From d74ed5a29e78fd0c1e425bbd7345fa0d7fecb35a Mon Sep 17 00:00:00 2001
From: Ethan Sarp <11684270+esarp@users.noreply.github.com>
Date: Fri, 19 Dec 2025 16:02:31 -0600
Subject: [PATCH] [mypyc] Implement bytes.endswith

---
 mypyc/lib-rt/CPy.h                 |  2 +-
 mypyc/lib-rt/bytes_ops.c           | 38 ++++++++++++++++++++++++++++++
 mypyc/primitives/bytes_ops.py      | 10 ++++++++
 mypyc/test-data/fixtures/ir.py     |  2 ++
 mypyc/test-data/irbuild-bytes.test | 13 ++++++++++
 mypyc/test-data/run-bytes.test     | 21 +++++++++++++++++
 6 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/mypyc/lib-rt/CPy.h b/mypyc/lib-rt/CPy.h
index df251da13fe5..488772d883c9 100644
--- a/mypyc/lib-rt/CPy.h
+++ b/mypyc/lib-rt/CPy.h
@@ -784,7 +784,7 @@ PyObject *CPyBytes_Join(PyObject *sep, PyObject *iter);
 CPyTagged CPyBytes_Ord(PyObject *obj);
 PyObject *CPyBytes_Multiply(PyObject *bytes, CPyTagged count);
 int CPyBytes_Startswith(PyObject *self, PyObject *subobj);
-
+int CPyBytes_Endswith(PyObject *self, PyObject *subobj);
 int CPyBytes_Compare(PyObject *left, PyObject *right);
 
 
diff --git a/mypyc/lib-rt/bytes_ops.c b/mypyc/lib-rt/bytes_ops.c
index 25718b4603b3..e4122013cb0f 100644
--- a/mypyc/lib-rt/bytes_ops.c
+++ b/mypyc/lib-rt/bytes_ops.c
@@ -209,3 +209,41 @@ int CPyBytes_Startswith(PyObject *self, PyObject *subobj) {
     }
     return ret;
 }
+
+int CPyBytes_Endswith(PyObject *self, PyObject *subobj) {
+    if (PyBytes_CheckExact(self) && PyBytes_CheckExact(subobj)) {
+        if (self == subobj) {
+            return 1;
+        }
+
+        Py_ssize_t subobj_len = PyBytes_GET_SIZE(subobj);
+        if (subobj_len == 0) {
+            return 1;
+        }
+
+        Py_ssize_t self_len = PyBytes_GET_SIZE(self);
+        if (subobj_len > self_len) {
+            return 0;
+        }
+
+        const char *self_buf = PyBytes_AS_STRING(self);
+        const char *subobj_buf = PyBytes_AS_STRING(subobj);
+
+        return memcmp(self_buf + (self_len - subobj_len), subobj_buf, (size_t)subobj_len) == 0 ? 1 : 0;
+    }
+    _Py_IDENTIFIER(endswith);
+    PyObject *name = _PyUnicode_FromId(&PyId_endswith);
+    if (name == NULL) {
+        return 2;
+    }
+    PyObject *result = PyObject_CallMethodOneArg(self, name, subobj);
+    if (result == NULL) {
+        return 2;
+    }
+    int ret = PyObject_IsTrue(result);
+    Py_DECREF(result);
+    if (ret < 0) {
+        return 2;
+    }
+    return ret;
+}
diff --git a/mypyc/primitives/bytes_ops.py b/mypyc/primitives/bytes_ops.py
index 728da4181135..05880bedad39 100644
--- a/mypyc/primitives/bytes_ops.py
+++ b/mypyc/primitives/bytes_ops.py
@@ -150,6 +150,16 @@
     error_kind=ERR_MAGIC,
 )
 
+# bytes.endswith(bytes)
+method_op(
+    name="endswith",
+    arg_types=[bytes_rprimitive, bytes_rprimitive],
+    return_type=c_int_rprimitive,
+    c_function_name="CPyBytes_Endswith",
+    truncated_type=bool_rprimitive,
+    error_kind=ERR_MAGIC,
+)
+
 # Join bytes objects and return a new bytes.
 # The first argument is the total number of the following bytes.
 bytes_build_op = custom_op(
diff --git a/mypyc/test-data/fixtures/ir.py b/mypyc/test-data/fixtures/ir.py
index 592f6676e95e..8aaadc238fe6 100644
--- a/mypyc/test-data/fixtures/ir.py
+++ b/mypyc/test-data/fixtures/ir.py
@@ -180,6 +180,7 @@ def join(self, x: Iterable[object]) -> bytes: ...
     def decode(self, encoding: str=..., errors: str=...) -> str: ...
     def translate(self, t: bytes) -> bytes: ...
     def startswith(self, t: bytes) -> bool: ...
+    def endswith(self, t: bytes) -> bool: ...
     def __iter__(self) -> Iterator[int]: ...
 
 class bytearray:
@@ -194,6 +195,7 @@ def __setitem__(self, i: int, o: int) -> None: ...
     def __getitem__(self, i: int) -> int: ...
     def decode(self, x: str = ..., y: str = ...) -> str: ...
     def startswith(self, t: bytes) -> bool: ...
+    def endswith(self, t: bytes) -> bool: ...
 
 class bool(int):
     def __init__(self, o: object = ...) -> None: ...
diff --git a/mypyc/test-data/irbuild-bytes.test b/mypyc/test-data/irbuild-bytes.test
index 5e7c546eb25a..e454994d4492 100644
--- a/mypyc/test-data/irbuild-bytes.test
+++ b/mypyc/test-data/irbuild-bytes.test
@@ -261,3 +261,16 @@ L0:
     r0 = CPyBytes_Startswith(a, b)
     r1 = truncate r0: i32 to builtins.bool
     return r1
+
+[case testBytesEndsWith]
+def f(a: bytes, b: bytes) -> bool:
+    return a.endswith(b)
+[out]
+def f(a, b):
+    a, b :: bytes
+    r0 :: i32
+    r1 :: bool
+L0:
+    r0 = CPyBytes_Endswith(a, b)
+    r1 = truncate r0: i32 to builtins.bool
+    return r1
diff --git a/mypyc/test-data/run-bytes.test b/mypyc/test-data/run-bytes.test
index 6e4b57152a4b..35679685f4cb 100644
--- a/mypyc/test-data/run-bytes.test
+++ b/mypyc/test-data/run-bytes.test
@@ -221,6 +221,27 @@ def test_startswith() -> None:
     assert test.startswith(b'some')
     assert not test.startswith(b'other')
 
+def test_endswith() -> None:
+    # Test default behavior
+    test = b'some string'
+    assert test.endswith(b'string')
+    assert test.endswith(b'some string')
+    assert not test.endswith(b'other')
+    assert not test.endswith(b'some string but longer')
+
+    # Test empty cases
+    assert test.endswith(b'')
+    assert b''.endswith(b'')
+    assert not b''.endswith(test)
+
+    # Test bytearray to verify slow paths
+    assert test.endswith(bytearray(b'string'))
+    assert not test.endswith(bytearray(b'other'))
+
+    test = bytearray(b'some string')
+    assert test.endswith(b'string')
+    assert not test.endswith(b'other')
+
 [case testBytesSlicing]
 def test_bytes_slicing() -> None:
     b = b'abcdefg'