defer-assignment

Summary: Assignment can be deferred

Category: Performance

Avoid

package policy

allow if {
    resp := http.send({"method": "GET", "url": "http://example.com"})

    # this check does not depend on the response above
    # and thus the resp := ... assignment can be deferred to
    # after the check
    input.user.name in allowed_users

    resp.status_code == 200

    # more done with response here
}

Prefer

package policy

allow if {
    input.user.name in allowed_users

    # the next expression *does* depend on `resp`
    resp := http.send({"method": "GET", "url": "http://example.com"})

    resp.status_code == 200

    # more done with response here
}

Rationale

Assignments are normally cheap, but certainly not always. If the right-hand side of an assignment is expensive, deferring the assignment to where it's needed can save a considerable amount of time. Even for less expensive assignments, code tends to be more readable when assignments are placed close to where they're used.

This rule uses a fairly simplistic heuristic to determine if an assignment can be deferred:

• The next expression is not an assignment
• The next expression does not depend on the assignment
• The next expression does not initialize iteration

It is possible that the rule will be improved to cover more cases in the future.

Configuration Options

This linter rule provides the following configuration options:

rules:
  performance:
    defer-assignment:
      # one of "error", "warning", "ignore"
      level: error

Related Resources

• GitHub: Source Code