Make sha1 optional in gix-hash

[Christoph Rüßler (cruessler)]

This PR makes the sha1 flag optional in gix-hash. It modifies justfile to run cargo check as well as cargo nextest with 3 configurations: with sha1 only, with sha256 only, with both sha1 and sha256.

It’s mostly done, but still opened as a draft, so I can wait for CI to be green before I’m going to mark it as ready.

I haven’t checked all of gix-hash’s comments yet, some might need minor changes in case they still reference a sha1-only world.

[Christoph Rüßler (cruessler)]

I just went through all instances of feature = "sha1" to check whether there was any context that we would need to update in comments or code, but I only found one TODO: that I was able to remove as the tests that it mentioned should be added were already there.

[Sebastian Thiel (Byron)]

This is awesome, and I say so after a full armchair review.
Ok, after writing this I had to check it out and compile the variations on gix-hash myself, but it turned out as good as CI implies :).

Actually, I tried this:

cargo test -p gix-hash --no-default-features

I thought this should trigger a compile error, but it doesn't because basically everything one depends on (like gix-testtools) will reference the gix-hash crate, which in turn enables the default hash sha1.

While I don't think this needs to be solved in this PR, I think now we'd have to push the hash selection all the way up to the gix crate 😅.

That would probably reveal a couple of (expected) issues with missing attributes in the gix-hash test suite, while actually fulfilling this PR's promise, which effectively is the ability to compile gix without sha1 support.

Does this follow-up sound interesting to you?

[Christoph Rüßler (cruessler)]

I’m not entirely sure I get what you mean. :-)

This is the error messages I get when trying to compile gix-hash:

branch-8 on  make-sha-1-optional is 📦 v0.49.0 via 🦀 v1.92.0
❯ cargo check --package gix-hash --no-default-features
    Checking gix-hash v0.21.1 (/home/christoph/worktrees/gitoxide/branch-8/gix-hash)
error: Please set either the `sha1` or the `sha256` feature flag
  --> gix-hash/src/lib.rs:13:1
   |
13 | compile_error!("Please set either the `sha1` or the `sha256` feature flag");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[…]

Some errors have detailed explanations: E0004, E0308, E0665.
For more information about an error, try `rustc --explain E0004`.
warning: `gix-hash` (lib) generated 39 warnings
error: could not compile `gix-hash` (lib) due to 15 previous errors; 39 warnings emitted

Is there something missing?

Apart from that, I’m very much interested in moving hash selection to gix (and possibly other crates that need to be involved). 😄

[Sebastian Thiel (Byron)]

I am talking about cargo test -p gix-hash --no-default-features, which doesn't fail.

And indeed, to fix it one would have to remove the default sha1 feature, and leave the selection to gix.
But… I realise this probably doesn't work as so many crates need access to a selected hash.
So gix-object for instance also needs to expose the hash selection, and those who need it, and… it's a nightmare.
Maybe one can let the tests for each consumer of gix-hash set its hash, which would make sense as eventually we have to add hash-specific tests and that needs a way to be controlled.

Then, one will probably get around exposing the hash toggle in every consumer of gix-hash.