Use well known TryFrom instead of custom FromObject / ToObjet tratis

[cafce25]

Maybe it's just me overlooking something but both traits in nvim_types::conversion are just a specialized version of TryFrom/TryInto.
Is there a technical reason?
Else I suggest to rewrite conversion.rs to use TryFrom instead or delete it all together.

I'm currently exploring nvim-oxi and while toying around with it I wrote a bunch of TryFrom<Object> implementations before I realized FromObject is a thing, if it's down to development time needed I could do the conversion and create a PR.

[noib3]

It's mostly a matter of ergonomics. If we were to use TryFrom most functions in the nvim_oxi::api module would go from

use nvim_oxi::api;

pub fn get_option<Opt>(name: &str) -> Result<Opt, api::Error>
where
    Opt: FromObject, 
{
    ..
}

to

use nvim_oxi::api;

pub fn get_option<Err, Opt>(name: &str) -> Result<Opt, api::Error>
where
    Opt: TryFrom<Object, Error = Err>,
    Err: std::error::Error + Into<api::Error>,
{
    ..
}

and we'd also need to add a way to turn any std::error::Error into a generic variant of api::Error.

It also becomes more verbose when you're calling the function because you have an extra generic:

api::get_option::<bool>("modified") ->  api::get_option::<MyError, bool>("modified")

Tbh I don't think it's worth it.

[cafce25]

I don't think adding a new generic is necessary a quick test shows

pub fn get_option<Opt>(name: &str) -> Result<Opt>
where
    Opt: TryFrom<Object>,
    Error: From<Opt::Error>,
{
    …
}

should work (it checks, i haven't tested it extensively)

Also I think the ergonomics improve quite a bit for users of the library.

But ultimately it's up to you. I'd be happy to implement it if you consider merging it.

[noib3]

I've been experimenting with this on a new branch and I believe both of my concerns can be resolved.

Like you pointed out we don't actually need to spell out the error type associated w/ the TryFrom implementation, and we can introduce a new ToApiError trait together with a blanket impl to automatically convert any StdError into a nvim_oxi::api::Error.

This is a first rough sketch of this. If you want to work on the rest I'd consider merging a PR.

[cafce25]

I've hit a bit of a showstopper for this I think, my attempt at converting this over either has a conflicting

impl<T> TryFrom<Object> for Option<T>

because of the

impl<T, U> TryFrom<U> for T where U: Into<T>;

in core or does not properly convert values which might be null in neovim to an Option<T>.