Transform.relabeled_clone calls own constructor with wrong number of arguments

[ris]

In ​https://github.com/django/django/blob/1.7/django/db/models/lookups.py#L71 :

    def relabeled_clone(self, relabels):
        return self.__class__(self.lhs.relabeled_clone(relabels))

relabeled_clone here calls Transform's own constructor with one argument (ignoring bound self), but (​https://github.com/django/django/blob/1.7/django/db/models/lookups.py#L59):

    def __init__(self, lhs, lookups):
        self.lhs = lhs
        self.init_lookups = lookups[:]

init takes two (non-bound) arguments, so this screws up when you try and use a QuerySet employing a custom Transform as a subquery.

[Akis Kesoglou]

I'm marking the ticket as accepted based on the discussion with @akaariai in #django-dev.

[ris]

Updating this with example models.py for creating this failure:

from django.db import models
from django.db.models import Transform

class Sqrt ( Transform ):
	lookup_name = "sqrt"

	def as_sql ( self , qn , connection ):
		lhs , params = qn.compile ( self.lhs )
		return "sqrt(%s)" % lhs , params
models.FloatField.register_lookup ( Sqrt )

class ModelA ( models.Model ):
	x = models.FloatField ()

class ModelB ( models.Model ):
	a = models.ForeignKey ( ModelA )

Issuing the query:

ModelB.objects.filter ( a__pk__in = ModelA.objects.filter ( x__sqrt__lt = 5 ) )

raises the above exception.

I've used this test case to verify that this bug is still present in django 1.8.2.

[ris]

This appears to be fixed in commit 08232ef84d4959826ad5136f183c9fc5bedf0599 (also backported to 1.8.x @ b4b13759f82e9e09951bb72875b1c6e384dca6a9). Closing.