What causes "no valid choice to pick for image name" in cross-rs/cross?

Run the build from a proper git tag or branch checkout so the ref matches a known arm

no valid choice to pick for image name

Error message

no valid choice to pick for image name

What it means

determine_image_name builds the list of Docker image tags from the current git ref. The match on the ref type (tag, branch, etc.) has no arm covering the encountered ref, so the function bails with this error. It means the CI/git state does not correspond to any tag or recognized branch form the tool knows how to name an image for.

Solutions

Run the build from a proper git tag or branch checkout so the ref matches a known arm
Check `git rev-parse --symbolic-full-name HEAD` and confirm it resolves to refs/heads/* or refs/tags/*
Add a match arm for the new ref type (e.g. default to repository name) in determine_image_name

Example fix

// before
_ => eyre::bail!("no valid choice to pick for image name"),
// after
_ => {
    tags.push(target.image_name(repository, "local"));
}

Defensive patterns

Strategy: validation

Validate before calling

let r = std::process::Command::new("git").args(["rev-parse","--symbolic-full-name","HEAD"]).output()?;
let name = String::from_utf8_lossy(&r.stdout).trim().to_string();
if !(name.starts_with("refs/heads/") || name.starts_with("refs/tags/")) {
    anyhow::bail!("build must run from a branch or tag ref, got: {name}");
}

Type guard

fn is_supported_ref(full_name: &str) -> bool {
    full_name.starts_with("refs/heads/") || full_name.starts_with("refs/tags/")
}

Prevention

Only run image builds in CI on branch push or tag events
Fail fast at pipeline start if the git ref is detached or unrecognized
Keep the ref-type match and CI event types in sync when changing CI providers

When it happens

Trigger: Calling build_docker_image when the current git ref is neither a tag nor a branch pattern matched above (e.g. detached HEAD, an unusual ref like refs/notes/*, or running locally where the ref resolution returns an unmatched variant).

Common situations: Running the xtask docker build outside the expected CI environment (no tag/branch context), or a new CI ref type appearing after a CI system change.

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 cross-rs/cross@8c1a8aa4b6 (2026-09-13). Data as JSON: /api/errors/8619d4ed503b510a. Report an issue: GitHub.

Appendix: source

Thrown at xtask/src/build_docker_image.rs:434

        }
        ("branch", ref_name) => {
            if let Some(gh_queue) = ref_name.strip_prefix("gh-readonly-queue/") {
                let (_, source) = gh_queue
                    .split_once('/')
                    .ok_or_else(|| eyre::eyre!("invalid gh-readonly-queue branch name"))?;
                tags.push(target.image_name(repository, source));
            } else {
                tags.push(target.image_name(repository, ref_name));
            }

            if ["staging", "trying"]
                .iter()
                .any(|branch| branch != &ref_name)
            {
                tags.push(target.image_name(repository, "edge"));
            }
        }
        _ => eyre::bail!("no valid choice to pick for image name"),
    }
    Ok(tags)
}

pub fn job_summary(
    results: &[Result<ImageTarget, (ImageTarget, eyre::ErrReport)>],
) -> cross::Result<String> {
    let mut summary = "# SUMMARY\n\n".to_string();
    let success: Vec<_> = results.iter().filter_map(|r| r.as_ref().ok()).collect();
    let errors: Vec<_> = results.iter().filter_map(|r| r.as_ref().err()).collect();

    if !success.is_empty() {
        summary.push_str("## Success\n\n| Target |\n| ------ |\n");
    }

    for target in success {
        writeln!(summary, "| {} |", target.alt())?;
    }

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