Make .app files deterministic in releases

lib/mix/lib/mix/release.ex

@@ -851,10 +851,13 @@ defmodule Mix.Release do
         source_file = Path.join(source, file)
         target_file = Path.join(target, file)
 
-        with true <- is_list(strip_options) and String.ends_with?(file, ".beam"),
-             {:ok, binary} <- strip_beam(File.read!(source_file), strip_options) do
-          File.write!(target_file, binary)
-        else
+        case Path.extname(file) do
+          ".beam" ->
+            process_beam_file(source_file, target_file, strip_options)
+
+          ".app" ->
+            process_app_file(source_file, target_file)
+
           _ ->
             # Use File.cp!/3 to preserve file mode for any executables stored
             # in the ebin directory.
@@ -868,6 +871,25 @@ defmodule Mix.Release do
     end
   end
 
+  defp process_beam_file(source_file, target_file, strip_options) do
+    with true <- is_list(strip_options),
+         {:ok, binary} <- strip_beam(File.read!(source_file), strip_options) do
+      File.write!(target_file, binary)
+    else
+      _ -> File.cp!(source_file, target_file)
+    end
+  end
+
+  defp process_app_file(source_file, target_file) do
+    with {:ok, [{:application, app, info}]} <- :file.consult(source_file) do
+      # Remove :config_mtime so that .app files are deterministic between builds
+      new_info = Keyword.delete(info, :config_mtime)
+      File.write!(target_file, :io_lib.format("~tp.~n", [{:application, app, new_info}]))
+    else
+      _ -> File.cp!(source_file, target_file)
+    end
+  end
+
   @doc """
   Strips a beam file for a release.
 

lib/mix/test/mix/release_test.exs

@@ -686,19 +686,13 @@ defmodule Mix.ReleaseTest do
     test "copies and strips beams" do
       assert copy_ebin(release([]), @eex_ebin, tmp_path("eex_ebin"))
 
-      assert size!(Path.join(@eex_ebin, "eex.app")) ==
-               size!(tmp_path("eex_ebin/eex.app"))
-
       assert size!(Path.join(@eex_ebin, "Elixir.EEx.beam")) >
                size!(tmp_path("eex_ebin/Elixir.EEx.beam"))
     end
 
     test "copies without stripping beams" do
       assert copy_ebin(release(strip_beams: false), @eex_ebin, tmp_path("eex_ebin"))
 
-      assert size!(Path.join(@eex_ebin, "eex.app")) ==
-               size!(tmp_path("eex_ebin/eex.app"))
-
       assert size!(Path.join(@eex_ebin, "Elixir.EEx.beam")) ==
                size!(tmp_path("eex_ebin/Elixir.EEx.beam"))
     end
@@ -722,6 +716,13 @@ defmodule Mix.ReleaseTest do
 
       assert mode!(source_so_path) == mode!(tmp_path("mix_release/libtest_nif.so"))
     end
+
+    test "removes config_mtime from app files" do
+      assert copy_ebin(release([]), @eex_ebin, tmp_path("eex_ebin"))
+
+      {:ok, [{:application, :eex, info}]} = :file.consult(tmp_path("eex_ebin/eex.app"))
+      refute Keyword.get(info, :config_mtime)
+    end
   end
 
   describe "copy_app/2" do
@@ -730,19 +731,13 @@ defmodule Mix.ReleaseTest do
     test "copies and strips beams" do
       assert copy_app(release(applications: [eex: :permanent]), :eex)
 
-      assert size!(Path.join(@eex_ebin, "eex.app")) ==
-               size!(Path.join(@release_lib, "eex-#{@elixir_version}/ebin/eex.app"))
-
       assert size!(Path.join(@eex_ebin, "Elixir.EEx.beam")) >
                size!(Path.join(@release_lib, "eex-#{@elixir_version}/ebin/Elixir.EEx.beam"))
     end
 
     test "copies without stripping beams" do
       assert copy_app(release(strip_beams: false, applications: [eex: :permanent]), :eex)
 
-      assert size!(Path.join(@eex_ebin, "eex.app")) ==
-               size!(Path.join(@release_lib, "eex-#{@elixir_version}/ebin/eex.app"))
-
       assert size!(Path.join(@eex_ebin, "Elixir.EEx.beam")) ==
                size!(Path.join(@release_lib, "eex-#{@elixir_version}/ebin/Elixir.EEx.beam"))
     end
@@ -760,6 +755,14 @@ defmodule Mix.ReleaseTest do
       refute File.exists?(Path.join(@release_lib, "runtime_tools-#{@runtime_tools_version}/ebin"))
       refute File.exists?(Path.join(@release_lib, "runtime_tools-#{@runtime_tools_version}/priv"))
     end
+
+    test "removes config_mtime from app files" do
+      assert copy_app(release(strip_beams: false, applications: [eex: :permanent]), :eex)
+
+      eex_app_path = Path.join(@release_lib, "eex-#{@elixir_version}/ebin/eex.app")
+      {:ok, [{:application, :eex, info}]} = :file.consult(eex_app_path)
+      refute Keyword.get(info, :config_mtime)
+    end
   end
 
   describe "strip_beam/1" do