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diff --git a/doc/user/project/merge_requests/blocking_merge_requests.md b/doc/user/project/merge_requests/blocking_merge_requests.md new file mode 100644 index 00000000000..0506a7cb4a5 --- /dev/null +++ b/doc/user/project/merge_requests/blocking_merge_requests.md @@ -0,0 +1,133 @@ +--- +type: reference, concepts +--- + +# Blocking merge requests **(PREMIUM)** + +> Introduced in GitLab Premium 12.2 + +Blocking merge requests allow dependencies between MRs to be expressed. If a +merge request is blocked by another MR, it cannot be merged until that blocking +MR is itself merged. + +NOTE: **Note:** +Blocking merge requests are a **PREMIUM** feature, but this restriction is only +enforced for the blocked merge request. A merge request in a **CORE** or +**STARTER** project can block a **PREMIUM** merge request, but not vice-versa. + +## Use cases + +* Ensure changes to a library are merged before changes to a project that + imports the library +* Prevent a documentation-only merge request from being merged before the MR + implementing the feature to be documented +* Require an MR updating a permissions matrix to be merged before merging an + MR from someone who hasn't yet been granted permissions + +It is common for a single logical change to span several merge requests. These +MRs may all be in a single project, or they may be spread out across multiple +projects, and the order in which they are merged can be significant. + +For example, given a project `mycorp/awesome-project` that imports a library +at `myfriend/awesome-lib`, adding a feature in `awesome-project` may **also** +require changes to `awesome-lib`, and so necessitate two merge requests. Merging +the `awesome-project` MR before the `awesome-lib` one would break the `master` +branch. + +The `awesome-project` MR could be [marked as WIP](work_in_progress_merge_requests.md), +and the reason for the WIP stated included in the comments. However, this +requires the state of the `awesome-lib` MR to be manually tracked, and doesn't +scale well if the `awesome-project` MR depends on changes to **several** other +projects. + +By marking the `awesome-project` MR as blocked on the `awesome-lib` MR instead, +the status of the dependency is automatically tracked by GitLab, and the WIP +state can be used to communicate the readiness of the code in each individual +MR instead. + +## Configuration + +To continue the above example, you can configure a block when creating the +new MR in `awesome-project` (or by editing it, if it already exists). The block +needs to be configured on the MR that will be **blocked**, rather than on the +**blocking** MR. There is a "Blocking merge requests" section in the form: + + + +Anyone who can edit a merge request can change the list of blocking merge +requests. + +New blocks can be added by reference, by URL, or by using autcompletion. To +remove a block, press the "X" by its reference. + +As blocks can be specified across projects, it's possible that someone else has +added a block for a merge request in a project you don't have access to. These +are shown as a simple count: + + + +If necessary, you can remove all the blocks like this by pressing the "X", just +as you would for a single, visible block. + +Once you're finished, press the "Save changes" button to submit the request, or +"Cancel" to return without making any changes. + +The list of configured blocks, and the status of each one, is shown in the merge +request widget: + + + +Until all blocking merge requests have, themselves, been merged, the "Merge" +button will be disabled. In particular, note that **closed** merge requests +still block their dependents - it is impossible to automatically determine if +merge requests that were blocked by that MR when it was open, are still blocked +when it is closed. + +If a merge request has been closed **and** the block is no longer relevant, it +must be removed as a blocking MR, following the instructions above, before +merge. + +## Limitations + +* API support: [gitlab-ee#12551](https://gitlab.com/gitlab-org/gitlab-ee/issues/12551) +* Blocking relationships are not preserved across project export/import: [gitlab-ee#12549](https://gitlab.com/gitlab-org/gitlab-ee/issues/12549) +* Complex merge order dependencies are not supported: [gitlab-ee#11393](https://gitlab.com/gitlab-org/gitlab-ee/issues/11393) + +The last item merits a little more explanation. Blocking merge requests can be +described as a graph of dependencies. The simplest possible graph has one +merge request blocking another: + +```mermaid +graph LR; + myfriend/awesome-lib!10-->mycorp/awesome-project!100; +``` + +A more complex (and still supported) graph might have several MRs blocking +another from being merged: + +```mermaid +graph LR; + myfriend/awesome-lib!10-->mycorp/awesome-project!100; + herfriend/another-lib!1-->mycorp/awesome-project!100; +``` + +We also support one MR blocking several others from being merged: + +```mermaid +graph LR; + herfriend/another-lib!1-->myfriend/awesome-lib!10; + herfriend/another-lib!1-->mycorp/awesome-project!100; +``` + +What is **not** supported is a "deep", or "nested" graph of dependencies, e.g.: + +```mermaid +graph LR; + herfriend/another-lib!1-->myfriend/awesome-lib!10; + myfriend/awesome-lib!10-->mycorp/awesome-project!100; +``` + +In this example, `myfriend/awesome-lib!10` would be blocked from being merged by +`herfriend/another-lib!1`, and would also block `mycorp/awesome-project!100` +from being merged. This is **not** yet supported. + |