Baggage should be reverted after scopedSpan#end when using Otel

[wapkch]

According to #879, for async baggage propagation, we do not close baggageInScope.

But the baggage cannot be reverted even after scopedSpan#end when using micrometer-tracing-bridge-otel, but if using micrometer-tracing-bridge-brave, the baggage will be reverted.

Tested with the latest version (1.4.1):

    @Bean
    CommandLineRunner commandLineRunner1(Tracer tracer) {
        return args -> {
            ScopedSpan scopedSpan = tracer.startScopedSpan("test");

            try {
                // We do not close baggageInScope for async baggage propagation.
                BaggageInScope baggageInScope = tracer.getBaggage("xyz").makeCurrent("123");

                ExecutorService executorService = ContextExecutorService.wrap(Executors.newCachedThreadPool(), ContextSnapshot::captureAll);
                executorService.execute(() -> {
                    try {
                        // do some work...
                        Thread.sleep(3000);
                        // check baggage
                        String xyz = tracer.getBaggage("xyz").get();
                        Assert.state(xyz.equals("123"), "Baggage should be propagated");
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                });
            } finally {
                scopedSpan.end();
            }

            String xyz = tracer.getBaggage("xyz").get();
            Assert.state(xyz == null, "Baggage should be reverted"); // failed when using otel, succeed when using brave
        };
    }

[marcingrzejszczak]

You haven't closed the baggageInScope variable.

For Brave baggage is always tied to the span so even if you've left the opened scope for baggage, the span scope is closed.

For OTel span and baggage scopes are separate. You've opened a baggage scope and never closed it. This is why you have the problem you've mentioned.