Make System.Transactions.Local trimmable on Windows (#75176) (#75377)

* Make System.Transactions.Local trimmable on Windows

Remove `IsTrimmable=false` from the project, so this assembly is still trimmed with `partial` trimming on Windows.

Add a "LibraryBuild" ILLink warning, so when the distributed transaction code is not trimmed, the app developer gets a warning that it is not guaranteed to work.

Fix #75031

* Fix x86 build. Move the ILLink suppression to a method that is completely trimmed on x86.

4 files changed, 32 insertions, 5 deletions

diff --git a/src/libraries/System.Transactions.Local/src/ILLink/ILLink.Suppressions.LibraryBuild.xml b/src/libraries/System.Transactions.Local/src/ILLink/ILLink.Suppressions.LibraryBuild.xml
new file mode 100644
index 00000000000..d002d008a2a
--- /dev/null
+++ b/src/libraries/System.Transactions.Local/src/ILLink/ILLink.Suppressions.LibraryBuild.xml
@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<linker>
+  <assembly fullname="System.Transactions.Local">
+    <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
+      <argument>ILLink</argument>
+      <argument>IL2026</argument>
+      <property name="Scope">member</property>
+      <property name="Target">M:System.Transactions.DtcProxyShim.DtcProxyShimFactory.ConnectToProxyCore(System.String,System.Guid,System.Object,System.Boolean@,System.Byte[]@,System.Transactions.DtcProxyShim.ResourceManagerShim@)</property>
+      <property name="Justification">This warning is left in the product so developers get an ILLink warning when trimming an app using this transaction support</property>
+    </attribute>
+  </assembly>
+</linker>
diff --git a/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj b/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj
index 034f32afcf5..ff37cf621bb 100644
--- a/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj
+++ b/src/libraries/System.Transactions.Local/src/System.Transactions.Local.csproj
@@ -5,7 +5,6 @@
     <TargetFrameworks>$(NetCoreAppCurrent)-windows;$(NetCoreAppCurrent)</TargetFrameworks>
     <NoWarn>CA1805;IDE0059;CS1591</NoWarn>
     <TargetPlatformIdentifier>$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)'))</TargetPlatformIdentifier>
-    <IsTrimmable Condition="'$(TargetPlatformIdentifier)' == 'windows'">false</IsTrimmable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Transactions\CommittableTransaction.cs" />
diff --git a/src/libraries/System.Transactions.Local/src/System/Transactions/DtcProxyShim/DtcProxyShimFactory.cs b/src/libraries/System.Transactions.Local/src/System/Transactions/DtcProxyShim/DtcProxyShimFactory.cs
index e15983a52ab..e8fe3c9554c 100644
--- a/src/libraries/System.Transactions.Local/src/System/Transactions/DtcProxyShim/DtcProxyShimFactory.cs
+++ b/src/libraries/System.Transactions.Local/src/System/Transactions/DtcProxyShim/DtcProxyShimFactory.cs
@@ -47,7 +47,10 @@ internal sealed class DtcProxyShimFactory
         object? pvConfigPararms,
         [MarshalAs(UnmanagedType.Interface)] out ITransactionDispenser ppvObject);
 
-    [UnconditionalSuppressMessage("Trimming", "IL2050", Justification = "Leave me alone")]
+    [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.")]
+    private static void DtcGetTransactionManager(string? nodeName, out ITransactionDispenser localDispenser) =>
+        DtcGetTransactionManagerExW(nodeName, null, Guids.IID_ITransactionDispenser_Guid, 0, null, out localDispenser);
+
     public void ConnectToProxy(
         string? nodeName,
         Guid resourceManagerIdentifier,
@@ -61,9 +64,22 @@ internal sealed class DtcProxyShimFactory
             throw new PlatformNotSupportedException(SR.DistributedNotSupportOn32Bits);
         }
 
+        ConnectToProxyCore(nodeName, resourceManagerIdentifier, managedIdentifier, out nodeNameMatches, out whereabouts, out resourceManagerShim);
+    }
+
+    private void ConnectToProxyCore(
+        string? nodeName,
+        Guid resourceManagerIdentifier,
+        object managedIdentifier,
+        out bool nodeNameMatches,
+        out byte[] whereabouts,
+        out ResourceManagerShim resourceManagerShim)
+    {
         lock (_proxyInitLock)
         {
-            DtcGetTransactionManagerExW(nodeName, null, Guids.IID_ITransactionDispenser_Guid, 0, null, out ITransactionDispenser? localDispenser);
+#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)
diff --git a/src/libraries/System.Transactions.Local/src/System/Transactions/TransactionsEtwProvider.cs b/src/libraries/System.Transactions.Local/src/System/Transactions/TransactionsEtwProvider.cs
index ec230efce89..f9d4e77006f 100644
--- a/src/libraries/System.Transactions.Local/src/System/Transactions/TransactionsEtwProvider.cs
+++ b/src/libraries/System.Transactions.Local/src/System/Transactions/TransactionsEtwProvider.cs
@@ -573,7 +573,7 @@ namespace System.Transactions
         }
 
         [Event(ENLISTMENT_CREATED_LTM_EVENTID, Keywords = Keywords.TraceLtm, Level = EventLevel.Informational, Task = Tasks.Enlistment, Opcode = Opcodes.Create, Message = "Enlistment Created (LTM). ID is {0}, type is {1}, options is {2}")]
-        [UnconditionalSuppressMessage("AssemblyLoadTrimming", "IL2026", Justification = "Only string/int are passed")]
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode", Justification = "Only string/int are passed")]
         private void EnlistmentCreatedLtm(int enlistmentIdentifier, string enlistmentType, string enlistmentOptions)
         {
             SetActivityId(string.Empty);
@@ -581,7 +581,7 @@ namespace System.Transactions
         }
 
         [Event(ENLISTMENT_CREATED_OLETX_EVENTID, Keywords = Keywords.TraceOleTx, Level = EventLevel.Informational, Task = Tasks.Enlistment, Opcode = Opcodes.Create, Message = "Enlistment Created (OLETX). ID is {0}, type is {1}, options is {2}")]
-        [UnconditionalSuppressMessage("AssemblyLoadTrimming", "IL2026", Justification = "Only string/int are passed")]
+        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode", Justification = "Only string/int are passed")]
         private void EnlistmentCreatedOleTx(int enlistmentIdentifier, string enlistmentType, string enlistmentOptions)
         {
             SetActivityId(string.Empty);