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redundant-existence-check

Summary: Redundant existence check

Category: Bugs

Avoid

package policy

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

is_admin(user) if {
    user
    "admin" in user.roles
}

Prefer

package policy

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

# alternatively

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

is_admin(user) if {
    "admin" in user.roles
}

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.

Exceptions​

Function arguments where a boolean value is expected will be flagged as redundant existence checks, even though the intent was to check the boolean condition.

report(user, is_admin) if {
    is_admin

    # more conditions
}

For these cases, prefer to be explicit about what the assertion is checking:

report(user, is_admin) if {
    is_admin == false # or true, != false, etc.

    # more conditions
}

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!