SQLite doesn't like double parens

[jhorman]

This sample program shows the problem

from peewee import Model
from peewee import fn
from peewee import SqliteDatabase

db = SqliteDatabase(':memory:')

class User(Model):
    class Meta:
        db = db

User.create_table()

list(User.select().where(fn.Exists(User.select(User.id))))

Func always wraps the nodes in parens: https:/coleifer/peewee/blob/2.2.5/peewee.py#L1141

And nested selects are always in parens: https:/coleifer/peewee/blob/2.2.5/peewee.py#L1174

One approach might just be in the isinstance(node, Func) detect if the sql to wrap already startswith('(') and endswith(')'), but maybe there is something more clever.

[coleifer]

SELECT t1."id"
FROM "users" AS t1 
WHERE Exists((SELECT t2."id" FROM "users" AS t2))

[jhorman]

Nice, thanks!