C#: Only create a single empty location element.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Locations/EmptyLocation.cs

@@ -0,0 +1,37 @@
+using System.IO;
+
+namespace Semmle.Extraction.CSharp.Entities
+{
+    /// <summary>
+    /// Only used in buildless extraction to ensure that we create a single * empty location.
+    /// </summary>
+    public class EmptyLocation : SourceLocation
+    {
+        private readonly File generatedFile;
+
+        private EmptyLocation(Context cx) : base(cx, null)
+        {
+            generatedFile = GeneratedFile.Create(cx);
+        }
+
+        public override void Populate(TextWriter trapFile)
+        {
+            trapFile.locations_default(this, generatedFile, 0, 0, 0, 0);
+        }
+
+        public override void WriteId(EscapingTextWriter trapFile)
+        {
+            WriteStarId(trapFile);
+        }
+
+        public static EmptyLocation Create(Context cx) => EmptyLocationFactory.Instance.CreateEntity(cx, typeof(GeneratedLocation), null);
+
+        private class EmptyLocationFactory : CachedEntityFactory<string?, EmptyLocation>
+        {
+            public static EmptyLocationFactory Instance { get; } = new EmptyLocationFactory();
+
+            public override EmptyLocation Create(Context cx, string? init) => new EmptyLocation(cx);
+        }
+    }
+
+}

csharp/extractor/Semmle.Extraction.CSharp/Entities/Locations/GeneratedLocation.cs

@@ -14,14 +14,18 @@ private GeneratedLocation(Context cx)
 
         public override void Populate(TextWriter trapFile)
         {
+            if (Context.ExtractionContext.IsStandalone)
+            {
+                return;
+            }
+
             trapFile.locations_default(this, generatedFile, 0, 0, 0, 0);
         }
 
         public override void WriteId(EscapingTextWriter trapFile)
         {
             if (Context.ExtractionContext.IsStandalone)
             {
-                WriteStarId(trapFile);
                 return;
             }
 

csharp/extractor/Semmle.Extraction.CSharp/Extractor/Analyser.cs

@@ -238,6 +238,12 @@ private void DoAnalyseCompilation()
 
                 compilationEntity = Entities.Compilation.Create(cx);
 
+                if (cx.ExtractionContext.IsStandalone)
+                {
+                    // Add a single empty location
+                    Entities.EmptyLocation.Create(cx);
+                }
+
                 ExtractionContext.CompilationInfos.ForEach(ci => trapWriter.Writer.compilation_info(compilationEntity, ci.key, ci.value));
 
                 ReportProgressTaskDone(currentTaskId, assemblyPath, trapWriter.TrapFile, stopwatch.Elapsed, AnalysisAction.Extracted);