denoland/deno · error · TypeError

Missing bench function

Error message

Missing bench function

What it means

This is `deno fmt`'s summary error for files that could not be formatted at all, as opposed to files that merely need formatting. Per-file failures (parse errors, unreadable files, decode failures) increment `failed_files_count`, and `finish()` reports how many of the checked files errored. The details of each failure are printed above the summary during the run.

Source

Thrown at cli/js/40_bench.js:122

  let benchDesc;
  const defaults = {
    ignore: false,
    baseline: false,
    only: false,
    sanitizeExit: true,
    permissions: null,
  };

  if (typeof nameOrFnOrOptions === "string") {
    if (!nameOrFnOrOptions) {
      throw new TypeError("The bench name can't be empty");
    }
    if (typeof optionsOrFn === "function") {
      benchDesc = { fn: optionsOrFn, name: nameOrFnOrOptions, ...defaults };
    } else {
      if (!maybeFn || typeof maybeFn !== "function") {
        throw new TypeError("Missing bench function");
      }
      if (optionsOrFn.fn != undefined) {
        throw new TypeError(
          "Unexpected 'fn' field in options, bench function is already provided as the third argument",
        );
      }
      if (optionsOrFn.name != undefined) {
        throw new TypeError(
          "Unexpected 'name' field in options, bench name is already provided as the first argument",
        );
      }
      benchDesc = {
        ...defaults,
        ...optionsOrFn,
        fn: maybeFn,
        name: nameOrFnOrOptions,
      };
    }

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Run `deno fmt` without `--check` and read the per-file error lines printed above the summary; fix the reported syntax error
2. Isolate the broken file with `deno fmt path/to/file.ts` to see its full error
3. Search for leftover conflict markers (`grep -rn '<<<<<<<'`) after a messy merge
4. If the file should not be formatted, exclude it via `"fmt": { "exclude": [...] }` in deno.json

Example fix

# before
$ deno fmt
# Error formatting .../broken.ts: Unexpected token
# Failed to format 1 of 12 checked files

# after (fix the syntax error in broken.ts, e.g. remove stray comma)
$ deno fmt  # ok

# Surface per-file errors before the summary by running fmt verbosely
deno fmt 2>&1 | grep -B1 'Error formatting' || true

In scripts wrapping the CLI, run fmt without --check, capture exit code, and treat 'Failed to format N of M' as a per-file error signal: re-run `deno fmt <file>` for each file named above the summary to get the underlying syntax error, fix it, then retry the full run.

When it happens

Trigger: Any matched file raises while formatting: a TypeScript/JavaScript/JSON/JSONC/Markdown file with a syntax error the dprint plugin cannot parse, a file that cannot be read (permissions), or a file whose contents cannot be decoded. Note the summary counts both, so run without `--check` to see each per-file error message.

Common situations: A half-finished refactor left a syntax error in a file that fmt scans; a JSON file with trailing commas or comments outside the configured plugin expectations; a file locked by another process on Windows; merge-conflict markers (`<<<<<<<`) left in a source file.

Related errors

• The bench name can't be empty
• Unexpected 'fn' field in options, bench function is already
• Panic formatting: {}
• Did not format non-workspace directory. Run again specifying
• Formatting succeeded initially, but failed when ensuring a s

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/ecd73a132d022fdc. Report an issue: GitHub.