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Use disallow instantiation flag for classes without the __new__ method #4568

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Use disallow instantiation flag for classes without the __new__ method #4568

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07389fa
Use disallow instantiation flag for classes without the __new__ method
ahlinc Sep 19, 2024
9bd1576
fix tests
ahlinc Sep 19, 2024
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15 changes: 10 additions & 5 deletions pytests/tests/test_pyclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -71,9 +71,16 @@ def __new__(cls):


@pytest.mark.parametrize(
"cls", [pyclasses.ClassWithoutConstructor, ClassWithoutConstructor]
"cls, exc_message",
[
(
pyclasses.ClassWithoutConstructor,
"cannot create 'builtins.ClassWithoutConstructor' instances",
),
(ClassWithoutConstructor, "No constructor defined for ClassWithoutConstructor"),
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This type is defined just above; we can change the message to match the expected Rust one to simplify the test. (Then there's just the differences across versions.)

],
)
def test_no_constructor_defined_propagates_cause(cls: Type):
def test_no_constructor_defined_propagates_cause(cls: Type, exc_message: str):
original_error = ValueError("Original message")
with pytest.raises(Exception) as exc_info:
try:
Expand All @@ -82,9 +89,7 @@ def test_no_constructor_defined_propagates_cause(cls: Type):
cls() # should raise TypeError("No constructor defined for ...")

assert exc_info.type is TypeError
assert exc_info.value.args == (
"No constructor defined for ClassWithoutConstructor",
)
assert exc_info.value.args == (exc_message,)
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This test will be run on all of Python 3.7 through 3.13, so I think the parameterized test is a good start but this will need to account for the variety between versions too.

assert exc_info.value.__context__ is original_error


Expand Down
12 changes: 10 additions & 2 deletions src/pyclass/create_type_object.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -428,8 +428,15 @@ impl PyTypeBuilder {
unsafe { self.push_slot(ffi::Py_tp_base, self.tp_base) }

if !self.has_new {
// Safety: This is the correct slot type for Py_tp_new
unsafe { self.push_slot(ffi::Py_tp_new, no_constructor_defined as *mut c_void) }
#[cfg(not(Py_3_10))]
{
// Safety: This is the correct slot type for Py_tp_new
unsafe { self.push_slot(ffi::Py_tp_new, no_constructor_defined as *mut c_void) }
}
#[cfg(Py_3_10)]
{
self.class_flags |= ffi::Py_TPFLAGS_DISALLOW_INSTANTIATION;
}
}

let tp_dealloc = if self.has_traverse || unsafe { ffi::PyType_IS_GC(self.tp_base) == 1 } {
Expand Down Expand Up @@ -523,6 +530,7 @@ fn bpo_45315_workaround(py: Python<'_>, class_name: CString) {
}

/// Default new implementation
#[cfg(not(Py_3_10))]
unsafe extern "C" fn no_constructor_defined(
subtype: *mut ffi::PyTypeObject,
_args: *mut ffi::PyObject,
Expand Down
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