Page History

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• Distributing GPLv2+CPEx licensed component in Apache software is hard

  • it would be way easier to use plain javac  from a JDK

  • nb-javac  has to be downloaded by end-user on demand via autoupdate

• On demand download is problematic

  • user needs internet connection 

  • download server needs to be on (nb-javac isn't yet on Maven central)

  • e.g. sometimes download fails

• Testing matrix is complicated

  • each supported JDK needs to be tested twice - with nb-javac  and without nb-javac 

• Every bug/problem one needs to know whether nb-javac  was or wasn't in use

  • Recent version nb-javac-15  isn't really stable

• nb-javac  is a fork of JDK's javac

  • nobody likes forks

  • ironically Arvind's team is part of JDK organization - e.g. it maintains own fork of JDK's `javac`

• Upstream JDK javac hasn't been IDE ready up to JDK15
  • see below for details
• Without NbJavac one needs to run NetBeans on latest JDK to get latest language features
  • Serious disadvantage compared to competitors IDEs
  • They have their own Java parsers and support latest features on any JDK

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Eliminating the need for nb-javac

Clearly there are numerous drawbacks and Apache NetBeans needs a way out. Let's get rid of nb-javac  as we know it. Let's replace it with JDK's own javac ! However there are some problems...

•  javac  in JDK15 isn't good enough
• compile on save doesn't work
• re-compilation of a single method doesn't work
• runs out of memory more often than `nb-javac`.

Before NetBeans can really get rid of nb-javac , the `javac` in JDK is needs to be good enough.

Using JDK 17 javac Instead

Let's now assume JDK17 offers good enough javac , now NetBeans can suggest people to use JDK17 when using Apache NetBeans IDE

• not a big problem, JDK17 is LTS, but then?
• if people wanted to use language features of JDK19, they'd have to run on 19!
• that's not what competition does - they support latest language features running on JDK11 LTS or even JDK8 LTS

The story may end here and it might even be a good enough story for Apache NetBeans IDE. However...

Automatically Generating nb-javac

However, I don't like it. It is not good enough story yet. There are parties that want to run on LTS and support the latest Java features. To address their needs let's take JDK17's `javac` and let run it on JDK8! Of course, there are issues:

• latest `javac` is written in the language syntax of modern Java
  • such syntax cannot be compiled to JDK8 bytecode with `javac`
• latest `javac` is using APIs not available on JDK8
  • one needs to rewrite these calls to some older APIs
  • the behavior needs to be tested to remain the same

The great revelation is that both these problems can be solved with Apache NetBeans tools! Rather than maintaining manual patches like nb-javac  does, let's write advanced refactoring rules and apply them automatically. For example Optional.isEmpty()  method has been added in JDK11. Let's add following rule:

$1.isEmpty() :: $1 instanceof java.util.Optional
=>
!$1.isPresent()
;;

That automatically rewrites all occurences of optional.isEmpty()  to !optional.isPresent()  and that is going to compile on JDK8. Few more (~30) rules like this and the `javac` is almost ready to run on JDK8! Run few tests to verify the behavior remains the same after transformation and that's all. People can use Apache NetBeans with `javac` from the latest JDK or they can use the automatic port of the same code running on JDK8. Ideally the behavior shall be identical. No more questions: Are you using nb-javac or not? No more duplicated testing matrix.

What does nb-javac do that's different to vanilla javac?

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