* How developers contribute to GNU Emacs

Here is how software developers can contribute to Emacs.  (Non-developers: see
http://www.gnu.org/software/emacs/manual/html_node/emacs/Contributing.html
or run the shell command 'info "(emacs)Contributing"'.)

** The Emacs repository

Emacs development uses Git on Savannah for its main repository.
Briefly, the following shell commands build and run Emacs from scratch:

	git config --global user.name 'Your Name'
	git config --global user.email 'your.name@example.com'
	git config --global transfer.fsckObjects true
	git clone git://git.sv.gnu.org/emacs.git
	cd emacs
	./autogen.sh
	./configure
	make
	src/emacs

For more details, see
http://www.emacswiki.org/emacs/GitQuickStartForEmacsDevs and
http://www.emacswiki.org/emacs/GitForEmacsDevs or see the file
admin/notes/git-workflow.

** Getting involved with development

You can subscribe to the emacs-devel@gnu.org mailing list, paying
attention to postings with subject lines containing "emacs-announce",
as these discuss important events like feature freezes.  See
http://lists.gnu.org/mailman/listinfo/emacs-devel for mailing list
instructions and archives.  You can develop and commit changes in your
own copy of the repository, and discuss proposed changes on the
mailing list.  Frequent contributors to Emacs can request write access
there.

** Committing changes by others

If committing changes written by someone else, commit in their name,
not yours.  You can use 'git commit --author="AUTHOR"' to specify a
change's author.

** Commit messages

Ordinarily, a change you commit should contain a log entry in its
commit message and should not touch the repository's ChangeLog files.
Here is an example commit message (indented):

	Deactivate shifted region

	Do not silently extend a region that is not highlighted;
	this can happen after a shift (Bug#19003).
	* doc/emacs/mark.texi (Shift Selection): Document the change.
	* lisp/window.el (handle-select-window):
	* src/frame.c (Fhandle_switch_frame, Fselected_frame):
	Deactivate the mark.

Occasionally, commit messages are collected and prepended to a
ChangeLog file, where they can be corrected.  It saves time to get
them right the first time, so here are guidelines for formatting them:

- Start with a single unindented summary line explaining the change;
  do not end this line with a period.  If that line starts with a
  semicolon and a space "; ", the commit message will be ignored when
  generating the ChangeLog file.  Use this for minor commits that do
  not need separate ChangeLog entries, such as changes in etc/NEWS.

- After the summary line, there should be an empty line, then
  unindented ChangeLog entries.

- Limit lines in commit messages to 78 characters, unless they consist
  of a single word of at most 140 characters; this is enforced by a
  commit hook.  It's nicer to limit the summary line to 50 characters;
  this isn't enforced.  If the change can't be summarized so briefly,
  add a paragraph after the empty line and before the individual file
  descriptions.

- If only a single file is changed, the summary line can be the normal
  file first line (starting with the asterisk).  Then there is no
  individual files section.

- If the commit has more than one author, the commit message should
  contain separate lines to mention the other authors, like the
  following:

	Co-authored-by: Joe Schmoe <j.schmoe@example.org>

- If the commit is a tiny change that is exempt from copyright paperwork,
  the commit message should contain a separate line like the following:

	Copyright-paperwork-exempt: yes

- The commit message should contain "Bug#NNNNN" if it is related to
  bug number NNNNN in the debbugs database.  This string is often
  parenthesized, as in "(Bug#19003)".

- Commit messages should contain only printable UTF-8 characters.

- Commit messages should not contain the "Signed-off-by:" lines that
  are used in some other projects.

- Any lines of the commit message that start with "; " are omitted
  from the generated ChangeLog.

- Explaining the rationale for a design choice is best done in comments
  in the source code.  However, sometimes it is useful to describe just
  the rationale for a change; that can be done in the commit message
  between the summary line and the file entries.

- Emacs generally follows the GNU coding standards for ChangeLogs: see
  http://www.gnu.org/prep/standards/html_node/Change-Logs.html
  or run 'info "(standards)Change Logs"'.  One exception is that
  commits still sometimes quote `like-this' (as the standards used to
  recommend) rather than 'like-this' or ‘like this’ (as they do now),
  as `...' is so widely used elsewhere in Emacs.

- Some commenting rules in the GNU coding standards also apply
  to ChangeLog entries: they must be in English, and be complete
  sentences starting with a capital and ending with a period (except
  the summary line should not end in a period).  See
  http://www.gnu.org/prep/standards/html_node/Comments.html
  or run 'info "(standards)Comments"'.

  They are preserved indefinitely, and have a reasonable chance of
  being read in the future, so it's better that they have good
  presentation.

- Use the present tense; describe "what the change does", not "what
  the change did".

- Preferred form for several entries with the same content:

	* lisp/help.el (view-lossage):
	* lisp/kmacro.el (kmacro-edit-lossage):
	* lisp/edmacro.el (edit-kbd-macro): Fix docstring, lossage is now 300.

  (Rather than anything involving "ditto" and suchlike.)

- There is no standard or recommended way to identify revisions in
  ChangeLog entries.  Using Git SHA1 values limits the usability of
  the references to Git, and will become much less useful if Emacs
  switches to a different VCS.  So we recommend against that.

  One way to identify revisions is by quoting their summary line.
  Another is with an action stamp - an RFC3339 date followed by !
  followed by the committer's email - for example,
  "2014-01-16T05:43:35Z!esr@thyrsus.com".  Often, "my previous commit"
  will suffice.

- There is no need to mention files such as NEWS and MAINTAINERS, or
  to indicate regeneration of files such as 'lib/gnulib.mk', in the
  ChangeLog entry.  "There is no need" means you don't have to, but
  you can if you want to.

** Generating ChangeLog entries

- You can use Emacs functions to write ChangeLog entries; see
  http://www.gnu.org/software/emacs/manual/html_node/emacs/Change-Log-Commands.html
  or run 'info "(emacs)Change Log Commands"'.

- If you use Emacs VC, one way to format ChangeLog entries is to create
  a top-level ChangeLog file manually, and update it with 'C-x 4 a' as
  usual.  Do not register the ChangeLog file under git; instead, use
  'C-c C-a' to insert its contents into your *vc-log* buffer.
  Or if 'log-edit-hook' includes 'log-edit-insert-changelog' (which it
  does by default), they will be filled in for you automatically.

- Alternatively, you can use the vc-dwim command to maintain commit
  messages.  When you create a source directory, run the shell command
  'git-changelog-symlink-init' to create a symbolic link from
  ChangeLog to .git/c/ChangeLog.  Edit this ChangeLog via its symlink
  with Emacs commands like 'C-x 4 a', and commit the change using the
  shell command 'vc-dwim --commit'.  Type 'vc-dwim --help' for more.

** Branches

Future development normally takes place on the master branch.
Sometimes specialized features are developed on other branches before
possibly being merged to the master.  Release branches are named
"emacs-NN" where NN is the major version number, and are mainly
intended for more-conservative changes such as bug fixes.  Typically,
collective development is active on the master branch and possibly on
the current release branch.  Periodically, the current release branch
is merged into the master, using the gitmerge function described in
admin/notes/git-workflow.

If you are fixing a bug that exists in the current release, be sure to
commit it to the release branch; it will be merged to the master
branch later by the gitmerge function.

Documentation fixes (in doc strings, in manuals, and in comments)
should always go to the release branch, if the documentation to be
fixed exists and is relevant to the release-branch codebase.  Doc
fixes are always considered "safe" -- even when a release branch is in
feature freeze, it can still receive doc fixes.

When you know that the change will be difficult to merge to the
master (e.g., because the code on master has changed a lot), you can
apply the change to both master and branch yourself.  It could also
happen that a change is cherry-picked from master to the release
branch, and so doesn't need to be merged back.  In these cases,
say in the release branch commit message that there is no need to merge
the commit to master, by starting the commit message with "Backport:".
The gitmerge function excludes these commits from the merge to the master.

Some changes should not be merged to master at all, for whatever
reasons.  These should be marked by including something like "Do not
merge to master" or anything that matches gitmerge-skip-regexp (see
admin/gitmerge.el) in the commit message.

** Other process information

** Emacs Mailing lists.

Discussion about Emacs development takes place on emacs-devel@gnu.org.

Bug reports and fixes, feature requests and implementations should be
sent to bug-gnu-emacs@gnu.org, the bug/feature list.  This is coupled
to the http://debbugs.gnu.org tracker.

The Savannah info page http://savannah.gnu.org/mail/?group=emacs
describes how to subscribe to the mailing lists, or see the list
archives.

To email a patch you can use a shell command like 'git format-patch -1'
to create a file, and then attach the file to your email.  This nicely
packages the patch's commit message and changes.  To send just one
such patch without additional remarks, you can use a command like
'git send-email --to=bug-gnu-emacs@gnu.org 0001-DESCRIPTION.patch'.

** Issue tracker (a.k.a. "bug tracker")

The Emacs issue tracker at http://debbugs.gnu.org lets you view bug
reports and search the database for bugs matching several criteria.
Messages posted to the bug-gnu-emacs@gnu.org mailing list, mentioned
above, are recorded by the tracker with the corresponding bugs/issues.

GNU ELPA has a 'debbugs' package that allows accessing the tracker
database from Emacs.

** Documenting your changes

Any change that matters to end-users should have an entry in etc/NEWS.

Doc-strings should be updated together with the code.

Think about whether your change requires updating the manuals.  If you
know it does not, mark the NEWS entry with "---".  If you know
that *all* the necessary documentation updates have been made, mark
the entry with "+++".  Otherwise do not mark it.

If your change requires updating the manuals to document new
functions/commands/variables/faces, then use the proper Texinfo
command to index them; for instance, use @vindex for variables and
@findex for functions/commands.  For the full list of predefine indices, see
http://www.gnu.org/software/texinfo/manual/texinfo/html_node/Predefined-Indices.html
or run the shell command 'info "(texinfo)Predefined Indices"'.

For more specific tips on Emacs's doc style, see
http://www.gnu.org/software/emacs/manual/html_node/elisp/Documentation-Tips.html
Use 'checkdoc' to check for documentation errors before submitting a patch.

** Testing your changes

Please test your changes before committing them or sending them to the
list.  If possible, add a new test along with any bug fix or new
functionality you commit (of course, some changes cannot be easily
tested).

Emacs uses ERT, Emacs Lisp Regression Testing, for testing.  See
http://www.gnu.org/software/emacs/manual/html_node/ert/
or run 'info "(ert)"' for for more information on writing and running
tests.

If your test lasts longer than 2-3 seconds, mark it in its
'ert-deftest' definition with ":tags '(:expensive-test)".

To run tests on the entire Emacs tree, run "make check" from the
top-level directory.  Most tests are in the directory
"test/automated".  From the "test/automated" directory, run "make
<filename>" to run the tests for <filename>.el(c).  See "test/README"
for more information.

** Understanding Emacs internals

The best way to understand Emacs internals is to read the code.  Some
source files, such as xdisp.c, have extensive comments describing the
design and implementation.  The following resources may also help:

http://www.gnu.org/software/emacs/manual/html_node/elisp/Tips.html
http://www.gnu.org/software/emacs/manual/html_node/elisp/GNU-Emacs-Internals.html

or run 'info "(elisp)Tips"' or 'info "(elisp)GNU Emacs Internals"'.

The file etc/DEBUG describes how to debug Emacs bugs.

*** Non-ASCII characters in Emacs files

If you introduce non-ASCII characters into Emacs source files, use the
UTF-8 encoding unless it cannot do the job for some good reason.
Although it is generally a good idea to add 'coding:' cookies to
non-ASCII source files, cookies are not needed in UTF-8-encoded *.el
files intended for use only with Emacs version 24.5 and later.

*** Useful files in the admin/ directory

See all the files in admin/notes/* .  In particular, see
admin/notes/newfile, see admin/notes/repo.

The file admin/MAINTAINERS records the areas of interest of frequent
Emacs contributors.  If you are making changes in one of the files
mentioned there, it is a good idea to consult the person who expressed
an interest in that file, and/or get his/her feedback for the changes.
If you are a frequent contributor and have interest in maintaining
specific files, please record those interests in that file, so that
others could be aware of that.

*** git vs rename

Git does not explicitly represent a file renaming; it uses a percent
changed heuristic to deduce that a file was renamed.  So if you are
planning to make extensive changes to a file after renaming it (or
moving it to another directory), you should:

- Create a feature branch.

- Commit the rename without any changes.

- Make other changes.

- Merge the feature branch to the master branch, instead of squashing
  the commits into one.  The commit message on this merge should
  summarize the renames and all the changes.


\f
This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
\f
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