Sprinkle some more readonly around (dotnet#81297)

* Sprinkle some more readonly around

* Revert a few changes / address feedback

src/libraries/Common/src/System/Data/ProviderBase/DbMetaDataFactory.cs

@@ -10,7 +10,7 @@ namespace System.Data.ProviderBase
 {
     internal class DbMetaDataFactory
     {
-        private DataSet _metaDataCollectionsDataSet;
+        private readonly DataSet _metaDataCollectionsDataSet;
         private string _normalizedServerVersion;
         private string _serverVersionString;
         // well known column names

src/libraries/Common/src/System/Net/DebugSafeHandleMinusOneIsInvalid.cs

@@ -12,7 +12,7 @@ namespace System.Net
     //
     internal abstract class DebugSafeHandleMinusOneIsInvalid : SafeHandleMinusOneIsInvalid
     {
-        private string _trace;
+        private readonly string _trace;
 
         protected DebugSafeHandleMinusOneIsInvalid(bool ownsHandle) : base(ownsHandle)
         {

src/libraries/Common/src/System/Net/DebugSafeHandleZeroOrMinusOneIsInvalid.cs

@@ -12,7 +12,7 @@ namespace System.Net
     //
     internal abstract class DebugSafeHandleZeroOrMinusOneIsInvalid : SafeHandleZeroOrMinusOneIsInvalid
     {
-        private string _trace;
+        private readonly string _trace;
 
         protected DebugSafeHandleZeroOrMinusOneIsInvalid(bool ownsHandle) : base(ownsHandle)
         {

src/libraries/Common/src/System/Net/NetworkInformation/HostInformationPal.Windows.cs

@@ -21,7 +21,7 @@ internal static class HostInformationPal
         private static bool s_enableDns;
 
         private static volatile bool s_initialized;
-        private static object s_syncObject = new object();
+        private static readonly object s_syncObject = new object();
 
         public static string GetHostName()
         {

src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationExtensions.cs

@@ -11,8 +11,8 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public static class FileConfigurationExtensions
     {
-        private static string FileProviderKey = "FileProvider";
-        private static string FileLoadExceptionHandlerKey = "FileLoadExceptionHandler";
+        private const string FileProviderKey = "FileProvider";
+        private const string FileLoadExceptionHandlerKey = "FileLoadExceptionHandler";
 
         /// <summary>
         /// Sets the default <see cref="IFileProvider"/> to be used for file-based providers.

src/libraries/Microsoft.Extensions.Configuration/src/ConfigurationReloadToken.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public class ConfigurationReloadToken : IChangeToken
     {
-        private CancellationTokenSource _cts = new CancellationTokenSource();
+        private readonly CancellationTokenSource _cts = new CancellationTokenSource();
 
         /// <summary>
         /// Indicates if this token will proactively raise callbacks. Callbacks are still guaranteed to be invoked, eventually.

src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs

@@ -25,7 +25,7 @@ public sealed class ServiceProvider : IServiceProvider, IDisposable, IAsyncDispo
 
         private bool _disposed;
 
-        private ConcurrentDictionary<Type, Func<ServiceProviderEngineScope, object?>> _realizedServices;
+        private readonly ConcurrentDictionary<Type, Func<ServiceProviderEngineScope, object?>> _realizedServices;
 
         internal CallSiteFactory CallSiteFactory { get; }
 

src/libraries/Microsoft.Extensions.DependencyModel/src/Resolution/AppBaseCompilationAssemblyResolver.cs

@@ -10,7 +10,7 @@ namespace Microsoft.Extensions.DependencyModel.Resolution
 {
     public class AppBaseCompilationAssemblyResolver : ICompilationAssemblyResolver
     {
-        private static string RefsDirectoryName = "refs";
+        private const string RefsDirectoryName = "refs";
         private readonly IFileSystem _fileSystem;
         private readonly string _basePath;
         private readonly DependencyContextPaths _dependencyContextPaths;

src/libraries/Microsoft.Extensions.DependencyModel/src/RuntimeAssetGroup.cs

@@ -8,8 +8,8 @@ namespace Microsoft.Extensions.DependencyModel
 {
     public class RuntimeAssetGroup
     {
-        private IReadOnlyList<string>? _assetPaths;
-        private IReadOnlyList<RuntimeFile>? _runtimeFiles;
+        private readonly IReadOnlyList<string>? _assetPaths;
+        private readonly IReadOnlyList<RuntimeFile>? _runtimeFiles;
 
         public RuntimeAssetGroup(string? runtime, params string[] assetPaths) : this(runtime, (IEnumerable<string>)assetPaths) { }
 

src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PhysicalFilesWatcher.cs

@@ -41,7 +41,7 @@ public class PhysicalFilesWatcher : IDisposable
         private Timer? _timer;
         private bool _timerInitialized;
         private object _timerLock = new();
-        private Func<Timer> _timerFactory;
+        private readonly Func<Timer> _timerFactory;
         private bool _disposed;
 
         /// <summary>

src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Internal/InMemoryFileInfo.cs

@@ -8,7 +8,7 @@ namespace Microsoft.Extensions.FileSystemGlobbing.Internal
 {
     internal sealed class InMemoryFileInfo : FileInfoBase
     {
-        private InMemoryDirectoryInfo _parent;
+        private readonly InMemoryDirectoryInfo _parent;
 
         public InMemoryFileInfo(string file, InMemoryDirectoryInfo parent)
         {

src/libraries/Microsoft.Extensions.FileSystemGlobbing/src/Internal/PatternContexts/PatternContext.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Extensions.FileSystemGlobbing.Internal.PatternContexts
 {
     public abstract class PatternContext<TFrame> : IPatternContext where TFrame : struct
     {
-        private Stack<TFrame> _stack = new();
+        private readonly Stack<TFrame> _stack = new();
         protected TFrame Frame;
 
         public virtual void Declare(Action<IPathSegment, bool> declare) { }

src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs

@@ -25,10 +25,10 @@ public partial class HostBuilder : IHostBuilder
         private const string HostBuildingEventName = "HostBuilding";
         private const string HostBuiltEventName = "HostBuilt";
 
-        private List<Action<IConfigurationBuilder>> _configureHostConfigActions = new List<Action<IConfigurationBuilder>>();
-        private List<Action<HostBuilderContext, IConfigurationBuilder>> _configureAppConfigActions = new List<Action<HostBuilderContext, IConfigurationBuilder>>();
-        private List<Action<HostBuilderContext, IServiceCollection>> _configureServicesActions = new List<Action<HostBuilderContext, IServiceCollection>>();
-        private List<IConfigureContainerAdapter> _configureContainerActions = new List<IConfigureContainerAdapter>();
+        private readonly List<Action<IConfigurationBuilder>> _configureHostConfigActions = new List<Action<IConfigurationBuilder>>();
+        private readonly List<Action<HostBuilderContext, IConfigurationBuilder>> _configureAppConfigActions = new List<Action<HostBuilderContext, IConfigurationBuilder>>();
+        private readonly List<Action<HostBuilderContext, IServiceCollection>> _configureServicesActions = new List<Action<HostBuilderContext, IServiceCollection>>();
+        private readonly List<IConfigureContainerAdapter> _configureContainerActions = new List<IConfigureContainerAdapter>();
         private IServiceFactoryAdapter _serviceProviderFactory;
         private bool _hostBuilt;
         private IConfiguration? _hostConfiguration;

src/libraries/Microsoft.Extensions.Hosting/src/Internal/ConfigureContainerAdapter.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Extensions.Hosting.Internal
 {
     internal sealed class ConfigureContainerAdapter<TContainerBuilder> : IConfigureContainerAdapter
     {
-        private Action<HostBuilderContext, TContainerBuilder> _action;
+        private readonly Action<HostBuilderContext, TContainerBuilder> _action;
 
         public ConfigureContainerAdapter(Action<HostBuilderContext, TContainerBuilder> action)
         {

src/libraries/Microsoft.Extensions.Hosting/src/Internal/ServiceFactoryAdapter.cs

@@ -11,7 +11,7 @@ internal sealed class ServiceFactoryAdapter<TContainerBuilder> : IServiceFactory
     {
         private IServiceProviderFactory<TContainerBuilder>? _serviceProviderFactory;
         private readonly Func<HostBuilderContext>? _contextResolver;
-        private Func<HostBuilderContext, IServiceProviderFactory<TContainerBuilder>>? _factoryResolver;
+        private readonly Func<HostBuilderContext, IServiceProviderFactory<TContainerBuilder>>? _factoryResolver;
 
         public ServiceFactoryAdapter(IServiceProviderFactory<TContainerBuilder> serviceProviderFactory)
         {

src/libraries/Microsoft.Extensions.Http/src/Logging/LoggingHttpMessageHandler.cs

@@ -15,7 +15,7 @@ namespace Microsoft.Extensions.Http.Logging
     /// </summary>
     public class LoggingHttpMessageHandler : DelegatingHandler
     {
-        private ILogger _logger;
+        private readonly ILogger _logger;
         private readonly HttpClientFactoryOptions? _options;
 
         private static readonly Func<string, bool> _shouldNotRedactHeaderValue = (header) => false;

src/libraries/Microsoft.Extensions.Http/src/Logging/LoggingScopeHttpMessageHandler.cs

@@ -15,7 +15,7 @@ namespace Microsoft.Extensions.Http.Logging
     /// </summary>
     public class LoggingScopeHttpMessageHandler : DelegatingHandler
     {
-        private ILogger _logger;
+        private readonly ILogger _logger;
         private readonly HttpClientFactoryOptions? _options;
 
         private static readonly Func<string, bool> _shouldNotRedactHeaderValue = (header) => false;

src/libraries/Microsoft.Extensions.Http/src/ValueStopwatch.cs

@@ -8,9 +8,9 @@ namespace Microsoft.Extensions.Internal
 {
     internal struct ValueStopwatch
     {
-        private static readonly double TimestampToTicks = TimeSpan.TicksPerSecond / (double)Stopwatch.Frequency;
+        private static readonly double s_timestampToTicks = TimeSpan.TicksPerSecond / (double)Stopwatch.Frequency;
 
-        private long _startTimestamp;
+        private readonly long _startTimestamp;
 
         public bool IsActive => _startTimestamp != 0;
 
@@ -32,7 +32,7 @@ public TimeSpan GetElapsedTime()
 
             long end = Stopwatch.GetTimestamp();
             long timestampDelta = end - _startTimestamp;
-            long ticks = (long)(TimestampToTicks * timestampDelta);
+            long ticks = (long)(s_timestampToTicks * timestampDelta);
             return new TimeSpan(ticks);
         }
     }

src/libraries/Microsoft.Extensions.Logging.Abstractions/src/FormattedLogValues.cs

@@ -17,8 +17,10 @@ namespace Microsoft.Extensions.Logging
     {
         internal const int MaxCachedFormatters = 1024;
         private const string NullFormat = "[null]";
-        private static int _count;
-        private static ConcurrentDictionary<string, LogValuesFormatter> _formatters = new ConcurrentDictionary<string, LogValuesFormatter>();
+
+        private static int s_count;
+        private static readonly ConcurrentDictionary<string, LogValuesFormatter> s_formatters = new ConcurrentDictionary<string, LogValuesFormatter>();
+
         private readonly LogValuesFormatter? _formatter;
         private readonly object?[]? _values;
         private readonly string _originalMessage;
@@ -30,18 +32,18 @@ public FormattedLogValues(string? format, params object?[]? values)
         {
             if (values != null && values.Length != 0 && format != null)
             {
-                if (_count >= MaxCachedFormatters)
+                if (s_count >= MaxCachedFormatters)
                 {
-                    if (!_formatters.TryGetValue(format, out _formatter))
+                    if (!s_formatters.TryGetValue(format, out _formatter))
                     {
                         _formatter = new LogValuesFormatter(format);
                     }
                 }
                 else
                 {
-                    _formatter = _formatters.GetOrAdd(format, f =>
+                    _formatter = s_formatters.GetOrAdd(format, f =>
                     {
-                        Interlocked.Increment(ref _count);
+                        Interlocked.Increment(ref s_count);
                         return new LogValuesFormatter(f);
                     });
                 }

src/libraries/Microsoft.Extensions.Logging.Console/src/ConsoleLoggerProvider.cs

@@ -23,7 +23,7 @@ public class ConsoleLoggerProvider : ILoggerProvider, ISupportExternalScope
         private ConcurrentDictionary<string, ConsoleFormatter> _formatters;
         private readonly ConsoleLoggerProcessor _messageQueue;
 
-        private IDisposable? _optionsReloadToken;
+        private readonly IDisposable? _optionsReloadToken;
         private IExternalScopeProvider _scopeProvider = NullExternalScopeProvider.Instance;
 
         /// <summary>

src/libraries/Microsoft.Extensions.Logging.Console/src/FormatterOptionsMonitor.cs

@@ -11,7 +11,8 @@ internal sealed class FormatterOptionsMonitor<[DynamicallyAccessedMembers(Dynami
         IOptionsMonitor<TOptions>
         where TOptions : ConsoleFormatterOptions
     {
-        private TOptions _options;
+        private readonly TOptions _options;
+
         public FormatterOptionsMonitor(TOptions options)
         {
             _options = options;

src/libraries/Microsoft.Extensions.Logging.Console/src/JsonConsoleFormatter.cs

@@ -16,7 +16,7 @@ namespace Microsoft.Extensions.Logging.Console
 {
     internal sealed class JsonConsoleFormatter : ConsoleFormatter, IDisposable
     {
-        private IDisposable? _optionsReloadToken;
+        private readonly IDisposable? _optionsReloadToken;
 
         public JsonConsoleFormatter(IOptionsMonitor<JsonConsoleFormatterOptions> options)
             : base(ConsoleFormatterNames.Json)

src/libraries/Microsoft.Extensions.Logging.Console/src/SimpleConsoleFormatter.cs

@@ -22,7 +22,7 @@ internal sealed class SimpleConsoleFormatter : ConsoleFormatter, IDisposable
 #else
         private static bool IsAndroidOrAppleMobile => false;
 #endif
-        private IDisposable? _optionsReloadToken;
+        private readonly IDisposable? _optionsReloadToken;
 
         public SimpleConsoleFormatter(IOptionsMonitor<SimpleConsoleFormatterOptions> options)
             : base(ConsoleFormatterNames.Simple)

src/libraries/Microsoft.Extensions.Logging.Console/src/SystemdConsoleFormatter.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Extensions.Logging.Console
 {
     internal sealed class SystemdConsoleFormatter : ConsoleFormatter, IDisposable
     {
-        private IDisposable? _optionsReloadToken;
+        private readonly IDisposable? _optionsReloadToken;
 
         public SystemdConsoleFormatter(IOptionsMonitor<ConsoleFormatterOptions> options)
             : base(ConsoleFormatterNames.Systemd)

src/libraries/Microsoft.Extensions.Logging/src/LoggerFactory.cs

@@ -18,10 +18,10 @@ public class LoggerFactory : ILoggerFactory
         private readonly List<ProviderRegistration> _providerRegistrations = new List<ProviderRegistration>();
         private readonly object _sync = new object();
         private volatile bool _disposed;
-        private IDisposable? _changeTokenRegistration;
+        private readonly IDisposable? _changeTokenRegistration;
         private LoggerFilterOptions _filterOptions;
         private IExternalScopeProvider? _scopeProvider;
-        private LoggerFactoryOptions _factoryOptions;
+        private readonly LoggerFactoryOptions _factoryOptions;
 
         /// <summary>
         /// Creates a new <see cref="LoggerFactory"/> instance.

src/libraries/Microsoft.Extensions.Logging/src/LoggerFactoryScopeProvider.cs

@@ -132,7 +132,7 @@ private sealed class ActivityLogScope : IReadOnlyList<KeyValuePair<string, objec
         {
             private string? _cachedToString;
             private const int MaxItems = 5;
-            private KeyValuePair<string, object?>[] _items = new KeyValuePair<string, object?>[MaxItems];
+            private readonly KeyValuePair<string, object?>[] _items = new KeyValuePair<string, object?>[MaxItems];
 
             public ActivityLogScope(Activity activity, ActivityTrackingOptions activityTrackingOption)
             {

src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/src/ConfigurationChangeTokenSource.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Extensions.Options
     /// <typeparam name="TOptions"></typeparam>
     public class ConfigurationChangeTokenSource<TOptions> : IOptionsChangeTokenSource<TOptions>
     {
-        private IConfiguration _config;
+        private readonly IConfiguration _config;
 
         /// <summary>
         /// Constructor taking the <see cref="IConfiguration"/> instance to watch.

src/libraries/Microsoft.NETCore.Platforms/src/GenerateRuntimeGraph.cs

@@ -395,7 +395,7 @@ private static bool CompatibilityMapEquals(IDictionary<string, IEnumerable<strin
             return true;
         }
 
-        private static XNamespace s_dgmlns = @"http://schemas.microsoft.com/vs/2009/dgml";
+        private static readonly XNamespace s_dgmlns = @"http://schemas.microsoft.com/vs/2009/dgml";
         private static void WriteRuntimeGraph(RuntimeGraph graph, string dependencyGraphFilePath)
         {
 

src/libraries/Microsoft.NETCore.Platforms/src/RuntimeGroupCollection.cs

@@ -12,9 +12,9 @@ namespace Microsoft.NETCore.Platforms.BuildTasks
 {
     public class RuntimeGroupCollection
     {
-        private ICollection<RuntimeGroup> allRuntimeGroups;
-        private Dictionary<string, List<RuntimeGroup>> runtimeGroupsByBaseRID;
-        private HashSet<RID> knownRIDs;
+        private readonly ICollection<RuntimeGroup> allRuntimeGroups;
+        private readonly Dictionary<string, List<RuntimeGroup>> runtimeGroupsByBaseRID;
+        private readonly HashSet<RID> knownRIDs;
 
         public RuntimeGroupCollection(ICollection<RuntimeGroup> runtimeGroups)
         {

src/libraries/Microsoft.NETCore.Platforms/src/RuntimeVersion.cs

@@ -11,9 +11,9 @@ namespace Microsoft.NETCore.Platforms.BuildTasks
     /// </summary>
     public sealed class RuntimeVersion : IComparable, IComparable<RuntimeVersion>, IEquatable<RuntimeVersion>
     {
-        private string versionString;
-        private Version version;
-        private bool hasMinor;
+        private readonly string versionString;
+        private readonly Version version;
+        private readonly bool hasMinor;
 
         public RuntimeVersion(string versionString)
         {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/DesigntimeLicenseContextSerializer.cs

@@ -62,9 +62,10 @@ private static void SerializeWithBinaryFormatter(Stream o, string cryptoKey, Des
 
         private sealed class StreamWrapper : Stream
         {
-            private Stream _stream;
+            private readonly Stream _stream;
             private bool _readFirstByte;
             internal byte _firstByte;
+
             public StreamWrapper(Stream stream)
             {
                 _stream = stream;

src/libraries/System.Configuration.ConfigurationManager/src/System/Diagnostics/FilterElement.cs

@@ -7,7 +7,7 @@ namespace System.Diagnostics
 {
     internal sealed class FilterElement : TypedElement
     {
-        private static ConditionalWeakTable<TraceFilter, string> s_initData = new();
+        private static readonly ConditionalWeakTable<TraceFilter, string> s_initData = new();
 
         public FilterElement() : base(typeof(TraceFilter)) { }
 

src/libraries/System.Configuration.ConfigurationManager/src/System/Diagnostics/ListenerElementsCollection.cs

@@ -82,12 +82,12 @@ internal sealed class ListenerElement : TypedElement
         private static readonly ConfigurationProperty s_propName = new("name", typeof(string), null, ConfigurationPropertyOptions.IsRequired | ConfigurationPropertyOptions.IsKey);
         private static readonly ConfigurationProperty s_propOutputOpts = new("traceOutputOptions", typeof(TraceOptions), TraceOptions.None, ConfigurationPropertyOptions.None);
 
-        private ConfigurationProperty _propListenerTypeName;
-        private bool _allowReferences;
+        private readonly ConfigurationProperty _propListenerTypeName;
+        private readonly bool _allowReferences;
         private StringDictionary _attributes;
         internal bool _isAddedByDefault;
 
-        private static ConditionalWeakTable<TraceListener, string> s_initData = new();
+        private static readonly ConditionalWeakTable<TraceListener, string> s_initData = new();
 
         public ListenerElement(bool allowReferences) : base(typeof(TraceListener))
         {

src/libraries/System.Configuration.ConfigurationManager/src/System/Diagnostics/TypedElement.cs

@@ -9,9 +9,9 @@ internal class TypedElement : ConfigurationElement
         protected static readonly ConfigurationProperty s_propTypeName = new("type", typeof(string), string.Empty, ConfigurationPropertyOptions.IsRequired | ConfigurationPropertyOptions.IsTypeStringTransformationRequired);
         protected static readonly ConfigurationProperty s_propInitData = new("initializeData", typeof(string), string.Empty, ConfigurationPropertyOptions.None);
 
-        protected ConfigurationPropertyCollection _properties;
+        protected readonly ConfigurationPropertyCollection _properties;
         protected object _runtimeObject;
-        private Type _baseType;
+        private readonly Type _baseType;
 
         public TypedElement(Type baseType) : base()
         {

src/libraries/System.Data.Common/src/System/Data/TypeLimiter.cs

@@ -16,7 +16,7 @@ internal sealed class TypeLimiter
         [ThreadStatic]
         private static Scope? s_activeScope;
 
-        private Scope m_instanceScope;
+        private readonly Scope m_instanceScope;
 
         private const string AppDomainDataSetDefaultAllowedTypesKey = "System.Data.DataSetDefaultAllowedTypes";
 
@@ -183,7 +183,7 @@ private sealed class Scope : IDisposable
             /// <summary>
             /// Types which are allowed within the context of this scope.
             /// </summary>
-            private HashSet<Type> m_allowedTypes;
+            private readonly HashSet<Type> m_allowedTypes;
 
             /// <summary>
             /// This thread's previous scope.