8000 Bug: [no-unnecessary-type-assertion] False positive for non-null assertion on `unknown` · Issue #10831 · typescript-eslint/typescript-eslint · GitHub
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Bug: [no-unnecessary-type-assertion] False positive for non-null assertion on unknown #10831

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matthewvalentine opened this issue Feb 13, 2025 · 0 comments · Fixed by #10875
Closed
4 tasks done

Bug: [no-unnecessary-type-assertion] False positive for non-null assertion on unknown #10831

matthewvalentine opened this issue Feb 13, 2025 · 0 comments · Fixed by #10875
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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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@matthewvalentine
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matthewvalentine commented Feb 13, 2025 •
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Before You File a Bug Report Please Confirm You Have Done The Following...

  • I have tried restarting my IDE and the issue persists.
  • I have updated to the latest version of the packages.
  • I have searched for related issues and found none that matched my issue.
  • I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.7.2&fileType=.ts&code=MYewdgzgLgBAZiEAuGBXMBrMIDuYYC8MYqANqQNwBQoksARgIYBOKI9AVgKbCxEIgAhNVrQYTAF4oA3gF9C8RMKA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Jge1tiacTJTIAhtEK0ipWkOTJE0fJQ5N0UOdA7RI4MAF8QOoA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

const foo: unknown = null;
const bar: object = foo!;
const baz: {} = foo!;

ESLint Config

module.exports = {
  "rules": {
    "@typescript-eslint/no-unnecessary-type-assertion": "error"
  }
}

tsconfig

{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

Expected Result

I expected no error, because the non-null assertion is actually necessary. Typescript will allow you to assign a non-null asserted unknown to object or {}, but won't if it isn't non-null asserted. Because an unknown value can be null | undefined, whereas object and {} disallow that.

Actual Result

There is an error on the non-null assertion. If autofixed, it turns into a Typescript error instead, because the assertion was not unnecessary.

Additional Info

No response
@matthewvalentine matthewvalentine added bug Something isn't working package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Feb 13, 2025
@kirkwaiblinger kirkwaiblinger changed the title Bug: [no-unnecessary-type-assertion] <short description of the issue> False positive for non-null assertion on unknown Bug: [no-unnecessary-type-assertion] False positive for non-null assertion on unknown Feb 13, 2025
@kirkwaiblinger kirkwaiblinger added accepting prs Go ahead, send a pull request that resolves this issue and removed triage Waiting for team members to take a look labels Feb 13, 2025
@yeonjuan yeonjuan mentioned this issue Feb 24, 2025
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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
@github-actions github-actions bot locked as resolved and limited conversation to collaborators Mar 11, 2025
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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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fix(eslint-plugin): [no-unnecessary-type-assertion] handle unknown yeonjuan/typescript-eslint
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