I have a written a bit of rust by now, but one problem I always seem to encounter it that the features a create supports never seem to be documented. Neither what features are available, what they each do or which are default. Is that really the case, or am I missing something?

I constantly seem to include something from the docs, only to be told by the compiler that it does not exist, and then I have to open the source for the create to figure out if it's hidden behind a feature flag.

Also, is it really true that I can't disable a single feature from the default set, without having to copy the default list and manually removing it?

top 10 comments

sorted by: hot top controversial new old

[–] hunger 13 points 1 year ago

https://docs.rs/document-features/latest/document_features/ helps to document features.

But yes, features are under-documented.

[–] Vorpal 12 points 1 year ago

A few crates do document this, but it is often missing indeed.

Sometimes I have seen it documented as comments in Cargo.toml as well.

[–] [email protected] 6 points 1 year ago (1 children)

I constantly seem to include something from the docs, only to be told by the compiler that it does not exist, and then I have to open the source for the create to figure out if it’s hidden behind a feature flag.

As others mentioned, the situation is not perfect. And you may need to check Cargo.toml. Maybe even the source.

But as for the quoted part above, the docs should definitely indicate if a part of the API is behind a feature. Let's take rustix as an example.

Here is the module list:

Here is the view from inside a module:

Here is the view from a function page:

This is also true for platform support. Take this extension trait from std:

Now, it's true that one could be navigating to method docs in the middle of a long doc page, where those indicators at the top may be missed. But that's a UI issue. And it could be argued that repeating those indicators over and over would introduce too much clutter.

[–] pileghoff 4 points 1 year ago (1 children)

Is that always suppose to be shown? My counter example (the one that prompted this thread) is embassy_executor::Executor. When looking in the docs i dont see anywhere that its locked behind a feature flag, you have to look in the source

[–] [email protected] 5 points 1 year ago (2 children)

So, this is being worked on. But for now, that crate needs this line in lib.rs

#![cfg_attr(docsrs, feature(doc_auto_cfg))]

And this line in Cargo.toml's [package.metadata.docs.rs] section:

rustdoc-args = ["--cfg", "docsrs"]

With these changes, feature gating will be displayed in the docs.

To replicate this locally:

RUSTDOCFLAGS='--cfg docsrs' cargo doc --features=nightly,defmt,pender-callback,arch-cortex-m,executor-thread,executor-interrupt

[–] pileghoff 1 points 1 year ago (1 children)

Sadly, this does not seem to be the norm in my experience. I have not attemped to adding this myself, but I wanted to ask: are there any hurdles or other good reasons to not just adding this to every create? Why isn't it the default?

[–] [email protected] 2 points 1 year ago

are there any hurdles or other good reasons to not just adding this to every create?

I'm no expert. But my guess would be that many crate authors may simply not be aware of this feature. It wasn't always there, and it's still unstable. You would have to reach the "Unstable features" page of the rustdoc book to know about it.

Or maybe some know about it, but don't want to use an unstable feature, or are just waiting for it to possibly automatically work without any modifications.

Of course, I would assume none of this applies to the embassy devs. That Cargo.toml file has a flavors field, which is something I've never seen before 😉 So, I'm assuming they are way more knowledgable (and up-to-date) about the Rust ecosystem than me.

[–] snaggen 1 points 1 year ago (1 children)

Didn't know about this, looking forward for this to be stabilized. But a comment on your command, it is easier to use --all-features instead of listing them all.

[–] [email protected] 1 points 1 year ago* (last edited 1 year ago)

--all-features doesn't work with that particular crate because two of the features conflict with each other. The features list in my command is the one used for docs.rs from the crate's Cargo.toml.

[–] somegeek 2 points 1 year ago

Yep. I guess that's the case for now.