Add new feature use_sha for opt-in sha2 dependency

[jaewan-github]

Introduce a new opt-in feature 'use_sha' to enable the 'sha2' dependency and use Sha256 for keymap hashing.

When 'use_sha' is disabled (default), a custom hash function using built-in DefaultHasher is used instead, without 'sha2' dependency.

BREAKING CHANGE: If you want to keep the old behavior (using Sha256), you must explicitly enable the 'use_sha' feature. This breaking change is necessary because Cargo does not support excluding dependencies when a feature is enabled (features are strictly additive), so the dependency must be opt-in.

Tested:

• cargo test --lib --no-default-features --features wayland_frontend (default, using builtin hash)
• cargo test --lib --no-default-features --features wayland_frontend,use_sha (using Sha256)
• Added 'test_keymap_file_creation' test to verify KeymapFile works.

Description

This adds a new use_sha feature and change default keymap id generation with chaining DefaultHasher.
To keep the old behavior explicit feature use_sha is required.

Note

This introduces breaking change. Tell me if you prefer not doing this, or completely remove the sha2 dependency

Motivation

sha2 crates brings huge dependency while smithay only uses it for generating good hash value.

It would be helpful to provide an option to opt-in the sha2 crate usage.

Existing Issue

#2110

I created the issue with bit more details.

Disclaimer about the AI uses

I haven't used AI for writing CL, but only used to proofread my commit message.

Checklist

• I agree to smithay's Developer Certificate of Origin.

[kelnos]

Not sure what you mean about the feature situation. use_sha could be in default features, and then if you don't want it, pass --no-default-features (and then explicitly pass the features you do want). Or are you saying that even that won't remove the dependency? If so, that feels like a cargo bug...

[jaewan-github]

Not sure what you mean about the feature situation. use_sha could be in default features, and then if you don't want it, pass --no-default-features (and then explicitly pass the features you do want). Or are you saying that even that won't remove the dependency? If so, that feels like a cargo bug...

Your understanding is correct. I'll follow your suggest to make use_sha as default.

[jaewan-github]

Done as you suggested. It would be a great help if you take another look on this.

[ids1024]

We might not need a use_sha2 feature here, if this method of hashing is effective for preventing unintentional collisions. I used sha2 since SipHash technically shouldn't be sufficient for that, and sha2 just seemed to be the most common hash crate (and was already in cosmic-comp's dependency tree).

Technically maybe a maliciously constructed keymap could be sent with virtual-keyboard-unstable-v1, but I'm not sure what that would achieve, and a client using that is already privileged.