noUnusedLocals and noUnusedParameters should flag write-only variables

TypeScript Version: nightly (2.1.0-dev.20161010)

Code

(compile with --noUnusedParameters)

function f(a, b) {
    console.log(arguments)
}

Expected behavior:

No error

Actual behavior:

a.ts(1,12): error TS6133: 'a' is declared but never used.
a.ts(1,15): error TS6133: 'b' is declared but never used.

[RyanCavanaugh]

You can prefix the names with _ if you intend to not use them, or create a public signature

function f(_a, _b) {
    console.log(arguments)
}

function f(a, b);
function f() {
    console.log(arguments)
}

While I'm here, should --noUnusedLocals flag this?

function f() {
    let x;
    x = 1;
    return 0;
}

[mhegazy]

Not per the original design.

Should --noUnusedParameters flag this?

function f(x: number, y: number): void {
    console.log(x)
    if (x > 0)
        f(x - 1, y)
}

[mhegazy]

no, why? both x and y are "used".

These are just patterns I've noticed while looking through the code. I think write-only locals occur often enough to justify detecting, especially for people who prefer imperative-style let x; if (...) { x = ... } else { x = ... } to conditional expressions. Presumably we would only have to stop counting writes as uses, just like we don't count initialization as a use.

[mhegazy]

Presumably we would only have to stop counting writes as uses, just like we don't count initialization as a use.

this sounds reasonable.