Inconsistent behaviour of concatDelayError

[jebl01]

Expected behavior

Flux.concatDelayError should always delay errors

Actual behavior

For a publisher of publishers errors are not delayed

Steps to reproduce

The following test is a minor modification of the test FluxConatMapTest.publisherOfPublisherDelayError. Just like that test, I expect this to succeed, but it fails with the message:
java.lang.AssertionError: expectation "expectNext(3)" failed (expected: onNext(3); actual: onError(java.lang.Exception: test))

@Test
public void publisherOfPublisherDelayErrorX() {
	StepVerifier.create(
			Flux.concatDelayError(
					Flux.just(
							Flux.just(1, 2),
							Flux.error(new Exception("test")),
							Flux.just(3, 4))))
			.expectNext(1, 2, 3, 4)
			.verifyErrorMessage("test");
}

Note that when calling Flux.concatDelayError with sources... instead of a publisher of publishers, the above test is successful.

Reactor Core version

3.1.0.RELEASE

JVM version

1.8.0_121

OS version

Darwin 57172 15.6.0 Darwin Kernel Version 15.6.0: Sun Jun 4 21:43:07 PDT 2017; root:xnu-3248.70.3~1/RELEASE_X86_64 x86_64

[simonbasle]

This is indeed a bug with the Callable optimization pattern in concatMap, which doesn't take the delayError fully into account for Callable sources.