swc-project/swc · error

failed to find input source map file {:?} in {:?} file as ei

Error message

failed to find input source map file {:?} in {:?} file as either {:?} or with appended .map

What it means

The input file's `sourceMappingURL` comment names an external map file; swc resolved it relative to the input file's directory and also tried the legacy fallback `<inputfile>.map`; neither exists on disk, so processing aborts. The message includes the sourceMappingURL value, the input file path, and the candidate map path that was checked.

Source

Thrown at crates/swc/src/lib.rs:494

                            };

                            let map_path = match data_url {
                                Some(data_url) => {
                                    let mut map_path = dir.join(data_url);
                                    if !map_path.exists() {
                                        // Old behavior. This check would prevent
                                        // regressions.
                                        // Perhaps it shouldn't be supported. Sometimes
                                        // developers don't want to expose their source
                                        // code.
                                        // Map files are for internal troubleshooting
                                        // convenience.
                                        let fallback_map_path =
                                            PathBuf::from(format!("{}.map", filename.display()));
                                        if fallback_map_path.exists() {
                                            map_path = fallback_map_path;
                                        } else {
                                            bail!(
                                                "failed to find input source map file {:?} in \
                                                 {:?} file as either {:?} or with appended .map",
                                                data_url,
                                                filename.display(),
                                                map_path.display(),
                                            )
                                        }
                                    }

                                    Some(map_path)
                                }
                                None => {
                                    // Old behavior.
                                    let map_path =
                                        PathBuf::from(format!("{}.map", filename.display()));
                                    if map_path.exists() {
                                        Some(map_path)
                                    } else {

View on GitHub (pinned to 5176682b65)

Solutions

1. Restore the .map file at the exact path the comment references, relative to the input file
2. Or remove the `//# sourceMappingURL=` comment from the input file
3. Or tell swc not to read input maps (e.g. `inputSourceMap: false` in @swc/core options) when they are intentionally absent

Example fix

// before
//# sourceMappingURL=./maps/index.js.map   /* file missing */
// after: either ship ./maps/index.js.map, or drop the comment / disable reading it
const out = await transformFile('index.js', { inputSourceMap: false });

// JavaScript - verify referenced external map exists before compiling
import fs from 'node:fs';
import path from 'node:path';
function assertInputSourceMapExists(source, filePath) {
  const m = source.match(/\/\/[#@]\s*sourceMappingURL=(\S+)/);
  if (!m || m[1].startsWith('data:')) return;
  const candidates = [
    path.resolve(path.dirname(filePath), m[1]),
    `${filePath}.map`,
  ];
  if (!candidates.some((p) => fs.existsSync(p))) {
    throw new Error(`missing source map for ${filePath}: ${m[1]}`);
  }
}

When it happens

Trigger: Compiling a JS file containing `//# sourceMappingURL=foo.js.map` where foo.js.map was deleted or never deployed next to the file; map in a different directory than the referencing file; case mismatches on case-sensitive filesystems.

Common situations: Committing or deploying compiled .js without the .map; CI copying only .js artifacts; moving/renaming files after build; consuming transpiled sources from CDNs where maps aren't shipped.

Related errors

• failed to parse inline source map: not base64: {url:?}
• determine_export_name({:?})
• unexpected: root directory is given as a input file
• The requested module '{specifier}' does not provide an expor
• Cannot use import.meta outside a module

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/9cf6c094c4f1798d. Report an issue: GitHub.