Reduce List resize allocations in PopulateItemGroups hot path (#7083)

nareshjo · web-flow · commit 5b05c1e4757e · 2026-01-28T08:11:53.000-08:00
diff --git a/src/NuGet.Core/NuGet.Packaging/ContentModel/ContentItemCollection.cs b/src/NuGet.Core/NuGet.Packaging/ContentModel/ContentItemCollection.cs
@@ -115,6 +115,13 @@ public void PopulateItemGroups(PatternSet definition, IList<ContentItemGroup> co
 
                 if (groupAssets != null)
                 {
+                    // Pre-size the list to avoid repeated array allocations during Add operations.
+                    // Callers typically pass a List but check just to be safe.
+                    if (contentItemGroupList is List<ContentItemGroup> list)
+                    {
+                        list.Capacity = Math.Max(list.Capacity, contentItemGroupList.Count + groupAssets.Count);
+                    }
+
                     foreach (var (item, assets) in groupAssets)
                     {
                         contentItemGroupList.Add(new ContentItemGroup(

Original file line number	Diff line number	Diff line change
`@@ -115,6 +115,13 @@ public void PopulateItemGroups(PatternSet definition, IList<ContentItemGroup> co`
`115`	`115`
`116`	`116`	`if (groupAssets != null)`
`117`	`117`	`{`
	`118`	`+ // Pre-size the list to avoid repeated array allocations during Add operations.`
	`119`	`+ // Callers typically pass a List but check just to be safe.`
	`120`	`+ if (contentItemGroupList is List<ContentItemGroup> list)`
	`121`	`+ {`
	`122`	`+ list.Capacity = Math.Max(list.Capacity, contentItemGroupList.Count + groupAssets.Count);`
	`123`	`+ }`
	`124`	`+`
`118`	`125`	`foreach (var (item, assets) in groupAssets)`
`119`	`126`	`{`
`120`	`127`	`contentItemGroupList.Add(new ContentItemGroup(`