What causes "Cannot use both --fix-formatting and --message flags together" in gitbutlerapp/gitbutler?

Drop --message to only reformat the existing message

Cannot use both --fix-formatting and --message flags…

Error message

Cannot use both --fix-formatting and --message flags together

What it means

`edit_commit_message_by_id_and_reword_commit` treats --fix-formatting and --message as mutually exclusive sources for the new commit message: --fix-formatting reformats the existing message while --message supplies a replacement. Supplying both is ambiguous and is rejected.

Solutions

Drop --message to only reformat the existing message
Drop --fix-formatting to set the message verbatim
Run twice if both are needed: first reword --message, then reword --fix-formatting

Example fix

// before
but reword <commit> --fix-formatting --message "msg"
// after
but reword <commit> --fix-formatting

Defensive patterns

Strategy: validation

Validate before calling

if (args.fixFormatting && args.message)
  throw new Error('Use either --fix-formatting or --message, not both');

Type guard

const flagsAreExclusive = (a, b) => !(a != null && b != null);

Prevention

Make flag sets mutually exclusive in CLI argument parsing before execution
In generated commands, pick one message source explicitly
If formatting plus customization is needed, chain two invocations

When it happens

Trigger: Running `but reword --fix-formatting --message "text"` (reword_target path) with both flags set on the same invocation.

Common situations: Script/template that always passes --message but also gained --fix-formatting; user wanting formatting plus tweaks in one call.

Understand the failure class

Background: "mutually exclusive" flag errors: what "can't supply both nx and xx", "--raw is not compatible with -i" and "cannot be used with" mean, and how to fix them — this error's family across 29 libraries.

Related errors

AI-assisted analysis of gitbutlerapp/gitbutler@58e5313667 (2026-09-18). Data as JSON: /api/errors/fb09344e266a3d65. Report an issue: GitHub.

Appendix: source

Thrown at crates/but/src/command/legacy/reword.rs:279

}

fn edit_commit_message_by_id_and_reword_commit(
    ctx: &mut Context,
    commit_oid: gix::ObjectId,
    out: &mut OutputChannel,
    message: Option<&str>,
    format: bool,
    show_diff_in_editor: ShowDiffInEditor,
    perm: &mut RepoExclusive,
) -> Result<()> {
    // Get commit details directly - no need to iterate through stacks
    let commit_details = but_api::diff::commit_details(ctx, commit_oid, ComputeLineStats::No)?;
    let current_message = commit_details.commit.inner.message.to_string();

    // Get new message from provided argument, format flag, or editor
    let new_message = if format {
        if message.is_some() {
            bail!("Cannot use both --fix-formatting and --message flags together");
        }
        // Format the current message without opening an editor
        Some(but_action::commit_format::format_commit_message(
            &current_message,
        ))
    } else if let Some(message) = message {
        Some(normalize_commit_message(message).to_owned())
    } else {
        get_commit_message_from_editor(
            &*ctx.repo.get()?,
            ctx.settings.context_lines,
            commit_details,
            current_message.clone(),
            &current_message,
            show_diff_in_editor,
        )?
    }
    .filter(|new_message| should_update_commit_message(&current_message, new_message));

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