GitoxideLabs/gitoxide · error

the squash target must have exactly one parent

Error message

the squash target must have exactly one parent

What it means

The squash algorithm rewrites the target commit's single-parent base onto the new combined tree; it therefore requires the target to have exactly one parent. If the target is a root commit (no parents) or a merge commit (multiple parents), the rewrite cannot be expressed and the plan is rejected.

Solutions

1. Choose a non-root, non-merge commit as the squash target.
2. If the goal is to edit the root commit, use a root-aware edit/rebase workflow instead of squash.
3. Linearize history first so the intended target becomes an ordinary single-parent commit.

Example fix

// before: squashing into the root commit
plan_squash(repo, &graph, tip, root_commit)?
// error: the squash target must have exactly one parent

// after: squash into the root's first non-root descendant's parent chain,
// or use a root-edit operation
plan_squash(repo, &graph, tip, first_non_root_commit)?

// Rust: ensure the target has exactly one parent
let parents = graph.parents_of(target)?;
if parents.len() != 1 { eprintln!("squash target must not be a root or merge commit"); }

fn is_single_parent(commit: ObjectId, graph: &HistoryGraph) -> bool {
    graph.parents_of(commit).map(|p| p.len() == 1).unwrap_or(false)
}

When it happens

Trigger: Calling squash planning with a `target` whose `graph.parents_of(target)` yields anything other than exactly one parent — a root commit (0 parents) or a merge commit (2+ parents).

Common situations: Squashing into the repository's very first commit (root, no parent); accidentally choosing a merge commit as the squash target.

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

• the squash source must have exactly one parent
• descendant merge commits cannot be squashed
• the squash target must be a strict ancestor of the source
• copying a commit requires it to have exactly one parent
• copying a commit cannot rewrite root or merge commits

AI-assisted analysis of GitoxideLabs/gitoxide@e73179060b (2026-09-08). Data as JSON: /api/errors/0c58437473b4f802. Report an issue: GitHub.

Appendix: source

Thrown at gix-tix/src/edit/rebase.rs:459

    graph: &HistoryGraph,
    source: ObjectId,
    target: ObjectId,
) -> Result<Plan> {
    if source == target || !graph.is_ancestor(target, source) {
        anyhow::bail!("the squash target must be a strict ancestor of the source");
    }
    let source_parents = graph
        .parents_of(source)
        .context("the squash source is not in the loaded history")?;
    let [source_parent] = source_parents.as_slice() else {
        anyhow::bail!("the squash source must have exactly one parent");
    };
    let source_parent = *source_parent;
    let target_parents = graph
        .parents_of(target)
        .context("the squash target is not in the loaded history")?;
    let [base] = target_parents.as_slice() else {
        anyhow::bail!("the squash target must have exactly one parent");
    };
    let base = *base;
    let scope = graph
        .descendants_in_parent_order(target)
        .context("the squash target is not in the loaded history")?;
    let scope_set: HashSet<_> = scope.iter().copied().collect();
    let mut non_leaves = HashSet::new();
    for id in &scope {
        let parents = graph
            .parents_of(*id)
            .context("an affected squash commit is incomplete")?;
        if parents.len() > 1 {
            anyhow::bail!("descendant merge commits cannot be squashed");
        }
        non_leaves.extend(parents.into_iter().filter(|parent| scope_set.contains(parent)));
    }
    let tips: Vec<_> = scope.iter().copied().filter(|id| !non_leaves.contains(id)).collect();
    let mut steps = Vec::with_capacity(scope.len().saturating_sub(1));

View on GitHub (pinned to e73179060b)