8000 [no-unused-vars] False positives with members of exported namespace in .d.ts file · Issue #2867 · typescript-eslint/typescript-eslint · GitHub
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[no-unused-vars] False positives with members of exported namespace in .d.ts file #2867

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andersk opened this issue Dec 11, 2020 · 20 comments · Fixed by #10714
Closed
3 tasks done

[no-unused-vars] False positives with members of exported namespace in .d.ts file #2867

andersk opened this issue Dec 11, 2020 · 20 comments · Fixed by #10714
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accepting prs Go ahead, send a pull request that resolves this issue bug Something isn't working locked due to age Please open a new issue if you'd like to say more. See https://typescript-eslint.io/contributing. package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin

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@andersk
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andersk commented Dec 11, 2020
  • I have tried restarting my IDE and the issue persists.
  • I have updated to the latest version of the packages.
  • I have read the FAQ and my problem is not listed.

Repro

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "rules": {
    "@typescript-eslint/no-unused-vars": "error"
  }
}
// foo.d.ts
export namespace Foo {
  const bar: string;
  namespace Baz {
    const quux: string;
  }
}

Expected Result

No error. In a .d.ts file, members of an exported namespace are implicitly exported, unless the namespace contains an explicit braced export {} declaration.

Actual Result

/tmp/test/foo.d.ts
  2:9   error  'bar' is defined but never used   @typescript-eslint/no-unused-vars
  3:13  error  'Baz' is defined but never used   @typescript-eslint/no-unused-vars
  4:11  error  'quux' is defined but never used  @typescript-eslint/no-unused-vars

✖ 3 problems (3 errors, 0 warnings)

Additional Info

Similar to #2456, which was about a different kind of implicit export in .d.ts files, namely interface declarations.

Versions

package version
@typescript-eslint/eslint-plugin 4.9.1
@typescript-eslint/parser 4.9.1
TypeScript 4.1.2
ESLint 7.15.0
node 14.15.1
@andersk andersk added package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Dec 11, 2020
@bradzacher
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Why are you exporting your namespace here?

Also in declaration files - you should be declareing your namespaces.

@bradzacher bradzacher added awaiting response Issues waiting for a reply from the OP or another party and removed triage Waiting for team members to take a look labels Dec 11, 2020
@andersk
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andersk commented Dec 11, 2020

@bradzacher In a .d.ts file, export declare is the same as just export. It declares a namespace that’s an exported member of the module, to be used like import {Foo} from "./foo"; Foo.Baz.quux.

Just declare namespace without export would be different; that would declare a namespace that’s a global variable, to be used like import "./foo"; Foo.Baz.quux

@bradzacher
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How are you creating your declaration files for your modules?

I thought the general pattern was

declare module './foo' {
  export namespace Foo {
    // ..
  }
}

and not just declaring your namespaces in the root.

@andersk
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andersk commented Dec 11, 2020

With a text editor?

A foo.d.ts file can either (a) declare types for third-party modules with declare module 'lodash', or (b) declare types for foo.js in the same directory at the root. For a module in the same directory, declare module './foo' is actually illegal (TS2436: Ambient module declaration cannot specify relative module name); you can only do (b).

8000
@bradzacher bradzacher added bug Something isn't working and removed awaiting response Issues waiting for a reply from the OP or another party labels Dec 11, 2020
@bradzacher
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The issue is that our selectors target Program > Namespace, so because your namespace is exported it doesn't match this.

typescript-eslint/packages/eslint-plugin/src/rules/no-unused-vars.ts

Line 259 in 84a77cc

[ambientDeclarationSelector(AST_NODE_TYPES.Program, true)](

Happy to accept a PR - simple fix.

@danielrsantana

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@dopecodez
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I'll take a look at this 👨🏽‍💻

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@dopecodez dopecodez mentioned this issue Dec 25, 2020
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@typescript-eslint typescript-eslint locked as off-topic and limited conversation to collaborators Jan 2, 2021
@bradzacher bradzacher added the has pr there is a PR raised to close this label Jan 2, 2021
@bradzacher
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To anyone seeing this issue.

This issue is ONLY about @typescript-eslint/no-unused-vars reporting false-positives for exported namespaces in .d.ts files.

ALL OTHER ISSUES ARE NOT RELATED TO THIS ISSUE.

We have an FAQ you should read before commenting

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@JoshuaKGoldberg JoshuaKGoldberg added the accepting prs Go ahead, send a pull request that resolves this issue label Oct 25, 2021
@JoshuaKGoldberg JoshuaKGoldberg removed the has pr there is a PR raised to close this label Aug 5, 2023
@jakebailey
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I was hoping to add this rule to DefinitelyTyped (microsoft/DefinitelyTyped-tools#968), but noticed this problem as well as most namespaces on DT have implicit export modifiers. I may look into this (though please don't take this as cookie licking and please still attempt it even if I forget or fail).

A gotcha is that this namespace does not have any unused vars:

export namespace Foo {
    const value: 1234;

    export import Something = something.Something;
}

Yay namespaces.

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@github-actions github-actions bot added the locked due to age Please open a new issue if you'd like to say more. See https://typescript-eslint.io/contributing. label Mar 11, 2025
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