What causes "--step must be > 0" in chenglou/pretext?

Pass a positive step, e.g. `--step=10` (the default).

chenglou/pretext · error · Error

--step must be > 0

Error message

--step must be > 0

What it means

Thrown after `--step` parses as a valid integer but is zero or negative. The sweep loop increments width by `step`, so a non-positive step would loop forever or make no progress.

Source

Thrown at scripts/corpus-sweep.ts:127

}

function parseBrowser(value: string | null): BrowserKind {
  const browser = (value ?? process.env['CORPUS_CHECK_BROWSER'] ?? 'chrome').toLowerCase()
  if (browser !== 'chrome' && browser !== 'safari') {
    throw new Error(`Unsupported browser ${browser}; expected chrome or safari`)
  }
  return browser
}

async function loadSources(): Promise<CorpusMeta[]> {
  return await Bun.file('corpora/sources.json').json()
}

function parseOptions(): SweepOptions {
  const start = parseNumberFlag('start', 300)
  const end = parseNumberFlag('end', 900)
  const step = parseNumberFlag('step', 10)
  if (step <= 0) throw new Error('--step must be > 0')
  if (end < start) throw new Error('--end must be >= --start')
  if (parseStringFlag('samples') !== null) {
    throw new Error('--samples is obsolete for corpus-sweep; use the default step-based sweep or sampled font-matrix/taxonomy runs instead')
  }

  return {
    id: parseStringFlag('id'),
    all: hasFlag('all'),
    start,
    end,
    step,
    port: parseNumberFlag('port', Number.parseInt(process.env['CORPUS_CHECK_PORT'] ?? '0', 10)),
    browser: parseBrowser(parseStringFlag('browser')),
    output: parseStringFlag('output'),
    timeoutMs: parseNumberFlag('timeout', Number.parseInt(process.env['CORPUS_CHECK_TIMEOUT_MS'] ?? '180000', 10)),
    font: parseStringFlag('font'),
    lineHeight: parseOptionalNumberFlag('lineHeight'),
    diagnose: hasFlag('diagnose'),

View on GitHub (pinned to ac49b09b7d)

Solutions

Pass a positive step, e.g. `--step=10` (the default).
If you want a single width, use the taxonomy/check script with a positional width instead of zeroing the step.

Example fix

// before
bun run scripts/corpus-sweep.ts --id=ja-kumo-no-ito --step=0
// after
bun run scripts/corpus-sweep.ts --id=ja-kumo-no-ito --step=10

Defensive patterns

Strategy: validation

Validate before calling

const step = parseNumberFlag('step', 10)
if (step <= 0) {
  console.error('--step must be > 0')
  process.exit(2)
}

Prevention

Keep --step at its default (10) unless you have a reason to change it.
For single-width checks, pass the width positionally to the taxonomy/check script instead of zeroing the step.

When it happens

Trigger: `--step=0` or `--step=-10`.

Common situations: Trying to disable stepping; a sign error; copy-pasting a value intended for a different flag.

Related errors

AI-assisted analysis of chenglou/pretext@ac49b09b7d (2026-08-12). Data as JSON: /api/errors/2f39f335337bc2d1. Report an issue: GitHub.