I have a question about the semantics of the `java...

# compiler

[tschuchort]

I have a question about the semantics of the javaSourceRoots compiler option. Both KaptOptions and K2JVMCompilerArguments have a javaSourceRoots member. So far I have been passing both paths to Kotlin source files and Java source files as K2JVMCompilerArguments.freeArgs to the compiler and it has worked fine for the most part. Now we have noticed a problem that nested classes in Java sources can not be resolved by compiler plugins. This problem seems to go away when javaSourceRoots is set to the parent directory where the Java source files are located, but not when paths to the Java source files directly are added to javaSourceRoots .
1. Why can we give the compiler direct paths to Kotlin files but all the Java files have to be located in the same directory? We can see that the same parameter in KaptOptions accepts paths to files and not to a parent directory: https://github.com/JetBrains/kotlin/blob/e2521718ddef33d25158032dee649b1fa6f5b73a/[…]t3/kapt3-compiler/src/org/jetbrains/kotlin/kapt3/Kapt3Plugin.kt
2. Why is this option needed at all? The K2JVMCompiler is able to find and compile Java sources without it, but apparently not nested classes?

[udalov]

I don’t know about the kapt part of this at all, but accepting single .java files in the compiler was implemented as a kind of a hack, where we are running the Java lexer manually beforehand and are recording fully qualified names of all classes that we find:
https://github.com/JetBrains/kotlin/blob/master/compiler/cli/src/org/jetbrains/kotlin/cli/jvm/index/SingleJavaFileRootsIndex.kt

IIRC running the Java parser was not feasible at this point because of performance reasons.

There might very well be some bug in that code, that doesn’t catch some nested classes in some cases.