emacs/admin/notes/repo

NOTES ON COMMITTING TO EMACS'S REPOSITORY    -*- outline -*-

* Install changes only on one branch, let them get merged elsewhere if needed.

In particular, install bug-fixes only on the release branch (if there
is one) and let them get synced to the master; do not install them by
hand on the master as well.  E.g. if there is an active "emacs-24" branch
and you have a bug-fix appropriate for the next emacs-24.x release,
install it only on the emacs-24 branch, not on the master as well.

Installing things manually into more than one branch makes merges more
difficult.

https://lists.gnu.org/r/emacs-devel/2010-03/msg01124.html

The exception is, if you know that the change will be difficult to
merge to the master (eg because the master code has changed a lot).
In that case, it's helpful if you can apply the change to both master
and branch yourself (when committing the branch change, indicate
in the commit log that it should not be merged to the master, by
including the phrase "Not to be merged to master", or any other phrase
that matches "merge").

* Installing changes from your personal branches.

If your branch has only a single commit, or many different real
commits, it is fine to do a merge.  If your branch has only a very
small number of "real" commits, but several "merge from masters", it is
preferred that you take your branch's diff, apply it to the master, and
commit directly, not merge.  This keeps the history cleaner.

In general, when working on some feature in a separate branch, it is
preferable not to merge from master until you are done with the
feature.  Unless you really need some change that was done on the
master while you were developing on the branch, you don't really need
those merges; just merge once, when you are done with the feature, and
Git will take care of the rest.  Git is much better in this than CVS,
so interim merges are unnecessary.

Or use shelves; or rebase; or do something else.  See the thread for
yet another fun excursion into the exciting world of version control.

https://lists.gnu.org/r/emacs-devel/2010-04/msg00086.html

* feature and scratch branches

Besides the master branch, which is where development takes place, and
the "emacs-NN" release branches, we also have branches whose names
start with "scratch/" and "feature/".  The "feature/" prefix is used
for feature branches that are intended to live for some time, while
"scratch/" is for one-off throw-away-after-use branches.

We do not intend to "git merge" from scratch branches, so force-pushes
are tolerated, as well as commits with poor style, incomplete commit
messages, etc.

We do expect to "git merge" from feature branches so: no force push,
and no commits that don't have a proper commit message.

Automatic tests are run for feature/* branches on EMBA.
See: https://emba.gnu.org/emacs/emacs/-/pipelines

* Installing changes from gnulib

Some of the files in Emacs are copied from gnulib.  To synchronize
these files from the version of gnulib that you have checked out into
a sibling directory of your branch, type "admin/merge-gnulib"; this
will check out the latest version of gnulib if there is no sibling
directory already.  It is a good idea to run "git status" afterwards,
so that if a gnulib module added a file, you can record the new file
using "git add".  After synchronizing from gnulib, do a "make" in the
usual way.

To change the set of gnulib modules, change the GNULIB_MODULES
variable in admin/merge-gnulib before running it.

If you remove a gnulib module, or if a gnulib module
removes a file, then remove the corresponding files by hand.

* How to merge changes from emacs-24 to master

[The section on git merge procedure has not yet been written.]

You may see conflicts in autoload md5sums in comments.  Strictly
speaking, the right thing to do is merge everything else, resolve the
conflict by choosing either the master or branch version, then run
'make -C lisp autoloads' to update the md5sums to the correct master
value before committing.

* Re-adding a file that has been removed from the repository

Let's suppose you've done:

git rm file; git commit -a

You can just restore a copy of the file and then re-add it;
git does not have per-file history so this will not harm
anything.

Alternatively, you can do

git revert XXXXX

where XXXXX is the hash of the commit in which file was removed.
This backs out the entire changeset the deletion was part of,
which is often more appropriate.

* Undoing a commit (uncommitting)

If you have not pushed the commit, you may be able to use 'git reset
--hard' with a hash argument to revert the your local repo copy to the
pre-commit state.

If you have pushed  commit, resetting will be ineffective because it
will only vanish the commit in your local copy.  Instead, use 'git
revert', giving it the commit ID as argument.  This will create a
new commit that backs out the change.  Then push that.

Note that git will generate a log message for the revert that includes
a git hash.  Please edit this to refer to the commit by the first line
of its log comment, or by committer and date, or by something else
that is not the hash.  As noted previously, it is best to avoid hashes
in comments in case we someday have to change version-control systems
again.

* Bisecting

This is a semi-automated way to find the revision that introduced a bug.
Browse 'git help bisect' for technical instructions.

It is recommended to start a bisection with the admin/git-bisect-start
script.  Using that script ensures that commits in branches that are
the result of merging external trees into the Emacs repository, as
well as certain commits on which Emacs fails to build, are skipped
during the bisection process.  That script can also be executed
automatically when 'git bisect start' is called, with the help of a
wrapper script that is included in its commentary section.

* Maintaining ChangeLog history

Older ChangeLog entries are kept in history files named ChangeLog.1,
ChangeLog.2, etc., and can be edited just as any other source files
can.  Newer ChangeLog entries are stored in the repository as commit
messages, which cannot be edited directly.

'make ChangeLog' copies newer ChangeLog entries into a file
'ChangeLog' that is intended to be put into the distribution tarball.
This ChangeLog file is not put into the repository.

'make change-history' copies all newer ChangeLog entries into the
start of the newest ChangeLog history file.  These ChangeLog entries
are thereafter considered to be old, so later uses of 'make ChangeLog'
and/or 'make change-history' will no longer copy the entries.

To alter ChangeLog history, run 'make change-history' and commit the
changes made by that command.  Then edit the ChangeLog history files
manually and commit those changes in a second, distinct commit.
Altering ChangeLog history like this can make things harder for those
who handle merging branches and Emacs releases, so reserve it for
correcting more serious mistakes.