How to Contribute to Lucene
Getting the source code
First of all, you need the Lucene source code.
Get the source code on your local drive using SVN. Most development is done on the "trunk":
svn checkout http://svn.apache.org/repos/asf/lucene/java/trunk/ lucene-trunk
Depending on where you are located the European mirror might be faster or slower:
svn checkout http://svn.eu.apache.org/repos/asf/lucene/java/trunk/ lucene-trunk
Making Changes
Before you start, send a message to the developer mailing list (Note: you have to subscribe before you can post), or file a bug report in Jira. Describe your proposed changes and check that they fit in with what others are doing and have planned for the project. Be patient, it may take folks a while to understand your requirements.
Modify the source code and add some (very) nice features using your favorite IDE.
But take care about the following points:
- Code compatibility:
- All core code to be included in 2.X releases should be compatible with Java 1.4.
- All contrib code should be compatible with either Java 5 or 1.4.
- All code to be included in 3.X releases should be compatible with Java 5.
All public classes and methods should have informative Javadoc comments.
Code should be formatted according to Sun's conventions with one exception:
- indent two spaces per level, not four.
- Contributions should pass existing unit tests.
New unit tests should be provided to demonstrate bugs and fixes (http://www.junit.org).
- In the trunk, the java source code is in the directory src/java and the java test code is in the directory src/test.
Generating a patch
Unit Tests
To run your test case from ant use the following:
> cd lucene-trunk > ant -Dtestcase=NameOfYourUnitTest test-core
In case your contribution fixes a bug, try and make your test case fail to show the presence of the bug. A test case showing the presence of a bug is also a good contribution by itself.
Once your test case passes, please make sure that all unit tests (core, contrib, and back-compatibility) succeed before constructing your patch, by running this:
> cd lucene-trunk > ant clean test test-tag
After a while, if you see
BUILD SUCCESSFUL
all is ok, but if you see
BUILD FAILED
please, read carefully the errors messages and check your code.
Since running all test cases can take some time, after any change try running a previously failing single test case first.
Creating a patch
Check to see what files you have modified with:
svn stat
Add any new files with:
svn add src/.../MyNewClass.java
Edit the CHANGES.txt file, adding a description of your change, including the bug number it fixes.
In order to create a patch, just type:
svn diff > LUCENE-NNN.patch
This will report all modifications done on Lucene sources on your local disk and save them into the LUCENE-NNN.patch file. Read the patch file. Make sure it includes ONLY the modifications required to fix a single issue.
Note the LUCENE-NNN.patch patch file name. Please use this naming pattern when creating patches for uploading to JIRA. Once you create a new JIRA issue, note its name and use that name when naming your patch file. For example, if you are creating a patch for a JIRA issue named LUCENE-123, then name your patch filename LUCENE-123.patch. If you are creating a new version of an existing patch, use the existing patch's file name. JIRA will automatically "gray out" the old patch and clearly mark your newly uploaded patch as the latest.
Please do not:
- reformat code unrelated to the bug being fixed: formatting changes should be separate patches/commits.
- comment out code that is now obsolete: just remove it.
- insert comments around each change, marking the change: folks can use subversion to figure out what's changed and by whom.
- make things public which are not required by end users.
- Add @author tags to your code. (Instead, give yourself credit in the CHANGES.txt file.)
Please do:
- try to adhere to the coding style of files you edit;
- comment code whose function or rationale is not obvious;
update documentation (e.g., package.html files, this wiki, etc.)
Contributing your work
Finally, patches should be attached to a bug report in Jira.
Please be patient. Committers are busy people too. If no one responds to your patch after a few days, please make friendly reminders. Please incorporate other's suggestions into into your patch if you think they're reasonable. Finally, remember that even a patch that is not committed is useful to the community.
Stay involved
Contributors should join the Lucene mailing lists. In particular, the commit list (to see changes as they are made), the dev list (to join discussions of changes) and the user list (to help others).
Helpful Resources
The following resources may prove helpful when developing Lucene contributions. (These are not an endorsement of any specific development tools)