Add changelog documentation

CONTRIBUTING.md

@@ -247,13 +247,7 @@ request is as follows:
 1. Fork the project into your personal space on GitLab.com
 1. Create a feature branch, branch away from `master`
 1. Write [tests](https://gitlab.com/gitlab-org/gitlab-development-kit#running-the-tests) and code
-1. Add your changes to the [CHANGELOG.md](CHANGELOG.md):
-  1. If you are fixing a ~regression issue, you can add your entry to the next
-     patch release (e.g. `8.12.5` if current version is `8.12.4`)
-  1. Otherwise, add your entry to the next minor release (e.g. `8.13.0` if
-     current version is `8.12.4`
-  1. Please add your entry at a random place among the entries of the targeted
-     release
+1. [Generate a changelog entry with `bin/changelog`][changelog]
 1. If you are writing documentation, make sure to follow the
    [documentation styleguide][doc-styleguide]
 1. If you have multiple commits please combine them into one commit by
@@ -469,6 +463,7 @@ available at [http://contributor-covenant.org/version/1/1/0/](http://contributor
 [contributor-covenant]: http://contributor-covenant.org
 [rss-source]: https://github.com/bbatsov/ruby-style-guide/blob/master/README.md#source-code-layout
 [rss-naming]: https://github.com/bbatsov/ruby-style-guide/blob/master/README.md#naming
+[changelog]: doc/development/changelog.md "Generate a changelog entry"
 [doc-styleguide]: doc/development/doc_styleguide.md "Documentation styleguide"
 [scss-styleguide]: doc/development/scss_styleguide.md "SCSS styleguide"
 [newlines-styleguide]: doc/development/newlines_styleguide.md "Newlines styleguide"

doc/development/README.md

@@ -21,6 +21,7 @@
 
 ## Process
 
+- [Generate a changelog entry with `bin/changelog`](changelog.md)
 - [Code review guidelines](code_review.md) for reviewing code and having code reviewed.
 - [Merge request performance guidelines](merge_request_performance_guidelines.md)
   for ensuring merge requests do not negatively impact GitLab performance

doc/development/changelog.md

+# Generate a changelog entry
+
+This guide contains instructions for generating a changelog entry data file, as
+well as information and history about our changelog process.
+
+## Overview
+
+Each bullet point, or **entry**, in our [`CHANGELOG.md`][changelog.md] file is
+generated from a single data file in the [`changelogs/unreleased/`][unreleased]
+(or corresponding EE) folder. The file is expected to be a [YAML] file in the
+following format:
+
+```yaml
+---
+title: "Going through change[log]s"
+merge_request: 1972
+author: Ozzy Osbourne
+```
+
+The `merge_request` value is a reference to a merge request that adds this
+entry, and the `author` key is used to give attribution to community
+contributors. Both are optional.
+
+If you're working on the GitLab EE repository, the entry will be added to
+`changelogs/unreleased-ee/` instead.
+
+[changelog.md]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md
+[unreleased]: https://gitlab.com/gitlab-org/gitlab-ce/tree/master/changelogs/
+[YAML]: https://en.wikipedia.org/wiki/YAML
+
+## Instructions
+
+A `bin/changelog` script is available to generate the changelog entry file
+automatically.
+
+Its simplest usage is to provide the value for `title`:
+
+```text
+$ bin/changelog Hey DZ, I added a feature to GitLab!
+create changelogs/unreleased/my-feature.yml
+---
+title: Hey DZ, I added a feature to GitLab!
+merge_request:
+author:
+```
+
+The entry filename is based on the name of the current Git branch. If you run
+the command above on a branch called `feature/hey-dz`, it will generate a
+`changelogs/unreleased/feature-hey-dz` file.
+
+### Arguments
+
+| Argument          | Shorthand | Purpose                                       |
+| ----------------- | --------- | --------------------------------------------- |
+| `--amend`         |           | Amend the previous commit                     |
+| `--merge-request` | `-m`      | Merge Request ID                              |
+| `--dry-run`       | `-n`      | Don't actually write anything, just print     |
+| `--git-username`  | `-u`      | Use Git user.name configuration as the author |
+| `--help`          | `-h`      | Print help message                            |
+
+#### `--amend`
+
+You can pass the **`--amend`** argument to automatically stage the generated
+file and amend it to the previous commit.
+
+If you use **`--amend`** and don't provide a title, it will automatically use
+the "subject" of the previous commit, which is the first line of the commit
+message:
+
+```text
+$ git show --oneline
+ab88683 Added an awesome new feature to GitLab
+
+$ bin/changelog --amend
+create changelogs/unreleased/feature-hey-dz.yml
+---
+title: Added an awesome new feature to GitLab
+merge_request:
+author:
+```
+
+#### `--merge-request` or `-m`
+
+Use the **`--merge-request`** or **`-m`** argument to provide the
+`merge_request` value:
+
+```text
+$ bin/changelog Hey DZ, I added a feature to GitLab! -m 1983
+create changelogs/unreleased/feature-hey-dz.yml
+---
+title: Hey DZ, I added a feature to GitLab!
+merge_request: 1983
+author:
+```
+
+#### `--dry-run` or `-n`
+
+Use the **`--dry-run`** or **`-n`** argument to prevent actually writing or
+committing anything:
+
+```text
+$ bin/changelog --amend --dry-run
+create changelogs/unreleased/feature-hey-dz.yml
+---
+title: Added an awesome new feature to GitLab
+merge_request:
+author:
+
+$ ls changelogs/unreleased/
+```
+
+#### `--git-username` or `-u`
+
+Use the **`--git-username`** or **`-u`** argument to automatically fill in the
+`author` value with your configured Git `user.name` value:
+
+```text
+$ git config user.name
+Jane Doe
+
+$ bin/changelog --u Hey DZ, I added a feature to GitLab!
+create changelogs/unreleased/feature-hey-dz.yml
+---
+title: Hey DZ, I added a feature to GitLab!
+merge_request:
+author: Jane Doe
+```
+
+## History and Reasoning
+
+Our `CHANGELOG` file was previously updated manually by each contributor that
+felt their change warranted an entry. When two merge requests added their own
+entries at the same spot in the list, it created a merge conflict in one as soon
+as the other was merged. When we had dozens of merge requests fighting for the
+same changelog entry location, this quickly became a major source of merge
+conflicts and delays in development.
+
+This led us to a [boring solution] of "add your entry in a random location in
+the list." This actually worked pretty well as we got further along in each
+monthly release cycle, but at the start of a new cycle, when a new version
+section was added and there were fewer places to "randomly" add an entry, the
+conflicts became a problem again until we had a sufficient number of entries.
+
+On top of all this, it created an entirely different headache for [release managers]
+when they cherry-picked a commit into a stable branch for a patch release. If
+the commit included an entry in the `CHANGELOG`, it would include the entire
+changelog for the latest version in `master`, so the release manager would have
+to manually remove the later entries. They often would have had to do this
+multiple times per patch release. This was compounded when we had to release
+multiple patches at once due to a security issue.
+
+We needed to automate all of this manual work. So we [started brainstorming].
+After much discussion we settled on the current solution of one file per entry,
+and then compiling the entries into the overall `CHANGELOG.md` file during the
+[release process].
+
+[boring solution]: https://about.gitlab.com/handbook/#boring-solutions
+[release managers]: https://gitlab.com/gitlab-org/release-tools/blob/master/doc/release-manager.md
+[started brainstorming]: https://gitlab.com/gitlab-org/gitlab-ce/issues/17826
+[release process]: https://gitlab.com/gitlab-org/release-tools
+
+---
+
+[Return to Development documentation](README.md)