Compiler doesn't pick incremental changes to multibindings in some circumstances

[matejdro]

When:

• We have classes with @ContributesMultibinding annotation in a library module
• Said library module includes Jetpack Compose compiler
• New incremental compilation is enabled (kotlin.incremental.useClasspathSnapshot=true in gradle.properties)

Changes on those annotations may not get picked up when making incremental builds.

Steps to reproduce:

1. Download and open Project.zip
2. Run project
3. Check logcat
4. Note that logs will print two entries (as it should)
5. Open LibraryMultibinds.kt
6. Comment out @ContributesMultibinding annotation
7. Run again and check logcat
8. Logs print two entries again, even though we have commented one

[vRallev]

I've seen this under similar circumstances too, but only for code removals like you pointed out. In some cases Anvil's generated code stayed around and referenced deleted code, which caused compilation failures.

[matejdro]

New incremental compilation is now enabled by default in Kotlin 1.8.20: https://kotlinlang.org/docs/whatsnew1820.html#new-jvm-incremental-compilation-by-default-in-gradle

And since many Android projects include Jetpack Compose compiler, I suspect this issue will now get much more widespread.

[hungvietnguyen]

The sample project was very useful! I found that when @ContributesMultibinding(AppScope::class) is added to class LibraryMultibinds in :mylibrary, the new IC doesn't detect a change because the new IC relies on the Kotlin class metadata in LibraryMultibinds.class and in this case the Kotlin class metadata doesn't change (whether this is a bug is TBD [1]).

Because of this, the :app:kaptGenerateStubsDebugKotlin task is UP-TO-DATE. (This seems correct for this task because its output shouldn't depend on changes to annotations of classes on the classpath.)

However, Anvil seems to rely on the :app:kaptGenerateStubsDebugKotlin task being run in order to do some work (e.g., to generate app/build/anvil/src-gen-debug/anvil/module/com/matejdro/multibindsanvildemo/AppComponent.kt which contains references to AppMultibinds and LibraryMultibinds). This can be seen at this code comment.

I guess we'll need to figure out [1] first. From there, it will be clear whether the bug is in the new IC or in Anvil.

[hungvietnguyen]

in this case the Kotlin class metadata doesn't change (whether this is a bug is TBD [1]).

I've filed https://youtrack.jetbrains.com/issue/KT-57919/Kotlin-class-metadata-doesnt-contain-info-about-class-annotations for the Kotlin team to take a look.

[vRallev]

Thanks!

[sav007]

Hey team is there any workaround for this issue? We found that every time we touch any class with ContributesMultibinding we have to run with --rerun-tasks but it's not great experience. Is there any other possible workaround?

Also is it the root cause because of this https://kotlinlang.org/docs/whatsnew1820.html#new-jvm-incremental-compilation-by-default-in-gradle?

If yes does it mean turning it somehow off should address the issue?

Btw we are on 1.8.20 so this issue persist not only in 1.8.10.

Update: disabling incremental compilation kotlin.incremental=false helps to resolve the issue as well :(

[matejdro]

Can you try turning new incremental compilation off with kotlin.incremental.useClasspathSnapshot=true?

[ZacSweers]

The old IC uses metadata too iirc, don't think changing the IC will help

[sav007]

otlin.incremental.useClasspathSnapshot=true the first what we tried, and it didn't work for us. As mentioned earlier kotlin.incremental=false only works in our case.

[matejdro]

The old IC uses metadata too iirc, don't think changing the IC will help

For us, issue only occurs when new IC is turned on (on 1.8.10, we did not update to 1.8.20 yet).

otlin.incremental.useClasspathSnapshot=true the first what we tried

Did you try setting it to false?

[hungvietnguyen]

I wanted to provide a bit more context on why only the new IC has this issue.

Both the new IC and the old IC rely on Kotlin class metadata to detect a change. Because the Kotlin class metadata currently doesn't contain info about class annotations (https://youtrack.jetbrains.com/issue/KT-57919), if we add/remove a class annotation, both the new and old IC will not detect a change.

The difference is that the new IC supports compile avoidance, which means that the task (in this case, :app:kaptGenerateStubsDebugKotlin) will be UP-TO-DATE, whereas with the old IC, that task will still run, then think that there are no changes, and won't recompile any files.

As long as the :app:kaptGenerateStubsDebugKotlin task runs, Anvil will be able to do its work as seen at this code comment.

Therefore, the new IC make its easier for this bug to show up, especially when used with Anvil.

[hungvietnguyen]

@sav007

We found that every time we touch any class with ContributesMultibinding we have to run with --rerun-tasks but it's not great experience.

This bug should only happen if you add/remove the ContributesMultibinding annotation. It should not happen if you "touch any class with ContributesMultibinding" but do not add/remove that annotation.

Btw, the workaround is to set kotlin.incremental.useClasspathSnapshot=false (note: false not true). Setting kotlin.incremental=false will not be great for performance.

If you don't find the above to be the case, then that is probably a different bug.

[matejdro]

As long as the :app:kaptGenerateStubsDebugKotlin task runs, Anvil will be able to do its work as seen at this code comment.

Would the workaround be to just set upToDateWhen { false } on the stubs task? Presumably it would not cause that big of a deal if only app module contains kapt, since it's compiled incrementally anyway (just not avoided)?

[hungvietnguyen]

Would the workaround be to just set upToDateWhen { false } on the stubs task?

Yes, I think that's another workaround. However, there will be some performance impact: Even if the task can run fast, it runs for all builds even when we don't make any changes.