nobu	2017-08-29 19:49:40 +0900 (Tue, 29 Aug 2017)

  New Revision: 59684

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=59684

  Log:
    array.c: join encoding
    
    * array.c (ary_join_1): copy the encoding of the converted string
      of the first element by to_str too, as an initial encoding.

  Modified files:
    trunk/array.c
    trunk/test/ruby/test_array.rb
Index: array.c
===================================================================
--- array.c	(revision 59683)
+++ array.c	(revision 59684)
@@ -1994,7 +1994,10 @@ ary_join_1(VALUE obj, VALUE ary, VALUE s https://github.com/ruby/ruby/blob/trunk/array.c#L1994
 	if (RB_TYPE_P(val, T_STRING)) {
 	  str_join:
 	    rb_str_buf_append(result, val);
-	    *first = FALSE;
+	    if (*first) {
+		rb_enc_copy(result, val);
+		*first = FALSE;
+	    }
 	}
 	else if (RB_TYPE_P(val, T_ARRAY)) {
 	    obj = val;
@@ -2025,10 +2028,6 @@ ary_join_1(VALUE obj, VALUE ary, VALUE s https://github.com/ruby/ruby/blob/trunk/array.c#L2028
 		goto ary_join;
 	    }
 	    val = rb_obj_as_string(val);
-	    if (*first) {
-		rb_enc_copy(result, val);
-		*first = FALSE;
-	    }
 	    goto str_join;
 	}
     }
Index: test/ruby/test_array.rb
===================================================================
--- test/ruby/test_array.rb	(revision 59683)
+++ test/ruby/test_array.rb	(revision 59684)
@@ -1085,6 +1085,7 @@ class TestArray < Test::Unit::TestCase https://github.com/ruby/ruby/blob/trunk/test/ruby/test_array.rb#L1085
     assert_equal(Encoding::US_ASCII, [1, [u]].join.encoding)
     assert_equal(Encoding::UTF_8, [u, [e]].join.encoding)
     assert_equal(Encoding::UTF_8, [u, [1]].join.encoding)
+    assert_equal(Encoding::UTF_8, [Struct.new(:to_str).new(u)].join.encoding)
     bug5379 = '[ruby-core:39776]'
     assert_equal(Encoding::US_ASCII, [[], u, nil].join.encoding, bug5379)
     assert_equal(Encoding::UTF_8, [[], "\u3042", nil].join.encoding, bug5379)

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