Improve Emails on push integration to be more like git-multimail
<!-- The first section "Release notes" is required if you want to have your release post blog MR auto generated. Currently in BETA, details on the **release post item generator** can be found in the handbook: https://about.gitlab.com/handbook/marketing/blog/release-posts/#release-post-item-generator and this video: https://www.youtube.com/watch?v=rfn9ebgTwKg. The next four sections: "Problem to solve", "Intended users", "User experience goal", and "Proposal", are strongly recommended in your first draft, while the rest of the sections can be filled out during the problem validation or breakdown phase. However, keep in mind that providing complete and relevant information early helps our product team validate the problem and start working on a solution. --> ### Release notes <!-- What is the problem and solution you're proposing? This content sets the overall vision for the feature and serves as the release notes that will populate in various places, including the [release post blog](https://about.gitlab.com/releases/categories/releases/) and [Gitlab project releases](https://gitlab.com/gitlab-org/gitlab/-/releases). " --> The Emails on push integration sends a single email for all commits/tags pushed to a branch. Due to the size limit the diff quickly gets too large when multiple commits are pushed. The [git-multimail](https://github.com/git-multimail/git-multimail) hook sends an email for every commit in a thread started with a message containing the git log and diffstat. With each commit having its own email the size limit is reached much less often. The settings for the Emails on push integration gains an option to use separate emails per commit like git-multimail. ### Problem to solve <!-- What problem do we solve? Try to define the who/what/why of the opportunity as a user story. For example, "As a (who), I want (what), so I can (why/value)." --> As a developer of a project I want to reduce the need to view the diff for changes commited by others in the web interface, and be able to reply to the Email on push messages to provide feedback on changes via email to the person who pushed the changes. ### Intended users <!-- Who will use this feature? If known, include any of the following: types of users (e.g. Developer), personas, or specific company roles (e.g. Release Manager). It's okay to write "Unknown" and fill this field in later. Personas are described at https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/ * [Delaney (Development Team Lead)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead) * [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer) * [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer) * [Sidney (Systems Administrator)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator) --> * [Delaney (Development Team Lead)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#delaney-development-team-lead) * [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer) * [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer) * [Sidney (Systems Administrator)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator) ### User experience goal <!-- What is the single user experience workflow this problem addresses? For example, "The user should be able to use the UI/API/.gitlab-ci.yml with GitLab to <perform a specific task>" https://about.gitlab.com/handbook/engineering/ux/ux-research-training/user-story-mapping/ --> The user should be able to commit on changes by email without needing to use the web interface to view the changes. ### Proposal <!-- How are we going to solve the problem? Try to include the user journey! https://about.gitlab.com/handbook/journeys/#user-journey --> 1. User pushes multiple commits to GitLab 2. Email on push integration is triggered 3. Email on push integration collects git log and diffstat of all commits being pushed per branch for the initial email 4. Email on push integration collects git log and diff for each commit 5. Email on push integration records the Message-ID for the initial email 6. Email on push integration uses that Message-ID in In-Reply-To & References header of followup emails for every commit. Those emails contain the git log for that commit and the diff 7. The recipients get an email thread with all the changes being pushed. Allowing them to review those changes in their email client without needing to use the GitLab web interface. ### Further details <!-- Include use cases, benefits, goals, or any other details that will help us understand the problem better. --> The Email on push integration serves to notify contributors to a project of changes. With an email thread per push, it reduces the need to use the web interface to view the changes (diff) allowing for more timely feedback on those changes. Instead of replying to the single email for all the commits, a user can reply to the email for the commit in question. ### Permissions and Security <!-- What permissions are required to perform the described actions? Are they consistent with the existing permissions as documented for users, groups, and projects as appropriate? Is the proposed behavior consistent between the UI, API, and other access methods (e.g. email replies)? Consider adding checkboxes and expectations of users with certain levels of membership https://docs.gitlab.com/ee/user/permissions.html * [ ] Add expected impact to members with no access (0) * [ ] Add expected impact to Guest (10) members * [ ] Add expected impact to Reporter (20) members * [ ] Add expected impact to Developer (30) members * [ ] Add expected impact to Maintainer (40) members * [ ] Add expected impact to Owner (50) members --> * [x] Add expected impact to Developer (30) members * [x] Add expected impact to Maintainer (40) members * [x] Add expected impact to Owner (50) members All these users are expected to be recipients of the Email on push integration, allowing them to provide feedback via email to each other. ### Documentation <!-- See the Feature Change Documentation Workflow https://docs.gitlab.com/ee/development/documentation/workflow.html#for-a-product-change * Add all known Documentation Requirements in this section. See https://docs.gitlab.com/ee/development/documentation/feature-change-workflow.html#documentation-requirements * If this feature requires changing permissions, update the permissions document. See https://docs.gitlab.com/ee/user/permissions.html --> The new option for the Email on push integration needs to be documented. The option also need to be added to the REST API and its documentation. ### Availability & Testing <!-- This section needs to be retained and filled in during the workflow planning breakdown phase of this feature proposal, if not earlier. What risks does this change pose to our availability? How might it affect the quality of the product? What additional test coverage or changes to tests will be needed? Will it require cross-browser testing? Please list the test areas (unit, integration and end-to-end) that needs to be added or updated to ensure that this feature will work as intended. Please use the list below as guidance. * Unit test changes * Integration test changes * End-to-end test change See the test engineering planning process and reach out to your counterpart Software Engineer in Test for assistance: https://about.gitlab.com/handbook/engineering/quality/test-engineering/#test-planning --> * Unit test changes ### What does success look like, and how can we measure that? <!-- Define both the success metrics and acceptance criteria. Note that success metrics indicate the desired business outcomes, while acceptance criteria indicate when the solution is working correctly. If there is no way to measure success, link to an issue that will implement a way to measure this. Create tracking issue using the the Snowplow event tracking template. See https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Snowplow%20event%20tracking.md --> Success is determined by having an option to make the Emails on push integration behave more like git-multimail. ### What is the type of buyer? <!-- What is the buyer persona for this feature? See https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/buyer-persona/ In which enterprise tier should this feature go? See https://about.gitlab.com/handbook/product/pricing/#four-tiers --> Core/Free tier. ### Is this a cross-stage feature? <!-- Communicate if this change will affect multiple Stage Groups or product areas. We recommend always start with the assumption that a feature request will have an impact into another Group. Loop in the most relevant PM and Product Designer from that Group to provide strategic support to help align the Group's broader plan and vision, as well as to avoid UX and technical debt. https://about.gitlab.com/handbook/product/#cross-stage-features --> Unlikely. ### Links / references <!-- Label reminders - you should have one of each of the following labels. Use the following resources to find the appropriate labels: - https://gitlab.com/gitlab-org/gitlab/-/labels - https://about.gitlab.com/handbook/product/categories/features/ -->
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