Cleanup and allocation improvements.

Common/Internal/Argument.cs

@@ -198,6 +198,7 @@ public static T NotNullAndCast<T>(
     /// <returns><paramref name="value"/> if it is greater than or equal to zero.</returns>
     public static int PositiveOrZero([NotNull, InvokerParameterName] string name, int value) {
         if (value < 0) {
+            // ReSharper disable once HeapView.BoxingAllocation
             throw new ArgumentOutOfRangeException(name, value, "Value must be positive or zero.");
         }
 
@@ -213,6 +214,7 @@ public static int PositiveOrZero([NotNull, InvokerParameterName] string name, in
     /// <returns><paramref name="value"/> if it is greater than zero.</returns>
     public static int PositiveNonZero([NotNull, InvokerParameterName] string name, int value) {
         if (value <= 0) {
+            // ReSharper disable once HeapView.BoxingAllocation
             throw new ArgumentOutOfRangeException(name, value, "Value must be positive and not zero.");
         }
 

Common/Internal/AsyncData.cs

@@ -5,9 +5,9 @@ namespace MirrorSharp.Internal {
     internal struct AsyncData {
         public static readonly AsyncData Empty = new AsyncData(new ArraySegment<byte>(new byte[0]), false, () => null);
 
-        private ArraySegment<byte> _first;
+        private readonly ArraySegment<byte> _first;
         private readonly Func<Task<ArraySegment<byte>?>> _getNextAsync;
-        private bool _getNextCalled;
+        private readonly bool _getNextCalled;
 
         public AsyncData(ArraySegment<byte> first, bool mightHaveNext, Func<Task<ArraySegment<byte>?>> getNextAsync) {
             _first = first;

Common/Internal/CharArrayString.cs

@@ -0,0 +1,11 @@
+using System.Collections.Immutable;
+
+namespace MirrorSharp.Internal {
+    internal struct CharArrayString {
+        public CharArrayString(ImmutableArray<char> chars) {
+            Chars = chars;
+        }
+
+        public ImmutableArray<char> Chars { get; }
+    }
+}

Common/Internal/Connection.cs

@@ -49,6 +49,7 @@ public async Task ReceiveAndProcessAsync(CancellationToken cancellationToken) {
             }
         }
 
+        // ReSharper disable once HeapView.ClosureAllocation
         private async Task ReceiveAndProcessInternalAsync(CancellationToken cancellationToken) {
             var first = await _socket.ReceiveAsync(new ArraySegment<byte>(_inputBuffer), cancellationToken).ConfigureAwait(false);
             if (first.MessageType == WebSocketMessageType.Close) {
@@ -73,7 +74,7 @@ await handler.ExecuteAsync(
                 new AsyncData(
                     new ArraySegment<byte>(_inputBuffer, 1, first.Count - 1),
                     !first.EndOfMessage,
-                    // can we avoid this allocation?
+                    // Can we avoid this allocation?
                     async () => {
                         if (last.EndOfMessage)
                             return null;
@@ -86,6 +87,7 @@ await handler.ExecuteAsync(
 
             if (!last.EndOfMessage) {
                 await ReceiveToEndAsync(cancellationToken).ConfigureAwait(false);
+                // ReSharper disable once HeapView.BoxingAllocation
                 throw new InvalidOperationException($"Received message has unread data after command '{(char)commandId}'.");
             }
 
@@ -99,12 +101,16 @@ private async Task ReceiveToEndAsync(CancellationToken cancellationToken) {
 
         private ICommandHandler ResolveHandler(byte commandId) {
             var handlerIndex = commandId - (byte)'A';
-            if (handlerIndex < 0 || handlerIndex > _handlers.Length - 1)
+            if (handlerIndex < 0 || handlerIndex > _handlers.Length - 1) {
+                // ReSharper disable once HeapView.BoxingAllocation
                 throw new FormatException($"Invalid command: '{(char)commandId}'.");
+            }
 
             var handler = _handlers[handlerIndex];
-            if (handler == null)
+            if (handler == null) {
+                // ReSharper disable once HeapView.BoxingAllocation
                 throw new FormatException($"Unknown command: '{(char)commandId}'.");
+            }
             return handler;
         }
 

Common/Internal/FastConvert.cs

@@ -40,8 +40,10 @@ public static char Utf8ByteArrayToChar(ArraySegment<byte> bytes) {
                 CharPool.Return(buffer);
             }
 
-            if (charCount != 1)
+            if (charCount != 1) {
+                // ReSharper disable once HeapView.BoxingAllocation
                 throw new FormatException($"Expected one char, but conversion produced {charCount}.");
+            }
 
             return buffer[0];
         }

Common/Internal/FastUtf8JsonWriter.cs

@@ -53,7 +53,7 @@ public void WriteProperty(string name, string value) {
             WriteValue(value);
         }
 
-        public void WriteProperty(string name, CharListString value) {
+        public void WriteProperty(string name, CharArrayString value) {
             WritePropertyName(name);
             WriteValue(value);
         }
@@ -107,10 +107,10 @@ public void WriteValue(string value) {
             WriteEndValue();
         }
 
-        public void WriteValue(CharListString value) {
+        public void WriteValue(CharArrayString value) {
             WriteStartValue();
             WriteRawByte(Utf8.Quote);
-            foreach (var @char in value) {
+            foreach (var @char in value.Chars) {
                 WriteUnquotedChar(@char);
             }
             WriteRawByte(Utf8.Quote);

Common/Internal/Handlers/SetOptionsHandler.cs

@@ -11,6 +11,9 @@
 using MirrorSharp.Internal.Languages;
 using MirrorSharp.Internal.Results;
 
+// ReSharper disable HeapView.DelegateAllocation
+// ReSharper disable HeapView.ClosureAllocation
+
 namespace MirrorSharp.Internal.Handlers {
     internal class SetOptionsHandler : ICommandHandler {
         private static readonly char[] Comma = { ',' };

Common/Internal/Handlers/Shared/CompletionSupport.cs

@@ -94,7 +94,7 @@ private Task SendCompletionListAsync(CompletionList completionList, ICommandResu
             var completionSpan = completionList.Span;
             var writer = sender.StartJsonMessage("completions");
 
-            writer.WriteProperty("commitChars", new CharListString(completionList.Rules.DefaultCommitCharacters));
+            writer.WriteProperty("commitChars", new CharArrayString(completionList.Rules.DefaultCommitCharacters));
             writer.WritePropertyName("span");
             writer.WriteSpan(completionSpan);
 

Common/Internal/Handlers/SignatureHelpStateHandler.cs

@@ -16,8 +16,10 @@ public SignatureHelpStateHandler([NotNull] ISignatureHelpSupport signatureHelp)
 
         public Task ExecuteAsync(AsyncData data, WorkSession session, ICommandResultSender sender, CancellationToken cancellationToken) {
             var @char = FastConvert.Utf8ByteArrayToChar(data.GetFirst());
-            if (@char != 'F')
+            if (@char != 'F') {
+                // ReSharper disable once HeapView.BoxingAllocation
                 throw new FormatException($"Unknown SignatureHelp command '{@char}'.");
+            }
 
             return _signatureHelp.ForceSignatureHelpAsync(session, sender, cancellationToken);
         }

Common/Internal/Handlers/SlowUpdateHandler.cs

@@ -16,7 +16,6 @@
 
 namespace MirrorSharp.Internal.Handlers {
     internal class SlowUpdateHandler : ICommandHandler {
-        private static readonly IReadOnlyCollection<CodeAction> NoCodeActions = new CodeAction[0];
         [CanBeNull] private readonly ISlowUpdateExtension _extension;
 
         public SlowUpdateHandler([CanBeNull] ISlowUpdateExtension extension) {
@@ -27,6 +26,8 @@ public SlowUpdateHandler([CanBeNull] ISlowUpdateExtension extension) {
 
         public async Task ExecuteAsync(AsyncData data, WorkSession session, ICommandResultSender sender, CancellationToken cancellationToken) {
             var compilation = await session.Project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
+            // Temporary suppression, need to figure out the best approach here.
+            // ReSharper disable once HeapView.BoxingAllocation
             var diagnostics = (IList<Diagnostic>)await compilation.WithAnalyzers(session.Analyzers).GetAllDiagnosticsAsync(cancellationToken).ConfigureAwait(false);
             object extensionResult = null;
             if (_extension != null) {
@@ -55,7 +56,7 @@ private async Task SendSlowUpdateAsync(IReadOnlyList<Diagnostic> diagnostics, Wo
                 writer.WritePropertyName("span");
                 writer.WriteSpan(diagnostic.Location.SourceSpan);
                 var actions = await GetCodeActionsAsync(diagnostic, session, cancellationToken).ConfigureAwait(false);
-                if (actions.Count > 0) {
+                if (actions.Length > 0) {
                     writer.WritePropertyStartArray("actions");
                     WriteActions(writer, actions, session);
                     writer.WriteEndArray();
@@ -71,7 +72,7 @@ private async Task SendSlowUpdateAsync(IReadOnlyList<Diagnostic> diagnostics, Wo
             await sender.SendJsonMessageAsync(cancellationToken).ConfigureAwait(false);
         }
 
-        private static void WriteActions(IFastJsonWriterInternal writer, IReadOnlyCollection<CodeAction> actions, WorkSession session) {
+        private static void WriteActions(IFastJsonWriterInternal writer, ImmutableArray<CodeAction> actions, WorkSession session) {
             foreach (var action in actions) {
                 if (action is CodeActionWithOptions)
                     continue;
@@ -89,22 +90,24 @@ private static void WriteActions(IFastJsonWriterInternal writer, IReadOnlyCollec
             }
         }
 
-        private async Task<IReadOnlyCollection<CodeAction>> GetCodeActionsAsync(Diagnostic diagnostic, WorkSession session, CancellationToken cancellationToken) {
-            List<CodeAction> actions = null;
+        private async ValueTask<ImmutableArray<CodeAction>> GetCodeActionsAsync(Diagnostic diagnostic, WorkSession session, CancellationToken cancellationToken) {
+            // I don't think this can be avoided.
+            // ReSharper disable once HeapView.ClosureAllocation
+            ImmutableArray<CodeAction>.Builder actionsBuilder = null;
             Action<CodeAction, ImmutableArray<Diagnostic>> registerCodeFix = (action, _) => {
-                if (actions == null)
-                    actions = new List<CodeAction>();
-                actions.Add(action);
+                if (actionsBuilder == null)
+                    actionsBuilder = ImmutableArray.CreateBuilder<CodeAction>();
+                actionsBuilder.Add(action);
             };
             var fixContext = new CodeFixContext(session.Document, diagnostic, registerCodeFix, cancellationToken);
             var providers = ImmutableDictionary.GetValueOrDefault(session.CodeFixProviders, diagnostic.Id);
             if (providers == null)
-                return NoCodeActions;
+                return ImmutableArray<CodeAction>.Empty;
 
             foreach (var provider in providers) {
                 await provider.RegisterCodeFixesAsync(fixContext).ConfigureAwait(false);
             }
-            return actions ?? NoCodeActions;
+            return actionsBuilder?.ToImmutable() ?? ImmutableArray<CodeAction>.Empty;
         }
     }
 }

Common/Internal/IFastJsonWriterInternal.cs

@@ -2,7 +2,7 @@
 
 namespace MirrorSharp.Internal {
     internal interface IFastJsonWriterInternal : IFastJsonWriter {
-        void WriteProperty(string name, CharListString value);
-        void WriteValue(CharListString value);
+        void WriteProperty(string name, CharArrayString value);
+        void WriteValue(CharArrayString value);
     }
 }

Common/Internal/Languages/LanguageBase.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
@@ -19,6 +19,7 @@ protected LanguageBase(
             [NotNull] ParseOptions defaultParseOptions,
             [NotNull] CompilationOptions defaultCompilationOptions
         ) {
+            // ReSharper disable HeapView.BoxingAllocation
             Name = name;
             HostServices = MefHostServices.Create(new[] {
                 Assembly.Load(new AssemblyName("Microsoft.CodeAnalysis.Workspaces")),
@@ -39,6 +40,7 @@ [NotNull] CompilationOptions defaultCompilationOptions
                 DefaultAnalyzerReferences.SelectMany(r => r.GetAnalyzers(Name))
             );
             DefaultSignatureHelpProviders = CreateDefaultSignatureHelpProviders();
+            // ReSharper restore HeapView.BoxingAllocation
         }
 
         public string Name { get; }

Common/Internal/Reflection/RoslynReflectionFast.cs

@@ -2,6 +2,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using Microsoft.CodeAnalysis.CodeActions;
@@ -21,32 +22,13 @@ internal static class RoslynReflectionFast {
             RoslynTypes.CodeAction
                 .GetProperty("NestedCodeActions", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance)
                 ?.GetMethod.CreateDelegate<Func<CodeAction, ImmutableArray<CodeAction>>>();
+
+        public static bool IsInlinable(CodeAction action) => _getIsInlinable(action);
+        public static ImmutableArray<CodeAction> GetNestedCodeActions(CodeAction action) => _getNestedCodeActions(action);
 
-        // Roslyn v1
-        private static readonly Func<CodeAction, bool> _getIsInvokable =
-            RoslynTypes.CodeAction
-                .GetProperty("IsInvokable", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance)
-                ?.GetMethod.CreateDelegate<Func<CodeAction, bool>>();
-
-        private static readonly Func<CodeAction, ImmutableArray<CodeAction>> _getCodeActions =
-            RoslynTypes.CodeAction
-                .GetMethod("GetCodeActions", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance)
-                ?.CreateDelegate<Func<CodeAction, ImmutableArray<CodeAction>>>();
-
-        public static bool IsInlinable(CodeAction action) {
-            if (_getIsInlinable == null) // Roslyn v1
-                return !_getIsInvokable(action);
-
-            return _getIsInlinable(action);
-        }
-
-        public static ImmutableArray<CodeAction> GetNestedCodeActions(CodeAction action) {
-            if (_getNestedCodeActions == null) // Roslyn v1
-                return _getCodeActions(action);
-
-            return _getNestedCodeActions(action);
-        }
-
+        [SuppressMessage("ReSharper", "HeapView.ClosureAllocation")]
+        [SuppressMessage("ReSharper", "HeapView.DelegateAllocation")]
+        [SuppressMessage("ReSharper", "HeapView.ObjectAllocation.Possible")]
         public static IEnumerable<Lazy<ISignatureHelpProviderWrapper, OrderableLanguageMetadataData>> GetSignatureHelpProvidersSlow(MefHostServices hostServices) {
             var mefHostServicesType = typeof(MefHostServices).GetTypeInfo();
             var getExports = EnsureFound(

Common/Internal/Reflection/SignatureHelpItemData.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -27,33 +28,15 @@ int parameterCount
             ParameterCount = parameterCount;
         }
 
-        // Roslyn v1
-        [UsedImplicitly] // see FromInternalTypeExpressionSlow
-        public SignatureHelpItemData(
-            Func<CancellationToken, IEnumerable<SymbolDisplayPart>> documentationFactory,
-            ImmutableArray<SymbolDisplayPart> prefixParts,
-            ImmutableArray<SymbolDisplayPart> separatorParts,
-            ImmutableArray<SymbolDisplayPart> suffixParts,
-            IEnumerable<SignatureHelpParameterData> parameters,
-            int parameterCount
-        ) {
-            DocumentationFactory = documentationFactory != null
-                ? (Func<CancellationToken, IEnumerable<TaggedText>>)(t => documentationFactory(t).ToTaggedText())
-                : null;
-            PrefixDisplayParts = prefixParts.ToTaggedText();
-            SeparatorDisplayParts = separatorParts.ToTaggedText();
-            SuffixDisplayParts = suffixParts.ToTaggedText();
-            Parameters = parameters;
-            ParameterCount = parameterCount;
-        }
-
         public Func<CancellationToken, IEnumerable<TaggedText>> DocumentationFactory { get; }
         public ImmutableArray<TaggedText> PrefixDisplayParts { get; }
         public ImmutableArray<TaggedText> SeparatorDisplayParts { get; }
         public ImmutableArray<TaggedText> SuffixDisplayParts { get; }
         public IEnumerable<SignatureHelpParameterData> Parameters { get; }
         public int ParameterCount { get; }
-
+
+        [SuppressMessage("ReSharper", "HeapView.ClosureAllocation")]
+        [SuppressMessage("ReSharper", "HeapView.DelegateAllocation")]
         public static Expression FromInternalTypeExpressionSlow(Expression expression) {
             var displayPartsType = expression.Property("PrefixDisplayParts").Type;
             var constructor = typeof(SignatureHelpItemData).GetTypeInfo()

Common/Internal/Reflection/SignatureHelpParameterData.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -14,18 +15,12 @@ public SignatureHelpParameterData(IList<TaggedText> displayParts, IList<TaggedTe
             SuffixDisplayParts = suffixDisplayParts;
         }
 
-        // Roslyn v1
-        [UsedImplicitly] // see FromInternalTypeExpressionSlow
-        public SignatureHelpParameterData(IList<SymbolDisplayPart> displayParts, IList<SymbolDisplayPart> prefixDisplayParts, IList<SymbolDisplayPart> suffixDisplayParts) {
-            DisplayParts = displayParts.ToTaggedText();
-            PrefixDisplayParts = prefixDisplayParts.ToTaggedText();
-            SuffixDisplayParts = suffixDisplayParts.ToTaggedText();
-        }
-
         public IList<TaggedText> DisplayParts { get; }
         public IList<TaggedText> PrefixDisplayParts { get; }
         public IList<TaggedText> SuffixDisplayParts { get; }
 
+        [SuppressMessage("ReSharper", "HeapView.ClosureAllocation")]
+        [SuppressMessage("ReSharper", "HeapView.DelegateAllocation")]
         public static Expression FromInternalTypeExpressionSlow(Expression expression) {
             var displayPartsType = expression.Property("DisplayParts").Type;
             var constructor = typeof(SignatureHelpParameterData).GetTypeInfo()