Infer tighter return types for math.max() and math.min()

[munificent]

Right now, this code:

void expectInt(int i) {}

main() {
  expectInt(math.min(1, 2));
}

generates a warning:

[warning] math.min(1, 2) (num) will need runtime check to cast to type int

It would be really nice if DDC could infer the tighter int return type if it knows the arguments are both ints. A "real" solution likely involves either generic methods:

T min<T extends num>(T a, T b) { ... }

or maybe some kind of TypeScript-style overloading. In the absence of either of those, it could be worth special-casing min and max in the same way that the spec does for the arithmetic operators.

[jmesserly]

Maybe I tend to approach these too much from the JS perspective, but ... we could just treat int and double the same. It doesn't make any difference to the generated code. I'm not even sure we'll actually emit the cast if you wrote it (maybe just as a null check)

[jmesserly]

FWIW, looks like generic methods DEP would fix this: https://github.com/leafpetersen/dep-generic-methods/blob/master/proposal.md#functions

we'll need to implement it soon, at least for the SDK. We're currently ignoring a bunch of unsound casts for a hard coded list of types: https://github.com/dart-lang/dev_compiler/blob/5e0e7d27c36a8d7d6858ddf3b7a66892de6539ae/lib/runtime/_operations.js#L180

see also #28

[vsmenon]

We're hitting this several times in Angular too - see:
https://travis-ci.org/angular/angular/jobs/74151416

This should be captured by @leafpetersen 's inference-based generic method work.

[jmesserly]

yeah. I have a quick fix about to send out, but Leaf can definite feel free to delete it after :)

[jmesserly]

https://codereview.chromium.org/1253903004/

[jmesserly]

@munificent this is now fixed! I used your suggestion: special case min/max, until we get generic methods.

I take it you were trying out --strong mode? if you're willing to give it another go, I can kick out a dev compiler release and roll it into SDK, would show up in next SDK dev build. Or you could try pub global activate dev_compiler; dartdevc filename.dart ... should give more or less the same results as analyzer_cli.

[munificent]

Awesome, thank you for the quick fix! ❤️