PersistentHashWalkMapper: do not ignore comparison operator

[matthiasdiener]

Consider the following example:

from pymbolic.primitives import Comparison, Variable

from pymbolic.mapper.persistent_hash import PersistentHashWalkMapper
from hashlib import sha256

expr1 = Comparison(Variable('_in0'), '<', Variable('_in1'))
expr2 = Comparison(Variable('_in0'), '>', Variable('_in1'))  # only differ in operator

pm1 = PersistentHashWalkMapper(sha256())
pm2 = PersistentHashWalkMapper(sha256())

pm1(expr1)
print(f"{pm1.key_hash.hexdigest()=}")

pm2(expr2)
print(f"{pm2.key_hash.hexdigest()=}")

before:

pm1.key_hash.hexdigest()='53780ab5ba3e7dc99573958a5a54fa8ed3f88972ab670832c1915653853bc0c4'
pm2.key_hash.hexdigest()='53780ab5ba3e7dc99573958a5a54fa8ed3f88972ab670832c1915653853bc0c4'  # same hash

after:

pm1.key_hash.hexdigest()='1a9b95805d65a0336e03cc7d8e2b7b2f335b1171b8d9e4743263ea2bc6e7763e'
pm2.key_hash.hexdigest()='9d3fa846784ec819667ea13b1447ef440dc994501a87c58f6fd9c0f66ddc4fbe'

(I guess there may be more occurrences of this kind of issue?)

[inducer]

Oh boy. 🤦 I didn't even know this PersistentHashWalkMapper is there. It's pretty awful. #125 should make that entirely unnecessary. I'll add code to #125 to deprecate it.