gitbutlerapp/gitbutler · error

`but merge` does not yet support triangular remotes

Error message

`but merge` does not yet support triangular remotes (fetch `{fetch_remote_name}`, push `{push_remote_name}`). Merge via a pull request instead, or configure a single remote for the target branch.

What it means

Triangular workflows (fetch from one remote, push to another) are unsupported for `but merge`: the post-land reconcile reads the fetch remote's tracking ref, so pushing to a different remote would not advance it and reconciliation would silently no-op. `branch_land` refuses up front before mutating anything.

Solutions

  1. Configure a single remote for the target branch (same remote for fetch and push), then re-run `but merge`
  2. Land via a pull request instead (push the branch and open a PR on the hosting platform)
  3. Temporarily align remotes (`git remote set-url --push origin <fetch-url>`) if a direct landing is required

Example fix

// before (triangular)
{fetch: "upstream", push: "origin"}
// after (single remote)
{fetch: "origin", push: "origin"}
// or land via PR instead of `but merge`
Defensive patterns

Strategy: validation

Validate before calling

let fetch_remote = &base_branch.remote_name;
let push_remote = &base_branch.push_remote_name;
if !push_remote.is_empty() && push_remote != fetch_remote {
    println!("triangular setup unsupported by `but merge`; use a PR");
    return Ok(());
}

Try / catch

match land_result {
    Err(e) if e.to_string().contains("triangular remotes") => {
        open_pull_request_instead();
    }
    other => other?,
}

Prevention

When it happens

Trigger: Calling `but merge` when the configured target branch has `push_remote_name != fetch_remote_name` (e.g. fetch from `upstream`, push to `origin` fork setup).

Common situations: Open-source fork workflows (push to fork, pull from upstream); repos migrated to split push/pull remotes; CI configurations setting distinct push/pull URLs.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of gitbutlerapp/gitbutler@58e5313667 (2026-09-18). Data as JSON: /api/errors/4a5c91bb06ca6520. Report an issue: GitHub.

Appendix: source

Thrown at crates/but-api/src/land/mod.rs:213

    let target_branch_name = base_branch.short_name.clone();
    if target_branch_name.is_empty() {
        bail!("Configured target branch has no branch name");
    }
    let fetch_remote_name = base_branch.remote_name.clone();
    let push_remote_name = if base_branch.push_remote_name.is_empty() {
        fetch_remote_name.clone()
    } else {
        base_branch.push_remote_name.clone()
    };
    if push_remote_name.is_empty() {
        bail!("Configured target branch has no push remote");
    }

    // Triangular remotes (fetch remote != push remote) are out of scope for now: the post-land
    // reconcile reads the fetch remote's tracking ref, so a push to a different remote would not
    // advance it and the reconcile would silently no-op. Refuse before mutating anything.
    if push_remote_name != fetch_remote_name {
        bail!(
            "`but merge` does not yet support triangular remotes (fetch `{fetch_remote_name}`, \
             push `{push_remote_name}`). Merge via a pull request instead, or configure a single \
             remote for the target branch."
        );
    }

    let target_display = format!("{push_remote_name}/{target_branch_name}");
    let push_remote_url = if base_branch.push_remote_url.is_empty() {
        &base_branch.remote_url
    } else {
        &base_branch.push_remote_url
    };
    let update_target_locally = {
        let repo = ctx.repo.get()?;
        remote_points_at_current_repo(&repo, push_remote_url)?
    };

    // Safety guards a non-CLI caller must not be able to bypass: never publish lower stack segments

View on GitHub (pinned to 58e5313667)