C# 14: Support extension types.

csharp/extractor/Semmle.Extraction.CSharp/CodeAnalysisExtensions/SymbolExtensions.cs

@@ -4,6 +4,7 @@
 using System.IO;
 using System.Linq;
 using Microsoft.CodeAnalysis;
+using Semmle.Util;
 using Semmle.Extraction.CSharp.Entities;
 
 namespace Semmle.Extraction.CSharp
@@ -164,6 +165,7 @@ public static void BuildTypeId(this ITypeSymbol type, Context cx, EscapingTextWr
                     case TypeKind.Enum:
                     case TypeKind.Delegate:
                     case TypeKind.Error:
+                    case TypeKind.Extension:
                         var named = (INamedTypeSymbol)type;
                         named.BuildNamedTypeId(cx, trapFile, symbolBeingDefined, constructUnderlyingTupleType);
                         return;
@@ -275,6 +277,20 @@ private static void BuildFunctionPointerTypeId(this IFunctionPointerTypeSymbol f
         public static IEnumerable<IFieldSymbol?> GetTupleElementsMaybeNull(this INamedTypeSymbol type) =>
             type.TupleElements;
 
+        private static void BuildExtensionTypeId(this INamedTypeSymbol named, Context cx, EscapingTextWriter trapFile)
+        {
+            trapFile.Write("extension(");
+            if (named.ExtensionMarkerName is not null)
+            {
+                trapFile.Write(named.ExtensionMarkerName);
+            }
+            else
+            {
+                trapFile.Write("unknown");
+            }
+            trapFile.Write(")");
+        }
+
         private static void BuildQualifierAndName(INamedTypeSymbol named, Context cx, EscapingTextWriter trapFile, ISymbol symbolBeingDefined)
         {
             if (named.ContainingType is not null)
@@ -289,8 +305,18 @@ private static void BuildQualifierAndName(INamedTypeSymbol named, Context cx, Es
                 named.ContainingNamespace.BuildNamespace(cx, trapFile);
             }
 
-            var name = named.IsFileLocal ? named.MetadataName : named.Name;
-            trapFile.Write(name);
+            if (named.IsFileLocal)
+            {
+                trapFile.Write(named.MetadataName);
+            }
+            else if (named.IsExtension)
+            {
+                named.BuildExtensionTypeId(cx, trapFile);
+            }
+            else
+            {
+                trapFile.Write(named.Name);
+            }
         }
 
         private static void BuildTupleId(INamedTypeSymbol named, Context cx, EscapingTextWriter trapFile, ISymbol symbolBeingDefined)
@@ -391,6 +417,7 @@ public static void BuildDisplayName(this ITypeSymbol type, Context cx, TextWrite
                     case TypeKind.Enum:
                     case TypeKind.Delegate:
                     case TypeKind.Error:
+                    case TypeKind.Extension:
                         var named = (INamedTypeSymbol)type;
                         named.BuildNamedTypeDisplayName(cx, trapFile, constructUnderlyingTupleType);
                         return;
@@ -465,6 +492,20 @@ public static void BuildFunctionPointerSignature(IFunctionPointerTypeSymbol funp
         private static void BuildFunctionPointerTypeDisplayName(this IFunctionPointerTypeSymbol funptr, Context cx, TextWriter trapFile) =>
             BuildFunctionPointerSignature(funptr, trapFile, s => s.BuildDisplayName(cx, trapFile));
 
+        private static void BuildExtensionTypeDisplayName(this INamedTypeSymbol named, Context cx, TextWriter trapFile)
+        {
+            trapFile.Write("extension(");
+            if (named.ExtensionParameter?.Type is ITypeSymbol type)
+            {
+                type.BuildDisplayName(cx, trapFile);
+            }
+            else
+            {
+                trapFile.Write("unknown");
+            }
+            trapFile.Write(")");
+        }
+
         private static void BuildNamedTypeDisplayName(this INamedTypeSymbol namedType, Context cx, TextWriter trapFile, bool constructUnderlyingTupleType)
         {
             if (!constructUnderlyingTupleType && namedType.IsTupleType)
@@ -484,6 +525,12 @@ private static void BuildNamedTypeDisplayName(this INamedTypeSymbol namedType, C
                 return;
             }
 
+            if (namedType.IsExtension)
+            {
+                namedType.BuildExtensionTypeDisplayName(cx, trapFile);
+                return;
+            }
+
             if (namedType.IsAnonymousType)
             {
                 namedType.BuildAnonymousName(cx, trapFile);
@@ -596,6 +643,87 @@ public static bool IsSourceDeclaration(this IParameterSymbol parameter)
             return true;
         }
 
+        /// <summary>
+        /// Return true if this method is a compiler-generated extension method.
+        /// </summary>
+        public static bool IsCompilerGeneratedExtensionMethod(this IMethodSymbol method) =>
+            method.TryGetExtensionMethod(out _);
+
+        /// <summary>
+        /// Returns true if this method is a compiler-generated extension method,
+        /// and outputs the original extension method declaration.
+        /// </summary>
+        public static bool TryGetExtensionMethod(this IMethodSymbol method, out IMethodSymbol? declaration)
+        {
+            declaration = null;
+            if (method.IsImplicitlyDeclared && method.ContainingSymbol is INamedTypeSymbol containingType)
+            {
+                // Extension types are declared within the same type as the generated
+                // extension method implementation.
+                var extensions = containingType.GetMembers()
+                    .OfType<INamedTypeSymbol>()
+                    .Where(t => t.IsExtension);
+                // Find the (possibly unbound) original extension method that maps to this implementation (if any).
+                var unboundDeclaration = extensions.SelectMany(e => e.GetMembers())
+                    .OfType<IMethodSymbol>()
+                    .FirstOrDefault(m => SymbolEqualityComparer.Default.Equals(m.AssociatedExtensionImplementation, method.ConstructedFrom));
+
+                var isFullyConstructed = method.IsBoundGenericMethod();
+                if (isFullyConstructed && unboundDeclaration?.ContainingType is INamedTypeSymbol extensionType)
+                {
+                    try
+                    {
+                        // Use the type arguments from the constructed extension method to construct the extension type.
+                        var arguments = method.TypeArguments.ToArray();
+                        var (extensionTypeArguments, extensionMethodArguments) = arguments.SplitAt(extensionType.TypeParameters.Length);
+
+                        // Construct the extension type.
+                        var boundExtensionType = extensionType.IsUnboundGenericType()
+                            ? extensionType.Construct(extensionTypeArguments.ToArray())
+                            : extensionType;
+
+                        // Find the extension method declaration within the constructed extension type.
+                        var extensionDeclaration = boundExtensionType.GetMembers()
+                            .OfType<IMethodSymbol>()
+                            .First(c => SymbolEqualityComparer.Default.Equals(c.OriginalDefinition, unboundDeclaration));
+
+                        // If the extension declaration is unbound apply the remaning type arguments and construct it.
+                        declaration = extensionDeclaration.IsUnboundGenericMethod()
+                            ? extensionDeclaration.Construct(extensionMethodArguments.ToArray())
+                            : extensionDeclaration;
+                    }
+                    catch
+                    {
+                        // If anything goes wrong, fall back to the unbound declaration.
+                        declaration = unboundDeclaration;
+                    }
+                }
+                else
+                {
+                    declaration = unboundDeclaration;
+                }
+
+            }
+            return declaration is not null;
+        }
+
+        /// <summary>
+        /// Returns true if this method is an unbound generic method.
+        /// </summary>
+        public static bool IsUnboundGenericMethod(this IMethodSymbol method) =>
+            method.IsGenericMethod && SymbolEqualityComparer.Default.Equals(method.ConstructedFrom, method);
+
+        /// <summary>
+        /// Returns true if this method is a bound generic method.
+        /// </summary>
+        public static bool IsBoundGenericMethod(this IMethodSymbol method) => method.IsGenericMethod && !method.IsUnboundGenericMethod();
+
+        /// <summary>
+        /// Returns true if this type is an unbound generic type.
+        /// </summary>
+        public static bool IsUnboundGenericType(this INamedTypeSymbol type) =>
+            type.IsGenericType && SymbolEqualityComparer.Default.Equals(type.ConstructedFrom, type);
+
         /// <summary>
         /// Gets the base type of `symbol`. Unlike `symbol.BaseType`, this excludes effective base
         /// types of type parameters as well as `object` base types.

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Invocation.cs

@@ -24,6 +24,16 @@ private Invocation(ExpressionNodeInfo info)
 
         private bool IsExplicitDelegateInvokeCall() => Kind == ExprKind.DELEGATE_INVOCATION && Context.GetModel(Syntax.Expression).GetSymbolInfo(Syntax.Expression).Symbol is IMethodSymbol m && m.MethodKind == MethodKind.DelegateInvoke;
 
+        private bool IsOperatorCall() => Kind == ExprKind.OPERATOR_INVOCATION;
+
+        private bool IsValidMemberAccessKind()
+        {
+            return Kind == ExprKind.METHOD_INVOCATION ||
+                IsEventDelegateCall() ||
+                IsExplicitDelegateInvokeCall() ||
+                IsOperatorCall();
+        }
+
         protected override void PopulateExpression(TextWriter trapFile)
         {
             if (IsNameof(Syntax))
@@ -37,7 +47,7 @@ protected override void PopulateExpression(TextWriter trapFile)
             var target = TargetSymbol;
             switch (Syntax.Expression)
             {
-                case MemberAccessExpressionSyntax memberAccess when Kind == ExprKind.METHOD_INVOCATION || IsEventDelegateCall() || IsExplicitDelegateInvokeCall():
+                case MemberAccessExpressionSyntax memberAccess when IsValidMemberAccessKind():
                     memberName = memberAccess.Name.Identifier.Text;
                     if (Syntax.Expression.Kind() == SyntaxKind.SimpleMemberAccessExpression)
                         // Qualified method call; `x.M()`
@@ -113,14 +123,31 @@ private static bool IsDynamicCall(ExpressionNodeInfo info)
 
         public SymbolInfo SymbolInfo => info.SymbolInfo;
 
+        private static bool IsOperatorLikeCall(ExpressionNodeInfo info)
+        {
+            return info.SymbolInfo.Symbol is IMethodSymbol method &&
+                method.TryGetExtensionMethod(out var original) &&
+                original!.MethodKind == MethodKind.UserDefinedOperator;
+        }
+
         public IMethodSymbol? TargetSymbol
         {
             get
             {
                 var si = SymbolInfo;
 
-                if (si.Symbol is not null)
-                    return si.Symbol as IMethodSymbol;
+                if (si.Symbol is ISymbol symbol)
+                {
+                    var method = symbol as IMethodSymbol;
+                    // Case for compiler-generated extension methods.
+                    if (method is not null &&
+                        method.TryGetExtensionMethod(out var original))
+                    {
+                        return original;
+                    }
+
+                    return method;
+                }
 
                 if (si.CandidateReason == CandidateReason.OverloadResolutionFailure)
                 {
@@ -196,15 +223,25 @@ private static bool IsLocalFunctionInvocation(ExpressionNodeInfo info)
 
         private static ExprKind GetKind(ExpressionNodeInfo info)
         {
-            return IsNameof((InvocationExpressionSyntax)info.Node)
-                ? ExprKind.NAMEOF
-                : IsDelegateLikeCall(info)
-                    ? IsDelegateInvokeCall(info)
-                        ? ExprKind.DELEGATE_INVOCATION
-                        : ExprKind.FUNCTION_POINTER_INVOCATION
-                    : IsLocalFunctionInvocation(info)
-                        ? ExprKind.LOCAL_FUNCTION_INVOCATION
-                        : ExprKind.METHOD_INVOCATION;
+            if (IsNameof((InvocationExpressionSyntax)info.Node))
+            {
+                return ExprKind.NAMEOF;
+            }
+            if (IsDelegateLikeCall(info))
+            {
+                return IsDelegateInvokeCall(info)
+                    ? ExprKind.DELEGATE_INVOCATION
+                    : ExprKind.FUNCTION_POINTER_INVOCATION;
+            }
+            if (IsLocalFunctionInvocation(info))
+            {
+                return ExprKind.LOCAL_FUNCTION_INVOCATION;
+            }
+            if (IsOperatorLikeCall(info))
+            {
+                return ExprKind.OPERATOR_INVOCATION;
+            }
+            return ExprKind.METHOD_INVOCATION;
         }
 
         private static bool IsNameof(InvocationExpressionSyntax syntax)

csharp/extractor/Semmle.Extraction.CSharp/Entities/Method.cs

@@ -14,18 +14,37 @@ internal abstract class Method : CachedSymbol<IMethodSymbol>, IExpressionParentE
         protected Method(Context cx, IMethodSymbol init)
             : base(cx, init) { }
 
+        private SyntheticExtensionParameter? SyntheticParameter { get; set; }
+
+        private int SynthesizeExtensionParameter()
+        {
+            // Synthesize implicit parameter for extension methods declared using extension(...) syntax.
+            if (Symbol.ContainingSymbol is INamedTypeSymbol type &&
+                type.IsExtension && type.ExtensionParameter is IParameterSymbol parameter &&
+                !string.IsNullOrEmpty(parameter.Name) && !Symbol.IsStatic)
+            {
+                var originalSyntheticParam = OriginalDefinition.SyntheticParameter;
+                SyntheticParameter = SyntheticExtensionParameter.Create(Context, this, parameter, originalSyntheticParam);
+                return 1;
+            }
+
+            return 0;
+        }
+
         protected void PopulateParameters()
         {
             var originalMethod = OriginalDefinition;
+            var positionOffset = SynthesizeExtensionParameter();
+
             IEnumerable<IParameterSymbol> parameters = Symbol.Parameters;
             IEnumerable<IParameterSymbol> originalParameters = originalMethod.Symbol.Parameters;
 
             foreach (var p in parameters.Zip(originalParameters, (paramSymbol, originalParam) => new { paramSymbol, originalParam }))
             {
                 var original = SymbolEqualityComparer.Default.Equals(p.paramSymbol, p.originalParam)
                     ? null
-                    : Parameter.Create(Context, p.originalParam, originalMethod);
-                Parameter.Create(Context, p.paramSymbol, this, original);
+                    : Parameter.Create(Context, p.originalParam, originalMethod, null, positionOffset);
+                Parameter.Create(Context, p.paramSymbol, this, original, positionOffset);
             }
 
             if (Symbol.IsVararg)
@@ -302,9 +321,9 @@ public static void AddExplicitInterfaceQualifierToId(Context cx, EscapingTextWri
         /// <summary>
         /// Whether this method has unbound type parameters.
         /// </summary>
-        public bool IsUnboundGeneric => IsGeneric && SymbolEqualityComparer.Default.Equals(Symbol.ConstructedFrom, Symbol);
+        public bool IsUnboundGeneric => Symbol.IsUnboundGenericMethod();
 
-        public bool IsBoundGeneric => IsGeneric && !IsUnboundGeneric;
+        public bool IsBoundGeneric => Symbol.IsBoundGenericMethod();
 
         protected IMethodSymbol ConstructedFromSymbol => Symbol.ConstructedFrom;
 

csharp/extractor/Semmle.Extraction.CSharp/Entities/OrdinaryMethod.cs

@@ -23,7 +23,11 @@ protected OrdinaryMethod(Context cx, IMethodSymbol init)
                 ? Symbol.ContainingType.GetSymbolLocation()
                 : BodyDeclaringSymbol.GetSymbolLocation();
 
-        public override bool NeedsPopulation => base.NeedsPopulation || IsCompilerGeneratedDelegate();
+        public override bool NeedsPopulation =>
+            (base.NeedsPopulation || IsCompilerGeneratedDelegate()) &&
+            // Exclude compiler-generated extension methods. A call to such a method
+            // is replaced by a call to the defining extension method.
+            !Symbol.IsCompilerGeneratedExtensionMethod();
 
         public override void Populate(TextWriter trapFile)
         {

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/NamedType.cs

@@ -20,6 +20,8 @@ private NamedType(Context cx, INamedTypeSymbol init, bool constructUnderlyingTup
         public static NamedType Create(Context cx, INamedTypeSymbol type) =>
             NamedTypeFactory.Instance.CreateEntityFromSymbol(cx, type);
 
+        public NamedType OriginalDefinition => Create(Context, Symbol.OriginalDefinition);
+
         /// <summary>
         /// Creates a named type entity from a tuple type. Unlike <see cref="Create"/>, this
         /// will create an entity for the underlying `System.ValueTuple` struct.
@@ -90,6 +92,25 @@ public override void Populate(TextWriter trapFile)
             {
                 trapFile.anonymous_types(this);
             }
+
+            if (Symbol.IsExtension && Symbol.ExtensionParameter is IParameterSymbol parameter)
+            {
+                // For some reason an extension type has a receiver parameter with an empty name
+                // even when there is no parameter.
+                if (!string.IsNullOrEmpty(parameter.Name))
+                {
+                    var originalType = OriginalDefinition;
+                    // In case this is a constructed generic, we also need to create the unbound parameter.
+                    var originalParameter = SymbolEqualityComparer.Default.Equals(Symbol, originalType.Symbol.ExtensionParameter) || originalType.Symbol.ExtensionParameter is null
+                        ? null
+                        : Parameter.Create(Context, originalType.Symbol.ExtensionParameter, originalType);
+                    Parameter.Create(Context, parameter, this, originalParameter);
+                }
+
+                // Use the parameter type as the receiver type.
+                var receiverType = Type.Create(Context, parameter.Type).TypeRef;
+                trapFile.extension_receiver_type(this, receiverType);
+            }
         }
 
         private readonly Lazy<Type[]> typeArgumentsLazy;

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs

@@ -105,6 +105,7 @@ public Kinds.TypeKind GetTypeKind(Context cx, bool constructUnderlyingTupleType)
                         case TypeKind.Pointer: return Kinds.TypeKind.POINTER;
                         case TypeKind.FunctionPointer: return Kinds.TypeKind.FUNCTION_POINTER;
                         case TypeKind.Error: return Kinds.TypeKind.UNKNOWN;
+                        case TypeKind.Extension: return Kinds.TypeKind.EXTENSION;
                         default:
                             cx.ModelError(Symbol, $"Unhandled type kind '{Symbol.TypeKind}'");
                             return Kinds.TypeKind.UNKNOWN;
@@ -366,7 +367,7 @@ private class DelegateTypeParameter : Parameter
             private DelegateTypeParameter(Context cx, IParameterSymbol init, IEntity parent, Parameter? original)
                 : base(cx, init, parent, original) { }
 
-            public static new DelegateTypeParameter Create(Context cx, IParameterSymbol param, IEntity parent, Parameter? original = null) =>
+            public static DelegateTypeParameter Create(Context cx, IParameterSymbol param, IEntity parent, Parameter? original = null) =>
                // We need to use a different cache key than `param` to avoid mixing up
                // `DelegateTypeParameter`s and `Parameter`s
                DelegateTypeParameterFactory.Instance.CreateEntity(cx, (typeof(DelegateTypeParameter), new SymbolEqualityWrapper(param)), (param, parent, original));