Seal internal types in libraries (dotnet#50225)

docs/coding-guidelines/coding-style.md

@@ -23,7 +23,7 @@ The general rule we follow is "use Visual Studio defaults".
    Consider enabling "View White Space (Ctrl+R, Ctrl+W)" or "Edit -> Advanced -> View White Space" if using Visual Studio to aid detection.
 9. If a file happens to differ in style from these guidelines (e.g. private members are named `m_member`
    rather than `_member`), the existing style in that file takes precedence.
-10. We only use `var` when it's obvious what the variable type is (e.g. `var stream = new FileStream(...)` not `var stream = OpenStandardInput()`).
+10. We only use `var` when the type is explicitly named on the right-hand side, typically due to either `new` or an explicit cast, e.g. `var stream = new FileStream(...)` not `var stream = OpenStandardInput()`.
 11. We use language keywords instead of BCL types (e.g. `int, string, float` instead of `Int32, String, Single`, etc) for both type references as well as method calls (e.g. `int.Parse` instead of `Int32.Parse`). See issue [#13976](https://github.com/dotnet/runtime/issues/13976) for examples.
 12. We use PascalCasing to name all our constant local variables and fields. The only exception is for interop code where the constant value should exactly match the name and value of the code you are calling via interop.
 13. We use PascalCasing for all method names, including local functions.
@@ -35,6 +35,7 @@ The general rule we follow is "use Visual Studio defaults".
     - Never use single-line form (for example: `if (source == null) throw new ArgumentNullException("source");`)
     - Using braces is always accepted, and required if any block of an `if`/`else if`/.../`else` compound statement uses braces or if a single statement body spans multiple lines.
     - Braces may be omitted only if the body of *every* block associated with an `if`/`else if`/.../`else` compound statement is placed on a single line.
+19. Make all internal and private types static or sealed unless derivation from them is required.  As with any implementation detail, they can be changed if/when derivation is required in the future.
 
 An [EditorConfig](https://editorconfig.org "EditorConfig homepage") file (`.editorconfig`) has been provided at the root of the runtime repository, enabling C# auto-formatting conforming to the above guidelines.
 

src/coreclr/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.CoreCLR.cs

@@ -13,7 +13,7 @@ internal interface IArraySortHelper<TKey>
     }
 
     [TypeDependency("System.Collections.Generic.GenericArraySortHelper`1")]
-    internal partial class ArraySortHelper<T>
+    internal sealed partial class ArraySortHelper<T>
         : IArraySortHelper<T>
     {
         private static readonly IArraySortHelper<T> s_defaultArraySortHelper = CreateArraySortHelper();
@@ -37,7 +37,7 @@ private static IArraySortHelper<T> CreateArraySortHelper()
         }
     }
 
-    internal partial class GenericArraySortHelper<T>
+    internal sealed partial class GenericArraySortHelper<T>
         : IArraySortHelper<T>
     {
     }
@@ -48,7 +48,7 @@ internal interface IArraySortHelper<TKey, TValue>
     }
 
     [TypeDependency("System.Collections.Generic.GenericArraySortHelper`2")]
-    internal partial class ArraySortHelper<TKey, TValue>
+    internal sealed partial class ArraySortHelper<TKey, TValue>
         : IArraySortHelper<TKey, TValue>
     {
         private static readonly IArraySortHelper<TKey, TValue> s_defaultArraySortHelper = CreateArraySortHelper();
@@ -72,7 +72,7 @@ private static IArraySortHelper<TKey, TValue> CreateArraySortHelper()
         }
     }
 
-    internal partial class GenericArraySortHelper<TKey, TValue>
+    internal sealed partial class GenericArraySortHelper<TKey, TValue>
         : IArraySortHelper<TKey, TValue>
     {
     }

src/coreclr/System.Private.CoreLib/src/System/Resources/ManifestBasedResourceGroveler.CoreCLR.cs

@@ -6,7 +6,7 @@
 
 namespace System.Resources
 {
-    internal partial class ManifestBasedResourceGroveler
+    internal sealed partial class ManifestBasedResourceGroveler
     {
         // Internal version of GetSatelliteAssembly that avoids throwing FileNotFoundException
         private static Assembly? InternalGetSatelliteAssembly(Assembly mainAssembly,

src/coreclr/System.Private.CoreLib/src/System/Threading/Timer.CoreCLR.cs

@@ -8,7 +8,7 @@
 
 namespace System.Threading
 {
-    internal partial class TimerQueue
+    internal sealed partial class TimerQueue
     {
         #region interface to native per-AppDomain timer
 

src/libraries/Common/src/Extensions/EmptyDisposable.cs

@@ -5,7 +5,7 @@
 
 namespace Microsoft.Extensions.FileProviders
 {
-    internal class EmptyDisposable : IDisposable
+    internal sealed class EmptyDisposable : IDisposable
     {
         public static EmptyDisposable Instance { get; } = new EmptyDisposable();
 

src/libraries/Common/src/Extensions/Logging/NullExternalScopeProvider.cs

@@ -10,7 +10,7 @@ namespace Microsoft.Extensions.Logging
     /// <summary>
     /// Scope provider that does nothing.
     /// </summary>
-    internal class NullExternalScopeProvider : IExternalScopeProvider
+    internal sealed class NullExternalScopeProvider : IExternalScopeProvider
     {
         private NullExternalScopeProvider()
         {

src/libraries/Common/src/Extensions/Logging/NullScope.cs

@@ -8,7 +8,7 @@ namespace Microsoft.Extensions.Logging
     /// <summary>
     /// An empty scope without any logic
     /// </summary>
-    internal class NullScope : IDisposable
+    internal sealed class NullScope : IDisposable
     {
         public static NullScope Instance { get; } = new NullScope();
 

src/libraries/Common/src/Interop/Android/System.Security.Cryptography.Native.Android/Interop.Ssl.cs

@@ -12,7 +12,7 @@ internal static partial class AndroidCrypto
         [DllImport(Interop.Libraries.CryptoNative, EntryPoint = "AndroidCryptoNative_SSLStreamRelease")]
         internal static extern void SSLStreamRelease(IntPtr ptr);
 
-        internal class SslException : Exception
+        internal sealed class SslException : Exception
         {
             internal SslException()
             {

src/libraries/Common/src/Interop/Interop.Ldap.cs

@@ -15,7 +15,7 @@ internal static partial class Interop
 namespace System.DirectoryServices.Protocols
 {
     [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-    internal class Luid
+    internal sealed class Luid
     {
         private readonly int _lowPart;
         private readonly int _highPart;

src/libraries/Common/src/Interop/Linux/OpenLdap/Interop.Ldap.cs

@@ -27,7 +27,7 @@ internal struct SaslDefaultCredentials
     /// where we will have to resolve the result.
     /// </summary>
     [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
-    internal class SaslInteractiveChallenge
+    internal sealed class SaslInteractiveChallenge
     {
         public ulong saslChallengeType;
         public string challenge;

src/libraries/Common/src/Interop/OSX/Interop.CoreFoundation.CFProxy.cs

@@ -45,7 +45,7 @@ internal struct CFStreamClientContext
             public IntPtr CopyDescription;
         }
 
-        internal class CFProxy
+        internal sealed class CFProxy
         {
             private SafeCFDictionaryHandle _dictionary;
 

src/libraries/Common/src/Interop/OSX/System.Security.Cryptography.Native.Apple/Interop.SslErr.cs

@@ -7,7 +7,7 @@ internal static partial class Interop
 {
     internal static partial class AppleCrypto
     {
-        internal class SslException : Exception
+        internal sealed class SslException : Exception
         {
             internal SslException()
             {

src/libraries/Common/src/Interop/Windows/Advapi32/Interop.ENUM_SERVICE_STATUS.cs

@@ -8,7 +8,7 @@ internal static partial class Interop
     internal static partial class Advapi32
     {
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-        internal class ENUM_SERVICE_STATUS
+        internal sealed class ENUM_SERVICE_STATUS
         {
             internal string? serviceName;
             internal string? displayName;

src/libraries/Common/src/Interop/Windows/Advapi32/Interop.ENUM_SERVICE_STATUS_PROCESS.cs

@@ -8,7 +8,7 @@ internal static partial class Interop
     internal static partial class Advapi32
     {
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-        internal class ENUM_SERVICE_STATUS_PROCESS
+        internal sealed class ENUM_SERVICE_STATUS_PROCESS
         {
             internal string? serviceName;
             internal string? displayName;

src/libraries/Common/src/Interop/Windows/CryptUI/Interop.CryptUIDlgCertificate.cs

@@ -10,7 +10,7 @@ internal static partial class Interop
     internal static partial class CryptUI
     {
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-        internal class CRYPTUI_VIEWCERTIFICATE_STRUCTW
+        internal sealed class CRYPTUI_VIEWCERTIFICATE_STRUCTW
         {
             internal uint dwSize;
             internal IntPtr hwndParent;
@@ -33,7 +33,7 @@ internal class CRYPTUI_VIEWCERTIFICATE_STRUCTW
         }
 
         [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-        internal class CRYPTUI_SELECTCERTIFICATE_STRUCTW
+        internal sealed class CRYPTUI_SELECTCERTIFICATE_STRUCTW
         {
             internal uint dwSize;
             internal IntPtr hwndParent;

src/libraries/Common/src/Interop/Windows/SspiCli/SecurityPackageInfoClass.cs

@@ -7,7 +7,7 @@
 namespace System.Net
 {
     // _SecPkgInfoW in sspi.h.
-    internal class SecurityPackageInfoClass
+    internal sealed class SecurityPackageInfoClass
     {
         internal int Capabilities;
         internal short Version;

src/libraries/Common/src/Interop/Windows/WinMm/Interop.MMCKINFO.cs

@@ -8,7 +8,7 @@ internal static partial class Interop
     internal static partial class WinMM
     {
         [StructLayout(LayoutKind.Sequential)]
-        internal class MMCKINFO
+        internal sealed class MMCKINFO
         {
             internal int ckID;
             internal int cksize;

src/libraries/Common/src/Interop/Windows/WinMm/Interop.mmioRead.cs

@@ -9,7 +9,7 @@ internal static partial class Interop
     internal static partial class WinMM
     {
         [StructLayout(LayoutKind.Sequential)]
-        internal class WAVEFORMATEX
+        internal sealed class WAVEFORMATEX
         {
             internal short wFormatTag;
             internal short nChannels;

src/libraries/Common/src/System/CodeDom/CodeTypeReference.cs

@@ -25,7 +25,7 @@ internal enum CodeTypeReferenceOptions
 #if !FEATURE_SERIALIZATION
     public class CodeTypeReference : CodeObject
 #else
-    internal class CodeTypeReference : CodeObject
+    internal sealed class CodeTypeReference : CodeObject
 #endif
     {
         private string? _baseType;

src/libraries/Common/src/System/CodeDom/CodeTypeReferenceCollection.cs

@@ -12,7 +12,7 @@ namespace System.Runtime.Serialization
 #if !FEATURE_SERIALIZATION
     public class CodeTypeReferenceCollection : CollectionBase
 #else
-    internal class CodeTypeReferenceCollection : CollectionBase
+    internal sealed class CodeTypeReferenceCollection : CollectionBase
 #endif
     {
         public CodeTypeReferenceCollection() { }

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

@@ -5,7 +5,7 @@ namespace System.Data.Common
 {
     // DbConnectionPoolKey: Base class implementation of a key to connection pool groups
     //  Only connection string is used as a key
-    internal class DbConnectionPoolKey : ICloneable
+    internal sealed class DbConnectionPoolKey : ICloneable
     {
         private string? _connectionString;
 
@@ -14,17 +14,17 @@ internal DbConnectionPoolKey(string? connectionString)
             _connectionString = connectionString;
         }
 
-        protected DbConnectionPoolKey(DbConnectionPoolKey key)
+        private DbConnectionPoolKey(DbConnectionPoolKey key)
         {
             _connectionString = key.ConnectionString;
         }
 
-        public virtual object Clone()
+        public object Clone()
         {
             return new DbConnectionPoolKey(this);
         }
 
-        internal virtual string? ConnectionString
+        internal string? ConnectionString
         {
             get
             {

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

@@ -18,7 +18,7 @@ namespace System.Data.ProviderBase
     //   Get remaining time in appropriate format to pass to subsystem timeouts
     //   Check for timeout via IsExpired for checks in managed code.
     //   Simply abandon to GC when done.
-    internal class TimeoutTimer
+    internal sealed class TimeoutTimer
     {
         //-------------------
         // Fields

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

@@ -5,7 +5,7 @@
 
 namespace System.Net
 {
-    internal class CaseInsensitiveAscii : IEqualityComparer, IComparer
+    internal sealed class CaseInsensitiveAscii : IEqualityComparer, IComparer
     {
         // ASCII char ToLower table
         internal static readonly CaseInsensitiveAscii StaticInstance = new CaseInsensitiveAscii();

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

@@ -18,7 +18,7 @@ namespace System.Net
     //
     // For now the state is not included as part of the closure.  It is too common a pattern (for example with socket receive)
     // to have several pending IOs differentiated by their state object.  We don't want that pattern to break the cache.
-    internal class CallbackClosure
+    internal sealed class CallbackClosure
     {
         private readonly AsyncCallback? _savedCallback;
         private readonly ExecutionContext? _savedContext;

src/libraries/Common/src/System/Net/Http/WinInetProxyHelper.cs

@@ -10,7 +10,7 @@ namespace System.Net.Http
 {
     // This class is only used on OS versions where WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY
     // is not supported (i.e. before Win8.1/Win2K12R2) in the WinHttpOpen() function.
-    internal class WinInetProxyHelper
+    internal sealed class WinInetProxyHelper
     {
         private const int RecentAutoDetectionInterval = 120_000; // 2 minutes in milliseconds.
         private readonly string? _autoConfigUrl, _proxy, _proxyBypass;

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/DynamicTable.cs

@@ -3,7 +3,7 @@
 
 namespace System.Net.Http.HPack
 {
-    internal class DynamicTable
+    internal sealed class DynamicTable
     {
         private HeaderField[] _buffer;
         private int _maxSize;

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackDecoder.cs

@@ -11,7 +11,7 @@
 
 namespace System.Net.Http.HPack
 {
-    internal class HPackDecoder
+    internal sealed class HPackDecoder
     {
         private enum State : byte
         {

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HPackDecodingException.cs

@@ -7,7 +7,7 @@ namespace System.Net.Http.HPack
 {
     // TODO: Should this be public?
     [Serializable]
-    internal class HPackDecodingException : Exception
+    internal sealed class HPackDecodingException : Exception
     {
         public HPackDecodingException()
         {

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/HuffmanDecodingException.cs

@@ -7,7 +7,7 @@ namespace System.Net.Http.HPack
 {
     // TODO: Should this be public?
     [Serializable]
-    internal class HuffmanDecodingException : Exception, ISerializable
+    internal sealed class HuffmanDecodingException : Exception, ISerializable
     {
         public HuffmanDecodingException()
         {
@@ -18,7 +18,7 @@ public HuffmanDecodingException(string message)
         {
         }
 
-        protected HuffmanDecodingException(SerializationInfo info, StreamingContext context)
+        private HuffmanDecodingException(SerializationInfo info, StreamingContext context)
             : base(info, context)
         {
         }

src/libraries/Common/src/System/Net/Http/aspnetcore/Http2/Hpack/IntegerDecoder.cs

@@ -6,7 +6,7 @@
 
 namespace System.Net.Http.HPack
 {
-    internal class IntegerDecoder
+    internal sealed class IntegerDecoder
     {
         private int _i;
         private int _m;

src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackDecoder.cs

@@ -13,7 +13,7 @@
 
 namespace System.Net.Http.QPack
 {
-    internal class QPackDecoder : IDisposable
+    internal sealed class QPackDecoder : IDisposable
     {
         private enum State
         {

src/libraries/Common/src/System/Net/Http/aspnetcore/Http3/QPack/QPackEncoder.cs

@@ -9,7 +9,7 @@
 
 namespace System.Net.Http.QPack
 {
-    internal class QPackEncoder
+    internal sealed class QPackEncoder
     {
         private IEnumerator<KeyValuePair<string, string>>? _enumerator;
 

src/libraries/Common/src/System/Net/Mail/MailAddress.cs

@@ -5,7 +5,7 @@
 
 namespace System.Net.Mail
 {
-    internal class MailAddress
+    internal sealed class MailAddress
     {
         public MailAddress(string address)
         {

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

@@ -9,7 +9,7 @@
 
 namespace System.Net
 {
-    internal partial class NTAuthentication
+    internal sealed partial class NTAuthentication
     {
         private bool _isServer;
 

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

@@ -8,7 +8,7 @@
 
 namespace System.Net
 {
-    internal class TlsStream : NetworkStream
+    internal sealed class TlsStream : NetworkStream
     {
         private readonly SslStream _sslStream;
         private readonly string _host;

src/libraries/Common/src/System/Runtime/InteropServices/ComEventsSink.cs

@@ -11,7 +11,7 @@ namespace System.Runtime.InteropServices
     /// managed delegates to COM's connection point based events.
     /// </summary>
     [SupportedOSPlatform("windows")]
-    internal partial class ComEventsSink : IDispatch, ICustomQueryInterface
+    internal sealed partial class ComEventsSink : IDispatch, ICustomQueryInterface
     {
         private Guid _iidSourceItf;
         private ComTypes.IConnectionPoint? _connectionPoint;