Fix #3812 and fix const of inplace assignments (#4065)

* Fix #3812 and fix const of inplace assignments

* Fix missing tests

* Revert operator overloading changes

* calculate answer first for tests

* Simplify tests

* Add more tests

* Add a couple more tests

* Add test_inplace_lshift, test_inplace_rshift for completeness.

* Update tests

* Shortcircuit on self assigment and address reviewer comment

* broaden skip for self assignment

* One more reviewer comment

* Document opt behavior and make consistent

* Revert unnecessary change

* Clarify comment

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>

include/pybind11/pytypes.h

@@ -155,23 +155,23 @@ public:
     object operator-() const;
     object operator~() const;
     object operator+(object_api const &other) const;
-    object operator+=(object_api const &other) const;
+    object operator+=(object_api const &other);
     object operator-(object_api const &other) const;
-    object operator-=(object_api const &other) const;
+    object operator-=(object_api const &other);
     object operator*(object_api const &other) const;
-    object operator*=(object_api const &other) const;
+    object operator*=(object_api const &other);
     object operator/(object_api const &other) const;
-    object operator/=(object_api const &other) const;
+    object operator/=(object_api const &other);
     object operator|(object_api const &other) const;
-    object operator|=(object_api const &other) const;
+    object operator|=(object_api const &other);
     object operator&(object_api const &other) const;
-    object operator&=(object_api const &other) const;
+    object operator&=(object_api const &other);
     object operator^(object_api const &other) const;
-    object operator^=(object_api const &other) const;
+    object operator^=(object_api const &other);
     object operator<<(object_api const &other) const;
-    object operator<<=(object_api const &other) const;
+    object operator<<=(object_api const &other);
     object operator>>(object_api const &other) const;
-    object operator>>=(object_api const &other) const;
+    object operator>>=(object_api const &other);
 
     PYBIND11_DEPRECATED("Use py::str(obj) instead")
     pybind11::str str() const;
@@ -334,12 +334,15 @@ public:
     }
 
     object &operator=(const object &other) {
+        // Skip inc_ref and dec_ref if both objects are the same
+        if (!this->is(other)) {
             other.inc_ref();
             // Use temporary variable to ensure `*this` remains valid while
             // `Py_XDECREF` executes, in case `*this` is accessible from Python.
             handle temp(m_ptr);
             m_ptr = other.m_ptr;
             temp.dec_ref();
+        }
         return *this;
     }
 
@@ -353,6 +356,20 @@ public:
         return *this;
     }
 
+#define PYBIND11_INPLACE_OP(iop)                                                                  \
+    object iop(object_api const &other) { return operator=(handle::iop(other)); }
+
+    PYBIND11_INPLACE_OP(operator+=)
+    PYBIND11_INPLACE_OP(operator-=)
+    PYBIND11_INPLACE_OP(operator*=)
+    PYBIND11_INPLACE_OP(operator/=)
+    PYBIND11_INPLACE_OP(operator|=)
+    PYBIND11_INPLACE_OP(operator&=)
+    PYBIND11_INPLACE_OP(operator^=)
+    PYBIND11_INPLACE_OP(operator<<=)
+    PYBIND11_INPLACE_OP(operator>>=)
+#undef PYBIND11_INPLACE_OP
+
     // Calling cast() on an object lvalue just copies (via handle::cast)
     template <typename T>
     T cast() const &;
@@ -2364,26 +2381,35 @@ bool object_api<D>::rich_compare(object_api const &other, int value) const {
         return result;                                                                            \
     }
 
+#define PYBIND11_MATH_OPERATOR_BINARY_INPLACE(iop, fn)                                            \
+    template <typename D>                                                                         \
+    object object_api<D>::iop(object_api const &other) {                                          \
+        object result = reinterpret_steal<object>(fn(derived().ptr(), other.derived().ptr()));    \
+        if (!result.ptr())                                                                        \
+            throw error_already_set();                                                            \
+        return result;                                                                            \
+    }
+
 PYBIND11_MATH_OPERATOR_UNARY(operator~, PyNumber_Invert)
 PYBIND11_MATH_OPERATOR_UNARY(operator-, PyNumber_Negative)
 PYBIND11_MATH_OPERATOR_BINARY(operator+, PyNumber_Add)
-PYBIND11_MATH_OPERATOR_BINARY(operator+=, PyNumber_InPlaceAdd)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator+=, PyNumber_InPlaceAdd)
 PYBIND11_MATH_OPERATOR_BINARY(operator-, PyNumber_Subtract)
-PYBIND11_MATH_OPERATOR_BINARY(operator-=, PyNumber_InPlaceSubtract)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator-=, PyNumber_InPlaceSubtract)
 PYBIND11_MATH_OPERATOR_BINARY(operator*, PyNumber_Multiply)
-PYBIND11_MATH_OPERATOR_BINARY(operator*=, PyNumber_InPlaceMultiply)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator*=, PyNumber_InPlaceMultiply)
 PYBIND11_MATH_OPERATOR_BINARY(operator/, PyNumber_TrueDivide)
-PYBIND11_MATH_OPERATOR_BINARY(operator/=, PyNumber_InPlaceTrueDivide)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator/=, PyNumber_InPlaceTrueDivide)
 PYBIND11_MATH_OPERATOR_BINARY(operator|, PyNumber_Or)
-PYBIND11_MATH_OPERATOR_BINARY(operator|=, PyNumber_InPlaceOr)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator|=, PyNumber_InPlaceOr)
 PYBIND11_MATH_OPERATOR_BINARY(operator&, PyNumber_And)
-PYBIND11_MATH_OPERATOR_BINARY(operator&=, PyNumber_InPlaceAnd)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator&=, PyNumber_InPlaceAnd)
 PYBIND11_MATH_OPERATOR_BINARY(operator^, PyNumber_Xor)
-PYBIND11_MATH_OPERATOR_BINARY(operator^=, PyNumber_InPlaceXor)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator^=, PyNumber_InPlaceXor)
 PYBIND11_MATH_OPERATOR_BINARY(operator<<, PyNumber_Lshift)
-PYBIND11_MATH_OPERATOR_BINARY(operator<<=, PyNumber_InPlaceLshift)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator<<=, PyNumber_InPlaceLshift)
 PYBIND11_MATH_OPERATOR_BINARY(operator>>, PyNumber_Rshift)
-PYBIND11_MATH_OPERATOR_BINARY(operator>>=, PyNumber_InPlaceRshift)
+PYBIND11_MATH_OPERATOR_BINARY_INPLACE(operator>>=, PyNumber_InPlaceRshift)
 
 #undef PYBIND11_MATH_OPERATOR_UNARY
 #undef PYBIND11_MATH_OPERATOR_BINARY

tests/test_pytypes.cpp

@@ -756,4 +756,38 @@ TEST_SUBMODULE(pytypes, m) {
         }
         return o;
     });
+
+    // testing immutable object augmented assignment: #issue 3812
+    m.def("inplace_append", [](py::object &a, const py::object &b) {
+        a += b;
+        return a;
+    });
+    m.def("inplace_subtract", [](py::object &a, const py::object &b) {
+        a -= b;
+        return a;
+    });
+    m.def("inplace_multiply", [](py::object &a, const py::object &b) {
+        a *= b;
+        return a;
+    });
+    m.def("inplace_divide", [](py::object &a, const py::object &b) {
+        a /= b;
+        return a;
+    });
+    m.def("inplace_or", [](py::object &a, const py::object &b) {
+        a |= b;
+        return a;
+    });
+    m.def("inplace_and", [](py::object &a, const py::object &b) {
+        a &= b;
+        return a;
+    });
+    m.def("inplace_lshift", [](py::object &a, const py::object &b) {
+        a <<= b;
+        return a;
+    });
+    m.def("inplace_rshift", [](py::object &a, const py::object &b) {
+        a >>= b;
+        return a;
+    });
 }

tests/test_pytypes.py

@@ -739,3 +739,75 @@ def test_populate_obj_str_attrs():
     new_attrs = {k: v for k, v in new_o.__dict__.items() if not k.startswith("_")}
     assert all(isinstance(v, str) for v in new_attrs.values())
     assert len(new_attrs) == pop
+
+
+@pytest.mark.parametrize(
+    "a,b", [("foo", "bar"), (1, 2), (1.0, 2.0), (list(range(3)), list(range(3, 6)))]
+)
+def test_inplace_append(a, b):
+    expected = a + b
+    assert m.inplace_append(a, b) == expected
+
+
+@pytest.mark.parametrize("a,b", [(3, 2), (3.0, 2.0), (set(range(3)), set(range(2)))])
+def test_inplace_subtract(a, b):
+    expected = a - b
+    assert m.inplace_subtract(a, b) == expected
+
+
+@pytest.mark.parametrize("a,b", [(3, 2), (3.0, 2.0), ([1], 3)])
+def test_inplace_multiply(a, b):
+    expected = a * b
+    assert m.inplace_multiply(a, b) == expected
+
+
+@pytest.mark.parametrize("a,b", [(6, 3), (6.0, 3.0)])
+def test_inplace_divide(a, b):
+    expected = a / b
+    assert m.inplace_divide(a, b) == expected
+
+
+@pytest.mark.parametrize(
+    "a,b",
+    [
+        (False, True),
+        (
+            set(),
+            {
+                1,
+            },
+        ),
+    ],
+)
+def test_inplace_or(a, b):
+    expected = a | b
+    assert m.inplace_or(a, b) == expected
+
+
+@pytest.mark.parametrize(
+    "a,b",
+    [
+        (True, False),
+        (
+            {1, 2, 3},
+            {
+                1,
+            },
+        ),
+    ],
+)
+def test_inplace_and(a, b):
+    expected = a & b
+    assert m.inplace_and(a, b) == expected
+
+
+@pytest.mark.parametrize("a,b", [(8, 1), (-3, 2)])
+def test_inplace_lshift(a, b):
+    expected = a << b
+    assert m.inplace_lshift(a, b) == expected
+
+
+@pytest.mark.parametrize("a,b", [(8, 1), (-2, 2)])
+def test_inplace_rshift(a, b):
+    expected = a >> b
+    assert m.inplace_rshift(a, b) == expected