refactor(identity): call Into::into instead of copying the slice

[drHuangMHT]

Description

Fixes:

rust-libp2p/identity/src/secp256k1.rs

Lines 136 to 138 in 02040ff

	// FIXME: Once `generic-array` hits 1.0, we should be able to just use `Into` here.
	let mut array = [0u8; 32];
	array.copy_from_slice(generic_array.as_slice());

Related: #3850

Notes & open questions

Internal change.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[dariusc93]

LGTM. Left a small minor comment.

Can you update the changelog, and, if applicable, Cargo.toml?

[dariusc93]

I wonder if we should have it in separate variables before passing it to Message::parse

eg

Suggested change

	let message = Message::parse(&Sha256::digest(msg).into());
	let digest = Sha256::digest(msg);
	let message = Message::parse(&digest.into());

Thoughts? Not that it should impact anything from a glance over, but just thinking about readability.

[drHuangMHT]

I believe the information is sufficient since the method is called digest. Calling into introduces some ambiguity but I don't think it matters.

[elenaf9]

I am not sure, but I think the FIXME note was added because we don't want to use Into until generic-array is at a stable version >= 1.0.0?

If so, then I think that reasoning still applies, because we still indirectly depend on generic-array v.0.14.0 and not on a stable version >= v1.0.0. Am I missing something?

[drHuangMHT]

I am not sure, but I think the FIXME note was added because we don't want to use Into until generic-array is at a stable version >= 1.0.0?

If so, then I think that reasoning still applies, because we still indirectly depend on generic-array v.0.14.0 and not on a stable version >= v1.0.0. Am I missing something?

Oops I forgot to check the actual dependency tree. But it compiles for some reason.

[elenaf9]

Oops I forgot to check the actual dependency tree. But it compiles for some reason.

I believe we were already able to use Into at the point where the above FIXME was added, but it was decided against it because of the mentioned stabilization. But not sure why that decision was made; as far as I can tell we're just converting between GenericArray and a slice?

[drHuangMHT]

I believe we were already able to use Into at the point where the above FIXME was added, but it was decided against it because of the mentioned stabilization.

as far as I can tell we're just converting between GenericArray and a slice?

I think so.

But not sure why that decision was made;

I have no idea because that's not even our direct dependency.

[jxs]

LGTM! Yeah I also wondered that @elenaf9, the FIXME was introduced with #3850
but no further explanation exists, I'd say we merge this, thoughts?