Sym·poly·mathesy

by Chris Krycho

Using cargo tree to Explain Dependencies

Or, the equivalent of npm why, yarn why, pnpm why, etc. that you might be looking for.

To figure out why a Rust package is in your dependencies list:

$ cargo tree --invert <package name>

We use --invert here because you want to see everything which leads to the named package, rather than see the whole tree of dependencies from the root, which might include that package multiple times via different paths.

If you need to see what set of Cargo features cause the package to be pulled in, you can combine this with the --edges flag to specify the relevant dependency kind:

$ cargo tree --invert <package name> --edges features

Putting those together, if you want to answer what dependency’s features are resuling in your having the notify crate in your dependencies, you would do:

$ cargo tree --invert notify --edges features

Or, for short:

$ cargo tree -i notify -e features

A tiny bit of background (which will hopefully help others find their way here via the magic of SEO): In the Node ecosystem, I am used to doing this with pnpm why, yarn why, or npm why. Today I was [resolving an issue][pr] for integrating some improvements I made to the way we publish The Rust Programming Language today, and needed to figure out why exactly notify kept ending up in my dependency chain. This was what got me over the last hurdle when it was coming in via a dependency I thought I had fixed, but had missed.