Fix pagination restart issue and cover by unit test.

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimeline.kt

@@ -55,8 +55,6 @@ import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
-import kotlinx.coroutines.flow.distinctUntilChanged
-import kotlinx.coroutines.flow.filter
 import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.getAndUpdate
 import kotlinx.coroutines.flow.launchIn
@@ -213,8 +211,8 @@ class RustTimeline(
 
     override val timelineItems: Flow<List<MatrixTimelineItem>> = combine(
         _timelineItems,
-        backPaginationStatus.filter { !it.isPaginating }.distinctUntilChanged(),
+        backPaginationStatus,
-        forwardPaginationStatus.filter { !it.isPaginating }.distinctUntilChanged(),
+        forwardPaginationStatus,
         matrixRoom.roomInfoFlow.map { it.creator },
         isTimelineInitialized,
     ) { timelineItems,

libraries/matrix/impl/src/test/kotlin/io/element/android/libraries/matrix/impl/fixtures/fakes/FakeRustTimeline.kt

@@ -8,10 +8,12 @@
 package io.element.android.libraries.matrix.impl.fixtures.fakes
 
 import org.matrix.rustcomponents.sdk.NoPointer
+import org.matrix.rustcomponents.sdk.PaginationStatusListener
 import org.matrix.rustcomponents.sdk.TaskHandle
 import org.matrix.rustcomponents.sdk.Timeline
 import org.matrix.rustcomponents.sdk.TimelineDiff
 import org.matrix.rustcomponents.sdk.TimelineListener
+import uniffi.matrix_sdk_ui.LiveBackPaginationStatus
 
 class FakeRustTimeline : Timeline(NoPointer) {
     private var listener: TimelineListener? = null
@@ -23,4 +25,16 @@ class FakeRustTimeline : Timeline(NoPointer) {
     fun emitDiff(diff: List<TimelineDiff>) {
         listener!!.onUpdate(diff)
     }
+
+    private var paginationStatusListener: PaginationStatusListener? = null
+    override suspend fun subscribeToBackPaginationStatus(listener: PaginationStatusListener): TaskHandle {
+        this.paginationStatusListener = listener
+        return FakeRustTaskHandle()
+    }
+
+    fun emitPaginationStatus(status: LiveBackPaginationStatus) {
+        paginationStatusListener!!.onUpdate(status)
+    }
+
+    override suspend fun fetchMembers() = Unit
 }

libraries/matrix/impl/src/test/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimelineTest.kt

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2025 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+@file:OptIn(ExperimentalCoroutinesApi::class)
+
+package io.element.android.libraries.matrix.impl.timeline
+
+import app.cash.turbine.test
+import com.google.common.truth.Truth.assertThat
+import io.element.android.libraries.featureflag.api.FeatureFlagService
+import io.element.android.libraries.featureflag.test.FakeFeatureFlagService
+import io.element.android.libraries.matrix.api.room.MatrixRoom
+import io.element.android.libraries.matrix.api.timeline.MatrixTimelineItem
+import io.element.android.libraries.matrix.api.timeline.Timeline
+import io.element.android.libraries.matrix.api.timeline.item.virtual.VirtualTimelineItem
+import io.element.android.libraries.matrix.impl.fixtures.fakes.FakeRustRoomListService
+import io.element.android.libraries.matrix.impl.fixtures.fakes.FakeRustTimeline
+import io.element.android.libraries.matrix.impl.fixtures.fakes.FakeRustTimelineDiff
+import io.element.android.libraries.matrix.impl.room.RoomContentForwarder
+import io.element.android.libraries.matrix.test.room.FakeMatrixRoom
+import io.element.android.libraries.matrix.test.room.aRoomInfo
+import io.element.android.services.toolbox.api.systemclock.SystemClock
+import io.element.android.services.toolbox.test.systemclock.A_FAKE_TIMESTAMP
+import io.element.android.services.toolbox.test.systemclock.FakeSystemClock
+import io.element.android.tests.testutils.testCoroutineDispatchers
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.runCurrent
+import kotlinx.coroutines.test.runTest
+import org.junit.Test
+import org.matrix.rustcomponents.sdk.TimelineChange
+import uniffi.matrix_sdk_ui.LiveBackPaginationStatus
+import org.matrix.rustcomponents.sdk.Timeline as InnerTimeline
+
+class RustTimelineTest {
+    @Test
+    fun `ensure that the timeline emits new loading item when pagination does not bring new events`() = runTest {
+        val inner = FakeRustTimeline()
+        val systemClock = FakeSystemClock()
+        val sut = createRustTimeline(
+            inner = inner,
+            systemClock = systemClock,
+        )
+        sut.timelineItems.test {
+            // Give time for the listener to be set
+            runCurrent()
+            inner.emitDiff(
+                listOf(
+                    FakeRustTimelineDiff(
+                        item = null,
+                        change = TimelineChange.RESET,
+                    )
+                )
+            )
+            with(awaitItem()) {
+                assertThat(size).isEqualTo(1)
+                // Typing notification
+                assertThat((get(0) as MatrixTimelineItem.Virtual).virtual).isEqualTo(VirtualTimelineItem.TypingNotification)
+            }
+            with(awaitItem()) {
+                assertThat(size).isEqualTo(2)
+                // The loading
+                assertThat((get(0) as MatrixTimelineItem.Virtual).virtual).isEqualTo(
+                    VirtualTimelineItem.LoadingIndicator(
+                        direction = Timeline.PaginationDirection.BACKWARDS,
+                        timestamp = A_FAKE_TIMESTAMP,
+                    )
+                )
+                // Typing notification
+                assertThat((get(1) as MatrixTimelineItem.Virtual).virtual).isEqualTo(VirtualTimelineItem.TypingNotification)
+            }
+            systemClock.epochMillisResult = A_FAKE_TIMESTAMP + 1
+            // Start pagination
+            sut.paginate(Timeline.PaginationDirection.BACKWARDS)
+            // Simulate SDK starting pagination
+            inner.emitPaginationStatus(LiveBackPaginationStatus.Paginating)
+            // No new events received
+            // Simulate SDK stopping pagination, more event to load
+            inner.emitPaginationStatus(LiveBackPaginationStatus.Idle(hitStartOfTimeline = false))
+            // expect an item to be emitted, with an updated timestamp
+            with(awaitItem()) {
+                assertThat(size).isEqualTo(2)
+                // The loading
+                assertThat((get(0) as MatrixTimelineItem.Virtual).virtual).isEqualTo(
+                    VirtualTimelineItem.LoadingIndicator(
+                        direction = Timeline.PaginationDirection.BACKWARDS,
+                        timestamp = A_FAKE_TIMESTAMP + 1,
+                    )
+                )
+                // Typing notification
+                assertThat((get(1) as MatrixTimelineItem.Virtual).virtual).isEqualTo(VirtualTimelineItem.TypingNotification)
+            }
+        }
+    }
+}
+
+private fun TestScope.createRustTimeline(
+    inner: InnerTimeline,
+    mode: Timeline.Mode = Timeline.Mode.LIVE,
+    systemClock: SystemClock = FakeSystemClock(),
+    matrixRoom: MatrixRoom = FakeMatrixRoom().apply { givenRoomInfo(aRoomInfo()) },
+    coroutineScope: CoroutineScope = backgroundScope,
+    dispatcher: CoroutineDispatcher = testCoroutineDispatchers().io,
+    roomContentForwarder: RoomContentForwarder = RoomContentForwarder(FakeRustRoomListService()),
+    featureFlagsService: FeatureFlagService = FakeFeatureFlagService(),
+    onNewSyncedEvent: () -> Unit = {},
+): RustTimeline {
+    return RustTimeline(
+        inner = inner,
+        mode = mode,
+        systemClock = systemClock,
+        matrixRoom = matrixRoom,
+        coroutineScope = coroutineScope,
+        dispatcher = dispatcher,
+        roomContentForwarder = roomContentForwarder,
+        featureFlagsService = featureFlagsService,
+        onNewSyncedEvent = onNewSyncedEvent,
+    )
+}

services/toolbox/test/src/main/kotlin/io/element/android/services/toolbox/test/systemclock/FakeSystemClock.kt

@@ -11,8 +11,8 @@ import io.element.android.services.toolbox.api.systemclock.SystemClock
 
 const val A_FAKE_TIMESTAMP = 123L
 
-class FakeSystemClock : SystemClock {
+class FakeSystemClock(
-    override fun epochMillis(): Long {
+    var epochMillisResult: Long = A_FAKE_TIMESTAMP
-        return A_FAKE_TIMESTAMP
+) : SystemClock {
-    }
+    override fun epochMillis() = epochMillisResult
 }