I’ve been using alchemist and its built-in functions to work with mix tasks from Emacs: to execute a specific test, to execute tests in a file, to list all tasks etc. They work ok if you don’t work with umbrella apps. Umbrella project is an application split into multiple subprojects. alchemist uses custom Elixir app under the hood. This Elixir app is initialized only for a specific application. So it’s either initialized for a subproject or an umbrella project. Maybe there are customizable variables that allow you to work with umbrella projects and subprojects at the same time but I couldn’t find any.

I spend my days writing Elixir code and sometimes I want to execute a Mix task from the root directory for the whole project (for example, to run a credo check) and sometimes I want to execute a task from a subproject (for example, to fetch deps only for this subproject). mix.el allows you to do it. Also, it allows you to add additional parameters before executing a mix task.