oven-sh/bun · error · Error

${input}: missing default export

Error message

${input}: missing default export

What it means

After dynamically importing the input file, the generator reads `mod.default` and expects either a single StringMapSpec object or an array of them. A falsy default export (or none at all) cannot be generated from, so it aborts with the input path in the message.

Source

Thrown at src/codegen/generate-string-map.ts:293

  // No `#![allow]` — this is `include!`d, and inner attributes aren't legal
  // mid-module. Per-item allows are emitted where needed instead.
  return [
    `// Generated by src/codegen/generate-string-map.ts from ${rel} — do not edit.`,
    ``,
    ...arr.map(s => buildOne(s)),
    ``,
  ].join("\n\n");
}

// ── CLI ─────────────────────────────────────────────────────────────────────
if (import.meta.main) {
  const [, , input, output] = process.argv;
  if (!input || !output) {
    throw new Error("usage: bun src/codegen/generate-string-map.ts <input.string-map.ts> <out.rs>");
  }
  const mod = await import(path.resolve(input));
  const specs = mod.default as StringMapSpec<unknown> | StringMapSpec<unknown>[];
  if (!specs) throw new Error(`${input}: missing default export`);
  writeIfNotChanged(output, generateStringMaps(specs, input));
}

View on GitHub (pinned to 8c5296ac45)

Solutions

1. Add `export default` to the spec object or array in the input file.
2. If the module intentionally has multiple named specs, default-export them as an array.

Example fix

// before
export const spec = { name: "Map", entries: [] };

// after
const spec = { name: "Map", entries: [] };
export default spec;

const mod = await import(path.resolve(input));
if (!mod.default) throw new Error(`${input}: missing default export`);

function isStringMapSpec(v: unknown): v is StringMapSpec<unknown> {
  return (
    typeof v === "object" && v !== null &&
    typeof (v as any).name === "string" &&
    Array.isArray((v as any).entries)
  );
}
const specs = Array.isArray(mod.default) ? mod.default : [mod.default];
if (!specs.every(isStringMapSpec)) throw new Error(`${input}: bad default export shape`);

When it happens

Trigger: The input .string-map.ts exports its spec via a named export (`export const spec = ...`), exports `undefined` conditionally, or is an empty file.

Common situations: Converting an existing spec module to named exports; refactoring so the default export is behind a flag that evaluates falsy.

Related errors

• generate-string-map: duplicate key ${JSON.stringify(k)} in $
• generate-string-map: ${name}: emitCaseInsensitive requires A
• generate-string-map: ${name}: keys ${JSON.stringify(k)} coll
• ${name}: ${entries.length} entries exceed u16 indexOf range
• file did not exist after write: ${outputPath}

AI-assisted analysis of oven-sh/bun@8c5296ac45 (2026-08-16). Data as JSON: /api/errors/69aa295dd8cc393d. Report an issue: GitHub.