swc-project/swc · error

failed to parse `global_defs.{k}` of minifier options: {err:

Error message

failed to parse `global_defs.{k}` of minifier options: {err:?}

What it means

While converting terser-compatible compress options (TerserCompressOptions::into_config), every `global_defs` key is parsed as a JavaScript expression with parse_file_as_expr. Keys are meant to be dotted identifier paths (optionally @-prefixed, e.g. "process.env.NODE_ENV" or "@clones"); a key that is not a valid expression panics with the parser error.

Source

Thrown at crates/swc_ecma_minifier/src/option/terser.rs:303

            evaluate: self.evaluate.unwrap_or(self.defaults),
            expr: self.expression,
            global_defs: self
                .global_defs
                .into_iter()
                .map(|(k, v)| {
                    let parse = |input: String| {
                        let fm = cm.new_source_file(FileName::Anon.into(), input);

                        parse_file_as_expr(
                            &fm,
                            Default::default(),
                            Default::default(),
                            None,
                            &mut Vec::new(),
                        )
                        .map(drop_span)
                        .unwrap_or_else(|err| {
                            panic!("failed to parse `global_defs.{k}` of minifier options: {err:?}")
                        })
                    };
                    let key = parse(if let Some(k) = k.strip_prefix('@') {
                        k.to_string()
                    } else {
                        k.to_string()
                    });

                    (
                        key,
                        if k.starts_with('@') {
                            parse(
                                v.as_str()
                                    .unwrap_or_else(|| {
                                        panic!(
                                            "Value of `global_defs.{k}` must be a string literal: "
                                        )
                                    })

View on GitHub (pinned to 5176682b65)

Solutions

1. Make every global_defs key a valid dotted identifier path: "process.env.NODE_ENV", "defines.some.value"
2. If the key started with '@', remember only the value semantics change (parsed as expression); the key after the prefix must still parse as an expression
3. Validate keys against an identifier(.identifier)* pattern before building the minifier options
4. Check the {err:?} payload in the panic for the exact syntax error position

Example fix

// before
compress: { global_defs: { "my const": true } } // panic: failed to parse `global_defs.my const`

// after
compress: { global_defs: { "my_const": true } }

// JS: every global_defs key must be a dotted path (optional leading @)
const keyOk = k => /^@?[A-Za-z_$][\w$]*(\.[A-Za-z_$][\w$]*)*$/.test(k);
for (const k of Object.keys(globalDefs)) {
  if (!keyOk(k)) throw new Error(`invalid global_defs key: ${k}`);
}

When it happens

Trigger: Setting global_defs with keys containing spaces, brackets, keywords, or stray punctuation (e.g. "my const", "a[0]", "let x"); passing terser CLI --define arguments verbatim as keys.

Common situations: Porting a terser config where keys were treated as opaque strings, JSON configs generated from templates that inject whitespace, typos or smart quotes in define names.

Understand the failure class

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

Related errors

• Value of `global_defs.{k}` must be a string literal:
• failed to parse `pure_funcs` of minifier options: {err:?}
• `{raw}` is not a valid ecmascript version
• failed to parse jsx option {}: '{}' is not an expression
• Error occurred while loading config file at ${config}: ${e}

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/f268fc779e7ee15e. Report an issue: GitHub.