BUG: DType reference leak in _convert_from_type (descriptor.c) #31676

Bug Description

In numpy/_core/src/multiarray/descriptor.c, PyArray_DiscoverDTypeFromScalarType returns a new reference, but PyArray_GetDefaultDescr does NOT steal it. The DType reference is leaked unconditionally.

Location

numpy/_core/src/multiarray/descriptor.c:1599-1601

Code

PyObject *DType = PyArray_DiscoverDTypeFromScalarType(typ);  // NEW REF
if (DType != NULL) {
    return PyArray_GetDefaultDescr((PyArray_DTypeMeta *)DType);  // DType LEAKED!
}

Impact

PyArray_GetDefaultDescr returns a new reference (via Py_INCREF or NPY_DT_CALL_default_descr). It does NOT steal the DType reference. Therefore DType is leaked on every successful call to _convert_from_type with a scalar type. This triggers on every custom scalar type → dtype conversion.

Suggested Fix

PyObject *DType = PyArray_DiscoverDTypeFromScalarType(typ);
if (DType != NULL) {
    PyArray_Descr *ret = PyArray_GetDefaultDescr((PyArray_DTypeMeta *)DType);
    Py_DECREF(DType);
    return ret;
}

Environment

• NumPy version: current main
• Affected: numpy.dtype() conversions from custom scalar types