Unable to inject @JvmInline value classes

[drinkthestars]

Injecting a @JvmInline value class fails in the following manner:

Code:

@JvmInline value class Foo(val value: Int)

@Module
@InstallIn(SingletonComponent::class)
object FooModule {
    @Provides
    fun provideFoo() = Foo(value = 123)
}

class FooBar @Inject constructor(
    private val foo: Foo
) { /** ... **/ }

class UsesFooBar @Inject constructor(
    private val fooBar: FooBar
) { /** Uses fooBar **/ }

Fails with:

[Dagger/MissingBinding] FooBar cannot be provided without an @Inject constructor or an @Provides-annotated method.
  public abstract static class SingletonC implements FooApplication_GeneratedInjector

Not sure if this is a bug, or if it's just impossible to support with kapt (i.e. needs something like KSP) 🤔. Thanks!

[drinkthestars]

could be related to #2855

[Chang-Eric]

I think this will likely be something that needs KSP as we probably will just see Foo as an Integer after kapt. Added some labels but we can revisit in the future when KSP is done.

[drinkthestars]

Sounds good, thank you!

[reddaly]

I think this will likely be something that needs KSP as we probably will just see Foo as an Integer after kapt. Added some labels but we can revisit in the future when KSP is done.

Is there a bug I can track related to "when KSP is done?"

[Chang-Eric]

@reddaly #2349

[bj0]

The alpha version of KSP support was released with dagger 1.48, so I tested this again:

@JvmInline
value class PluginContext(val context: Context)



@Module
abstract class UiModule {

...

    companion object {
        @Provides
        @PluginScope
        fun providePluginContext(ctx: Context): PluginContext {
            return PluginContext(ctx)
        }
   }
}  

Just adding this provider (no requesters yet) ksp throws an error:

e: [ksp] java.lang.IllegalArgumentException: not a valid name: UiModule_Companion_ProvidePluginContext-wwunPCQFactory

[Chang-Eric]

To clarify, KSP is a prerequisite to fixing this, but is not itself the solution.

[dawidhyzy]

@Chang-Eric is this fixed with the current KSP implementation?

[Chang-Eric]

It is not fixed, as mentioned above. To clarify in case it is causing confusion, the current behavior is mixed, some cases work, some don't. This is because this is the behavior that existed due to kapt.

[gildor]

Is it possible to at least improve error message? Now the message is extremely confusing, it doesn't mention anything about missing param, but about class which includes this param

[bcorso]

Is it possible to at least improve error message?

AFAICT, no (at least in KAPT) because it looks like KAPT generates an invalid Java stub, which limits what Dagger can report.

In particular, take the example in the original question:

@JvmInline value class Foo(val value: Int)

class FooBar @Inject constructor(foo: Foo)

If you look at the Java stub generated by KAPT, you will see:

public final class FooBar {
    private FooBar(int foo) {
        super();
    }
}

Note that the constructor of the class is missing the @Inject annotation. Hence, Dagger complains about a missing binding for FooBar and never even gets to Foo.