Perf: Reimplement Lookup.Scope tables without ItemDictionary

src/Build.UnitTests/BackEnd/Lookup_Tests.cs

@@ -264,14 +264,14 @@ public void Removes()
             lookup.AddNewItem(item2);
 
             // Remove one item
-            lookup.RemoveItem(item1);
+            lookup.RemoveItems("i1", [item1]);
 
             // We see one item
             Assert.Single(lookup.GetItems("i1"));
             Assert.Equal("a2", lookup.GetItems("i1").First().EvaluatedInclude);
 
             // Remove the other item
-            lookup.RemoveItem(item2);
+            lookup.RemoveItems("i1", [item2]);
 
             // We see no items
             Assert.Empty(lookup.GetItems("i1"));
@@ -326,7 +326,7 @@ public void RemoveItemPopulatedInLowerScope()
             Assert.Single(lookup.GetItems("i1"));
 
             // Remove that item
-            lookup.RemoveItem(item1);
+            lookup.RemoveItems("i1", [item1]);
 
             // We see no items
             Assert.Empty(lookup.GetItems("i1"));
@@ -372,7 +372,7 @@ public void RemoveItemAddedInLowerScope()
             Assert.Single(lookup.GetItems("i1"));
 
             // Remove that item
-            lookup.RemoveItem(item1);
+            lookup.RemoveItems("i1", [item1]);
 
             // We see no items
             Assert.Empty(lookup.GetItems("i1"));
@@ -824,7 +824,7 @@ public void ModifyItemModifiedInPreviousScope()
             // Add an item with m=m1 and n=n1
             ProjectItemInstance item1 = new ProjectItemInstance(project, "i1", "a2", project.FullPath);
             item1.SetMetadata("m", "m1");
-            lookup.PopulateWithItem(item1);
+            table1.Add(item1);
 
             lookup.EnterScope("x");
 
@@ -865,7 +865,7 @@ public void ModifyItemTwiceInSameScope1()
             // Add an item with m=m1 and n=n1
             ProjectItemInstance item1 = new ProjectItemInstance(project, "i1", "a2", project.FullPath);
             item1.SetMetadata("m", "m1");
-            lookup.PopulateWithItem(item1);
+            table1.Add(item1);
 
             lookup.EnterScope("x");
 
@@ -902,7 +902,7 @@ public void ModifyItemTwiceInSameScope2()
             item1.SetMetadata("m", "m1");
             item1.SetMetadata("n", "n1");
             item1.SetMetadata("o", "o1");
-            lookup.PopulateWithItem(item1);
+            table1.Add(item1);
 
             Lookup.Scope enteredScope = lookup.EnterScope("x");
 
@@ -1028,7 +1028,7 @@ public void ModifyItemPreviouslyModifiedAndGottenThroughGetItem()
             // Add an item with m=m1 and n=n1
             ProjectItemInstance item1 = new ProjectItemInstance(project, "i1", "a2", project.FullPath);
             item1.SetMetadata("m", "m1");
-            lookup.PopulateWithItem(item1);
+            table1.Add(item1);
 
             Lookup.Scope enteredScope = lookup.EnterScope("x");
 
@@ -1132,7 +1132,7 @@ public void RemoveItemPreviouslyModifiedAndGottenThroughGetItem()
             // Add an item with m=m1 and n=n1
             ProjectItemInstance item1 = new ProjectItemInstance(project, "i1", "a2", project.FullPath);
             item1.SetMetadata("m", "m1");
-            lookup.PopulateWithItem(item1);
+            table1.Add(item1);
 
             lookup.EnterScope("x");
 
@@ -1149,7 +1149,7 @@ public void RemoveItemPreviouslyModifiedAndGottenThroughGetItem()
             ProjectItemInstance item1b = group2.First();
 
             // Remove the item
-            lookup.RemoveItem(item1b);
+            lookup.RemoveItems(item1.ItemType, [item1b]);
 
             // There's now no items at all
             ICollection<ProjectItemInstance> group3 = lookup.GetItems(item1.ItemType);
@@ -1186,7 +1186,7 @@ public void RemoveItemFromProjectPreviouslyModifiedAndGottenThroughGetItem()
             ProjectItemInstance item1b = group2.First();
 
             // Remove the item
-            lookup.RemoveItem(item1b);
+            lookup.RemoveItems(item1.ItemType, [item1b]);
 
             // There's now no items at all
             ICollection<ProjectItemInstance> group3 = lookup.GetItems(item1.ItemType);

src/Build.UnitTests/BackEnd/TargetUpToDateChecker_Tests.cs

@@ -291,7 +291,8 @@ public void MultiInputItemsThatCorrelatesWithMultipleTransformOutputItems()
 
             // Even though they were all up to date, we still expect to see an empty marker
             // so that lookups can correctly *not* find items of that type
-            Assert.True(changedTargetInputs.HasEmptyMarker("MoreItems"));
+            Assert.True(changedTargetInputs.ItemTypes.Contains("MoreItems"));
+            Assert.Empty(changedTargetInputs["MoreItems"]);
         }
 
         [Fact]

src/Build.UnitTests/BackEnd/TaskExecutionHost_Tests.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
@@ -1282,7 +1283,7 @@ private void InitializeHost(bool throwOnExecute)
             itemsByName.Add(item2);
             _twoItems = new ITaskItem[] { new TaskItem(item), new TaskItem(item2) };
 
-            _bucket = new ItemBucket(new Dictionary<string, ICollection<ProjectItemInstance>>().Keys, new Dictionary<string, string>(), new Lookup(itemsByName, new PropertyDictionary<ProjectPropertyInstance>()), 0);
+            _bucket = new ItemBucket(FrozenSet<string>.Empty, new Dictionary<string, string>(), new Lookup(itemsByName, new PropertyDictionary<ProjectPropertyInstance>()), 0);
             _bucket.Initialize(null);
             _host.FindTask(null);
             _host.InitializeForBatch(talc, _bucket, null);

src/Build/BackEnd/Components/RequestBuilder/BatchingEngine.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using Microsoft.Build.BackEnd.Logging;
 using Microsoft.Build.Collections;
@@ -311,6 +312,7 @@ private static List<ItemBucket> BucketConsumedItems(
             ErrorUtilities.VerifyThrow(consumedMetadataReferences.Count > 0, "Need item metadata consumed by the batchable object.");
 
             var buckets = new List<ItemBucket>();
+            FrozenSet<string> itemNames = itemListsToBeBatched.Keys.ToFrozenSet(MSBuildNameIgnoreCaseComparer.Default);
 
             // Get and iterate through the list of item names that we're supposed to batch on.
             foreach (KeyValuePair<string, ICollection<ProjectItemInstance>> entry in itemListsToBeBatched)
@@ -346,7 +348,7 @@ private static List<ItemBucket> BucketConsumedItems(
                         }
                         else
                         {
-                            matchingBucket = new ItemBucket(itemListsToBeBatched.Keys, itemMetadataValues, lookup, buckets.Count);
+                            matchingBucket = new ItemBucket(itemNames, itemMetadataValues, lookup, buckets.Count);
                             if (loggingContext != null)
                             {
                                 matchingBucket.Initialize(loggingContext);

src/Build/BackEnd/Components/RequestBuilder/IntrinsicTasks/ItemGroupIntrinsicTask.cs

@@ -281,7 +281,7 @@ private void ExecuteRemove(ProjectItemGroupTaskItemInstance child, ItemBucket bu
                         child.Location);
                 }
 
-                bucket.Lookup.RemoveItems(itemsToRemove);
+                bucket.Lookup.RemoveItems(child.ItemType, itemsToRemove);
             }
         }
 

src/Build/BackEnd/Components/RequestBuilder/ItemBucket.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Collections.Frozen;
 using System.Collections.Generic;
 using System.Diagnostics;
 using Microsoft.Build.BackEnd.Logging;
@@ -74,7 +75,7 @@ private ItemBucket(Dictionary<string, string> metadata)
         /// <param name="lookup">The <see cref="Lookup"/> to use for the items in the bucket.</param>
         /// <param name="bucketSequenceNumber">A sequence number indication what order the buckets were created in.</param>
         internal ItemBucket(
-            Dictionary<string, ICollection<ProjectItemInstance>>.KeyCollection itemNames, // PERF: directly use the KeyCollection to avoid boxing the enumerator.
+            FrozenSet<string> itemNames,
             Dictionary<string, string> metadata,
             Lookup lookup,
             int bucketSequenceNumber)
@@ -87,15 +88,9 @@ internal ItemBucket(
             // Push down the items, so that item changes in this batch are not visible to parallel batches
             _lookupEntry = _lookup.EnterScope("ItemBucket()");
 
-            // Add empty item groups for each of the item names, so that (unless items are added to this bucket) there are
+            // Truncate lookups for each of the item names, so that (unless items are added to this bucket) there are
             // no item types visible in this bucket among the item types being batched on
-            if (itemNames != null)
-            {
-                foreach (string name in itemNames)
-                {
-                    _lookup.PopulateWithItems(name, new List<ProjectItemInstance>());
-                }
-            }
+            _lookup.TruncateLookupsForItemTypes(itemNames);
 
             _metadata = metadata;