Running mix format from an umbrella project root crashes with:

** (MatchError) no match of right hand side value: {[%{name: MyUmbrella.MixProject, ...}], []}
    (mix) lib/mix/project_stack.ex:68: Mix.ProjectStack.on_recursing_root/1

Reproduction

1. Create umbrella with mix new my_umbrella --umbrella
2. Add Ash/Spark to a sub-app
3. Configure Spark.Formatter plugin in sub-app's .formatter.exs
4. Run mix format from umbrella root

Root Cause

Regression from #228 fix. The Mix.Task.run("compile") call added in 9eddbeb
causes recursive compilation during formatting, which Mix.ProjectStack doesn't support.

Workaround

Run format from within sub-apps instead of umbrella root.

Fix submitted in #230