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There are many ways you can help make Groovy a better piece of software - and we can use all the help we can get. Please dive in and help! 
Try surfing the documentation - if something is confusing or not clear, let us know - or better still fix it for us. All of this website is maintained in a wiki, so please go right ahead and fix things if they are wrong or contribute new documentation.
Download the code & try it out and see what you think. Browse the source code.
Got an itch to scratch, want to tune some operation or add some feature?
Want to do some hacking on Groovy? Try surfing the issue tracker for open issues or features that need to be implemented, take ownership of an issue and try to fix it.
If you'd rather a more gentle introduction to coding on the Groovy project, how about you look at the test coverage artifacts and help us get it even more green by supplying more test cases to get us closer to 100% coverage.
If you find a bug or problem
Please raise a new issue in our issue tracker.
If you can create a JUnit test case (either via Groovy or Java code) then your issue is more likely to be resolved quicker.
Take a look at some of the existing unit tests cases, find one and modify it to try reproduce your problem.
Then we can add your issue to Git and then we'll know when its really fixed and
we can ensure that the problem stays fixed in future releases.
Submitting patches
We gladly accept patches if you can find ways to improve, tune or fix Groovy in some way.
Most IDEs can create nice patches now very easily. If you're a command line person try the following to create the patch
or
Once you've created a patch the best way to submit it is to raise a new issue in the issue tracker (see below) and maybe send us a mail on the developer list letting us know about the patch.
Using the issue tracker
Before you can raise an issue in the issue tracker you need to register with it. This is quick & painless.
If you want to have a go at fixing an issue you need to be in the list of groovy-developers on the issue tracker. To join the group, please mail the groovy-dev mail list with the email address you used to register with the issue tracker and we'll add you to the group.
Here's a list of some issues contributors could have a look at, to get started contributing to Groovy:
Improvements that need your help
The following table is a summary of the fields where we would like to improve Groovy but do not find enough time to implement those features. For each of them, you will find a short description, an idea of the skills you need to implement them and the level of difficulty. Of course, getting into Groovy Core can be sometimes hard, so we should always work as a team and each subject below would be followed by a mentor.
| Feature | Description | Skills | Difficulty | Team | Status |
|---|---|---|---|---|---|
| Grammar rewrite | The current Groovy grammar is written using ANTLR 2. For maintenance reasons, we would like to migrate the grammar to ANTLR 3 or ANTLR 4. Originally planned for Groovy 3, we will probably not be able to do that if no one helps. It is an important background task which covers the grammar of Groovy, the grammar of Java and a good knowledge of the Groovy AST (for backwards compatibility). | Grammar writing (Antlr helps a lot!), parsers, Groovy AST (nice to have) | Hard | Mentor: Jochen Theodorou | Delayed |
| Bytecode optimizations | Since Groovy 2.0, we have two flavours of bytecode: the dynamic bytecode, corresponding to the main and legacy Groovy, and a "static" bytecode, triggered using the @CompileStatic annotation, which is closer to what Java produces. Both need specific bytecode optimizations. | ASM, JVM Bytecode | Hard | Mentor: Cédric Champeau | In progress |
| Javascript backend | Groovy runs on the JVM, but we would also like to see a Javascript backend. Of course, a prototype would have limited capabilities compared to what the JVM one offers, mostly because the Groovy language is not only a language but also a rich API relying internally on JDK APIs. | Javascript, Groovy compiler internals | Hard | Mentor: Guillaume Laforge | Idea |
| Lambda support | JDK 8 will offer support for lambdas. Lambdas are close to what Groovy offers with closures, but the syntax, implementation and more importantly semantics are quite different. A future version of Groovy should be able to support both closures (Groovy) and lambdas (JDK 8). | JVM bytecode, grammar | Hard | Mentor: Jochen Theodorou | Not started |
| Lazy datastructures and comprehensions | The idea would be to have Groovy support generators, lazy evaluations, ... See for example http://blog.bloidonia.com/post/22117894718/groovy-stream-a-lazy-generator-class-for-groovy It is also important to take a look at what APIs are being written in JDK 8 because most of the APIs written for the new lambdas are specifically lazy. | Algorithmics | Medium | Mentor: Paul King | Prototype |
| New MOP | The new MOP (Meta Object Protocol) is a key feature of Groovy 3. The objective is to rewrite the MOP totally, in order to provide a more consistent, powerful and performant MOP. See http://groovy.codehaus.org/MOP+2.0+ideas | Language theory | Medium | Mentor: Jochen Theodorou | In progress |
| Bugfixes | As the language is widely used, we have a lot of bug reports. Unfortunately, the team is too small to tackle them all. If you find a bug that you think you can work on, do not hesitate to help! | Easy to hard | Mentor: any member of Groovy core | In progress | |
| Modularization | Groovy 2 came with the concept of modularization and is now splitted into modules. Each module is a logical group of features (for example, XML, JSON, Swing, ...). While Groovy core was reduced by half, there's still plenty of room for improvement and further modularization. | Architecture | Easy | Mentor: Paul King | In progress |
| Documentation | On every project, documentation is never enough, nor up-to-date. Groovy falls into that trap too. A very good way to get into Groovy is to start documentation, fix documentation or improve javadocs. There are also side projects like a new website, a new Groovy Web Console which require some time but were never started. | Easy | Mentor: Guillaume Laforge | In progress | |
| Specification | Help joining the specification effort. The Groovy language has evolved a lot and there's no complete specification available yet. | Medium | Mentor: Guillaume Laforge | Standbye | |
| Security | Help us improving java.security support in Groovy. We have, for example, unit tests failing periodically because of security tests (Security Manager related). No one in the team is an expert in that domain so any help would be very appreciated! | Java security | Medium | Mentor: Cédric Champeau | Standbye |
| Groovy for Android | A lot of us would like to see Groovy run on Android. There are some technical challenges but the good news is that some hackers (Marcin Erdmann and Erik Pragt) managed to do it for Groovy 1.7. It's not production ready yet, and we would like to have, at some point, support in the Groovy distribution itself (aka, no patch required). Running Groovy is one thing, doing something with it is another, so a side project for this is definitely to make Groovy a language of choice to build Android applications. We think some projects like Griffon, for example, have a strong interest in that, by making the design of UIs much easier. See http://skillsmatter.com/podcast/groovy-grails/groovy-android | Android, JVM | Medium | Mentor: Cédric Champeau | Prototype |
| Groovy Console | The Groovy Console is a very nice tool. However, there are several things that can be improved: syntax highlighting, especially for large scripts, which is too slow, the AST Browser which can be improved in several ways (displaying node metadata, more focused bytecode view, ...) | Swing, Groovy | Easy to medium | Mentor: | Standbye |