[Bug #22322] Take transcoder names from declared transcoders

Fix use-after-free of dangling pointers.

test/ruby/test_econv.rb

@@ -856,6 +856,20 @@ class TestEncodingConverter < Test::Unit::TestCase
       "\222\xA1x".encode("iso-2022-jp", "stateless-iso-2022-jp", :invalid => :replace))
   end
 
+  def test_inspect_decorator_source_name
+    decorator_names = %w[
+      amp_escape xml_text_escape xml_attr_content_escape xml_attr_quote
+      universal_newline crlf_newline cr_newline lf_newline
+    ]
+    all_assertions_foreach(nil, *decorator_names) do |decorator|
+      ec = Encoding::Converter.new('', decorator)
+      inspect = ec.inspect
+      10_000.times {"A"*100}
+      GC.start(full_mark: true, immediate_sweep: true)
+      assert_equal inspect, ec.inspect
+    end
+  end
+
   def test_convpath
     eucjp = Encoding::EUC_JP
     utf8 = Encoding::UTF_8

transcode.c

@@ -1045,6 +1045,8 @@ rb_econv_open0(const char *sname, const char *dname, int ecflags)
             SIZED_FREE_N(entries, num_trans);
             return NULL;
         }
+        sname = entries[0]->sname;
+        dname = entries[num_trans-1]->dname;
     }
 
     ec = rb_econv_open_by_transcoder_entries(num_trans, entries);