Preserving mtime needs to be invoked per task

Author: José Valim

lib/mix/lib/mix/tasks/compile.elixir.ex

@@ -69,8 +69,11 @@ defmodule Mix.Tasks.Compile.Elixir do
     stale      = Mix.Utils.extract_stale(to_watch, [compile_path])
 
     if opts[:force] or stale != [] do
-      File.mkdir_p! compile_path
-      compile_files opts[:quick], project, compile_path, to_compile, stale
+      Mix.Utils.preserving_mtime(compile_path, fn ->
+        File.mkdir_p! compile_path
+        compile_files opts[:quick], project, compile_path, to_compile, stale
+      end)
+
       :ok
     else
       :noop

lib/mix/lib/mix/tasks/compile.erlang.ex

@@ -28,8 +28,11 @@ defmodule Mix.Tasks.Compile.Erlang do
     if files == [] do
       :noop
     else
-      File.mkdir_p! compile_path
-      compile_files project, files, compile_path
+      Mix.Utils.preserving_mtime(compile_path, fn ->
+        File.mkdir_p! compile_path
+        compile_files project, files, compile_path
+      end)
+
       :ok
     end
   end

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

@@ -65,12 +65,10 @@ defmodule Mix.Tasks.Compile do
     compile_path = Mix.project[:compile_path]
 
     changed =
-      Mix.Utils.preserving_mtime(compile_path, fn ->
-        Enum.reduce get_compilers, false, fn(compiler, acc) ->
-          res = Mix.Task.run "compile.#{compiler}", args
-          acc or res != :noop
-        end
-      end)
+      Enum.reduce get_compilers, false, fn(compiler, acc) ->
+        res = Mix.Task.run "compile.#{compiler}", args
+        acc or res != :noop
+      end
 
     # If any of the tasks above returns something different
     # than :noop, it means they produced something, so we