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repeated-computation

Summary: Repeated built-in call in the same scope

Category: Performance

Avoid

package policy

allow if {
    count(input.subjects) > 0
    count(input.subjects) < 100
}

Prefer

package policy

allow if {
    subject_count := count(input.subjects)
    subject_count > 0
    subject_count < 100
}

Rationale​

Some built-in functions allocate or otherwise perform work for each call. When the same deterministic built-in is called multiple times with the same stable arguments in the same scope, the result can be assigned once and reused.

This is especially useful for aggregate built-ins such as count, where repeating the call makes the policy do the same work more than once.

Exceptions​

This rule is intentionally conservative. It only reports deterministic built-in calls with arguments that are constants or stable input/data references. Calls that depend on local variables are ignored because the variable binding may change across scopes.

Calls inside comprehensions and every bodies are also ignored. These forms introduce nested scopes where variables can be shadowed, so a textually identical call is not always the same computation.

Configuration Options​

This linter rule provides the following configuration options:

rules:
  performance:
    repeated-computation:
      # one of "error", "warning", "ignore"
      level: error