Today I Learned

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Mix xref and Elixir compiler warnings

The release of Elixir v1.3 added a mix task called xref for performing cross reference checks of your code. mix xref gives us some handy tools!

Find unreachable code:

❯ mix xref unreachable
lib/exonk8s/foo.ex:16: SomeModule.non_existant/0

Find callers of modules and functions:

❯ mix xref callers SomeModule
lib/exonk8s/foo.ex:16: SomeModule.non_existant/0

Generate a dependency graph:

> mix xref graph
lib/exonk8s.ex
├── lib/exonk8s/repo.ex
└── lib/router.ex
    └── lib/exonk8s/musician_controller.ex (compile)
        ├── lib/exonk8s/foo.ex
        ├── lib/exonk8s/musician.ex
        └── lib/exonk8s/repo.ex
...snipped for brevity

The release of Elixir v1.6 added the module attribute @deprecated to enable library authors to warn users of deprecated functions.

❯ mix xref deprecated
Compiling 2 files (.ex)
Foo Loaded
warning: ExOnK8s.Foo.lazy/0 is deprecated. You should be more eager.
  lib/exonk8s/musician_controller.ex:10

lib/exonk8s/musician_controller.ex:10: ExOnK8s.Foo.lazy/0

Lastly I should note that xref deprecated and xref unreachable are included in the compiler warnings, so you you’ve likely seen these at work even if you didn’t know they were there.

Learn more

Looking for help? At Hashrocket, we 💜 Elixir! From our many Elixir client projects, to sponsoring the Chicago Elixir Meetup, to the source code for this application, we are invested in this community. Contact us today to talk about your Elixir project.