From bf5f0cf3805493f64c7a9e516124f9c2f842d1bc Mon Sep 17 00:00:00 2001
From: Sam Harwell <Sam.Harwell@microsoft.com>
Date: Tue, 28 Feb 2023 12:53:32 -0600
Subject: [PATCH] Avoid delegate allocations in IExtensionManagerExtensions

Fixes 2GB allocations seen in https://devdiv.visualstudio.com/0bdbc590-a062-4c3f-b0f6-9383f67865ee/_workitems/edit/1746674.
---
 .../IExtensionManagerExtensions.cs                | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/Workspaces/Core/Portable/ExtensionManager/IExtensionManagerExtensions.cs b/src/Workspaces/Core/Portable/ExtensionManager/IExtensionManagerExtensions.cs
index 6f80379b1ee24..0f44c6707c040 100644
--- a/src/Workspaces/Core/Portable/ExtensionManager/IExtensionManagerExtensions.cs
+++ b/src/Workspaces/Core/Portable/ExtensionManager/IExtensionManagerExtensions.cs
@@ -6,6 +6,7 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using System.Threading.Tasks;
@@ -109,12 +110,13 @@ public static async Task<T> PerformFunctionAsync<T>(
             return defaultValue;
         }
 
+        [SuppressMessage("Style", "IDE0039:Use local function", Justification = "Avoid per-call delegate allocation")]
         public static Func<SyntaxNode, ImmutableArray<TExtension>> CreateNodeExtensionGetter<TExtension>(
             this IExtensionManager extensionManager, IEnumerable<TExtension> extensions, Func<TExtension, ImmutableArray<Type>> nodeTypeGetter)
         {
             var map = new ConcurrentDictionary<Type, ImmutableArray<TExtension>>();
 
-            ImmutableArray<TExtension> GetExtensions(Type t1)
+            Func<Type, ImmutableArray<TExtension>> getExtensions = (Type t1) =>
             {
                 var query = from e in extensions
                             let types = extensionManager.PerformFunction(e, () => nodeTypeGetter(e), ImmutableArray<Type>.Empty)
@@ -122,16 +124,17 @@ ImmutableArray<TExtension> GetExtensions(Type t1)
                             select e;
 
                 return query.ToImmutableArray();
-            }
+            };
 
-            return n => map.GetOrAdd(n.GetType(), GetExtensions);
+            return n => map.GetOrAdd(n.GetType(), getExtensions);
         }
 
+        [SuppressMessage("Style", "IDE0039:Use local function", Justification = "Avoid per-call delegate allocation")]
         public static Func<SyntaxToken, ImmutableArray<TExtension>> CreateTokenExtensionGetter<TExtension>(
             this IExtensionManager extensionManager, IEnumerable<TExtension> extensions, Func<TExtension, ImmutableArray<int>> tokenKindGetter)
         {
             var map = new ConcurrentDictionary<int, ImmutableArray<TExtension>>();
-            ImmutableArray<TExtension> GetExtensions(int k)
+            Func<int, ImmutableArray<TExtension>> getExtensions = (int k) =>
             {
                 var query = from e in extensions
                             let kinds = extensionManager.PerformFunction(e, () => tokenKindGetter(e), ImmutableArray<int>.Empty)
@@ -139,9 +142,9 @@ ImmutableArray<TExtension> GetExtensions(int k)
                             select e;
 
                 return query.ToImmutableArray();
-            }
+            };
 
-            return t => map.GetOrAdd(t.RawKind, GetExtensions);
+            return t => map.GetOrAdd(t.RawKind, getExtensions);
         }
     }
 }