Extensions: interceptors (#79010)

Author: jcouv

src/Compilers/CSharp/Portable/Lowering/ExtensionMethodReferenceRewriter.cs

@@ -74,6 +74,8 @@ public static BoundNode VisitCall(BoundTreeRewriter rewriter, BoundCall node)
 
             static BoundExpression visitArgumentsAndFinishRewrite(BoundTreeRewriter rewriter, BoundCall node, BoundExpression? rewrittenReceiver)
             {
+                Debug.Assert(node.Method.MethodKind == MethodKind.LocalFunction || node.Method.IsStatic || node.ReceiverOpt is not null);
+
                 return updateCall(
                     node,
                     VisitMethodSymbolWithExtensionRewrite(rewriter, node.Method),

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_Call.cs

@@ -147,6 +147,18 @@ private void InterceptCallAndAdjustArguments(
                 return;
             }
 
+            if (interceptor.GetIsNewExtensionMember())
+            {
+                if (interceptor.TryGetCorrespondingExtensionImplementationMethod() is { } implementationMethod)
+                {
+                    interceptor = implementationMethod;
+                }
+                else
+                {
+                    throw ExceptionUtilities.Unreachable();
+                }
+            }
+
             Debug.Assert(nameSyntax != null);
             Debug.Assert(interceptor.IsDefinition);
             Debug.Assert(!interceptor.ContainingType.IsGenericType);
@@ -228,9 +240,12 @@ private void InterceptCallAndAdjustArguments(
                 this._diagnostics.Add(ErrorCode.WRN_InterceptorSignatureMismatch, attributeLocation, method, interceptor);
             }
 
-            method.TryGetThisParameter(out var methodThisParameter);
-            var interceptorThisParameterForCompare = needToReduce ? interceptor.Parameters[0] :
+            ParameterSymbol? methodThisParameter;
+            _ = method.TryGetInstanceExtensionParameter(out methodThisParameter) || method.TryGetThisParameter(out methodThisParameter);
+
+            ParameterSymbol? interceptorThisParameterForCompare = needToReduce ? interceptor.Parameters[0] :
                 interceptor.TryGetThisParameter(out var interceptorThisParameter) ? interceptorThisParameter : null;
+
             switch (methodThisParameter, interceptorThisParameterForCompare)
             {
                 case (not null, null):

src/Compilers/CSharp/Portable/Symbols/Source/SourceMethodSymbolWithAttributes.cs

@@ -1036,23 +1036,9 @@ private void DecodeInterceptsLocationChecksumBased(DecodeWellKnownAttributeArgum
             }
             thisNamespaceNames.Free();
 
-            if (ContainingType.IsGenericType)
+            bool hadError = ReportBadInterceptsLocation(diagnostics, attributeLocation);
+            if (hadError)
             {
-                diagnostics.Add(ErrorCode.ERR_InterceptorContainingTypeCannotBeGeneric, attributeLocation, this);
-                return;
-            }
-
-            if (MethodKind != MethodKind.Ordinary)
-            {
-                diagnostics.Add(ErrorCode.ERR_InterceptorMethodMustBeOrdinary, attributeLocation);
-                return;
-            }
-
-            Debug.Assert(_lazyCustomAttributesBag.IsEarlyDecodedWellKnownAttributeDataComputed);
-            var unmanagedCallersOnly = this.GetUnmanagedCallersOnlyAttributeData(forceComplete: false);
-            if (unmanagedCallersOnly != null)
-            {
-                diagnostics.Add(ErrorCode.ERR_InterceptorCannotUseUnmanagedCallersOnly, attributeLocation);
                 return;
             }
 
@@ -1194,23 +1180,9 @@ private void DecodeInterceptsLocationAttributeExperimentalCompat(
                 return;
             }
 
-            if (ContainingType.IsGenericType)
+            bool hadError = ReportBadInterceptsLocation(diagnostics, attributeLocation);
+            if (hadError)
             {
-                diagnostics.Add(ErrorCode.ERR_InterceptorContainingTypeCannotBeGeneric, attributeLocation, this);
-                return;
-            }
-
-            if (MethodKind != MethodKind.Ordinary)
-            {
-                diagnostics.Add(ErrorCode.ERR_InterceptorMethodMustBeOrdinary, attributeLocation);
-                return;
-            }
-
-            Debug.Assert(_lazyCustomAttributesBag.IsEarlyDecodedWellKnownAttributeDataComputed);
-            var unmanagedCallersOnly = this.GetUnmanagedCallersOnlyAttributeData(forceComplete: false);
-            if (unmanagedCallersOnly != null)
-            {
-                diagnostics.Add(ErrorCode.ERR_InterceptorCannotUseUnmanagedCallersOnly, attributeLocation);
                 return;
             }
 
@@ -1374,6 +1346,31 @@ static void reportFeatureNotEnabled(BindingDiagnosticBag diagnostics, AttributeS
             }
         }
 
+        private bool ReportBadInterceptsLocation(BindingDiagnosticBag diagnostics, Location attributeLocation)
+        {
+            if (!this.GetIsNewExtensionMember() && ContainingType.IsGenericType)
+            {
+                diagnostics.Add(ErrorCode.ERR_InterceptorContainingTypeCannotBeGeneric, attributeLocation, this);
+                return true;
+            }
+
+            if (MethodKind != MethodKind.Ordinary)
+            {
+                diagnostics.Add(ErrorCode.ERR_InterceptorMethodMustBeOrdinary, attributeLocation);
+                return true;
+            }
+
+            Debug.Assert(_lazyCustomAttributesBag.IsEarlyDecodedWellKnownAttributeDataComputed);
+            var unmanagedCallersOnly = this.GetUnmanagedCallersOnlyAttributeData(forceComplete: false);
+            if (unmanagedCallersOnly != null)
+            {
+                diagnostics.Add(ErrorCode.ERR_InterceptorCannotUseUnmanagedCallersOnly, attributeLocation);
+                return true;
+            }
+
+            return false;
+        }
+
         private void DecodeUnmanagedCallersOnlyAttribute(ref DecodeWellKnownAttributeArguments<AttributeSyntax, CSharpAttributeData, AttributeLocation> arguments)
         {
             Debug.Assert(arguments.AttributeSyntaxOpt != null);