Compiler strict mode check for unused function arguments with else keyword

[ethanjli]

Hi! I'm trying out OPA v0.50.0 with strict mode enabled on the compiler, and I wanted to check if I should expect to be getting an error for an unused parameter in certain situations with functions using the else keyword, or if that error is unintended behavior in such situations. Specifically, here is an example of a function where I'm getting such an error in v0.50.0: https://play.openpolicyagent.org/p/OESvMjvfTg (the Rego playground is still running on v0.49.0 so it doesn't report the error). If I'm understanding the situation correctly, it appears that the error is reported because the subject argument isn't used in the else = false branch of the function definition:

is_authenticated(subject) {
	subject.authenticated
	subject.identity != ""
} else = false # opa v0.50.0 emits the error on this line; the error isn't emitted if `else = false` is removed

If this kind of situation is now supposed to trigger an unused variable error starting in v0.50.0, are there any workarounds in v0.50.0 which would allow me to simultaneously:

1. Continue using the compiler in strict mode (ideally still with errors about unused function params), and
2. Define functions which default to false rather than undefined

When searching about topics related to this behavior, so far I've found:

• The default keyword should be honored on functions opa#2445

[ashutosh-narkar]

@ethanjli honoring a function with a default value would be a workaround. Also something like below:

is_authenticated(subject) {
        subject.authenticated
        subject.identity != ""
} else = false {
        _ := subject
}

But this seems like a bug. Can you please open an issue with these details?

[ethanjli]

I will file an issue (update: the issue is now opened, at open-policy-agent/opa#5758). Thanks for your guidance on this!