mvn compile without clean doesn't work for annotation-processor generated sources

[Marquis Wong <Ma...@imc.com.INVALID>]

Hello,


I've been investigating why mvn install without clean doesn't work for my project. I've traced it down to using Dagger, though I think most (all?) code-generating annotation processors will be affected.


I've created a simple project that reproduces the problem: https://github.com/marquiswang/incremental-compile-dagger-test


The README describes exactly how it goes wrong. It basically means that if you are using Dagger, you always need to do a mvn clean install in order to successfully compile your code.


I've got a slightly-hacky patch for IncrementalBuildHelper<https://github.com/apache/maven-shared-incremental/blob/master/src/main/java/org/apache/maven/shared/incremental/IncrementalBuildHelper.java> that I think is a pretty good way to solve the problem. Basically, we need to treat the generatedSourcesDirectory (by default target/generated-sources/annotations) the same as the outputDirectory and delete files from it when re-compiling during an incremental build. I'll share the patch as soon as I get permission from my employer, but it is pretty straightforward.


Does this make sense? If so I can clean up the patch and convert it to a PR.


Thanks,

Marquis Wong

Marquis Wong
Software Engineer
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