GitGitGadget is intended to help with the code contribution process of the Git project itself.
Git's code contribution process follows the example of the Linux development (that is also used in other projects such as Cygwin, BusyBox etc): centered around one mailing list (git@vger.kernel.org), everything is discussed in one place (except security bugs, which are handled at git-security@googlegroups.com, i.e. yet another mailing list):
- bug reports,
- request for help,
- questions about design decisions,
- feature requests,
- mentoring new contributors, and
- patch submissions.
That's right: Git's development uses Git on the contributors' side and on the maintainer side, yet the code is transferred via mail between contributors and the maintainer. Most notably, there is no codified review process other than the free-form discussion via mails, and the convenience of Pull Requests and web-based code review is completely missing.
As a consequence, code submissions are therefore frequently reviewed purely based on the patches, without taking any context into account other than what was provided in the mail sent by the submitter.
Another consequence is that contributors often miss that they are expected to respond or work more on their submitted patches, as the current status of any given patch series is described only in one of the bi-weekly "What's cooking" mails sent by the Git maintainer, which contain not only information about one, but about all active patch submissions.
Yet another consequence of requiring contributors to send patches as verbatim, inlined diffs in mails, and to respond with answers interjected in the quoted mails (as opposed to, say, top-posting), is that most developers are deterred enough from contributing fixes that they simply don't (the requirements are in direct opposition of what both the most popular desktop mail client, Outlook, and the most popular web-based mail client, GMail, offer).
The idea is to allow developers to contribute patches and interact with the reviewers by using a very familiar interface: GitHub Pull Requests.
GitGitGadget's job is to send the patches to the Git mailing list in the correct format.
Hopefully, future versions of GitGitGadget will add more convenience to the dialog.
GitGitGadget was originally modeled after the workflow of one single Git contributor, Johannes Schindelin, who automated the patch contribution process via a shell script.
This process was still too manual, and too limited to one contributor's needs, and still needed too much manual work to serve as the base for any other developer's needs.
To remedy this, the shell script was first converted into a node.js script, and then into a Typescript project with the intention to turn this into a hybrid web application performing its interaction with contributors via GitHub based on the Probot framework and performing its background maintenance tasks in the form of Azure Pipelines. When the web application design became too limiting, it was converted into an Azure Function that backs the GitHub App and triggers an Azure Pipeline when given specific commands.
A convenient way to implement a UI based on GitHub Pull Requests is to create a GitHub App that triggers an Azure Function that is implemented in Javascript.
The backend is implemented as an Azure Pipeline, using Typescript to allow for type-safe and convenient development, and Visual Studio Code is a natural fit to develop both the Pipeline and the Function.
While many developers may not be familiar with Typescript, it is similar enough to (and a superset of) Javascript, which is a really well-known language. This is important, to lower the bar of entry for anybody who finds GitGitGadget lacking a feature: they can easily implement that feature without having to learn a completely new language first.
Besides, the node.js ecosystem provides a rich set of support libraries, ready to use at one's fingertips.
The principal way to interact with GitGitGadget is by opening a Pull Request at https://github.com/gitgitgadget/git. The patch submission is then triggered by a command given in a single comment to that PR. GitGitGadget will follow up with a comment describing details of the patch submission, such as the link to the cover letter in Git's mailing list archive.
Any other interesting information that can be inferred automatically will be added in the form of further comments to the same Pull Request.
The idea is to implement this user interface as a web app on Azure, backed by the repository https://github.com/gitgitgadget/gitgitgadget and deployed automatically.
The repositories https://github.com/gitster/git (and https://lore.kernel.org/git)) are monitored via dedicated Azure Pipelines, backed by Typescript code in https://github.com/gitgitgadget/gitgitgadget.
The patches will be submitted in the required form, as mails to the Git mailing
list. The description of the Pull Request will be used as cover letter, after
extracting Cc: lines from the footer (if any).
The mails will be sent via the dedicated account gitgitgadget@gmail.com, with
From: "<author> via GitGitGadget" <gitgitgadget@gmail.com> headers, and
linking to the corresponding PR/commits on GitHub.
GitGitGadget stores its metadata in the form of Git notes, in
refs/notes/gitgitgadget in https://github.com/gitgitgadget/git.
Note: GitGitGadget uses Git notes, not only to keep a record, and to make debugging easier, but also to be able to fix bugs manually when necessary.
We follow the original idea as refs/notes/amlog in
https://github.com/git/git (which inspired this design): first, we add the
Message-Id as a blob, then annotate that with a JSON structure (stable: sorted
by key name) that contains metadata about that mail.
Metadata includes (but is not limited to): the original commit
(Submitted-as:), the commit in https://github.com/git/git
(Integrated-as:), the Pull Request in https://github.com/gitgitgadget/git
(Pull-Request:), the latest patch series iteration of which this commit was
part (Iteration:), etc. If the identical commit has been submitted as part of
(an) earlier patch series iteration(s), the Message-Ids of the corresponding
mails should be also made available, as Submitted-as-v<iteration>:.
Likewise, we will add as notes the URLs of the handled PRs, and in the future also the URLs of handled PR comments.
Global metadata is stored in the Git note for the empty blob. This includes all metadata not corresponding to a particular PR, such as the list of GitHub accounts permitted to use GitGitGadget.
By virtue of running the Azure Pipeline in a dedicated agent pool with a single agent, GitGitGadget does not need to worry about concurrency: there is really only one job that is run at any given time.