sebastienros.jint/Jint/Runtime/Environments/FunctionEnvironment.cs

using System.Runtime.CompilerServices;
using Esprima.Ast;
using Jint.Collections;
using Jint.Native;
using Jint.Native.Function;
using Jint.Native.Iterator;
using Jint.Native.Object;
using Jint.Runtime.Interpreter;
using Jint.Runtime.Interpreter.Expressions;

namespace Jint.Runtime.Environments
{
    /// <summary>
    /// https://tc39.es/ecma262/#sec-function-environment-records
    /// </summary>
    internal sealed class FunctionEnvironment : DeclarativeEnvironment
    {
        private enum ThisBindingStatus
        {
            Lexical,
            Initialized,
            Uninitialized
        }

        private JsValue? _thisValue;
        private ThisBindingStatus _thisBindingStatus;
        internal readonly Function _functionObject;

        public FunctionEnvironment(
            Engine engine,
            Function functionObject,
            JsValue newTarget) : base(engine)
        {
            _functionObject = functionObject;
            NewTarget = newTarget;
            if (functionObject._functionDefinition?.Function is ArrowFunctionExpression)
            {
                _thisBindingStatus = ThisBindingStatus.Lexical;
            }
            else
            {
                _thisBindingStatus = ThisBindingStatus.Uninitialized;
            }
        }


        internal override bool HasThisBinding() => _thisBindingStatus != ThisBindingStatus.Lexical;

        internal override bool HasSuperBinding() =>
            _thisBindingStatus != ThisBindingStatus.Lexical && !_functionObject._homeObject.IsUndefined();

        public JsValue BindThisValue(JsValue value)
        {
            if (_thisBindingStatus != ThisBindingStatus.Initialized)
            {
                _thisValue = value;
                _thisBindingStatus = ThisBindingStatus.Initialized;
                return value;
            }

            ExceptionHelper.ThrowReferenceError(_functionObject._realm, "'this' has already been bound");
            return null!;
        }

        internal override JsValue GetThisBinding()
        {
            if (_thisBindingStatus != ThisBindingStatus.Uninitialized)
            {
                return _thisValue!;
            }

            ThrowUninitializedThis();
            return null!;
        }

        [MethodImpl(MethodImplOptions.NoInlining)]
        private void ThrowUninitializedThis()
        {
            var message = "Cannot access uninitialized 'this'";
            if (NewTarget is ScriptFunction { _isClassConstructor: true, _constructorKind: ConstructorKind.Derived })
            {
                // help with better error message
                message = "Must call super constructor in derived class before accessing 'this' or returning from derived constructor";
            }

            ExceptionHelper.ThrowReferenceError(_engine.ExecutionContext.Realm, message);
        }

        public JsValue GetSuperBase()
        {
            var home = _functionObject._homeObject;
            return home.IsUndefined()
                ? Undefined
                : ((ObjectInstance) home).GetPrototypeOf() ?? Null;
        }

        // optimization to have logic near record internal structures.

        internal void InitializeParameters(
            Key[] parameterNames,
            bool hasDuplicates,
            JsValue[]? arguments)
        {
            if (parameterNames.Length == 0)
            {
                return;
            }

            var value = hasDuplicates ? Undefined : null;
            var directSet = !hasDuplicates && (_dictionary is null || _dictionary.Count == 0);
            for (uint i = 0; i < (uint) parameterNames.Length; i++)
            {
                var paramName = parameterNames[i];
                if (directSet || _dictionary is null || !_dictionary.ContainsKey(paramName))
                {
                    var parameterValue = value;
                    if (arguments != null)
                    {
                        parameterValue = i < (uint) arguments.Length ? arguments[i] : Undefined;
                    }

                    _dictionary ??= new HybridDictionary<Binding>();
                    _dictionary[paramName] = new Binding(parameterValue!, canBeDeleted: false, mutable: true, strict: false);
                }
            }
        }

        internal void AddFunctionParameters(EvaluationContext context, IFunction functionDeclaration, JsValue[] arguments)
        {
            var empty = _dictionary is null || _dictionary.Count == 0;
            ref readonly var parameters = ref functionDeclaration.Params;
            var count = parameters.Count;
            for (var i = 0; i < count; i++)
            {
                SetFunctionParameter(context, parameters[i], arguments, i, empty);
            }
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SetFunctionParameter(
            EvaluationContext context,
            Node? parameter,
            JsValue[] arguments,
            int index,
            bool initiallyEmpty)
        {
            if (parameter is Identifier identifier)
            {
                var argument = arguments.At(index);
                SetItemSafely(identifier.Name, argument, initiallyEmpty);
            }
            else
            {
                SetFunctionParameterUnlikely(context, parameter, arguments, index, initiallyEmpty);
            }
        }

        private void SetFunctionParameterUnlikely(
            EvaluationContext context,
            Node? parameter,
            JsValue[] arguments,
            int index,
            bool initiallyEmpty)
        {
            var argument = arguments.At(index);

            if (parameter is RestElement restElement)
            {
                HandleRestElementArray(context, restElement, arguments, index, initiallyEmpty);
            }
            else if (parameter is ArrayPattern arrayPattern)
            {
                HandleArrayPattern(context, initiallyEmpty, argument, arrayPattern);
            }
            else if (parameter is ObjectPattern objectPattern)
            {
                HandleObjectPattern(context, initiallyEmpty, argument, objectPattern);
            }
            else if (parameter is AssignmentPattern assignmentPattern)
            {
                HandleAssignmentPatternOrExpression(context, assignmentPattern.Left, assignmentPattern.Right, argument, initiallyEmpty);
            }
            else if (parameter is AssignmentExpression assignmentExpression)
            {
                HandleAssignmentPatternOrExpression(context, assignmentExpression.Left, assignmentExpression.Right, argument, initiallyEmpty);
            }
        }

        private void HandleObjectPattern(EvaluationContext context, bool initiallyEmpty, JsValue argument, ObjectPattern objectPattern)
        {
            if (argument.IsNullOrUndefined())
            {
                ExceptionHelper.ThrowTypeError(_functionObject._realm, "Destructed parameter is null or undefined");
            }

            var argumentObject = TypeConverter.ToObject(_engine.Realm , argument);

            ref readonly var properties = ref objectPattern.Properties;
            var processedProperties = properties.Count > 0 && properties[properties.Count - 1] is RestElement
                ? new HashSet<JsValue>()
                : null;

            var jsValues = _engine._jsValueArrayPool.RentArray(1);
            foreach (var property in properties)
            {
                var oldEnv = _engine.ExecutionContext.LexicalEnvironment;
                var paramVarEnv = JintEnvironment.NewDeclarativeEnvironment(_engine, oldEnv);
                PrivateEnvironment? privateEnvironment = null; // TODO PRIVATE check when implemented
                _engine.EnterExecutionContext(paramVarEnv, paramVarEnv, _engine.ExecutionContext.Realm, privateEnvironment);

                try
                {
                    if (property is Property p)
                    {
                        var propertyName = p.GetKey(_engine);
                        processedProperties?.Add(propertyName.ToString());
                        jsValues[0] = argumentObject.Get(propertyName);
                        SetFunctionParameter(context, p.Value, jsValues, 0, initiallyEmpty);
                    }
                    else
                    {
                        if (((RestElement) property).Argument is Identifier restIdentifier)
                        {
                            var rest = _engine.Realm.Intrinsics.Object.Construct((argumentObject.Properties?.Count ?? 0) - processedProperties!.Count);
                            argumentObject.CopyDataProperties(rest, processedProperties);
                            SetItemSafely(restIdentifier.Name, rest, initiallyEmpty);
                        }
                        else
                        {
                            ExceptionHelper.ThrowSyntaxError(_functionObject._realm, "Object rest parameter can only be objects");
                        }
                    }
                }
                finally
                {
                    _engine.LeaveExecutionContext();
                }
            }

            _engine._jsValueArrayPool.ReturnArray(jsValues);
        }

        private void HandleArrayPattern(EvaluationContext context, bool initiallyEmpty, JsValue argument, ArrayPattern arrayPattern)
        {
            if (argument.IsNull())
            {
                ExceptionHelper.ThrowTypeError(_functionObject._realm, "Destructed parameter is null");
            }

            JsArray? array;
            if (argument is JsArray { HasOriginalIterator: true } ai)
            {
                array = ai;
            }
            else
            {
                if (!argument.TryGetIterator(_functionObject._realm, out var iterator))
                {
                    ExceptionHelper.ThrowTypeError(context.Engine.Realm, "object is not iterable");
                }

                array = _engine.Realm.Intrinsics.Array.ArrayCreate(0);
                var max = arrayPattern.Elements.Count;
                if (max > 0 && arrayPattern.Elements[max - 1]?.Type == Nodes.RestElement)
                {
                    // need to consume all
                    max = int.MaxValue;
                }
                var protocol = new ArrayPatternProtocol(_engine, array, iterator, max);
                protocol.Execute();
            }

            var arrayContents = array.ToArray();
            for (var i = 0; i < arrayPattern.Elements.Count; i++)
            {
                SetFunctionParameter(context, arrayPattern.Elements[i], arrayContents, i, initiallyEmpty);
            }
        }

        private void HandleRestElementArray(
            EvaluationContext context,
            RestElement restElement,
            JsValue[] arguments,
            int index,
            bool initiallyEmpty)
        {
            // index + 1 == parameters.count because rest is last
            int restCount = arguments.Length - (index + 1) + 1;
            uint count = restCount > 0 ? (uint) restCount : 0;

            uint targetIndex = 0;
            var rest = new JsValue[count];
            for (var argIndex = index; argIndex < arguments.Length; ++argIndex)
            {
                rest[targetIndex++] = arguments[argIndex];
            }

            var array = new JsArray(_engine, rest);
            if (restElement.Argument is Identifier restIdentifier)
            {
                SetItemSafely(restIdentifier.Name, array, initiallyEmpty);
            }
            else if (restElement.Argument is BindingPattern bindingPattern)
            {
                SetFunctionParameter(context, bindingPattern, new [] { array }, 0, initiallyEmpty);
            }
            else
            {
                ExceptionHelper.ThrowSyntaxError(_functionObject._realm, "Rest parameters can only be identifiers or arrays");
            }
        }

        private void HandleAssignmentPatternOrExpression(
            EvaluationContext context,
            Node left,
            Node right,
            JsValue argument,
            bool initiallyEmpty)
        {
            var idLeft = left as Identifier;
            if (idLeft != null
                && right is Identifier idRight
                && string.Equals(idLeft.Name, idRight.Name, StringComparison.Ordinal))
            {
                ExceptionHelper.ThrowReferenceNameError(_functionObject._realm, idRight.Name);
            }

            if (argument.IsUndefined())
            {
                var expression = right.As<Expression>();
                var jintExpression = JintExpression.Build(expression);

                var oldEnv = _engine.ExecutionContext.LexicalEnvironment;
                var paramVarEnv = JintEnvironment.NewDeclarativeEnvironment(_engine, oldEnv);

                _engine.EnterExecutionContext(new ExecutionContext(null, paramVarEnv, paramVarEnv, null, _engine.Realm, null));
                try
                {
                    argument = jintExpression.GetValue(context);
                }
                finally
                {
                    _engine.LeaveExecutionContext();
                }

                if (idLeft != null && right.IsFunctionDefinition())
                {
                    ((Function) argument).SetFunctionName(idLeft.Name);
                }
            }

            SetFunctionParameter(context, left, new[]
            {
                argument
            }, 0, initiallyEmpty);
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void SetItemSafely(Key name, JsValue argument, bool initiallyEmpty)
        {
            if (initiallyEmpty)
            {
                _dictionary ??= new HybridDictionary<Binding>();
                _dictionary[name] = new Binding(argument, canBeDeleted: false, mutable: true, strict: false);
            }
            else
            {
                SetItemCheckExisting(name, argument);
            }
        }

        private void SetItemCheckExisting(Key name, JsValue argument)
        {
            _dictionary ??= new HybridDictionary<Binding>();
            if (!_dictionary.TryGetValue(name, out var existing))
            {
                _dictionary[name] = new Binding(argument, canBeDeleted: false, mutable: true, strict: false);
            }
            else
            {
                if (existing.Mutable)
                {
                    _dictionary[name] = existing.ChangeValue(argument);
                }
                else
                {
                    ExceptionHelper.ThrowTypeError(_functionObject._realm, "Can't update the value of an immutable binding.");
                }
            }
        }

        private sealed class ArrayPatternProtocol : IteratorProtocol
        {
            private readonly JsArray _instance;
            private readonly int _max;
            private long _index;

            public ArrayPatternProtocol(
                Engine engine,
                JsArray instance,
                IteratorInstance iterator,
                int max) : base(engine, iterator, 0)
            {
                _instance = instance;
                _max = max;
            }

            protected override void ProcessItem(JsValue[] arguments, JsValue currentValue)
            {
                _instance.SetIndexValue((uint) _index, currentValue, updateLength: false);
                _index++;
            }

            protected override bool ShouldContinue => _index < _max;

            protected override void IterationEnd()
            {
                if (_index > 0)
                {
                    _instance.SetLength((uint) _index);
                    IteratorClose(CompletionType.Normal);
                }
            }
        }
    }
}