# fix(trail): fetch existing remote branch before create

`1fd4f9f`→[main](/content/gh/entireio/cli/commits/main/index.html)·

dipree·4w ago·1 file·+35 added/-11 removed

Address PR review feedback:
- validate branch names before trail create reaches git subcommands
- reject leading-dash branch names before invoking git
- when a requested branch is missing locally but already exists on origin,
fetch it instead of creating a new local branch at HEAD
- make the non-fast-forward hint refer to the target branch

## Sessions

b73b63b3e546View transcript

[?\
Fix Trail Creation Branch Handling and ValidationPi·Opus 4.8·1 step](/content/gh/entireio/cli/session/019ed956-c81a-74d1-9437-9fb289e1410f#timeline-b73b63b3e546/index.html)

## Changes

1

- cmd/entire/cli

- Mtrail_cmd.go+35/-11

```
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localBranchCreated := false
	var remoteBranchPushed bool

// Don't delete a remote branch we didn't create during cleanup.
	existedOnOrigin, existErr := branchExistsOnOrigin(branch)
	if existErr != nil {
		fmt.Fprintf(errW, "Warning: could not check whether branch %s already exists on origin: %v\n", branch, existErr)
		existedOnOrigin = true
	}

if needsCreation {
		if err := createBranch(repo, branch); err != nil {
			return fmt.Errorf("failed to create branch %q: %w", branch, err)
		}
		if existedOnOrigin {
			if err := fetchBranchFromOrigin(branch); err != nil {
				return fmt.Errorf("failed to fetch branch %q from origin: %w", branch, err)
			}
			localBranchCreated = true
			fmt.Fprintf(w, "Fetched branch %s from origin\n", branch)
		} else {
			if err := createBranch(repo, branch); err != nil {
				return fmt.Errorf("failed to create branch %q: %w", branch, err)
			}
			localBranchCreated = true
			fmt.Fprintf(w, "Created branch %s\n", branch)
		}
		localBranchCreated = true
		fmt.Fprintf(w, "Created branch %s\n", branch)
	} else if currentBranch != branch {
		fmt.Fprintf(w, "Note: trail will be created for branch %q (not the current branch)\n", branch)
	}
2 unmodified lines

// deliver it before creating the trail rather than letting the server
	// backfill it at the base tip.
	{
		// Don't delete a remote branch we didn't create during cleanup.
		existedOnOrigin, existErr := branchExistsOnOrigin(branch)
		if existErr != nil {
			fmt.Fprintf(errW, "Warning: could not check whether branch %s already exists on origin: %v\n", branch, existErr)
			existedOnOrigin = true
		}
		if err := pushBranchToOrigin(branch); err != nil {
			cleanupCreatedTrailBranch(repo, branch, localBranchCreated, false, errW)
			return fmt.Errorf("failed to push branch %q to origin: %w\nhint: the trail was not created because its branch could not be delivered to the remote.\n  - if this is an auth error, link your GitHub account and retry\n  - if this is a non-fast-forward, update your base (git fetch && git rebase) and retry", branch, err)
		}
		remoteBranchPushed = !existedOnOrigin
		fmt.Fprintf(w, "Pushed branch %s to origin\n", branch)
732 unmodified lines

}
}

func fetchBranchFromOrigin(branchName string) error {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
	defer cancel()
	if err := ValidateBranchName(ctx, branchName); err != nil {
		return err
	}
	refspec := fmt.Sprintf("refs/heads/%%s:refs/heads/%%s", branchName, branchName)
	cmd := exec.CommandContext(ctx, "git", "fetch", "--no-tags", "origin", refspec)
	if output, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("%s: %w", strings.TrimSpace(string(output)), err)
	}
	return nil
}

// pushBranchToOrigin pushes a branch to the origin remote.
func pushBranchToOrigin(branchName string) error {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)