sebastienros.jint/Jint/Runtime/Interpreter/Statements/JintTryStatement.cs

using Esprima.Ast;
using Jint.Native;
using Jint.Runtime.Environments;

namespace Jint.Runtime.Interpreter.Statements
{
    /// <summary>
    /// https://tc39.es/ecma262/#sec-try-statement
    /// </summary>
    internal sealed class JintTryStatement : JintStatement<TryStatement>
    {
        private JintBlockStatement _block = null!;
        private JintBlockStatement? _catch;
        private JintBlockStatement? _finalizer;

        public JintTryStatement(TryStatement statement) : base(statement)
        {

        }

        protected override void Initialize(EvaluationContext context)
        {
            _block = new JintBlockStatement(_statement.Block);
            if (_statement.Finalizer != null)
            {
                _finalizer = new JintBlockStatement(_statement.Finalizer);
            }
        }

        internal override bool SupportsResume => true;

        protected override Completion ExecuteInternal(EvaluationContext context)
        {
            var engine = context.Engine;

            var b = _block.Execute(context);

            if (b.Type == CompletionType.Throw)
            {
                b = ExecuteCatch(context, b, engine);
            }

            if (_finalizer != null)
            {
                var f = _finalizer.Execute(context);
                if (f.Type == CompletionType.Normal)
                {
                    return b;
                }

                return f.UpdateEmpty(JsValue.Undefined);
            }

            return b.UpdateEmpty(JsValue.Undefined);
        }

        private Completion ExecuteCatch(EvaluationContext context, Completion b, Engine engine)
        {
            // execute catch
            if (_statement.Handler is not null)
            {
                // initialize lazily
                if (_catch is null)
                {
                    _catch = new JintBlockStatement(_statement.Handler.Body);
                }

                // https://tc39.es/ecma262/#sec-runtime-semantics-catchclauseevaluation

                var thrownValue = b.Value;
                var oldEnv = engine.ExecutionContext.LexicalEnvironment;
                var catchEnv = JintEnvironment.NewDeclarativeEnvironment(engine, oldEnv, catchEnvironment: true);

                var boundNames = new List<string>();
                _statement.Handler.Param.GetBoundNames(boundNames);

                foreach (var argName in boundNames)
                {
                    catchEnv.CreateMutableBinding(argName, false);
                }

                engine.UpdateLexicalEnvironment(catchEnv);

                var catchParam = _statement.Handler?.Param;
                catchParam.BindingInitialization(context, thrownValue, catchEnv);

                b = _catch.Execute(context);

                engine.UpdateLexicalEnvironment(oldEnv);
            }

            return b;
        }
    }
}