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Contributing to Lucene Guide
Working with Code
Getting the source code
First of all, you need the Lucene source code.
Get the source code using: git clone https://github.com/apache/lucene
Please note that it is important to preserve the files' original line breaks - some of them have their checksums verified during build.
If you are using Windows you might want to override the default Git configuration when cloning the repository:
git clone --config core.autocrlf=false https://github.com/apache/lucene
Pre-requisites
Be sure that you are using an appropriate version of the JDK. Please check README for the required JDK version for current main branch.
Some build tasks (in particular ./gradlew check) require Perl and Python 3.
Building with Gradle
Lucene uses Gradle for build control. Gradle is itself Java-based and may be incompatible with newer Java versions; you can still build and test Lucene with these Java releases, see jvms.txt for more information.
NOTE: DO NOT use the gradle command that is perhaps installed on your machine. This may result in using a different gradle version than the project requires and this is known to lead to very cryptic errors. The "gradle wrapper" (gradlew script) does everything required to build the project from scratch: it downloads the correct version of gradle, sets up sane local configurations and is tested on multiple environments.
The first time you run gradlew, it will create a file "gradle.properties" that contains machine-specific settings. Normally you can use this file as-is, but it can be modified if necessary.
Type ./gradlew helpWorkflow to show typical workflow tasks (help/workflow.txt).
Also run ./gradlew help, this will print a list of help guides that introduce and explain
various parts of the build system, including typical workflow tasks.
Code formatting and checks
If you've modified any sources, run ./gradlew tidy to apply code formatting conventions automatically (see help/formatting.txt).
Please make sure that all unit tests and validations succeed before constructing your patch: ./gradlew check. This will assemble Lucene and run all validation tasks (including tests). There are various commands to check the code; type ./gradlew helpTest for more information (help/tests.txt).
In case your contribution fixes a bug, please create a new test case that fails before your fix, to show the presence of the bug and ensure it never re-occurs. A test case showing the presence of a bug is also a good contribution by itself.
IDE support
- IntelliJ - IntelliJ idea can import and build gradle-based projects out of the box. It will default to running tests by calling the gradle wrapper, and while this works, it is can be a bit slow. If instead you configure IntelliJ to use its own built-in test runner by (in 2024 version) navigating to settings for Build Execution & Deployment/Build Tools/Gradle (under File/Settings menu on some platforms) and selecting "Build and Run using: IntelliJ IDEA" and "Run Tests using: IntelliJ IDEA", then some tests will run faster. However some other tests will not run using this configuration.
- Eclipse - Basic support (help/IDEs.txt).
- Netbeans - Not tested.
Benchmarking
Use the tool suite at luceneutil to benchmark your code changes if you think that your change may have measurably changed the performance of a task. Apache Lucene also contains an off the shelf benchmark module.
This is the same suite that is run in the nightly benchmarks.
The instructions for running the benchmarks can be found in the luceneutil README.
The Lucene community is also interested in other implementations of these benchmark tasks. Feel free to share your findings (especially if your implementation performs better!) through the Lucene mailing lists or open PRs, issues on the luceneutil project directly.
Contributing your work
You can open a pull request at https://github.com/apache/lucene.
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 others' suggestions into your patch if you think they're reasonable. Finally, remember that even a patch that is not committed is useful to the community.
Opening a pull request
Please refer to GitHub's documentation for an explanation of how to create a pull request.
You should open a pull request against the main branch. Committers will backport it to the maintenance branches once the change is merged into main (as far as it is possible).
Creating a patch
Note that you do not need to create a patch if you already opened a pull request.
Patches should be attached to an issue. Since GitHub does not accept attachments with extension .patch, please rename your patch file XXX.patch to XXX.patch.txt or something like that.
Please refer to git diff documentation for information of how to create a patch.
Before creating your patch, you may want to get 'main' up to date with the latest from upstream. This will help avoid the possibility of others finding merge conflicts when applying your patch. This can be done with git pull if main is the current branch.
Add a CHANGES entry
You may want to add a CHANGES entry to CHANGES.txt. A CHANGES entry should start with the issue or pull request number GITHUB#XXX that is followed by the description of the change and contributors' name. Please see the existing entries for reference.
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).
Please keep discussions about Lucene on list so that everyone benefits. Emailing individual committers with questions about specific Lucene issues is discouraged. See http://people.apache.org/~hossman/#private_q.
Getting your feet wet: where to begin?
New to Lucene? Want to find issues that you can work on without taking on the whole world?
The rough criteria for picking your first issues are:
- Nobody has done any work on the issue yet.
- The issue is likely not controversial.
- The issue is likely self-contained with limited scope.
Developer tips
For more contribution guidelines and tips, see DeveloperTips.