impossible-not

Summary: Impossible not condition

Category: Bugs

Type: Aggregate - runs both on single files as well as when more than one file is provided for linting

Avoid

package policy

report contains violation if {
    # ... some conditions
}

package policy_test

import data.policy

test_report_is_empty {
    # evaluation will stop here, as even an empty set is "true"
    not policy.report
}

Prefer

package policy

report contains violation if {
    # ... some conditions
}

package policy_test

import data.policy

test_report_is_empty {
    count(policy.report) == 0
}

Rationale

The not keyword negates the expression that follows it. A common mistake, especially in tests, is to use not to test the result of evaluating a partial (i.e. multi-value) rule. However, as even an empty set is considered "truthy", the not will in that case always evaluate to false. There are more cases where not is impossible, or a constant condition, but references to partial rules are by far the most common. For tests where you want to assert the set is empty or has a specific number of items, use the built-in count function instead.

Configuration Options

This linter rule provides the following configuration options:

rules:
  bugs:
    impossible-not:
      # one of "error", "warning", "ignore"
      level: error

Related Resources

• Regal Docs: constant-condition
• GitHub: Source Code