pkcs8 & pkcs1 should not have duplicate implementations for Decodeable/Encodeable

[Scarjit]

This is related to #410.

The crate could use the Integer proc macro, if pkcs8's Version enum get's a repr attribute.

This would remove this duplicate code:

pkcs1

formats/pkcs1/src/version.rs

Lines 54 to 72 in 9ac5281

	impl Decodable<'_> for Version {
	fn decode(decoder: &mut Decoder<'_>) -> der::Result<Self> {
	Version::try_from(u8::decode(decoder)?).map_err(|_| Self::TAG.value_error())
	}
	}
	impl Encodable for Version {
	fn encoded_len(&self) -> der::Result<der::Length> {
	der::Length::ONE.for_tlv()
	}
	fn encode(&self, encoder: &mut Encoder<'_>) -> der::Result<()> {
	u8::from(*self).encode(encoder)
	}
	}
	impl FixedTag for Version {
	const TAG: Tag = Tag::Integer;
	}

pkcs8

formats/pkcs8/src/version.rs

Lines 28 to 42 in 9ac5281

	impl Decodable<'_> for Version {
	fn decode(decoder: &mut Decoder<'_>) -> der::Result<Self> {
	Version::try_from(u8::decode(decoder)?).map_err(|_| Self::TAG.value_error())
	}
	}
	impl Encodable for Version {
	fn encoded_len(&self) -> der::Result<der::Length> {
	der::Length::from(1u8).for_tlv()
	}
	fn encode(&self, encoder: &mut Encoder<'_>) -> der::Result<()> {
	u8::from(*self).encode(encoder)
	}
	}

formats/pkcs8/src/version.rs

Lines 61 to 63 in 9ac5281

	impl FixedTag for Version {
	const TAG: Tag = Tag::Integer;
	}

[tarcieri]

FWIW, there's already two open PRs about this: #410 #363

The reason these crates don't use custom derive for this is to avoid pulling in the der_derive, proc_macro2, proc-macro-error, proc-macro-error-attr, quote, and syn crates to eliminate a dozen lines of duplicated code.

pkcs1 and pkcs8 are hard dependencies of several crates which otherwise don't have a dependency on the Rust proc macro stack. syn in particular has not-insignificant compile times.

[tarcieri]

Going to go ahead and close this. If you still have concerns I suggest following this up on #410