Resolve ILLink warnings in System.Diagnostics.DiagnosticSource

src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.cs

@@ -19,13 +19,15 @@ public virtual void Dispose() { }
         public virtual System.IDisposable Subscribe(System.IObserver<System.Collections.Generic.KeyValuePair<string, object?>> observer, System.Func<string, object?, object?, bool>? isEnabled) { throw null; }
         public virtual System.IDisposable Subscribe(System.IObserver<System.Collections.Generic.KeyValuePair<string, object?>> observer, System.Predicate<string>? isEnabled) { throw null; }
         public override string ToString() { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("The type of object being written to DiagnosticSource cannot be discovered statically.")]
         public override void Write(string name, object? value) { }
     }
     public abstract partial class DiagnosticSource
     {
         protected DiagnosticSource() { }
         public abstract bool IsEnabled(string name);
         public virtual bool IsEnabled(string name, object? arg1, object? arg2 = null) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("The type of object being written to DiagnosticSource cannot be discovered statically.")]
         public abstract void Write(string name, object? value);
     }
 }

src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSource.csproj

@@ -12,6 +12,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.Diagnostics.DiagnosticSource.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\RequiresUnreferencedCodeAttribute.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.1'">
     <Compile Include="System.Diagnostics.DiagnosticSourceActivity.cs" />

src/libraries/System.Diagnostics.DiagnosticSource/ref/System.Diagnostics.DiagnosticSourceActivity.cs

@@ -192,7 +192,9 @@ public abstract partial class DiagnosticSource
     {
         public virtual void OnActivityExport(System.Diagnostics.Activity activity, object? payload) { }
         public virtual void OnActivityImport(System.Diagnostics.Activity activity, object? payload) { }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("The type of object being written to DiagnosticSource cannot be discovered statically.")]
         public System.Diagnostics.Activity StartActivity(System.Diagnostics.Activity activity, object? args) { throw null; }
+        [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCode("The type of object being written to DiagnosticSource cannot be discovered statically.")]
         public void StopActivity(System.Diagnostics.Activity activity, object? args) { }
     }
     public enum ActivitySamplingResult

src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <CLSCompliant>false</CLSCompliant>
@@ -31,6 +31,7 @@
   <ItemGroup Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) != '.NETCoreApp'">
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicDependencyAttribute.cs" />
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\DynamicallyAccessedMemberTypes.cs" />
+    <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\RequiresUnreferencedCodeAttribute.cs" />
     <Compile Include="$(CoreLibSharedDir)System\Diagnostics\CodeAnalysis\UnconditionalSuppressMessageAttribute.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' != 'netstandard1.1'">

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticListener.cs

@@ -3,6 +3,7 @@
 
 using System.Threading;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Diagnostics
 {
@@ -255,6 +256,7 @@ public override bool IsEnabled(string name, object? arg1, object? arg2 = null)
         /// <summary>
         /// Override abstract method
         /// </summary>
+        [RequiresUnreferencedCode(WriteRequiresUnreferencedCode)]
         public override void Write(string name, object? value)
         {
             for (DiagnosticSubscription? curSubscription = _subscriptions; curSubscription != null; curSubscription = curSubscription.Next)

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticSource.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Diagnostics
 {
@@ -15,6 +16,8 @@ namespace System.Diagnostics
     /// </summary>
     public abstract partial class DiagnosticSource
     {
+        internal const string WriteRequiresUnreferencedCode = "The type of object being written to DiagnosticSource cannot be discovered statically.";
+
         /// <summary>
         /// Write is a generic way of logging complex payloads.  Each notification
         /// is given a name, which identifies it as well as a object (typically an anonymous type)
@@ -31,6 +34,7 @@ public abstract partial class DiagnosticSource
         /// <param name="name">The name of the event being written.</param>
         /// <param name="value">An object that represent the value being passed as a payload for the event.
         /// This is often an anonymous type which contains several sub-values.</param>
+        [RequiresUnreferencedCode(WriteRequiresUnreferencedCode)]
         public abstract void Write(string name, object? value);
 
         /// <summary>

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticSourceActivity.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Diagnostics
 {
@@ -24,6 +25,7 @@ public abstract partial class DiagnosticSource
         /// <param name="args">An object that represent the value being passed as a payload for the event.</param>
         /// <returns>Started Activity for convenient chaining</returns>
         /// <seealso cref="Activity"/>
+        [RequiresUnreferencedCode(WriteRequiresUnreferencedCode)]
         public Activity StartActivity(Activity activity, object? args)
         {
             activity.Start();
@@ -41,6 +43,7 @@ public Activity StartActivity(Activity activity, object? args)
         /// <param name="activity">Activity to be stopped</param>
         /// <param name="args">An object that represent the value being passed as a payload for the event.</param>
         /// <seealso cref="Activity"/>
+        [RequiresUnreferencedCode(WriteRequiresUnreferencedCode)]
         public void StopActivity(Activity activity, object? args)
         {
             // Stop sets the end time if it was unset, but we want it set before we issue the write

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticSourceEventSource.cs

@@ -717,7 +717,9 @@ public FilterAndTransform(string filterAndPayloadSpec, int startIdx, int endIdx,
                         if (eventNameFilter != null)
                             eventNameFilterPredicate = (string eventName) => eventNameFilter == eventName;
 
-                        var subscription = newListener.Subscribe(new CallbackObserver<KeyValuePair<string, object?>>(delegate (KeyValuePair<string, object?> evnt)
+                        [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
+                            Justification = "DiagnosticSource.Write is marked with RequiresUnreferencedCode.")]
+                        void OnEventWritten(KeyValuePair<string, object?> evnt)
                         {
                             // The filter given to the DiagnosticSource may not work if users don't is 'IsEnabled' as expected.
                             // Thus we look for any events that may have snuck through and filter them out before forwarding.
@@ -727,7 +729,9 @@ public FilterAndTransform(string filterAndPayloadSpec, int startIdx, int endIdx,
                             var outputArgs = this.Morph(evnt.Value);
                             var eventName = evnt.Key;
                             writeEvent(newListener.Name, eventName, outputArgs);
-                        }), eventNameFilterPredicate);
+                        }
+
+                        var subscription = newListener.Subscribe(new CallbackObserver<KeyValuePair<string, object?>>(OnEventWritten), eventNameFilterPredicate);
                         _liveSubscriptions = new Subscriptions(subscription, _liveSubscriptions);
                     }
                 }));
@@ -948,41 +952,55 @@ internal static void CreateActivityListener(DiagnosticSourceEventSource eventSou
                     return false;
                 };
 
-                eventSource._activityListener.ActivityStarted = activity =>
+                eventSource._activityListener.ActivityStarted = activity => OnActivityStarted(eventSource, activity);
+
+                eventSource._activityListener.ActivityStopped = activity => OnActivityStopped(eventSource, activity);
+
+                ActivitySource.AddActivityListener(eventSource._activityListener);
+            }
+
+            [DynamicDependency(DynamicallyAccessedMemberTypes.PublicProperties, typeof(Activity))]
+            [DynamicDependency(DynamicallyAccessedMemberTypes.PublicProperties, typeof(ActivityContext))]
+            [DynamicDependency(DynamicallyAccessedMemberTypes.PublicProperties, typeof(ActivityEvent))]
+            [DynamicDependency(DynamicallyAccessedMemberTypes.PublicProperties, typeof(ActivityLink))]
+            [DynamicDependency(nameof(DateTime.Ticks), typeof(DateTime))]
+            [DynamicDependency(nameof(TimeSpan.Ticks), typeof(TimeSpan))]
+            [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
+                Justification = "Activity's properties are being preserved with the DynamicDependencies on OnActivityStarted.")]
+            private static void OnActivityStarted(DiagnosticSourceEventSource eventSource, Activity activity)
+            {
+                FilterAndTransform? list = eventSource._activitySourceSpecs;
+                while (list != null)
                 {
-                    FilterAndTransform? list = eventSource._activitySourceSpecs;
-                    while (list != null)
+                    if ((list.Events & ActivityEvents.ActivityStart) != 0 &&
+                        (activity.Source.Name == list.SourceName || list.SourceName == "*") &&
+                        (list.ActivityName == null || list.ActivityName == activity.OperationName))
                     {
-                        if ((list.Events & ActivityEvents.ActivityStart) != 0 &&
-                            (activity.Source.Name == list.SourceName || list.SourceName == "*") &&
-                            (list.ActivityName == null || list.ActivityName == activity.OperationName))
-                        {
-                            eventSource.ActivityStart(activity.Source.Name, activity.OperationName, list.Morph(activity));
-                            return;
-                        }
-
-                        list = list.Next;
+                        eventSource.ActivityStart(activity.Source.Name, activity.OperationName, list.Morph(activity));
+                        return;
                     }
-                };
 
-                eventSource._activityListener.ActivityStopped = activity =>
+                    list = list.Next;
+                }
+            }
+
+            [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
+                Justification = "Activity's properties are being preserved with the DynamicDependencies on OnActivityStarted.")]
+            private static void OnActivityStopped(DiagnosticSourceEventSource eventSource, Activity activity)
+            {
+                FilterAndTransform? list = eventSource._activitySourceSpecs;
+                while (list != null)
                 {
-                    FilterAndTransform? list = eventSource._activitySourceSpecs;
-                    while (list != null)
+                    if ((list.Events & ActivityEvents.ActivityStop) != 0 &&
+                        (activity.Source.Name == list.SourceName || list.SourceName == "*") &&
+                        (list.ActivityName == null || list.ActivityName == activity.OperationName))
                     {
-                        if ((list.Events & ActivityEvents.ActivityStop) != 0 &&
-                            (activity.Source.Name == list.SourceName || list.SourceName == "*") &&
-                            (list.ActivityName == null || list.ActivityName == activity.OperationName))
-                        {
-                            eventSource.ActivityStop(activity.Source.Name, activity.OperationName, list.Morph(activity));
-                            return;
-                        }
-
-                        list = list.Next;
+                        eventSource.ActivityStop(activity.Source.Name, activity.OperationName, list.Morph(activity));
+                        return;
                     }
-                };
 
-                ActivitySource.AddActivityListener(eventSource._activityListener);
+                    list = list.Next;
+                }
             }
 
             // Move all wildcard nodes at the end of the list.
@@ -1067,6 +1085,7 @@ private void Dispose()
                 }
             }
 
+            [RequiresUnreferencedCode(DiagnosticSource.WriteRequiresUnreferencedCode)]
             public List<KeyValuePair<string, string?>> Morph(object? args)
             {
                 // Transform the args into a bag of key-value strings.
@@ -1105,7 +1124,11 @@ private void Dispose()
                                 Interlocked.CompareExchange(ref _implicitTransformsTable,
                                     new ConcurrentDictionary<Type, TransformSpec?>(1, 8), null);
                             }
-                            implicitTransforms = _implicitTransformsTable.GetOrAdd(argType, type => MakeImplicitTransforms(type));
+                            implicitTransforms = _implicitTransformsTable.GetOrAdd(argType, type => MakeImplicitTransformsWrapper(type));
+
+                            [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2026:RequiresUnreferencedCode",
+                                Justification = "The Morph method has RequiresUnreferencedCode, but the trimmer can't see through lamdba calls.")]
+                            static TransformSpec? MakeImplicitTransformsWrapper(Type transformType) => MakeImplicitTransforms(transformType);
                         }
 
                         // implicitTransformas now fetched from cache or constructed, use it to Fetch all the implicit fields.
@@ -1145,6 +1168,7 @@ private void Dispose()
 
             // Given a type generate all the implicit transforms for type (that is for every field
             // generate the spec that fetches it).
+            [RequiresUnreferencedCode(DiagnosticSource.WriteRequiresUnreferencedCode)]
             private static TransformSpec? MakeImplicitTransforms(Type type)
             {
                 TransformSpec? newSerializableArgs = null;
@@ -1239,6 +1263,7 @@ public TransformSpec(string transformSpec, int startIdx, int endIdx, TransformSp
             /// if the spec is OUTSTR=EVENT_VALUE.PROP1.PROP2.PROP3 and the ultimate value of PROP3 is
             /// 10 then the return key value pair is  KeyValuePair("OUTSTR","10")
             /// </summary>
+            [RequiresUnreferencedCode(DiagnosticSource.WriteRequiresUnreferencedCode)]
             public KeyValuePair<string, string?> Morph(object? obj)
             {
                 for (PropertySpec? cur = _fetches; cur != null; cur = cur.Next)
@@ -1289,6 +1314,7 @@ public PropertySpec(string propertyName, PropertySpec? next)
                 /// Given an object fetch the property that this PropertySpec represents.
                 /// obj may be null when IsStatic is true, otherwise it must be non-null.
                 /// </summary>
+                [RequiresUnreferencedCode(DiagnosticSource.WriteRequiresUnreferencedCode)]
                 public object? Fetch(object? obj)
                 {
                     PropertyFetch? fetch = _fetchForExpectedType;
@@ -1331,9 +1357,7 @@ public PropertyFetch(Type? type)
                     /// <summary>
                     /// Create a property fetcher for a propertyName
                     /// </summary>
-                    [DynamicDependency("#ctor(System.Type)", typeof(EnumeratePropertyFetch<>))]
-                    [DynamicDependency("#ctor(System.Type,System.Reflection.PropertyInfo)", typeof(RefTypedFetchProperty<,>))]
-                    [DynamicDependency("#ctor(System.Type,System.Reflection.PropertyInfo)", typeof(ValueTypedFetchProperty<,>))]
+                    [RequiresUnreferencedCode(DiagnosticSource.WriteRequiresUnreferencedCode)]
                     public static PropertyFetch FetcherForProperty(Type? type, string propertyName)
                     {
                         if (propertyName == null)
@@ -1385,7 +1409,7 @@ public static PropertyFetch FetcherForProperty(Type? type, string propertyName)
                             PropertyInfo? propertyInfo = typeInfo.GetDeclaredProperty(propertyName);
                             if (propertyInfo == null)
                             {
-                                Logger.Message($"Property {propertyName} not found on {type}");
+                                Logger.Message($"Property {propertyName} not found on {type}. Ensure the name is spelled correctly. If you published the application with PublishTrimmed=true, ensure the property was not trimmed away.");
                                 return new PropertyFetch(type);
                             }
                             // Delegate creation below is incompatible with static properties.