[Pitch] #warning

Evolution Pitches
41

I would prefer that warning/error/todo/fixme were provided as special functions that take StaticString, rather than #directives.

I find that TODOs are really often related to temporary values in cases when the data sources are not yet set up, something like:

// TODO: Hook up to weather data source
let outsideTemperature  = 123

So I wrote 2 really useful functions:

func TODO(_ message: StaticString? = nil) {
	if let s = message { print("TODO: \(s)") }
}

@discardableResult
func TODO<T>(_ message: StaticString? = nil, _ temporaryValue: T) -> T {
	if let s = message { print("TODO: \(s)") }
	return temporaryValue
}

They use print, but the compiler could implement to issue a warning at compile-time and to just forward the temporaryValue as the expression result, at runtime. So now when I write my temporary value, it's coupled to the fact that it's a TODO temporary, with an explanatory message.

 let outsideTemperature = TODO("Hook up to weather data source", 123)

and I can find all of my TODOs by pulling up the call hierarchy for these 2 functions.

I think this generic value pass-through would be really useful to have in warning, error, TODO and FIXME (the exact names could vary, i'm just following the comment convention).

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