[explicit-function-return-type] Is type inference not allowed?

[ghost]

Repro

{
  "rules": {
    "@typescript-eslint/explicit-function-return-type": "error"
  }
}

const fn1: (i: number) => string = function(i) { return i.toString(); }; // Error
const fn2: (i: number) => string = i => i.toString(); //Error

Expected Result
Expect no error because these functions are inferred to return string.

Actual Result
Error. (Missing return type on function.)

Additional Info

Versions

package	version
@typescript-eslint/eslint-plugin	1.6.0
@typescript-eslint/parser	1.6.0
TypeScript	3.4.3
ESLint	5.16.0
node	10.15.3
npm	6.4.1

[bradzacher]

Check out the options for the rule: https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/explicit-function-return-type.md#options

I believe you'll want allowTypedFunctionExpressions

[hanneswidrig]

This might be a dumb question but I am trying to understand how I use these rules for [explicit-function-return-type] inside my React Typescript application on Create-React-App 3.0.

{
  "plugins": ["react", "react-hooks", "@typescript-eslint"],
  "extends": [
    "plugin:@typescript-eslint/recommended",
    "prettier",
    "prettier/@typescript-eslint"
  ],
  "rules": {
    "react-hooks/rules-of-hooks": "error",
    "react-hooks/exhaustive-deps": "warn",
    "allowExpressions ": true,
    "allowTypedFunctionExpressions": true
  },
  "parser": "@typescript-eslint/parser",
  "globals": {
    "Atomics": "readonly",
    "SharedArrayBuffer": "readonly"
  },
  "env": {
    "browser": true,
    "es6": true
  },
  "parserOptions": {
    "project": "./tsconfig.json",
    "ecmaFeatures": {
      "jsx": true
    },
    "ecmaVersion": 2018,
    "sourceType": "module"
  }
}

This is my .eslintrc.json file. I am wondering how I add those rules like AllowExpressions.

"@typescript-eslint/explicit-function-return-type": 0, Adding this to the rules made it go away but I am not sure if this is completely turning off all rules. I still want to require function return type when it's not inferred.

[bradzacher]

@hanneswidrig

Check out the eslint docs for configuring rules.
https://eslint.org/docs/user-guide/configuring#using-configuration-files

The available options for this rule are listed here
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/explicit-function-return-type.md#options

Let me know if you need more help.

[hanneswidrig]

@bradzacher I just figured it out, thanks for the resources though.

For anyone working with React and wondering about this, see the example below.