Remove unnecessary list allocations (#6529)

Fixes #6062
dotnet · Jun 17, 2021 · c86ab72 · c86ab72
1 parent f4b792b
commit c86ab72
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Showing 3 changed files with 32 additions and 34 deletions.
diff --git a/src/Build/Evaluation/ExpressionShredder.cs b/src/Build/Evaluation/ExpressionShredder.cs
@@ -65,7 +65,7 @@ internal static SemiColonTokenizer SplitSemiColonSeparatedList(string expression
         /// where metadata key is like "itemname.metadataname" or "metadataname".
         /// PERF: Tables are null if there are no entries, because this is quite a common case.
         /// </summary>
-        internal static ItemsAndMetadataPair GetReferencedItemNamesAndMetadata(List<string> expressions)
+        internal static ItemsAndMetadataPair GetReferencedItemNamesAndMetadata(IEnumerable<string> expressions)
         {
             ItemsAndMetadataPair pair = new ItemsAndMetadataPair(null, null);
 

diff --git a/src/Build/Evaluation/LazyItemEvaluator.LazyItemOperation.cs b/src/Build/Evaluation/LazyItemEvaluator.LazyItemOperation.cs
@@ -230,7 +230,6 @@ protected void DecorateItemsWithMetadata(IEnumerable<ItemBatchingContext> itemBa
                         // End of legal area for metadata expressions.
                         _expander.Metadata = null;
                     }
-
                     // End of pseudo batching
                     ////////////////////////////////////////////////////
                     // Start of old code
@@ -283,17 +282,18 @@ protected void DecorateItemsWithMetadata(IEnumerable<ItemBatchingContext> itemBa
                 }
             }
 
-            protected bool NeedToExpandMetadataForEachItem(ImmutableList<ProjectMetadataElement> metadata, out ItemsAndMetadataPair itemsAndMetadataFound)
+            private static IEnumerable<string> GetMetadataValuesAndConditions(ImmutableList<ProjectMetadataElement> metadata)
             {
-                List<string> values = new List<string>(metadata.Count * 2);
-
                 foreach (var metadataElement in metadata)
                 {
-                    values.Add(metadataElement.Value);
-                    values.Add(metadataElement.Condition);
+                    yield return metadataElement.Value;
+                    yield return metadataElement.Condition;
                 }
+            }
 
-                itemsAndMetadataFound = ExpressionShredder.GetReferencedItemNamesAndMetadata(values);
+            protected bool NeedToExpandMetadataForEachItem(ImmutableList<ProjectMetadataElement> metadata, out ItemsAndMetadataPair itemsAndMetadataFound)
+            {
+                itemsAndMetadataFound = ExpressionShredder.GetReferencedItemNamesAndMetadata(GetMetadataValuesAndConditions(metadata));
 
                 bool needToExpandMetadataForEachItem = false;
 

diff --git a/src/Build/Evaluation/LazyItemEvaluator.cs b/src/Build/Evaluation/LazyItemEvaluator.cs
@@ -612,38 +612,36 @@ private void ProcessItemSpec(string rootDirectory, string itemSpec, IElementLoca
             }
         }
 
+        private static IEnumerable<string> GetExpandedMetadataValuesAndConditions(ICollection<ProjectMetadataElement> metadata, Expander<P, I> expander)
+        {
+            // Since we're just attempting to expand properties in order to find referenced items and not expanding metadata,
+            // unexpected errors may occur when evaluating property functions on unexpanded metadata. Just ignore them if that happens.
+            // See: https://github.com/Microsoft/msbuild/issues/3460
+            const ExpanderOptions expanderOptions = ExpanderOptions.ExpandProperties | ExpanderOptions.LeavePropertiesUnexpandedOnError;
+
+            // Expand properties here, because a property may have a value which is an item reference (ie "@(Bar)"), and
+            // if so we need to add the right item reference.
+            foreach (var metadatumElement in metadata)
+            {
+                yield return expander.ExpandIntoStringLeaveEscaped(
+                    metadatumElement.Value,
+                    expanderOptions,
+                    metadatumElement.Location);
+
+                yield return expander.ExpandIntoStringLeaveEscaped(
+                    metadatumElement.Condition,
+                    expanderOptions,
+                    metadatumElement.ConditionLocation);
+            }
+        }
+
         private void ProcessMetadataElements(ProjectItemElement itemElement, OperationBuilderWithMetadata operationBuilder)
         {
             if (itemElement.HasMetadata)
             {
                 operationBuilder.Metadata.AddRange(itemElement.Metadata);
 
-                var values = new List<string>(itemElement.Metadata.Count * 2);
-
-                // Expand properties here, because a property may have a value which is an item reference (ie "@(Bar)"), and
-                // if so we need to add the right item reference.
-                foreach (var metadatumElement in itemElement.Metadata)
-                {
-                    // Since we're just attempting to expand properties in order to find referenced items and not expanding metadata,
-                    // unexpected errors may occur when evaluating property functions on unexpanded metadata. Just ignore them if that happens.
-                    // See: https://github.com/Microsoft/msbuild/issues/3460
-                    const ExpanderOptions expanderOptions = ExpanderOptions.ExpandProperties | ExpanderOptions.LeavePropertiesUnexpandedOnError;
-
-                    var valueWithPropertiesExpanded = _expander.ExpandIntoStringLeaveEscaped(
-                        metadatumElement.Value,
-                        expanderOptions,
-                        metadatumElement.Location);
-
-                    var conditionWithPropertiesExpanded = _expander.ExpandIntoStringLeaveEscaped(
-                        metadatumElement.Condition,
-                        expanderOptions,
-                        metadatumElement.ConditionLocation);
-
-                    values.Add(valueWithPropertiesExpanded);
-                    values.Add(conditionWithPropertiesExpanded);
-                }
-
-                var itemsAndMetadataFound = ExpressionShredder.GetReferencedItemNamesAndMetadata(values);
+                var itemsAndMetadataFound = ExpressionShredder.GetReferencedItemNamesAndMetadata(GetExpandedMetadataValuesAndConditions(itemElement.Metadata, _expander));
                 if (itemsAndMetadataFound.Items != null)
                 {
                     foreach (var itemType in itemsAndMetadataFound.Items)