Danger :no_entry_sign:

License Gem

Formalize your Pull Request etiquette.

Getting StartedUsageDSLPluginsLocal

Getting Started

Add this line to your application's Gemfile:

gem 'danger'

Next, use Bundler to install the gem.

bundle install

After the gem is installed, you can run Danger's interactive getting started guide:

bundle exec danger init

The guide will create a default Dangerfile and take you through the process of setting up an account for feedback on GitHub.

Usage on CI

bundle exec danger

This will look at your Dangerfile and update the pull request accordingly. While you are setting up Danger, you may want to use: --verbose for more debug information.

CI Support

Danger currently is supported on Travis CI, Circle CI, Xcode Bots via Buildasaur, BuildKite, Jenkins, Semaphore, Drone CI and TeamCity. These work via environment variables, so it's easy to extend to include your own.

What happens?

Danger runs at the end of a CI build, she will execute a Dangerfile. This file is given some special variables based on the git diff and the Pull Request being running. You can use these variables in Ruby to provide messages, warnings and failures for your build. You set up Danger with a GitHub user account and she will post updates via comments on the Pull Request, and can fail your build too.


    Danger :no_entry_sign:
:sparkles: lines_of_code The total amount of lines of code in the diff
:pencil2: modified_files The list of modified files
:ship: added_files The list of added files
:recycle: deleted_files The list of removed files
:abc: pr_title The title of the PR
:book: pr_body The body of the PR
:busts_in_silhouette: pr_author The author who submitted the PR
:bookmark: pr_labels The labels added to the PR

The Dangerfile is a Ruby file, so really, you can do anything. However, at this stage you might need selling on the idea a bit more, so lets take some real examples:

Dealing with WIP pull requests

# Sometimes its a README fix, or something like that - which isn't relevant for
# including in a CHANGELOG for example
declared_trivial = pr_title.include? "#trivial"

# Just to let people know
warn("PR is classed as Work in Progress", sticky: false) if pr_title.include? "[WIP]"

Being cautious around specific files

# Devs shouldn't ship changes to this file
fail("Developer Specific file shouldn't be changed", sticky: false) if modified_files.include?("Artsy/View_Controllers/App_Navigation/ARTopMenuViewController+DeveloperExtras.m")

# Did you make analytics changes? Well you should also include a change to our analytics spec
made_analytics_changes = modified_files.include?("/Artsy/App/ARAppDelegate+Analytics.m")
made_analytics_specs_changes = modified_files.include?("/Artsy_Tests/Analytics_Tests/ARAppAnalyticsSpec.m")
if made_analytics_changes
  fail("Analytics changes should have reflected specs changes") if !made_analytics_specs_changes

  # And pay extra attention anyway
  message('Analytics dict changed, double check for ?: `@""` on new entries')
  message('Also, double check the [Analytics Eigen schema](https://docs.google.com/spreadsheets/u/1/d/1bLbeOgVFaWzLSjxLOBDNOKs757-zBGoLSM1lIz3OPiI/edit#gid=497747862) if the changes are non-trivial.')

Pinging people when a specific file has changed

markdown("@orta something changed in elan!") if modified_files.include? "/components/lib/variables/colors.json"

If you wish to ping a person on a PR you'll need to use the markdown method rather than the message, warn or fail methods. This is because the HTML generated by the latter methods doesn't trigger GitHub's notification detection.

Exposing aspects of CI logs into the PR discussion

build_log = File.read(File.join(ENV["CIRCLE_ARTIFACTS"], "xcode_test_raw.log"))
snapshots_url = build_log.match(%r{https://eigen-ci.s3.amazonaws.com/\d+/index.html})
fail("There were [snapshot errors](#{snapshots_url})") if snapshots_url

Available commands

Command Description
fail Causes the PR to fail and print out the error on the PR
warn Prints out a warning to the PR, but still enables the merge button
message Show neutral messages on the PR
markdown Print raw markdown below the summary tables on the PR


Danger was built with a platform in mind: she can be used with any kind of software project and allows you to write your own action to have structured source code.

In your Dangerfile you can import local or remote actions using

import "./danger_plugins/work_in_progress_warning"
# or
import "https://raw.githubusercontent.com/danger/danger/master/danger_plugins/work_in_progress_warning.rb"

# Call those actions using

custom_plugin(variable: "value")

To create a new plugin run

danger new_plugin

This will generate a new Ruby file which you can modify to fit your needs.


You can access more detailed information by accessing the following variables

  Danger :no_entry_sign:
env.request_source.pr_json The full JSON for the pull request
env.scm.diff The full Diff file for the diff.
env.ci_source To get information like the repo slug or pull request ID

These are considered implementation details though, and may be subject to change in future releases. We're very open to turning useful bits into the official API.

Test locally with danger local

You can use danger local to run Danger in an environment similar to how she will be ran on CI. By default Danger will look at the most recently merged PR, then run your Dangerfile against that Pull Request. This is really useful when making changes.

If you have a specific PR in mind that you'd like to work against, make sure you have it merged in your current git history, then append --use-merged-pr=[id] to the command.

Adding a new CI

If the CI server you're using isn't available yet, you can build it yourself:

Take a look at some of the already existing integrations. The class has 2 mandatory methods:

  • self.validates? which should detect if the CI is active (detecting via ENV variables, mostly)
  • initialize which should set 2 variables:
    • self.repo_slug the repo slug, in org/repo or user/repo format.
    • self.pull_request_id the number of the pull request that the CI is testing (often available in ENV variables)

We'd love to see pull requests for new integrations!

Suppress Violations

You can tell Danger to ignore a specific warning or error by commenting on the PR body:

> Danger: Ignore "Developer Specific file shouldn't be changed"


Danger can keep its history if a warning/error/message is marked as sticky. When the violation is resolved, Danger will update the comment to cross it out. If you don't want this behavior, just use sticky: false.

fail("PR needs labels", sticky: false) if pr_labels.empty?

Multiple Dangers

If one Danger is not enough for you, you can run several ones on the same PR. Just use the danger_id param. For example:

bundle exec danger --danger_id=unit_tests

You can have each instance of Danger running on a different CI provider and even doing different validations. An use case would be:

  • basic runs on a Linux environment (such as Circle CI) and validates the PR itself (title, etc)
  • compilation runs on a Mac after running unit tests for your iOS app and comments about warnings, test failures, etc
  • uitests runs on a Mac after running UI Unit tests and comments about test failures

Useful bits of knowledge

  • You can set the base branch in the command line arguments see: bundle exec danger --help, if you commonly merge into non-master branches.
  • Appending --verbose to bundle exec danger will expose all of the variables that Danger provides, and their values in the shell.

Here are some real-world Dangerfiles: artsy/eigen, danger/danger, artsy/elan and more!

Usage with GitHub Enterprise

Danger allows usage with GitHub Enterprise by setting 2 environment variables:

  • DANGER_GITHUB_HOST to the host that GitHub is running on
  • DANGER_GITHUB_API_HOST to the host that the GitHub Enterprise API is reachable on.

License, Contributor's Guidelines and Code of Conduct

We try to keep as much discussion as possible in GitHub issues, but also have a slack, if you'd like an invite ping @Orta a DM on twitter with your email.

This project is open source under the MIT license, which means you have full access to the source code and can modify it to fit your own needs.

This project subscribes to the Moya Contributors Guidelines which TLDR: means we give out push access easily and often.

Contributors subscribe to the Contributor Code of Conduct based on the Contributor Covenant version 1.3.0.