admin: Add documentation for gitmerge.el

* gitmerge.el: New file.
* notes/git-workflow: Add documentation for using it.

1 files changed, 51 insertions, 5 deletions

diff --git a/admin/notes/git-workflow b/admin/notes/git-workflow
index 71ebd2abc96..d1d105a8a7a 100644
--- a/admin/notes/git-workflow
+++ b/admin/notes/git-workflow
@@ -68,11 +68,57 @@ and add "Backport:" to the commit string.  Then
 git push
 
 
-Merging emacs-24 to trunk
-=========================
-
-This has yet to be written.
-
+Merging emacs-24 to trunk/master
+================================
+
+It is recommended to use the file gitmerge.el in the admin directory
+for merging 'emacs-24' into 'master'.  It will take care of many
+things which would otherwise have to be done manually, like ignoring
+commits that should not land in master, fixing up ChangeLogs and
+automatically dealing with certain types of conflicts.  If you really
+want to, you can do the merge manually, but then you're on your own.
+If you still choose to do that, make absolutely sure that you *always*
+use the 'merge' command to transport commits from 'emacs-24' to
+'master'.  *Never* use 'cherry-pick'!  If you don't know why, then you
+shouldn't manually do the merge in the first place; just use
+gitmerge.el instead.
+
+How to use gitmerge.el:
+
+Enter the Emacs repository, checkout 'master' and make sure it's
+up-to-date by doing a pull.  Then start Emacs with
+
+  emacs -l admin/gitmerge.el -f gitmerge
+
+You'll be asked for the branch to merge, which will default to
+'origin/emacs-24', which you should accept.  Merging a local tracking
+branch is discouraged, since it might not be up-to-date, or worse,
+contain commits from you which are not yet pushed upstream.
+
+You will now see the list of commits from 'emacs-24' which are not yet
+merged to 'master'.  You might also see commits that are already
+marked for "skipping", which means that they will be merged with a
+different merge strategy ('ours'), which will effectively ignore the
+commit's diff while still being seen as merged, so it won't turn up
+again in future merges.  Recognizing these kinds of commits is done
+with a simple regexp searching the log for strings like 'backport' or
+'merge', so you'll probably see false positives as well as false
+negatives.  Carefully go through the commits, investigate them by
+hitting 'l', 'd' and 'f', and mark or unmark them for skipping with
+'s'.  When you're done, hit 'm' to start the merge.
+
+You'll likely get conflicts during the process which cannot be dealt
+with automatically.  In that case, the merge will stop and show you
+the list of conflicted files.  Resolve those conflicts as usual using
+smerge and restart gitmerge (remember to enter the repository when
+doing that).  You don't have to 'add' the resolved files and 'commit'
+the resulting merge, but if you really want to, feel free to do that.
+Note you can also resume gitmerge in a new Emacs session, since the
+current state will be saved to disk.
+
+When everything's done, look hard at the resulting merge.  Skipping
+commits requires separate merges, so don't be surprised to see more
+than one merge commit.  If you're happy, push.
 
 Warnings about X11 forwarding
 =============================