Support trimming distributed transactions if unused, without a feature switch.

src/libraries/System.Transactions.Local/ref/System.Transactions.Local.cs

@@ -191,7 +191,7 @@ public static partial class TransactionManager
  [System.Diagnostics.CodeAnalysis.DisallowNullAttribute]
  public static System.Transactions.HostCurrentTransactionCallback? HostCurrentCallback { get { throw null; } set { } }
  public static System.TimeSpan MaximumTimeout { get { throw null; } set { } }
- public static bool ImplicitDistributedTransactions { get; set; }
+ public static bool ImplicitDistributedTransactions { get; [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("Distributed transactions support may not be compatible with trimming. If your program creates a distributed transaction via System.Transactions, the correctness of the application cannot be guaranteed after trimming.")] set; }
  public static event System.Transactions.TransactionStartedEventHandler? DistributedTransactionStarted { add { } remove { } }
  public static void RecoveryComplete(System.Guid resourceManagerIdentifier) { }
  public static System.Transactions.Enlistment Reenlist(System.Guid resourceManagerIdentifier, byte[] recoveryInformation, System.Transactions.IEnlistmentNotification enlistmentNotification) { throw null; }

src/libraries/System.Transactions.Local/src/System/Transactions/DtcProxyShim/DtcProxyShimFactory.cs

@@ -21,6 +21,11 @@ internal sealed class DtcProxyShimFactory
  // at the same time.
  private static readonly object _proxyInitLock = new();
 
+ // This object will perform the actual distributed transaction connection.
+ // It will be set only if TransactionManager.ImplicitDefaultTransactions
+ // is set to true, allowing the relevant code to be trimmed otherwise.
+ internal static ITransactionConnector? s_transactionConnector;
+
  // Lock to protect access to listOfNotifications.
  private readonly object _notificationLock = new();
 
@@ -39,6 +44,7 @@ internal DtcProxyShimFactory(EventWaitHandle notificationEventHandle)
 
  // https://docs.microsoft.com/previous-versions/windows/desktop/ms678898(v=vs.85)
  [DllImport(Interop.Libraries.Xolehlp, CharSet = CharSet.Unicode, ExactSpelling = true, PreserveSig = false)]
+ [RequiresUnreferencedCode(TransactionManager.DistributedTransactionTrimmingWarning)]
  private static extern void DtcGetTransactionManagerExW(
  [MarshalAs(UnmanagedType.LPWStr)] string? pszHost,
  [MarshalAs(UnmanagedType.LPWStr)] string? pszTmName,
@@ -47,7 +53,7 @@ private static extern void DtcGetTransactionManagerExW(
  object? pvConfigPararms,
  [MarshalAs(UnmanagedType.Interface)] out ITransactionDispenser ppvObject);
 
- [RequiresUnreferencedCode("Distributed transactions support may not be compatible with trimming. If your program creates a distributed transaction via System.Transactions, the correctness of the application cannot be guaranteed after trimming.")]
+ [RequiresUnreferencedCode(TransactionManager.DistributedTransactionTrimmingWarning)]
  private static void DtcGetTransactionManager(string? nodeName, out ITransactionDispenser localDispenser) =>
  DtcGetTransactionManagerExW(nodeName, null, Guids.IID_ITransactionDispenser_Guid, 0, null, out localDispenser);
 
@@ -64,14 +70,15 @@ public void ConnectToProxy(
  throw new PlatformNotSupportedException(SR.DistributedNotSupportedOn32Bits);
  }
 
- if (!TransactionManager.ImplicitDistributedTransactions)
+ if (s_transactionConnector is null)
  {
  throw new NotSupportedException(SR.ImplicitDistributedTransactionsDisabled);
  }
 
- ConnectToProxyCore(nodeName, resourceManagerIdentifier, managedIdentifier, out nodeNameMatches, out whereabouts, out resourceManagerShim);
+ s_transactionConnector.ConnectToProxyCore(this, nodeName, resourceManagerIdentifier, managedIdentifier, out nodeNameMatches, out whereabouts, out resourceManagerShim);
  }
 
+ [RequiresUnreferencedCode(TransactionManager.DistributedTransactionTrimmingWarning)]
  private void ConnectToProxyCore(
  string? nodeName,
  Guid resourceManagerIdentifier,
@@ -82,9 +89,7 @@ private void ConnectToProxyCore(
  {
  lock (_proxyInitLock)
  {
-#pragma warning disable IL2026 // This warning is left in the product so developers get an ILLink warning when trimming an app using this transaction support
  DtcGetTransactionManager(nodeName, out ITransactionDispenser? localDispenser);
-#pragma warning restore IL2026
 
  // Check to make sure the node name matches.
  if (nodeName is not null)
@@ -371,4 +376,38 @@ internal ITransactionReceiver GetCachedReceiver()
 
  internal void ReturnCachedReceiver(ITransactionReceiver receiver)
  => _cachedReceivers.Enqueue(receiver);
+
+ internal interface ITransactionConnector
+ {
+ void ConnectToProxyCore(
+ DtcProxyShimFactory proxyShimFactory,
+ string? nodeName,
+ Guid resourceManagerIdentifier,
+ object managedIdentifier,
+ out bool nodeNameMatches,
+ out byte[] whereabouts,
+ out ResourceManagerShim resourceManagerShim);
+ }
+
+ [RequiresUnreferencedCode(TransactionManager.DistributedTransactionTrimmingWarning)]
+ internal sealed class DtcTransactionConnector : ITransactionConnector
+ {
+ public void ConnectToProxyCore(
+ DtcProxyShimFactory proxyShimFactory,
+ string? nodeName,
+ Guid resourceManagerIdentifier,
+ object managedIdentifier,
+ out bool nodeNameMatches,
+ out byte[] whereabouts,
+ out ResourceManagerShim resourceManagerShim)
+ {
+ proxyShimFactory.ConnectToProxyCore(
+ nodeName,
+ resourceManagerIdentifier,
+ managedIdentifier,
+ out nodeNameMatches,
+ out whereabouts,
+ out resourceManagerShim);
+ }
+ }
 }

src/libraries/System.Transactions.Local/src/System/Transactions/TransactionManager.cs

@@ -6,6 +6,9 @@
 using System.IO;
 using System.Threading;
 using System.Transactions.Configuration;
+#if WINDOWS
+using System.Transactions.DtcProxyShim;
+#endif
 using System.Transactions.Oletx;
 
 namespace System.Transactions
@@ -29,6 +32,10 @@ public static class TransactionManager
  private static TransactionTable? s_transactionTable;
 
  private static TransactionStartedEventHandler? s_distributedTransactionStartedDelegate;
+
+ internal const string DistributedTransactionTrimmingWarning =
+ "Distributed transactions support may not be compatible with trimming. If your program creates a distributed transaction via System.Transactions, the correctness of the application cannot be guaranteed after trimming.";
+
  public static event TransactionStartedEventHandler? DistributedTransactionStarted
  {
  add
@@ -391,7 +398,31 @@ public static TimeSpan MaximumTimeout
  }
  }
 
- public static bool ImplicitDistributedTransactions { get; set; }
+#if WINDOWS
+ public static bool ImplicitDistributedTransactions
+ {
+ get => DtcProxyShimFactory.s_transactionConnector is not null;
+ [RequiresUnreferencedCode(DistributedTransactionTrimmingWarning)]
+ set
+ {
+ if (value)
+ {
+ DtcProxyShimFactory.s_transactionConnector ??= new DtcProxyShimFactory.DtcTransactionConnector();
+ }
+ else
+ {
+ DtcProxyShimFactory.s_transactionConnector = null;
+ }
+ }
+ }
+#else
+ public static bool ImplicitDistributedTransactions
+ {
+ get;
+ [RequiresUnreferencedCode(DistributedTransactionTrimmingWarning)]
+ set;
+ }
+#endif
 
  // This routine writes the "header" for the recovery information, based on the
  // type of the calling object and its provided parameter collection. This information