Use existing feature switch

src/libraries/System.Linq/src/System/Linq/Enumerable.cs

@@ -67,8 +67,5 @@ internal static bool TryGetSpan<TSource>(this IEnumerable<TSource> source, out R
 
             return result;
         }
-
-        [FeatureSwitchDefinition("System.Linq.Enumerable.ValueTypeTrimFriendlySelect")]
-        internal static bool ValueTypeTrimFriendlySelect { get; } = AppContext.TryGetSwitch("System.Linq.Enumerable.ValueTypeTrimFriendlySelect", out bool isEnabled) ? isEnabled : false;
     }
 }

src/libraries/System.Linq/src/System/Linq/OfType.SpeedOpt.cs

@@ -172,7 +172,7 @@ public override IEnumerable<TResult2> Select<TResult2>(Func<TResult, TResult2> s
                         new IEnumerableWhereSelectIterator<object, TResult2>(objectSource, isTResult, localSelector);
                 }
 
-                return new IteratorSelectIterator<TResult, TResult2>(this, selector);
+                return base.Select(selector);
             }
         }
     }

src/libraries/System.Linq/src/System/Linq/Select.cs

@@ -4,7 +4,6 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Runtime.CompilerServices;
 using static System.Linq.Utilities;
 
 namespace System.Linq
@@ -26,7 +25,19 @@ public static IEnumerable<TResult> Select<TSource, TResult>(
 
             if (source is Iterator<TSource> iterator)
             {
-                return SelectImplementation(selector, iterator);
+                // With native AOT, calling into the `Select` generic virtual method results in NxM
+                // expansion of native code. If the option is enabled, we don't call the generic virtual
+                // for value types. We don't do the same for reference types because reference type
+                // expansion can happen lazily at runtime and the AOT compiler does postpone it (we
+                // don't need more code, just more data structures describing the new types).
+                if (IsSizeOptimized && typeof(TResult).IsValueType)
+                {
+                    return new IEnumerableSelectIterator<TSource, TResult>(iterator, selector);
+                }
+                else
+                {
+                    return iterator.Select(selector);
+                }
             }
 
             if (source is IList<TSource> ilist)
@@ -52,24 +63,6 @@ public static IEnumerable<TResult> Select<TSource, TResult>(
             return new IEnumerableSelectIterator<TSource, TResult>(source, selector);
         }
 
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static IEnumerable<TResult> SelectImplementation<TSource, TResult>(Func<TSource, TResult> selector, Iterator<TSource> iterator)
-        {
-            // With native AOT, calling into the `Select` generic virtual method results in NxM
-            // expansion of native code. If the option is enabled, we don't call the generic virtual
-            // for value types. We don't do the same for reference types because reference type
-            // expansion can happen lazily at runtime and the AOT compiler does postpone it (we
-            // don't need more code, just more data structures describing the new types).
-            if (ValueTypeTrimFriendlySelect && typeof(TResult).IsValueType)
-            {
-                if (IsSizeOptimized)
-                    return new IEnumerableSelectIterator<TSource, TResult>(iterator, selector);
-                return new IteratorSelectIterator<TSource, TResult>(iterator, selector);
-            }
-
-            return iterator.Select(selector);
-        }
-
         public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, int, TResult> selector)
         {
             if (source is null)

src/libraries/System.Linq/tests/SkipWhileTests.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
-using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 
 namespace System.Linq.Tests
@@ -61,31 +60,12 @@ public void RunOnce()
             Assert.Equal(Enumerable.Range(10, 10), Enumerable.Range(0, 20).RunOnce().SkipWhile((i, idx) => idx < 10));
         }
 
-        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
-        public static void SkipErrorWhenSourceErrors_TrimFriendlySelectTrue()
-        {
-            RemoteExecutor.Invoke(() =>
-            {
-                AppContext.SetSwitch("System.Linq.Enumerable.ValueTypeTrimFriendlySelect", true);
-
-                var source = NumberRangeGuaranteedNotCollectionType(-2, 5).Select(i => (decimal)i).Select(m => 1 / m).Skip(4);
-                var valuesFromEnumerable = source.ToList();
-                List<decimal> expectedValues = [(decimal)1/2];
-                Assert.Equal(expectedValues, valuesFromEnumerable);
-            }).Dispose();
-        }
-
-        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
-        public void SkipErrorWhenSourceErrors_TrimFriendlySelectFalse()
+        [Fact]
+        public void SkipErrorWhenSourceErrors()
         {
-            RemoteExecutor.Invoke(() =>
-            {
-                AppContext.SetSwitch("System.Linq.Enumerable.ValueTypeTrimFriendlySelect", false);
-
-                var source = NumberRangeGuaranteedNotCollectionType(-2, 5).Select(i => (decimal)i).Select(m => 1 / m).Skip(4);
-                using var en = source.GetEnumerator();
-                Assert.Throws<DivideByZeroException>(() => en.MoveNext());
-            }).Dispose();
+            var source = NumberRangeGuaranteedNotCollectionType(-2, 5).Select(i => (decimal)i).Select(m => 1 / m).Skip(4);
+            using var en = source.GetEnumerator();
+            Assert.Throws<DivideByZeroException>(() => en.MoveNext());
         }
 
         [Fact]

src/libraries/System.Linq/tests/System.Linq.Tests.csproj

@@ -1,6 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
     <DebuggerSupport Condition="'$(DebuggerSupport)' == '' and '$(TargetOS)' == 'browser'">true</DebuggerSupport>
   </PropertyGroup>