GitoxideLabs/gitoxide · error

HEAD changed while preparing to attach

Error message

HEAD changed while preparing to attach

What it means

Between remembering the HEAD state and validating before the actual attach, HEAD was re-read and no longer matches: it is not detached or its commit id changed. The library throws this to avoid attaching based on stale state. It is a concurrency/staleness guard in `validate_attach`.

Solutions

1. Ensure no other process is operating on the repository, then retry the attach.
2. Re-run the whole attach flow from the start so the remembered state is re-captured.
3. Check `git reflog` to see what moved HEAD during the operation.

for attempt in 0..3 {
    match attach_reporting(...) {
        Err(e) if e.to_string().contains("HEAD changed while preparing") => {
            std::thread::sleep(backoff(attempt));
            continue; // re-capture state and retry
        }
        other => { other?; break; }
    }
}

When it happens

Trigger: Calling attach_reporting where another process (or user) moves HEAD (checkout, commit on a branch, reset) after `remembered_branch` captured `head_id` but before validation completes, so `!head.is_detached() || head.id() != Some(head_id)`.

Common situations: Another terminal or IDE performing checkouts concurrently; background tooling (hooks, CI agents) touching the same repo; a slow operation raced by the user switching branches.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• the HEAD pin changed while preparing to attach
• the remembered branch changed while preparing to attach
• change ID is no longer present in the Tix view
• Tried to use as tree, but was
• Tried to use as commit, but was

AI-assisted analysis of GitoxideLabs/gitoxide@e73179060b (2026-09-08). Data as JSON: /api/errors/a85d8e5089394df9. Report an issue: GitHub.

Appendix: source

Thrown at gix-tix/src/edit/time_travel.rs:509

        .context("attaching requires a valid HEAD pin")?;
    let branch = pin
        .target
        .try_name()
        .context("the HEAD pin must point to a local branch")?
        .to_owned();
    if !branch.as_bstr().starts_with(b"refs/heads/") {
        anyhow::bail!("the HEAD pin must point to a local branch");
    }
    Ok(RememberedBranch {
        branch,
        branch_tip: pin.id,
    })
}

fn validate_attach(repository: &gix::Repository, head_id: ObjectId, remembered: &RememberedBranch) -> Result<()> {
    let head = repository.head().context("could not read HEAD before attaching")?;
    if !head.is_detached() || head.id().map(gix::Id::detach) != Some(head_id) {
        anyhow::bail!("HEAD changed while preparing to attach");
    }
    drop(head);
    let pin = history::all_pins(repository)?
        .into_iter()
        .find(history::Pin::is_head)
        .context("the HEAD pin disappeared while preparing to attach")?;
    if pin.target.try_name() != Some(remembered.branch.as_ref()) || pin.id != remembered.branch_tip {
        anyhow::bail!("the HEAD pin changed while preparing to attach");
    }
    let branch_id = repository
        .find_reference(remembered.branch.as_ref())
        .context("the remembered branch disappeared while preparing to attach")?
        .try_id()
        .context("the remembered branch must be a direct reference")?
        .detach();
    if branch_id != remembered.branch_tip {
        anyhow::bail!("the remembered branch changed while preparing to attach");
    }

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