Allow owned values and fat pointers in Span::record

[jyn514]

Motivation

Previously, using record("x", "y") would give an error:

error[E0277]: the size for values of type `str` cannot be known at compilation time
    --> src/main.rs:3:22
     |
243  |                 span.record("x", "y");
     |                      ^^^^^^ doesn't have a size known at compile-time
     |
     = help: the trait `Sized` is not implemented for `str`
note: required by a bound in `Span::record`
    --> /home/jnelson/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/tracing-0.1.32/src/span.rs:1184:30
     |
1184 |     pub fn record<Q: ?Sized, V>(&self, field: &Q, value: &V) -> &Self
     |                              ^ required by this bound in `Span::record`

Solution

Take Q: Value directly instead of Q: &Value. This doesn't break any existing code, because there's a generic impl<T: Value> Value for &T: https://docs.rs/tracing/0.1.35/tracing/trait.Value.html#impl-Value-for-%26%27a%20T

There's a simpler change which is just to remove the implicit Sized restriction on Q, but that still wouldn't allow passing false instead of &false.

[hawkw]

thanks, this looks good to me!

[davidbarsky]

approved, but i'm unreasonably paranoid that the previous impls don't work. not blocking: can you maybe add a unit test for the previous, ref-based usage?

[jyn514]

Sure thing, done :)