How to mark an API as volatile

Certain parts of my public API are subject to changes.

I don't want to hide them, but I do want to warn people that using them may break code later on with newer versions.

Is there an attribute I can set on the volatile functions?

Usually such interfaces are hidden behind a feature flag with a name like "unstable".

#[cfg(feature = "unstable")]

You can enable feature flags for, so that it's still visible there even if it's off by default.

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OK, that's what I'm doing right now, but I was hoping for a way to give some warnings like the standard Rust API's.

What do you mean by "standard Rust APIs"? If that's about nightly features, then they are using the same idea, only on the compiler level, not managed by Cargo.

I don't think there's any option to make them warn on every use, except the deprecated attribute.

You can pass a note to the deprecated attribute to make it a bit clearer what's going on.

If you used this method:

#[deprecated(note = "this method is in active development and may change")]
fn test() {

It would show this in the console:

warning: use of deprecated item 'test': this method is in active development and may change
 --> src/
8 |     test();
  |     ^^^^
  = note: `#[warn(deprecated)]` on by default

The deprecated attribute looks like something I can use.

Is there any other similar attributes that I can consider?

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