merge revision(s) 09295ea796900fb7b05d29e93364090e21598566: [Backport #19543]

	IO::Buffer#resize: Free internal buffer if new size is zero (#7569)

	`#resize(0)` on an IO::Buffer with internal buffer allocated will
	result in calling `realloc(data->base, 0)`. The behavior of `realloc`
	with size = 0 is implementation-defined (glibc frees the object
	and returns NULL, while BSDs return an inaccessible object). And
	thus such usage is deprecated in standard C (upcoming C23 will make it
	UB).

	To avoid this problem, just `free`s the memory when the new size is zero.
	---
	 io_buffer.c                 |  5 +++++
	 test/ruby/test_io_buffer.rb | 18 ++++++++++++++++++
	 2 files changed, 23 insertions(+)

1 files changed, 18 insertions, 0 deletions

diff --git a/test/ruby/test_io_buffer.rb b/test/ruby/test_io_buffer.rb
index e3f7021b26..fdfea00dfe 100644
--- a/test/ruby/test_io_buffer.rb
+++ b/test/ruby/test_io_buffer.rb
@@ -142,6 +142,24 @@ class TestIOBuffer < Test::Unit::TestCase
     assert_equal message, buffer.get_string(0, message.bytesize)
   end
 
+  def test_resize_zero_internal
+    buffer = IO::Buffer.new(1)
+
+    buffer.resize(0)
+    assert_equal 0, buffer.size
+
+    buffer.resize(1)
+    assert_equal 1, buffer.size
+  end
+
+  def test_resize_zero_external
+    buffer = IO::Buffer.for('1')
+
+    assert_raise IO::Buffer::AccessError do
+      buffer.resize(0)
+    end
+  end
+
   def test_compare_same_size
     buffer1 = IO::Buffer.new(1)
     assert_equal buffer1, buffer1