Revert "Don't ignore escape characters in regex"

This change will be on v1.1 only as it may break applications.

This reverts commit 337c040.

Author: José Valim

lib/elixir/lib/regex.ex

@@ -484,13 +484,18 @@ defmodule Regex do
     [List.to_integer(ns) | precompile_replacement(rest)]
   end
 
-  defp precompile_replacement(<<?\\, ?\\, rest :: binary>>) do
-    [<<?\\>> | precompile_replacement(rest)]
+  defp precompile_replacement(<<?\\, x, rest :: binary>>) when x < ?0 or x > ?9 do
+    case precompile_replacement(rest) do
+      [head | t] when is_binary(head) ->
+        [<<x, head :: binary>> | t]
+      other ->
+        [<<x>> | other]
+    end
   end
 
-  defp precompile_replacement(<<?\\, x, rest :: binary>>) when x in ?0..?9 do
+  defp precompile_replacement(<<?\\, rest :: binary>>) when byte_size(rest) > 0 do
     {ns, rest} = pick_int(rest)
-    [List.to_integer([x|ns]) | precompile_replacement(rest)]
+    [List.to_integer(ns) | precompile_replacement(rest)]
   end
 
   defp precompile_replacement(<<x, rest :: binary>>) do

lib/elixir/test/elixir/regex_test.exs

@@ -197,11 +197,6 @@ defmodule RegexTest do
     assert Regex.replace(~r(b), "abcbe", "d") == "adcde"
     assert Regex.replace(~r(b), "abcbe", "d", global: false) == "adcbe"
 
-    assert Regex.replace(~r/ /, "first third", "\\second\\") ==
-           "first\\second\\third"
-    assert Regex.replace(~r/ /, "first third", "\\\\second\\\\") ==
-           "first\\second\\third"
-
     assert Regex.replace(~r[a(b)c], "abcabc", fn -> "ac" end) == "acac"
     assert Regex.replace(~r[a(b)c], "abcabc", fn "abc" -> "ac" end) == "acac"
     assert Regex.replace(~r[a(b)c], "abcabc", fn "abc", "b" -> "ac" end) == "acac"