[BUG] ctuple declaration on inherited membed function when parent class imported .pxd yields "Signature not compatible with previous declaration" error

[raffienficiaud]

Describe the bug

When we declare a class that derives from another class, and some member functions are inherited, the return type of the inherited member does not accept a declaration as a ctuple. In that case cythonize returns an error indicating

Signature not compatible with previous declaration

It works perfectly with simpler types that do not have a parenthesis (such as tuple, double...) and it also works when the parent and child class are within the same .pyx file.

Code to reproduce the behaviour:

The following does not work
parent.pxd

# cython: language_level=3

cdef class Parent:
    cpdef (double, double) func(self, double[:] a, double[:] b)

and child.pyx

# cython: language_level=3

from parent cimport Parent

cdef class Child(Parent):
    cpdef (double, double) func(self, double[:] a, double[:] b):
        return 0,1

---

The following works:

parent.pxd

# cython: language_level=3

cdef class Parent:
    cpdef tuple func(self, double[:] a, double[:] b)

and child.pyx

# cython: language_level=3
from parent cimport Parent

cdef class Child(Parent):
    cpdef tuple func(self, double[:] a, double[:] b):
        return 0,1

---

The following works:

child.pxd # note here this is "child.pxd" and not "parent.pxd"

# cython: language_level=3

cdef class Parent:
    cpdef (double, double) func(self, double[:] a, double[:] b)

and child.pyx

# cython: language_level=3

cdef class Parent:
    cpdef (double, double) func(self, double[:] a, double[:] b):
        pass


cdef class Child(Parent):
    cpdef (double, double) func(self, double[:] a, double[:] b):
        return 0,1

Expected behaviour

The return type of the inherited member function can always be ctuple even if/when we are spanning several cython modules.

OS

No response

Python version

3.11

Cython version

3.0.10

Additional context

The command for running is simply cythonize child.pyx