Crash on running ESLint

[ficristo]

What version of TypeScript are you using? 3.1.6

What version of typescript-eslint-parser are you using? 21.0.1

What code were you trying to parse? See https://github.com/quadre-code/quadre/pull/103 I cannot hunt down to specific code...

What did you expect to happen? Eslint should pass.

What happened?

TypeError: Cannot read property 'type' of undefined
    at isForInRef (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:406:24)
    at variable.references.some.ref (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:443:21)
    at Array.some (<anonymous>)
    at isUsedVariable (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:442:40)
    at collectUnusedVariables (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:565:26)
    at collectUnusedVariables (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:572:17)
    at collectUnusedVariables (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:572:17)
    at Program:exit (F:\github\quadre\node_modules\eslint\lib\rules\no-unused-vars.js:617:36)
    at listeners.(anonymous function).forEach.listener (F:\github\quadre\node_modules\eslint\lib\util\safe-emitter.js:47:58)
    at Array.forEach (<anonymous>)

Some more info At the moment I cannot update ESLint to version 5.* To see the error on my project I run grunt eslint --stack --debug. Is it possible the crash is because I do not use eslint-plugin-typescript and its typescript/no-unused-vars rule? Nonetheless I would expect an ESLint error and not a crash.

[mysticatea]

Thank you for this issue.

However, we cannot guarantee that ESLint core rules work properly on TypeScript syntax because the rules don't know TypeScript syntax. It's the reason that eslint-plugin-typescript has some copies of core rules.

I'd like to recommend to disable no-unused-vars rule because TypeScript compiler itself verifies it.

[ficristo]

I tryed to use eslint-plugin-typescript without success: https://github.com/bradzacher/eslint-plugin-typescript/issues/171 In the end I disabled the rule for ts and tsx files. If you think this is the expected behaviour feel free to close this issue.

@mysticatea thank you for your fast reply and help!

[armano2]

@mysticatea i was able to reproduce this by this code (tested on master branch)

enum Foo {
    BAR = 'bar'
}

[mysticatea]

@armano2 In that case, I guess that no-unused-vars misunderstands EnumMember variables as regular variables because core rules don't know enum syntax. However, enum members make variables (see also https://github.com/eslint/typescript-eslint-parser/issues/552#issuecomment-439276282). I think that this is a case that we have to make the alternative rule in eslint-plugin-typescript.

[armano2]

@mysticatea not really issue is with missing parent on identifier https://gist.github.com/armano2/3d27d7de6291ea01ef4893d8c3475132 - AST, scope, source

function isForInRef(ref) {
            let target = ref.identifier.parent;

[mysticatea]

Oh. Interesting. Reference#Identifier must not be null. And ESLint should set parent property of all nodes before gives nodes to rules.

[armano2]

@mysticatea damn i found whats wrong xdddddd

in visitor-keys there is TSEnumMember: ["initializer"],

and should be TSEnumMember: ["id", "initializer"],

[mysticatea]

Ahhh!! Thank you so much for found!

[armano2]

do you want me do to PR with this?

[mysticatea]

If you have time. Otherwise, I will do.

[armano2]

ok pushed PR