Merge changes from topic "b241229236_stable_sort_flagged" into tm-qpr-dev am: 00f287b876 am: d69698aa6e

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/19194469

Change-Id: I6cd7473f90338c04c903b26fc79b09ead315a678
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

9 files changed, 773 insertions, 29 deletions

diff --git a/packages/SystemUI/src/com/android/systemui/flags/Flags.java b/packages/SystemUI/src/com/android/systemui/flags/Flags.java
index e17ae28c9e95..d05097b053a4 100644
--- a/packages/SystemUI/src/com/android/systemui/flags/Flags.java
+++ b/packages/SystemUI/src/com/android/systemui/flags/Flags.java
@@ -75,7 +75,9 @@ public class Flags {
 
     public static final UnreleasedFlag STABILITY_INDEX_FIX = new UnreleasedFlag(114, true);
 
-    // next id: 115
+    public static final UnreleasedFlag SEMI_STABLE_SORT = new UnreleasedFlag(115, true);
+
+    // next id: 116
 
     /***************************************/
     // 200 - keyguard/lockscreen
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/NotifPipelineFlags.kt b/packages/SystemUI/src/com/android/systemui/statusbar/notification/NotifPipelineFlags.kt
index 2f0a1aa9b0d5..e3e8a99f6db3 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/notification/NotifPipelineFlags.kt
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/NotifPipelineFlags.kt
@@ -57,4 +57,8 @@ class NotifPipelineFlags @Inject constructor(
     val isStabilityIndexFixEnabled: Boolean by lazy {
         featureFlags.isEnabled(Flags.STABILITY_INDEX_FIX)
     }
+
+    val isSemiStableSortEnabled: Boolean by lazy {
+        featureFlags.isEnabled(Flags.SEMI_STABLE_SORT)
+    }
 }
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ListAttachState.kt b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ListAttachState.kt
index f8449ae8807b..84ab0d1190f0 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ListAttachState.kt
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ListAttachState.kt
@@ -68,6 +68,9 @@ data class ListAttachState private constructor(
      */
     var stableIndex: Int = -1
 
+    /** Access the index of the [section] or -1 if the entry does not have one */
+    val sectionIndex: Int get() = section?.index ?: -1
+
     /** Copies the state of another instance. */
     fun clone(other: ListAttachState) {
         parent = other.parent
@@ -95,11 +98,13 @@ data class ListAttachState private constructor(
      * This can happen if the entry is removed from a group that was broken up or if the entry was
      * filtered out during any of the filtering steps.
      */
-    fun detach() {
+    fun detach(includingStableIndex: Boolean) {
         parent = null
         section = null
         promoter = null
-        // stableIndex = -1  // TODO(b/241229236): Clear this once we fix the stability fragility
+        if (includingStableIndex) {
+            stableIndex = -1
+        }
     }
 
     companion object {
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilder.java b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilder.java
index 225236f95179..3ae2545e4e10 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilder.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilder.java
@@ -54,6 +54,9 @@ import com.android.systemui.statusbar.notification.collection.listbuilder.OnBefo
 import com.android.systemui.statusbar.notification.collection.listbuilder.OnBeforeSortListener;
 import com.android.systemui.statusbar.notification.collection.listbuilder.OnBeforeTransformGroupsListener;
 import com.android.systemui.statusbar.notification.collection.listbuilder.PipelineState;
+import com.android.systemui.statusbar.notification.collection.listbuilder.SemiStableSort;
+import com.android.systemui.statusbar.notification.collection.listbuilder.SemiStableSort.StableOrder;
+import com.android.systemui.statusbar.notification.collection.listbuilder.ShadeListBuilderHelper;
 import com.android.systemui.statusbar.notification.collection.listbuilder.ShadeListBuilderLogger;
 import com.android.systemui.statusbar.notification.collection.listbuilder.pluggable.DefaultNotifStabilityManager;
 import com.android.systemui.statusbar.notification.collection.listbuilder.pluggable.Invalidator;
@@ -96,12 +99,14 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
     // used exclusivly by ShadeListBuilder#notifySectionEntriesUpdated
     // TODO replace temp with collection pool for readability
     private final ArrayList<ListEntry> mTempSectionMembers = new ArrayList<>();
-    private final NotifPipelineFlags mFlags;
+    private NotifPipelineFlags mFlags;
     private final boolean mAlwaysLogList;
 
     private List<ListEntry> mNotifList = new ArrayList<>();
     private List<ListEntry> mNewNotifList = new ArrayList<>();
 
+    private final SemiStableSort mSemiStableSort = new SemiStableSort();
+    private final StableOrder<ListEntry> mStableOrder = this::getStableOrderRank;
     private final PipelineState mPipelineState = new PipelineState();
     private final Map<String, GroupEntry> mGroups = new ArrayMap<>();
     private Collection<NotificationEntry> mAllEntries = Collections.emptyList();
@@ -529,7 +534,7 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
             List<NotifFilter> filters) {
         Trace.beginSection("ShadeListBuilder.filterNotifs");
         final long now = mSystemClock.uptimeMillis();
-        for (ListEntry entry : entries)  {
+        for (ListEntry entry : entries) {
             if (entry instanceof GroupEntry) {
                 final GroupEntry groupEntry = (GroupEntry) entry;
 
@@ -960,7 +965,8 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
      * filtered out during any of the filtering steps.
      */
     private void annulAddition(ListEntry entry) {
-        entry.getAttachState().detach();
+        // NOTE(b/241229236): Don't clear stableIndex until we fix stability fragility
+        entry.getAttachState().detach(/* includingStableIndex= */ mFlags.isSemiStableSortEnabled());
     }
 
     private void assignSections() {
@@ -980,7 +986,16 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
 
     private void sortListAndGroups() {
         Trace.beginSection("ShadeListBuilder.sortListAndGroups");
-        // Assign sections to top-level elements and sort their children
+        if (mFlags.isSemiStableSortEnabled()) {
+            sortWithSemiStableSort();
+        } else {
+            sortWithLegacyStability();
+        }
+        Trace.endSection();
+    }
+
+    private void sortWithLegacyStability() {
+        // Sort all groups and the top level list
         for (ListEntry entry : mNotifList) {
             if (entry instanceof GroupEntry) {
                 GroupEntry parent = (GroupEntry) entry;
@@ -993,16 +1008,15 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
         // Check for suppressed order changes
         if (!getStabilityManager().isEveryChangeAllowed()) {
             mForceReorderable = true;
-            boolean isSorted = isShadeSorted();
+            boolean isSorted = isShadeSortedLegacy();
             mForceReorderable = false;
             if (!isSorted) {
                 getStabilityManager().onEntryReorderSuppressed();
             }
         }
-        Trace.endSection();
     }
 
-    private boolean isShadeSorted() {
+    private boolean isShadeSortedLegacy() {
         if (!isSorted(mNotifList, mTopLevelComparator)) {
             return false;
         }
@@ -1016,6 +1030,43 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
         return true;
     }
 
+    private void sortWithSemiStableSort() {
+        // Sort each group's children
+        boolean allSorted = true;
+        for (ListEntry entry : mNotifList) {
+            if (entry instanceof GroupEntry) {
+                GroupEntry parent = (GroupEntry) entry;
+                allSorted &= sortGroupChildren(parent.getRawChildren());
+            }
+        }
+        // Sort each section within the top level list
+        mNotifList.sort(mTopLevelComparator);
+        if (!getStabilityManager().isEveryChangeAllowed()) {
+            for (List<ListEntry> subList : getSectionSubLists(mNotifList)) {
+                allSorted &= mSemiStableSort.stabilizeTo(subList, mStableOrder, mNewNotifList);
+            }
+            applyNewNotifList();
+        }
+        assignIndexes(mNotifList);
+        if (!allSorted) {
+            // Report suppressed order changes
+            getStabilityManager().onEntryReorderSuppressed();
+        }
+    }
+
+    private Iterable<List<ListEntry>> getSectionSubLists(List<ListEntry> entries) {
+        return ShadeListBuilderHelper.INSTANCE.getSectionSubLists(entries);
+    }
+
+    private boolean sortGroupChildren(List<NotificationEntry> entries) {
+        if (getStabilityManager().isEveryChangeAllowed()) {
+            entries.sort(mGroupChildrenComparator);
+            return true;
+        } else {
+            return mSemiStableSort.sort(entries, mStableOrder, mGroupChildrenComparator);
+        }
+    }
+
     /** Determine whether the items in the list are sorted according to the comparator */
     @VisibleForTesting
     public static <T> boolean isSorted(List<T> items, Comparator<? super T> comparator) {
@@ -1212,7 +1263,7 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
                 o2.getSectionIndex());
         if (cmp != 0) return cmp;
 
-        cmp = Integer.compare(
+        cmp = mFlags.isSemiStableSortEnabled() ? 0 : Integer.compare(
                 getStableOrderIndex(o1),
                 getStableOrderIndex(o2));
         if (cmp != 0) return cmp;
@@ -1241,7 +1292,7 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
 
 
     private final Comparator<NotificationEntry> mGroupChildrenComparator = (o1, o2) -> {
-        int cmp = Integer.compare(
+        int cmp = mFlags.isSemiStableSortEnabled() ? 0 : Integer.compare(
                 getStableOrderIndex(o1),
                 getStableOrderIndex(o2));
         if (cmp != 0) return cmp;
@@ -1272,9 +1323,25 @@ public class ShadeListBuilder implements Dumpable, PipelineDumpable {
             // let the stability manager constrain or allow reordering
             return -1;
         }
+        // NOTE(b/241229236): Can't use cleared section index until we fix stability fragility
         return entry.getPreviousAttachState().getStableIndex();
     }
 
+    @Nullable
+    private Integer getStableOrderRank(ListEntry entry) {
+        if (getStabilityManager().isEntryReorderingAllowed(entry)) {
+            // let the stability manager constrain or allow reordering
+            return null;
+        }
+        if (entry.getAttachState().getSectionIndex()
+                != entry.getPreviousAttachState().getSectionIndex()) {
+            // stable index is only valid within the same section; otherwise we allow reordering
+            return null;
+        }
+        final int stableIndex = entry.getPreviousAttachState().getStableIndex();
+        return stableIndex == -1 ? null : stableIndex;
+    }
+
     private boolean applyFilters(NotificationEntry entry, long now, List<NotifFilter> filters) {
         final NotifFilter filter = findRejectingFilter(entry, now, filters);
         entry.getAttachState().setExcludingFilter(filter);
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/listbuilder/SemiStableSort.kt b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/listbuilder/SemiStableSort.kt
new file mode 100644
index 000000000000..9ec8e07e73b3
--- /dev/null
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/listbuilder/SemiStableSort.kt
@@ -0,0 +1,200 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.systemui.statusbar.notification.collection.listbuilder
+
+import androidx.annotation.VisibleForTesting
+import kotlin.math.sign
+
+class SemiStableSort {
+    val preallocatedWorkspace by lazy { ArrayList<Any>() }
+    val preallocatedAdditions by lazy { ArrayList<Any>() }
+    val preallocatedMapToIndex by lazy { HashMap<Any, Int>() }
+    val preallocatedMapToIndexComparator: Comparator<Any> by lazy {
+        Comparator.comparingInt { item -> preallocatedMapToIndex[item] ?: -1 }
+    }
+
+    /**
+     * Sort the given [items] such that items which have a [stableOrder] will all be in that order,
+     * items without a [stableOrder] will be sorted according to the comparator, and the two sets of
+     * items will be combined to have the fewest elements out of order according to the [comparator]
+     * . The result will be placed into the original [items] list.
+     */
+    fun <T : Any> sort(
+        items: MutableList<T>,
+        stableOrder: StableOrder<in T>,
+        comparator: Comparator<in T>,
+    ): Boolean =
+        withWorkspace<T, Boolean> { workspace ->
+            val ordered =
+                sortTo(
+                    items,
+                    stableOrder,
+                    comparator,
+                    workspace,
+                )
+            items.clear()
+            items.addAll(workspace)
+            return ordered
+        }
+
+    /**
+     * Sort the given [items] such that items which have a [stableOrder] will all be in that order,
+     * items without a [stableOrder] will be sorted according to the comparator, and the two sets of
+     * items will be combined to have the fewest elements out of order according to the [comparator]
+     * . The result will be put into [output].
+     */
+    fun <T : Any> sortTo(
+        items: Iterable<T>,
+        stableOrder: StableOrder<in T>,
+        comparator: Comparator<in T>,
+        output: MutableList<T>,
+    ): Boolean {
+        if (DEBUG) println("\n> START from ${items.map { it to stableOrder.getRank(it) }}")
+        // If array already has elements, use subList to ensure we only append
+        val result = output.takeIf { it.isEmpty() } ?: output.subList(output.size, output.size)
+        items.filterTo(result) { stableOrder.getRank(it) != null }
+        result.sortBy { stableOrder.getRank(it)!! }
+        val isOrdered = result.isSorted(comparator)
+        withAdditions<T> { additions ->
+            items.filterTo(additions) { stableOrder.getRank(it) == null }
+            additions.sortWith(comparator)
+            insertPreSortedElementsWithFewestMisOrderings(result, additions, comparator)
+        }
+        return isOrdered
+    }
+
+    /**
+     * Rearrange the [sortedItems] to enforce that items are in the [stableOrder], and store the
+     * result in [output]. Items with a [stableOrder] will be in that order, items without a
+     * [stableOrder] will remain in same relative order as the input, and the two sets of items will
+     * be combined to have the fewest elements moved from their locations in the original.
+     */
+    fun <T : Any> stabilizeTo(
+        sortedItems: Iterable<T>,
+        stableOrder: StableOrder<in T>,
+        output: MutableList<T>,
+    ): Boolean {
+        // Append to the output array if present
+        val result = output.takeIf { it.isEmpty() } ?: output.subList(output.size, output.size)
+        sortedItems.filterTo(result) { stableOrder.getRank(it) != null }
+        val stableRankComparator = compareBy<T> { stableOrder.getRank(it)!! }
+        val isOrdered = result.isSorted(stableRankComparator)
+        if (!isOrdered) {
+            result.sortWith(stableRankComparator)
+        }
+        if (result.isEmpty()) {
+            sortedItems.filterTo(result) { stableOrder.getRank(it) == null }
+            return isOrdered
+        }
+        withAdditions<T> { additions ->
+            sortedItems.filterTo(additions) { stableOrder.getRank(it) == null }
+            if (additions.isNotEmpty()) {
+                withIndexOfComparator(sortedItems) { comparator ->
+                    insertPreSortedElementsWithFewestMisOrderings(result, additions, comparator)
+                }
+            }
+        }
+        return isOrdered
+    }
+
+    private inline fun <T : Any, R> withWorkspace(block: (ArrayList<T>) -> R): R {
+        preallocatedWorkspace.clear()
+        val result = block(preallocatedWorkspace as ArrayList<T>)
+        preallocatedWorkspace.clear()
+        return result
+    }
+
+    private inline fun <T : Any> withAdditions(block: (ArrayList<T>) -> Unit) {
+        preallocatedAdditions.clear()
+        block(preallocatedAdditions as ArrayList<T>)
+        preallocatedAdditions.clear()
+    }
+
+    private inline fun <T : Any> withIndexOfComparator(
+        sortedItems: Iterable<T>,
+        block: (Comparator<in T>) -> Unit
+    ) {
+        preallocatedMapToIndex.clear()
+        sortedItems.forEachIndexed { i, item -> preallocatedMapToIndex[item] = i }
+        block(preallocatedMapToIndexComparator as Comparator<in T>)
+        preallocatedMapToIndex.clear()
+    }
+
+    companion object {
+
+        /**
+         * This is the core of the algorithm.
+         *
+         * Insert [preSortedAdditions] (the elements to be inserted) into [existing] without
+         * changing the relative order of any elements already in [existing], even though those
+         * elements may be mis-ordered relative to the [comparator], such that the total number of
+         * elements which are ordered incorrectly according to the [comparator] is fewest.
+         */
+        private fun <T> insertPreSortedElementsWithFewestMisOrderings(
+            existing: MutableList<T>,
+            preSortedAdditions: Iterable<T>,
+            comparator: Comparator<in T>,
+        ) {
+            if (DEBUG) println("  To $existing insert $preSortedAdditions with fewest misordering")
+            var iStart = 0
+            preSortedAdditions.forEach { toAdd ->
+                if (DEBUG) println("    need to add $toAdd to $existing, starting at $iStart")
+                var cmpSum = 0
+                var cmpSumMax = 0
+                var iCmpSumMax = iStart
+                if (DEBUG) print("      ")
+                for (i in iCmpSumMax until existing.size) {
+                    val cmp = comparator.compare(toAdd, existing[i]).sign
+                    cmpSum += cmp
+                    if (cmpSum > cmpSumMax) {
+                        cmpSumMax = cmpSum
+                        iCmpSumMax = i + 1
+                    }
+                    if (DEBUG) print("sum[$i]=$cmpSum, ")
+                }
+                if (DEBUG) println("inserting $toAdd at $iCmpSumMax")
+                existing.add(iCmpSumMax, toAdd)
+                iStart = iCmpSumMax + 1
+            }
+        }
+
+        /** Determines if a list is correctly sorted according to the given comparator */
+        @VisibleForTesting
+        fun <T> List<T>.isSorted(comparator: Comparator<T>): Boolean {
+            if (this.size <= 1) {
+                return true
+            }
+            val iterator = this.iterator()
+            var previous = iterator.next()
+            var current: T?
+            while (iterator.hasNext()) {
+                current = iterator.next()
+                if (comparator.compare(previous, current) > 0) {
+                    return false
+                }
+                previous = current
+            }
+            return true
+        }
+    }
+
+    fun interface StableOrder<T> {
+        fun getRank(item: T): Int?
+    }
+}
+
+val DEBUG = false
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/listbuilder/ShadeListBuilderHelper.kt b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/listbuilder/ShadeListBuilderHelper.kt
new file mode 100644
index 000000000000..d8f75f61c05a
--- /dev/null
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/listbuilder/ShadeListBuilderHelper.kt
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.systemui.statusbar.notification.collection.listbuilder
+
+import com.android.systemui.statusbar.notification.collection.ListEntry
+
+object ShadeListBuilderHelper {
+    fun getSectionSubLists(entries: List<ListEntry>): Iterable<List<ListEntry>> =
+        getContiguousSubLists(entries, minLength = 1) { it.sectionIndex }
+
+    inline fun <T : Any, K : Any> getContiguousSubLists(
+        itemList: List<T>,
+        minLength: Int = 1,
+        key: (T) -> K,
+    ): Iterable<List<T>> {
+        val subLists = mutableListOf<List<T>>()
+        val numEntries = itemList.size
+        var currentSectionStartIndex = 0
+        var currentSectionKey: K? = null
+        for (i in 0 until numEntries) {
+            val sectionKey = key(itemList[i])
+            if (currentSectionKey == null) {
+                currentSectionKey = sectionKey
+            } else if (currentSectionKey != sectionKey) {
+                val length = i - currentSectionStartIndex
+                if (length >= minLength) {
+                    subLists.add(itemList.subList(currentSectionStartIndex, i))
+                }
+                currentSectionStartIndex = i
+                currentSectionKey = sectionKey
+            }
+        }
+        val length = numEntries - currentSectionStartIndex
+        if (length >= minLength) {
+            subLists.add(itemList.subList(currentSectionStartIndex, numEntries))
+        }
+        return subLists
+    }
+}
diff --git a/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilderTest.java b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilderTest.java
index 896ce2b3994b..09f8a10f88c7 100644
--- a/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilderTest.java
+++ b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/ShadeListBuilderTest.java
@@ -34,6 +34,7 @@ import static org.mockito.Mockito.atLeast;
 import static org.mockito.Mockito.atLeastOnce;
 import static org.mockito.Mockito.clearInvocations;
 import static org.mockito.Mockito.inOrder;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
@@ -136,6 +137,7 @@ public class ShadeListBuilderTest extends SysuiTestCase {
     public void setUp() {
         MockitoAnnotations.initMocks(this);
         allowTestableLooperAsMainThread();
+        when(mNotifPipelineFlags.isStabilityIndexFixEnabled()).thenReturn(true);
 
         mListBuilder = new ShadeListBuilder(
                 mDumpManager,
@@ -1996,22 +1998,89 @@ public class ShadeListBuilderTest extends SysuiTestCase {
     }
 
     @Test
+    public void testActiveOrdering_withLegacyStability() {
+        when(mNotifPipelineFlags.isSemiStableSortEnabled()).thenReturn(false);
+        assertOrder("ABCDEFG", "ABCDEFG", "ABCDEFG", true); // no change
+        assertOrder("ABCDEFG", "ACDEFXBG", "ACDEFXBG", true); // X
+        assertOrder("ABCDEFG", "ACDEFBG", "ACDEFBG", true); // no change
+        assertOrder("ABCDEFG", "ACDEFBXZG", "ACDEFBXZG", true); // Z and X
+        assertOrder("ABCDEFG", "AXCDEZFBG", "AXCDEZFBG", true); // Z and X + gap
+    }
+
+    @Test
+    public void testStableOrdering_withLegacyStability() {
+        when(mNotifPipelineFlags.isSemiStableSortEnabled()).thenReturn(false);
+        mStabilityManager.setAllowEntryReordering(false);
+        assertOrder("ABCDEFG", "ABCDEFG", "ABCDEFG", true); // no change
+        assertOrder("ABCDEFG", "ACDEFXBG", "XABCDEFG", false); // X
+        assertOrder("ABCDEFG", "ACDEFBG", "ABCDEFG", false); // no change
+        assertOrder("ABCDEFG", "ACDEFBXZG", "XZABCDEFG", false); // Z and X
+        assertOrder("ABCDEFG", "AXCDEZFBG", "XZABCDEFG", false); // Z and X + gap
+    }
+
+    @Test
     public void testStableOrdering() {
+        when(mNotifPipelineFlags.isSemiStableSortEnabled()).thenReturn(true);
         mStabilityManager.setAllowEntryReordering(false);
-        assertOrder("ABCDEFG", "ACDEFXBG", "XABCDEFG"); // X
-        assertOrder("ABCDEFG", "ACDEFBG", "ABCDEFG"); // no change
-        assertOrder("ABCDEFG", "ACDEFBXZG", "XZABCDEFG"); // Z and X
-        assertOrder("ABCDEFG", "AXCDEZFBG", "XZABCDEFG"); // Z and X + gap
-        verify(mStabilityManager, times(4)).onEntryReorderSuppressed();
+        // No input or output
+        assertOrder("", "", "", true);
+        // Remove everything
+        assertOrder("ABCDEFG", "", "", true);
+        // Literally no changes
+        assertOrder("ABCDEFG", "ABCDEFG", "ABCDEFG", true);
+
+        // No stable order
+        assertOrder("", "ABCDEFG", "ABCDEFG", true);
+
+        // F moved after A, and...
+        assertOrder("ABCDEFG", "AFBCDEG", "ABCDEFG", false);   // No other changes
+        assertOrder("ABCDEFG", "AXFBCDEG", "AXBCDEFG", false); // Insert X before F
+        assertOrder("ABCDEFG", "AFXBCDEG", "AXBCDEFG", false); // Insert X after F
+        assertOrder("ABCDEFG", "AFBCDEXG", "ABCDEFXG", false); // Insert X where F was
+
+        // B moved after F, and...
+        assertOrder("ABCDEFG", "ACDEFBG", "ABCDEFG", false);   // No other changes
+        assertOrder("ABCDEFG", "ACDEFXBG", "ABCDEFXG", false); // Insert X before B
+        assertOrder("ABCDEFG", "ACDEFBXG", "ABCDEFXG", false); // Insert X after B
+        assertOrder("ABCDEFG", "AXCDEFBG", "AXBCDEFG", false); // Insert X where B was
+
+        // Swap F and B, and...
+        assertOrder("ABCDEFG", "AFCDEBG", "ABCDEFG", false);   // No other changes
+        assertOrder("ABCDEFG", "AXFCDEBG", "AXBCDEFG", false); // Insert X before F
+        assertOrder("ABCDEFG", "AFXCDEBG", "AXBCDEFG", false); // Insert X after F
+        assertOrder("ABCDEFG", "AFCXDEBG", "AXBCDEFG", false); // Insert X between CD (or: ABCXDEFG)
+        assertOrder("ABCDEFG", "AFCDXEBG", "ABCDXEFG", false); // Insert X between DE (or: ABCDEFXG)
+        assertOrder("ABCDEFG", "AFCDEXBG", "ABCDEFXG", false); // Insert X before B
+        assertOrder("ABCDEFG", "AFCDEBXG", "ABCDEFXG", false); // Insert X after B
+
+        // Remove a bunch of entries at once
+        assertOrder("ABCDEFGHIJKL", "ACEGHI", "ACEGHI", true);
+
+        // Remove a bunch of entries and scramble
+        assertOrder("ABCDEFGHIJKL", "GCEHAI", "ACEGHI", false);
+
+        // Add a bunch of entries at once
+        assertOrder("ABCDEFG", "AVBWCXDYZEFG", "AVBWCXDYZEFG", true);
+
+        // Add a bunch of entries and reverse originals
+        // NOTE: Some of these don't have obviously correct answers
+        assertOrder("ABCDEFG", "GFEBCDAVWXYZ", "ABCDEFGVWXYZ", false); // appended
+        assertOrder("ABCDEFG", "VWXYZGFEBCDA", "VWXYZABCDEFG", false); // prepended
+        assertOrder("ABCDEFG", "GFEBVWXYZCDA", "ABCDEFGVWXYZ", false); // closer to back: append
+        assertOrder("ABCDEFG", "GFEVWXYZBCDA", "VWXYZABCDEFG", false); // closer to front: prepend
+        assertOrder("ABCDEFG", "GFEVWBXYZCDA", "VWABCDEFGXYZ", false); // split new entries
+
+        // Swap 2 pairs ("*BC*NO*"->"*NO*CB*"), remove EG, add UVWXYZ throughout
+        assertOrder("ABCDEFGHIJKLMNOP", "AUNOVDFHWXIJKLMYCBZP", "AUVBCDFHWXIJKLMNOYZP", false);
     }
 
     @Test
     public void testActiveOrdering() {
-        assertOrder("ABCDEFG", "ACDEFXBG", "ACDEFXBG"); // X
-        assertOrder("ABCDEFG", "ACDEFBG", "ACDEFBG"); // no change
-        assertOrder("ABCDEFG", "ACDEFBXZG", "ACDEFBXZG"); // Z and X
-        assertOrder("ABCDEFG", "AXCDEZFBG", "AXCDEZFBG"); // Z and X + gap
-        verify(mStabilityManager, never()).onEntryReorderSuppressed();
+        when(mNotifPipelineFlags.isSemiStableSortEnabled()).thenReturn(true);
+        assertOrder("ABCDEFG", "ACDEFXBG", "ACDEFXBG", true); // X
+        assertOrder("ABCDEFG", "ACDEFBG", "ACDEFBG", true); // no change
+        assertOrder("ABCDEFG", "ACDEFBXZG", "ACDEFBXZG", true); // Z and X
+        assertOrder("ABCDEFG", "AXCDEZFBG", "AXCDEZFBG", true); // Z and X + gap
     }
 
     @Test
@@ -2063,6 +2132,52 @@ public class ShadeListBuilderTest extends SysuiTestCase {
     }
 
     @Test
+    public void stableOrderingDisregardedWithSectionChange() {
+        when(mNotifPipelineFlags.isSemiStableSortEnabled()).thenReturn(true);
+        // GIVEN the first sectioner's packages can be changed from run-to-run
+        List<String> mutableSectionerPackages = new ArrayList<>();
+        mutableSectionerPackages.add(PACKAGE_1);
+        mListBuilder.setSectioners(asList(
+                new PackageSectioner(mutableSectionerPackages, null),
+                new PackageSectioner(List.of(PACKAGE_1, PACKAGE_2, PACKAGE_3), null)));
+        mStabilityManager.setAllowEntryReordering(false);
+
+        // WHEN the list is originally built with reordering disabled (and section changes allowed)
+        addNotif(0, PACKAGE_1).setRank(4);
+        addNotif(1, PACKAGE_1).setRank(5);
+        addNotif(2, PACKAGE_2).setRank(1);
+        addNotif(3, PACKAGE_2).setRank(2);
+        addNotif(4, PACKAGE_3).setRank(3);
+        dispatchBuild();
+
+        // VERIFY the order and that entry reordering has not been suppressed
+        verifyBuiltList(
+                notif(0),
+                notif(1),
+                notif(2),
+                notif(3),
+                notif(4)
+        );
+        verify(mStabilityManager, never()).onEntryReorderSuppressed();
+
+        // WHEN the first section now claims PACKAGE_3 notifications
+        mutableSectionerPackages.add(PACKAGE_3);
+        dispatchBuild();
+
+        // VERIFY the re-sectioned notification is inserted at #1 of the first section, which
+        // is the correct position based on its rank, rather than #3 in the new section simply
+        // because it was #3 in its previous section.
+        verifyBuiltList(
+                notif(4),
+                notif(0),
+                notif(1),
+                notif(2),
+                notif(3)
+        );
+        verify(mStabilityManager, never()).onEntryReorderSuppressed();
+    }
+
+    @Test
     public void testStableChildOrdering() {
         // WHEN the list is originally built with reordering disabled
         mStabilityManager.setAllowEntryReordering(false);
@@ -2335,26 +2450,35 @@ public class ShadeListBuilderTest extends SysuiTestCase {
         return addGroupChildWithTag(index, packageId, groupId, null);
     }
 
-    private void assertOrder(String visible, String active, String expected) {
+    private void assertOrder(String visible, String active, String expected,
+            boolean isOrderedCorrectly) {
         StringBuilder differenceSb = new StringBuilder();
+        NotifSection section = new NotifSection(mock(NotifSectioner.class), 0);
         for (char c : active.toCharArray()) {
             if (visible.indexOf(c) < 0) differenceSb.append(c);
         }
         String difference = differenceSb.toString();
 
+        int globalIndex = 0;
         for (int i = 0; i < visible.length(); i++) {
-            addNotif(i, String.valueOf(visible.charAt(i)))
-                    .setRank(active.indexOf(visible.charAt(i)))
+            final char c = visible.charAt(i);
+            // Skip notifications which aren't active anymore
+            if (!active.contains(String.valueOf(c))) continue;
+            addNotif(globalIndex++, String.valueOf(c))
+                    .setRank(active.indexOf(c))
+                    .setSection(section)
                     .setStableIndex(i);
-
         }
 
-        for (int i = 0; i < difference.length(); i++) {
-            addNotif(i + visible.length(), String.valueOf(difference.charAt(i)))
-                    .setRank(active.indexOf(difference.charAt(i)))
+        for (char c : difference.toCharArray()) {
+            addNotif(globalIndex++, String.valueOf(c))
+                    .setRank(active.indexOf(c))
+                    .setSection(section)
                     .setStableIndex(-1);
         }
 
+        clearInvocations(mStabilityManager);
+
         dispatchBuild();
         StringBuilder resultSb = new StringBuilder();
         for (int i = 0; i < expected.length(); i++) {
@@ -2364,6 +2488,9 @@ public class ShadeListBuilderTest extends SysuiTestCase {
         assertEquals("visible [" + visible + "] active [" + active + "]",
                 expected, resultSb.toString());
         mEntrySet.clear();
+
+        verify(mStabilityManager, isOrderedCorrectly ? never() : times(1))
+                .onEntryReorderSuppressed();
     }
 
     private int nextId(String packageName) {
diff --git a/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/listbuilder/SemiStableSortTest.kt b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/listbuilder/SemiStableSortTest.kt
new file mode 100644
index 000000000000..1cdd023dd01c
--- /dev/null
+++ b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/listbuilder/SemiStableSortTest.kt
@@ -0,0 +1,210 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.systemui.statusbar.notification.collection.listbuilder
+
+import android.testing.AndroidTestingRunner
+import android.testing.TestableLooper.RunWithLooper
+import android.util.Log
+import androidx.test.filters.SmallTest
+import com.android.systemui.SysuiTestCase
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@SmallTest
+@RunWith(AndroidTestingRunner::class)
+@RunWithLooper
+class SemiStableSortTest : SysuiTestCase() {
+
+    var shuffleInput: Boolean = false
+    var testStabilizeTo: Boolean = false
+    var sorter: SemiStableSort? = null
+
+    @Before
+    fun setUp() {
+        shuffleInput = false
+        sorter = null
+    }
+
+    private fun stringStabilizeTo(
+        stableOrder: String,
+        activeOrder: String,
+    ): Pair<String, Boolean> {
+        val actives = activeOrder.toMutableList()
+        val result = mutableListOf<Char>()
+        return (sorter ?: SemiStableSort())
+            .stabilizeTo(
+                actives,
+                { ch -> stableOrder.indexOf(ch).takeIf { it >= 0 } },
+                result,
+            )
+            .let { ordered -> result.joinToString("") to ordered }
+    }
+
+    private fun stringSort(
+        stableOrder: String,
+        activeOrder: String,
+    ): Pair<String, Boolean> {
+        val actives = activeOrder.toMutableList()
+        if (shuffleInput) {
+            actives.shuffle()
+        }
+        return (sorter ?: SemiStableSort())
+            .sort(
+                actives,
+                { ch -> stableOrder.indexOf(ch).takeIf { it >= 0 } },
+                compareBy { activeOrder.indexOf(it) },
+            )
+            .let { ordered -> actives.joinToString("") to ordered }
+    }
+
+    private fun testCase(
+        stableOrder: String,
+        activeOrder: String,
+        expected: String,
+        expectOrdered: Boolean,
+    ) {
+        val (mergeResult, ordered) =
+            if (testStabilizeTo) stringStabilizeTo(stableOrder, activeOrder)
+            else stringSort(stableOrder, activeOrder)
+        val resultPass = expected == mergeResult
+        val orderedPass = ordered == expectOrdered
+        val pass = resultPass && orderedPass
+        val resultSuffix =
+            if (resultPass) "result=$expected" else "expected=$expected got=$mergeResult"
+        val orderedSuffix =
+            if (orderedPass) "ordered=$ordered" else "expected ordered to be $expectOrdered"
+        val readableResult = "stable=$stableOrder active=$activeOrder $resultSuffix $orderedSuffix"
+        Log.d("SemiStableSortTest", "${if (pass) "PASS" else "FAIL"}: $readableResult")
+        if (!pass) {
+            throw AssertionError("Test case failed: $readableResult")
+        }
+    }
+
+    private fun runAllTestCases() {
+        // No input or output
+        testCase("", "", "", true)
+        // Remove everything
+        testCase("ABCDEFG", "", "", true)
+        // Literally no changes
+        testCase("ABCDEFG", "ABCDEFG", "ABCDEFG", true)
+
+        // No stable order
+        testCase("", "ABCDEFG", "ABCDEFG", true)
+
+        // F moved after A, and...
+        testCase("ABCDEFG", "AFBCDEG", "ABCDEFG", false) // No other changes
+        testCase("ABCDEFG", "AXFBCDEG", "AXBCDEFG", false) // Insert X before F
+        testCase("ABCDEFG", "AFXBCDEG", "AXBCDEFG", false) // Insert X after F
+        testCase("ABCDEFG", "AFBCDEXG", "ABCDEFXG", false) // Insert X where F was
+
+        // B moved after F, and...
+        testCase("ABCDEFG", "ACDEFBG", "ABCDEFG", false) // No other changes
+        testCase("ABCDEFG", "ACDEFXBG", "ABCDEFXG", false) // Insert X before B
+        testCase("ABCDEFG", "ACDEFBXG", "ABCDEFXG", false) // Insert X after B
+        testCase("ABCDEFG", "AXCDEFBG", "AXBCDEFG", false) // Insert X where B was
+
+        // Swap F and B, and...
+        testCase("ABCDEFG", "AFCDEBG", "ABCDEFG", false) // No other changes
+        testCase("ABCDEFG", "AXFCDEBG", "AXBCDEFG", false) // Insert X before F
+        testCase("ABCDEFG", "AFXCDEBG", "AXBCDEFG", false) // Insert X after F
+        testCase("ABCDEFG", "AFCXDEBG", "AXBCDEFG", false) // Insert X between CD (Alt: ABCXDEFG)
+        testCase("ABCDEFG", "AFCDXEBG", "ABCDXEFG", false) // Insert X between DE (Alt: ABCDEFXG)
+        testCase("ABCDEFG", "AFCDEXBG", "ABCDEFXG", false) // Insert X before B
+        testCase("ABCDEFG", "AFCDEBXG", "ABCDEFXG", false) // Insert X after B
+
+        // Remove a bunch of entries at once
+        testCase("ABCDEFGHIJKL", "ACEGHI", "ACEGHI", true)
+
+        // Remove a bunch of entries and scramble
+        testCase("ABCDEFGHIJKL", "GCEHAI", "ACEGHI", false)
+
+        // Add a bunch of entries at once
+        testCase("ABCDEFG", "AVBWCXDYZEFG", "AVBWCXDYZEFG", true)
+
+        // Add a bunch of entries and reverse originals
+        // NOTE: Some of these don't have obviously correct answers
+        testCase("ABCDEFG", "GFEBCDAVWXYZ", "ABCDEFGVWXYZ", false) // appended
+        testCase("ABCDEFG", "VWXYZGFEBCDA", "VWXYZABCDEFG", false) // prepended
+        testCase("ABCDEFG", "GFEBVWXYZCDA", "ABCDEFGVWXYZ", false) // closer to back: append
+        testCase("ABCDEFG", "GFEVWXYZBCDA", "VWXYZABCDEFG", false) // closer to front: prepend
+        testCase("ABCDEFG", "GFEVWBXYZCDA", "VWABCDEFGXYZ", false) // split new entries
+
+        // Swap 2 pairs ("*BC*NO*"->"*NO*CB*"), remove EG, add UVWXYZ throughout
+        testCase("ABCDEFGHIJKLMNOP", "AUNOVDFHWXIJKLMYCBZP", "AUVBCDFHWXIJKLMNOYZP", false)
+    }
+
+    @Test
+    fun testSort() {
+        testStabilizeTo = false
+        shuffleInput = false
+        sorter = null
+        runAllTestCases()
+    }
+
+    @Test
+    fun testSortWithSingleInstance() {
+        testStabilizeTo = false
+        shuffleInput = false
+        sorter = SemiStableSort()
+        runAllTestCases()
+    }
+
+    @Test
+    fun testSortWithShuffledInput() {
+        testStabilizeTo = false
+        shuffleInput = true
+        sorter = null
+        runAllTestCases()
+    }
+
+    @Test
+    fun testStabilizeTo() {
+        testStabilizeTo = true
+        sorter = null
+        runAllTestCases()
+    }
+
+    @Test
+    fun testStabilizeToWithSingleInstance() {
+        testStabilizeTo = true
+        sorter = SemiStableSort()
+        runAllTestCases()
+    }
+
+    @Test
+    fun testIsSorted() {
+        val intCmp = Comparator<Int> { x, y -> Integer.compare(x, y) }
+        SemiStableSort.apply {
+            assertTrue(emptyList<Int>().isSorted(intCmp))
+            assertTrue(listOf(1).isSorted(intCmp))
+            assertTrue(listOf(1, 2).isSorted(intCmp))
+            assertTrue(listOf(1, 2, 3).isSorted(intCmp))
+            assertTrue(listOf(1, 2, 3, 4).isSorted(intCmp))
+            assertTrue(listOf(1, 2, 3, 4, 5).isSorted(intCmp))
+            assertTrue(listOf(1, 1, 1, 1, 1).isSorted(intCmp))
+            assertTrue(listOf(1, 1, 2, 2, 3, 3).isSorted(intCmp))
+            assertFalse(listOf(2, 1).isSorted(intCmp))
+            assertFalse(listOf(2, 1, 2).isSorted(intCmp))
+            assertFalse(listOf(1, 2, 1).isSorted(intCmp))
+            assertFalse(listOf(1, 2, 3, 2, 5).isSorted(intCmp))
+            assertFalse(listOf(5, 2, 3, 4, 5).isSorted(intCmp))
+            assertFalse(listOf(1, 2, 3, 4, 1).isSorted(intCmp))
+        }
+    }
+}
diff --git a/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/listbuilder/ShadeListBuilderHelperTest.kt b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/listbuilder/ShadeListBuilderHelperTest.kt
new file mode 100644
index 000000000000..20369546d68a
--- /dev/null
+++ b/packages/SystemUI/tests/src/com/android/systemui/statusbar/notification/collection/listbuilder/ShadeListBuilderHelperTest.kt
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.systemui.statusbar.notification.collection.listbuilder
+
+import android.testing.AndroidTestingRunner
+import android.testing.TestableLooper.RunWithLooper
+import androidx.test.filters.SmallTest
+import com.android.systemui.SysuiTestCase
+import com.android.systemui.statusbar.notification.collection.listbuilder.ShadeListBuilderHelper.getContiguousSubLists
+import com.google.common.truth.Truth.assertThat
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@SmallTest
+@RunWith(AndroidTestingRunner::class)
+@RunWithLooper
+class ShadeListBuilderHelperTest : SysuiTestCase() {
+
+    @Test
+    fun testGetContiguousSubLists() {
+        assertThat(getContiguousSubLists("AAAAAA".toList()) { it })
+            .containsExactly(
+                listOf('A', 'A', 'A', 'A', 'A', 'A'),
+            )
+            .inOrder()
+        assertThat(getContiguousSubLists("AAABBB".toList()) { it })
+            .containsExactly(
+                listOf('A', 'A', 'A'),
+                listOf('B', 'B', 'B'),
+            )
+            .inOrder()
+        assertThat(getContiguousSubLists("AAABAA".toList()) { it })
+            .containsExactly(
+                listOf('A', 'A', 'A'),
+                listOf('B'),
+                listOf('A', 'A'),
+            )
+            .inOrder()
+        assertThat(getContiguousSubLists("AAABAA".toList(), minLength = 2) { it })
+            .containsExactly(
+                listOf('A', 'A', 'A'),
+                listOf('A', 'A'),
+            )
+            .inOrder()
+        assertThat(getContiguousSubLists("AAABBBBCCDEEE".toList()) { it })
+            .containsExactly(
+                listOf('A', 'A', 'A'),
+                listOf('B', 'B', 'B', 'B'),
+                listOf('C', 'C'),
+                listOf('D'),
+                listOf('E', 'E', 'E'),
+            )
+            .inOrder()
+        assertThat(getContiguousSubLists("AAABBBBCCDEEE".toList(), minLength = 2) { it })
+            .containsExactly(
+                listOf('A', 'A', 'A'),
+                listOf('B', 'B', 'B', 'B'),
+                listOf('C', 'C'),
+                listOf('E', 'E', 'E'),
+            )
+            .inOrder()
+    }
+}