## Tl;dr; This issue is preliminary work for https://gitlab.com/gitlab-org/gitlab-ee/issues/7380. This issue has to be solved either way and considered as a checkpoint in the big picture. ### Problem to Solve Currently, GitLab Runner can fetch source code from only branch/tag refs, such as `refs/heads/branch_name` or `refs/tags/tag_name`. However, in order to support https://gitlab.com/gitlab-org/gitlab-ee/issues/7380 workflow, GitLab Runner has to be able to fetch source code from *custom* refs. Today, we have a custom ref on the merge request context. This ref is formatted `refs/merge-requests/:iid/head` and it points to the HEAD sha of the source branch. We should use this ref sooner than later because it's quite breaking change as it could break the other functionlities e.g. https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25504#note_145792438. We should measure the impact before we stepping into https://gitlab.com/gitlab-org/gitlab-ee/issues/7380, which uses `refs/merge-requests/:iid/merge` ref. ### Design and design requirements #### FE design specs! :gem: [specs](https://gitlab-org.gitlab.io/gitlab-design/hosted/dimitrie/ee%237380-run-build-on-merged-code-2-spec-previews/) #### Merge request widget Relies on the same logic that would be implemented with https://gitlab.com/gitlab-org/gitlab-ce/issues/40246 | Requirements | Mockups | | ------ | ------ | | Merge request is merge-able | <ul data-sourcepos="93:1-94:0" dir="auto"><li data-sourcepos="93:1-94:0">We will show merge widget as normal (no changes)</li></ul> | | Merge request is __not__ merge-able | <ul data-sourcepos="93:1-94:0" dir="auto"><li data-sourcepos="93:1-94:0">We will show merge widget as normal (no changes)</li></ul> | | Merge request is being merged | <ul data-sourcepos="104:1-105:0" dir="auto"><li data-sourcepos="104:1-105:0">Merge button has spinner and states <code>Merging</code> (no changes)</li></ul> | | Fork merge request <ul><li>Warning `Merge request pipelines are enabled but will not activate due to this being a fork merge request`</li><li>Warning merge button (Merge when pipeline succeeds will also be warning colored as we rely on a normal branch pipeline in those cases)</li></ul> |  | | Invalid merge request as target-branch advanced (linear history)<ul><li>merge button disabled</li><li>warning target branch has advanced, update source branch and retry merge</li></ul> |  | | Invalid merge request pipeline as target-branch advanced (non-linear history)<ul><li>merge when pipeline succeeds button (which triggers new pipeline when pressed)</li><li>warning target branch has advanced, retry merge</li></ul> |  | | Merge request pipeline failed <ul><li>merge when pipeline succeeds button (which triggers new pipeline when pressed)</li><li>warning pipeline failed, retry merge or fix failure</li></ul> |  | | Merge request is converted from WIP to non-WIP | <ul><li>Merge request pipeline is automatically triggered</li><li>merge when pipeline succeeds button is shown (no changes)</li></ul> | ##### Merge request widget pipeline block | Requirements | Mockups | | ------ | ------ | | Normal branch pipeline <ul><li>Unchanged</li></ul> |  | | Detached merge request pipeline <ul><li>Ref now shows merge request ID/Link before the source branch</li></ul> |  | | Merged result merge request pipeline <ul><li>Ref now shows merge request ID/Link before source branch and adds target branch</li></ul> |  | #### Pipeline list view | Requirements | Mockups | | ------ | ------ | | Normal branch pipeline <ul><li>Ref unchanged</li></ul> |  | | Detached merge request pipeline <ul><li>Ref now shows merge request ID/Link</li><li>merge request tag is removed</li><li>`Detached` tag is added</li></ul> |  | | Merged result merge request pipeline <ul><li>Ref now shows merge request ID/Link</li><li>merge request tag is removed</li></ul> |  | #### Pipeline detail view widget | Requirements | Mockups | | ------ | ------ | | Normal branch pipeline <ul><li>Copy `from` changed to `for`</li></ul> |  | | Detached merge request pipeline <ul><li>Ref now shows merge request ID/Link before the source branch</li><li>merge request tag is removed</li><li>`Detached` tag is added</li><li>Copy `from` changed to `for`</li></ul> |  | | Merged result merge request pipeline <ul><li>Ref now shows merge request ID/Link before source branch and adds target branch</li><li>merge request tag is removed</li><li>Copy `from` changed to `for`</li></ul> |  | #### Job detail view sidebar | Requirements | Mockups | | ------ | ------ | | Normal branch pipeline <ul><li>Copy `from` changed to `for`</li></ul> |  | | Detached merge request pipeline <ul><li>Ref now shows merge request ID/Link before the source branch</li><li>Copy `from` changed to `for`</li></ul> |  | | Merged result merge request pipeline <ul><li>Ref now shows merge request ID/Link before source branch and adds target branch</li><li>Copy `from` changed to `for`</li></ul> |  | #### Merge request list view | Requirements | Mockups | | --- | --- | | <ul data-sourcepos="167:1-168:0" dir="auto"><li data-sourcepos="167:1-168:0">Pipeline status will include normal pipeline statuses, merge request pipelines statusses, merge request pipeline statuses, and post merge pipeline statusses, which ever one is the latest and thus most important</li></ul> |  | #### Project settings merge request settings | Requirements | Mockups | | --- | --- | | <ul data-sourcepos="173:1-176:0" dir="auto"><li data-sourcepos="173:1-173:49">Added option for enabling merge request pipelines for merged result</li><li data-sourcepos="174:1-174:64">Restructured content (FE only, as same checkboxes still apply)</li></ul> |  | #### Put the feature behind the feature flag `ci_detached_pipeline`