rego_compile_error: assigned var {name} unused

This error is caused by a variable being assigned a value, but never used. This is often the result of a typo or mis-named variable being assigned.

note

This error is only shown when running OPA with the --strict (or -S) flag.

Stage	Category	Message
parsing	rego_compile_error	rego_compile_error: assigned var {name} unused

Examples

This a simple example of this error is when a variable is assigned a value, but never used:

package policy

import future.keywords.if

allow if {
	user := input.user
	input.user == "admin"
}

When compiled, this will result in the following error because the variable user is never used:

1 error occurred: policy.rego:6: rego_compile_error: assigned var user unused

Another common reason for this message is when making a typo or mis-naming a variable. For example:

package policy

import future.keywords.contains
import future.keywords.if

deny contains message if {
	input.user != "admin"

	msg := "user is not admin"
}

Here, we can see the intent, the message should be set to user is not admin if the user is not an admin. However, the variable msg is assigned instead.

How To Fix It

Based on the examples above, we can see that there are two main ways to fix this error:

• Remove the assignments of unused variables. In the first example, we can simply remove the line user := input.user. The other option is of course to use the variable that was assigned. Often orphaned variables like this are the result a refactoring and can be safely removed if they aren't making the rule more readable.
• Check for typos and mis-named variables. As well as normal typos, it's also easy to make mistakes and swap variables for alternative names. For example, sometimes msg instead of message or user instead of username.

While it's also possible to ignore this error by unsetting the --strict (-S) flag, it's highly recommended to fix the underlying issue as outlined in the points above.

Community

For questions, discussions and announcements related to OPA, or Styra products, services and open source projects, please join the Styra Community on Slack.