merge revision(s) 6370674: [Backport #20752]

	[Bug #20752] Slice of readonly `IO::Buffer` also should be readonly

Author: k0kubun

io_buffer.c

@@ -1532,6 +1532,7 @@ rb_io_buffer_slice(struct rb_io_buffer *buffer, VALUE self, size_t offset, size_
     struct rb_io_buffer *slice = NULL;
     TypedData_Get_Struct(instance, struct rb_io_buffer, &rb_io_buffer_type, slice);
 
+    slice->flags |= (buffer->flags & RB_IO_BUFFER_READONLY);
     slice->base = (char*)buffer->base + offset;
     slice->size = length;
 

test/ruby/test_io_buffer.rb

@@ -236,6 +236,18 @@ def test_slice_bounds_error
     end
   end
 
+  def test_slice_readonly
+    hello = %w"Hello World".join(" ").freeze
+    buffer = IO::Buffer.for(hello)
+    slice = buffer.slice
+    assert_predicate slice, :readonly?
+    assert_raise IO::Buffer::AccessError do
+      # This breaks the literal in string pool and many other tests in this file.
+      slice.set_string("Adios", 0, 5)
+    end
+    assert_equal "Hello World", hello
+  end
+
   def test_locked
     buffer = IO::Buffer.new(128, IO::Buffer::INTERNAL|IO::Buffer::LOCKED)
 

version.h

@@ -11,7 +11,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 5
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 104
+#define RUBY_PATCHLEVEL 105
 
 #include "ruby/version.h"
 #include "ruby/internal/abi.h"