From aaa0f5f82201f2f4944f73d05961731f99856420 Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Fri, 30 Jan 2026 15:19:09 -0800
Subject: [PATCH] Add tests for bytes narrowing

---
 mypy/checker.py                     |  1 -
 test-data/unit/check-narrowing.test | 77 +++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index d371f40ccaae..09f69d5a2c3b 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -8630,7 +8630,6 @@ def reduce_and_conditional_type_maps(ms: list[TypeMap], *, use_meet: bool) -> Ty
 
 
 BUILTINS_CUSTOM_EQ_CHECKS: Final = {
-    "builtins.bytes",
     "builtins.bytearray",
     "builtins.memoryview",
     "builtins.list",
diff --git a/test-data/unit/check-narrowing.test b/test-data/unit/check-narrowing.test
index b9bb0c1efa6a..74ddfdf9fff5 100644
--- a/test-data/unit/check-narrowing.test
+++ b/test-data/unit/check-narrowing.test
@@ -3389,3 +3389,80 @@ def foo(x: str | array) -> str:
         return result
     raise
 [builtins fixtures/tuple.pyi]
+
+[case testNarrowingOptionalBytes]
+from __future__ import annotations
+def f(x: bytes | None):
+    if x == b"asdf":
+        reveal_type(x)  # N: Revealed type is "builtins.bytes"
+    else:
+        reveal_type(x)  # N: Revealed type is "builtins.bytes | None"
+[builtins fixtures/primitives.pyi]
+
+[case testNarrowingBytesLikeWithPromotion]
+# flags: --strict-equality --warn-unreachable --strict-bytes
+from __future__ import annotations
+
+def check_test(x: bytes) -> None: ...
+check_test(bytearray(b"asdf"))  # E: Argument 1 to "check_test" has incompatible type "bytearray"; expected "bytes"
+
+def main(
+    v_bytes: bytes,
+    v_bytearray: bytearray,
+    v_memoryview: memoryview,
+    v_all: bytes | bytearray | memoryview,
+) -> None:
+    if v_bytes == v_bytearray:
+        reveal_type(v_bytes)  # N: Revealed type is "builtins.bytes"
+        reveal_type(v_bytearray)  # N: Revealed type is "builtins.bytearray"
+    if v_bytes == v_memoryview:
+        reveal_type(v_bytes)  # N: Revealed type is "builtins.bytes"
+        reveal_type(v_memoryview)  # N: Revealed type is "builtins.memoryview"
+    if v_bytearray == v_memoryview:
+        reveal_type(v_bytearray)  # N: Revealed type is "builtins.bytearray"
+        reveal_type(v_memoryview)  # N: Revealed type is "builtins.memoryview"
+
+    if v_all == v_bytes:
+        reveal_type(v_all)  # N: Revealed type is "builtins.bytes"
+        reveal_type(v_bytes)  # N: Revealed type is "builtins.bytes"
+    if v_all == v_bytearray:
+        reveal_type(v_all)  # N: Revealed type is "builtins.bytes | builtins.bytearray | builtins.memoryview"
+        reveal_type(v_bytearray)  # N: Revealed type is "builtins.bytearray"
+    if v_all == v_memoryview:
+        reveal_type(v_all)  # N: Revealed type is "builtins.bytes | builtins.bytearray | builtins.memoryview"
+        reveal_type(v_memoryview)  # N: Revealed type is "builtins.memoryview"
+[builtins fixtures/primitives.pyi]
+
+[case testNarrowingBytesLikeNoPromotion]
+# flags: --strict-equality --warn-unreachable --no-strict-bytes
+from __future__ import annotations
+
+def check_test(x: bytes) -> None: ...
+check_test(bytearray(b"asdf"))
+
+def main(
+    v_bytes: bytes,
+    v_bytearray: bytearray,
+    v_memoryview: memoryview,
+    v_all: bytes | bytearray | memoryview,
+) -> None:
+    if v_bytes == v_bytearray:
+        reveal_type(v_bytes)  # N: Revealed type is "builtins.bytes"
+        reveal_type(v_bytearray)  # N: Revealed type is "builtins.bytearray"
+    if v_bytes == v_memoryview:
+        reveal_type(v_bytes)  # N: Revealed type is "builtins.bytes"
+        reveal_type(v_memoryview)  # N: Revealed type is "builtins.memoryview"
+    if v_bytearray == v_memoryview:
+        reveal_type(v_bytearray)  # N: Revealed type is "builtins.bytearray"
+        reveal_type(v_memoryview)  # N: Revealed type is "builtins.memoryview"
+
+    if v_all == v_bytes:
+        reveal_type(v_all)  # N: Revealed type is "builtins.bytes"
+        reveal_type(v_bytes)  # N: Revealed type is "builtins.bytes"
+    if v_all == v_bytearray:
+        reveal_type(v_all)  # N: Revealed type is "builtins.bytes | builtins.bytearray | builtins.memoryview"
+        reveal_type(v_bytearray)  # N: Revealed type is "builtins.bytearray"
+    if v_all == v_memoryview:
+        reveal_type(v_all)  # N: Revealed type is "builtins.bytes | builtins.bytearray | builtins.memoryview"
+        reveal_type(v_memoryview)  # N: Revealed type is "builtins.memoryview"
+[builtins fixtures/primitives.pyi]