Fix incremental compilation when a Scala project depends on a Java project #414
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This PR depends on #411
Before this PR, JavaModule#compile simply called javac
unconditionally, thus generating new classfiles every time. But if a
Scala project depends on a Java project, this will throw off the
incremental compilation algorithm which will unnecessarily recompile
files. To avoid this we now use Zinc to compile Java projects too (as a
bonus this means that Java compilation becomes incremental). This
required some refactoring in ZincWorkerImpl to be able to compile stuff
without having to pass Scala-specific options.
The issue solved by this commit could be reproduced by running in the
Mill repository:
$ mill main.compile $ mill -i @ main.compile()
and observing that before this commit, the
main.compile()
call endedup recompiling code.