merge revision(s) fdf39963490cf2cf95b30d91bb9b35964c2c2350: [Backport #18421]

	Empty and return the buffer if zero size is given [Bug #18421]

	In `IO#readpartial` and `IO#read_nonblock`, as well as `IO#read`.
	---
	 io.c                 |  8 ++++++--
	 test/ruby/test_io.rb | 21 +++++++++++++++++++++
	 2 files changed, 27 insertions(+), 2 deletions(-)

3 files changed, 28 insertions, 3 deletions

diff --git a/io.c b/io.c
index 521b0b0e9a..9720aed06e 100644
--- a/io.c
+++ b/io.c
@@ -2982,8 +2982,10 @@ io_getpartial(int argc, VALUE *argv, VALUE io, int no_exception, int nonblock)
     GetOpenFile(io, fptr);
     rb_io_check_byte_readable(fptr);
 
-    if (len == 0)
+    if (len == 0) {
+	io_set_read_length(str, 0, shrinkable);
 	return str;
+    }
 
     if (!nonblock)
         READ_CHECK(fptr);
@@ -3126,8 +3128,10 @@ io_read_nonblock(rb_execution_context_t *ec, VALUE io, VALUE length, VALUE str,
     GetOpenFile(io, fptr);
     rb_io_check_byte_readable(fptr);
 
-    if (len == 0)
+    if (len == 0) {
+	io_set_read_length(str, 0, shrinkable);
 	return str;
+    }
 
     n = read_buffered_data(RSTRING_PTR(str), len, fptr);
     if (n <= 0) {
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 58a739be22..5b84fd6a4d 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1482,6 +1482,13 @@ class TestIO < Test::Unit::TestCase
     end)
   end
 
+  def test_readpartial_zero_size
+    File.open(IO::NULL) do |r|
+      assert_empty(r.readpartial(0, s = "01234567"))
+      assert_empty(s)
+    end
+  end
+
   def test_readpartial_buffer_error
     with_pipe do |r, w|
       s = ""
@@ -1527,6 +1534,13 @@ class TestIO < Test::Unit::TestCase
     end)
   end
 
+  def test_read_zero_size
+    File.open(IO::NULL) do |r|
+      assert_empty(r.read(0, s = "01234567"))
+      assert_empty(s)
+    end
+  end
+
   def test_read_buffer_error
     with_pipe do |r, w|
       s = ""
@@ -1564,6 +1578,13 @@ class TestIO < Test::Unit::TestCase
     }
   end
 
+  def test_read_nonblock_zero_size
+    File.open(IO::NULL) do |r|
+      assert_empty(r.read_nonblock(0, s = "01234567"))
+      assert_empty(s)
+    end
+  end
+
   def test_write_nonblock_simple_no_exceptions
     pipe(proc do |w|
       w.write_nonblock('1', exception: false)
diff --git a/version.h b/version.h
index 924fe5a599..aeaeaeb323 100644
--- a/version.h
+++ b/version.h
@@ -12,7 +12,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 4
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 186
+#define RUBY_PATCHLEVEL 187
 
 #define RUBY_RELEASE_YEAR 2022
 #define RUBY_RELEASE_MONTH 3