Collect test candidates eagerly

[ghost]

concat produces a lazy sequence, which makes its repeated usage in a
loop a potential stack overflow hazard (when the produced seq gets
realized and has to recur over its subseqs).

Background: I've been trying to introduce clojure to a java/kotlin project. Clojure tests kept on dying with a StackOverflowError in CI during test discovery, with stacktrace mentioning concat. I couldn't debug the issue very well - it wasn't reliably reproducible locally - but noticed that apparently all AOTted classes in test classpath were being scanned for tests, which is a lot of classes. I've run grep on jovial, found a single use of concat in a loop and tried to replace it with a non-lazy equivalent. Tests run fine with the patched version. I'm not 100% convinced that concat's laziness was the sole culprit due to flakiness of local test runs, but if it helps it helps.

[ghost]

I've actually taken the time to sit down and repro the overflow, it's proven to not be too hard. It's here, but I suspect tweaking the numbers in infinite-fns and/or creating more namespaces (and importing them in the test) might be necessary depending on the local JVM, machine and alignment of stars.

The stacktrace in JUnit report (truncated, of course):

org.gradle.api.internal.tasks.testing.TestSuiteExecutionException: Could not complete execution for Gradle Test Executor 1.
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:63)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at [email protected]/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at [email protected]/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at [email protected]/java.lang.reflect.Method.invoke(Method.java:568)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
	at jdk.proxy1/jdk.proxy1.$Proxy2.stop(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)
	at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:133)
	at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:71)
	at app//worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)
	at app//worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
Caused by: org.junit.platform.commons.JUnitException: TestEngine with ID 'org.ajoberstar.jovial.clojure-test' failed to discover tests
	at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discoverEngineRoot(EngineDiscoveryOrchestrator.java:111)
	at org.junit.platform.launcher.core.EngineDiscoveryOrchestrator.discover(EngineDiscoveryOrchestrator.java:85)
	at org.junit.platform.launcher.core.DefaultLauncher.discover(DefaultLauncher.java:92)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:99)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:79)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:75)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:61)
	... 18 more
Caused by: java.lang.StackOverflowError
	at clojure.lang.LazySeq.sval(LazySeq.java:42)
	at clojure.lang.LazySeq.seq(LazySeq.java:51)
	at clojure.lang.RT.seq(RT.java:535)
	at clojure.core$seq__5419.invokeStatic(core.clj:139)
	at clojure.core$concat$fn__5510.invoke(core.clj:727)
	at clojure.lang.LazySeq.sval(LazySeq.java:42)
	at clojure.lang.LazySeq.seq(LazySeq.java:51)
	at clojure.lang.RT.seq(RT.java:535)
	at clojure.core$seq__5419.invokeStatic(core.clj:139)
	at clojure.core$concat$fn__5510.invoke(core.clj:727)
	at clojure.lang.LazySeq.sval(LazySeq.java:42)
	at clojure.lang.LazySeq.seq(LazySeq.java:51)
	at clojure.lang.RT.seq(RT.java:535)

[ajoberstar]

Apologies for the delay on this, I lost track of this PR being open. I appreciate the work you did to dig into this and fix this! Thanks!