Modify SyntaxNodeExtensions.GetMembers to instead execute a given lambda over the collection.

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Extensions/SyntaxNodeExtensions.cs

@@ -757,15 +757,29 @@ public static SyntaxTokenList GetModifiers(this SyntaxNode? member)
             _ => null,
         };
 
-    public static IEnumerable<MemberDeclarationSyntax> GetMembers(this SyntaxNode? node)
-        => node switch
+    public static void ForEachMember<TArg>(this SyntaxNode? node, Action<MemberDeclarationSyntax, TArg> callback, TArg arg)
+    {
+        // Separated out to allow for struct-based enumeration.
+        switch (node)
         {
-            CompilationUnitSyntax compilation => compilation.Members,
-            BaseNamespaceDeclarationSyntax @namespace => @namespace.Members,
-            TypeDeclarationSyntax type => type.Members,
-            EnumDeclarationSyntax @enum => @enum.Members,
-            _ => [],
-        };
+            case CompilationUnitSyntax compilation:
+                foreach (var member in compilation.Members)
+                    callback(member, arg);
+                break;
+            case BaseNamespaceDeclarationSyntax @namespace:
+                foreach (var member in @namespace.Members)
+                    callback(member, arg);
+                break;
+            case TypeDeclarationSyntax type:
+                foreach (var member in type.Members)
+                    callback(member, arg);
+                break;
+            case EnumDeclarationSyntax @enum:
+                foreach (var member in @enum.Members)
+                    callback(member, arg);
+                break;
+        }
+    }
 
     public static bool IsInExpressionTree(
         [NotNullWhen(true)] this SyntaxNode? node,

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Services/SyntaxFacts/CSharpSyntaxFacts.cs

@@ -913,24 +913,24 @@ private void AppendMembers(SyntaxNode? node, ArrayBuilder<SyntaxNode> list, bool
     {
         Debug.Assert(topLevel || methodLevel);
 
-        foreach (var member in node.GetMembers())
-        {
-            if (IsTopLevelNodeWithMembers(member))
+        node.ForEachMember(static (member, arg) =>
             {
-                if (topLevel)
+                var (@this, list, topLevel, methodLevel) = arg;
+                if (@this.IsTopLevelNodeWithMembers(member))
+                {
+                    if (topLevel)
+                    {
+                        list.Add(member);
+                    }
+
+                    @this.AppendMembers(member, list, topLevel, methodLevel);
+                }
+                else if (methodLevel && @this.IsMethodLevelMember(member))
                 {
                     list.Add(member);
                 }
-
-                AppendMembers(member, list, topLevel, methodLevel);
-                continue;
-            }
-
-            if (methodLevel && IsMethodLevelMember(member))
-            {
-                list.Add(member);
-            }
-        }
+            },
+            (this, list, topLevel, methodLevel));
     }
 
     public TextSpan GetMemberBodySpanForSpeculativeBinding(SyntaxNode node)