sindresorhus/eslint-plugin-unicorn

[consistent-destructuring] incorrect fix for ts `in` type guard

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#1,112 opened on Feb 18, 2021

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bughelp wanted

Description

const { a }: { a: string } & ({ b: number } | { c: number } | {}) = params
const value = 'b' in params ? params.b : 'c' in params ? params.c : null

// incorrect fixed
const { a, b, c }: { a: string } & ({ b: number } | { c: number } | {}) = params
const value = 'b' in params ? b : 'c' in params ? c : null

Reference: https://www.typescriptlang.org/docs/handbook/advanced-types.html#type-guards-and-differentiating-types

The fixed codes is not runnable anymore. Playground

Contributor guide

Tech stack
javascripttypescriptnodejs
Domain
toolingdeveloper experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
ESLint rule developmentTypeScript type guardsAST
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Examine the consistent destructuring rule source in rules/consistent destructuring.js. The rule currently incorrectly destructures properties when using the 'in' type guard. The fix should detect when the right hand side of 'in' operator is a parameter of a destructuring pattern and avoid destructuring that property. The playground link provides a clear reproduction. Also check the rule's tests to ensure the fix covers edge cases.