Use LC_CTYPE env for Locale.current[0].charset

Becauese existing library such as sub-mail uses the API.

GitHub: fix #2

Debian Bug: #690572

Reported by Stefano Zacchiroli. Thanks!!!
Reported by Hleb Valoshka. Thanks!!!

lib/locale/driver/env.rb

@@ -34,16 +34,24 @@ module Driver
     module Env
       module_function
 
-      # Gets the locale from environment variable. (LC_ALL > LC_MESSAGES > LANG)
+      # Gets the locale from environment variable.
+      # Priority order except charset is LC_ALL > LC_MESSAGES > LANG.
+      # Priority order for charset is LC_ALL > LC_CTYPE > LANG.
       # Returns: the locale as Locale::Tag::Posix.
       def locale
-        # At least one environment valiables should be set on *nix system.
-        [ENV["LC_ALL"], ENV["LC_MESSAGES"], ENV["LANG"]].each do |loc|
-          if loc != nil and loc.size > 0
-            return Locale::Tag::Posix.parse(loc)
-          end
-        end
-        nil
+        lc_all = Private.parse(ENV["LC_ALL"])
+        return lc_all if lc_all
+
+        lc_messages = Private.parse(ENV["LC_MESSAGES"])
+        lang = Private.parse(ENV["LANG"])
+
+        tag = lc_messages || lang
+        return nil if tag.nil?
+
+        lc_ctype = Private.parse(ENV["LC_CTYPE"])
+        tag.charset = lc_ctype.charset if lc_ctype
+
+        tag
       end
 
       # Gets the locales from environment variables. (LANGUAGE > LC_ALL > LC_MESSAGES > LANG)

test/test_detect_general.rb

@@ -36,6 +36,7 @@ def setup
 
   def test_lc_all
     ENV["LC_ALL"] = "ja_JP.eucJP"
+    ENV["LC_CTYPE"] = "fr_FR.ISO-8859-1"  #Ignored.
     ENV["LC_MESSAGES"] = "zh_CN.UTF-8"  #Ignored.
     ENV["LANG"] = "ko_KR.UTF-8"  #Ignored.
     ENV["LANGUAGE"] = nil
@@ -52,8 +53,9 @@ def test_lc_all
 
   def test_lc_messages
     ENV["LC_ALL"] = nil
+    ENV["LC_CTYPE"] = nil
     ENV["LC_MESSAGES"] = "ja_JP.eucJP"
-    ENV["LANG"] = "ko_KR.UTF-8"  #Ignored.
+    ENV["LANG"] = "ko_KR.UTF-8"  #Ignored except charset.
     ENV["LANGUAGE"] = nil
 
     lang = Locale.current[0]
@@ -66,8 +68,26 @@ def test_lc_messages
     assert_equal "UTF-8", Locale.charset
   end
 
+  def test_lc_messages_with_lc_ctype
+    ENV["LC_ALL"] = nil
+    ENV["LC_CTYPE"] = "fr_FR.ISO-8859-1"
+    ENV["LC_MESSAGES"] = "ja_JP.eucJP"
+    ENV["LANG"] = "ko_KR.UTF-8"  #Ignored.
+    ENV["LANGUAGE"] = nil
+
+    lang = Locale.current[0]
+    assert_equal Locale::Tag::Posix, lang.class
+    assert_equal "ja", lang.language
+    assert_equal "JP", lang.region
+    assert_equal "ISO-8859-1", lang.charset
+    assert_equal Locale::Tag::Posix.new("ja", "JP", "ISO-8859-1"), lang
+
+    assert_equal "ISO-8859-1", Locale.charset
+  end
+
   def test_lang
     ENV["LC_ALL"] = nil
+    ENV["LC_CTYPE"] = nil
     ENV["LC_MESSAGES"] = nil
     ENV["LANG"] = "ja_JP.eucJP"
     ENV["LANGUAGE"] = nil
@@ -82,8 +102,26 @@ def test_lang
     assert_equal "eucJP", Locale.charset
   end
 
+  def test_lang_with_ctype
+    ENV["LC_ALL"] = nil
+    ENV["LC_CTYPE"] = "fr_FR.ISO-8859-1"
+    ENV["LC_MESSAGES"] = nil
+    ENV["LANG"] = "ja_JP.eucJP"
+    ENV["LANGUAGE"] = nil
+
+    lang = Locale.current[0]
+    assert_equal Locale::Tag::Posix, lang.class
+    assert_equal "ja", lang.language
+    assert_equal "JP", lang.region
+    assert_equal "ISO-8859-1", lang.charset
+    assert_equal Locale::Tag::Posix.new("ja", "JP", "ISO-8859-1"), lang
+
+    assert_equal "ISO-8859-1", Locale.charset
+  end
+
   def test_lang_complex
     ENV["LC_ALL"] = "zh_CN.UTF-8"  # Ignored.
+    ENV["LC_CTYPE"] = "fr_FR.ISO-8859-1" #Ingored.
     ENV["LC_MESSAGES"] = "ko_KR.UTF-8" #Ingored.
     ENV["LANG"] = "en_US.UTF-8"  # Ignored.
     ENV["LANGUAGE"] ="ja_JP.eucJP:zh_CN.UTF-8"