Implement bytes.__bytes__

This commit implement `bytes.__bytes__` in cpython 3.11 for typing
module.

* https://docs.python.org/3.11/whatsnew/3.11.html#other-cpython-implementation-changes
* https://bugs.python.org/issue24234

Signed-off-by: snowapril <sinjihng@gmail.com>

extra_tests/snippets/bytes.py

@@ -615,6 +615,16 @@ assert b'\xe4\xb8\xad\xe6\x96\x87\xe5\xad\x97'.decode('utf-8') == '中文字'
 assert b'rust%bpython%b' % (b' ', b'!') == b'rust python!'
 assert b'x=%i y=%f' % (1, 2.5) == b'x=1 y=2.500000'
 
+# __bytes__
+foo = b'foo\x00bar'
+assert foo.__bytes__() == foo
+assert type(foo.__bytes__()) == bytes
+class bytes_subclass(bytes):
+    pass
+bar = bytes_subclass(b'bar\x00foo')
+assert bar.__bytes__() == bar
+assert type(bar.__bytes__()) == bytes
+
 class A:
     def __bytes__(self):
         return b"bytess"

vm/src/builtins/bytes.rs

@@ -128,6 +128,15 @@ impl PyBytes {
         &self.inner.elements
     }
 
+    #[pymethod(magic)]
+    fn bytes(zelf: PyRef<Self>, vm: &VirtualMachine) -> PyRef<Self> {
+        if zelf.is(&vm.ctx.types.bytes_type) {
+            zelf
+        } else {
+            PyBytes::from(zelf.inner.clone()).into_ref(vm)
+        }
+    }
+
     #[pymethod(magic)]
     fn sizeof(&self) -> usize {
         size_of::<Self>() + self.inner.elements.len() * size_of::<u8>()