leading_coefficient() for multivariate polynomials exists but fails with a strange error

[mezzarobba]

Steps To Reproduce

sage: P.<x,y> = QQ[]
sage: x.leading_coefficient()

Expected Behavior

Not sure. I think the method is new (i.e. this used to raise an AttributeError). It should probably do the same as lc(), at least if the definitions are compatible.

Actual Behavior

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
File ~/co/sage/src/sage/categories/modules_with_basis.py:1676, in ModulesWithBasis.ElementMethods.support(self)
   1675 try:
-> 1676     return self._support_view
   1677 except AttributeError:

File ~/co/sage/src/sage/structure/element.pyx:495, in sage.structure.element.Element.__getattr__()
    494 """
--> 495 return self.getattr_from_category(name)
    496

File ~/co/sage/src/sage/structure/element.pyx:508, in sage.structure.element.Element.getattr_from_category()
    507     cls = P._abstract_element_class
--> 508 return getattr_from_other_class(self, cls, name)
    509

File ~/co/sage/src/sage/cpython/getattr.pyx:363, in sage.cpython.getattr.getattr_from_other_class()
    362     dummy_error_message.name = name
--> 363     raise AttributeError(dummy_error_message)
    364 attribute = <object>attr

AttributeError: 'sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular' object has no attribute '_support_view'

During handling of the above exception, another exception occurred:

TypeError                                 Traceback (most recent call last)
Cell In[2], line 1
----> 1 x.leading_coefficient()

File ~/co/sage/src/sage/categories/modules_with_basis.py:1923, in ModulesWithBasis.ElementMethods.leading_coefficient(self, *args, **kwds)
   1896 def leading_coefficient(self, *args, **kwds):
   1897     r"""
   1898     Return the leading coefficient of ``self``.
   1899
   (...)
   1921         -5
   1922     """
-> 1923     return self.leading_item(*args, **kwds)[1]

File ~/co/sage/src/sage/categories/modules_with_basis.py:1864, in ModulesWithBasis.ElementMethods.leading_item(self, *args, **kwds)
   1831 def leading_item(self, *args, **kwds):
   1832     r"""
   1833     Return the pair ``(k, c)`` where
   1834
   (...)
   1862         ([3], -5)
   1863     """
-> 1864     k = self.leading_support(*args, **kwds)
   1865     return k, self[k]

File ~/co/sage/src/sage/categories/modules_with_basis.py:1829, in ModulesWithBasis.ElementMethods.leading_support(self, *args, **kwds)
   1802 def leading_support(self, *args, **kwds):
   1803     r"""
   1804     Return the maximal element of the support of ``self``.
   1805
   (...)
   1827         [3]
   1828     """
-> 1829     return max(self.support(), *args, **kwds)

File ~/co/sage/src/sage/categories/modules_with_basis.py:1680, in ModulesWithBasis.ElementMethods.support(self)
   1678 from sage.structure.support_view import SupportView
   1679 zero = self.parent().base_ring().zero()
-> 1680 mc = self.monomial_coefficients(copy=False)
   1681 support_view = SupportView(mc, zero=zero)
   1682 try:
   1683     # Try to cache it for next time, but this may fail for Cython classes

TypeError: monomial_coefficients() got an unexpected keyword argument 'copy'

Additional Information

Probably an unintended consequence of #38767. The same issue likely applies to leading_monomial() and possibly some other methods.

Environment

Sage 10.5.rc0

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide

[fchapoton]

@mantepse : is this a side effect of your recent changes ?

[mantepse]

I am I'll but can check once I've recovered. Very likely, yes.