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use-contains

Summary: Use the contains keyword

Category: Idiomatic

Notice: Rule made obsolete by OPA 1.0​

Since Regal v0.30.0, this rule is only enabled for projects that have either been explicitly configured to target versions of OPA before 1.0, or if no configuration is provided — where Regal is able to determine that an older version of OPA/Rego is being targeted. Consult the documentation on Regal's configuration for information on how to best work with older versions of OPA and Rego.

Since OPA v1.0, this rule is no longer needed as the Rego v1 syntax is now mandatory, and using contains is now the de-facto way to define multi-value rules.

Avoid

package policy

import future.keywords.in

report[item] if {
    some item in input.items
    startswith(item, "report")
}

# unconditionally add an item to report
report["report1"]

Prefer

package policy

import future.keywords.contains
import future.keywords.if
import future.keywords.in

report contains item if {
    some item in input.items
    startswith(item, "report")
}

# unconditionally add an item to report
report contains "report1"

Rationale​

The contains keyword helps to clearly distinguish multi-value rules (or "partial rules") from single-value rules ("complete rules"). Just like the if keyword, contains additionally makes the rule read the same way in English as OPA interprets its meaning — a set that contains one or more values given some (optional) conditions.

OPA version 1.0, which is planned for 2024, will make the contains keyword mandatory. This rule helps you get ahead of the curve and start using it today.

Note: don't forget to import future.keywords.contains! Or from OPA v0.59.0 and onwards, import rego.v1.

Tip: When either of the imports mentioned above are found in a Rego file, the contains keyword will be inserted automatically at any applicable location by the opa fmt tool.

Configuration Options​

This linter rule provides the following configuration options:

rules:
  idiomatic:
    use-contains:
      # 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!