noUnusedLocals should be reported as a warning, not an error

[octogonz]

Search Terms

TS6133 6133 noUnusedLocals

This is related but more general: #13408

Suggestion

This ts.Diagnostic message is classified as an Error not a warning:

    "'{0}' is declared but its value is never read.": {
        "category": "Error",
        "code": 6133,
        "reportsUnnecessary": true
    },

Examples

Suppose someone is writing new code and not quite finished yet.

const x: number = 123;
const y: number = 321;
const product: number = x*y;

// TODO: Do something with "product"

They have not used x yet, but they certainly plan to use it when they are done writing their code. When you run tsc the output looks like this:

src/index.ts:9:5 - error TS6133: 'x' is declared but its value is never read.

With a professional build orchestrator, this "compiler error" will:

• be printed in bright red, distracting attention from legitimate errors (e.g. calling a function that is not defined)
• prevent downstream dependency projects from building
• possibly also prevent other tasks (e.g. Jest) from running for the current project (we don't run tests if the code doesn't compile)

Proposal: Make it a warning instead:

    "'{0}' is declared but its value is never read.": {
        "category": "Warning",
        "code": 6133,
        "reportsUnnecessary": true
    },

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[RyanCavanaugh]

This is entirely predicated on #13408, so should just be tracked there.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.