C#: Force population of compiler generated delegates used for lambdas.

Author: michaelnebel

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

@@ -18,7 +18,12 @@ protected OrdinaryMethod(Context cx, IMethodSymbol init)
 
         public IMethodSymbol SourceDeclaration => Symbol.OriginalDefinition;
 
-        public override Microsoft.CodeAnalysis.Location ReportingLocation => Symbol.GetSymbolLocation();
+        public override Microsoft.CodeAnalysis.Location ReportingLocation =>
+            IsCompilerGeneratedDelegate()
+                ? Symbol.ContainingType.GetSymbolLocation()
+                : Symbol.GetSymbolLocation();
+
+        public override bool NeedsPopulation => base.NeedsPopulation || IsCompilerGeneratedDelegate();
 
         public override void Populate(TextWriter trapFile)
         {
@@ -47,6 +52,18 @@ public override void Populate(TextWriter trapFile)
             ExtractCompilerGenerated(trapFile);
         }
 
+        private bool IsCompilerGeneratedDelegate()
+        {
+            // Lambdas with parameter defaults or a `params` parameter are implemented
+            // using compiler generated delegate types.
+            if (Symbol.MethodKind == MethodKind.DelegateInvoke &&
+                Symbol.ContainingType is INamedTypeSymbol nt)
+            {
+                return nt.TypeKind == TypeKind.Delegate && nt.IsImplicitlyDeclared;
+            }
+            return false;
+        }
+
         public static new OrdinaryMethod Create(Context cx, IMethodSymbol method)
         {
             if (method.MethodKind == MethodKind.ReducedExtension)