F() expressions don't retain parentheses into final SQL

[Russell Keith-Magee]

Reported by Brent Hagany on django-users:

I'm having some trouble getting F() expressions to obey my parentheses
when I don't want the default order of operations. For example, given
the model:

class MyModel(models.Model):
   wins = models.DecimalField(max_digits=1, decimal_places=0)
   losses = models.DecimalField(max_digits=1, decimal_places=0)
   win_percentage = models.DecimalField(max_digits=4, decimal_places=3, default=Decimal('0.000'))

I get the following results when trying to calculate the
win_percentage:

In [1]: MyModel.objects.create(wins=2, losses=4)
Out[1]: <MyModel: MyModel object>

In [2]: MyModel.objects.all().update(win_percentage=F('wins') / (F
('wins') + F('losses')))
Out[2]: 1

# I expect this to return Decimal("0.333")
In [3]: MyModel.objects.get(pk=1).win_percentage
Out[3]: Decimal("5.000")

It appears to be ignoring the parentheses around F('wins') + F
('losses'), and so instead of 2 / (2 + 4) = .333, I'm getting 2 / 2 +
4 = 5.

[Russell Keith-Magee]

(In [11581]) Fixed #11886 -- Corrected handling of F() expressions that use parentheses. Thanks to Brent Hagany for the report.

[Russell Keith-Magee]

(In [11582]) [1.1.X] Fixed #11886 -- Corrected handling of F() expressions that use parentheses. Thanks to Brent Hagany for the report.

Merge of r11581 from trunk.