Warn if RequiresXXXCode is placed on an entrypoint (#110185)

Fixes #109811.

Motivated by real-world first party code that did this :(.

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Logging/MessageContainer.cs

@@ -128,6 +128,11 @@ internal static MessageContainer CreateErrorMessage(MessageOrigin? origin, Diagn
             if (context.IsWarningSubcategorySuppressed(subcategory))
                 return null;
 
+            // If the warning comes from compiler-generated code, it would not be actionable. The assumption is that
+            // compiler-generated code doesn't have issues.
+            if (origin.MemberDefinition is MethodDesc originMethod && originMethod.GetTypicalMethodDefinition() is not EcmaMethod)
+                return null;
+
             if (TryLogSingleWarning(context, code, origin, subcategory))
                 return null;
 
@@ -145,6 +150,11 @@ internal static MessageContainer CreateErrorMessage(MessageOrigin? origin, Diagn
             if (context.IsWarningSubcategorySuppressed(subcategory))
                 return null;
 
+            // If the warning comes from compiler-generated code, it would not be actionable. The assumption is that
+            // compiler-generated code doesn't have issues.
+            if (origin.MemberDefinition is MethodDesc originMethod && originMethod.GetTypicalMethodDefinition() is not EcmaMethod)
+                return null;
+
             if (TryLogSingleWarning(context, (int)id, origin, subcategory))
                 return null;
 

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/UsageBasedMetadataManager.cs

@@ -641,6 +641,19 @@ protected override void GetDependenciesDueToMethodCodePresenceInternal(ref Depen
                     if (DiagnosticUtilities.TryGetRequiresAttribute(method, DiagnosticUtilities.RequiresAssemblyFilesAttribute, out _))
                         Logger.LogWarning(new MessageOrigin(method), DiagnosticId.RequiresAssemblyFilesOnStaticConstructor, method.GetDisplayName());
                 }
+
+                if (method is EcmaMethod maybeEntrypoint
+                    && (maybeEntrypoint.Module.EntryPoint == method || (method.IsUnmanagedCallersOnly && maybeEntrypoint.GetUnmanagedCallersOnlyExportName() != null)))
+                {
+                    if (DiagnosticUtilities.TryGetRequiresAttribute(method, DiagnosticUtilities.RequiresUnreferencedCodeAttribute, out _))
+                        Logger.LogWarning(new MessageOrigin(method), DiagnosticId.RequiresUnreferencedCodeOnEntryPoint, method.GetDisplayName());
+
+                    if (DiagnosticUtilities.TryGetRequiresAttribute(method, DiagnosticUtilities.RequiresDynamicCodeAttribute, out _))
+                        Logger.LogWarning(new MessageOrigin(method), DiagnosticId.RequiresDynamicCodeOnEntryPoint, method.GetDisplayName());
+
+                    if (DiagnosticUtilities.TryGetRequiresAttribute(method, DiagnosticUtilities.RequiresAssemblyFilesAttribute, out _))
+                        Logger.LogWarning(new MessageOrigin(method), DiagnosticId.RequiresAssemblyFilesOnEntryPoint, method.GetDisplayName());
+                }
             }
 
             if (method.GetTypicalMethodDefinition() is Internal.TypeSystem.Ecma.EcmaMethod ecmaMethod)

src/tools/illink/src/ILLink.RoslynAnalyzer/CompilationExtensions.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Immutable;
+using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 
@@ -160,5 +161,10 @@ public static SimpleNameSyntax GetUnqualifiedName (this NameSyntax name)
 				SimpleNameSyntax simple => simple,
 				_ => throw new InvalidOperationException ("Unreachable"),
 			};
+
+		public static INamedTypeSymbol? TaskType (this Compilation compilation)
+			=> compilation.GetTypeByMetadataName (typeof (Task).FullName!);
+		public static INamedTypeSymbol? TaskOfTType (this Compilation compilation)
+			=> compilation.GetTypeByMetadataName (typeof (Task<>).FullName!);
 	}
 }

src/tools/illink/src/ILLink.RoslynAnalyzer/ISymbolExtensions.cs

@@ -203,5 +203,27 @@ public static bool IsConstructor ([NotNullWhen (returnValue: true)] this ISymbol
 
 		public static bool IsStaticConstructor ([NotNullWhen (returnValue: true)] this ISymbol? symbol)
 			=> (symbol as IMethodSymbol)?.MethodKind == MethodKind.StaticConstructor;
+
+		public static bool IsEntryPoint (this IMethodSymbol methodSymbol, Compilation compilation)
+			=> methodSymbol.Name is WellKnownMemberNames.EntryPointMethodName or WellKnownMemberNames.TopLevelStatementsEntryPointMethodName &&
+			   methodSymbol.IsStatic &&
+			   (methodSymbol.ReturnsVoid ||
+				methodSymbol.ReturnType.SpecialType == SpecialType.System_Int32 ||
+				SymbolEqualityComparer.Default.Equals(methodSymbol.ReturnType.OriginalDefinition, compilation.TaskType()) ||
+				SymbolEqualityComparer.Default.Equals(methodSymbol.ReturnType.OriginalDefinition, compilation.TaskOfTType()));
+
+		public static bool IsUnmanagedCallersOnlyEntryPoint (this IMethodSymbol methodSymbol)
+		{
+			foreach (var attr in methodSymbol.GetAttributes ()) {
+				if (attr.AttributeClass is { } attrClass && attrClass.HasName ("System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute")) {
+					foreach (var namedArgument in attr.NamedArguments) {
+						if (namedArgument.Key == "EntryPoint")
+							return true;
+					}
+				}
+			}
+
+			return false;
+		}
 	}
 }

src/tools/illink/src/ILLink.RoslynAnalyzer/RequiresAnalyzerBase.cs

@@ -32,6 +32,7 @@ public abstract class RequiresAnalyzerBase : DiagnosticAnalyzer
 
 		private protected abstract DiagnosticDescriptor RequiresAttributeMismatch { get; }
 		private protected abstract DiagnosticDescriptor RequiresOnStaticCtor { get; }
+		private protected abstract DiagnosticDescriptor RequiresOnEntryPoint { get; }
 
 		private protected virtual ImmutableArray<(Action<SyntaxNodeAnalysisContext> Action, SyntaxKind[] SyntaxKind)> ExtraSyntaxNodeActions { get; } = ImmutableArray<(Action<SyntaxNodeAnalysisContext> Action, SyntaxKind[] SyntaxKind)>.Empty;
 		private protected virtual ImmutableArray<(Action<SymbolAnalysisContext> Action, SymbolKind[] SymbolKind)> ExtraSymbolActions { get; } = ImmutableArray<(Action<SymbolAnalysisContext> Action, SymbolKind[] SymbolKind)>.Empty;
@@ -51,8 +52,15 @@ public override void Initialize (AnalysisContext context)
 				var incompatibleMembers = GetSpecialIncompatibleMembers (compilation);
 				context.RegisterSymbolAction (symbolAnalysisContext => {
 					var methodSymbol = (IMethodSymbol) symbolAnalysisContext.Symbol;
-					if (methodSymbol.IsStaticConstructor () && methodSymbol.HasAttribute (RequiresAttributeName))
-						ReportRequiresOnStaticCtorDiagnostic (symbolAnalysisContext, methodSymbol);
+
+					if (methodSymbol.HasAttribute (RequiresAttributeName)) {
+						if (methodSymbol.IsStaticConstructor ())
+							ReportRequiresOnStaticCtorDiagnostic (symbolAnalysisContext, methodSymbol);
+
+						if (methodSymbol.IsEntryPoint (symbolAnalysisContext.Compilation) || methodSymbol.IsUnmanagedCallersOnlyEntryPoint ())
+							ReportRequiresOnEntryPointDiagnostic (symbolAnalysisContext, methodSymbol);
+					}
+
 					CheckMatchingAttributesInOverrides (symbolAnalysisContext, methodSymbol);
 				}, SymbolKind.Method);
 
@@ -238,6 +246,14 @@ private void ReportRequiresOnStaticCtorDiagnostic (SymbolAnalysisContext symbolA
 				ctor.GetDisplayName ()));
 		}
 
+		private void ReportRequiresOnEntryPointDiagnostic (SymbolAnalysisContext symbolAnalysisContext, IMethodSymbol entryPoint)
+		{
+			symbolAnalysisContext.ReportDiagnostic (Diagnostic.Create (
+				RequiresOnEntryPoint,
+				entryPoint.Locations[0],
+				entryPoint.GetDisplayName ()));
+		}
+
 		private void ReportMismatchInAttributesDiagnostic (SymbolAnalysisContext symbolAnalysisContext, ISymbol member, ISymbol baseMember, bool isInterface = false, ISymbol? origin = null)
 		{
 			origin ??= member;

src/tools/illink/src/ILLink.RoslynAnalyzer/RequiresAssemblyFilesAnalyzer.cs

@@ -32,7 +32,9 @@ public sealed class RequiresAssemblyFilesAnalyzer : RequiresAnalyzerBase
 
 		static readonly DiagnosticDescriptor s_requiresAssemblyFilesOnStaticCtor = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresAssemblyFilesOnStaticConstructor);
 
-		public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create (s_locationRule, s_getFilesRule, s_requiresAssemblyFilesRule, s_requiresAssemblyFilesAttributeMismatch, s_requiresAssemblyFilesOnStaticCtor);
+		static readonly DiagnosticDescriptor s_requiresAssemblyFilesOnEntryPoint = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresAssemblyFilesOnEntryPoint);
+
+		public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create (s_locationRule, s_getFilesRule, s_requiresAssemblyFilesRule, s_requiresAssemblyFilesAttributeMismatch, s_requiresAssemblyFilesOnStaticCtor, s_requiresAssemblyFilesOnEntryPoint);
 
 		private protected override string RequiresAttributeName => RequiresAssemblyFilesAttribute;
 
@@ -48,6 +50,8 @@ public sealed class RequiresAssemblyFilesAnalyzer : RequiresAnalyzerBase
 
 		private protected override DiagnosticDescriptor RequiresOnStaticCtor => s_requiresAssemblyFilesOnStaticCtor;
 
+		private protected override DiagnosticDescriptor RequiresOnEntryPoint => s_requiresAssemblyFilesOnEntryPoint;
+
 		internal override bool IsAnalyzerEnabled (AnalyzerOptions options)
 		{
 			var isSingleFileAnalyzerEnabled = options.GetMSBuildPropertyValue (MSBuildPropertyOptionNames.EnableSingleFileAnalyzer);

src/tools/illink/src/ILLink.RoslynAnalyzer/RequiresDynamicCodeAnalyzer.cs

@@ -20,11 +20,12 @@ public sealed class RequiresDynamicCodeAnalyzer : RequiresAnalyzerBase
 		public const string FullyQualifiedRequiresDynamicCodeAttribute = "System.Diagnostics.CodeAnalysis." + RequiresDynamicCodeAttribute;
 
 		static readonly DiagnosticDescriptor s_requiresDynamicCodeOnStaticCtor = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresDynamicCodeOnStaticConstructor);
+		static readonly DiagnosticDescriptor s_requiresDynamicCodeOnEntryPoint = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresDynamicCodeOnEntryPoint);
 		static readonly DiagnosticDescriptor s_requiresDynamicCodeRule = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresDynamicCode);
 		static readonly DiagnosticDescriptor s_requiresDynamicCodeAttributeMismatch = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresDynamicCodeAttributeMismatch);
 
 		public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics =>
-			ImmutableArray.Create (s_requiresDynamicCodeRule, s_requiresDynamicCodeAttributeMismatch, s_requiresDynamicCodeOnStaticCtor);
+			ImmutableArray.Create (s_requiresDynamicCodeRule, s_requiresDynamicCodeAttributeMismatch, s_requiresDynamicCodeOnStaticCtor, s_requiresDynamicCodeOnEntryPoint);
 
 		private protected override string RequiresAttributeName => RequiresDynamicCodeAttribute;
 
@@ -40,6 +41,8 @@ public sealed class RequiresDynamicCodeAnalyzer : RequiresAnalyzerBase
 
 		private protected override DiagnosticDescriptor RequiresOnStaticCtor => s_requiresDynamicCodeOnStaticCtor;
 
+		private protected override DiagnosticDescriptor RequiresOnEntryPoint => s_requiresDynamicCodeOnEntryPoint;
+
 		internal override bool IsAnalyzerEnabled (AnalyzerOptions options) =>
 			options.IsMSBuildPropertyValueTrue (MSBuildPropertyOptionNames.EnableAotAnalyzer);
 

src/tools/illink/src/ILLink.RoslynAnalyzer/RequiresUnreferencedCodeAnalyzer.cs

@@ -23,6 +23,7 @@ public sealed class RequiresUnreferencedCodeAnalyzer : RequiresAnalyzerBase
 		static readonly DiagnosticDescriptor s_makeGenericTypeRule = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.MakeGenericType);
 		static readonly DiagnosticDescriptor s_makeGenericMethodRule = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.MakeGenericMethod);
 		static readonly DiagnosticDescriptor s_requiresUnreferencedCodeOnStaticCtor = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresUnreferencedCodeOnStaticConstructor);
+		static readonly DiagnosticDescriptor s_requiresUnreferencedCodeOnEntryPoint = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresUnreferencedCodeOnEntryPoint);
 
 		static readonly DiagnosticDescriptor s_typeDerivesFromRucClassRule = DiagnosticDescriptors.GetDiagnosticDescriptor (DiagnosticId.RequiresUnreferencedCodeOnBaseClass);
 
@@ -45,7 +46,7 @@ private Action<SymbolAnalysisContext> typeDerivesFromRucBase {
 		}
 
 		public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics =>
-			ImmutableArray.Create (s_makeGenericMethodRule, s_makeGenericTypeRule, s_requiresUnreferencedCodeRule, s_requiresUnreferencedCodeAttributeMismatch, s_typeDerivesFromRucClassRule, s_requiresUnreferencedCodeOnStaticCtor);
+			ImmutableArray.Create (s_makeGenericMethodRule, s_makeGenericTypeRule, s_requiresUnreferencedCodeRule, s_requiresUnreferencedCodeAttributeMismatch, s_typeDerivesFromRucClassRule, s_requiresUnreferencedCodeOnStaticCtor, s_requiresUnreferencedCodeOnEntryPoint);
 
 		private protected override string RequiresAttributeName => RequiresUnreferencedCodeAttribute;
 
@@ -61,6 +62,8 @@ private Action<SymbolAnalysisContext> typeDerivesFromRucBase {
 
 		private protected override DiagnosticDescriptor RequiresOnStaticCtor => s_requiresUnreferencedCodeOnStaticCtor;
 
+		private protected override DiagnosticDescriptor RequiresOnEntryPoint => s_requiresUnreferencedCodeOnEntryPoint;
+
 		internal override bool IsAnalyzerEnabled (AnalyzerOptions options) =>
 			options.IsMSBuildPropertyValueTrue (MSBuildPropertyOptionNames.EnableTrimAnalyzer);
 

src/tools/illink/src/ILLink.Shared/DiagnosticId.cs

@@ -187,6 +187,7 @@ public enum DiagnosticId
 		_unused_DynamicallyAccessedMembersOnTypeReferencesCompilerGeneratedMemberOnBase = 2120,
 		RedundantSuppression = 2121,
 		TypeNameIsNotAssemblyQualified = 2122,
+		RequiresUnreferencedCodeOnEntryPoint = 2123,
 		_EndTrimAnalysisWarningsSentinel,
 
 		// Single-file diagnostic ids.
@@ -195,6 +196,7 @@ public enum DiagnosticId
 		RequiresAssemblyFiles = 3002,
 		RequiresAssemblyFilesAttributeMismatch = 3003,
 		RequiresAssemblyFilesOnStaticConstructor = 3004,
+		RequiresAssemblyFilesOnEntryPoint = 3005,
 
 		// Dynamic code diagnostic ids.
 		RequiresDynamicCode = 3050,
@@ -204,6 +206,7 @@ public enum DiagnosticId
 		GenericRecursionCycle = 3054,
 		CorrectnessOfAbstractDelegatesCannotBeGuaranteed = 3055,
 		RequiresDynamicCodeOnStaticConstructor = 3056,
+		RequiresDynamicCodeOnEntryPoint = 3057,
 		_EndAotAnalysisWarningsSentinel,
 
 		// Feature guard diagnostic ids.

src/tools/illink/src/ILLink.Shared/SharedStrings.resx

@@ -1179,6 +1179,24 @@
   <data name="RequiresAssemblyFilesOnStaticConstructorTitle" xml:space="preserve">
     <value>The use of 'RequiresAssemblyFilesAttribute' on static constructors is disallowed since is a method not callable by the user, is only called by the runtime. Placing the attribute directly on the static constructor will have no effect, instead use 'RequiresUnreferencedCodeAttribute' on the type which will handle warning and silencing from the static constructor.</value>
   </data>
+  <data name="RequiresUnreferencedCodeOnEntryPointMessage" xml:space="preserve">
+    <value>'RequiresUnreferencedCodeAttribute' cannot be placed directly on application entry point '{0}'.</value>
+  </data>
+  <data name="RequiresUnreferencedCodeOnEntryPointTitle" xml:space="preserve">
+    <value>The use of 'RequiresUnreferencedCodeAttribute' on entry points is disallowed since the method will be called from outside the visible app.</value>
+  </data>
+  <data name="RequiresDynamicCodeOnEntryPointMessage" xml:space="preserve">
+    <value>'RequiresDynamicCodeAttribute' cannot be placed directly on application entry point '{0}'.</value>
+  </data>
+  <data name="RequiresDynamicCodeOnEntryPointTitle" xml:space="preserve">
+    <value>The use of 'RequiresDynamicCodeAttribute' on entry points is disallowed since the method will be called from outside the visible app.</value>
+  </data>
+  <data name="RequiresAssemblyFilesOnEntryPointMessage" xml:space="preserve">
+    <value>'RequiresAssemblyFilesAttribute' cannot be placed directly on application entry point '{0}'.</value>
+  </data>
+  <data name="RequiresAssemblyFilesOnEntryPointTitle" xml:space="preserve">
+    <value>The use of 'RequiresAssemblyFilesAttribute' on entry points is disallowed since the method will be called from outside the visible app.</value>
+  </data>
   <data name="UnrecognizedInternalAttributeMessage" xml:space="preserve">
     <value>The internal attribute name '{0}' being used in the xml is not supported by ILLink, check the spelling and the supported internal attributes.</value>
   </data>

src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

@@ -3088,6 +3088,8 @@ protected virtual void ProcessMethod (MethodDefinition method, in DependencyInfo
 				Tracer.AddDirectDependency (method.DeclaringType, new DependencyInfo (DependencyKind.InstantiatedByCtor, method), marked: false);
 			} else if (method.IsStaticConstructor () && Annotations.HasLinkerAttribute<RequiresUnreferencedCodeAttribute> (method))
 				Context.LogWarning (methodOrigin, DiagnosticId.RequiresUnreferencedCodeOnStaticConstructor, method.GetDisplayName ());
+			else if (method == method.Module.EntryPoint && Annotations.HasLinkerAttribute<RequiresUnreferencedCodeAttribute>(method))
+				Context.LogWarning (methodOrigin, DiagnosticId.RequiresUnreferencedCodeOnEntryPoint, method.GetDisplayName ());
 
 			if (method.IsConstructor) {
 				if (!Annotations.ProcessSatelliteAssemblies && KnownMembers.IsSatelliteAssemblyMarker (method))

src/tools/illink/test/ILLink.RoslynAnalyzer.Tests/RequiresCapabilityTests.cs

@@ -100,6 +100,12 @@ public Task RequiresOnStaticConstructor ()
 			return RunTest (nameof (RequiresOnStaticConstructor));
 		}
 
+		[Fact]
+		public Task RequiresOnEntryPoint ()
+		{
+			return RunTest ();
+		}
+
 		[Fact]
 		public Task RequiresOnVirtualsAndInterfaces ()
 		{

src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/MemberTypes.cs

@@ -17,7 +17,9 @@ public class MemberTypes
 		// This is an easy way to suppress all trim related warnings in the Main method
 		// This test is about marking, not diagnostics and this Main will produce several warnings due to it accssing
 		// some problematic APIs (Delegate.Create for example) via reflection.
+		[UnconditionalSuppressMessage("Reflection", "IL2123", Justification = "The RUC suppresses warnings in an entrypoint, but we don't mind")]
 		[RequiresUnreferencedCode("test")]
+		[KeptAttributeAttribute(typeof(UnconditionalSuppressMessageAttribute))]
 		[KeptAttributeAttribute(typeof(RequiresUnreferencedCodeAttribute))]
 		public static void Main ()
 		{

src/tools/illink/test/Mono.Linker.Tests.Cases/RequiresCapability/RequiresOnAttribute.cs

@@ -14,6 +14,9 @@ class RequiresOnAttribute
 	{
 		// Using these as a simple way to suppress all warning in Main
 		// it causes lot of warning due to DAM marking everything in the class.
+		[UnconditionalSuppressMessage ("Reflection", "IL2123", Justification = "The RUC suppresses warnings in an entrypoint, but we don't mind")]
+		[UnconditionalSuppressMessage ("Reflection", "IL3057", Justification = "The RDC suppresses warnings in an entrypoint, but we don't mind")]
+		[UnconditionalSuppressMessage ("Reflection", "IL3005", Justification = "The RAF suppresses warnings in an entrypoint, but we don't mind")]
 		[RequiresUnreferencedCode ("main")]
 		[RequiresDynamicCode ("main")]
 		[RequiresAssemblyFiles ("main")]

src/tools/illink/test/Mono.Linker.Tests.Cases/RequiresCapability/RequiresOnAttributeCtor.cs

@@ -17,6 +17,7 @@ namespace Mono.Linker.Tests.Cases.RequiresCapability
 	public class RequiresOnAttributeCtor
 	{
 		// Simple way to suppress all warnings in Main
+		[UnconditionalSuppressMessage ("Reflection", "IL2123", Justification = "The RUC suppresses warnings in an entrypoint, but we don't mind")]
 		[RequiresUnreferencedCode ("main")]
 		public static void Main ()
 		{