rego_parse_error: unexpected assign token

In some cases when an assign token (:=) precedes some invalid Rego code, the parser will raise this error.

info

This used to be one of the common, difficult-to-understand errors in OPA prior to version v0.66.0. If you encounter it, please check your OPA version.

Stage	Category	Message
parsing	rego_parse_error	unexpected unexpected assign token

Examples

A simple example of a policy that contains this error follows, note the unmatched " after a :=:

package policy

a := "

The code above will raise the following error:

1 error occurred: policy.rego:3: rego_parse_error: unexpected assign token: expected rule value term (e.g., a := <VALUE> { ... })
	a := "
	  ^

The parser error is pointing to the := token, which in this case is not the issue.

How To Fix It

While the fix for this error depends on other elements on the line of Rego, the error message will usually point to you to the line in question. Have a look for invalid code later on that line as it is likely the cause of the error.

info

In OPA versions prior to v0.66.0, you can use a trick to get more helpful error messages. By changing the := to =, the parser will raise a more helpful error message:

package policy

a = "

This new code will raise the following, more helpful, error:

3 errors occurred:
policy.rego:3: rego_parse_error: non-terminated string
	a = "
	    ^

Note however that generally this is not a recommended approach, see more detail here in the Regal docs.