jakarta.enterprise.inject.Specializes not working

[pat-karakun]

Describe the bug

Quarkus (version 3.26.1) does not seem to handle @Specializes (correctly):

• given
  • an interface Strategy
  • a default injectable bean DefaultStrategy (annotated with @Default) implementing that interface
  • a specialized injectable bean SpecializedStrategy (annotated with @Specializes) extending DefaultStrategy
• when injecting an instance of the interface in another bean GreetingResource
• then an AmbiguousResolutionException is thrown

java.lang.RuntimeException: io.quarkus.builder.BuildException: Build failure: Build failed due to errors
	[error]: Build step io.quarkus.arc.deployment.ArcProcessor#validate threw an exception: jakarta.enterprise.inject.spi.DeploymentException: jakarta.enterprise.inject.AmbiguousResolutionException: Ambiguous dependencies for type io.specializes.Strategy and qualifiers [@Default]
	- injection target: io.specializes.GreetingResource#strategy
	- declared on CLASS bean [types=[io.specializes.GreetingResource, java.lang.Object], qualifiers=[@Any, @Default], target=io.specializes.GreetingResource]
	- available beans:
		- CLASS bean [types=[io.specializes.DefaultStrategy, io.specializes.SpecializedStrategy, io.specializes.Strategy, java.lang.Object], qualifiers=[@Any, @Default], target=io.specializes.SpecializedStrategy]
		- CLASS bean [types=[io.specializes.DefaultStrategy, io.specializes.Strategy, java.lang.Object], qualifiers=[@Any, @Default], target=io.specializes.DefaultStrategy]
	at io.quarkus.arc.processor.BeanDeployment.processErrors(BeanDeployment.java:1594)
	at io.quarkus.arc.processor.BeanDeployment.init(BeanDeployment.java:341)
	at io.quarkus.arc.processor.BeanProcessor.initialize(BeanProcessor.java:178)
	at io.quarkus.arc.deployment.ArcProcessor.validate(ArcProcessor.java:488)
	at java.base/java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:732)
	at io.quarkus.deployment.ExtensionLoader$3.execute(ExtensionLoader.java:874)
	at io.quarkus.builder.BuildContext.run(BuildContext.java:255)
	at org.jboss.threads.ContextHandler$1.runWith(ContextHandler.java:18)
	at org.jboss.threads.EnhancedQueueExecutor$Task.doRunWith(EnhancedQueueExecutor.java:2651)
	at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2630)
	at org.jboss.threads.EnhancedQueueExecutor.runThreadBody(EnhancedQueueExecutor.java:1622)
	at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1589)
	at java.base/java.lang.Thread.run(Thread.java:840)
	at org.jboss.threads.JBossThread.run(JBossThread.java:501)

Expected behavior

There should be no build error and the specialized injectable bean SpecializedStrategy should be injected.

Actual behavior

There is a build error due to AmbiguousResolutionException

How to Reproduce?

Reproducer repo: https://github.com/pat-karakun/quarkus-cdi-specializes

Issue can be reproduced by running GreetingResourceTest.
More details in https://github.com/pat-karakun/quarkus-cdi-specializes/blob/main/README.md

Output of uname -a or ver

Linux ... 4.18.0-553.69.1.el8_10.x86_64 #1 SMP Thu Aug 7 18:10:00 EDT 2025 x86_64 x86_64 x86_64 GNU/Linux

Output of java -version

openjdk version "17.0.16" 2025-07-15 LTS OpenJDK Runtime Environment (Red_Hat-17.0.16.0.8-1) (build 17.0.16+8-LTS) OpenJDK 64-Bit Server VM (Red_Hat-17.0.16.0.8-1) (build 17.0.16+8-LTS, mixed mode, sharing)

Quarkus version or git rev

3.26.1

Build tool (ie. output of mvnw --version or gradlew --version)

Apache Maven 3.8.3

Additional information

No response

[quarkus-bot]

/cc @Ladicek (arc), @manovotn (arc), @mkouba (arc)

[mkouba]

Specialization is not supported by Quarkus/ArC. See also https://quarkus.io/guides/cdi-reference#supported_features_and_limitations. We only implement CDI Lite + a few CDI Full features (such as decorators).

However, we should probably fail the build with a proper error message 🤔. @Ladicek @manovotn WDYT?

[manovotn]

+1, the fact that it doesn't work is intended (specialization is not part of CDI Lite and Quarkus didn't aim to implement it).
We should be able to easily identify use of @Specializes and throw an error at build time.

If nobody else beats me to it, I can send a PR later today or tomorrow.

@pat-karakun as a side note, vast majority of cases where specialization is used can also be solved with @Alternative so you can look into that instead.

[pat-karakun]

@manovotn thanks for the hint, I was aware of @Alternative and already resorted to it in our project. Also used it as a comparision in the reproducer.

A specific error message would be great as the AmbiguousResolutionException doesn't really help.

[manovotn]

@manovotn thanks for the hint, I was aware of @Alternative and already resorted to it in our project. Also used it as a comparision in the reproducer.

A specific error message would be great as the AmbiguousResolutionException doesn't really help.

The PR was merged so there should now be an error message with explanation, thanks for bringing this to our attention :)