swc-project/swc · error

failed to parse targets

Error message

failed to parse targets

What it means

In From<Config> for EnvConfig in swc_ecma_preset_env, targets_to_versions failed to convert the configured targets (and optional browserslist path) into Versions. This fires at preset_env setup when the `targets` option is malformed — an invalid browserslist query, bad config file path, or wrongly shaped target map — so the transform cannot determine which syntax/features to compile down.

Source

Thrown at crates/swc_ecma_preset_env/src/lib.rs:711

struct CoreJSConfig {
    targets: Arc<Versions>,
    included_modules: FxHashSet<String>,
    excluded_modules: FxHashSet<String>,
    /// True if the browserslist query returned an empty result (unknown browser
    /// version).
    unknown_version: bool,
}

pub struct EnvConfig {
    config: Config,
    feature_config: Arc<FeatureConfig>,
    core_js_config: CoreJSConfig,
}

impl From<Config> for EnvConfig {
    fn from(mut config: Config) -> Self {
        let target_info = targets_to_versions(config.targets.take(), config.path.take())
            .expect("failed to parse targets");
        let is_any_target = target_info.versions.is_any_target();

        let (include, included_modules) = FeatureOrModule::split(config.include.clone());
        let (exclude, excluded_modules) = FeatureOrModule::split(config.exclude.clone());

        let feature_config = FeatureConfig {
            targets: Arc::clone(&target_info.versions),
            include,
            exclude,
            is_any_target,
            unknown_version: target_info.unknown_version,
            force_all_transforms: config.force_all_transforms,
            bugfixes: config.bugfixes,
        };
        let core_js_config = CoreJSConfig {
            targets: Arc::clone(&target_info.versions),
            included_modules,
            excluded_modules,

View on GitHub (pinned to 5176682b65)

Solutions

1. Check the `targets` field of the preset_env config for valid browserslist query syntax
2. Verify the browserslist config `path` points to an existing, valid file
3. Validate the same targets against the browserslist CLI
4. Use explicit version maps like { chrome: 80 } instead of free-form queries

When it happens

Trigger: Thrown at crates/swc_ecma_preset_env/src/lib.rs:711 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/f6b89c3ba675f4c1. Report an issue: GitHub.