Revert "encoding.c (rb_enc_get_index): return -1 for non-encoding capable objects"

* This reverts commit fb253d2032.
* The CI is failing, this seems a bug in the JSON C extension.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64174 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

encoding.c

@@ -793,26 +793,24 @@ rb_enc_get_index(VALUE obj)
 	obj = rb_sym2str(obj);
     }
     switch (BUILTIN_TYPE(obj)) {
+      as_default:
+      default:
       case T_STRING:
-      case T_SYMBOL:
       case T_REGEXP:
 	i = enc_get_index_str(obj);
 	break;
       case T_FILE:
 	tmp = rb_funcallv(obj, rb_intern("internal_encoding"), 0, 0);
-	if (NIL_P(tmp)) {
-	    tmp = rb_funcallv(obj, rb_intern("external_encoding"), 0, 0);
-	}
-	if (is_data_encoding(tmp)) {
-	    i = enc_check_encoding(tmp);
-	}
-	break;
+	if (NIL_P(tmp)) obj = rb_funcallv(obj, rb_intern("external_encoding"), 0, 0);
+	else obj = tmp;
+	if (NIL_P(obj)) break;
       case T_DATA:
 	if (is_data_encoding(obj)) {
 	    i = enc_check_encoding(obj);
 	}
-	break;
-      default:
+	else {
+	    goto as_default;
+	}
 	break;
     }
     return i;

spec/ruby/optional/capi/encoding_spec.rb

@@ -147,11 +147,6 @@ describe "C-API Encoding function" do
     it "returns -1 as the index for immediates" do
       @s.send(@method, 1).should == -1
     end
-
-    it "returns -1 for an object without an encoding" do
-      obj = Object.new
-      @s.send(@method, obj).should == -1
-    end
   end
 
   describe "rb_enc_set_index" do