Gradle构建因Kotlin，Scala和Java而失败

Question

I have a project written in Java, Scala and Kotlin.

But when I build this project in Gradle, it error with message:

11:19:51: Executing task 'build'...

:compileKotlin
Using Kotlin incremental compilation
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (3, 19):             
Unresolved reference: Flag
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (10, 18):     
Unresolved reference: GroupMessageResponder
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (13, 2): 
'doPost' overrides nothing
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (35, 23): 
Unresolved reference: Flag
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (38, 2): 
'getHelpMessage' overrides nothing
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (40, 2): 
'getKeyWordRegex' overrides nothing
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (42, 2): 
'instance' overrides nothing
:compileKotlin FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileKotlin'.
> Compilation error. See log for more details

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --
debug option to get more log output.

BUILD FAILED in 1s
1 actionable task: 1 executed
Compilation error. See log for more details
11:19:53: Task execution finished 'build'.

Those errors are all about 'Unresolved reference', and those 'reference' are all written in Scala or Java.

But run this project in IDEA works fine .

I thought this was caused by Gradle compile Kotlin first, which should compiled in last, so those 'reference' could not be found.

And this is my build.gradle : build.gradle

UPDATE:

A part of output of gradle clean testClasses --info :

...SKIP...
> Task :compileKotlin
Using Kotlin incremental compilation

e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (3, 19): 
Unresolved reference: Flag
e: F:\Code\Project\Avalon\src\main\kotlin\avalon\group\Execute.kt: (11, 18): 
Unresolved reference: GroupMessageResponder
...SKIP....

> Task :compileKotlin
[KOTLIN] deleting F:\Code\Project\Avalon\build\classes\kotlin\main on error
[KOTLIN] deleting F:\Code\Project\Avalon\build\classes\kotlin\main on error

:compileKotlin (Thread[Task worker Thread 3,5,main]) completed. Took 15.981 secs.

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileKotlin'.
> Compilation error. See log for more details

* Try:
Run with --stacktrace option to get the stack trace. Run with --debug option 
to get more log output.

BUILD FAILED in 24s
2 actionable tasks: 2 executed
Stopped 0 worker daemon(s).

Full output posted here .

Answer 1

The problem you have are the different languages.

Some Kotlin and Java

Let's assume you just have kotlin and java. Than you can access from ( -> means A accesses classes of B)

kotlin -> java 
java -> kotlin

The reason you can do that, is because during the compilation ( compileKotlin ) Kotlin take care of this crossCompilation / jointCompilation / whatever-other-name between those two languages.

---

Kotlin and Scala (one direction)

But if you have the case:

kotlin -> scala

than you must consider the the following: when compileKotlin runs, it compiles all .java and .kt files to class files, but non of the .scala files (because it doesn't know anything about scala ). When you now access scala classes from kotlin , than you must first compile those .scala classes, to ensure that the compileKotlin compilation process find those .class files for a successful compilation.

You can define that scala must run before kotlin with eg

compileKotlin.dependsOn compileScala

---

Kotlin and Scala (both directions)

So good so far, but the problem is, when you have

kotlin -> scala
scala -> kotlin

Because this scenario is not working.

You need to compile the scala classes first, to successfully compile the kotlin classes (see description above). But on the other hand, you need the kotlin classes to be compiled, to successfully compile the scala classes. That's a problem.

The solution would be, that one of the languages allows jointCompilation for all of the languages (but this will never happen).

So for two JVM languages, where both are not Java , you must decide, which direction of access is allowed. But you can't allow both directions of access.

In such cases, it often helps, to put the logic into a java class, and access this java class instead of the eg scala class.

The problem is also the same for eg groovy , java and some other jvm language, like in the post https://discuss.gradle.org/t/kotlin-groovy-and-java-compilation/14903/10

Answer 2

The missing link to let Scala call Kotlin code would be to add the following in build.gradle

compileScala.classpath += files(compileKotlin.destinationDir)

Based on https://discuss.gradle.org/t/kotlin-groovy-and-java-compilation/14903/3