Warn and reset mime on future files

Author: ericmj

lib/mix/lib/mix/utils.ex

@@ -99,9 +99,17 @@ defmodule Mix.Utils do
   end
 
   def last_modified(path) do
+    now = :calendar.local_time
+
     case File.stat(path) do
-      {:ok, %File.Stat{mtime: mtime}} -> mtime
-      {:error, _} -> {{1970, 1, 1}, {0, 0, 0}}
+      {:ok, %File.Stat{mtime: mtime}} when mtime > now ->
+        Mix.shell.error("warning: mtime (modified time) for \"#{path}\" was set to the future, resetting to now")
+        File.touch!(path, now)
+        mtime
+      {:ok, %File.Stat{mtime: mtime}} ->
+        mtime
+      {:error, _} ->
+        {{1970, 1, 1}, {0, 0, 0}}
     end
   end
 

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

@@ -79,6 +79,9 @@ defmodule Mix.Tasks.Compile.ElixirTest do
       File.touch!("lib/a.ex", future)
       Mix.Tasks.Compile.Elixir.run []
 
+      assert_received {:mix_shell, :error, ["warning: mtime (modified time) for \"lib/a.ex\" was set to the future, resetting to now"]}
+      refute_received {:mix_shell, :error, ["warning: mtime (modified time) for \"lib/b.ex\" was set to the future, resetting to now"]}
+
       assert_received {:mix_shell, :info, ["Compiled lib/a.ex"]}
       refute_received {:mix_shell, :info, ["Compiled lib/b.ex"]}