ActivityContextManager drops an active span when a first child span ends

[PavelChernyshov]

Hi,

I've noticed a strange behavior, which I believe is not right.

Consider the following code:

func testContextPropagationTwoSequentialChildSpans() {
        let parentSpan = defaultTracer.spanBuilder(spanName: "Parent").setActive(true).startSpan()
        OpenTelemetry.instance.contextProvider.setActiveSpan(parentSpan)

        let child1 = defaultTracer.spanBuilder(spanName: "child1").startSpan()
        child1.end()

        let child2 = defaultTracer.spanBuilder(spanName: "child2").startSpan()
        child2.end()

        parentSpan.end()

        XCTAssertEqual(parentSpan.context.traceId, child1.context.traceId)
        XCTAssertEqual(parentSpan.context.traceId, child2.context.traceId) <<<Fails here
    }

I would expect the second child span to share the context with the parent, but in reality it's a root one.

The test is available here

I'm not ready to contribute a patch at this point, os.activity is kind of new to me and I haven't dug deep enough into ActivityContextManager to be sure not to break something else.

However, this is what I observed:

• When child1 ends it clears contextMap.
• When child2 is started ActivityContextManager.getCurrentContextValue(forKey:) returns nil.

Other things here that raise my brow:

• I would expect .setActive(_ active: Bool) to work for the DefaultTracer implementation as well.

Thanks, Pavel.