Deduplicate Git Ignore (.gitignore)

dedupe.ts

/**
 * Remove duplicates from .gitignore
 *
 * This function reads the .gitignore file, removes duplicates, and overwrites the gitignore file.
 *
 * @param pathToLocalRepo - Path to the local git repository. Default is the current working directory.
 */
async function dedupeGitIgnore(pathToLocalRepo: string | null = null): Promise<void> {
  if (!pathToLocalRepo) {
    pathToLocalRepo = Deno.cwd();
  }

  stopIfDirNotExist(pathToLocalRepo);

  const input = await readGitIgnore(pathToLocalRepo);
  const output: string[] = [];
  const seen: Set<string> = new Set();

  input.forEach((line, index) => {
    if (line === '' || !seen.has(line)) {
      seen.add(line);
      output.push(line);
    } else if (line.startsWith('#')) {
      // Preserve duplicate comment lines
      output.push(line);
    }
  });

  const gitignore_path = `${pathToLocalRepo}/.gitignore`;

  await Deno.writeTextFile(gitignore_path, output.join('\n') + '\n');
}

async function readGitIgnore(path_to_local_repo: string): Promise<string[]> {
  const gitignore_path = `${path_to_local_repo}/.gitignore`;
  try {
    const data = await Deno.readTextFile(gitignore_path);
    return data.trim().split('\n');
  } catch (e) {
    if (e instanceof Deno.errors.NotFound) {
      return [];
    }
    throw e;
  }
}

function stopIfDirNotExist(path_to_local_repo: string): void {
  try {
    const stats = Deno.statSync(path_to_local_repo);
    if (!stats.isDirectory) {
      throw new Error(`Directory not found: ${path_to_local_repo}`);
    }
  } catch (e) {
    if (e instanceof Deno.errors.NotFound) {
      throw new Error(`Directory not found: ${path_to_local_repo}`);
    }
    throw e;
  }
}

dedupeGitIgnore();

Run with

deno run dedupe.ts

or

deno run --allow-read --allow-write dedupe.ts