Implement function scoped Warning

[Uzlopak]

Just for demonstration purposes

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Uzlopak]

this one slows it down, because it has to lookup the name

[mcollina]

why is this needed?

[Uzlopak]

Because a function has a non writable name.

[mcollina]

Why do you need to change it

[Eomm]

Because we accept a name parameter as input, that can be read by the user.

@Uzlopak What if we rename it to group instead?

[Uzlopak]

I think name is important to detect DeprecationWarnings so that node would ignore them.

The function name is usually set by doing function NAME () {} or const NAME = () => {}, where NAME is the desired Function Name. But I dont know how I could do it at runtime. Maybe by doing abusing new Function, which is basically a eval call. Also some runtimes disable, i think cloudflare, disallow new Function because it is under the hood an eval.

It could be also done by doing:

const NAME = 'DeprecationWarning'
const container = {
  [NAME]: () => {}
}

console.log(container[NAME].name) // 'DeprecationWarning'

But something like

function createNamedFunction (name, fn = () => {}) {
  const container = {
    [name]: fn
  }
    return container[name]
}

const bla = createNamedFunction('DeprecationWarning', () => {})
console.log(bla.name) //  '' <-- empty

[Uzlopak]

Removed the bottleneck

[jsumners]

For what it's worth, especially considering the large object literal definitions (multiple lines), I would do:

let warningContainer = { [name]: function () {} }
if (unlimited === true) {
  warningContainer[name] = /* stuff */
} else {
  /* other stuff */
}

Ternaries are difficult to read and should be reserved for much simpler cases, in my opinion.

[Uzlopak]

It would be

  let warningContainer = {
    [name]: function (a, b, c) {
      if (warning.emitted === true && warning.unlimited !== true) {
        return
      }
      warning.emitted = true

      process.emitWarning(warning.format(a, b, c), warning.name, warning.code)
    }
  }
  if (unlimited) {
    warningContainer = {
      [name]: function (a, b, c) {
        warning.emitted = true

        process.emitWarning(warning.format(a, b, c), warning.name, warning.code)
      }
    }
  }

Do you want it this way?

[jsumners]

I think it is easier to read, yes. And with your suggestion, you don't have to redefine the whole object, just replace the method.

[mcollina]

Can you update the docs? Code looks good.

[Uzlopak]

@mcollina
Fixed docs

[mcollina]

I really like this

[mcollina]

Can you update the PR title and description?

[Eomm]

warn x 156,722,644 ops/sec ±0.16% (102 runs sampled)
(node:38030) [FST_ERROR_CODE_1] FastifyWarning: message
(Use `node --trace-warnings ...` to show where the warning was created)
(node:38030) [FST_ERROR_CODE_2] FastifyWarning: message