What causes "JSON output isn't supported" in GitoxideLabs/gitoxide?

Use the human output format and parse the text

JSON output isn't supported

Error message

JSON output isn't supported

What it means

The branch `list` command supports only human-readable output; a non-Human OutputFormat (e.g. JSON) bails before enumerating references. JSON serialization for branch listing is not implemented in gitoxide-core.

Solutions

Use the human output format and parse the text
Enumerate branches via the gix library (`repo.references()?` / remote refs) and serialize to JSON yourself
File or track an upstream feature request for JSON branch output

Example fix

// before
branch::list(repo, &mut out, OutputFormat::Json, options)?;
// after
branch::list(repo, &mut out, OutputFormat::Human, options)?;

Defensive patterns

Strategy: validation

Validate before calling

if format != OutputFormat::Human {
    eprintln!("branch list: JSON not supported; using Human");
    format = OutputFormat::Human;
}

Try / catch

match branch::list(repo, out, format, options) {
    Err(e) if e.to_string().contains("JSON output isn't supported") => {
        // fall back to human output or use gix library refs API
    }
    other => other?,
}

Prevention

Use Human output for branch listing
Enumerate branches via gix::Repository references API for structured data
Check format support per subcommand before invoking with JSON

When it happens

Trigger: Calling `repository::branch::list` with `format != OutputFormat::Human`, e.g. the CLI branch listing invoked with a JSON format flag.

Common situations: Scripts or tools expecting machine-readable branch listings from gix; IDE integrations requesting JSON output uniformly.

Related errors

AI-assisted analysis of GitoxideLabs/gitoxide@e73179060b (2026-09-08). Data as JSON: /api/errors/5fabb05dfb97e343. Report an issue: GitHub.

Appendix: source

Thrown at gitoxide-core/src/repository/branch.rs:21

pub mod list {
    pub enum Kind {
        Local,
        All,
    }

    pub struct Options {
        pub kind: Kind,
    }
}

pub fn list(
    repo: gix::Repository,
    out: &mut dyn std::io::Write,
    format: OutputFormat,
    options: list::Options,
) -> anyhow::Result<()> {
    if format != OutputFormat::Human {
        anyhow::bail!("JSON output isn't supported");
    }

    let platform = repo.references()?;

    let (show_local, show_remotes) = match options.kind {
        list::Kind::Local => (true, false),
        list::Kind::All => (true, true),
    };

    if show_local {
        let mut branch_names: Vec<String> = platform
            .local_branches()?
            .flatten()
            .map(|branch| branch.name().shorten().to_string())
            .collect();

        branch_names.sort();

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