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I would like to contribute but I don't know where to start
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.
|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|
|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|
|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.
|Android, JVM||Medium||Mentor: Cédric Champeau||Prototype|