60.4 Sending Patches for GNU Emacs
If you would like to write bug fixes or improvements for GNU Emacs,
that is very helpful. When you send your changes, please follow these
guidelines to make it easy for the maintainers to use them. If you
don't follow these guidelines, your information might still be useful,
but using it will take extra work. Maintaining GNU Emacs is a lot of
work in the best of circumstances, and we can't keep up unless you do
your best to help.
- Send an explanation with your changes of what problem they fix or what
improvement they bring about. For a bug fix, just include a copy of the
bug report, and explain why the change fixes the bug.
(Referring to a bug report is not as good as including it, because then
we will have to look it up, and we have probably already deleted it if
we've already fixed the bug.)
- Always include a proper bug report for the problem you think you have
fixed. We need to convince ourselves that the change is right before
installing it. Even if it is correct, we might have trouble
understanding it if we don't have a way to reproduce the problem.
- Include all the comments that are appropriate to help people reading the
source in the future understand why this change was needed.
- Don't mix together changes made for different reasons.
Send them individually.
If you make two changes for separate reasons, then we might not want to
install them both. We might want to install just one. If you send them
all jumbled together in a single set of diffs, we have to do extra work
to disentangle them—to figure out which parts of the change serve
which purpose. If we don't have time for this, we might have to ignore
your changes entirely.
If you send each change as soon as you have written it, with its own
explanation, then two changes never get tangled up, and we can consider
each one properly without any extra work to disentangle them.
- Send each change as soon as that change is finished. Sometimes people
think they are helping us by accumulating many changes to send them all
together. As explained above, this is absolutely the worst thing you
Since you should send each change separately, you might as well send it
right away. That gives us the option of installing it immediately if it
- Use ‘diff -c’ to make your diffs. Diffs without context are hard
to install reliably. More than that, they are hard to study; we must
always study a patch to decide whether we want to install it. Unidiff
format is better than contextless diffs, but not as easy to read as
If you have GNU diff, use ‘diff -c -F'^[_a-zA-Z0-9$]+ *('’ when
making diffs of C code. This shows the name of the function that each
change occurs in.
- Avoid any ambiguity as to which is the old version and which is the new.
Please make the old version the first argument to diff, and the new
version the second argument. And please give one version or the other a
name that indicates whether it is the old version or your new changed
- Write the change log entries for your changes. This is both to save us
the extra work of writing them, and to help explain your changes so we
can understand them.
The purpose of the change log is to show people where to find what was
changed. So you need to be specific about what functions you changed;
in large functions, it's often helpful to indicate where within the
function the change was.
On the other hand, once you have shown people where to find the change,
you need not explain its purpose in the change log. Thus, if you add a
new function, all you need to say about it is that it is new. If you
feel that the purpose needs explaining, it probably does—but put the
explanation in comments in the code. It will be more useful there.
Please read the ChangeLog files in the src and lisp
directories to see what sorts of information to put in, and to learn the
style that we use. If you would like your name to appear in the header
line, showing who made the change, send us the header line.
See Change Log.
- When you write the fix, keep in mind that we can't install a change that
would break other systems. Please think about what effect your change
will have if compiled on another type of system.
Sometimes people send fixes that might be an improvement in
general—but it is hard to be sure of this. It's hard to install
such changes because we have to study them very carefully. Of course,
a good explanation of the reasoning by which you concluded the change
was correct can help convince us.
The safest changes are changes to the configuration files for a
particular machine. These are safe because they can't create new bugs
on other machines.
Please help us keep up with the workload by designing the patch in a
form that is clearly safe to install.