Regal

Regal is a linter for Rego, with the goal of making your Rego magnificent!

regal

adj : of notable excellence or magnificence : splendid

- Merriam Webster

Goals

• Identify common mistakes, bugs and inefficiencies in Rego policies, and suggest better approaches
• Provide advice on best practices, coding style, and tooling
• Allow users, teams and organizations to enforce custom rules on their policy code

Regal rules are to as large extent as possible written in Rego themselves, using the JSON representation of the Rego abstract syntax tree (AST) as input, a few additional custom built-in functions and some indexed data structures to help with linting.

Getting Started

Download Regal

MacOS and Linux

brew install styrainc/packages/regal

Manual download options

MacOS (Apple Silicon)

curl -L -o regal "https://github.com/StyraInc/regal/releases/latest/download/regal_Darwin_arm64"

MacOS (x86_64)

curl -L -o regal "https://github.com/StyraInc/regal/releases/latest/download/regal_Darwin_x86_64"

Linux (x86_64)

curl -L -o regal "https://github.com/StyraInc/regal/releases/latest/download/regal_Linux_x86_64"
chmod +x regal

Windows

curl.exe -L -o regal.exe "https://github.com/StyraInc/regal/releases/latest/download/regal_Windows_x86_64.exe"

Docker

docker pull ghcr.io/styrainc/regal:latest

See all versions, and checksum files, at the Regal releases page, and published Docker images at the packages page.

Try it out!

First, author some Rego!

policy/authz.rego

package authz

import future.keywords

default allow = false

deny if {
	"admin" != input.user.roles[_]
}

allow if not deny

Next, run regal lint pointed at one or more files or directories to have them linted.

regal lint policy/

Rule:         	not-equals-in-loop
Description:  	Use of != in loop
Category:     	bugs
Location:     	policy/authz.rego:8:10
Text:         	"admin" != input.user.roles[_]
Documentation:	https://docs.styra.com/regal/rules/bugs/not-equals-in-loop

Rule:         	implicit-future-keywords
Description:  	Use explicit future keyword imports
Category:     	imports
Location:     	policy/authz.rego:3:8
Text:         	import future.keywords
Documentation:	https://docs.styra.com/regal/rules/imports/implicit-future-keywords

Rule:         	use-assignment-operator
Description:  	Prefer := over = for assignment
Category:     	style
Location:     	policy/authz.rego:5:1
Text:         	default allow = false
Documentation:	https://docs.styra.com/regal/rules/style/use-assignment-operator

1 file linted. 3 violations found.

Note If you're running Regal on an existing policy library, you may want to disable the style category initially, as it will likely generate a lot of violations. You can do this by passing the --disable-category style flag to regal lint.

Rules

Regal comes with a set of built-in rules, grouped by category.

• bugs: Common mistakes, potential bugs and inefficiencies in Rego policies.
• custom: Custom, rules where enforcement can be adjusted to match your preferences.
• idiomatic: Suggestions for more idiomatic constructs.
• imports: Best practices for imports.
• style: Rego Style Guide rules.
• testing: Rules for testing and development.

The following rules are currently available:

Category	Title	Description
bugs	constant-condition	Constant condition
bugs	invalid-metadata-attribute	Invalid attribute in metadata annotation
bugs	not-equals-in-loop	Use of != in loop
bugs	rule-named-if	Rule named "if"
bugs	rule-shadows-builtin	Rule name shadows built-in
bugs	top-level-iteration	Iteration in top-level assignment
bugs	unused-return-value	Non-boolean return value unused
custom	naming-convention	Naming convention violation
idiomatic	custom-has-key-construct	Custom function may be replaced by in and object.keys
idiomatic	custom-in-construct	Custom function may be replaced by in keyword
idiomatic	non-raw-regex-pattern	Use raw strings for regex patterns
idiomatic	use-in-operator	Use in to check for membership
idiomatic	use-some-for-output-vars	Use some to declare output variables
imports	avoid-importing-input	Avoid importing input
imports	implicit-future-keywords	Use explicit future keyword imports
imports	import-shadows-import	Import shadows another import
imports	redundant-alias	Redundant alias
imports	redundant-data-import	Redundant import of data
style	avoid-get-and-list-prefix	Avoid get_ and list_ prefix for rules and functions
style	todo-comment	Avoid TODO comments
style	external-reference	Reference to input, data or rule ref in function body
style	file-length	Max file length exceeded
style	function-arg-return	Function argument used for return value
style	line-length	Line too long
style	no-whitespace-comment	Comment should start with whitespace
style	prefer-snake-case	Prefer snake_case for names
style	prefer-some-in-iteration	Prefer some .. in for iteration
style	detached-metadata	Detached metadata annotation
style	unconditional-assignment	Unconditional assignment in rule body
style	use-assignment-operator	Prefer := over = for assignment
style	opa-fmt	File should be formatted with opa fmt
testing	identically-named-tests	Multiple tests with same name
testing	metasyntactic-variable	Metasyntactic variable name
testing	print-or-trace-call	Call to print or trace function
testing	test-outside-test-package	Test outside of test package
testing	todo-test	TODO test encountered
testing	file-missing-test-suffix	Files containing tests should have a _test.rego suffix

By default, all rules except for those in the custom category are currently enabled.

If you'd like to see more rules, please open an issue for your feature request, or better yet, submit a PR! See the custom rules page for more information on how to develop your own rules, for yourself or for inclusion in Regal.

Custom Rules

The custom category is a special one, as the rules in this category allow you to enforce rules that are specific to your project, team or organization. This typically includes things like naming conventions, where you might want to ensure that, for example, all package names adhere to an organizational standard, like having a prefix matching the organization name.

Since these rules require configuration provided by the user, they are disabled by default. In order to enable them, see the configuration options available for each rule for how to configure them according to your requirements.

For more advanced requirements, see the guide on writing custom rules in Rego.

Configuration

A custom configuration file may be used to override the default configuration options provided by Regal. The most common use case for this is to change the severity level of a rule. These three levels are available:

• ignore — disable the rule entirely
• warning — report the violation without changing the exit code of the lint command
• error — report the violation and have the lint command exit with a non-zero exit code (default)

Additionally, some rules may have configuration options of their own. See the documentation page for a rule to learn more about it.

.regal/config.yaml

# Files can be excluded from all lint
# rules according to glob-patterns
ignore:
  files:
    - file1.rego
    - "*_tmp.rego"
rules:
  style:
    todo-comment:
      # don't report on todo comments
      level: ignore
    line-length:
      # custom rule configuration
      max-line-length: 100
      # warn on too long lines, but don't fail
      level: warning
    opa-fmt:
      # not needed as error is the default, but
      # being explicit won't hurt
      level: error
      # Files can be ignored.
      # In this example, test files are ignored
      ignore:
        files:
          - "*_test.rego"
  custom:
    # custom rule configuration
    naming-convention:
      level: error
      conventions:
        # ensure all package names start with "acmecorp" or "system"
        - pattern: '^acmecorp\.[a-z_\.]+$|^system\.[a-z_\.]+$'
          targets:
            - package

Regal will automatically search for a configuration file (.regal/config.yaml) in the current directory, and if not found, traverse the parent directories either until either one is found, or the top of the directory hierarchy is reached. If no configuration file is found, Regal will use the default configuration.

A custom configuration may be also be provided using the --config-file/-c option for regal lint, which when provided will be used to override the default configuration.

CLI flags

For development, rules may also quickly be enabled or disabled using the relevant CLI flags for the regal lint command.

• --disable-all disables all rules
• --disable-category disables all rules in a category, overriding --enable-all (may be repeated)
• --disable disables a specific rule, overriding --enable-all and --enable-category (may be repeated)
• --enable-all enables all rules
• --enable-category enables all rules in a category, overriding --disable-all (may be repeated)
• --enable enables a specific rule, overriding --disable-all and --disable-category (may be repeated)
• --ignore-files ignores files using glob patterns, overriding ignore in the config file (may be repeated)

All CLI flags override configuration provided in file.

Exit Codes

Exit codes are used to indicate the result of the lint command. The --fail-level provided for regal lint may be used to change the exit code behavior, and allows a value of either warning or error (default).

If --fail-level error is supplied, exit code will be zero even if warnings are present:

• 0: no errors were found
• 0: one or more warnings were found
• 3: one or more errors were found

This is the default behavior.

If --fail-level warning is supplied, warnings will result in a non-zero exit code:

• 0: no errors or warnings were found
• 2: one or more warnings were found
• 3: one or more errors were found

Inline Ignore Directives

If you'd like to ignore a specific violation, you can add an ignore directive above the line in question:

package policy

# regal ignore:prefer-snake-case
camelCase := "yes"

The format of an ignore directive is regal ignore:<rule-name>,<rule-name>..., where <rule-name> is the name of the rule to ignore. Multiple rules may be added to the same ignore directive, separated by commas.

Note that at this point in time, Regal only considers the line following the ignore directive, i.e. it does not ignore entire blocks of code (like rules, functions or even packages). See configuration if you want to ignore certain rules altogether.

Output Formats

The regal lint command allows specifying the output format by using the --format flag. The available output formats are:

• pretty (default) - Human-readable table-like output where each violation is printed with a detailed explanation
• compact - Human-readable output where each violation is printed on a single line
• json - JSON output, suitable for programmatic consumption
• github - GitHub workflow command output, ideal for use in GitHub Actions. Annotates PRs and creates a job summary from the linter report

Resources

Documentation

• Custom Rules describes how to develop your own rules
• Development for info about how to hack on Regal itself
• Rego Style Guide contains notes on implementing the Rego Style Guide rules
• Pre-Commit Hooks describes how to use Regal in pre-commit hooks

Talks

Regal the Rego Linter, CNCF London meetup, June 2023

Blogs

• Guarding the Guardrails - Introducing Regal the Rego Linter

Status

Regal is currently in beta. End-users should not expect any drastic changes, but any API may change without notice. If you want to embed Regal in another project or product, please reach out!

Roadmap

The roadmap for Regal currently looks like this:

• 50 rules!
• Add custom (or organizational, opinionated, or...) category for built-in "custom", or organizational rules, to enforce things like naming conventions. The most common customizations should not require writing custom rules, but be made available in configuration.
• Simplify custom rules authoring by providing command for scaffolding
• Make more rules consider nested AST nodes
• GitHub Action

The roadmap is updated when all the current items have been completed.

Community

For questions, discussions and announcements related to Styra products, services and open source projects, please join the Styra community on Slack!