argument-always-wildcard

Summary: Argument is always a wildcard

Category: Bugs

Avoid

package policy

import rego.v1

# there's only one definition of the last_name function in
# this package, and the second argument is never used
last_name(name, _) := lname if {
    parts := split(name, " ")
    lname := parts[count(parts) - 1]
}

Prefer

package policy

import rego.v1

last_name(name) := lname if {
    parts := split(name, " ")
    lname := parts[count(parts) - 1]
}

Rationale

Function definitions may use wildcard variables as arguments to indicate that the value is not used in the body of the function. This helps make the function definition more readable, as it's immediately clear which of the arguments are used in that definition of the function. This is particularly useful for incrementally defined functions:

package policy

import rego.v1

default authorized(_, _) := false

authorized(user, _) if {
    # some logic to determine if authorized
}

# or

authorized(user, _) if {
    # some further logic to determine if authorized
}

In the example above, the second argument is a wildcard in all definitions, and could just as well be removed for a cleaner definition. More likely, the argument was meant to be used, if only in one of the definitions:

package policy

import rego.v1

default authorized(_, _) := false

authorized(user, _) if {
    # some logic to determine if authorized
}

# or

authorized(_, request) if {
    # some further logic to determine if authorized
}

Configuration Options

This linter rule provides the following configuration options:

rules:
  bugs:
    argument-always-wildcard:
      # one of "error", "warning", "ignore"
      level: error
      # function name patterns for which this rule should make an exception
      # default is to ignore any function name starting with "mock_" as these
      # commonly don't need named arguments
      except-function-name-pattern: "^mock_"

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!