redundant-existence-check

Summary: Redundant existence check

Category: Bugs

Avoid

package policy

import rego.v1

employee if {
    input.user.email
    endswith(input.user.email, "@acmecorp.com")
}

Prefer

package policy

import rego.v1

employee if {
    endswith(input.user.email, "@acmecorp.com")
}

# alternatively

employee if endswith(input.user.email, "@acmecorp.com")

Rationale

Checking that a reference (like input.user.email) is defined before immediately using it is redundant. If the reference is undefined, the next expression will fail anyway, as the value will be checked before the rest of the expression is evaluated. While an extra check doesn't "hurt", it also serves no purpose, similarly to an unused variable.

Note: This rule only applies to references that are immediately used in the next expression. If the reference is used later in the rule, it won't be flagged. While the existence check could be redundant even in that case, it could also be used to avoid making some expensive computation, an http.send call, or whatnot.

Configuration Options

This linter rule provides the following configuration options:

rules:
  bugs:
    redundant-existence-check:
      # one of "error", "warning", "ignore"
      level: error

Community

If you think you've found a problem with this rule or its documentation, would like to suggest improvements, new rules, or just talk about Regal in general, please join us in the #regal channel in the Styra Community Slack!