Merge pull request #7646 from hvitved/csharp/roslyn-tuple-elements-workaround

C#: Workaround Roslyn bug in `INamedTypeSymbol.TupleElements`

Author: hvitved

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

@@ -90,7 +90,11 @@ protected override void Populate(TextWriter trapFile)
                     var tts = (TupleTypeSyntax)syntax;
                     var tt = (TupleType)type;
                     Emit(trapFile, loc ?? syntax.GetLocation(), parent, type);
-                    tts.Elements.Zip(tt.TupleElements, (s, t) => Create(Context, s.Type, this, t.Type)).Enumerate();
+                    foreach (var (s, t) in tts.Elements.Zip(tt.TupleElements, (s, t) => (s, t?.Type)))
+                    {
+                        if (t is not null)
+                            Create(Context, s.Type, this, t);
+                    }
                     return;
                 case SyntaxKind.GenericName:
                     Emit(trapFile, loc ?? syntax.GetLocation(), parent, type);

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

@@ -24,7 +24,7 @@ private class TupleTypeFactory : CachedEntityFactory<INamedTypeSymbol, TupleType
 
         private TupleType(Context cx, INamedTypeSymbol init) : base(cx, init)
         {
-            tupleElementsLazy = new Lazy<Field[]>(() => Symbol.TupleElements.Select(t => Field.Create(cx, t)).ToArray());
+            tupleElementsLazy = new Lazy<Field?[]>(() => Symbol.GetTupleElementsMaybeNull().Select(t => t is null ? null : Field.Create(cx, t)).ToArray());
         }
 
         // All tuple types are "local types"
@@ -47,7 +47,10 @@ public override void Populate(TextWriter trapFile)
 
             var index = 0;
             foreach (var element in TupleElements)
-                trapFile.tuple_element(this, index++, element);
+            {
+                if (element is not null)
+                    trapFile.tuple_element(this, index++, element);
+            }
 
             // Note: symbol.Locations seems to be very inconsistent
             // about what locations are available for a tuple type.
@@ -56,9 +59,10 @@ public override void Populate(TextWriter trapFile)
                 trapFile.type_location(this, Context.CreateLocation(l));
         }
 
-        private readonly Lazy<Field[]> tupleElementsLazy;
-        public Field[] TupleElements => tupleElementsLazy.Value;
+        private readonly Lazy<Field?[]> tupleElementsLazy;
+        public Field?[] TupleElements => tupleElementsLazy.Value;
 
-        public override IEnumerable<Type> TypeMentions => TupleElements.Select(e => e.Type);
+        public override IEnumerable<Type> TypeMentions =>
+            TupleElements.OfType<Field>().Select(e => e.Type);
     }
 }

csharp/extractor/Semmle.Extraction.CSharp/SymbolExtensions.cs

@@ -280,17 +280,30 @@ private static void BuildAssembly(IAssemblySymbol asm, EscapingTextWriter trapFi
         private static void BuildFunctionPointerTypeId(this IFunctionPointerTypeSymbol funptr, Context cx, EscapingTextWriter trapFile, ISymbol symbolBeingDefined) =>
             BuildFunctionPointerSignature(funptr, trapFile, s => s.BuildOrWriteId(cx, trapFile, symbolBeingDefined));
 
+        /// <summary>
+        /// Workaround for a Roslyn bug: https://github.com/dotnet/roslyn/issues/53943
+        /// </summary>
+        public static IEnumerable<IFieldSymbol?> GetTupleElementsMaybeNull(this INamedTypeSymbol type) =>
+            type.TupleElements;
+
         private static void BuildNamedTypeId(this INamedTypeSymbol named, Context cx, EscapingTextWriter trapFile, ISymbol symbolBeingDefined, bool constructUnderlyingTupleType)
         {
             if (!constructUnderlyingTupleType && named.IsTupleType)
             {
                 trapFile.Write('(');
-                trapFile.BuildList(",", named.TupleElements,
-                    f =>
+                trapFile.BuildList(",", named.GetTupleElementsMaybeNull(),
+                    (i, f) =>
                     {
-                        trapFile.Write((f.CorrespondingTupleField ?? f).Name);
-                        trapFile.Write(":");
-                        f.Type.BuildOrWriteId(cx, trapFile, symbolBeingDefined, constructUnderlyingTupleType: false);
+                        if (f is null)
+                        {
+                            trapFile.Write($"null({i})");
+                        }
+                        else
+                        {
+                            trapFile.Write((f.CorrespondingTupleField ?? f).Name);
+                            trapFile.Write(":");
+                            f.Type.BuildOrWriteId(cx, trapFile, symbolBeingDefined, constructUnderlyingTupleType: false);
+                        }
                     }
                     );
                 trapFile.Write(")");
@@ -464,8 +477,14 @@ private static void BuildNamedTypeDisplayName(this INamedTypeSymbol namedType, C
                 trapFile.Write('(');
                 trapFile.BuildList(
                     ",",
-                    namedType.TupleElements.Select(f => f.Type),
-                    t => t.BuildDisplayName(cx, trapFile));
+                    namedType.GetTupleElementsMaybeNull(),
+                    (i, f) =>
+                    {
+                        if (f is null)
+                            trapFile.Write($"null({i})");
+                        else
+                            f.Type.BuildDisplayName(cx, trapFile);
+                    });
                 trapFile.Write(")");
                 return;
             }

csharp/extractor/Semmle.Extraction/TrapExtensions.cs

@@ -232,19 +232,33 @@ public static TextWriter AppendList<T>(this EscapingTextWriter trapFile, string
         /// <param name="items">The list of items.</param>
         /// <param name="action">The action on each item.</param>
         /// <returns>The original trap builder (fluent interface).</returns>
-        public static T1 BuildList<T1, T2>(this T1 trapFile, string separator, IEnumerable<T2> items, Action<T2> action)
+        public static T1 BuildList<T1, T2>(this T1 trapFile, string separator, IEnumerable<T2> items, Action<int, T2> action)
             where T1 : TextWriter
         {
             var first = true;
+            var i = 0;
             foreach (var item in items)
             {
                 if (first)
                     first = false;
                 else
                     trapFile.Write(separator);
-                action(item);
+                action(i++, item);
             }
             return trapFile;
         }
+
+        /// <summary>
+        /// Builds a trap builder using a separator and an action for each item in the list.
+        /// </summary>
+        /// <typeparam name="T">The type of the items.</typeparam>
+        /// <param name="trapFile">The trap builder to append to.</param>
+        /// <param name="separator">The separator string (e.g. ",")</param>
+        /// <param name="items">The list of items.</param>
+        /// <param name="action">The action on each item.</param>
+        /// <returns>The original trap builder (fluent interface).</returns>
+        public static T1 BuildList<T1, T2>(this T1 trapFile, string separator, IEnumerable<T2> items, Action<T2> action)
+            where T1 : TextWriter =>
+            trapFile.BuildList(separator, items, (_, item) => action(item));
     }
 }