Patch rust dependency

11/19/22

25/4/1444

---

Say we want to debug a dependency of a project, lets make a quick fixture.

cargo new patchit

cargo add regex

We can see our dependencies with:

cargo tree

patchit v0.1.0
└── regex v1.7.0
    ├── aho-corasick v0.7.19
    │   └── memchr v2.5.0 // lets patch this one
    ├── memchr v2.5.0 // which means also this one
    └── regex-syntax v0.6.28

Ok say we want to debug memchr:

First we need to get its source, either download it from github or more easily run:

cargo vendor

This will download all dependencies under vendor folder, and it will recommend to replace crates-io sources under config.toml but we're only interested in the downloading part.

And we're only interested in debugging one dependency, we can simply do this by adding this to cargo.toml:

[patch.crates-io]
memchr = { path = "vendor/memchr" }

That's it! Now you can modify vendor/memchr sources and it will be automatically picked up.