From 37f66dd998281f47d7490d2ba4202d20177b4dca Mon Sep 17 00:00:00 2001
From: sobolevn <mail@sobolevn.me>
Date: Wed, 11 Aug 2021 21:53:52 +0300
Subject: [PATCH] `id()` for `bytes` stays the same after `* 1`, refs #2840

---
 extra_tests/snippets/bytes.py | 24 +++++++++++++++++++++++-
 vm/src/builtins/bytes.rs      | 18 +++++++++++++-----
 2 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/extra_tests/snippets/bytes.py b/extra_tests/snippets/bytes.py
index 3a9ca55d4..00723ad94 100644
--- a/extra_tests/snippets/bytes.py
+++ b/extra_tests/snippets/bytes.py
@@ -623,4 +623,26 @@ assert bytes(A()) == b"bytess"
 
 # Issue #2125
 b = b'abc'
-assert bytes(b) is b
\ No newline at end of file
+assert bytes(b) is b
+
+
+# Regression to
+# https://github.com/RustPython/RustPython/issues/2840
+
+a = b'123abc!?'
+assert id(a) == id(a)
+assert id(a) != id(a * -1)
+assert id(a) != id(a * 0)
+assert id(a) == id(a * 1)  # only case when `id` stays the same
+assert id(a) != id(a * 2)
+
+
+class SubBytes(bytes):
+    pass
+
+b = SubBytes(b'0123abc*&')
+assert id(b) == id(b)
+assert id(b) != id(b * -1)
+assert id(b) != id(b * 0)
+assert id(b) != id(b * 1)
+assert id(b) != id(b * 2)
diff --git a/vm/src/builtins/bytes.rs b/vm/src/builtins/bytes.rs
index cc829539e..e39254a10 100644
--- a/vm/src/builtins/bytes.rs
+++ b/vm/src/builtins/bytes.rs
@@ -21,8 +21,8 @@ use crate::slots::{BufferProtocol, Comparable, Hashable, Iterable, PyComparisonO
 use crate::utils::Either;
 use crate::vm::VirtualMachine;
 use crate::{
-    IntoPyObject, PyClassImpl, PyComparisonValue, PyContext, PyIterable, PyObjectRef, PyRef,
-    PyResult, PyValue, TryFromObject, TypeProtocol,
+    IdProtocol, IntoPyObject, PyClassImpl, PyComparisonValue, PyContext, PyIterable, PyObjectRef,
+    PyRef, PyResult, PyValue, TryFromObject, TypeProtocol,
 };
 
 use crate::builtins::memory::{BufferOptions, PyBuffer};
@@ -430,11 +430,19 @@ impl PyBytes {
 
     #[pymethod(name = "__mul__")]
     #[pymethod(name = "__rmul__")]
-    fn mul(&self, value: isize, vm: &VirtualMachine) -> PyResult<PyBytes> {
-        if value > 0 && self.inner.len() as isize > std::isize::MAX / value {
+    fn mul(zelf: PyRef<Self>, value: isize, vm: &VirtualMachine) -> PyResult<PyRef<Self>> {
+        if value > 0 && zelf.inner.len() as isize > std::isize::MAX / value {
             return Err(vm.new_overflow_error("repeated bytes are too long".to_owned()));
         }
-        Ok(self.inner.repeat(value).into())
+        if value == 1 && zelf.class().is(&vm.ctx.types.bytes_type) {
+            // Special case: when some `bytes` is multiplied by `1`,
+            // nothing really happens, we need to return an object itself
+            // with the same `id()` to be compatible with CPython.
+            // This only works for `bytes` itself, not its subclasses.
+            return Ok(zelf);
+        }
+        let bytes: PyBytes = zelf.inner.repeat(value).into();
+        Ok(bytes.into_ref(vm))
     }
 
     #[pymethod(name = "__mod__")]