codeql/csharp/extractor/Semmle.Extraction.CSharp/Entities/LocalFunction.cs

using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using System;
using System.IO;
using System.Linq;

namespace Semmle.Extraction.CSharp.Entities
{
    internal class LocalFunction : Method
    {
        private LocalFunction(Context cx, IMethodSymbol init) : base(cx, init)
        {
        }

        public override void WriteId(TextWriter trapFile)
        {
            throw new InvalidOperationException();
        }

        public override void WriteQuotedId(TextWriter trapFile)
        {
            trapFile.Write('*');
        }

        public static new LocalFunction Create(Context cx, IMethodSymbol field) => LocalFunctionFactory.Instance.CreateEntityFromSymbol(cx, field);

        private class LocalFunctionFactory : ICachedEntityFactory<IMethodSymbol, LocalFunction>
        {
            public static LocalFunctionFactory Instance { get; } = new LocalFunctionFactory();

            public LocalFunction Create(Context cx, IMethodSymbol init) => new LocalFunction(cx, init);
        }

        public override void Populate(TextWriter trapFile)
        {
            PopulateMethod(trapFile);

            // There is a "bug" in Roslyn whereby the IMethodSymbol associated with the local function symbol
            // is always static, so we need to go to the syntax reference of the local function to see whether
            // the "static" modifier is present.
            if (symbol.DeclaringSyntaxReferences.SingleOrDefault().GetSyntax() is LocalFunctionStatementSyntax fn)
            {
                foreach (var modifier in fn.Modifiers)
                {
                    Modifier.HasModifier(Context, trapFile, this, modifier.Text);
                }
            }

            var originalDefinition = IsSourceDeclaration ? this : Create(Context, symbol.OriginalDefinition);
            var returnType = Type.Create(Context, symbol.ReturnType);
            trapFile.local_functions(this, symbol.Name, returnType, originalDefinition);
            ExtractRefReturn(trapFile);
        }

        public override TrapStackBehaviour TrapStackBehaviour => TrapStackBehaviour.NeedsLabel;
    }
}