Avoid some int overflows in window.c

[emacs.git] / CONTRIBUTE

This file contains information on Emacs developer processes.

For information on contributing to Emacs as a non-developer, see
(info "(emacs)Contributing") or
http://www.gnu.org/software/emacs/manual/html_node/emacs/Contributing.html

* Information for Emacs Developers.

An "Emacs Developer" is someone who contributes a lot of code or
documentation to the Emacs repository. Generally, they have write
access to the Emacs git repository on Savannah
https://savannah.gnu.org/git/?group=emacs.

** Write access to the Emacs repository.

Once you become a frequent contributor to Emacs, we can consider
giving you write access to the version-control repository. Request
access on the emacs-devel@gnu.org mailing list.

** Using the Emacs repository

Emacs uses git for the source code repository.

See http://www.emacswiki.org/emacs/GitQuickStartForEmacsDevs to get
started, and http://www.emacswiki.org/emacs/GitForEmacsDevs for more
advanced information.

Alternately, see admin/notes/git-workflow.

If committing changes written by someone else, make the ChangeLog
entry in their name, not yours. git distinguishes between the author
and the committer; use the --author option on the commit command to
specify the actual author; the committer defaults to you.

** Commit messages

Typically, a patch creates ChangeLog entries by putting them into its
commit message, not by changing a ChangeLog file.  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.
        * 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.
        Fixes: bug#19003

The general format is as follows.

- Start with a single unindented summary line explaining the change,
  then 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.

- 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.

- 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.

- Emacs generally follows the GNU coding standards when it comes to
  ChangeLogs:
  http://www.gnu.org/prep/standards/html_node/Change-Logs.html .  One
  exception is that we still sometimes quote `like-this' (as the
  standards used to recommend) rather than 'like-this' (as they do
  now), because `...' is so widely used elsewhere in Emacs.

- Some of the rules in the GNU coding standards section 5.2
  "Commenting Your Work" 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).

  It is tempting to relax this rule for commit messages, since they
  are somewhat transient.  However, 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.)

- If the commit has authors other than yourself, the commit message
  should contain a separate line 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

- If the commit fixes a bug, append a separate line

        Fixes: bug#NNNN

  where NNNN is the bug number.

- In ChangeLog entries, there is no standard or recommended way to
  identify revisions.

  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 make separate ChangeLog entries for files such
  as NEWS, MAINTAINERS, and FOR-RELEASE, or to indicate regeneration
  of files such as 'configure'.  "There is no need" means you don't
  have to, but you can if you want to.

- If a commit message's first line starts with "; ", the message is
  ignored when generating ChangeLog history files via 'make changelog'
  or via 'make change-history'.  You can use "; " for minor commits
  that do not need separate ChangeLog entries.

** Generating ChangeLog entries

- You can use various Emacs functions to ease the process of writing
  ChangeLog entries; see (info "(emacs)Change Log Commands") or
  http://www.gnu.org/software/emacs/manual/html_node/emacs/Change-Log-Commands.html.

- 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 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

Development normally takes places on the trunk.
Sometimes specialized features are developed on separate branches
before possibly being merged to the trunk.

Development is discussed on the emacs-devel mailing list.

Sometime before the release of a new major version of Emacs a "feature
freeze" is imposed on the trunk, to prepare for creating a release
branch.  No new features may be added to the trunk after this point,
until the release branch is created. Announcements about the freeze
(and other important events) are made on the info-gnu-emacs mailing
list, and not anywhere else.

The trunk branch is named "master" in git; release branches are named
"emacs-nn" where "nn" is the major version.

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.

However, if you know that the change will be difficult to merge to the
trunk (eg because the trunk code has changed a lot), you can apply the
change to both trunk and branch yourself.  Indicate in the release
branch commit log that there is no need to merge the commit to the
trunk; start the commit message with "Backport:".  gitmerge.el will
then exclude that commit from the merge to trunk.


** Other process information

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

*** 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 trunk, _not_ squashing the commits into
  one. The commit message on this merge should summarize the renames
  and all the changes.

** 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 tracker at http://debbugs.gnu.org .

You can subscribe to the mailing lists, or see the list archives,
by following links from http://savannah.gnu.org/mail/?group=emacs .

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.

** Document 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.

Please see (info "(elisp)Documentation Tips") or
https://www.gnu.org/software/emacs/manual/html_node/elisp/Documentation-Tips.html
for more specific tips on Emacs's doc style.  Use `checkdoc' to check
for documentation errors before submitting a patch.

** Test your changes.

Please test your changes before committing them or sending them to the
list.

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

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/automated/Makefile" for more information.

** Understanding Emacs Internals.

The best way to understand Emacs Internals is to read the code,
but the nodes "Tips" and "GNU Emacs Internals" in the Appendix
of the Emacs Lisp Reference Manual may also help.

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


\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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