Raise on invalid .app files

lib/mix/lib/mix/tasks/compile.app.ex

@@ -187,11 +187,11 @@ defmodule Mix.Tasks.Compile.App do
         |> add_compile_env(current_properties)
         |> add_modules(modules, compile_path)
 
-      contents = :io_lib.format("~p.~n", [{:application, app, properties}])
+      contents = to_erl_term({:application, app, properties})
       :application.load({:application, app, properties})
 
       Mix.Project.ensure_structure()
-      File.write!(target, IO.chardata_to_string(contents))
+      File.write!(target, [contents, ?.])
       File.touch!(target, new_mtime)
 
       # If we just created the .app file, it will have touched
@@ -208,6 +208,53 @@ defmodule Mix.Tasks.Compile.App do
     end
   end
 
+  defp to_erl_term(tuple) when is_tuple(tuple) do
+    [?{, tuple |> Tuple.to_list() |> to_erl_head(), ?}]
+  end
+
+  defp to_erl_term(list) when is_list(list) do
+    [?[, to_erl_head(list), ?]]
+  end
+
+  defp to_erl_term(map) when is_map(map) do
+    inner =
+      Enum.map_intersperse(
+        :maps.to_list(:maps.iterator(map, :reversed)),
+        ?,,
+        fn {key, value} -> [to_erl_term(key), "=>", to_erl_term(value)] end
+      )
+
+    [?#, ?{, inner, ?}]
+  end
+
+  defp to_erl_term(map) when is_map(map) do
+    inner =
+      Enum.map_intersperse(
+        :maps.to_list(:maps.iterator(map, :reversed)),
+        ?,,
+        fn {key, value} -> [to_erl_term(key), "=>", to_erl_term(value)] end
+      )
+
+    [?#, ?{, inner, ?}]
+  end
+
+  defp to_erl_term(term) when is_function(term) or is_reference(term) or is_pid(term) do
+    Mix.raise(
+      "\"def application\" has a term which cannot be written to .app files: #{inspect(term)}"
+    )
+  end
+
+  defp to_erl_term(term) do
+    :io_lib.print(term)
+  end
+
+  defp to_erl_head([]), do: []
+  defp to_erl_head([h | t]), do: [to_erl_term(h) | to_erl_tail(t)]
+
+  defp to_erl_tail([h | t]), do: [?,, to_erl_term(h) | to_erl_tail(t)]
+  defp to_erl_tail([]), do: []
+  defp to_erl_tail(other), do: [?|, to_erl_term(other)]
+
   defp current_app_properties(target) do
     case :file.consult(target) do
       {:ok, [{:application, _app, properties}]} -> properties

lib/mix/test/mix/tasks/compile.app_test.exs

@@ -7,24 +7,6 @@ Code.require_file("../../test_helper.exs", __DIR__)
 defmodule Mix.Tasks.Compile.AppTest do
   use MixTest.Case
 
-  defmodule CustomProject do
-    def project do
-      [
-        app: :custom_project,
-        version: "0.2.0",
-        description: "Some UTF-8 dëscriptión"
-      ]
-    end
-
-    def application do
-      [
-        maxT: :infinity,
-        applications: [:example_app, mix: :optional],
-        extra_applications: [:logger, ex_unit: :optional]
-      ]
-    end
-  end
-
   defmodule CustomDeps do
     def project do
       [app: :custom_deps, version: "0.2.0", deps: deps()]
@@ -51,9 +33,13 @@ defmodule Mix.Tasks.Compile.AppTest do
     end
   end
 
-  defmodule InvalidProject do
+  defmodule CustomProject do
     def project do
-      [app: :invalid_project, version: "0.3.0"]
+      [
+        app: :custom_project,
+        version: "0.3.0",
+        description: "Some UTF-8 dëscriptión"
+      ]
     end
 
     def application do
@@ -124,20 +110,30 @@ defmodule Mix.Tasks.Compile.AppTest do
   test "uses custom application settings" do
     in_fixture("no_mixfile", fn ->
       Mix.Project.push(CustomProject)
+      env = [foo: [:one, "two", 3, 4], bar: [{} | %{foo: :bar}]]
+
+      Process.put(:application,
+        maxT: :infinity,
+        applications: [:example_app, mix: :optional],
+        extra_applications: [:logger, ex_unit: :optional],
+        env: env
+      )
 
       Mix.Tasks.Compile.Elixir.run([])
       Mix.Tasks.Compile.App.run([])
 
       properties = parse_resource_file(:custom_project)
-      assert Application.spec(:custom_project, :vsn) == ~c"0.2.0"
-      assert properties[:vsn] == ~c"0.2.0"
+      assert Application.spec(:custom_project, :vsn) == ~c"0.3.0"
+      assert properties[:vsn] == ~c"0.3.0"
       assert properties[:maxT] == :infinity
       assert properties[:optional_applications] == [:ex_unit, :mix]
       assert properties[:description] == ~c"Some UTF-8 dëscriptión"
 
       assert properties[:applications] ==
                [:kernel, :stdlib, :elixir, :logger, :ex_unit, :example_app, :mix]
 
+      assert properties[:env] == [foo: [:one, "two", 3, 4], bar: [{} | %{foo: :bar}]]
+
       refute Keyword.has_key?(properties, :extra_applications)
     end)
   end
@@ -160,7 +156,7 @@ defmodule Mix.Tasks.Compile.AppTest do
 
   test "validates properties" do
     in_fixture("no_mixfile", fn ->
-      Mix.Project.push(InvalidProject)
+      Mix.Project.push(CustomProject)
 
       Process.put(:application, [:not_a_keyword, applications: []])
       message = "Application configuration returned from application/0 should be a keyword list"
@@ -252,6 +248,15 @@ defmodule Mix.Tasks.Compile.AppTest do
       assert_raise Mix.Error, message, fn ->
         Mix.Tasks.Compile.App.run([])
       end
+
+      Process.put(:application, env: [foo: make_ref()])
+
+      message =
+        ~r"\"def application\" has a term which cannot be written to \.app files: #Reference"
+
+      assert_raise Mix.Error, message, fn ->
+        Mix.Tasks.Compile.App.run([])
+      end
     end)
   end