# Config in a monorepo

> Let a workspace package find its own config file, or the repository root's, without ever reading a config from above the repository — with search() and stopAt.

Source: https://seniority.interlace.tools/docs/recipes/monorepo

In a monorepo a package may have its own config file, or rely on the root's. Walking upward
finds either. Walking without a bound could also find one in a parent directory you have never
seen, such as a home-directory file or another checkout. `stopAt` sets the ceiling:

```js title="monorepo.mjs"
import { mkdirSync, writeFileSync } from 'node:fs';
import { relative } from 'node:path';

import { discover, search } from 'seniority';

// A stray config above the repository, the repository's own, and two packages.
mkdirSync('work/repo/packages/api', { recursive: true });
mkdirSync('work/repo/packages/web', { recursive: true });
writeFileSync('work/mytool.config.json', '{ "region": "somebody-else" }');
writeFileSync('work/repo/mytool.config.json', '{ "region": "eu-2" }');
writeFileSync('work/repo/packages/web/mytool.config.json', '{ "extends": "../../mytool.config.json", "port": 8080 }');

for (const pkg of ['api', 'web']) {
  const found = search('mytool.config.json', { cwd: `work/repo/packages/${pkg}`, stopAt: 'work/repo' });
  const loaded = await discover({ name: 'mytool', cwd: found.dir, env: {} });
  console.log(pkg, relative('.', found.path), JSON.stringify(loaded.data));
}

const unbounded = search('mytool.config.json', { cwd: 'work/repo/packages/api', stopAt: 'work/repo/packages' });
console.log('stopped below the root:', unbounded === undefined);
```

```text title="node monorepo.mjs"
api work/repo/mytool.config.json {"region":"eu-2"}
web work/repo/packages/web/mytool.config.json {"region":"eu-2","port":8080}
stopped below the root: true
```

- **`api`** has no file of its own, so it gets the repository's config. The stray file in
  `work/` is never read, because the walk stops at `work/repo`.
- **`web`** has its own config, which `extends` the root's, so both are merged.
- Pass the repository root as `stopAt`, and a start-up never depends on what happens to be in
  a parent directory. `discover({ upward: true, stopAt })` does the same walk in one call, for
  `<name>.config.*` files.