C#: Add class for making synthetic parameter entities.

Author: michaelnebel

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

@@ -0,0 +1,94 @@
+using System.IO;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace Semmle.Extraction.CSharp.Entities
+{
+    /// <summary>
+    /// Synthetic parameter for extension methods declared using the extension syntax.
+    /// That is, we add a synthetic parameter s to IsValid in the following example:
+    /// extension(string s) {
+    ///   public bool IsValid() { ... }
+    /// }
+    ///
+    /// Note, that we use the characteristics of the parameter of the extension type
+    /// to populate the database.
+    /// </summary>
+    internal class SyntheticExtensionParameter : FreshEntity, IParameter
+    {
+        private Method ExtensionMethod { get; }
+        private IParameterSymbol ExtensionParameter { get; }
+        private SyntheticExtensionParameter Original { get; }
+
+        private SyntheticExtensionParameter(Context cx, Method method, IParameterSymbol parameter, SyntheticExtensionParameter? original) : base(cx)
+        {
+            ExtensionMethod = method;
+            ExtensionParameter = parameter;
+            Original = original ?? this;
+        }
+
+        private static int Ordinal => 0;
+
+        private Parameter.Kind ParamKind
+        {
+            get
+            {
+                switch (ExtensionParameter.RefKind)
+                {
+                    case RefKind.Ref:
+                        return Parameter.Kind.Ref;
+                    case RefKind.In:
+                        return Parameter.Kind.In;
+                    case RefKind.RefReadOnlyParameter:
+                        return Parameter.Kind.RefReadOnly;
+                    default:
+                        return Parameter.Kind.None;
+                }
+            }
+        }
+
+        private string Name => ExtensionParameter.Name;
+
+        private bool IsSourceDeclaration => ExtensionMethod.Symbol.IsSourceDeclaration();
+
+        protected override void Populate(TextWriter trapFile)
+        {
+            PopulateNullability(trapFile, ExtensionParameter.GetAnnotatedType());
+            PopulateRefKind(trapFile, ExtensionParameter.RefKind);
+
+            var type = Type.Create(Context, ExtensionParameter.Type);
+            trapFile.@params(this, Name, type.TypeRef, Ordinal, ParamKind, ExtensionMethod, Original);
+
+            if (Context.OnlyScaffold)
+            {
+                return;
+            }
+
+            if (Context.ExtractLocation(ExtensionParameter))
+            {
+                var locations = Context.GetLocations(ExtensionParameter);
+                WriteLocationsToTrap(trapFile.param_location, this, locations);
+            }
+
+            if (IsSourceDeclaration)
+            {
+                foreach (var syntax in ExtensionParameter.DeclaringSyntaxReferences
+                    .Select(d => d.GetSyntax())
+                    .OfType<ParameterSyntax>()
+                    .Where(s => s.Type is not null))
+                {
+                    TypeMention.Create(Context, syntax.Type!, this, type);
+                }
+            }
+        }
+
+        public static SyntheticExtensionParameter Create(Context cx, Method method, IParameterSymbol parameter, SyntheticExtensionParameter? original)
+        {
+            var p = new SyntheticExtensionParameter(cx, method, parameter, original);
+            p.TryPopulate();
+            return p;
+        }
+    }
+
+}