(b => b.name === 'my-branch');
+			assert.strictEqual(updatedBranch?.commit, 'remote-commit-hash');
+			assert.strictEqual(repository.state.HEAD?.name, 'my-branch');
+		});
+	});
+
 	describe('checkoutFromFork', function () {
 		it('fetches, checks out, and configures a branch from a fork', async function () {
 			const url = 'git@github.com:owner/name.git';