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[no-unused-vars] false positive when generic param name masks name in parent scope #54

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armano2 opened this issue Nov 22, 2018 · 2 comments · Fixed by #688
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[no-unused-vars] false positive when generic param name masks name in parent scope #54

armano2 opened this issue Nov 22, 2018 · 2 comments · Fixed by #688
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bug Something isn't working has pr there is a PR raised to close this package: parser Issues related to @typescript-eslint/parser scope analyser Issues that are caused by bugs/incomplete cases in the scope analyser
Milestone
scope analysis re...

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@armano2
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armano2 commented Nov 22, 2018

Repro

{
  "rules": {
    "no-unused-vars": "off",
    "typescript/no-unused-vars": "error"
  }
}
type Foo = number

function test<Foo>(bar: Foo) {
    return bar
}

Expected Result
error that type Foo is not defined

Actual Result
all is good

Additional Info

There is few issues there:

  • markVariableAsUsed is iterating over all variables even if found first one,
  • type parameters are not validated

Versions

package version
eslint-plugin-typescript 1.0.0-rc.1
typescript-eslint-parser internal
typescript 3.1.1
@bradzacher bradzacher changed the title no-unused-vars incorrect results [no-unused-vars] false positive when generic param name masks name in parent scope Nov 25, 2018
@bradzacher
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Digging into this, I don't know what we can do about this without significant work.

Right now our rule sits on top of the base rule, so I think we would have to clone the base rule's code in order to handle this case properly.

This would be a good candidate for using the TS parser services if it reports unused vars.

This should be caught by something like no-redeclare. Though it won't because we haven't added ts-specific handling to that rule.

@armano2
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armano2 commented Jan 8, 2019 •
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@bradzacher right now there is no real solution for that. It's require some work on parser before we can start.
I started doing PR with support for additional data in scope for typescript "types" but its not near finish.
When it will be done, we can start thinking about solving this.

I made this issue for now just to inform ppl that we are aware about it and we will work on it.

no-redeclare is not possible now without scope analysis (unless we do it in bad way on our side)

type references and annotations are not in eslint scope for now.

@JamesHenry JamesHenry transferred this issue from bradzacher/eslint-plugin-typescript Jan 18, 2019
@bradzacher bradzacher added bug Something isn't working package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin package: parser Issues related to @typescript-eslint/parser and removed package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin labels Jan 18, 2019
@armano2 armano2 mentioned this issue Jan 21, 2019
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@bradzacher bradzacher added the scope analyser Issues that are caused by bugs/incomplete cases in the scope analyser label Apr 15, 2019
@nmain nmain mentioned this issue May 13, 2019
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@bradzacher bradzacher mentioned this issue Jul 10, 2019
Merged
@bradzacher bradzacher added the has pr there is a PR raised to close this label Jul 16, 2019
@typescript-eslint typescript-eslint locked as resolved and limited conversation to collaborators Feb 21, 2020
@bradzacher bradzacher added this to the scope analysis rewrite milestone Apr 6, 2020
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bug Something isn't working has pr there is a PR raised to close this package: parser Issues related to @typescript-eslint/parser scope analyser Issues that are caused by bugs/incomplete cases in the scope analyser
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scope analysis rewrite
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feat(eslint-plugin): add no-unused-vars-experimental typescript-eslint/typescript-eslint
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@armano2 @bradzacher