Question: Why extending @typescript-eslint/recommended automatically adds tsx and ts extensions?

[fregante]

Sorry, this is just a question. As far as I know eslint only runs on JS files and I have to use eslint --ext ts,tsx to run it on TypeScript files. There's no way around it… as far as I know. This is what your own docs say.

But actually I run eslint with just @typescript-eslint/recommended and eslint automatically picks up ts and tsx files. Why and most importantly how?!

Repro:

  npm init -y
  npm install eslint  @typescript-eslint/parser @typescript-eslint/eslint-plugin
  echo '// @ts-ignore' > index.ts
  echo '{}' > tsconfig.json
  echo '{"extends":["plugin:@typescript-eslint/recommended"]}' > .eslintrc
  npx eslint .

./index.ts
  1:1  error  Do not use "@ts-ignore" because it alters compilation errors  @typescript-eslint/ban-ts-comment

✖ 1 problem (1 error, 0 warnings)

🤔

We were wondering in xojs/eslint-config-xo-typescript#39

[bradzacher]

It's likely because of our eslint-recommended config which explicitly disables/enables some rules on .ts/.tsx files:

typescript-eslint/packages/eslint-plugin/src/configs/eslint-recommended.ts

Line 9 in 26de645

files: ['*.ts', '*.tsx'],

This causes ESLint to recognise we want to lint .ts/.tsx files, and thus it automatically includes them when looking for files.
Then because the recommended config contains no restrictions - it just (correctly) applies the rules to the files.

[fregante]

I have no idea how I missed that. I was just looking at this file https://github.com/typescript-eslint/typescript-eslint/blob/26de6459a38389fff86351c1aa0881b11dc2a76a/packages/eslint-plugin/src/configs/recommended.ts

Thank you for the quick answer!