Var, Call and other constructs in default rule

[anakrish]

I'm trying to understand which constructs are supported in a default rule.

The following errors out rego_parse_error: illegal default rule (value cannot contain var) https://play.openpolicyagent.org/p/t21XFFhcNN

package test
a = 8
default b = [a]

However, constructs work if enclosed within a comprehension in the default rule's value:
https://play.openpolicyagent.org/p/lOdShubvHT

package test
a = 8
default b = [x | startswith("pq", "p"); x = a ]

Is there a design rationale as to why the constructs are supported when enclosed within a comprehension?

[anderseknert]

Hi @anakrish 👋 That's an interesting observation! I would believe that to be a bug. Trying your example I had no problems depending on input, data and built-in functions inside of the comprehension, creating non-deterministic default values. I don't think that should ever work. I'll create an issue.

[anderseknert]

Created issue open-policy-agent/opa#5645