Make Complex#{inspect,to_s} work correctly if real part #inspect returns frozen string

Make static f_format function take a non-frozen string to append
to.

This does not result in an additional allocation for #inspect,
but it does result in an additional allocation for #to_s.

Fixes [Bug #20337]

1 files changed, 11 insertions, 0 deletions

diff --git a/test/ruby/test_complex.rb b/test/ruby/test_complex.rb
index c0cfb73235..bb131cee91 100644
--- a/test/ruby/test_complex.rb
+++ b/test/ruby/test_complex.rb
@@ -741,6 +741,17 @@ class Complex_Test < Test::Unit::TestCase
     assert_equal('(1+2i)', c.inspect)
   end
 
+  def test_inspect_to_s_frozen_bug_20337
+    assert_separately([], <<~'RUBY')
+      class Numeric
+        def inspect = super.freeze
+      end
+      c = Complex(Numeric.new, 1)
+      assert_match(/\A\(#<Numeric:/, c.inspect)
+      assert_match(/\A#<Numeric:/, c.to_s)
+    RUBY
+  end
+
   def test_marshal
     c = Complex(1,2)