Share entity base classes between CIL and source extraction

csharp/extractor/Semmle.Extraction/Entities/Base/FreshEntity.cs

@@ -0,0 +1,38 @@
+using System.IO;
+
+namespace Semmle.Extraction
+{
+    /// <summary>
+    /// An entity which has a default "*" ID assigned to it.
+    /// </summary>
+    public abstract class FreshEntity : UnlabelledEntity
+    {
+        protected FreshEntity(Context cx) : base(cx)
+        {
+        }
+
+        protected abstract void Populate(TextWriter trapFile);
+
+        protected void TryPopulate()
+        {
+            Context.Try(null, null, () => Populate(Context.TrapWriter.Writer));
+        }
+
+        /// <summary>
+        /// For debugging.
+        /// </summary>
+        public string DebugContents
+        {
+            get
+            {
+                using var writer = new StringWriter();
+                Populate(writer);
+                return writer.ToString();
+            }
+        }
+
+        public override Microsoft.CodeAnalysis.Location? ReportingLocation => null;
+
+        public override TrapStackBehaviour TrapStackBehaviour { get; }
+    }
+}