Enable CA1821, CA1825-CA1834 (#33041)

* Enable CA1821, CA1825-CA1834

Contributes to https://github.com/dotnet/aspnetcore/issues/24055

.editorconfig

@@ -91,9 +91,40 @@ dotnet_diagnostic.CA1802.severity = warning
 # CA1805: Do not initialize unnecessarily
 dotnet_diagnostic.CA1805.severity = warning
 
+# CA1823: Remove empty Finalizers
+dotnet_diagnostic.CA1821.severity = warning
+
 # CA1823: Avoid unused private fields
 dotnet_diagnostic.CA1823.severity = warning
 
+# CA1823: Avoid zero-length array allocations
+dotnet_diagnostic.CA1825.severity = warning
+
+# CA1826: Do not use Enumerable methods on indexable collections. Instead use the collection directly
+dotnet_diagnostic.CA1826.severity = warning
+
+# CA1827: Do not use Count() or LongCount() when Any() can be used
+dotnet_diagnostic.CA1827.severity = warning
+
+# CA1828: Do not use CountAsync() or LongCountAsync() when AnyAsync() can be used
+dotnet_diagnostic.CA1828.severity = warning
+
+# CA1829: Use Length/Count property instead of Count() when available
+dotnet_diagnostic.CA1829.severity = warning
+
+# CA1830: Prefer strongly-typed Append and Insert method overloads on StringBuilder
+dotnet_diagnostic.CA1830.severity = warning
+
+# CA1831: Use AsSpan or AsMemory instead of Range-based indexers when appropriate
+# CA1832: Use AsSpan or AsMemory instead of Range-based indexers when appropriate
+# CA1833: Use AsSpan or AsMemory instead of Range-based indexers when appropriate
+dotnet_diagnostic.CA1831.severity = warning
+dotnet_diagnostic.CA1832.severity = warning
+dotnet_diagnostic.CA1833.severity = warning
+
+# CA1834: Consider using 'StringBuilder.Append(char)' when applicable
+dotnet_diagnostic.CA1834.severity = warning
+
 # CA2012: Use ValueTask correctly
 dotnet_diagnostic.CA2012.severity = warning
 
@@ -110,5 +141,15 @@ dotnet_diagnostic.CA1507.severity = suggestion
 dotnet_diagnostic.CA1802.severity = suggestion
 # CA1805: Do not initialize unnecessarily
 dotnet_diagnostic.CA1805.severity = suggestion
+# CA1823: Avoid zero-length array allocations
+dotnet_diagnostic.CA1825.severity = suggestion
+# CA1826: Do not use Enumerable methods on indexable collections. Instead use the collection directly
+dotnet_diagnostic.CA1826.severity = suggestion
+# CA1827: Do not use Count() or LongCount() when Any() can be used
+dotnet_diagnostic.CA1827.severity = suggestion
+# CA1829: Use Length/Count property instead of Count() when available
+dotnet_diagnostic.CA1829.severity = suggestion
+# CA1834: Consider using 'StringBuilder.Append(char)' when applicable
+dotnet_diagnostic.CA1834.severity = suggestion
 # CA2012: Use ValueTask correctly
 dotnet_diagnostic.CA2012.severity = suggestion

eng/tools/BaselineGenerator/Program.cs

@@ -168,7 +168,7 @@ namespace PackageBaselineGenerator
                     foreach (var group in reader.NuspecReader.GetDependencyGroups())
                     {
                         // Don't bother generating empty ItemGroup elements.
-                        if (group.Packages.Count() == 0)
+                        if (!group.Packages.Any())
                         {
                             continue;
                         }

src/Components/Analyzers/test/Verifiers/DiagnosticVerifier.cs

@@ -109,7 +109,7 @@ namespace TestHelper
         /// <param name="expectedResults">Diagnostic Results that should have appeared in the code</param>
         private static void VerifyDiagnosticResults(IEnumerable<Diagnostic> actualResults, DiagnosticAnalyzer analyzer, params DiagnosticResult[] expectedResults)
         {
-            int expectedCount = expectedResults.Count();
+            int expectedCount = expectedResults.Length;
             int actualCount = actualResults.Count();
 
             if (expectedCount != actualCount)

src/Components/WebAssembly/WebAssembly/src/Services/WebAssemblyConsoleLogger.cs

@@ -119,9 +119,9 @@ namespace Microsoft.AspNetCore.Components.WebAssembly.Services
             logBuilder.Append(GetLogLevelString(logLevel));
             logBuilder.Append(_loglevelPadding);
             logBuilder.Append(logName);
-            logBuilder.Append("[");
+            logBuilder.Append('[');
             logBuilder.Append(eventId);
-            logBuilder.Append("]");
+            logBuilder.Append(']');
 
             if (!string.IsNullOrEmpty(message))
             {

src/Components/WebView/WebView/src/QueryString.cs

@@ -292,9 +292,9 @@ namespace Microsoft.AspNetCore.Components.WebView
 
         private static void AppendKeyValuePair(StringBuilder builder, string key, string? value, bool first)
         {
-            builder.Append(first ? "?" : "&");
+            builder.Append(first ? '?' : '&');
             builder.Append(UrlEncoder.Default.Encode(key));
-            builder.Append("=");
+            builder.Append('=');
             if (!string.IsNullOrEmpty(value))
             {
                 builder.Append(UrlEncoder.Default.Encode(value));

src/FileProviders/Embedded/src/Manifest/ManifestParser.cs

@@ -143,7 +143,7 @@ namespace Microsoft.Extensions.FileProviders.Embedded.Manifest
 
         private static string EnsureText(XElement element)
         {
-            if (element.Elements().Count() == 0 &&
+            if (!element.Elements().Any() &&
                 !element.IsEmpty &&
                 element.Nodes().Count() == 1 &&
                 element.FirstNode?.NodeType == XmlNodeType.Text)

src/Http/Headers/src/CookieHeaderValue.cs

@@ -94,7 +94,7 @@ namespace Microsoft.Net.Http.Headers
             var header = new StringBuilder();
 
             header.Append(_name.AsSpan());
-            header.Append("=");
+            header.Append('=');
             header.Append(_value.AsSpan());
 
             return header.ToString();

src/Http/Headers/src/SetCookieHeaderValue.cs

@@ -329,7 +329,7 @@ namespace Microsoft.Net.Http.Headers
         public void AppendToStringBuilder(StringBuilder builder)
         {
             builder.Append(_name.AsSpan());
-            builder.Append("=");
+            builder.Append('=');
             builder.Append(_value.AsSpan());
 
             if (Expires.HasValue)
@@ -388,7 +388,7 @@ namespace Microsoft.Net.Http.Headers
             builder.Append(name.AsSpan());
             if (value != null)
             {
-                builder.Append("=");
+                builder.Append('=');
                 builder.Append(value.AsSpan());
             }
         }

src/Http/Http.Abstractions/src/QueryString.cs

@@ -286,9 +286,9 @@ namespace Microsoft.AspNetCore.Http
 
         private static void AppendKeyValuePair(StringBuilder builder, string key, string? value, bool first)
         {
-            builder.Append(first ? "?" : "&");
+            builder.Append(first ? '?' : '&');
             builder.Append(UrlEncoder.Default.Encode(key));
-            builder.Append("=");
+            builder.Append('=');
             if (!string.IsNullOrEmpty(value))
             {
                 builder.Append(UrlEncoder.Default.Encode(value));

src/Http/Routing/src/DefaultLinkGenerator.cs

@@ -480,14 +480,14 @@ namespace Microsoft.AspNetCore.Routing
 
                 foreach (var kvp in values.OrderBy(kvp => kvp.Key))
                 {
-                    builder.Append("\"");
+                    builder.Append('"');
                     builder.Append(kvp.Key);
-                    builder.Append("\"");
-                    builder.Append(":");
-                    builder.Append(" ");
-                    builder.Append("\"");
+                    builder.Append('"');
+                    builder.Append(':');
+                    builder.Append(' ');
+                    builder.Append('"');
                     builder.Append(kvp.Value);
-                    builder.Append("\"");
+                    builder.Append('"');
                     builder.Append(", ");
                 }
 

src/Http/Routing/src/Patterns/RoutePatternParameterPart.cs

@@ -80,14 +80,14 @@ namespace Microsoft.AspNetCore.Routing.Patterns
         internal override string DebuggerToString()
         {
             var builder = new StringBuilder();
-            builder.Append("{");
+            builder.Append('{');
 
             if (IsCatchAll)
             {
-                builder.Append("*");
+                builder.Append('*');
                 if (!EncodeSlashes)
                 {
-                    builder.Append("*");
+                    builder.Append('*');
                 }
             }
 
@@ -95,22 +95,22 @@ namespace Microsoft.AspNetCore.Routing.Patterns
 
             foreach (var constraint in ParameterPolicies)
             {
-                builder.Append(":");
+                builder.Append(':');
                 builder.Append(constraint.ParameterPolicy);
             }
 
             if (Default != null)
             {
-                builder.Append("=");
+                builder.Append('=');
                 builder.Append(Default);
             }
 
             if (IsOptional)
             {
-                builder.Append("?");
+                builder.Append('?');
             }
 
-            builder.Append("}");
+            builder.Append('}');
             return builder.ToString();
         }
     }

src/Http/Routing/src/Tree/LinkGenerationDecisionTree.cs

@@ -248,7 +248,7 @@ namespace Microsoft.AspNetCore.Routing.Tree
                 {
                     matchesSb.Insert(0, branch);
                 }
-                sb.Append(matchesSb.ToString());
+                sb.Append(matchesSb);
                 sb.Append(" (Matches: ");
                 sb.AppendJoin(", ", node.Matches.Select(m => m.Entry.RouteTemplate.TemplateText));
                 sb.AppendLine(")");

src/Http/Routing/src/UriBuildingContext.cs

@@ -111,7 +111,7 @@ namespace Microsoft.AspNetCore.Routing
             {
                 if (_path.Length != 0)
                 {
-                    _path.Append("/");
+                    _path.Append('/');
                 }
             }
 
@@ -124,7 +124,7 @@ namespace Microsoft.AspNetCore.Routing
             // This prevents the leading slash from PathString segments from being encoded.
             if (_path.Length == 0 && value.Length > 0 && value[0] == '/')
             {
-                _path.Append("/");
+                _path.Append('/');
                 EncodeValue(value, 1, value.Length - 1, encodeSlashes);
             }
             else
@@ -305,7 +305,7 @@ namespace Microsoft.AspNetCore.Routing
                 while ((end = value.IndexOf('/', start, characterCount)) >= 0)
                 {
                     _urlEncoder.Encode(PathWriter, value, start, end - start);
-                    _path.Append("/");
+                    _path.Append('/');
 
                     start = end + 1;
                     characterCount = length - start;

src/Http/Routing/tools/Swaggatherer/SwaggathererApplication.cs

@@ -244,7 +244,7 @@ namespace Swaggatherer
                 // We don't yet handle complex segments
                 var part = template.Segments[i].Parts[0];
 
-                url.Append("/");
+                url.Append('/');
                 url.Append(part.IsLiteral ? part.Text : GenerateParameterValue(part));
             }
 

src/Identity/Extensions.Core/src/Base32.cs

@@ -46,7 +46,7 @@ namespace Microsoft.AspNetCore.Identity
             input = input.TrimEnd('=').ToUpperInvariant();
             if (input.Length == 0)
             {
-                return new byte[0];
+                return Array.Empty<byte>();
             }
 
             var output = new byte[input.Length * 5 / 8];

src/Identity/Specification.Tests/src/UserManagerSpecificationTests.cs

@@ -1826,7 +1826,7 @@ namespace Microsoft.AspNetCore.Identity.Test
             await manager.ConfirmEmailAsync(user, token);
             factors = await manager.GetValidTwoFactorProvidersAsync(user);
             Assert.NotNull(factors);
-            Assert.Equal(2, factors.Count());
+            Assert.Equal(2, factors.Count);
             IdentityResultAssert.IsSuccess(await manager.SetEmailAsync(user, null));
             factors = await manager.GetValidTwoFactorProvidersAsync(user);
             Assert.NotNull(factors);
@@ -1835,7 +1835,7 @@ namespace Microsoft.AspNetCore.Identity.Test
             IdentityResultAssert.IsSuccess(await manager.ResetAuthenticatorKeyAsync(user));
             factors = await manager.GetValidTwoFactorProvidersAsync(user);
             Assert.NotNull(factors);
-            Assert.Equal(2, factors.Count());
+            Assert.Equal(2, factors.Count);
             Assert.Equal("Authenticator", factors[1]);
         }
 

src/Identity/UI/src/Areas/Identity/Pages/V4/Account/Manage/EnableAuthenticator.cshtml.cs

@@ -182,12 +182,12 @@ namespace Microsoft.AspNetCore.Identity.UI.V4.Pages.Account.Manage.Internal
             int currentPosition = 0;
             while (currentPosition + 4 < unformattedKey.Length)
             {
-                result.Append(unformattedKey.Substring(currentPosition, 4)).Append(" ");
+                result.Append(unformattedKey.AsSpan(currentPosition, 4)).Append(' ');
                 currentPosition += 4;
             }
             if (currentPosition < unformattedKey.Length)
             {
-                result.Append(unformattedKey.Substring(currentPosition));
+                result.Append(unformattedKey.AsSpan(currentPosition));
             }
 
             return result.ToString().ToLowerInvariant();

src/Identity/test/InMemory.Test/InMemoryStore.cs

@@ -14,7 +14,7 @@ namespace Microsoft.AspNetCore.Identity.InMemory
     public class InMemoryStore<TUser, TRole> :
         InMemoryUserStore<TUser>,
         IUserRoleStore<TUser>,
-        IQueryableRoleStore<TRole>, 
+        IQueryableRoleStore<TRole>,
         IRoleClaimStore<TRole>
         where TRole : PocoRole
         where TUser : PocoUser
@@ -72,7 +72,7 @@ namespace Microsoft.AspNetCore.Identity.InMemory
             {
                 return Task.FromResult<IList<TUser>>(new List<TUser>());
             }
-            return Task.FromResult<IList<TUser>>(Users.Where(u => (u.Roles.Where(x => x.RoleId == role.Id).Count() > 0)).Select(x => x).ToList());
+            return Task.FromResult<IList<TUser>>(Users.Where(u => (u.Roles.Where(x => x.RoleId == role.Id).Any())).Select(x => x).ToList());
         }
 
         private readonly Dictionary<string, TRole> _roles = new Dictionary<string, TRole>();

src/Middleware/CORS/src/Infrastructure/CorsPolicy.cs

@@ -161,16 +161,16 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
             builder.Append(SupportsCredentials);
             builder.Append(", Origins: {");
             builder.AppendJoin(",", Origins);
-            builder.Append("}");
+            builder.Append('}');
             builder.Append(", Methods: {");
             builder.AppendJoin(",", Methods);
-            builder.Append("}");
+            builder.Append('}');
             builder.Append(", Headers: {");
             builder.AppendJoin(",", Headers);
-            builder.Append("}");
+            builder.Append('}');
             builder.Append(", ExposedHeaders: {");
             builder.AppendJoin(",", ExposedHeaders);
-            builder.Append("}");
+            builder.Append('}');
             return builder.ToString();
         }
 

src/Middleware/CORS/src/Infrastructure/CorsResult.cs

@@ -93,13 +93,13 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
             builder.Append(AllowedOrigin);
             builder.Append(", AllowExposedHeaders: {");
             builder.AppendJoin(",", AllowedExposedHeaders);
-            builder.Append("}");
+            builder.Append('}');
             builder.Append(", AllowHeaders: {");
             builder.AppendJoin(",", AllowedHeaders);
-            builder.Append("}");
+            builder.Append('}');
             builder.Append(", AllowMethods: {");
             builder.AppendJoin(",", AllowedMethods);
-            builder.Append("}");
+            builder.Append('}');
             return builder.ToString();
         }
     }

src/Middleware/Diagnostics.EntityFrameworkCore/src/DatabaseErrorPageMiddleware.cs

@@ -113,7 +113,7 @@ namespace Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore
                         var contextType = _localDiagnostic.Value!.ContextType;
                         var details = await httpContext.GetContextDetailsAsync(contextType!, _logger);
 
-                        if (details != null && (details.PendingModelChanges || details.PendingMigrations.Count() > 0))
+                        if (details != null && (details.PendingModelChanges || details.PendingMigrations.Any()))
                         {
                             var page = new DatabaseErrorPage
                             {

src/Middleware/HealthChecks.EntityFrameworkCore/test/DbContextHealthCheckTest.cs

@@ -39,7 +39,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
             // Arrange
             var services = CreateServices(async (c, ct) =>
             {
-                return 0 < await c.Blogs.CountAsync();
+                return await c.Blogs.AnyAsync();
             });
 
             using (var scope = services.GetRequiredService<IServiceScopeFactory>().CreateScope())
@@ -66,7 +66,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
             // Arrange
             var services = CreateServices(async (c, ct) =>
             {
-                return 0 < await c.Blogs.CountAsync();
+                return await c.Blogs.AnyAsync();
             }, failureStatus: HealthStatus.Degraded);
 
             using (var scope = services.GetRequiredService<IServiceScopeFactory>().CreateScope())
@@ -88,7 +88,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
             // Arrange
             var services = CreateServices(async (c, ct) =>
             {
-                return 0 < await c.Blogs.CountAsync();
+                return await c.Blogs.AnyAsync();
             }, failureStatus: HealthStatus.Unhealthy);
 
             using (var scope = services.GetRequiredService<IServiceScopeFactory>().CreateScope())
@@ -110,7 +110,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
             // Arrange
             var services = CreateServices(async (c, ct) =>
             {
-                return 0 < await c.Blogs.CountAsync();
+                return await c.Blogs.AnyAsync();
             }, failureStatus: null);
 
             using (var scope = services.GetRequiredService<IServiceScopeFactory>().CreateScope())

src/Middleware/Session/src/NoOpSessionStore.cs

@@ -21,7 +21,7 @@ namespace Microsoft.AspNetCore.Session
 
         public ICollection<EncodedKey> Keys { get; } = Array.Empty<EncodedKey>();
 
-        public ICollection<byte[]> Values { get; } = new byte[0][];
+        public ICollection<byte[]> Values { get; } = Array.Empty<byte[]>();
 
         public void Clear() { }
 

src/Mvc/Mvc.Abstractions/src/ModelBinding/ValueProviderResult.cs

@@ -32,7 +32,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// A <see cref="ValueProviderResult"/> that represents a lack of data.
         /// </summary>
-        public static ValueProviderResult None = new ValueProviderResult(new string[0]);
+        public static ValueProviderResult None = new ValueProviderResult(Array.Empty<string>());
 
         /// <summary>
         /// Creates a new <see cref="ValueProviderResult"/> using <see cref="CultureInfo.InvariantCulture"/>.

src/Mvc/Mvc.Core/src/MvcCoreLoggerExtensions.cs

@@ -766,7 +766,7 @@ namespace Microsoft.AspNetCore.Mvc
                 var routeKeys = action.RouteValues.Keys.ToArray();
                 var routeValues = action.RouteValues.Values.ToArray();
                 var stringBuilder = new StringBuilder();
-                stringBuilder.Append("{");
+                stringBuilder.Append('{');
                 for (var i = 0; i < routeValues.Length; i++)
                 {
                     if (i == routeValues.Length - 1)
@@ -778,7 +778,7 @@ namespace Microsoft.AspNetCore.Mvc
                         stringBuilder.Append($"{routeKeys[i]} = \"{routeValues[i]}\", ");
                     }
                 }
-                stringBuilder.Append("}");
+                stringBuilder.Append('}');
 
                 if (action.RouteValues.TryGetValue("page", out var page) && page != null)
                 {

src/Mvc/Mvc.TagHelpers/src/Cache/CacheTagKey.cs

@@ -306,7 +306,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Cache
             builder
                 .Append(CacheKeyTokenSeparator)
                 .Append(collectionName)
-                .Append("(");
+                .Append('(');
 
             for (var i = 0; i < values.Count; i++)
             {
@@ -323,7 +323,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Cache
                     .Append(item.Value);
             }
 
-            builder.Append(")");
+            builder.Append(')');
         }
 
         private static void CombineCollectionHashCode(

src/Razor/Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X/src/ViewComponentTagHelperTargetExtension.cs

@@ -170,9 +170,9 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X
 
         private void WriteTargetElementString(CodeWriter writer, TagHelperDescriptor tagHelper)
         {
-            Debug.Assert(tagHelper.TagMatchingRules.Count() == 1);
+            Debug.Assert(tagHelper.TagMatchingRules.Count == 1);
 
-            var rule = tagHelper.TagMatchingRules.First();
+            var rule = tagHelper.TagMatchingRules[0];
 
             writer.Write("[")
                 .WriteStartMethodInvocation(HtmlTargetElementAttributeTypeName)

src/Razor/Microsoft.AspNetCore.Mvc.Razor.Extensions.Version2_X/src/ViewComponentTagHelperTargetExtension.cs

@@ -170,9 +170,9 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions.Version2_X
 
         private void WriteTargetElementString(CodeWriter writer, TagHelperDescriptor tagHelper)
         {
-            Debug.Assert(tagHelper.TagMatchingRules.Count() == 1);
+            Debug.Assert(tagHelper.TagMatchingRules.Count == 1);
 
-            var rule = tagHelper.TagMatchingRules.First();
+            var rule = tagHelper.TagMatchingRules[0];
 
             writer.Write("[")
                 .WriteStartMethodInvocation(HtmlTargetElementAttributeTypeName)

src/Razor/Microsoft.AspNetCore.Mvc.Razor.Extensions/src/ViewComponentTagHelperTargetExtension.cs

@@ -170,9 +170,9 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions
 
         private void WriteTargetElementString(CodeWriter writer, TagHelperDescriptor tagHelper)
         {
-            Debug.Assert(tagHelper.TagMatchingRules.Count() == 1);
+            Debug.Assert(tagHelper.TagMatchingRules.Count == 1);
 
-            var rule = tagHelper.TagMatchingRules.First();
+            var rule = tagHelper.TagMatchingRules[0];
 
             writer.Write("[")
                 .WriteStartMethodInvocation(HtmlTargetElementAttributeTypeName)

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentBindLoweringPass.cs

@@ -775,7 +775,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
 
         private static IntermediateToken GetAttributeContent(IntermediateNode node)
         {
-            var template = node.FindDescendantNodes<TemplateIntermediateNode>().FirstOrDefault();
+            var nodes = node.FindDescendantNodes<TemplateIntermediateNode>();
+            var template = nodes.Count > 0 ? nodes[0] : default;
             if (template != null)
             {
                 // See comments in TemplateDiagnosticPass

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentEventHandlerLoweringPass.cs

@@ -242,7 +242,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
 
         private static IReadOnlyList<IntermediateToken> GetAttributeContent(IntermediateNode node)
         {
-            var template = node.FindDescendantNodes<TemplateIntermediateNode>().FirstOrDefault();
+            var nodes = node.FindDescendantNodes<TemplateIntermediateNode>();
+            var template = nodes.Count > 0 ? nodes[0] : default;
             if (template != null)
             {
                 // See comments in TemplateDiagnosticPass

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentMarkupBlockPass.cs

@@ -219,7 +219,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
                     // Treat node with errors as non-HTML
                     _foundNonHtml = true;
                 }
-                
+
                 // Visit Children
                 base.VisitDefault(node);
 
@@ -277,7 +277,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
                 var isVoid = Legacy.ParserHelpers.VoidElements.Contains(node.TagName);
                 var hasBodyContent = node.Body.Any();
 
-                Builder.Append("<");
+                Builder.Append('<');
                 Builder.Append(node.TagName);
 
                 foreach (var attribute in node.Attributes)
@@ -290,7 +290,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
                 if (!hasBodyContent && isVoid)
                 {
                     // void
-                    Builder.Append(">");
+                    Builder.Append('>');
                     return;
                 }
                 else if (!hasBodyContent)
@@ -299,12 +299,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
                     // add a close tag
                     Builder.Append("></");
                     Builder.Append(node.TagName);
-                    Builder.Append(">");
+                    Builder.Append('>');
                     return;
                 }
 
                 // start/end tag with body.
-                Builder.Append(">");
+                Builder.Append('>');
 
                 foreach (var item in node.Body)
                 {
@@ -313,12 +313,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
 
                 Builder.Append("</");
                 Builder.Append(node.TagName);
-                Builder.Append(">");
+                Builder.Append('>');
             }
 
             public override void VisitHtmlAttribute(HtmlAttributeIntermediateNode node)
             {
-                Builder.Append(" ");
+                Builder.Append(' ');
                 Builder.Append(node.AttributeName);
 
                 if (node.Children.Count == 0)
@@ -332,7 +332,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
                 // Visit Children
                 base.VisitDefault(node);
 
-                Builder.Append("\"");
+                Builder.Append('"');
             }
 
             public override void VisitHtmlAttributeValue(HtmlAttributeValueIntermediateNode node)

src/Razor/Microsoft.AspNetCore.Razor.Language/src/DefaultRazorIntermediateNodeLoweringPhase.cs

@@ -347,7 +347,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                     _builder.Add(new DirectiveTokenIntermediateNode()
                     {
                         Content = addTagHelperChunkGenerator.LookupText,
-                        DirectiveToken = CSharpCodeParser.AddTagHelperDirectiveDescriptor.Tokens.First(),
+                        DirectiveToken = CSharpCodeParser.AddTagHelperDirectiveDescriptor.Tokens[0],
                         Source = BuildSourceSpanFromNode(node),
                     });
 
@@ -385,7 +385,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                     _builder.Add(new DirectiveTokenIntermediateNode()
                     {
                         Content = removeTagHelperChunkGenerator.LookupText,
-                        DirectiveToken = CSharpCodeParser.RemoveTagHelperDirectiveDescriptor.Tokens.First(),
+                        DirectiveToken = CSharpCodeParser.RemoveTagHelperDirectiveDescriptor.Tokens[0],
                         Source = BuildSourceSpanFromNode(node),
                     });
 
@@ -423,7 +423,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                     _builder.Add(new DirectiveTokenIntermediateNode()
                     {
                         Content = tagHelperPrefixChunkGenerator.Prefix,
-                        DirectiveToken = CSharpCodeParser.TagHelperPrefixDirectiveDescriptor.Tokens.First(),
+                        DirectiveToken = CSharpCodeParser.TagHelperPrefixDirectiveDescriptor.Tokens[0],
                         Source = BuildSourceSpanFromNode(node),
                     });
 
@@ -1019,7 +1019,8 @@ namespace Microsoft.AspNetCore.Razor.Language
 
                 IReadOnlyList<SyntaxNode> children = node.ChildNodes();
                 var position = node.Position;
-                if (children.FirstOrDefault() is MarkupBlockSyntax markupBlock &&
+                if (children.Count > 0 &&
+                    children[0] is MarkupBlockSyntax markupBlock &&
                     markupBlock.Children.Count == 2 &&
                     markupBlock.Children[0] is MarkupTextLiteralSyntax &&
                     markupBlock.Children[1] is MarkupEphemeralTextLiteralSyntax)
@@ -1970,7 +1971,8 @@ namespace Microsoft.AspNetCore.Razor.Language
 
                 IReadOnlyList<SyntaxNode> children = node.ChildNodes();
                 var position = node.Position;
-                if (children.FirstOrDefault() is MarkupBlockSyntax markupBlock &&
+                if (children.Count > 0 &&
+                    children[0] is MarkupBlockSyntax markupBlock &&
                     markupBlock.Children.Count == 2 &&
                     markupBlock.Children[0] is MarkupTextLiteralSyntax &&
                     markupBlock.Children[1] is MarkupEphemeralTextLiteralSyntax)

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Intermediate/MethodDeclarationIntermediateNode.cs

@@ -46,11 +46,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Intermediate
             for (var i = 0; i <parameter.Modifiers.Count; i++)
             {
                 builder.Append(parameter.Modifiers[i]);
-                builder.Append(" ");
+                builder.Append(' ');
             }
 
             builder.Append(parameter.TypeName);
-            builder.Append(" ");
+            builder.Append(' ');
 
             builder.Append(parameter.ParameterName);
 

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/AddTagHelperChunkGenerator.cs

@@ -64,20 +64,20 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             var builder = new StringBuilder("AddTagHelper:{");
             builder.Append(LookupText);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(DirectiveText);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(TypePattern);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(AssemblyName);
-            builder.Append("}");
+            builder.Append('}');
 
             if (Diagnostics.Count > 0)
             {
                 builder.Append(" [");
                 var ids = string.Join(", ", Diagnostics.Select(diagnostic => $"{diagnostic.Id}{diagnostic.Span}"));
                 builder.Append(ids);
-                builder.Append("]");
+                builder.Append(']');
             }
 
             return builder.ToString();

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/CSharpCodeParser.cs

@@ -46,10 +46,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 builder.Description = Resources.TagHelperPrefixDirective_Description;
             });
 
-        internal static readonly IEnumerable<DirectiveDescriptor> DefaultDirectiveDescriptors = new DirectiveDescriptor[]
-        {
-        };
-
         internal static ISet<string> DefaultKeywords = new HashSet<string>()
         {
             SyntaxConstants.CSharp.TagHelperPrefixKeyword,
@@ -912,11 +908,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void SetupDirectiveParsers(IEnumerable<DirectiveDescriptor> directiveDescriptors)
         {
-            var allDirectives = directiveDescriptors.Concat(DefaultDirectiveDescriptors).ToList();
-
-            for (var i = 0; i < allDirectives.Count; i++)
+            foreach (var directiveDescriptor in directiveDescriptors)
             {
-                var directiveDescriptor = allDirectives[i];
                 CurrentKeywords.Add(directiveDescriptor.Directive);
                 MapDirectives((builder, transition) => ParseExtensibleDirective(builder, transition, directiveDescriptor), directiveDescriptor.Directive);
             }

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/DirectiveTokenChunkGenerator.cs

@@ -38,11 +38,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             var builder = new StringBuilder("DirectiveToken {");
             builder.Append(Descriptor.Name);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(Descriptor.Kind);
             builder.Append(";Opt:");
             builder.Append(Descriptor.Optional);
-            builder.Append("}");
+            builder.Append('}');
 
             return builder.ToString();
         }

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/RemoveTagHelperChunkGenerator.cs

@@ -64,20 +64,20 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             var builder = new StringBuilder("RemoveTagHelper:{");
             builder.Append(LookupText);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(DirectiveText);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(TypePattern);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(AssemblyName);
-            builder.Append("}");
+            builder.Append('}');
 
             if (Diagnostics.Count > 0)
             {
                 builder.Append(" [");
                 var ids = string.Join(", ", Diagnostics.Select(diagnostic => $"{diagnostic.Id}{diagnostic.Span}"));
                 builder.Append(ids);
-                builder.Append("]");
+                builder.Append(']');
             }
 
             return builder.ToString();

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/TagHelperParseTreeRewriter.cs

@@ -49,7 +49,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             // Internal for testing.
             // Null characters are invalid markup for HTML attribute values.
-            internal const string InvalidAttributeValueMarker = "\0";
+            internal const char InvalidAttributeValueMarker = '\0';
 
             private readonly RazorSourceDocument _source;
             private readonly string _tagHelperPrefix;
@@ -759,7 +759,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     {
                         if (AllowedChildren != null && _prefixedAllowedChildren == null)
                         {
-                            Debug.Assert(Info.BindingResult.Descriptors.Count() >= 1);
+                            Debug.Assert(Info.BindingResult.Descriptors.Any());
 
                             _prefixedAllowedChildren = AllowedChildren.Select(allowedChild => _tagHelperPrefix + allowedChild).ToList();
                         }

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/TagHelperPrefixDirectiveChunkGenerator.cs

@@ -49,19 +49,19 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             var builder = new StringBuilder("TagHelperPrefix:{");
             builder.Append(Prefix);
-            builder.Append(";");
+            builder.Append(';');
             builder.Append(DirectiveText);
-            builder.Append("}");
+            builder.Append('}');
 
             if (Diagnostics.Count > 0)
             {
                 builder.Append(" [");
                 var ids = string.Join(", ", Diagnostics.Select(diagnostic => $"{diagnostic.Id}{diagnostic.Span}"));
                 builder.Append(ids);
-                builder.Append("]");
+                builder.Append(']');
             }
 
             return builder.ToString();
         }
     }
-}
+}

src/Razor/Microsoft.AspNetCore.Razor.Language/src/RazorDiagnostic.cs

@@ -7,8 +7,8 @@ namespace Microsoft.AspNetCore.Razor.Language
 {
     public abstract class RazorDiagnostic : IEquatable<RazorDiagnostic>, IFormattable
     {
-        internal static readonly RazorDiagnostic[] EmptyArray = new RazorDiagnostic[0];
-        internal static readonly object[] EmptyArgs = new object[0];
+        internal static readonly RazorDiagnostic[] EmptyArray = Array.Empty<RazorDiagnostic>();
+        internal static readonly object[] EmptyArgs = Array.Empty<object>();
 
         public abstract string Id { get; }
 

src/Razor/Microsoft.AspNetCore.Razor.Language/src/RazorSourceDocument.cs

@@ -15,7 +15,7 @@ namespace Microsoft.AspNetCore.Razor.Language
     {
         internal const int LargeObjectHeapLimitInChars = 40 * 1024; // 40K Unicode chars is 80KB which is less than the large object heap limit.
 
-        internal static readonly RazorSourceDocument[] EmptyArray = new RazorSourceDocument[0];
+        internal static readonly RazorSourceDocument[] EmptyArray = Array.Empty<RazorSourceDocument>();
 
         /// <summary>
         /// Gets the encoding of the text in the original source document.

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Syntax/SyntaxSerializer.cs

@@ -197,11 +197,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Syntax
 
                 var builder = new StringBuilder("Directive:{");
                 builder.Append(node.DirectiveDescriptor.Directive);
-                builder.Append(";");
+                builder.Append(';');
                 builder.Append(node.DirectiveDescriptor.Kind);
-                builder.Append(";");
+                builder.Append(';');
                 builder.Append(node.DirectiveDescriptor.Usage);
-                builder.Append("}");
+                builder.Append('}');
 
                 var diagnostics = node.GetDiagnostics();
                 if (diagnostics.Length > 0)
@@ -209,7 +209,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Syntax
                     builder.Append(" [");
                     var ids = string.Join(", ", diagnostics.Select(diagnostic => $"{diagnostic.Id}{diagnostic.Span}"));
                     builder.Append(ids);
-                    builder.Append("]");
+                    builder.Append(']');
                 }
 
                 WriteSeparator();

src/Razor/Microsoft.AspNetCore.Razor.Language/test/DefaultRazorTagHelperBinderPhaseTest.cs

@@ -344,7 +344,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
             var formTagHelper = Assert.Single(tagHelperNodes);
             Assert.Equal("form", formTagHelper.TagHelperInfo.TagName);
-            Assert.Equal(2, formTagHelper.TagHelperInfo.BindingResult.Mappings[descriptor].Count());
+            Assert.Equal(2, formTagHelper.TagHelperInfo.BindingResult.Mappings[descriptor].Count);
         }
 
         [Fact]
@@ -398,7 +398,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
             var formTagHelper = Assert.Single(tagHelperNodes);
             Assert.Equal("form", formTagHelper.TagHelperInfo.TagName);
-            Assert.Equal(2, formTagHelper.TagHelperInfo.BindingResult.Mappings[descriptor].Count());
+            Assert.Equal(2, formTagHelper.TagHelperInfo.BindingResult.Mappings[descriptor].Count);
         }
 
         [Fact]
@@ -653,7 +653,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                     },
                     {
                         $@"
-@tagHelperPrefix 
+@tagHelperPrefix
 @addTagHelper Microsoft.AspNetCore.Razor.TagHelpers.ValidPlain*, {AssemblyA}
 @addTagHelper Microsoft.AspNetCore.Razor.TagHelpers.ValidInherited*, {AssemblyA}",
                         null
@@ -858,7 +858,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             visitor.Visit(syntaxTree.Root);
 
             // Assert
-            Assert.Equal(expected.Count(), visitor.Matches.Count());
+            Assert.Equal(expected.Length, visitor.Matches.Count);
 
             foreach (var expectedDescriptor in expected)
             {

src/Razor/Microsoft.AspNetCore.Razor.Language/test/Legacy/TagHelperParseTreeRewriterTest.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Func<string, string, KeyValuePair<string, string>> kvp =
                     (key, value) => new KeyValuePair<string, string>(key, value);
                 var empty = Enumerable.Empty<KeyValuePair<string, string>>();
-                var csharp = TagHelperParseTreeRewriter.Rewriter.InvalidAttributeValueMarker;
+                var csharp = TagHelperParseTreeRewriter.Rewriter.InvalidAttributeValueMarker.ToString();
 
                 // documentContent, expectedPairs
                 return new TheoryData<string, IEnumerable<KeyValuePair<string, string>>>

src/Razor/Microsoft.AspNetCore.Razor.Language/test/TagHelperDescriptorComparerTest.cs

@@ -134,7 +134,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             var hashes = new HashSet<int>(tagHelpers.Select(t => t.GetHashCode()));
 
             // Assert
-            Assert.Equal(hashes.Count(), tagHelpers.Count);
+            Assert.Equal(hashes.Count, tagHelpers.Count);
         }
 
         [Fact]
@@ -158,7 +158,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
             // Assert
             // Only 1 batch of taghelpers should remain after we filter by hash
-            Assert.Equal(hashes.Count(), tagHelpersPerBatch);
+            Assert.Equal(hashes.Count, tagHelpersPerBatch);
         }
 
         private static TagHelperDescriptor CreateTagHelperDescriptor(

src/Razor/Microsoft.CodeAnalysis.Razor/src/ComponentTagHelperDescriptorProvider.cs

@@ -288,7 +288,7 @@ namespace Microsoft.CodeAnalysis.Razor
             builder.TagMatchingRule(r =>
             {
                 r.TagName = attribute.Name;
-                r.ParentTag = component.TagMatchingRules.First().TagName;
+                r.ParentTag = component.TagMatchingRules[0].TagName;
             });
 
             if (attribute.IsParameterizedChildContentProperty())

src/Razor/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/SyntaxNodeWriter.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;

src/Razor/tools/RazorSyntaxGenerator/SourceWriter.cs

@@ -2087,7 +2087,7 @@ namespace RazorSyntaxGenerator
 
             var minimalFactoryfields = new HashSet<Field>(DetermineMinimalFactoryFields(nd));
 
-            if (withStringNames && minimalFactoryfields.Count(f => IsRequiredFactoryField(nd, f) && CanAutoConvertFromString(f)) == 0)
+            if (withStringNames && !minimalFactoryfields.Any(f => IsRequiredFactoryField(nd, f) && CanAutoConvertFromString(f)))
                 return; // no string-name overload necessary
 
             WriteLine();

src/Security/Authentication/Negotiate/src/Internal/ReflectedNegotiateState.cs

@@ -36,7 +36,7 @@ namespace Microsoft.AspNetCore.Authentication.Negotiate
             var ntAuthType = secAssembly.GetType("System.Net.NTAuthentication", throwOnError: true)!;
             _constructor = ntAuthType.GetConstructors(BindingFlags.NonPublic | BindingFlags.Instance).First();
             _getOutgoingBlob = ntAuthType.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance).Where(info =>
-                info.Name.Equals("GetOutgoingBlob") && info.GetParameters().Count() == 3).Single();
+                info.Name.Equals("GetOutgoingBlob") && info.GetParameters().Length == 3).Single();
             _isCompleted = ntAuthType.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance).Where(info =>
                 info.Name.Equals("get_IsCompleted")).Single();
             _protocol = ntAuthType.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance).Where(info =>

src/Security/Authentication/test/CertificateTests.cs

@@ -285,7 +285,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             var response = await server.CreateClient().GetAsync("https://example.com/");
             Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
         }
-        
+
         [Fact]
         public async Task VerifyValidationFailureCanBeHandled()
         {
@@ -489,7 +489,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.SubjectName.Name))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.X500DistinguishedName);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.SubjectName.Name, actual.First().Value);
@@ -499,7 +499,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.SerialNumber))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.SerialNumber);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.SerialNumber, actual.First().Value);
@@ -509,7 +509,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.DnsName, false)))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.Dns);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.DnsName, false), actual.First().Value);
@@ -519,7 +519,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.EmailName, false)))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.Email);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.EmailName, false), actual.First().Value);
@@ -529,7 +529,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.SimpleName, false)))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.Name);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.SimpleName, false), actual.First().Value);
@@ -539,7 +539,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.UpnName, false)))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.Upn);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.UpnName, false), actual.First().Value);
@@ -549,7 +549,7 @@ namespace Microsoft.AspNetCore.Authentication.Certificate.Test
             if (!string.IsNullOrEmpty(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.UrlName, false)))
             {
                 actual = responseAsXml.Elements("claim").Where(claim => claim.Attribute("Type").Value == ClaimTypes.Uri);
-                if (actual.Count() > 0)
+                if (actual.Any())
                 {
                     Assert.Single(actual);
                     Assert.Equal(Certificates.SelfSignedValidWithNoEku.GetNameInfo(X509NameType.UrlName, false), actual.First().Value);

src/Servers/HttpSys/src/RequestProcessing/ResponseBody.cs

@@ -210,7 +210,7 @@ namespace Microsoft.AspNetCore.Server.HttpSys
             else if (!hasData && !addTrailers)
             {
                 // No data
-                dataChunks = new HttpApiTypes.HTTP_DATA_CHUNK[0];
+                dataChunks = Array.Empty<HttpApiTypes.HTTP_DATA_CHUNK>();
                 return pins;
             }
 

src/Servers/Kestrel/Core/src/Middleware/Internal/LoggingStream.cs

@@ -148,9 +148,9 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
 
             var builder = new StringBuilder();
             builder.Append(method);
-            builder.Append("[");
+            builder.Append('[');
             builder.Append(buffer.Length);
-            builder.Append("]");
+            builder.Append(']');
 
             if (buffer.Length > 0)
             {
@@ -163,12 +163,12 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
             for (int i = 0; i < buffer.Length; i++)
             {
                 builder.Append(buffer[i].ToString("X2", CultureInfo.InvariantCulture));
-                builder.Append(" ");
+                builder.Append(' ');
 
                 var bufferChar = (char)buffer[i];
                 if (char.IsControl(bufferChar))
                 {
-                    charBuilder.Append(".");
+                    charBuilder.Append('.');
                 }
                 else
                 {
@@ -178,7 +178,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
                 if ((i + 1) % 16 == 0)
                 {
                     builder.Append("  ");
-                    builder.Append(charBuilder.ToString());
+                    builder.Append(charBuilder);
                     if (i != buffer.Length - 1)
                     {
                         builder.AppendLine();
@@ -187,8 +187,8 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
                 }
                 else if ((i + 1) % 8 == 0)
                 {
-                    builder.Append(" ");
-                    charBuilder.Append(" ");
+                    builder.Append(' ');
+                    charBuilder.Append(' ');
                 }
             }
 
@@ -206,7 +206,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Core.Internal
                 }
 
                 builder.Append(new string(' ', padLength));
-                builder.Append(charBuilder.ToString());
+                builder.Append(charBuilder);
             }
 
             _logger.LogDebug(builder.ToString());

src/Servers/Kestrel/shared/KnownHeaders.cs

@@ -350,7 +350,7 @@ namespace CodeGenerator
 
         static string AppendSwitchSection(int length, IList<KnownHeader> values)
         {
-            var useVarForFirstTerm = values.Count() > 1 && values.Select(h => h.FirstNameIgnoreCaseSegment()).Distinct().Count() == 1;
+            var useVarForFirstTerm = values.Count > 1 && values.Select(h => h.FirstNameIgnoreCaseSegment()).Distinct().Count() == 1;
             var firstTermVarExpression = values.Select(h => h.FirstNameIgnoreCaseSegment()).FirstOrDefault();
             var firstTermVar = $"firstTerm{length}";
 
@@ -1188,7 +1188,7 @@ $@"        private void Clear(long bitsToClear)
                                 return;
                             }}")}
                         }}
-                        {(hi.Index + 1 < loop.Headers.Count() ? $"goto case {hi.Index + 1};" : "return;")}")}
+                        {(hi.Index + 1 < loop.Headers.Length ? $"goto case {hi.Index + 1};" : "return;")}")}
                     default:
                         return;
                 }}
@@ -1272,7 +1272,7 @@ $@"        private void Clear(long bitsToClear)
                 {{{Each(loop.Headers.Where(header => header.Identifier != "ContentLength"), header => $@"
                     case {header.Index}:
                         goto Header{header.Identifier};")}
-                    {(!loop.ClassName.Contains("Trailers") ? $@"case {loop.Headers.Count() - 1}:
+                    {(!loop.ClassName.Contains("Trailers") ? $@"case {loop.Headers.Length - 1}:
                         goto HeaderContentLength;" : "")}
                     default:
                         goto ExtraHeaders;
@@ -1286,12 +1286,12 @@ $@"        private void Clear(long bitsToClear)
                         ")}_next = {header.Index + 1};
                         return true;
                     }}")}
-                {(!loop.ClassName.Contains("Trailers") ? $@"HeaderContentLength: // case {loop.Headers.Count() - 1}
+                {(!loop.ClassName.Contains("Trailers") ? $@"HeaderContentLength: // case {loop.Headers.Length - 1}
                     if (_collection._contentLength.HasValue)
                     {{
                         _current = new KeyValuePair<string, StringValues>(HeaderNames.ContentLength, HeaderUtilities.FormatNonNegativeInt64(_collection._contentLength.Value));
                         {(loop.ClassName.Contains("Request") ? "" : @"_currentKnownType = KnownHeaderType.ContentLength;
-                        ")}_next = {loop.Headers.Count()};
+                        ")}_next = {loop.Headers.Length};
                         return true;
                     }}" : "")}
                 ExtraHeaders:

src/Shared/Http2cat/Http2Utilities.cs

@@ -119,7 +119,7 @@ namespace Microsoft.AspNetCore.Http2Cat
         public static readonly byte[] _helloBytes = Encoding.ASCII.GetBytes("hello");
         public static readonly byte[] _worldBytes = Encoding.ASCII.GetBytes("world");
         public static readonly byte[] _helloWorldBytes = Encoding.ASCII.GetBytes("hello, world");
-        public static readonly byte[] _noData = new byte[0];
+        public static readonly byte[] _noData = Array.Empty<byte>();
         public static readonly byte[] _maxData = Encoding.ASCII.GetBytes(new string('a', Http2PeerSettings.MinAllowedMaxFrameSize));
 
         internal readonly Http2PeerSettings _clientSettings = new Http2PeerSettings();

src/Shared/HttpSys/NativeInterop/SocketAddress.cs

@@ -28,7 +28,7 @@ namespace Microsoft.AspNetCore.HttpSys.Internal
         private const int NumberOfIPv6Labels = 8;
         // Lower case hex, no leading zeros
         private const string IPv6NumberFormat = "{0:x}";
-        private const string IPv6StringSeparator = ":";
+        private const char IPv6StringSeparator = ':';
         private const string IPv4StringFormat = "{0:d}.{1:d}.{2:d}.{3:d}";
 
         internal const int IPv6AddressSize = 28;
@@ -206,7 +206,7 @@ namespace Microsoft.AspNetCore.HttpSys.Internal
             {
                 if (i > WriteableOffset)
                 {
-                    bytes.Append(",");
+                    bytes.Append(',');
                 }
                 bytes.Append(this[i].ToString(NumberFormatInfo.InvariantInfo));
             }

src/Shared/HttpSys/RequestProcessing/HeaderParser.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using Microsoft.Extensions.Primitives;
 
@@ -8,7 +9,7 @@ namespace Microsoft.AspNetCore.HttpSys.Internal
 {
     internal static class HeaderParser
     {
-        internal static IEnumerable<string> Empty = new string[0];
+        internal static IEnumerable<string> Empty = Array.Empty<string>();
 
         // Split on commas, except in quotes
         internal static IEnumerable<string> SplitValues(StringValues values)

src/Shared/StackTrace/StackFrame/MethodDisplayInfo.cs

@@ -37,19 +37,19 @@ namespace Microsoft.Extensions.StackTrace.Sources
             {
                 builder
                     .Append(DeclaringTypeName)
-                    .Append(".");
+                    .Append('.');
             }
 
             builder.Append(Name);
             builder.Append(GenericArguments);
 
-            builder.Append("(");
+            builder.Append('(');
             builder.AppendJoin(", ", Parameters.Select(p => p.ToString()));
-            builder.Append(")");
+            builder.Append(')');
 
             if (!string.IsNullOrEmpty(SubMethod))
             {
-                builder.Append("+");
+                builder.Append('+');
                 builder.Append(SubMethod);
                 builder.Append("()");
             }

src/Shared/StackTrace/StackFrame/ParameterDisplayInfo.cs

@@ -21,11 +21,11 @@ namespace Microsoft.Extensions.StackTrace.Sources
             {
                 builder
                     .Append(Prefix)
-                    .Append(" ");
+                    .Append(' ');
             }
 
             builder.Append(Type);
-            builder.Append(" ");
+            builder.Append(' ');
             builder.Append(Name);
 
             return builder.ToString();

src/SignalR/server/SignalR/test/HubConnectionHandlerTests.cs

@@ -4338,8 +4338,8 @@ namespace Microsoft.AspNetCore.SignalR.Tests
                     var messages = await messagePromise;
 
                     // add one because this includes the completion
-                    Assert.Equal(phrases.Count() + 1, messages.Count);
-                    for (var i = 0; i < phrases.Count(); i++)
+                    Assert.Equal(phrases.Length + 1, messages.Count);
+                    for (var i = 0; i < phrases.Length; i++)
                     {
                         Assert.Equal("echo:" + phrases[i], ((StreamItemMessage)messages[i]).Item);
                     }

src/Tools/Shared/TestHelpers/TemporaryCSharpProject.cs

@@ -75,7 +75,7 @@ namespace Microsoft.Extensions.Tools.Internal
         public TemporaryCSharpProject WithItem(ItemSpec item)
         {
             var sb = new StringBuilder("<");
-            sb.Append(item.Name).Append(" ");
+            sb.Append(item.Name).Append(' ');
             if (item.Include != null) sb.Append(" Include=\"").Append(item.Include).Append('"');
             if (item.Remove != null) sb.Append(" Remove=\"").Append(item.Remove).Append('"');
             if (item.Update != null) sb.Append(" Update=\"").Append(item.Update).Append('"');