swc-project/swc · error

unexpected: root directory is given as a input file

Error message

unexpected: root directory is given as a input file

What it means

While locating a referenced external source map, swc takes the parent directory of the input file's real path; `Path::parent()` returned None, which happens only when the path is the filesystem root (or degenerate empty form). SWC reports this as 'root directory given as input file' because a root path has no sibling directory in which to look for a .map file.

Source

Thrown at crates/swc/src/lib.rs:474

                    let content = url.path()[idx + "base64,".len()..].trim();

                    let res = BASE64_STANDARD
                        .decode(content.as_bytes())
                        .context("failed to decode base64-encoded source map")?;

                    Ok(Some(sourcemap::SourceMap::from_slice(&res).context(
                        "failed to read input source map from inlined base64 encoded string",
                    )?))
                };

            let read_file_sourcemap =
                |data_url: Option<&str>| -> Result<Option<sourcemap::SourceMap>, Error> {
                    match &**name {
                        FileName::Real(filename) => {
                            let dir = match filename.parent() {
                                Some(v) => v,
                                None => {
                                    bail!("unexpected: root directory is given as a input file")
                                }
                            };

                            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;

View on GitHub (pinned to 5176682b65)

Solutions

1. Pass a real filename in options.filename, e.g. "src/index.js" rather than "" or "/"
2. Log the filename immediately before the swc call to find where it degenerates
3. Guard callers: reject empty or root-only paths before invoking the compiler

Example fix

// before
const out = await swc.transform(src, { filename: inputPath /* "" */ });
// after
if (!inputPath || path.isAbsolute(inputPath) && path.parse(inputPath).root === inputPath) {
  throw new Error('valid filename required');
}
const out = await swc.transform(src, { filename: inputPath });

// JavaScript - reject degenerate filenames before calling swc
import path from 'node:path';
function assertUsableFilename(filename) {
  if (!filename || path.parse(filename).root === filename) {
    throw new Error(`invalid input filename: ${JSON.stringify(filename)}`);
  }
}

When it happens

Trigger: Invoking the compiler with FileName::Real("/") or an empty path - e.g. options.filename computed as '' or '/' by glue code - on a file that references a source map.

Common situations: Programmatic Compiler/swc API use where filename is built from an unset variable; CI containers where a path env var is empty; wrappers that pass the wrong field (directory instead of file path).

Related errors

• determine_export_name({:?})
• failed to parse inline source map: not base64: {url:?}
• failed to find input source map file {:?} in {:?} file as ei
• 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/5e0b568563044c49. Report an issue: GitHub.