In Rust, a library can define "features" that can be conditionally enabled or disabled when depending on it, which give a a built-in way to customize how much o

In Rust, a library can define "features" that can be conditionally enabled or disabled when depending on it, which give a a built-in way to customize how much of the library is actually included. Tokio is a great example of this; people might be surprised to learn that the total number of direct dependencies that are required by tokio is only two[1]; everything else is optional! Unfortunately, it doesn't seem like people are super diligent about looking into the default feature set that's used by their dependencies and proactively trimming that down. It doesn't help that the syntax for pulling in extra features is less verbose than removing optional but default ones (which requires both specifying "no-default-features" and then manually adding every one of the default features that you do still want back to the list of ones you pull in), and it _really_ doesn't help that the only way for libraries to expose the ability to prune unneeded features from their own dependencies to the users who inherit them is by manually making their own feature that maps to the features of every single one of their own dependencies. For example, if you're writing a library with five dependencies, and every one of them has one required dependency and four optional ones, giving the users of your library full control over what transitive features they pull in would mean making 20 features in your own library mapping to each of those transitive features, and that's not even counting the ones that you'd want to make for your own code in order to be a good citizen and not force downstream users to include all of your own code. More and more I'm coming to the opinion that the ergonomics around features being so much worse for trying to cut down on the bloat is actually the catalyst for a lot of the issues around compile times in Rust. It doesn't seem to be super widely discussed when things like this come up though, so maybe it's time that I try to write a blog post or something with my strong feelings on this so at least I'll have something to point to assuming the status quo continues indefinitely. [1]: https://github.com/tokio-rs/tokio/blob/ee19b0ed7371b069112b9c9ef9280b81f3438d26/tokio/Cargo.toml#L93 https://github.com/tokio-rs/tokio/blob/ee19b0ed7371b069112b9...