Fix escaped blocks in Enumerable#uniq

Keep the state for block-based `Enumerable#uniq` alive after it returns,
as `each` can retain and later invoke the internal block, making the
stack-allocated memo introduced in 29c669bb56 invalid.

enum.c

@@ -4878,19 +4878,11 @@ uniq_func(RB_BLOCK_CALL_FUNC_ARGLIST(i, set))
     return Qnil;
 }
 
-struct uniq_iter_memo {
-    VALUE set;
-    VALUE ary;
-};
-
 static VALUE
-uniq_iter(RB_BLOCK_CALL_FUNC_ARGLIST(i, memo_))
+uniq_iter(RB_BLOCK_CALL_FUNC_ARGLIST(i, hash))
 {
-    struct uniq_iter_memo *memo = (struct uniq_iter_memo *)memo_;
     ENUM_WANT_SVALUE();
-    if (rb_set_add_no_check(memo->set, rb_yield_values2(argc, argv))) {
-        rb_ary_push(memo->ary, i);
-    }
+    rb_hash_add_new_element(hash, rb_yield_values2(argc, argv), i);
     return Qnil;
 }
 
@@ -4918,18 +4910,18 @@ uniq_iter(RB_BLOCK_CALL_FUNC_ARGLIST(i, memo_))
 static VALUE
 enum_uniq(VALUE obj)
 {
+    VALUE ret;
     if (rb_block_given_p()) {
-        struct uniq_iter_memo memo;
-        memo.set = rb_obj_hide(rb_set_new());
-        memo.ary = rb_ary_new();
-        rb_block_call(obj, id_each, 0, 0, uniq_iter, (VALUE)&memo);
-        return memo.ary;
+        VALUE hash = rb_obj_hide(rb_hash_new());
+        rb_block_call(obj, id_each, 0, 0, uniq_iter, hash);
+        ret = rb_hash_values(hash);
     }
     else {
         VALUE set = rb_obj_hide(rb_set_new());
         rb_block_call(obj, id_each, 0, 0, uniq_func, set);
-        return rb_set_to_a(set);
+        ret = rb_set_to_a(set);
     }
+    return ret;
 }
 
 static VALUE

test/ruby/test_enum.rb

@@ -1295,6 +1295,15 @@ class TestEnumerable < Test::Unit::TestCase
                  olympics.uniq{|k,v| v})
     assert_equal([1, 2, 3, 4, 5, 10], (1..100).uniq{|x| (x**2) % 10 }.first(6))
     assert_equal([1, [1, 2]], Foo.new.to_enum.uniq)
+
+    b = Struct.new(:block) do
+      def each(&blk)
+        self.block = blk
+        nil
+      end
+    end.new
+    b.uniq {|x| x}
+    assert_nil(b.block.call(:foo))
   end
 
   def test_compact