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dubious-print-sprintf

Summary: Dubious use of print and sprintf

Category: Testing

Avoid

package policy

allow {
    # if any of input.name or input.domain are undefined, this will just print <undefined>
    print(sprintf("name is: %s domain is: %s", [input.name, input.domain]))

    input.name == "admin"
}

Prefer

package policy

allow {
    # if any of input.name or input.domain are undefined, this will still print the whole
    # sentence, with the value undefined printed as such, e.g.
    # name is: admin domain is: <undefined>
    print("name is:", input.name, "domain is:", input.domain)

    input.name == "admin"
}

Rationale​

Since print allows any number of arguments, there's rarely any benefit to using sprintf for formatting the output of a print call. But more importantly, the print function is unique in that it will allow any arguments passed to be undefined without terminating, but will print such values as <undefined>. Using sprintf will however nullify this benefit, and just print <undefined> without the context.

Note that using print is generally discouraged outside of development, and other rules exists to check for its use. However, in the context of development and testing, one may choose to allow print, in e.g. _test.rego files, while still wanting to avoid the use of sprintf in such cases.

Configuration Options​

This linter rule provides the following configuration options:

rules:
  testing:
    dubious-print-sprintf:
      # 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!