Correctly escape backslashes in PO composer (#139)

Fixes #138.

Author: maennchen

lib/expo/po/composer.ex

@@ -135,5 +135,6 @@ defmodule Expo.PO.Composer do
   defp escape_char(?\n), do: ~S(\n)
   defp escape_char(?\t), do: ~S(\t)
   defp escape_char(?\r), do: ~S(\r)
+  defp escape_char(?\\), do: <<?\\::utf8, ?\\::utf8>>
   defp escape_char(char), do: <<char>>
 end

test/expo/parser_test.exs

@@ -415,6 +415,45 @@ defmodule Expo.ParserTest do
     end
   end
 
+  describe "unescaping" do
+    test "unescapes special characters" do
+      assert [
+               %Message.Singular{
+                 msgid: ["backslash"],
+                 msgstr: [<<?\\::utf8>>]
+               },
+               %Message.Singular{
+                 msgid: ["double backslash"],
+                 msgstr: [<<?\\::utf8, ?\\::utf8>>]
+               },
+               %Message.Singular{
+                 msgid: ["tab"],
+                 msgstr: [<<?\t::utf8>>]
+               },
+               %Message.Singular{
+                 msgid: ["newline"],
+                 msgstr: [<<?\r::utf8, ?\n::utf8>>]
+               },
+               %Message.Singular{
+                 msgid: ["quote"],
+                 msgstr: [<<?"::utf8>>]
+               }
+             ] =
+               parse(~S"""
+               msgid "backslash"
+               msgstr "\\"
+               msgid "double backslash"
+               msgstr "\\\\"
+               msgid "tab"
+               msgstr "\t"
+               msgid "newline"
+               msgstr "\r\n"
+               msgid "quote"
+               msgstr "\""
+               """)
+    end
+  end
+
   defp parse(string) do
     case PO.parse_string(string) do
       {:ok, %Messages{messages: messages}} ->

test/expo/po_test.exs

@@ -417,7 +417,8 @@ defmodule Expo.POTest do
         headers: [],
         messages: [
           %Message.Singular{msgid: [~s("quotes")], msgstr: [~s(foo "bar" baz)]},
-          %Message.Singular{msgid: [~s(new\nlines\r)], msgstr: [~s(and\ttabs)]}
+          %Message.Singular{msgid: [~s(new\nlines\r)], msgstr: [~s(and\ttabs)]},
+          %Message.Singular{msgid: [~s(backslashes\\)], msgstr: [~s(and \\\\ double backslashes)]}
         ]
       }
 
@@ -427,6 +428,9 @@ defmodule Expo.POTest do
 
              msgid "new\nlines\r"
              msgstr "and\ttabs"
+
+             msgid "backslashes\\"
+             msgstr "and \\\\ double backslashes"
              """
     end