swc-project/swc · error

prettier failed

Error message

prettier failed

What it means

Despite the function name and the message saying 'prettier', make_pretty actually runs 'npx js-beautify --replace <file>' and bails when that exits non-zero; the name is historical. So the failing tool is js-beautify, not prettier. Common causes: npx cannot resolve or download js-beautify (offline, no install) or js-beautify rejects the file.

Source

Thrown at crates/dbg-swc/src/util/mod.rs:42

    op()
}

pub fn gzipped_size(code: &str) -> usize {
    let mut e = ZlibEncoder::new(Vec::new(), Compression::new(9));
    e.write_all(code.as_bytes()).unwrap();
    let compressed_bytes = e.finish().unwrap();
    compressed_bytes.len()
}

pub fn make_pretty(f: &Path) -> Result<()> {
    let mut c = Command::new("npx");
    c.stderr(Stdio::inherit());
    c.arg("js-beautify").arg("--replace").arg(f);

    let output = c.output().context("failed to run prettier")?;

    if !output.status.success() {
        bail!("prettier failed");
    }

    Ok(())
}

pub fn parse_js(fm: Arc<SourceFile>) -> Result<ModuleRecord> {
    let unresolved_mark = Mark::new();
    let top_level_mark = Mark::new();

    let mut errors = Vec::new();
    let comments = SingleThreadedComments::default();
    let res = parse_file_as_module(
        &fm,
        Syntax::Es(Default::default()),
        EsVersion::latest(),
        Some(&comments),
        &mut errors,
    )

View on GitHub (pinned to 5176682b65)

Solutions

1. Install the right tool: npm i -g js-beautify (the message says prettier but js-beautify is what runs)
2. Verify with 'npx js-beautify --version' in the same environment
3. Ensure network/registry access for npx or pre-install locally
4. If js-beautify fails on one specific file, inspect that file for encoding corruption first

Example fix

# before - message says prettier, tool is js-beautify
$ npm install -g prettier   # does not fix it
error: prettier failed

# after
$ npm install -g js-beautify
$ npx js-beautify --version
1.15.1

use std::process::Command;

fn js_beautify_available() -> bool {
    Command::new("npx")
        .args(["js-beautify", "--version"])
        .output()
        .map(|o| o.status.success())
        .unwrap_or(false)
}

// the message says 'prettier' but the tool invoked is js-beautify
assert!(js_beautify_available(), "install js-beautify: npm i -g js-beautify");

match make_pretty(&path) {
    Ok(()) => {}
    Err(e) if format!("{e:#}").contains("prettier failed") => {
        // cosmetic formatting only - continue without pretty-printing
        eprintln!("warning: js-beautify unavailable, skipping formatting: {e:#}");
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: dbg-swc code paths that format reduced/minimized test files invoke make_pretty on machines where 'npx js-beautify' fails to run: package missing and registry unreachable, or js-beautify exiting non-zero on the mutated file.

Common situations: Air-gapped CI where npx cannot fetch packages; developers installing prettier because the error message mentions it (wrong tool); files mangled by test reduction that js-beautify cannot reformat.

Related errors

• failed to run terser
• `deno bundle` failed with status code {}
• `npm run build` failed
• failed to run esbuild
• No `.js` or `.jsx` files found in `{}`

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/f096bd8f490c2d9d. Report an issue: GitHub.