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[prefer-readonly-parameter-types] extending ReadonlyArray gives false positive #1789

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ckknight opened this issue Mar 23, 2020 · 1 comment · Fixed by #1791
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[prefer-readonly-parameter-types] extending ReadonlyArray gives false positive #1789

ckknight opened this issue Mar 23, 2020 · 1 comment · Fixed by #1791
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documentation Documentation ("docs") that needs adding/updating package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin

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@ckknight
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Repro

{
  "rules": {
    "@typescript-eslint/prefer-readonly-parameter-types": "error"
  }
}
interface CustomArrayType extends ReadonlyArray<string> {
  readonly prop: string;
}
function custom1(arg: CustomArrayType) {}

Expected Result
No error

Actual Result
Parameter should be a read only type

Additional Info
This is the example within https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/prefer-readonly-parameter-types.md

Versions

package version
@typescript-eslint/eslint-plugin 2.25.0
@typescript-eslint/parser 2.25.0
TypeScript 3.8.3
ESLint 6.8.0
node 12.16.1
npm 6.13.4
@ckknight ckknight added package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Mar 23, 2020
@bradzacher
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sorry, the examples are incorrect, the tests are correct:

typescript-eslint/packages/eslint-plugin/tests/rules/prefer-readonly-parameter-types.test.ts

Lines 121 to 126 in 258fdd0

`
interface Test extends ReadonlyArray<string> {
readonly property: boolean
}
function foo(arg: Readonly<Test>) {}
`,

Because the type extends an array type, it is no longer classified as an array by TS.
Which means it's just treated as a plain old JS object.

@bradzacher bradzacher added documentation Documentation ("docs") that needs adding/updating and removed triage Waiting for team members to take a look labels Mar 23, 2020
@bradzacher bradzacher mentioned this issue Mar 23, 2020
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@ckknight @bradzacher