swc-project/swc · error

determine_export_name({:?})

Error message

determine_export_name({:?})

What it means

The UMD transform derives the global export name from the module's file name. Only `FileName::Real` and `FileName::Custom` carry a name `global_name` can use; `Anon`, `Url`, `Internal`, `Macros` and other variants hit `unimplemented!("determine_export_name(...)")` because no identifier can be derived.

Source

Thrown at crates/swc_ecma_transforms_module/src/umd/config.rs:87

        src.split('/').next_back().unwrap().to_camel_case().into()
    }

    pub fn determine_export_name(&self, filename: Lrc<FileName>) -> Ident {
        match &*filename {
            FileName::Real(ref path) => {
                let s = match path.file_stem() {
                    Some(stem) => self.global_name(&stem.to_string_lossy()),
                    None => self.global_name(&path.display().to_string()),
                };

                quote_ident!(s).into()
            }
            FileName::Custom(s) => {
                let s = self.global_name(s);
                quote_ident!(s).into()
            }
            _ => unimplemented!("determine_export_name({:?})", filename),
        }
    }
}

View on GitHub (pinned to d7d7434666)

Solutions

1. Create the source file with `FileName::Custom("myLib".into())` or a real path before running the UMD transform
2. Prefer `FileName::Custom` for virtual modules so the derived global name is deterministic (camelCased from the string)
3. If you use the high-level Compiler API, always pass a real `filename` in the compile options

Example fix

// before
let fm = cm.new_source_file(FileName::Anon.into(), code.to_string());

// after
let fm = cm.new_source_file(FileName::Custom("myLib".into()).into(), code.to_string());

// Rust: guard the filename before running the UMD transform
fn usable_for_umd(f: &FileName) -> bool {
    matches!(f, FileName::Real(_) | FileName::Custom(_))
}
assert!(usable_for_umd(&fm.name), "UMD requires a Real or Custom FileName");

fn has_export_name_source(f: &FileName) -> bool {
    matches!(f, FileName::Real(_) | FileName::Custom(_))
}

When it happens

Trigger: Run the UMD pass on a module whose SourceMap file was created with `FileName::Anon` — the common default in tests and ad-hoc tools (`cm.new_source_file(FileName::Anon.into(), code)`) — or with Url/Internal names.

Common situations: Tests and one-off compilers that never set a real filename; pipelines feeding virtual modules; plugins creating source files with generated internal names.

Related errors

• derive(Merge) does not support an enum
• corejs version other than 2 / 3
• not implemented
• emitting decorator metadata while using new proposal
• Invalid path "{path:?}"

AI-assisted analysis of swc-project/swc@d7d7434666 (2026-08-16). Data as JSON: /api/errors/48b8fdca8131767f. Report an issue: GitHub.