116 lines
5.5 KiB
Markdown
116 lines
5.5 KiB
Markdown
# Danger bot
|
|
|
|
The GitLab CI pipeline includes a `danger-review` job that uses [Danger](https://github.com/danger/danger)
|
|
to perform a variety of automated checks on the code under test.
|
|
|
|
Danger is a gem that runs in the CI environment, like any other analysis tool.
|
|
What sets it apart from, e.g., Rubocop, is that it's designed to allow you to
|
|
easily write arbitrary code to test properties of your code or changes. To this
|
|
end, it provides a set of common helpers and access to information about what
|
|
has actually changed in your environment, then simply runs your code!
|
|
|
|
If Danger is asking you to change something about your merge request, it's best
|
|
just to make the change. If you want to learn how Danger works, or make changes
|
|
to the existing rules, then this is the document for you.
|
|
|
|
## Operation
|
|
|
|
On startup, Danger reads a [`Dangerfile`](https://gitlab.com/gitlab-org/gitlab/blob/master/Dangerfile)
|
|
from the project root. GitLab's Danger code is decomposed into a set of helpers
|
|
and plugins, all within the [`danger/`](https://gitlab.com/gitlab-org/gitlab-foss/tree/master/danger/)
|
|
subdirectory, so ours just tells Danger to load it all. Danger will then run
|
|
each plugin against the merge request, collecting the output from each. A plugin
|
|
may output notifications, warnings, or errors, all of which are copied to the
|
|
CI job's log. If an error happens, the CI job (and so the entire pipeline) will
|
|
be failed.
|
|
|
|
On merge requests, Danger will also copy the output to a comment on the MR
|
|
itself, increasing visibility.
|
|
|
|
## Development guidelines
|
|
|
|
Danger code is Ruby code, so all our [usual backend guidelines](README.md#backend-guides)
|
|
continue to apply. However, there are a few things that deserve special emphasis.
|
|
|
|
### When to use Danger
|
|
|
|
Danger is a powerful tool and flexible tool, but not always the most appropriate
|
|
way to solve a given problem or workflow.
|
|
|
|
First, be aware of GitLab's [commitment to dogfooding](https://about.gitlab.com/handbook/engineering/#dogfooding).
|
|
The code we write for Danger is GitLab-specific, and it **may not** be most
|
|
appropriate place to implement functionality that addresses a need we encounter.
|
|
Our users, customers, and even our own satellite projects, such as [Gitaly](https://gitlab.com/gitlab-org/gitaly),
|
|
often face similar challenges, after all. Think about how you could fulfil the
|
|
same need while ensuring everyone can benefit from the work, and do that instead
|
|
if you can.
|
|
|
|
If a standard tool (e.g. `rubocop`) exists for a task, it is better to use it
|
|
directly, rather than calling it via Danger. Running and debugging the results
|
|
of those tools locally is easier if Danger isn't involved, and unless you're
|
|
using some Danger-specific functionality, there's no benefit to including it in
|
|
the Danger run.
|
|
|
|
Danger is well-suited to prototyping and rapidly iterating on solutions, so if
|
|
what we want to build is unclear, a solution in Danger can be thought of as a
|
|
trial run to gather information about a product area. If you're doing this, make
|
|
sure the problem you're trying to solve, and the outcomes of that prototyping,
|
|
are captured in an issue or epic as you go along. This will help us to address
|
|
the need as part of the product in a future version of GitLab!
|
|
|
|
### Implementation details
|
|
|
|
Implement each task as an isolated piece of functionality and place it in its
|
|
own directory under `danger` as `danger/<task-name>/Dangerfile`.
|
|
|
|
Add a line to the top-level `Dangerfile` to ensure it is loaded like:
|
|
|
|
```ruby
|
|
danger.import_dangerfile('danger/<task-name>')
|
|
```
|
|
|
|
Each task should be isolated from the others, and able to function in isolation.
|
|
If there is code that should be shared between multiple tasks, add a plugin to
|
|
`danger/plugins/...` and require it in each task that needs it. You can also
|
|
create plugins that are specific to a single task, which is a natural place for
|
|
complex logic related to that task.
|
|
|
|
Danger code is just Ruby code. It should adhere to our coding standards, and
|
|
needs tests, like any other piece of Ruby in our codebase. However, we aren't
|
|
able to test a `Dangerfile` directly! So, to maximize test coverage, try to
|
|
minimize the number of lines of code in `danger/`. A non-trivial `Dangerfile`
|
|
should mostly call plugin code with arguments derived from the methods provided
|
|
by Danger. The plugin code itself should have unit tests.
|
|
|
|
At present, we do this by putting the code in a module in `lib/gitlab/danger/...`,
|
|
and including it in the matching `danger/plugins/...` file. Specs can then be
|
|
added in `spec/lib/gitlab/danger/...`.
|
|
|
|
You'll only know if your `Dangerfile` works by pushing the branch that contains
|
|
it to GitLab. This can be quite frustrating, as it significantly increases the
|
|
cycle time when developing a new task, or trying to debug something in an
|
|
existing one. If you've followed the guidelines above, most of your code can
|
|
be exercised locally in RSpec, minimizing the number of cycles you need to go
|
|
through in CI. However, you can speed these cycles up somewhat by emptying the
|
|
`.gitlab/ci/rails.gitlab-ci.yml` file in your merge request. Just don't forget
|
|
to revert the change before merging!
|
|
|
|
You should add the `~Danger bot` label to the merge request before sending it
|
|
for review.
|
|
|
|
## Current uses
|
|
|
|
Here is a (non-exhaustive) list of the kinds of things Danger has been used for
|
|
at GitLab so far:
|
|
|
|
- Coding style
|
|
- Database review workflow
|
|
- Documentation review workflow
|
|
- Merge request metrics
|
|
- Reviewer roulette workflow
|
|
- Single codebase effort
|
|
|
|
## Limitations
|
|
|
|
- [`danger local` does not work on GitLab](https://github.com/danger/danger/issues/458)
|
|
- Danger output is not added to a merge request comment if working on a fork.
|