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

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Regal

Build Status OPA v0.55.0

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

regal

adj : of notable excellence or magnificence : splendid

- Merriam Webster

illustration of a viking representing the Regal logo

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://github.com/StyraInc/regal/blob/main/docs/rules/bugs/not-equals-in-loop.md

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

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

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.
  • 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
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 use-in-operator Use in to check for membership
imports redundant-data-import Redundant import of data
imports implicit-future-keywords Use explicit future keyword imports
imports import-shadows-import Import shadows another import
imports redundant-alias Redundant alias
imports avoid-importing-input Avoid importing input
style prefer-snake-case Prefer snake_case for names
style todo-comment Avoid TODO comments
style external-reference Reference to input, data or rule ref in function body
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 avoid-get-and-list-prefix Avoid get_ and list_ prefix for rules and functions
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 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 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.

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"

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.

Resources

Documentation

Talks

Regal the Rego Linter, CNCF London meetup, June 2023 Regal the Rego Linter

Blogs

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

  • More 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
  • VS Code extension

Community

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

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