[no-use-before-define] Not considering hoisting

[Tarnadas]

The no-use-before-define rule is not considering hoisting, therefore giving me errors, when declaring a function below its usage.

Repro

{
  "rules": {
    "@typescript-eslint/no-use-before-define": "error"
  }
}

fn(); // [eslint] 'fn' was used before it was defined. [@typescript-eslint/no-use-before-define]

function fn() {}

Expected Result

No linting error.

Actual Result

Linting error: [eslint] 'fn' was used before it was defined. [@typescript-eslint/no-use-before-define]

Versions

package	version
@typescript-eslint/eslint-plugin	1.2.0
@typescript-eslint/parser	1.2.0
TypeScript	3.2.4
ESLint	5.13.0
node	8.15.0

[platinumazure]

Hi @Tarnadas, thanks for the issue.

I can't speak to the typescript-eslint version of the rule, but in core ESLint, this would be functioning as designed. The entire point of this rule is to flag all uses before definitions-- not to flag if a variable use would be undefined. It is more of a stylistic/readability rule. The no-undef rule (or typescript-eslint's equivalent) detects if the value is actually not defined (for example, if you used let fn = function() {}, which is not hoisted.

Maintainers-- please correct me if I've misstated anything.

[Tarnadas]

Hey @platinumazure,
I just read through the ESLint page for this rule and it looks like you're right and this is WAI.

[aMarCruz]

@Tarnadas , use this:

{
  "rules": {
    "no-use-before-define": "off",
    "@typescript-eslint/no-use-before-define": ["error", {"functions": false, "typedefs": false}]
  }

Note there's a bug with typeof ignoring typedefs:false, but once fixed the rule must work like intended.