Preserve '.0' when Displaying Number

[dtolnay]

Tiny followup to #918.

let number: serde_json::Number = serde_json::from_str("1.0").unwrap();
println!("{}", number);

Previously: 1
Now: 1.0

[dtolnay]

Actually we should just serialize using ryu and itoa, like the Serializer does, or maybe even go through the Serializer itself. std::fmt produces a worse representation for floats, like 120000000000000000000000000000000000000000 instead of 1.2e41.

[iitalics]

shouldn't this be a more significant version bump than patch? it has broken a unit test of mine. nothing extreme but was not expecting to see this behavior change

[Directory]

rustaceans are afraid of MAJOR semvar version changes. it's like kryptonite to them.

[alteous]

Could this be configurable? I have a slightly unusual use case where I need to represent ones' complement integer, i.e., signed integers with a negative zero. I'm using f64::serialize but that means integers are displayed as 1.0 instead of 1 which looks weird in this context.

[iitalics]

@alteous it looks like you could configure some things through the Formatter trait

[alteous]

@iitalics that looks promising, thanks! I'll give it a try.