C#: Handle some broken types in BMN.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/NamedType.cs

@@ -166,7 +166,9 @@ private class UnderlyingTupleTypeFactory : CachedEntityFactory<INamedTypeSymbol,
         // Create typerefs for constructed error types in case they are fully defined elsewhere.
         // We cannot use `!this.NeedsPopulation` because this would not be stable as it would depend on
         // the assembly that was being extracted at the time.
-        private bool UsesTypeRef => Symbol.TypeKind == TypeKind.Error || SymbolEqualityComparer.Default.Equals(Symbol.OriginalDefinition, Symbol);
+        private bool UsesTypeRef =>
+            Symbol.TypeKind == TypeKind.Error ||
+            SymbolEqualityComparer.Default.Equals(Symbol.OriginalDefinition, Symbol);
 
         public override Type TypeRef => UsesTypeRef ? (Type)NamedTypeRef.Create(Context, Symbol) : this;
     }

csharp/extractor/Semmle.Extraction.CSharp/Entities/Types/Type.cs

@@ -25,6 +25,22 @@ public static bool ConstructedOrParentIsConstructed(INamedTypeSymbol symbol)
                 symbol.ContainingType is not null && ConstructedOrParentIsConstructed(symbol.ContainingType);
         }
 
+        /// <summary>
+        /// Returns true in case we suspect this is broken type.
+        /// </summary>
+        /// <param name="symbol">Type symbol</param>
+        private bool IsBrokenType(ITypeSymbol symbol)
+        {
+            if (!Context.ExtractionContext.IsStandalone || !symbol.FromSource())
+            {
+                return false;
+            }
+            // (1) public class { ... } is a broken type and doesn't have a name.
+            // (2) public class var { ... } is a an allowed type, but it overrides the var keyword for all uses.
+            //     It is probably a better heuristic to treat it as a broken type.
+            return string.IsNullOrEmpty(symbol.Name) || symbol.Name == "var";
+        }
+
         public Kinds.TypeKind GetTypeKind(Context cx, bool constructUnderlyingTupleType)
         {
             switch (Symbol.SpecialType)
@@ -48,6 +64,9 @@ public Kinds.TypeKind GetTypeKind(Context cx, bool constructUnderlyingTupleType)
                     if (Symbol.IsBoundNullable())
                         return Kinds.TypeKind.NULLABLE;
 
+                    if (IsBrokenType(Symbol))
+                        return Kinds.TypeKind.UNKNOWN;
+
                     switch (Symbol.TypeKind)
                     {
                         case TypeKind.Class: return Kinds.TypeKind.CLASS;