no-unused-variable error with object destructuring

[cartant]

Bug Report

• TSLint version: 5.4.2
• TypeScript version: 2.3.4
• Running TSLint via: CLI

TypeScript code being linted

To reproduce the problem, two files are required:

// main.ts
import { SomeClass } from "./some";
const person = { name: "alice" };
const { name } = person;

// some.ts
export class SomeClass {};

with tslint.json configuration:

{
    "defaultSeverity": "error",
    "rules": { "no-unused-variable": { "severity": "error" } }
}

Actual behavior

An internal error within the rule occurs:

Warning: Cannot read property 'flags' of undefined

Expected behavior

TSLint should execute without internal errors and should report that SomeClass and name are both unused.

Additional information

The import is required to effect the internal error. If the import is omitted, no internal error occurs.

With the import, the rule follows a code path into the getImplicitType function and the implementations of utils.isPropertyDeclaration and utils.isVariableDeclaration allow for the { name } = person node to be passed to checker.getTypeAtLocation - from within which the error is thrown.

[victornoel]

@cartant do you think this is the same as #3001?

[cartant]

@victornoel Maybe. That issue doesn't seem to include enough information for the reported problem to be reproduced, so who knows?

[victornoel]

@adidahiya any plan to fix this issue? it is really problematic…

[adidahiya]

Is this still an issue with TSLint 5.5.0?

[cartant]

@adidahiya I've revisted the harness I created and the error is still effected with:

• TSLint version: 5.5.0
• TypeScript version: 2.4.1
• Running TSLint via: CLI

---

TypeError: Cannot read property 'flags' of undefined
    at Object.getCheckFlags (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:10137:22)
    at getTypeOfSymbol (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:30957:20)
    at getTypeOfNode (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:47329:24)
    at Object.getTypeAtLocation (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:26823:31)
    at getImplicitType (...\tslint-no-unused-variable\node_modules\tslint\lib\rules\noUnusedVariableRule.js:269:24)
    at cb (...\tslint-no-unused-variable\node_modules\tslint\lib\rules\noUnusedVariableRule.js:259:20)
    at visitEachNode (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:15956:30)
    at Object.forEachChild (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:16143:24)
    at cb (...\tslint-no-unused-variable\node_modules\tslint\lib\rules\noUnusedVariableRule.js:264:19)
    at visitNode (...\tslint-no-unused-variable\node_modules\typescript\lib\typescript.js:15944:20)

[victornoel]

I concur :)

[SteveALee]

For information I had same hard to locate warning with "no-use-before-declare": true, in TSL 4.5.1

It would really help if all TSL errors were prefixed with [TSLint] or similar.

[victornoel]

@SteveALee open another issue for this please…

[SteveALee]

@victornoel your mean for the prefix?

[victornoel]

@SteveALee yes, I meant that if you have a need for prefixing tslint messages, open another issue for that

[SteveALee]

@victornoel please see #3060 :)