C#: Synthetic DateTime object creation for DateTime defaults via attributes.

Author: michaelnebel

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

@@ -211,6 +211,11 @@ private static bool ContainsPattern(SyntaxNode node) =>
                 return Default.CreateGenerated(cx, parent, childIndex, location, ValueAsString(null));
             }
 
+            if (type.SpecialType is SpecialType.System_DateTime)
+            {
+                return DateTimeObjectCreation.CreateGenerated(cx, parent, childIndex, type, defaultValue, location);
+            }
+
             // const literal:
             return Literal.CreateGenerated(cx, parent, childIndex, type, defaultValue, location);
         }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/ObjectCreation/DateTimeObjectCreation.cs

@@ -0,0 +1,70 @@
+using Microsoft.CodeAnalysis;
+using System.Linq;
+using System.IO;
+using Semmle.Extraction.Kinds;
+
+namespace Semmle.Extraction.CSharp.Entities.Expressions
+{
+    internal class DateTimeObjectCreation : Expression
+    {
+        private readonly IMethodSymbol constructorSymbol;
+
+        private DateTimeObjectCreation(IMethodSymbol constructorSymbol, ExpressionInfo info) : base(info)
+        {
+            this.constructorSymbol = constructorSymbol;
+        }
+
+        // Gets the value of a System.DateTime object as a string containing the ticks.
+        private static long ValueAsLong(object? value) =>
+            value is System.DateTime d ? d.Ticks : 0;
+
+        // Gets the System.DateTime(long) constructor from the `type` symbol.
+        private static IMethodSymbol? GetDateTimeConstructor(ITypeSymbol? type)
+        {
+            return type?.GetMembers()
+                .Where(m =>
+                    m is IMethodSymbol c &&
+                    c.GetName() == "ctor" &&
+                    c.Parameters.Length == 1 &&
+                    c.Parameters[0].Type.SpecialType == SpecialType.System_Int64)
+                .Cast<IMethodSymbol>()
+                .FirstOrDefault();
+        }
+
+
+        protected void PopulateExpression(TextWriter trapFile)
+        {
+            var constructor = Constructor.Create(Context, constructorSymbol);
+            trapFile.expr_call(this, constructor);
+        }
+
+        protected new Expression TryPopulate()
+        {
+            Context.Try(null, null, () => PopulateExpression(Context.TrapWriter.Writer));
+            return this;
+        }
+
+        // Gets an expression that represents a System.DateTime object creation.
+        // The `type` symbol must be a System.DateTime type and the value must be a System.DateTime object.
+        // The expression that is being created is a call to the System.DateTime(long) constructor, where
+        // the number of ticks from the `value` object is used as the argument to the constructor call.
+        public static Expression CreateGenerated(Context cx, IExpressionParentEntity parent, int childIndex, ITypeSymbol type, object? value, Extraction.Entities.Location location)
+        {
+            var constructorSymbol = GetDateTimeConstructor(type) ?? throw new InternalError("Could not find symbol for System.DateTime(long)");
+            var expr = new DateTimeObjectCreation(constructorSymbol, new ExpressionInfo(
+                cx,
+                AnnotatedTypeSymbol.CreateNotAnnotated(type),
+                location,
+                ExprKind.OBJECT_CREATION,
+                parent,
+                childIndex,
+                true,
+                null));
+
+            var longTypeSymbol = constructorSymbol.Parameters[0].Type;
+            Literal.CreateGenerated(cx, expr, 0, longTypeSymbol, ValueAsLong(value), location);
+
+            return expr.TryPopulate();
+        }
+    }
+}