reportFullDisplay finishing the wrong span

Description

There is a problem with the reportFullDisplay API:

ViewControllerA opens, starts a HTTP request, user clicks a button and opens ViewControllerB.
ViewControllerB starts an HTTP request.
ViewControllerA’s HTTP request ends and SentrySDK.reportFullyDisplayed is called.

This will finish TTFD for ViewControllerB, but it is still waiting for its request to respond.

Test inside SentryUIViewControllerPerformanceTrackerTests.swift from https://github.com/getsentry/sentry-cocoa/pull/4531 to reproduce the problem:

func test_waitForFullDisplay_NewViewControllerLoaded_BeforeReportTTFD_withBackgroundWork() throws {
    class CustomVC: UIViewController {
        var workSpan: Span?

        override func viewDidAppear(_ animated: Bool) {
            super.viewDidAppear(animated)
            //Start some work, it could be a http request
            workSpan = SentrySDK.span?.startChild(operation: "Work")
        }

        // We will use a function to finish the work
        // but it could be the request response
        func finishWork() {
            workSpan?.finish()
            SentrySDK.reportFullyDisplayed()
        }
    }

    let dateProvider = fixture.dateProvider
    let sut = fixture.getSut()
    let tracker = fixture.tracker
    let firstController = CustomVC()
    let secondController = CustomVC()

    var firstTracer: SentryTracer?
    var secondTracer: SentryTracer?

    sut.enableWaitForFullDisplay = true

    dateProvider.advance(by: 1)
    sut.viewControllerLoadView(firstController) {
        firstController.loadView()
        firstTracer = self.getStack(tracker).first as? SentryTracer
    }

    sut.viewControllerViewDidLoad(firstController) {
        firstController.viewDidLoad()
    }

    dateProvider.advance(by: 1)
    sut.viewControllerViewWillAppear(firstController) {
        firstController.viewWillAppear(false)
    }

    sut.viewControllerViewDidAppear(firstController) {
        firstController.viewDidAppear(false)
    }

    fixture.displayLinkWrapper.normalFrame()

    let firstFullDisplaySpan = try XCTUnwrap(firstTracer?.children.first { $0.operation == "ui.load.full_display" })

    XCTAssertFalse(firstFullDisplaySpan.isFinished)

    XCTAssertEqual(firstTracer?.traceId, SentrySDK.span?.traceId)

    dateProvider.advance(by: 1)
    sut.viewControllerLoadView(secondController) {
        secondController.loadView()
        secondTracer = self.getStack(tracker).first as? SentryTracer
    }

    // The work of the first controller asynchronously ended here, and a new frame was rendered
    // while the second controller hasn’t appeared yet.
    dateProvider.advance(by: 1)
    firstController.finishWork()
    fixture.displayLinkWrapper.normalFrame()

    dateProvider.advance(by: 1)
    sut.viewControllerViewWillAppear(secondController) {
        secondController.viewWillAppear(false)
    }
    sut.viewControllerViewDidAppear(secondController) {
        secondController.viewDidAppear(false)
    }
    fixture.displayLinkWrapper.normalFrame()

    dateProvider.advance(by: 1)
    let timeOfSecondControllerFinishWork = dateProvider.date()
    secondController.finishWork()

    fixture.displayLinkWrapper.normalFrame()

    XCTAssertTrue(firstFullDisplaySpan.isFinished)
    XCTAssertEqual(.deadlineExceeded, firstFullDisplaySpan.status)

    let secondFullDisplaySpan = try XCTUnwrap(secondTracer?.children.first { $0.operation == "ui.load.full_display" })

    XCTAssertEqual(secondFullDisplaySpan.timestamp, timeOfSecondControllerFinishWork)
}

getsentry / sentry-cocoa

reportFullDisplay finishing the wrong span #4533

Description