Enable Code Quality rule CA1851

.editorconfig

@@ -834,6 +834,12 @@ dotnet_diagnostic.CA1849.severity = warning
 # Prefer static HashData method over ComputeHash. (Not available on mono)
 dotnet_diagnostic.CA1850.severity = none
 
+# Possible multiple enumerations of IEnumerable collection.
+#dotnet_code_quality.CA1851.enumeration_methods =
+dotnet_code_quality.CA1851.linq_chain_methods = M:OpenRA.Traits.IRenderModifier.Modify*
+dotnet_code_quality.CA1851.assume_method_enumerates_parameters = true
+dotnet_diagnostic.CA1851.severity = warning
+
 # Seal internal types.
 dotnet_diagnostic.CA1852.severity = warning
 

OpenRA.Game/Exts.cs

@@ -147,7 +147,7 @@ public static T RandomOrDefault<T>(this IEnumerable<T> ts, MersenneTwister r)
 
 		static T Random<T>(IEnumerable<T> ts, MersenneTwister r, bool throws)
 		{
-			var xs = ts as ICollection<T>;
+			var xs = ts as IReadOnlyCollection<T>;
 			xs ??= ts.ToList();
 			if (xs.Count == 0)
 			{

OpenRA.Game/Game.cs

@@ -523,10 +523,11 @@ static string ChooseShellmap()
 				.Where(m => m.Status == MapStatus.Available && m.Visibility.HasFlag(MapVisibility.Shellmap))
 				.Select(m => m.Uid);
 
-			if (!shellmaps.Any())
+			var shellmap = shellmaps.RandomOrDefault(CosmeticRandom);
+			if (shellmap == null)
 				throw new InvalidDataException("No valid shellmaps available");
 
-			return shellmaps.Random(CosmeticRandom);
+			return shellmap;
 		}
 
 		public static void SwitchToExternalMod(ExternalMod mod, string[] launchArguments = null, Action onFailed = null)

OpenRA.Game/GameRules/ActorInfo.cs

@@ -130,6 +130,7 @@ public IEnumerable<TraitInfo> TraitsInConstructOrder()
 
 			// Continue resolving traits as long as possible.
 			// Each time we resolve some traits, this means dependencies for other traits may then be possible to satisfy in the next pass.
+#pragma warning disable CA1851 // Possible multiple enumerations of 'IEnumerable' collection
 			var readyToResolve = more.ToList();
 			while (readyToResolve.Count != 0)
 			{
@@ -138,6 +139,7 @@ public IEnumerable<TraitInfo> TraitsInConstructOrder()
 				readyToResolve.Clear();
 				readyToResolve.AddRange(more);
 			}
+#pragma warning restore CA1851
 
 			if (unresolved.Count != 0)
 			{
@@ -185,7 +187,7 @@ public static IEnumerable<Type> OptionalPrerequisitesOf(TraitInfo info)
 		public bool HasTraitInfo<T>() where T : ITraitInfoInterface { return traits.Contains<T>(); }
 		public T TraitInfo<T>() where T : ITraitInfoInterface { return traits.Get<T>(); }
 		public T TraitInfoOrDefault<T>() where T : ITraitInfoInterface { return traits.GetOrDefault<T>(); }
-		public IEnumerable<T> TraitInfos<T>() where T : ITraitInfoInterface { return traits.WithInterface<T>(); }
+		public IReadOnlyCollection<T> TraitInfos<T>() where T : ITraitInfoInterface { return traits.WithInterface<T>(); }
 
 		public BitSet<TargetableType> GetAllTargetTypes()
 		{

OpenRA.Game/Graphics/ChromeProvider.cs

@@ -234,7 +234,7 @@ public static Sprite[] TryGetPanelImages(string collectionName)
 			{
 				// PERF: We don't need to search for images if there are no definitions.
 				// PERF: It's more efficient to send an empty array rather than an array of 9 nulls.
-				if (!collection.Regions.Any())
+				if (collection.Regions.Count == 0)
 					return Array.Empty<Sprite>();
 
 				// Support manual definitions for unusual dialog layouts

OpenRA.Game/Graphics/Viewport.cs

@@ -299,10 +299,13 @@ IEnumerable<MPos> CandidateMouseoverCells(int2 world)
 
 		public void Center(IEnumerable<Actor> actors)
 		{
-			if (!actors.Any())
+			var actorsCollection = actors as IReadOnlyCollection<Actor>;
+			actorsCollection ??= actors.ToList();
+
+			if (actorsCollection.Count == 0)
 				return;
 
-			Center(actors.Select(a => a.CenterPosition).Average());
+			Center(actorsCollection.Select(a => a.CenterPosition).Average());
 		}
 
 		public void Center(WPos pos)

OpenRA.Game/Map/ActorReference.cs

@@ -139,7 +139,7 @@ public void Add(ActorInit init)
 			return removed;
 		}
 
-		public IEnumerable<T> GetAll<T>() where T : ActorInit
+		public IReadOnlyCollection<T> GetAll<T>() where T : ActorInit
 		{
 			return initDict.Value.WithInterface<T>();
 		}

OpenRA.Game/Map/CellRegion.cs

@@ -12,7 +12,6 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Linq;
 
 namespace OpenRA
 {
@@ -64,9 +63,9 @@ public static CellRegion Expand(CellRegion region, int cordon)
 		}
 
 		/// <summary>Returns the minimal region that covers at least the specified cells.</summary>
-		public static CellRegion BoundingRegion(MapGridType shape, IEnumerable<CPos> cells)
+		public static CellRegion BoundingRegion(MapGridType shape, IReadOnlyCollection<CPos> cells)
 		{
-			if (cells == null || !cells.Any())
+			if (cells == null || cells.Count == 0)
 				throw new ArgumentException("cells must not be null or empty.", nameof(cells));
 
 			var minU = int.MaxValue;

OpenRA.Game/Network/SyncReport.cs

@@ -201,8 +201,12 @@ struct EffectReport
 			public TypeInfo(Type type)
 			{
 				const BindingFlags Flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance;
-				var fields = type.GetFields(Flags).Where(fi => !fi.IsLiteral && !fi.IsStatic && fi.HasAttribute<SyncAttribute>());
-				var properties = type.GetProperties(Flags).Where(pi => pi.HasAttribute<SyncAttribute>());
+				var fields = type.GetFields(Flags)
+					.Where(fi => !fi.IsLiteral && !fi.IsStatic && fi.HasAttribute<SyncAttribute>())
+					.ToList();
+				var properties = type.GetProperties(Flags)
+					.Where(pi => pi.HasAttribute<SyncAttribute>())
+					.ToList();
 
 				foreach (var prop in properties)
 					if (!prop.CanRead || prop.GetIndexParameters().Length > 0)

OpenRA.Game/ObjectCreator.cs

@@ -134,8 +134,8 @@ public Type FindType(string className)
 		public ConstructorInfo GetCtor(Type type)
 		{
 			var flags = BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance;
-			var ctors = type.GetConstructors(flags).Where(x => x.HasAttribute<UseCtorAttribute>());
-			if (ctors.Count() > 1)
+			var ctors = type.GetConstructors(flags).Where(x => x.HasAttribute<UseCtorAttribute>()).ToList();
+			if (ctors.Count > 1)
 				throw new InvalidOperationException("ObjectCreator: UseCtor on multiple constructors; invalid.");
 			return ctors.FirstOrDefault();
 		}

OpenRA.Game/Player.cs

@@ -133,7 +133,7 @@ static FactionInfo ResolveFaction(World world, string factionName, MersenneTwist
 
 		static FactionInfo ResolveDisplayFaction(World world, string factionName)
 		{
-			var factions = world.Map.Rules.Actors[SystemActors.World].TraitInfos<FactionInfo>().ToArray();
+			var factions = world.Map.Rules.Actors[SystemActors.World].TraitInfos<FactionInfo>();
 
 			return factions.FirstOrDefault(f => f.InternalName == factionName) ?? factions.First();
 		}

OpenRA.Game/Primitives/TypeDictionary.cs

@@ -12,14 +12,20 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Linq;
 
 namespace OpenRA.Primitives
 {
 	public class TypeDictionary : IEnumerable<object>
 	{
-		static readonly Func<Type, List<object>> CreateList = type => new List<object>();
-		readonly Dictionary<Type, List<object>> data = new();
+		static readonly Func<Type, ITypeContainer> CreateTypeContainer = t =>
+			(ITypeContainer)typeof(TypeContainer<>).MakeGenericType(t).GetConstructor(Type.EmptyTypes).Invoke(null);
+
+		readonly Dictionary<Type, ITypeContainer> data = new();
+
+		ITypeContainer InnerGet(Type t)
+		{
+			return data.GetOrAdd(t, CreateTypeContainer);
+		}
 
 		public void Add(object val)
 		{
@@ -33,7 +39,7 @@ public void Add(object val)
 
 		void InnerAdd(Type t, object val)
 		{
-			data.GetOrAdd(t, CreateList).Add(val);
+			InnerGet(t).Add(val);
 		}
 
 		public bool Contains<T>()
@@ -48,35 +54,33 @@ public bool Contains(Type t)
 
 		public T Get<T>()
 		{
-			return (T)Get(typeof(T), true);
+			return Get<T>(true);
 		}
 
 		public T GetOrDefault<T>()
 		{
-			var result = Get(typeof(T), false);
-			if (result == null)
-				return default;
-			return (T)result;
+			return Get<T>(false);
 		}
 
-		object Get(Type t, bool throwsIfMissing)
+		T Get<T>(bool throwsIfMissing)
 		{
-			if (!data.TryGetValue(t, out var ret))
+			if (!data.TryGetValue(typeof(T), out var container))
 			{
 				if (throwsIfMissing)
-					throw new InvalidOperationException($"TypeDictionary does not contain instance of type `{t}`");
-				return null;
+					throw new InvalidOperationException($"TypeDictionary does not contain instance of type `{typeof(T)}`");
+				return default;
 			}
 
-			if (ret.Count > 1)
-				throw new InvalidOperationException($"TypeDictionary contains multiple instances of type `{t}`");
-			return ret[0];
+			var list = ((TypeContainer<T>)container).Objects;
+			if (list.Count > 1)
+				throw new InvalidOperationException($"TypeDictionary contains multiple instances of type `{typeof(T)}`");
+			return list[0];
 		}
 
-		public IEnumerable<T> WithInterface<T>()
+		public IReadOnlyCollection<T> WithInterface<T>()
 		{
-			if (data.TryGetValue(typeof(T), out var objs))
-				return objs.Cast<T>();
+			if (data.TryGetValue(typeof(T), out var container))
+				return ((TypeContainer<T>)container).Objects;
 			return Array.Empty<T>();
 		}
 
@@ -92,18 +96,19 @@ public void Remove<T>(T val)
 
 		void InnerRemove(Type t, object val)
 		{
-			if (!data.TryGetValue(t, out var objs))
+			if (!data.TryGetValue(t, out var container))
 				return;
-			objs.Remove(val);
-			if (objs.Count == 0)
+
+			container.Remove(val);
+			if (container.Count == 0)
 				data.Remove(t);
 		}
 
 		public void TrimExcess()
 		{
 			data.TrimExcess();
-			foreach (var objs in data.Values)
-				objs.TrimExcess();
+			foreach (var t in data.Keys)
+				InnerGet(t).TrimExcess();
 		}
 
 		public IEnumerator<object> GetEnumerator()
@@ -115,6 +120,36 @@ IEnumerator IEnumerable.GetEnumerator()
 		{
 			return GetEnumerator();
 		}
+
+		interface ITypeContainer
+		{
+			int Count { get; }
+			void Add(object value);
+			void Remove(object value);
+			void TrimExcess();
+		}
+
+		sealed class TypeContainer<T> : ITypeContainer
+		{
+			public List<T> Objects { get; } = new List<T>();
+
+			public int Count => Objects.Count;
+
+			public void Add(object value)
+			{
+				Objects.Add((T)value);
+			}
+
+			public void Remove(object value)
+			{
+				Objects.Remove((T)value);
+			}
+
+			public void TrimExcess()
+			{
+				Objects.TrimExcess();
+			}
+		}
 	}
 
 	public static class TypeExts

OpenRA.Game/SelectableExts.cs

@@ -62,10 +62,7 @@ static int BaseSelectionPriority(ISelectableInfo info, Modifiers modifiers)
 
 		public static Actor WithHighestSelectionPriority(this IEnumerable<ActorBoundsPair> actors, int2 selectionPixel, Modifiers modifiers)
 		{
-			if (!actors.Any())
-				return null;
-
-			return actors.MaxBy(a => CalculateActorSelectionPriority(a.Actor.Info, a.Bounds, selectionPixel, modifiers)).Actor;
+			return actors.MaxByOrDefault(a => CalculateActorSelectionPriority(a.Actor.Info, a.Bounds, selectionPixel, modifiers)).Actor;
 		}
 
 		public static FrozenActor WithHighestSelectionPriority(this IEnumerable<FrozenActor> actors, int2 selectionPixel, Modifiers modifiers)

OpenRA.Game/Support/AssemblyLoader.cs

@@ -349,7 +349,7 @@ static IEnumerable<string> GetRids(RuntimeFallbacks runtimeGraph)
 			return Enumerable.Concat(new[] { runtimeGraph.Runtime }, runtimeGraph?.Fallbacks ?? Enumerable.Empty<string>());
 		}
 
-		static IEnumerable<string> SelectAssets(IEnumerable<string> rids, IEnumerable<RuntimeAssetGroup> groups)
+		static IEnumerable<string> SelectAssets(IEnumerable<string> rids, IReadOnlyCollection<RuntimeAssetGroup> groups)
 		{
 			foreach (var rid in rids)
 			{

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -455,7 +455,7 @@ public interface ISelectableInfo : ITraitInfoInterface
 	public interface ISelection
 	{
 		int Hash { get; }
-		IEnumerable<Actor> Actors { get; }
+		IReadOnlyCollection<Actor> Actors { get; }
 
 		void Add(Actor a);
 		void Remove(Actor a);

OpenRA.Game/WPos.cs

@@ -11,7 +11,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using Eluant;
 using Eluant.ObjectBinding;
 using OpenRA.Scripting;
@@ -139,20 +138,21 @@ public static class IEnumerableExtensions
 	{
 		public static WPos Average(this IEnumerable<WPos> source)
 		{
-			var length = source.Count();
-			if (length == 0)
-				return WPos.Zero;
-
+			var length = 0;
 			var x = 0L;
 			var y = 0L;
 			var z = 0L;
 			foreach (var pos in source)
 			{
+				length++;
 				x += pos.X;
 				y += pos.Y;
 				z += pos.Z;
 			}
 
+			if (length == 0)
+				return WPos.Zero;
+
 			x /= length;
 			y /= length;
 			z /= length;

OpenRA.Mods.Cnc/Activities/Teleport.cs

@@ -10,7 +10,6 @@
 #endregion
 
 using System;
-using System.Linq;
 using OpenRA.Activities;
 using OpenRA.Mods.Cnc.Traits;
 using OpenRA.Mods.Common.Traits;
@@ -120,7 +119,7 @@ public override bool Tick(Actor self)
 			if (teleporter == null)
 				return null;
 
-			var restrictTo = maximumDistance == null ? null : self.World.Map.FindTilesInCircle(self.Location, maximumDistance.Value);
+			var restrictTo = maximumDistance == null ? null : self.World.Map.FindTilesInCircle(self.Location, maximumDistance.Value).ToHashSet();
 
 			if (maximumDistance != null)
 				destination = restrictTo.MinBy(x => (x - destination).LengthSquared);

OpenRA.Mods.Cnc/Traits/GpsWatcher.cs

@@ -80,7 +80,7 @@ void RefreshGranted()
 		{
 			var wasGranted = Granted;
 			var wasGrantedAllies = GrantedAllies;
-			var allyWatchers = owner.World.ActorsWithTrait<GpsWatcher>().Where(kv => kv.Actor.Owner.IsAlliedWith(owner));
+			var allyWatchers = owner.World.ActorsWithTrait<GpsWatcher>().Where(kv => kv.Actor.Owner.IsAlliedWith(owner)).ToList();
 
 			Granted = actors.Count > 0 && Launched;
 			GrantedAllies = allyWatchers.Any(w => w.Trait.Granted);