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[[Dive into Real World Mozilla]] > [[Dive into Real World Mozilla Day 3]] > Incremental Build Lab
== Overview ==
This lab is designed to give you first-hand experience creating and applying patches, and doing incremental builds of your source tree. The concepts introduced in this lab will help you understand how to make small changes to your tree, share those with others, or use other people's changes.
== Instructions ==
Because the source tree is so large, developers use patches as the basic unit of work for passing code back and forth. A patch is a text file that contains information necessary to add or remove lines from a source tree. Patches are created using the '''cvs diff''' command.
'''NOTE: All instructions below assume the use of an objdir. Replace all uses of ''objdir'' with your object directory path.'''
=== Making a change and doing incremental builds ===
* Make a small change to a file in your tree, for example, a .cpp file in '''mozilla/netwerk/protocol/http/src'''. Here is a possible change:
#include <stdio.h>
...
...''inside a function somewhere''...
/* DEBUG_<username> is defined at build time, and Faculty is the username in the lab */
#ifdef DEBUG_Faculty
printf("Hello World!\n");
#endif
...''inside a function somewhere''...
...
* Make sure your change compiles. You need to rebuild your tree in order to test using one of the following methods:
$ make -f client.mk build
or, to make things go faster, move to the parallel location in your ''objdir '' and run make there
$ cd mozilla/''objdir''/netwerk/protocol/http/src
$ make
=== Create a patch ===
* Now create a patch containing the changes you just made using the so called 'unified' format (-u), with 8 lines of context. By default the diff is printed to stdout, so you should redirect it to a file. Typically patches are created from the '''mozilla/''' root directory, so that they can be easily applied later on (i.e., people don't have to figure out where to apply the patch, and can just use their tree's root directory):
$ cd mozilla/netwerk/protocol/http
$ cvs diff -u8p . > patch.txt
* Trade patches with someone else in the class (use http://pastebin.mozilla.org and IRC), and take turns trying to apply their patch to your tree:
$ cd mozilla/netwerk/protocol/http
$ patch -p0 < patch.txt
* Here '''-p0''' means strip 0 leading directories from each filename in the patch. We do this because we are in the same location (i.e., ./) as the person who created the patch. If the directories were mis-aligned, we would have to strip leading directories using -p1, -p2, etc. * You can use the '''--dry-run ''' option to test and see what would happen if you did apply the patch. Some people like to call patch with the -s or --silent or --quiet option (all do the same thing). This will suppress all output except error messages, and can make it easier to see which parts don't work.
=== Backing-out a patch ===
* Now try backing-out this same patch. To do this you can call patch with the -R or --reverse option to tell it to swap the old and new files, basically reversing the patch.
$ cd mozilla/netwerk/protocol/http
$ patch -R -p0 < patch.txt
=== Applying a real patch ===
* Apply the patch: , using what you learned above. $ cd mozilla $ patch Remember the '''--dry-p1 < [run''patch_filename'']option and to examine the paths of files in the patch.
* Rebuild the necessary parts of your tree:
$ cd mozilla/''objdir'' $ cd modules/libimg $ make $ cd ../libpr0n $ make $ cd ../../browser/app $ make cleanxpcom
$ make
=== Life-cycle of a patch in review ===
== Resources ==
* [http://developer.mozilla.org/en/docs/Creating_a_patchCreating a patch for Mozilla]* [http://developer.mozilla.org/devnews/index.php/2007/07/10/getting-a-patch-checked-in/ Instructions for getting a patch checked into the tree]* There are many tutorials on using diff/patch, for example [http://tools.devchannel.org/devtoolschannel/04/06/02/1521207.shtml?tid=46 this one].
