Resolve ILLink warnings in System.Diagnostics.DiagnosticSource (#50265)

* Resolve ILLink warnings in System.Diagnostics.DiagnosticSource

Contributes to #45623

1. Mark DiagnosticSource.Write(string,object) as RequiresUnreferencedCode
2. Suppress the warnings for any .NET libraries that call the DiagnosticSource.Write() API, and annotate the .NET types being passed in to preserve their important properties.
    - This was done for HttpClient. ASP.NET and EF will need separate changes when those assemblies are made trim compatible
3. Annotate Activity and its small closure of types (ActivityLink, ActivityEvent, ActivityContext, etc) to ensure none of those properties are trimmed.
4. Suppress trim warnings inside DiagnosticSourceEventSource since the public Write method is marked with RequiresUnreferencedCode.

Author: eerhardt

Diff for: 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);
     }
 }

Diff for: 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" />

Diff for: 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

Diff for: src/libraries/System.Diagnostics.DiagnosticSource/src/ILLink/ILLink.Suppressions.xml

@@ -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'">

Diff for: src/libraries/System.Diagnostics.DiagnosticSource/src/System.Diagnostics.DiagnosticSource.csproj

@@ -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)

Diff for: src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticListener.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>

Diff for: 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.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

Diff for: src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/DiagnosticSourceActivity.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.