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/lib/mix/project.ex

@@ -259,10 +259,7 @@ defmodule Mix.Project do
         true -> "nofile"
       end
 
-    config = push_config(module, app)
-    warn_on_duplicate_app_name(config)
-
-    case Mix.ProjectStack.push(module, config, file) do
+    case Mix.ProjectStack.push(module, push_config(module, app), file) do
       :ok ->
         :ok
 
@@ -1073,24 +1070,6 @@ defmodule Mix.Project do
     end
   end
 
-  defp warn_on_duplicate_app_name(config) do
-    app = config[:app]
-    deps = Keyword.get(config, :deps, [])
-
-    dep_apps =
-      Enum.map(deps, fn
-        {dep_app, _opts} -> dep_app
-        dep_app -> dep_app
-      end)
-
-    if app in dep_apps do
-      # Use Mix.shell().error to print to stderr
-      Mix.shell().error(
-        "warning: the application name #{inspect(app)} is the same as one of its dependencies"
-      )
-    end
-  end
-
   defp default_config do
     [
       aliases: [],

lib/mix/test/mix/project_test.exs

@@ -161,30 +161,21 @@ defmodule Mix.ProjectTest do
   end
 
   test "warns when project app name matches a dependency" do
-    in_tmp("duplicate_app_name", fn ->
-      File.write!("mix.exs", """
-      defmodule DuplicateAppName.MixProject do
-        use Mix.Project
-
-        def project do
-          [
-            app: :foo,
-            version: "0.1.0",
-            deps: [{:foo, "~> 0.1.0"}]
-          ]
-        end
-      end
-      """)
+    Mix.shell(Mix.Shell.Process)
 
-      Mix.Project.in_project(:foo, ".", fn _ ->
-        :ok
-      end)
+    app = :clash_app
 
-      assert_receive {:mix_shell, :error,
-                      [
-                        "warning: the application name :foo is the same as one of its dependencies"
-                      ]}
-    end)
+    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