Add and use `Insert{Before,After}{,Last}` helpers

src/BizHawk.Client.Common/DisplayManager/FilterManager.cs

@@ -267,7 +267,7 @@ namespace BizHawk.Client.Common.FilterManager
 			if (currState.SurfaceDisposition == SurfaceDisposition.Texture)
 			{
 				var renderer = new Render();
-				Filters.Insert(Filters.Count, renderer);
+				Filters.Add(renderer);
 				Compile(channel, inSize, outsize, finalTarget);
 				return;
 			}

src/BizHawk.Client.Common/movie/bk2/Bk2Movie.IO.cs

@@ -3,6 +3,7 @@ using System.IO;
 
 using BizHawk.Common;
 using BizHawk.Common.IOExtensions;
+using BizHawk.Common.StringExtensions;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -21,8 +22,7 @@ namespace BizHawk.Client.Common
 				return;
 			}
 
-			var backupName = Filename;
-			backupName = backupName.Insert(Filename.LastIndexOf('.'), $".{DateTime.Now:yyyy-MM-dd HH.mm.ss}");
+			var backupName = Filename.InsertBeforeLast('.', insert: $".{DateTime.Now:yyyy-MM-dd HH.mm.ss}", out _);
 			backupName = Path.Combine(Session.BackupDirectory, Path.GetFileName(backupName));
 
 			Write(backupName, isBackup: true);

src/BizHawk.Client.EmuHawk/Extensions/ControlExtensions.cs

@@ -1,5 +1,6 @@
 #nullable enable
 
+using System.Collections;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Drawing;
@@ -12,6 +13,7 @@ using System.Windows.Forms;
 
 using BizHawk.Client.Common;
 using BizHawk.Common;
+using BizHawk.Common.CollectionExtensions;
 using BizHawk.Common.ReflectionExtensions;
 using BizHawk.Emulation.Common;
 
@@ -158,6 +160,20 @@ namespace BizHawk.Client.EmuHawk
 			return tabControl.TabPages.Cast<TabPage>();
 		}
 
+#pragma warning disable CS0618 // WinForms doesn't use generics ofc
+		public static bool InsertAfter(this ToolStripItemCollection items, ToolStripItem needle, ToolStripItem insert)
+			=> ((IList) items).InsertAfter(needle, insert: insert);
+
+		public static bool InsertAfterLast(this ToolStripItemCollection items, ToolStripItem needle, ToolStripItem insert)
+			=> ((IList) items).InsertAfterLast(needle, insert: insert);
+
+		public static bool InsertBefore(this ToolStripItemCollection items, ToolStripItem needle, ToolStripItem insert)
+			=> ((IList) items).InsertBefore(needle, insert: insert);
+
+		public static bool InsertBeforeLast(this ToolStripItemCollection items, ToolStripItem needle, ToolStripItem insert)
+			=> ((IList) items).InsertBeforeLast(needle, insert: insert);
+#pragma warning restore CS0618
+
 		public static void ReplaceDropDownItems(this ToolStripDropDownItem menu, params ToolStripItem[] items)
 		{
 			menu.DropDownItems.Clear();

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -79,9 +79,7 @@ namespace BizHawk.Client.EmuHawk
 #if BIZHAWKBUILD_SUPERHAWK
 			ToolStripMenuItemEx superHawkThrottleMenuItem = new() { Text = "SUPER·HAWK" };
 			superHawkThrottleMenuItem.Click += (_, _) => Config.SuperHawkThrottle = !Config.SuperHawkThrottle;
-			SpeedSkipSubMenu.DropDownItems.Insert(
-				SpeedSkipSubMenu.DropDownItems.IndexOf(MinimizeSkippingMenuItem),
-				superHawkThrottleMenuItem);
+			_ = SpeedSkipSubMenu.DropDownItems.InsertBefore(MinimizeSkippingMenuItem, insert: superHawkThrottleMenuItem);
 			ConfigSubMenu.DropDownOpened += (_, _) => superHawkThrottleMenuItem.Checked = Config.SuperHawkThrottle;
 #endif
 
@@ -159,9 +157,9 @@ namespace BizHawk.Client.EmuHawk
 					submenu.Enabled = false;
 				}
 			}
-			ConfigSubMenu.DropDownItems.Insert(
-				ConfigSubMenu.DropDownItems.IndexOf(CoresSubMenu) + 1,
-				new ToolStripMenuItemEx
+			_ = ConfigSubMenu.DropDownItems.InsertAfter(
+				CoresSubMenu,
+				insert: new ToolStripMenuItemEx
 				{
 					DropDownItems =
 					{
@@ -175,7 +173,7 @@ namespace BizHawk.Client.EmuHawk
 					Text = "Core Settings",
 				});
 
-			MainformMenu.Items.Insert(MainformMenu.Items.IndexOf(ToolsSubMenu) + 1, NullHawkVSysSubmenu);
+			_ = MainformMenu.Items.InsertAfter(ToolsSubMenu, insert: NullHawkVSysSubmenu);
 
 			// Hide Status bar icons and general StatusBar prep
 			MainStatusBar.Padding = new Padding(MainStatusBar.Padding.Left, MainStatusBar.Padding.Top, MainStatusBar.Padding.Left, MainStatusBar.Padding.Bottom); // Workaround to remove extra padding on right

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.cs

@@ -135,9 +135,7 @@ namespace BizHawk.Client.EmuHawk
 				};
 				if (this.ShowDialogWithTempMute(dialog).IsOk()) GoToFrame(int.Parse(dialog.PromptText));
 			};
-			EditSubMenu.DropDownItems.Insert(
-				EditSubMenu.DropDownItems.IndexOf(ReselectClipboardMenuItem) + 1,
-				goToFrameMenuItem);
+			_ = EditSubMenu.DropDownItems.InsertAfter(ReselectClipboardMenuItem, insert: goToFrameMenuItem);
 
 			RecentSubMenu.Image = Resources.Recent;
 			recentMacrosToolStripMenuItem.Image = Resources.Recent;

src/BizHawk.Client.EmuHawk/tools/Watch/RamWatch.cs

@@ -123,7 +123,7 @@ namespace BizHawk.Client.EmuHawk
 					i++;
 				}
 			};
-			WatchesSubMenu.DropDownItems.Insert(11, deduperMenuItem);
+			_ = WatchesSubMenu.DropDownItems.InsertBefore(toolStripSeparator3, insert: deduperMenuItem);
 
 			Settings = new RamWatchSettings();
 

src/BizHawk.Common/Extensions/CollectionExtensions.cs

@@ -10,6 +10,10 @@ namespace BizHawk.Common.CollectionExtensions
 	public static class CollectionExtensions
 #pragma warning restore MA0104
 	{
+		private const string ERR_MSG_IMMUTABLE_LIST = "immutable list passed to mutating method";
+
+		private const string WARN_NONGENERIC = "use generic overload";
+
 		public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(
 			this IEnumerable<TSource> source,
 			Func<TSource, TKey> keySelector,
@@ -247,6 +251,111 @@ namespace BizHawk.Common.CollectionExtensions
 			return -1;
 		}
 
+		public static bool InsertAfter<T>(this IList<T> list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.IndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint + 1, insert);
+			return true;
+		}
+
+		[Obsolete(WARN_NONGENERIC)]
+		public static bool InsertAfter<T>(this IList list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.IndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint + 1, insert);
+			return true;
+		}
+
+		public static bool InsertAfterLast<T>(this IList<T> list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.LastIndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint + 1, insert);
+			return true;
+		}
+
+		[Obsolete(WARN_NONGENERIC)]
+		public static bool InsertAfterLast<T>(this IList list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.LastIndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint + 1, insert);
+			return true;
+		}
+
+		public static bool InsertBefore<T>(this IList<T> list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.IndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint, insert);
+			return true;
+		}
+
+		[Obsolete(WARN_NONGENERIC)]
+		public static bool InsertBefore<T>(this IList list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.IndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint, insert);
+			return true;
+		}
+
+		public static bool InsertBeforeLast<T>(this IList<T> list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.LastIndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint, insert);
+			return true;
+		}
+
+		[Obsolete(WARN_NONGENERIC)]
+		public static bool InsertBeforeLast<T>(this IList list, T needle, T insert)
+		{
+			Debug.Assert(!list.IsReadOnly, ERR_MSG_IMMUTABLE_LIST);
+			var insertPoint = list.LastIndexOf(needle);
+			if (insertPoint < 0) return false;
+			list.Insert(insertPoint, insert);
+			return true;
+		}
+
+		public static int LastIndexOf<T>(this IList<T> list, T item)
+		{
+			if (list is T[] arr) return Array.LastIndexOf(arr, item);
+			if (list is List<T> bclList) return bclList.LastIndexOf(item);
+			if (item is null)
+			{
+				for (var i = list.Count - 1; i >= 0; i--) if (list[i] is null) return i;
+			}
+			else
+			{
+				for (var i = list.Count - 1; i >= 0; i--) if (item.Equals(list[i])) return i;
+			}
+			return -1;
+		}
+
+		[Obsolete(WARN_NONGENERIC)]
+		public static int LastIndexOf(this IList list, object? item)
+		{
+			if (item is null)
+			{
+				for (var i = list.Count - 1; i >= 0; i--) if (list[i] is null) return i;
+			}
+			else
+			{
+				for (var i = list.Count - 1; i >= 0; i--) if (item.Equals(list[i])) return i;
+			}
+			return -1;
+		}
+
 		public static T? FirstOrNull<T>(this IEnumerable<T> list, Func<T, bool> predicate)
 			where T : struct
 		{

src/BizHawk.Common/Extensions/StringExtensions.cs

@@ -62,6 +62,34 @@ namespace BizHawk.Common.StringExtensions
 		public static bool In(this string str, params string[] options)
 			=> options.Any(str.EqualsIgnoreCase);
 
+		public static string InsertAfter(this string str, char needle, string insert, out bool found)
+		{
+			var insertPoint = str.IndexOf(needle);
+			found = insertPoint >= 0;
+			return found ? str.Insert(insertPoint + 1, insert) : str;
+		}
+
+		public static string InsertAfterLast(this string str, char needle, string insert, out bool found)
+		{
+			var insertPoint = str.LastIndexOf(needle);
+			found = insertPoint >= 0;
+			return found ? str.Insert(insertPoint + 1, insert) : str;
+		}
+
+		public static string InsertBefore(this string str, char needle, string insert, out bool found)
+		{
+			var insertPoint = str.IndexOf(needle);
+			found = insertPoint >= 0;
+			return found ? str.Insert(insertPoint, insert) : str;
+		}
+
+		public static string InsertBeforeLast(this string str, char needle, string insert, out bool found)
+		{
+			var insertPoint = str.LastIndexOf(needle);
+			found = insertPoint >= 0;
+			return found ? str.Insert(insertPoint, insert) : str;
+		}
+
 		/// <returns>a copy of <paramref name="raw"/> with all characters outside <c>[0-9A-Za-z]</c> removed</returns>
 		public static string OnlyAlphanumeric(this string raw)
 			=> string.Concat(raw.Where(static c => c is (>= '0' and <= '9') or (>= 'A' and <= 'Z') or (>= 'a' and <= 'z')));