What causes "oldText must not be empty." in can1357/oh-my-pi?

Check oldText is non-empty before calling replaceText and skip/short-circuit the edit if it is.

oldText must not be empty.

Error message

oldText must not be empty.

What it means

replaceText() in the edit fuzzy-diff module throws this before doing any work when the caller passes an empty oldText string. An empty needle would match at position 0 of any file (or be meaningless for replacement), so the library rejects it eagerly instead of producing a bogus no-op or whole-file rewrite. It is a plain Error, thrown synchronously from the public replaceText entry point.

Source

Thrown at packages/coding-agent/src/edit/diff.ts:852

		if (trimmed.startsWith("@@") && lines.slice(i + 1).every(next => next.trim() === "")) {
			break;
		}

		const { hunk, linesConsumed } = parseOneHunk(lines.slice(i), i + 1, true);
		hunks.push(hunk);
		i += linesConsumed;
	}

	return hunks;
}

/**
 * Find and replace text in content using fuzzy matching.
 */
export function replaceText(content: string, oldText: string, newText: string, options: ReplaceOptions): ReplaceResult {
	if (oldText.length === 0) {
		throw new Error("oldText must not be empty.");
	}
	const threshold = options.threshold ?? DEFAULT_FUZZY_THRESHOLD;
	let normalizedContent = normalizeToLF(content);
	const normalizedOldText = normalizeToLF(oldText);
	const normalizedNewText = normalizeToLF(newText);

	if (options.all) {
		// Check for exact matches first
		const exactCount = normalizedContent.split(normalizedOldText).length - 1;
		if (exactCount > 0) {
			return {
				content: normalizedContent.split(normalizedOldText).join(normalizedNewText),
				count: exactCount,
			};
		}

		// Match against the immutable source so inserted replacement text cannot become a later candidate.
		const replacements: Array<{ startIndex: number; endIndex: number; text: string }> = [];

View on GitHub (pinned to 9690622007)

Solutions

Check oldText is non-empty before calling replaceText and skip/short-circuit the edit if it is.
Fix the upstream source producing the empty string (empty capture group, failed read, empty prompt field).
If the intent is 'insert', use an insert/edit API rather than a replace with empty oldText.

Example fix

// before
const res = replaceText(content, match[1] ?? '', replacement, { fuzzy: true });
// after
if (!match[1]) throw new Error(`No search text captured for replacement (offset ${match.index}).`);
const res = replaceText(content, match[1], replacement, { fuzzy: true });

Defensive patterns

Strategy: validation

Validate before calling

if (typeof oldText !== 'string' || oldText.length === 0) {
  throw new Error('replaceText requires non-empty oldText');
}
const result = replaceText(content, oldText, newText, options);

Type guard

function hasSearchText(t: unknown): t is string {
  return typeof t === 'string' && t.length > 0;
}

Try / catch

try {
  return replaceText(content, oldText, newText, options);
} catch (e) {
  if (e instanceof Error && e.message === 'oldText must not be empty.') {
    return { content, count: 0 }; // skip empty-search edits
  }
  throw e;
}

Prevention

Guard interpolated search strings from templates/LLM output before editing.
Use an explicit insert API for insertion instead of empty oldText.
Assert captured groups (match[1]) are non-empty before using them as search text.

When it happens

Trigger: Calling replaceText(content, '', newText, options), or building oldText from a variable that resolved to '' (empty regex capture, empty file read, default-initialized variable).

Common situations: Template-based editors where the search text is interpolated from config or LLM output that came back empty; scripted migrations reading an empty anchor file; agents emitting a replace call with an empty search block.

Related errors

AI-assisted analysis of can1357/oh-my-pi@9690622007 (2026-08-31). Data as JSON: /api/errors/040b4e5b6fc5bb20. Report an issue: GitHub.