Does anyone use Mix xref?


Recently I found out aboubt mix xref, which according to my understanding analyses the code for unreachable paths and deprecated functions.


It looks really nice, but I have some questions:

  • Isn’t this already part of the mix compile task that runs automatically every time you execute a non-compiled project?
  • In which scenarios do I have to manually run this command?
  • Do you guys use it in your CIs ?

Please let me know your answers !

mix xref was useful not only for finding unreachable code, it also supported looking for all callers or generating dependency graph of the application. So none of these functionalities was available during compilation.


But do you use it on a daily basis?

Do you use mix test --stale? If yes, you are using mix xref more than you might know that you use it.

Similar if you use the ElixirLS. It builds upon xrefs result asas well.


Do you use dbg module on daily basis? Do you use mix profile.* on daily basis? No, these tools have specific use cases, and when you need them you praise all J’s that decided that it should be part of the default release instead of spending X hours on searching solutions that will work.


I was using mix xref within CI.

In detail:

  • mix xref unreachable --abort-if-any
  • mix xref deprecated --abort-if-any

But as with Elixir v1.10 these checks will move into the compiler.
I will use instead:

  • mix compile --warnings-as-errors

I’m currently using mix xref callers MyApp.Schema – a module namespace that contains all my DB (Ecto) code. I’m integrating it in a GIT pre-commit hook that checks which modules use that namespace because I only want certain modules to directly use DB code.

So that’s one valid usage: you can enforce some limitations on your project at GIT pre-commit or CI server level. You can call it homemade linting.

Another very good usage is refactoring. When you move functions around – or rename them, or delete them – you want to minimise compilation or runtime errors so you first search who calls them and rework those as well along the way.


Saw the command thanks to the coming changes and ended up needing mix xref callers MyModule.function/1 to refactor things in a client project.