bootspec(generation): offer TryInto conversion from Generation to any…

[RaitoBezarius]

Description

… schema version

Enables replacing:

        // TODO: replace me when https://github.com/DeterminateSystems/bootspec/pull/109 lands.
        let bootspec: BootSpec = match boot_json.generation {
            BootspecGeneration::V1(bootspec) => bootspec,
            _ => return Err(anyhow!("Unsupported bootspec schema"))
        };

by

        let bootspec: BootSpec = boot_json.generation.try_into().map_err(|err| ...);

Checklist

• Built with cargo build
• Formatted with cargo fmt
• Linted with cargo clippy
• Ran tests with cargo test
• Added or updated relevant tests (leave unchecked if not applicable)
• Added or updated relevant documentation (leave unchecked if not applicable)

[lheckemann]

Looks good (just needs a cargo fmt), any other reason it's still a draft?

[RaitoBezarius]

Looks good (just needs a cargo fmt), any other reason it's still a draft?

It was more like a discussion on whether this PR is a good idea and I made it in 2 minutes so I was not sure of the quality :-)

[cole-h]

I'm generally in favor of making this library easier to use for consumers :)

[cole-h]

We shouldn't manually implement {Try,}Into ourselves since we get that for free from {Try,}From: https://doc.rust-lang.org/std/convert/trait.TryInto.html

Library authors should usually not directly implement this trait, but should prefer implementing the TryFrom trait, which offers greater flexibility and provides an equivalent TryInto implementation for free, thanks to a blanket implementation in the standard library. For more information on this, see the documentation for Into.

[cole-h]

I like the idea, but I don't like the fact we'd need a separate impl block for each generation. I think switching to TryFrom will make this point moot, though.

[cole-h]

I was wrong about TryFrom making us able to get rid of the "manually add a new impl block for each variant", but there is a derive_more crate that can help with this. I've opened #120 which should do what you want.