* encoding.c (rb_enc_compatible): If a string is empty and

  other's encoding is US-ASCII, returns the empty string's encoding.
  [ruby-list:46274]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@24506 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Wed Aug 12 07:41:31 2009  NARUSE, Yui  <[email protected]>
+
+	* encoding.c (rb_enc_compatible): If a string is empty and
+	  other's encoding is US-ASCII, returns the empty string's encoding.
+	  [ruby-list:46274]
+
 Wed Aug 12 07:38:12 2009  NARUSE, Yui  <[email protected]>
 
 	* encoding.c (is_data_encoding): fix condition.

encoding.c

@@ -709,9 +709,9 @@ rb_enc_compatible(VALUE str1, VALUE str2)
     enc2 = rb_enc_from_index(idx2);
 
     if (TYPE(str2) == T_STRING && RSTRING_LEN(str2) == 0)
-	return enc1;
+	return (idx1 == ENCINDEX_US_ASCII && rb_enc_asciicompat(enc2)) ? enc2 : enc1;
     if (TYPE(str1) == T_STRING && RSTRING_LEN(str1) == 0)
-	return enc2;
+	return (idx2 == ENCINDEX_US_ASCII && rb_enc_asciicompat(enc1)) ? enc1 : enc2;
     if (!rb_enc_asciicompat(enc1) || !rb_enc_asciicompat(enc2)) {
 	return 0;
     }

test/ruby/test_m17n.rb

@@ -7,6 +7,7 @@ def assert_encoding(encname, actual, message=nil)
   end
 
   module AESU
+    def ua(str) str.dup.force_encoding("US-ASCII") end
     def a(str) str.dup.force_encoding("ASCII-8BIT") end
     def e(str) str.dup.force_encoding("EUC-JP") end
     def s(str) str.dup.force_encoding("Windows-31J") end
@@ -1300,6 +1301,7 @@ def test_setbyte
 
   def test_compatible
     assert_nil Encoding.compatible?("",0)
+    assert_equal(Encoding::UTF_8, Encoding.compatible?(u(""), ua("abc")))
     assert_equal(Encoding::UTF_8, Encoding.compatible?(Encoding::UTF_8, Encoding::UTF_8))
     assert_equal(Encoding::UTF_8, Encoding.compatible?(Encoding::UTF_8, Encoding::US_ASCII))
     assert_equal(Encoding::ASCII_8BIT,