If you think you have found a bug in Emacs, please report it. We cannot promise to fix it, or always to agree that it is a bug, but we certainly want to hear about it. The same applies for new features you would like to see added. This section will help you to determine whether you found a bug, and if so, construct an effective bug report.
The general procedure when you find something that could be a bug is as follows:
report-emacs-bug, which assists
you in doing so. Submitting a bug report starts the process of
investigating and fixing the bug, where you will receive copies of
email messages discussing the bug, in which we might ask you to
provide more information, test possible fixes, etc.
Before reporting a bug, if at all possible, please check to see if we already know about it. Indeed, it may already have been fixed in a later release of Emacs, or in the development version. Here is a list of the main places you can read about known issues:
Instead of browsing the bug tracker as a web page, you can browse it
from Emacs using the debbugs package, which can be downloaded
via the Package Menu (see Emacs Lisp Packages). This package provides the
command M-x debbugs-gnu to list bugs, and M-x
debbugs-gnu-search to search for a specific bug. User tags, applied
by the Emacs maintainers, are shown by M-x debbugs-gnu-usertags.
If you like, you can subscribe to the list. Be aware that its purpose is to provide the Emacs maintainers with information about bugs and feature requests, so reports may contain fairly large amounts of data; spectators should not complain about this.
If Emacs accesses an invalid memory location (a.k.a. “segmentation fault”) or exits with an operating system error message that indicates a problem in the program (as opposed to something like “disk full”), then it is certainly a bug.
If the Emacs display does not correspond properly to the contents of the buffer, then it is a bug. But you should check that features like buffer narrowing (see Narrowing), which can hide parts of the buffer or change how it is displayed, are not responsible.
Taking forever to complete a command can be a bug, but you must make sure that it is really Emacs’s fault. Some commands simply take a long time. Type C-g (C-Break on MS-DOS) and then C-h l to see whether the input Emacs received was what you intended to type; if the input was such that you know it should have been processed quickly, report a bug. If you don’t know whether the command should take a long time, find out by looking in the manual or by asking for assistance.
If a command you are familiar with causes an Emacs error message in a case where its usual definition ought to be reasonable, it is probably a bug.
If a command does the wrong thing, that is a bug. But be sure you know for certain what it ought to have done. If you aren’t familiar with the command, it might actually be working right. If in doubt, read the command’s documentation (see Help by Command or Variable Name).
A command’s intended definition may not be the best possible definition for editing with. This is a very important sort of problem, but it is also a matter of judgment. Also, it is easy to come to such a conclusion out of ignorance of some of the existing features. It is probably best not to complain about such a problem until you have checked the documentation in the usual ways, feel confident that you understand it, and know for certain that what you want is not available. Ask other Emacs users, too. If you are not sure what the command is supposed to do after a careful reading of the manual, check the index and glossary for any terms that may be unclear.
If after careful rereading of the manual you still do not understand what the command should do, that indicates a bug in the manual, which you should report. The manual’s job is to make everything clear to people who are not Emacs experts—including you. It is just as important to report documentation bugs as program bugs.
If the built-in documentation for a function or variable disagrees with the manual, one of them must be wrong; that is a bug.
For problems with packages that are not part of Emacs, it is better to begin by reporting them to the package developers.
When you decide that there is a bug, it is important to report it, and to report it in a way which is useful. What is most useful is an exact description of what commands you type, starting with the shell command to run Emacs, until the problem happens, and the effects produced by typing those commands.
The most important principle in reporting a bug is to report facts. Hypotheses and verbal descriptions are no substitute for the detailed raw data. Reporting the facts is straightforward, but many people strain to posit explanations and report them instead of the facts. If the explanations are based on guesses about how Emacs is implemented, they might not be useful; meanwhile, lacking the facts, we will have no real information about the bug. If you want to actually debug the problem, and report explanations that are more than guesses, that is useful—but please include the raw facts as well.
For example, suppose that you type C-x C-f /glorp/baz.ugh RET, visiting a file which (you know) happens to be rather large, and Emacs displays ‘I feel pretty today’. The bug report would need to provide all that information. You should not assume that the problem is due to the size of the file and say, “I visited a large file, and Emacs displayed ‘I feel pretty today’.” This is what we mean by “guessing explanations”. The problem might be due to the fact that there is a ‘z’ in the file name. If this is so, then when we got your report, we would try out the problem with some large file, probably with no ‘z’ in its name, and not see any problem. There is no way we could guess that we should try visiting a file with a ‘z’ in its name.
You should not even say “visit a file” instead of C-x C-f. That’s because a file can be visited in more than one way, and there’s no certainty that all of them reproduce the problem. Similarly, rather than saying “if I have three characters on the line”, say “after I type RET A B C RET C-p”, if that is the way you entered the text—that is, tell us about the text which in your case produced the problem.
If possible, try quickly to reproduce the bug by invoking Emacs with
emacs -Q (so that Emacs starts with no initial
customizations; see Initial Options), and repeating the steps that
you took to trigger the bug. If you can reproduce the bug this way,
that rules out bugs in your personal customizations and makes the bug
much easier to reproduce. Then your bug report should begin by
stating that you started Emacs with emacs -Q, followed by
the exact sequence of steps for reproducing the bug. If possible,
inform us of the exact contents of any file that is needed to
reproduce the bug.
Some bugs are not reproducible from emacs -Q; some are not
easily reproducible at all. In that case, you should report what you
have—but, as before, please stick to the raw facts about what you
did to trigger the bug the first time.
If you have multiple issues that you want to report, please make a separate bug report for each.
Before reporting a bug, first try to see if the problem has already been reported (see Reading Existing Bug Reports and Known Problems).
If you are able to, try the latest release of Emacs to see if the problem has already been fixed. Even better is to try the latest development version. We recognize that this is not easy for some people, so do not feel that you absolutely must do this before making a report.
The best way to write a bug report for Emacs is to use the command M-x report-emacs-bug. This sets up a mail buffer (see Sending Mail) and automatically inserts some of the essential information. However, it cannot supply all the necessary information; you should still read and follow the guidelines below, so you can enter the other crucial information by hand before you send the message. You may feel that some of the information inserted by M-x report-emacs-bug is not relevant, but unless you are absolutely sure, it is best to leave it, so that the developers can decide for themselves.
When you have finished writing your report, type C-c C-c and it will be sent to the Emacs maintainers at bug-gnu-emacs. If you cannot send mail from inside Emacs, you can copy the text of your report to your normal mail client (if your system supports it, you can type C-c M-i to have Emacs do this for you) and send it to that address. Or you can simply send an email to that address describing the problem, including the necessary information mentioned below.
If you want to submit code to Emacs (to fix a problem or implement a new feature), the easiest way to do this is to send a patch to the Emacs issue tracker. Use the M-x submit-emacs-patch command for that, which works much the same as when reporting bugs; see Sending Patches for GNU Emacs.
In any case, your report will be sent to the ‘bug-gnu-emacs’ mailing list, and stored in the GNU Bug Tracker at https://debbugs.gnu.org. Please include a valid reply email address, in case we need to ask you for more information about your report. Submissions are moderated, so there may be a delay before your report actually appears on the tracker.
You do not need to know how the GNU Bug Tracker works in order to report a bug, but if you want to, you can read the tracker’s online documentation to see the various features you can use.
All mail sent to the ‘bug-gnu-emacs’ mailing list is also gatewayed to the ‘gnu.emacs.bug’ newsgroup. The reverse is also true, but we ask you not to post bug reports (or replies) via the newsgroup. It can make it much harder to contact you if we need to ask for more information, and it does not integrate well with the bug tracker.
If your data is more than 500,000 bytes, please don’t include it directly in the bug report; instead, offer to send it on request, or make it available online and say where. Large attachments are best sent compressed.
The GNU Bug Tracker will assign a bug number to your report; please use it in the following discussions, keeping the bug address in the list of recipients, so that the bug discussion is recorded by the tracker. The bug address will look like ‘nnnnn@debbugs.gnu.org’, where nnnnn is the bug number.
To enable maintainers to investigate a bug, your report should include all these things:
Of course, if the bug is that Emacs gets a fatal signal, then one can’t miss it. But if the bug is incorrect text, the maintainer might fail to notice what is wrong. Why leave it to chance?
Even if the problem you experience is a fatal signal, you should still say so explicitly. Suppose something strange is going on, such as, your copy of the source is out of sync, or you have encountered a bug in the C library on your system. (This has happened!) Your copy might crash and the copy here might not. If you said to expect a crash, then when Emacs here fails to crash, we would know that the bug was not happening. If you don’t say to expect a crash, then we would not know whether the bug was happening—we would not be able to draw any conclusion from our observations.
Usually, description of the behavior and of the way to reproduce the problem needs to specify one or more of the following aspects:
If you can tell us a way to cause the problem without visiting any files, please do so. This makes it much easier to debug. If you do need files, make sure you arrange for us to see their exact contents. For example, it can matter whether there are spaces at the ends of lines, or a newline after the last line in the buffer (nothing ought to care whether the last line is terminated, but try telling the bugs that).
One way to record the input to Emacs precisely is to write a dribble file. To start the file, use the command M-x open-dribble-file. From then on, Emacs copies all your input to the specified dribble file until the Emacs process is killed. Be aware that sensitive information (such as passwords) may end up recorded in the dribble file.
To get the error message text accurately, copy it from the *Messages* buffer into the bug report. Copy all of it, not just part.
-Q switch to prevent loading the init files).
If the problem does not occur then, you must report the precise
contents of any programs that you must load into the Lisp world in
order to cause the problem to occur.
The line numbers in the development sources don’t match those in your sources. It would take extra work for the maintainers to determine what code is in your version at a given line number, and we could not be certain.
TERM), the complete termcap
entry for the terminal from /etc/termcap (since that file is
not identical on all machines), and the output that Emacs actually
sent to the terminal.
The way to collect the terminal output is to invoke the command M-x open-termscript just after starting Emacs; it will prompt you for the name of the file where to record all terminal output until the Emacs process is killed. If the problem happens when Emacs starts up, put the Lisp expression
(open-termscript "~/termscript")
into your Emacs initialization file so that the termscript file will be open when Emacs displays the screen for the first time.
Be warned: it is often difficult, and sometimes impossible, to fix a terminal-dependent bug without access to a terminal of the type that stimulates the bug.
M-x report-emacs-bug includes this information automatically, but if you are not using that command for your report you can get the version number by typing M-x emacs-version RET. If that command does not work, you probably have something other than GNU Emacs, so you will have to report the bug somewhere else.
configure command when
Emacs was built (automatically included by M-x
report-emacs-bug).
Be precise about these changes. A description in English is not enough—send a unified context diff for them.
Adding files of your own, or porting to another machine, is a modification of the source.
echo LC_ALL=$LC_ALL LC_COLLATE=$LC_COLLATE LC_CTYPE=$LC_CTYPE \ LC_MESSAGES=$LC_MESSAGES LC_TIME=$LC_TIME LANG=$LANG
You can also use the locale command, if your system has it,
to display your locale settings.
Here are some things that are not necessary in a bug report:
Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.
This is often time-consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. You might as well save time by not searching for additional examples. It is better to send the bug report right away, go back to editing, and find another bug to report.
Of course, if you can find a simpler example to report instead of the original one, that is a convenience. Errors in the output will be easier to spot, running under the debugger will take less time, etc.
However, simplification is not vital; if you can’t do this or don’t have time to try, please report the bug with your original test case.
Debugging the core dump might be useful, but it can only be done on your machine, with your Emacs executable. Therefore, sending the core dump file to the Emacs maintainers won’t be useful. Above all, don’t include the core file in an email bug report! Such a large message can be extremely inconvenient.
System-call traces are very useful for certain special kinds of debugging, but in most cases they give little useful information. It is therefore strange that many people seem to think that the way to report information about a crash is to send a system-call trace. Perhaps this is a habit formed from experience debugging programs that don’t have source code or debugging symbols.
In most programs, a backtrace is normally far, far more informative than
a system-call trace. Even in Emacs, a simple backtrace is generally
more informative, though to give full information you should supplement
the backtrace by displaying variable values and printing them as Lisp
objects with pr (see above).
A patch for the bug is useful if it is a good one. But don’t omit the other information that a bug report needs, such as the test case, on the assumption that a patch is sufficient. We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all. And if we can’t understand what bug you are trying to fix, or why your patch should be an improvement, we mustn’t install it. See Sending Patches for GNU Emacs, for guidelines on how to make it easy for us to understand and install your patches.
Such guesses are usually wrong. Even experts can’t guess right about such things without first using the debugger to find the facts.
If you are willing to debug Emacs and provide additional information about the bug, here is some useful advice:
To debug the error, we suggest using Edebug. See Edebug in the Emacs Lisp Reference Manual, for information on debugging Emacs Lisp programs with the Edebug package.
This use of the debugger is possible only if you know how to make the bug happen again. If you can’t make it happen again, at least copy the whole error message.
debug-on-quit
non-nil will start the Lisp debugger and show a backtrace.
This backtrace is useful for debugging such long loops, so if you can
produce it, copy it into the bug report.
If you cannot get Emacs to respond to C-g (e.g., because
inhibit-quit is set), then you can try sending the signal
specified by debug-on-event (default SIGUSR2) from outside
Emacs to cause it to enter the debugger.
However, you need to think when you collect the additional information if you want it to show what causes the bug.
For example, many people send just a C-level backtrace, but that is not very useful by itself. A simple backtrace with arguments often conveys little about what is happening inside GNU Emacs, because most of the arguments listed in the backtrace are pointers to Lisp objects. The numeric values of these pointers have no significance whatever; all that matters is the contents of the objects they point to (and most of the contents are themselves pointers).
To provide useful information, you need to show the values of Lisp objects in Lisp notation. Do this for each variable which is a Lisp object, in several stack frames near the bottom of the stack. Look at the source to see which variables are Lisp objects, because the debugger thinks of them as integers.
To show a variable’s value in Lisp syntax, first print its value, then
use the user-defined GDB command pr to print the Lisp object in
Lisp syntax. (If you must use another debugger, call the function
debug_print with the object as an argument.) The pr
command is defined by the file .gdbinit, and it works only if you
are debugging a running process (not with a core dump).
To make Lisp errors stop Emacs and return to GDB, put a breakpoint at
Fsignal.
For a backtrace of Lisp functions running, type the GDB command
xbacktrace.
The file .gdbinit defines several other commands that are useful
for examining the data types and contents of Lisp objects. Their names
begin with ‘x’. These commands work at a lower level than
pr, and are less convenient, but they may work even when
pr does not, such as when debugging a core dump or when Emacs has
had a fatal signal.
More detailed advice and other useful techniques for debugging Emacs are available in the file etc/DEBUG in the Emacs distribution. That file also includes instructions for investigating problems whereby Emacs stops responding (many people assume that Emacs is “hung”, whereas in fact it might be in an infinite loop).
To find the file etc/DEBUG in your Emacs installation, use the
directory name stored in the variable data-directory.
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.
Every patch must have several pieces of information before we can properly evaluate it. They are described below.
When you have all these pieces, use the M-x submit-emacs-patch command to send the patch. The command will prompt you for the Subject of the patch and a patch file. It will then create and display a Message mode buffer with the patch file as an attachment, display the buffer, and let you explain more about the patch and add any other information as requested below. When you are done, type C-c C-c to send the patch via email to the developers. It will be sent to the GNU Bug Tracker at https://debbugs.gnu.org. The tracker will assign a number to your submission, just like it does with bug reports. The developers will usually respond, perhaps asking you for more details or any additional information, so be sure to include a valid reply email address.
Here’s what we ask you to provide as part of your patch submissions:
If you make two changes for separate reasons, then we might not want to install them both. We might want to install just one, or install them separately in different versions of Emacs. 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 postpone inclusion of your patches for a long time.
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.
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 is important.
git pull). You can commit your changes
to a private branch and generate a patch from the master version by
using git format-patch master. (This is the preferred method,
as it makes our job of applying the patch easier.) Or you can leave
your changes uncommitted and use git diff, as described below.
When producing the diffs, 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 one.
The purpose of the commit log is to explain the rationale of the changes, the way the modified code solves whatever problems your patch is trying to fix, and also show people where to find what was changed. So you need to be specific about what functions you changed and why. For the details about our style and requirements for good commit log messages, please see the “Commit messages” section of the file CONTRIBUTE in the Emacs source tree.
Please also look at the commit log entries of recent commits to see what sorts of information to put in, and to learn the style that we use. Note that, unlike some other projects, we do require commit logs for documentation, i.e., Texinfo files. See Change Logs, See Change Log Concepts in GNU Coding Standards.
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 files or portions of files that are only used for a particular machine or a particular system. These are safe because they can’t create new bugs on other machines or systems.
Please help us keep up with the workload by designing the patch in a form that is clearly safe to install.