Include Set subclass name in Set#inspect output

Fixes [Bug #21377]

Co-authored-by: zzak <[email protected]>

2 files changed, 19 insertions, 5 deletions

diff --git a/set.c b/set.c
index ba0f3b4ae9..ab90da7cf2 100644
--- a/set.c
+++ b/set.c
@@ -536,10 +536,14 @@ set_i_initialize_copy(VALUE set, VALUE other)
 static int
 set_inspect_i(st_data_t key, st_data_t arg)
 {
-    VALUE str = (VALUE)arg;
-    if (RSTRING_LEN(str) > 4) {
+    VALUE *args = (VALUE*)arg;
+    VALUE str = args[0];
+    if (args[1] == Qtrue) {
         rb_str_buf_cat_ascii(str, ", ");
     }
+    else {
+        args[1] = Qtrue;
+    }
     rb_str_buf_append(str, rb_inspect((VALUE)key));
 
     return ST_CONTINUE;
@@ -549,10 +553,16 @@ static VALUE
 set_inspect(VALUE set, VALUE dummy, int recur)
 {
     VALUE str;
+    VALUE klass_name = rb_class_path(CLASS_OF(set));
+
+    if (recur) {
+        str = rb_sprintf("%"PRIsVALUE"[...]", klass_name);
+        return rb_str_export_to_enc(str, rb_usascii_encoding());
+    }
 
-    if (recur) return rb_usascii_str_new2("Set[...]");
-    str = rb_str_buf_new2("Set[");
-    set_iter(set, set_inspect_i, str);
+    str = rb_sprintf("%"PRIsVALUE"[", klass_name);
+    VALUE args[2] = {str, Qfalse};
+    set_iter(set, set_inspect_i, (st_data_t)args);
     rb_str_buf_cat2(str, "]");
 
     return str;
diff --git a/test/ruby/test_set.rb b/test/ruby/test_set.rb
index 110c509463..87e1fd8d26 100644
--- a/test/ruby/test_set.rb
+++ b/test/ruby/test_set.rb
@@ -846,6 +846,10 @@ class TC_Set < Test::Unit::TestCase
 
     set1.add(set2)
     assert_equal('Set[Set[0], 1, 2, Set[1, 2, Set[...]]]', set2.inspect)
+
+    c = Class.new(Set)
+    c.set_temporary_name("_MySet")
+    assert_equal('_MySet[1, 2]', c[1, 2].inspect)
   end
 
   def test_to_s