discussion: eslint rule for /test/ - no-unused-vars: [error, {args: after-used, caughtErrors: all}]

[refack]

• Version: *
• Platform: *
• Subsystem: test

There still seems to be a small performance advantage to using functors that match the signature of the invocation:

> var o = 0;
> function trig(a, b, f) { const x = f(a,b); o = x; };
> function trig2(b, a, f) { const x = f(a,b); o = x; };
> console.time('0'); for (let i = 0; i < 1e8; ++i) (i%2 ? trig : trig2)(i+1, i+2, () => i);console.timeEnd('0')
0: 7371.239ms
> console.time('a,b'); for (let i = 0; i < 1e8; ++i) (i%2 ? trig : trig2)(i+1, i+2, (a,b) => i);console.timeEnd('a,b')
a,b: 7066.650ms

For for explicitness sake, would we consider requiring no unused arguments (or exception) in /test/?
i.e.:

/* eslint no-unused-vars: [error, {args: after-used, caughtErrors: all }] */

// "baz" is defined but never used
(function(foo, bar, baz) {
    return bar;
})();

try {
  foo();
} catch (e) {
  // "e" is defined but never used
}

Current impact on /test/: 297 error in 195 files

/cc @nodejs/testing @nodejs/performance

[Trott]

Ref: #10129

[refack]

Enough talk, time for action

[refack]

Update for TF&I, performance penalty is < 1%

> var o = 0;
> function trig(a, b, f) { const x = f(a,b); o = x; };
> function trig2(b, a, f) { const x = f(a,b); o = x; };
> console.time('0'); for (let i = 0; i < 1e8; ++i) (i%2 ? trig : trig2)(i+1, i+2, () => i);console.timeEnd('0')
0: 2449.016ms
> console.time('a,b'); for (let i = 0; i < 1e8; ++i) (i%2 ? trig : trig2)(i+1, i+2, (a,b) => i);console.timeEnd('a,b')
a,b: 2421.129ms
> console.time('0'); for (let i = 0; i < 1e9; ++i) (i%2 ? trig : trig2)(i+1, i+2, () => i);console.timeEnd('0')
0: 24336.730ms
> console.time('a,b'); for (let i = 0; i < 1e9; ++i) (i%2 ? trig : trig2)(i+1, i+2, (a,b) => i);console.timeEnd('a,b')
a,b: 24299.949ms
> process.version
'v8.4.0'