Crate Features
Following advice from Crate Features, you have
added optional features into your crate to reduce compilation times for when
they are not required by downstream users. This has been working well, however
in a recent release you have received a bug report what a specific combination
of enabled features triggers a compilation error. You have fixed the error,
which was introduced by some refactoring that moved a #[cfg] block. However,
you are wondering whether it is possible to catch these kinds of issues
automatically by CI rather than by downstream users.
Similar to using #ifdef statements in C and C++, using #[use] blocks is
inherently brittle. Using a crate such as cfg_if instead can help
make it more manageable, but it does not address the root issue: you really
need to test the code you write for all features.
Fortunately, the cargo-hack tool allows you to do just that.
cargo-hack
What cargo-hack lets you do is run some check (for example
cargo check to see if it will compile, or cargo test to run unit tests) for
every possible feature or even for every possible set of features.
To use cargo-hack, you need to give it two pieces of information: which
sets of features to test for and which command to run.
Feature Sets
For the set of features,
the two popular options are --each-feature and --feature-powerset. To illustrate
the different, consider if you have a crate with the features a, b, c and d.
| Flag | Feature Sets |
|---|---|
--each-feature | a; b; c |
--feature-powerset | a; b; c; a,b; a,c; b,c; a,b,c |
Commands
You also need to tell cargo-hack what command to run.
| Name | Description |
|---|---|
check | Runs cargo check for each of the selected feature sets |
test | Runs cargo test for each of the selected feature sets |
Examples
cargo-features-manager
https://github.com/ToBinio/cargo-features-manager https://corrode.dev/blog/tips-for-faster-rust-compile-times/#disable-unused-features-of-crate-dependencies