allocator-api2 default-feature?

Hi,

I'm updating some codebase and noticed the changes wrt allocator-api2.

https://github.com/rust-lang/hashbrown/pull/417

I want to lead with the fact that I am not an advanced Rust developer, so my question may be (probably is) stupid.

From my (limited) experience, I'm not sure I understand why this feature is on by default.

I would expect a custom allocator to be opt-in, specially since it forms the foundation of all the types. It feels weird hashbrown by default uses a different allocator (albeit a c/p of the official one) than the other pieces of code that I have.

I am concerned about minor updates that could change how the allocators work as they might go out of sync.

So to alleviate that, I turned off all default features and only enabled ahash.

Next to the question above, as to why it is default, I am wondering if the turning off default features and just adding ahash is the right way to address the concern?

Thanks.

Start by reading the referenced hashbrown pull request #417 and the crate's default-feature configuration for allocator-api2 and ahash. Determine whether allocator-api2 should remain enabled by default and whether disabling default features while enabling ahash is the supported configuration; done means the project has a clear decision and documented feature guidance.