Replace try! with ? in serde_derive

[dtolnay]

#2366

As of today, this regresses compile time of serde's generated code by 6.5–7.5% which is too bad. However try! has been disastrous for readability of the generated code coming out of cargo expand. I was expecting the performance problems in rustc to be fixed a long time ago but at this point it doesn't seem like that is going to happen.

[Mingun]

I see, that not all try! was replaced by ?. I would say, most of them. Is it so conceived?

[Baptistemontan]

So what about 91ec1c2 ? The crate itself should suffer from readability but it goes backward for generated code ?

[Mingun]

Yes, that is... very strange decision :)

[dtolnay]

It's specifically cargo expand readability that is the motivation.

People are not looking at cargo expand of the serde crate. They are looking at expanded derive macros.