Mix: warn when project app name matches a dependency

lib/mix/lib/mix/dep/loader.ex

@@ -19,7 +19,23 @@ defmodule Mix.Dep.Loader do
   current environment, behavior can be overridden via options.
   """
   def children(locked?) do
-    mix_children(Mix.Project.config(), locked?, []) ++ Mix.Dep.Umbrella.unloaded()
+    deps = mix_children(Mix.Project.config(), locked?, []) ++ Mix.Dep.Umbrella.unloaded()
+    # warn if project app matches a dep
+    warn_on_duplicate_app_name(Mix.Project.config()[:app], deps)
+
+    deps
+  end
+
+  def warn_on_duplicate_app_name(nil, _deps), do: :ok
+
+  def warn_on_duplicate_app_name(app, deps) do
+    dep_apps = Enum.map(deps, & &1.app)
+
+    if app in dep_apps do
+      Mix.shell().error(
+        "warning: the application name #{inspect(app)} is the same as one of its dependencies"
+      )
+    end
   end
 
   @doc """

lib/mix/test/mix/project_test.exs

@@ -160,6 +160,24 @@ defmodule Mix.ProjectTest do
     end)
   end
 
+  test "warns when project app name matches a dependency" do
+    Mix.shell(Mix.Shell.Process)
+
+    app = :clash_app
+
+    deps = [
+      %Mix.Dep{app: :clash_app},
+      %Mix.Dep{app: :other_dep}
+    ]
+
+    Mix.Dep.Loader.warn_on_duplicate_app_name(app, deps)
+
+    assert_received {:mix_shell, :error,
+                     [
+                       "warning: the application name :clash_app is the same as one of its dependencies"
+                     ]}
+  end
+
   test "in_project prints nice error message if fails to load file", context do
     in_tmp(context.test, fn ->
       File.write("mix.exs", """