Methods returning TemplateInstance reported as not blocking

[computerlove]

Describe the bug

When adding @RunOnVirtualThread on a method returning TemplateInstance the application does not build, with exception:

java.lang.RuntimeException: io.quarkus.builder.BuildException: Build failure: Build failed due to errors
        [error]: Build step io.quarkus.resteasy.reactive.server.deployment.ResteasyReactiveProcessor#setupEndpoints threw an exception: java.lang.RuntimeException: java.lang.RuntimeException: Failed to process method 'no.nte.services.ucmeteringvalues.rest.AdminResource#cashflowevents'
        at org.jboss.resteasy.reactive.common.processor.EndpointIndexer.createEndpoints(EndpointIndexer.java:325)
        at io.quarkus.resteasy.reactive.server.deployment.ResteasyReactiveProcessor.setupEndpoints(ResteasyReactiveProcessor.java:656)
        at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
        at java.base/java.lang.reflect.Method.invoke(Method.java:580)
        at io.quarkus.deployment.ExtensionLoader$3.execute(ExtensionLoader.java:858)
        at io.quarkus.builder.BuildContext.run(BuildContext.java:282)
        at org.jboss.threads.ContextHandler$1.runWith(ContextHandler.java:18)
        at org.jboss.threads.EnhancedQueueExecutor$Task.run(EnhancedQueueExecutor.java:2513)
        at org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1538)
        at java.base/java.lang.Thread.run(Thread.java:1583)
        at org.jboss.threads.JBossThread.run(JBossThread.java:501)
Caused by: java.lang.RuntimeException: Failed to process method 'org.acme.SomePage#get'
        at org.jboss.resteasy.reactive.common.processor.EndpointIndexer.createResourceMethod(EndpointIndexer.java:789)
        at org.jboss.resteasy.reactive.common.processor.EndpointIndexer.createEndpoints(EndpointIndexer.java:414)
        at org.jboss.resteasy.reactive.common.processor.EndpointIndexer.createEndpoints(EndpointIndexer.java:292)
        ... 10 more
Caused by: jakarta.enterprise.inject.spi.DeploymentException: Method 'get' of class 'org.acme.SomePage' is considered a non blocking method. @RunOnVirtualThread can only be used on  methods considered blocking
        at org.jboss.resteasy.reactive.common.processor.EndpointIndexer.isRunOnVirtualThread(EndpointIndexer.java:853)
        at org.jboss.resteasy.reactive.common.processor.EndpointIndexer.createResourceMethod(EndpointIndexer.java:729)
        ... 12 more

Expected behavior

The application builds, and invokation is done on virtual thread.

Actual behavior

Application does not build

How to Reproduce?

Use the app generator, generate a app with quarkus-resteasy-reactive-qute. Add @RunOnVirtualThread in SomePage on class or method level.

Output of uname -a or ver

linux

Output of java -version

21

Quarkus version or git rev

2.4.2

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

Apache Maven 3.9.3

Additional information

[computerlove]

Looking closer at this it seems that this is intentional. ResteasyReactiveQuteProcessor has

@BuildStep
NonBlockingReturnTypeBuildItem nonBlockingTemplateInstance() {
    return new NonBlockingReturnTypeBuildItem(TEMPLATE_INSTANCE);
}

Adding @Blocking to the class fixes the problem.

@geoand Should this behavior be documented in the Qute documentation, perhaps a better error message on build failure?

[quarkus-bot]

/cc @FroMage (resteasy-reactive), @stuartwdouglas (resteasy-reactive)

[geoand]

@computerlove I think we should do both.

cc @mkouba

[mkouba]

Well, the error message from the description is not about Qute and TemplateInstance at all: jakarta.enterprise.inject.spi.DeploymentException: Method 'get' of class 'org.acme.SomePage' uses @RunOnVirtualThread but the target JDK version doesn't support virtual threads. Please configure your build tool to target Java 19 or above.

Anyway, I'm not so sure it was a good idea to produce the NonBlockingReturnTypeBuildItem for TemplateInstance. It's not an async type per se so it's a little bit confusing. @geoand WDYT?

[computerlove]

It at least looks like I was in a confused state when creating the sample. The original exception is not the correct one.
I have updated it now.

The core exception is

Caused by: jakarta.enterprise.inject.spi.DeploymentException: Method 'get' of class 'org.acme.SomePage' is considered a non blocking method. @RunOnVirtualThread can only be used on methods considered blocking

Yeah, I had to look at ResteasyReactiveProcessor and ResteasyReactiveQuteProcessor for a long time before realizing why

public TemplateInstance get() { ... }

is considered blocking.