Ensure File.touch and File.touch! properly work with universal time

Operations that change mtime should work with universal times.

Closes #3722.

Author: José Valim

lib/elixir/lib/file.ex

@@ -358,30 +358,33 @@ defmodule File do
 
   @doc """
   Updates modification time (mtime) and access time (atime) of
-  the given file. File is created if it doesn’t exist.
+  the given file.
+
+  File is created if it doesn’t exist. Requires datetime in UTC.
   """
   @spec touch(Path.t, :calendar.datetime) :: :ok | {:error, posix}
-  def touch(path, time \\ :calendar.local_time) do
+  def touch(path, time \\ :calendar.universal_time) do
     path = IO.chardata_to_string(path)
-    case F.change_time(path, time) do
+    case :elixir_utils.change_universal_time(path, time) do
       {:error, :enoent} -> touch_new(path, time)
       other -> other
     end
   end
 
   defp touch_new(path, time) do
     case write(path, "", [:append]) do
-      :ok -> F.change_time(path, time)
+      :ok -> :elixir_utils.change_universal_time(path, time)
       {:error, _reason} = error -> error
     end
   end
 
   @doc """
   Same as `touch/2` but raises an exception if it fails.
-  Returns `:ok` otherwise.
+
+  Returns `:ok` otherwise. Requires datetime in UTC.
   """
   @spec touch!(Path.t, :calendar.datetime) :: :ok | no_return
-  def touch!(path, time \\ :calendar.local_time) do
+  def touch!(path, time \\ :calendar.universal_time) do
     case touch(path, time) do
       :ok -> :ok
       {:error, reason} ->
@@ -451,16 +454,16 @@ defmodule File do
   It returns `:ok` in case of success, returns `{:error, reason}` otherwise
 
   Note: The command `mv` in Unix systems behaves differently depending
-  if `source` is a file and the `destination` is an existing directory. 
-  We have chosen to explicitly disallow this behaviour. 
+  if `source` is a file and the `destination` is an existing directory.
+  We have chosen to explicitly disallow this behaviour.
 
   ## Examples
 
       # Rename file "a.txt" to "b.txt"
       File.rename "a.txt", "b.txt"
 
       # Rename directory "samples" to "tmp"
-      File.rename "samples", "tmp"  
+      File.rename "samples", "tmp"
   """
   @spec rename(Path.t, Path.t) :: :ok | {:error, posix}
   def rename(source, destination) do
@@ -1198,19 +1201,19 @@ defmodule File do
   is specified. This means any data streamed into the file must be
   converted to `iodata` type. If you pass `[:utf8]` in the modes parameter,
   the underlying stream will use `IO.write/2` and the `String.Chars` protocol
-  to convert the data. See `IO.binwrite/2` and `IO.write/2` . 
+  to convert the data. See `IO.binwrite/2` and `IO.write/2` .
 
   One may also consider passing the `:delayed_write` option if the stream
   is meant to be written to under a tight loop.
 
   ## Examples
-      
+
       # Read in 2048 byte chunks rather than lines
       File.stream!("./test/test.data", [], 2048)
       #=>  %File.Stream{line_or_bytes: 2048, modes: [:raw, :read_ahead, :binary],
       #=> path: "./test/test.data", raw: true}
 
-  See `Stream.run/1` for an example of streaming into a file. 
+  See `Stream.run/1` for an example of streaming into a file.
 
   """
   def stream!(path, modes \\ [], line_or_bytes \\ :line) do

lib/elixir/src/elixir_utils.erl

@@ -4,7 +4,8 @@
 -export([elixir_to_erl/1, get_line/1, split_last/1, meta_location/1,
   characters_to_list/1, characters_to_binary/1, macro_name/1,
   convert_to_boolean/4, returns_boolean/1, atom_concat/1,
-  read_file_type/1, read_link_type/1, relative_to_cwd/1, erl_call/4]).
+  read_file_type/1, read_link_type/1, relative_to_cwd/1,
+  change_universal_time/2, erl_call/4]).
 -include("elixir.hrl").
 -include_lib("kernel/include/file.hrl").
 
@@ -43,6 +44,11 @@ read_link_type(File) ->
     {error, _} = Error -> Error
   end.
 
+change_universal_time(Name, {{Y, M, D}, {H, Min, Sec}}=Time)
+  when is_integer(Y), is_integer(M), is_integer(D),
+       is_integer(H), is_integer(Min), is_integer(Sec)->
+    file:write_file_info(Name, #file_info{mtime=Time}, [{time, universal}]).
+
 relative_to_cwd(Path) ->
   case elixir_compiler:get_opt(internal) of
     true  -> Path;

lib/elixir/test/elixir/file_test.exs

@@ -1527,7 +1527,7 @@ defmodule FileTest do
       refute File.exists?(fixture)
       assert File.touch(fixture, time) == :ok
       assert {:ok, ""} == File.read(fixture)
-      assert File.stat!(fixture).mtime == time
+      assert File.stat!(fixture, time: :universal).mtime == time
     after
       File.rm(fixture)
     end

lib/mix/lib/mix/utils.ex

@@ -99,9 +99,9 @@ defmodule Mix.Utils do
   end
 
   def last_modified(path) do
-    now = :calendar.local_time
+    now = :calendar.universal_time
 
-    case File.stat(path) do
+    case File.stat(path, time: :universal) do
       {: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)