doc: Use GitLab MRs for patches, not the list

Though Wayland and the protocols still use mail-based patch review,
Weston can now move to GitLab MRs with review through that system.

Add some documentation on how to submit patches through GitLab,
specifically targeted at people who may be familiar with GitLab review,
but not familiar with our rebasing microcommit workflow.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

CONTRIBUTING.md

@@ -4,8 +4,48 @@ Contributing to Weston
 Sending patches
 ---------------
 
-Patches should be sent to **wayland-devel@lists.freedesktop.org**, using
+Patches should be sent via
-`git send-email`. See [git documentation] for help.
+[GitLab merge requests](https://docs.gitlab.com/ce/gitlab-basics/add-merge-request.html).
+Weston is
+[hosted on freedesktop.org's GitLab](https://gitlab.freedesktop.org/wayland/weston/):
+in order to submit code, you should create an account on this GitLab instance,
+fork the core Weston repository, push your changes to a branch in your new
+repository, and then submit these patches for review through a merge request.
+
+Weston formerly accepted patches via `git-send-email`, sent to
+**wayland-devel@lists.freedesktop.org**; these were
+[tracked using Patchwork](https://patchwork.freedesktop.org/projects/wayland/).
+Some old patches continue to be sent this way, and we may accept small new
+patches sent to the list, but please send all new patches through GitLab merge
+requests.
+
+Formatting and separating commits
+---------------------------------
+
+Unlike many projects using GitHub and GitLab, Weston has a
+[linear, 'recipe' style history](http://www.bitsnbites.eu/git-history-work-log-vs-recipe/).
+This means that every commit should be small, digestible, stand-alone, and
+functional. Rather than a purely chronological commit history like this:
+
+    doc: final docs for view transforms
+    fix tests when disabled, redo broken doc formatting
+    better transformed-view iteration (thanks Hannah!)
+    try to catch more cases in tests
+    tests: add new spline test
+    fix compilation on splines
+    doc: notes on reticulating splines
+    compositor: add spline reticulation for view transforms
+
+we aim to have a clean history which only reflects the final state, broken up
+into functional groupings:
+
+    compositor: add spline reticulation for view transforms
+    compositor: new iterator for view transforms
+    tests: add view-transform correctness tests
+    doc: fix Doxygen formatting for view transforms
+
+This ensures that the final patch series only contains the final state,
+without the changes and missteps taken along the development process.
 
 The first line of a commit message should contain a prefix indicating
 what part is affected by the patch followed by one sentence that
@@ -54,74 +94,37 @@ deserve, and the patches may cause redundant review effort.
 Tracking patches and following up
 ---------------------------------
 
-[Wayland Patchwork](http://patchwork.freedesktop.org/project/wayland/list/) is
+Once submitted to GitLab, your patches will be reviewed by the Weston
-used for tracking patches to Wayland and Weston. Xwayland patches are tracked
+development team on GitLab. Review may be entirely positive and result in your
-with the [Xorg project](https://patchwork.freedesktop.org/project/Xorg/list/)
+code landing instantly, in which case, great! You're done. However, we may ask
-instead. Libinput patches, even though they use the same mailing list as
+you to make some revisions: fixing some bugs we've noticed, working to a
-Wayland, are not tracked in the Wayland Patchwork.
+slightly different design, or adding documentation and tests.
 
-The following applies only to Wayland and Weston.
+If you do get asked to revise the patches, please bear in mind the notes above.
+You should use `git rebase -i` to make revisions, so that your patches follow
+the clear linear split documented above. Following that split makes it easier
+for reviewers to understand your work, and to verify that the code you're
+submitting is correct.
 
-If a patch is not found in Patchwork, there is a high possibility for it to be
+A common request is to split single large patch into multiple patches. This can
-forgotten. Patches attached to bug reports or not arriving to the mailing list
+happen, for example, if when adding a new feature you notice a bug in Weston's
-because of e.g. subscription issues will not be in Patchwork because Patchwork
+core which you need to fix to progress. Separating these changes into separate
-only collects patches sent to the list.
+commits will allow us to verify and land the bugfix quickly, pushing part of
+your work for the good of everyone, whilst revision and discussion continues on
+the larger feature part. It also allows us to direct you towards reviewers who
+best understand the different areas you are working on.
 
-When you send a revised version of a patch, it would be very nice to mark your
+When you have made any requested changes, please rebase the commits, verify
-old patch as superseded (or rejected, if that is applicable). You can change
+that they still individually look good, then force-push your new branch to
-the status of your own patches by registering to Patchwork - ownership is
+GitLab. This will update the merge request and notify everyone subscribed to
-identified by email address you use to register. Updating your patch status
+your merge request, so they can review it again.
-appropriately will help maintainer work.
 
-The following patch states are found in Patchwork:
+There are also
-
+[many GitLab CLI clients](https://about.gitlab.com/applications/#cli-clients),
-- **New**:
+if you prefer to avoid the web interface. It may be difficult to follow review
-    Patches under discussion or not yet processed.
+comments without using the web interface though, so we do recommend using this
-
+to go through the review process, even if you use other clients to track the
-- **Under review**:
+list of available patches.
-    Mostly unused state.
-
-- **Accepted**:
-    The patch is merged in the master branch upstream, as is or slightly
-    modified.
-
-- **Rejected**:
-    The idea or approach is rejected and cannot be fixed by revising
-    the patch.
-
-- **RFC**:
-    Request for comments, not meant to be merged as is.
-
-- **Not applicable**:
-    The email was not actually a patch, or the patch is not for Wayland or
-    Weston. Libinput patches are usually automatically ignored by Wayland
-    Patchwork, but if they get through, they will be marked as Not
-    applicable.
-
-- **Changes requested**:
-    Reviewers determined that changes to the patch are needed. The
-    submitter is expected to send a revised version. (You should
-    not wait for your patch to be set to this state before revising,
-    though.)
-
-- **Awaiting upstream**:
-    Mostly unused as the patch is waiting for upstream actions but
-    is not shown in the default list, which means it is easy to
-    overlook.
-
-- **Superseded**:
-    A revised version of the patch has been submitted.
-
-- **Deferred**:
-    Used mostly during freeze periods before releases, to temporarily
-    hide patches that cannot be merged during a freeze.
-
-Note, that in the default listing, only patches in *New* or *Under review* are
-shown.
-
-There is also a command line interface to Patchwork called `pwclient`, see
-http://patchwork.freedesktop.org/project/wayland/
-for links where to get it and the sample `.pwclientrc` for Wayland/Weston.
 
 
 Coding style