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How to write code for CVS * License of CVS CVS is Copyright (C) 1986-2006 The Free Software Foundation, Inc. This program 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 1, or (at your option) any later version. More details are available in the COPYING file but, in simplified terms, this means that any distributed modifications you make to this software must also be released under the GNU General Public License. This program 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. * Source Patches against the development version of CVS are most likely to be accepted: $ cvs -z3 -d:pserver:anonymous@cvs.sv.nongnu.org:/sources/cvs co ccvs See the Savannah sources page <http://savannah.nongnu.org/cvs/?group=cvs> for more information. * Compiler options If you are using GCC, you'll want to configure with -Wall, which can detect many programming errors. This is not the default because it might cause spurious warnings, but at least on some machines, there should be no spurious warnings. For example: $ CFLAGS="-g -Wall" ./configure Configure is not very good at remembering this setting; it will get wiped out whenever you do a ./config.status --recheck, so you'll need to use: $ CFLAGS="-g -Wall" ./config.status --recheck * Backwards Compatibility Only bug fixes are accepted into the stable branch. New features should be applied to the trunk. If it is not inextricable from a bug fix, CVS's output (to stdout/stderr) should not be changed on the stable branch in order to best support scripts and other tools which parse CVS's output. It is ok to change output between feature releases (on the trunk), though such changes should be noted in the NEWS file. Changes in the way CVS responds to command line options, config options, etc. should be accompanied by deprecation warnings for an entire stable series of releases before being changed permanently, if at all possible. * Indentation style CVS mostly uses a consistent indentation style which looks like this: void foo (arg) char *arg; { if (arg != NULL) { bar (arg); baz (arg); } switch (c) { case 'A': aflag = 1; break; } } The file cvs-format.el contains settings for emacs and the NEWS file contains a set of options for the indent program which I haven't tried but which are correct as far as I know. You will find some code which does not conform to this indentation style; the plan is to reindent it as those sections of the code are changed (one function at a time, perhaps). In a submitted patch it is acceptable to refrain from changing the indentation of large blocks of code to minimize the size of the patch; the person checking in such a patch should reindent it. * Portability The general rule for portability is that it is only worth including portability cruft for systems on which people are actually testing and using new CVS releases. Without testing, CVS will fail to be portable for any number of unanticipated reasons. The current consequence of that general rule seems to be that if it is in ANSI C and it is in SunOS4 (using /bin/cc), generally it is OK to use it without ifdefs (for example, assert() and void * as long as you add more casts to and from void * than ANSI requires. But not function prototypes). Such constructs are generally portable enough, including to NT, OS/2, VMS, etc. * Run-time behaviors Use assert() to check "can't happen" conditions internal to CVS. We realize that there are functions in CVS which instead return NULL or some such value (thus confusing the meaning of such a returned value), but we want to fix that code. Of course, bad input data, a corrupt repository, bad options, etc., should always print a real error message instead. Do not use arbitrary limits (such as PATH_MAX) except perhaps when the operating system or some external interface requires it. We spent a lot of time getting rid of them, and we don't want to put them back. If you find any that we missed, please report it as with other bugs. In most cases such code will create security holes (for example, for anonymous readonly access via the CVS protocol, or if a WWW cgi script passes client-supplied arguments to CVS). Although this is a long-term goal, it also would be nice to move CVS in the direction of reentrancy. This reduces the size of the data segment and will allow a multi-threaded server if that is desirable. It is also useful to write the code so that it can be easily be made reentrant later. For example, if you need to pass data from a Parse_Info caller to its callproc, you need a static variable. But use a single pointer so that when Parse_Info is fixed to pass along a void * argument, then the code can easily use that argument. * Coding standards in general Generally speaking the GNU coding standards are mostly used by CVS (but see the exceptions mentioned above, such as indentation style, and perhaps an exception or two we haven't mentioned). This is the file standards.text at the GNU FTP sites. * Regenerating Build Files On UNIX, if you wish to change the Build files, you will need Autoconf and Automake. Some combinations of Automake and Autoconf versions may break the CVS build if file timestamps aren't set correctly and people don't have the same versions the developers do, so the rules to run them automatically aren't included in the generated Makefiles unless you run configure with the --enable-maintainer-mode option. The CVS Makefiles and configure script were built using Automake 1.10 and Autoconf 2.61, respectively. There is a known bug in Autoconf 2.57 that will prevent the configure scripts it generates from working on some platforms. Other combinations of autotool versions may or may not work. If you get other versions to work, please send a report to <bug-cvs@nongnu.org>. * Writing patches (strategy) Only some kinds of changes are suitable for inclusion in the "official" CVS. Bugfixes, where CVS's behavior contradicts the documentation and/or expectations that everyone agrees on, should be OK (strategically). For features, the desirable attributes are that the need is clear and that they fit nicely into the architecture of CVS. Is it worth the cost (in terms of complexity or any other tradeoffs involved)? Are there better solutions? If the design is not yet clear (which is true of most features), then the design is likely to benefit from more work and community input. Make a list of issues, or write documentation including rationales for how one would use the feature. Discuss it with coworkers, a newsgroup, or a mailing list, and see what other people think. Distribute some experimental patches and see what people think. The intention is arrive at some kind of rough community consensus before changing the "official" CVS. Features like zlib, encryption, and the RCS library have benefitted from this process in the past. If longstanding CVS behavior, that people may be relying on, is clearly deficient, it can be changed, but only slowly and carefully. For example, the global -q option was introduced in CVS 1.3 but the command -q options, which the global -q replaced, were not removed until CVS 1.6. * Writing patches (tactics) When you first distribute a patch it may be suitable to just put forth a rough patch, or even just an idea. But before the end of the process the following should exist: - ChangeLog entry (see the GNU coding standards for details). - Changes to the NEWS file and cvs.texinfo, if the change is a user-visible change worth mentioning. - Somewhere, a description of what the patch fixes (often in comments in the code, or maybe the ChangeLog or documentation). - Most of the time, a test case (see TESTS). It can be quite frustrating to fix a bug only to see it reappear later, and adding the case to the testsuite, where feasible, solves this and other problems. See the TESTS file for notes on writing new tests. If you solve several unrelated problems, it is generally easier to consider the desirability of the changes if there is a separate patch for each issue. Use context diffs or unidiffs for patches. Include words like "I grant permission to distribute this patch under the terms of the GNU Public License" with your patch. By sending a patch to bug-cvs@nongnu.org, you implicitly grant this permission. Submitting a patch to bug-cvs is the way to reach the people who have signed up to receive such submissions (including CVS developers), but there may or may not be much (or any) response. If you want to pursue the matter further, you are probably best off working with the larger CVS community. Distribute your patch as widely as desired (mailing lists, newsgroups, web sites, whatever). Write a web page or other information describing what the patch is for. It is neither practical nor desirable for all/most contributions to be distributed through the "official" (whatever that means) mechanisms of CVS releases and CVS developers. Now, the "official" mechanisms do try to incorporate those patches which seem most suitable for widespread usage, together with test cases and documentation. So if a patch becomes sufficiently popular in the CVS community, it is likely that one of the CVS developers will eventually try to do something with it. But dealing with the CVS developers may be the last step of the process rather than the first. * What is the schedule for the next release? There isn't one. That is, upcoming releases are not announced (or even hinted at, really) until the feature freeze which is approximately 2 weeks before the final release (at this time test releases start appearing and are announced on info-cvs). This is intentional, to avoid a last minute rush to get new features in. * Mailing lists In addition to the mailing lists listed in the README file, developers should take particular note of the following mailling lists: bug-cvs: This is the list which users are requested to send bug reports to. General CVS development and design discussions also take place on this list. info-cvs: This list is intended for user questions, but general CVS development and design discussions sometimes take place on this list. cvs-cvs: The only messages sent to this list are sent automatically, via the CVS `loginfo' mechanism, when someone checks something in to the master CVS repository. cvs-test-results: The only messages sent to this list are sent automatically, daily, by a script which runs "make check" and "make remotecheck" on the master CVS sources. To subscribe to any of these lists, send mail to <list>-request@nongnu.org or visit http://savannah.nongnu.org/mail/?group=cvs and follow the instructions for the list you wish to subscribe to.
