firebase-auth publishes @UnknownInitialization but does not declare checker-qual, breaking Kotlin consumers

[qeepcologne]

[READ] Step 1: Are you in the right place?

Yes — this is a defect in the published com.google.firebase:firebase-auth artifact metadata.

[REQUIRED] Step 2: Describe your environment

• Android Studio version: n/a (Gradle CLI)
• Firebase Component: Authentication (com.google.firebase:firebase-auth:24.2.0, via firebase-bom:34.18.0)
• Component version: 24.2.0
• Kotlin: 2.4.10 · AGP: 9.4.0-rc01 · Gradle: 9.7.1 · JDK 21

[REQUIRED] Step 3: Describe the problem

firebase-auth publishes classes annotated with org.checkerframework.checker.initialization.qual.UnknownInitialization, but its POM does not declare org.checkerframework:checker-qual. Consumers therefore have no way to resolve that annotation, and any Kotlin code that compiles against the annotated API and lets a type be inferred fails to compile.

Confirmed by scanning the artifact contents — the annotation reference is inside firebase-auth itself, not a transitive dependency:

$ unzip -p firebase-auth-24.2.0.aar classes.jar | strings | grep UnknownInitialization
# present in 24.2.0 and 24.1.0

and it is absent from the published POM (all 17 declared dependencies checked; androidx.*, play-services-*, firebase-*, kotlin-stdlib — no checker-qual).

Nothing else on the compile classpath supplies it either. firebase-auth pulls only the com.google.guava:listenablefuture stub, not full Guava — and full Guava is what historically put checker-qual on the classpath transitively. That is presumably why this was latent: the annotation is present in 24.1.0 as well, so an unrelated dependency change is what removed the accidental path to it.

Steps to reproduce:

Compile Kotlin against FirebaseAuth.IdTokenListener with an inferred lambda parameter, with checker-qual absent from the classpath:

FirebaseAuth.IdTokenListener { auth ->   // `auth` type inferred
  // ...
}

Relevant Code / error:

Type annotation class 'org.checkerframework.checker.initialization.qual.UnknownInitialization'
of the inferred type is inaccessible. Check the module classpath for missing or conflicting dependencies.

This reproduces through the official Flutter plugin (firebase_auth 6.6.0), whose IdTokenChannelStreamHandler.kt:23 is exactly that shape — :firebase_auth:compileDebugKotlin fails outright.

Note javac tolerates this (the JLS says unresolvable annotations are ignored), so Java consumers do not notice; Kotlin needs the annotation to resolve the inferred type, so only Kotlin consumers break.

Workaround (in a consumer's build, for anyone finding this):

dependencies { compileOnly("org.checkerframework:checker-qual:3.49.5") }

Suggested fix: declare checker-qual in firebase-auth's POM so it lands on consumers' compile classpath, or strip the annotation from the published class files if it is not meant to be part of the public API surface.

[lehcar09]

Hi @qeepcologne, thank you for reaching out. I was able to reproduce the issue. I'll raise this to our engineers along with your suggestion on how to fix the issue. Thanks!