Compare updated template evaluator (#4092)

src/Sdk/WorkflowParser/EnumerableExtensions.cs

@@ -0,0 +1,23 @@
+#nullable disable // Temporary: should be removed and issues fixed manually
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace GitHub.Actions.WorkflowParser
+{
+    internal static class EnumerableExtensions
+    {
+        /// <summary>
+        /// Creates a HashSet with equality comparer <paramref name="comparer"/> based on the elements
+        /// in <paramref name="source"/>, using transformation function <paramref name="selector"/>.
+        /// </summary>
+        public static HashSet<TOut> ToHashSet<TIn, TOut>(
+            this IEnumerable<TIn> source,
+            Func<TIn, TOut> selector,
+            IEqualityComparer<TOut> comparer)
+        {
+            return new HashSet<TOut>(source.Select(selector), comparer);
+        }
+    }
+}