MiscOps.cs

// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Management.Automation.Host;
using System.Management.Automation.Internal;
using System.Management.Automation.Internal.Host;
using System.Management.Automation.Language;
using System.Management.Automation.Runspaces;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text.RegularExpressions;

using Microsoft.PowerShell.Commands;
using Microsoft.PowerShell.Commands.Internal.Format;

// ReSharper disable UnusedMember.Global

namespace System.Management.Automation
{
    internal static class PipelineOps
    {
        private static CommandProcessorBase AddCommand(PipelineProcessor pipe,
                                                       CommandParameterInternal[] commandElements,
                                                       CommandBaseAst commandBaseAst,
                                                       CommandRedirection[] redirections,
                                                       ExecutionContext context)
        {
            var commandAst = commandBaseAst as CommandAst;
            var invocationToken = commandAst != null ? commandAst.InvocationOperator : TokenKind.Unknown;
            bool dotSource = invocationToken == TokenKind.Dot;
            SessionStateInternal commandSessionState = null;
            int commandIndex = 0;

            Diagnostics.Assert(commandElements[0].ArgumentSpecified && !commandElements[0].ParameterNameSpecified,
                "Compiler will pass first parameter as an argument.");
            var mi = PSObject.Base(commandElements[0].ArgumentValue) as PSModuleInfo;
            if (mi != null)
            {
                if (mi.ModuleType == ModuleType.Binary && mi.SessionState == null)
                {
                    throw InterpreterError.NewInterpreterException(null, typeof(RuntimeException),
                        null, "CantInvokeInBinaryModule", ParserStrings.CantInvokeInBinaryModule, mi.Name);
                }
                else if (mi.SessionState == null)
                {
                    throw InterpreterError.NewInterpreterException(null, typeof(RuntimeException),
                        null, "CantInvokeInNonImportedModule", ParserStrings.CantInvokeInNonImportedModule, mi.Name);
                }
                else if (((invocationToken == TokenKind.Ampersand) || (invocationToken == TokenKind.Dot)) && (mi.LanguageMode != context.LanguageMode))
                {
                    // Disallow FullLanguage "& (Get-Module MyModule) MyPrivateFn" from ConstrainedLanguage because it always
                    // runs "internal" origin and so has access to all functions, including non-exported functions.
                    // Otherwise we end up leaking non-exported functions that run in FullLanguage.
                    throw InterpreterError.NewInterpreterException(null, typeof(RuntimeException), null,
                        "CantInvokeCallOperatorAcrossLanguageBoundaries", ParserStrings.CantInvokeCallOperatorAcrossLanguageBoundaries);
                }

                commandSessionState = mi.SessionState.Internal;
                commandIndex += 1;
            }

            object command;
            IScriptExtent commandExtent;
            var cpiCommand = commandElements[commandIndex];
            if (cpiCommand.ParameterNameSpecified)
            {
                command = cpiCommand.ParameterText;
                commandExtent = cpiCommand.ParameterExtent;
                if (cpiCommand.ArgumentSpecified)
                {
                    // BUG: we've seen something like:
                    //     & (gmo Module) -foo: bar
                    // The command is -foo:, and bar is an argument, but both are in commandElements[commandIndex],
                    // so we won't add 'bar' as an argument.
                }
            }
            else
            {
                command = PSObject.Base(cpiCommand.ArgumentValue);
                commandExtent = cpiCommand.ArgumentExtent;
            }

            string invocationName = (dotSource) ? "." : invocationToken == TokenKind.Ampersand ? "&" : null;
            CommandProcessorBase commandProcessor;
            var scriptBlock = command as ScriptBlock;
            if (scriptBlock != null)
            {
                commandProcessor = CommandDiscovery.CreateCommandProcessorForScript(scriptBlock, context, !dotSource, commandSessionState);
            }
            else
            {
                var commandInfo = command as CommandInfo;
                if (commandInfo != null)
                {
                    commandProcessor = context.CommandDiscovery.LookupCommandProcessor(commandInfo, context.EngineSessionState.CurrentScope.ScopeOrigin, !dotSource, commandSessionState);
                }
                else
                {
                    var commandName = command as string ?? PSObject.ToStringParser(context, command);
                    invocationName = invocationName ?? commandName;

                    if (string.IsNullOrEmpty(commandName))
                    {
                        throw InterpreterError.NewInterpreterException(command, typeof(RuntimeException),
                                                                       commandExtent, "BadExpression",
                                                                       ParserStrings.BadExpression,
                                                                       dotSource ? "." : "&");
                    }

                    try
                    {
                        // See if we need to resolve the command in a different session state
                        // as will be the case with modules...
                        // BUGBUG - this can be cleaned up by fixing the overload on execution context (but not easily.)
                        if (commandSessionState != null)
                        {
                            SessionStateInternal oldSessionState = context.EngineSessionState;
                            try
                            {
                                context.EngineSessionState = commandSessionState;
                                commandProcessor = context.CreateCommand(commandName, dotSource);
                            }
                            finally
                            {
                                context.EngineSessionState = oldSessionState;
                            }
                        }
                        else
                        {
                            commandProcessor = context.CreateCommand(commandName, dotSource);
                        }
                    }
                    catch (RuntimeException rte)
                    {
                        // CreateCommand doesn't have the context to set InvocationInfo properly
                        // so we'll do it here instead...
                        if (rte.ErrorRecord.InvocationInfo == null)
                        {
                            InvocationInfo invocationInfo = new InvocationInfo(null, commandExtent, context)
                            { InvocationName = invocationName };
                            rte.ErrorRecord.SetInvocationInfo(invocationInfo);
                        }

                        throw;
                    }
                }
            }

            InternalCommand cmd = commandProcessor.Command;
            commandProcessor.UseLocalScope = !dotSource &&
                                             (cmd is ScriptCommand || cmd is PSScriptCmdlet);

            bool isNativeCommand = commandProcessor is NativeCommandProcessor;
            for (int i = commandIndex + 1; i < commandElements.Length; ++i)
            {
                var cpi = commandElements[i];

                if (cpi.ParameterNameSpecified)
                {
                    // Skip adding the special -- parameter unless we're invoking a native command.
                    if (cpi.ParameterName.Equals("-", StringComparison.OrdinalIgnoreCase) && !isNativeCommand)
                    {
                        continue;
                    }
                }

                if (cpi.ArgumentSplatted)
                {
                    foreach (var splattedCpi in Splat(cpi.ArgumentValue, cpi.ArgumentAst))
                    {
                        commandProcessor.AddParameter(splattedCpi);
                    }
                }
                else
                {
                    commandProcessor.AddParameter(cpi);
                }
            }

            string helpTarget;
            HelpCategory helpCategory;
            if (commandProcessor.IsHelpRequested(out helpTarget, out helpCategory))
            {
                commandProcessor = CommandProcessorBase.CreateGetHelpCommandProcessor(context, helpTarget, helpCategory);
            }

            commandProcessor.Command.InvocationExtent = commandBaseAst.Extent;
            commandProcessor.Command.MyInvocation.ScriptPosition = commandBaseAst.Extent;
            commandProcessor.Command.MyInvocation.InvocationName = invocationName;

            pipe.Add(commandProcessor);

            bool redirectedError = false;
            bool redirectedWarning = false;
            bool redirectedVerbose = false;
            bool redirectedDebug = false;
            bool redirectedInformation = false;
            if (redirections != null)
            {
                foreach (var redirection in redirections)
                {
                    redirection.Bind(pipe, commandProcessor, context);
                    switch (redirection.FromStream)
                    {
                        case RedirectionStream.Error:
                            redirectedError = true;
                            break;

                        case RedirectionStream.Warning:
                            redirectedWarning = true;
                            break;

                        case RedirectionStream.Verbose:
                            redirectedVerbose = true;
                            break;

                        case RedirectionStream.Debug:
                            redirectedDebug = true;
                            break;

                        case RedirectionStream.Information:
                            redirectedInformation = true;
                            break;

                        case RedirectionStream.All:
                            redirectedError = true;
                            redirectedWarning = true;
                            redirectedVerbose = true;
                            redirectedDebug = true;
                            redirectedInformation = true;
                            break;
                    }
                }
            }

            // Pipe redirection can also be specified via the ExecutionContext pipes.
            if (!redirectedError)
            {
                if (context.ShellFunctionErrorOutputPipe != null)
                {
                    commandProcessor.CommandRuntime.ErrorOutputPipe = context.ShellFunctionErrorOutputPipe;
                }
                else
                {
                    commandProcessor.CommandRuntime.ErrorOutputPipe.ExternalWriter = context.ExternalErrorOutput;
                }
            }

            if (!redirectedWarning && (context.ExpressionWarningOutputPipe != null))
            {
                commandProcessor.CommandRuntime.WarningOutputPipe = context.ExpressionWarningOutputPipe;
                redirectedWarning = true;
            }

            if (!redirectedVerbose && (context.ExpressionVerboseOutputPipe != null))
            {
                commandProcessor.CommandRuntime.VerboseOutputPipe = context.ExpressionVerboseOutputPipe;
                redirectedVerbose = true;
            }

            if (!redirectedDebug && (context.ExpressionDebugOutputPipe != null))
            {
                commandProcessor.CommandRuntime.DebugOutputPipe = context.ExpressionDebugOutputPipe;
                redirectedDebug = true;
            }

            if (!redirectedInformation && (context.ExpressionInformationOutputPipe != null))
            {
                commandProcessor.CommandRuntime.InformationOutputPipe = context.ExpressionInformationOutputPipe;
                redirectedInformation = true;
            }

            // Warning, Verbose, Debug should pick up any redirection information from its parent command runtime object.
            if (context.CurrentCommandProcessor != null && context.CurrentCommandProcessor.CommandRuntime != null)
            {
                if (!redirectedWarning &&
                    context.CurrentCommandProcessor.CommandRuntime.WarningOutputPipe != null)
                {
                    commandProcessor.CommandRuntime.WarningOutputPipe = context.CurrentCommandProcessor.CommandRuntime.WarningOutputPipe;
                }

                if (!redirectedVerbose &&
                    context.CurrentCommandProcessor.CommandRuntime.VerboseOutputPipe != null)
                {
                    commandProcessor.CommandRuntime.VerboseOutputPipe = context.CurrentCommandProcessor.CommandRuntime.VerboseOutputPipe;
                }

                if (!redirectedDebug &&
                    context.CurrentCommandProcessor.CommandRuntime.DebugOutputPipe != null)
                {
                    commandProcessor.CommandRuntime.DebugOutputPipe = context.CurrentCommandProcessor.CommandRuntime.DebugOutputPipe;
                }

                if (!redirectedInformation &&
                    context.CurrentCommandProcessor.CommandRuntime.InformationOutputPipe != null)
                {
                    commandProcessor.CommandRuntime.InformationOutputPipe = context.CurrentCommandProcessor.CommandRuntime.InformationOutputPipe;
                }
            }

            return commandProcessor;
        }

        internal static IEnumerable<CommandParameterInternal> Splat(object splattedValue, Ast splatAst)
        {
            splattedValue = PSObject.Base(splattedValue);

            var markUntrustedData = false;
            if (ExecutionContext.HasEverUsedConstrainedLanguage)
            {
                // If the value to be splatted is untrusted, then make sure sub-values held by it are
                // also marked as untrusted.
                markUntrustedData = ExecutionContext.IsMarkedAsUntrusted(splattedValue);
            }

            IDictionary splattedTable = splattedValue as IDictionary;
            if (splattedTable != null)
            {
                foreach (DictionaryEntry de in splattedTable)
                {
                    string parameterName = de.Key.ToString();
                    object parameterValue = de.Value;
                    string parameterText = GetParameterText(parameterName);

                    if (markUntrustedData) { ExecutionContext.MarkObjectAsUntrusted(parameterValue); }

                    yield return CommandParameterInternal.CreateParameterWithArgument(
                        splatAst, parameterName, parameterText,
                        splatAst, parameterValue, false);
                }
            }
            else
            {
                IEnumerable enumerableValue = splattedValue as IEnumerable;
                if (enumerableValue != null)
                {
                    foreach (object obj in enumerableValue)
                    {
                        if (markUntrustedData) { ExecutionContext.MarkObjectAsUntrusted(obj); }

                        yield return SplatEnumerableElement(obj, splatAst);
                    }
                }
                else
                {
                    yield return SplatEnumerableElement(splattedValue, splatAst);
                }
            }
        }

        private static CommandParameterInternal SplatEnumerableElement(object splattedArgument, Ast splatAst)
        {
            var psObject = splattedArgument as PSObject;
            if (psObject != null)
            {
                var prop = psObject.Properties[ScriptParameterBinderController.NotePropertyNameForSplattingParametersInArgs];
                var baseObj = psObject.BaseObject;
                if (prop != null && prop.Value is string && baseObj is string)
                {
                    return CommandParameterInternal.CreateParameter((string)prop.Value, (string)baseObj, splatAst);
                }
            }

            return CommandParameterInternal.CreateArgument(splattedArgument, splatAst);
        }

        private static string GetParameterText(string parameterName)
        {
            Diagnostics.Assert(parameterName != null, "caller makes sure the parameterName is not null");
            int endPosition = parameterName.Length;
            while ((endPosition > 0) && char.IsWhiteSpace(parameterName[endPosition - 1]))
            {
                endPosition--;
            }

            if (endPosition == 0 || parameterName[endPosition - 1] == ':')
            {
                return "-" + parameterName;
            }

            string parameterText;
            if (endPosition == parameterName.Length)
            {
                parameterText = "-" + parameterName + ":";
            }
            else
            {
                string whitespaces = parameterName.Substring(endPosition);
                parameterText = "-" + parameterName.Substring(0, endPosition) + ":" + whitespaces;
            }

            return parameterText;
        }

        internal static void InvokePipeline(object input,
                                            bool ignoreInput,
                                            CommandParameterInternal[][] pipeElements,
                                            CommandBaseAst[] pipeElementAsts,
                                            CommandRedirection[][] commandRedirections,
                                            FunctionContext funcContext)
        {
            PipelineProcessor pipelineProcessor = new PipelineProcessor();
            ExecutionContext context = funcContext._executionContext;
            Pipe outputPipe = funcContext._outputPipe;

            try
            {
                if (context.Events != null)
                {
                    context.Events.ProcessPendingActions();
                }

                if (input == AutomationNull.Value && !ignoreInput)
                {
                    // We have seen something like:
                    //    $e | measure-object
                    // And $e is AutomationNull.Value.  We want to ensure
                    // measure-object runs w/o sending anything through the pipe,
                    // so we'll turn the pipe into Out-Null | ...
                    // This cleanly avoids any problems with the pipeline processing
                    // code dealing with null/AutomationNull input going directly to
                    // the first command (e.g. Measure-Object).
                    AddNoopCommandProcessor(pipelineProcessor, context);
                }

                CommandProcessorBase commandProcessor = null;
                CommandRedirection[] commandRedirection = null;

                for (int i = 0; i < pipeElements.Length; i++)
                {
                    commandRedirection = commandRedirections != null ? commandRedirections[i] : null;
                    commandProcessor = AddCommand(pipelineProcessor, pipeElements[i], pipeElementAsts[i],
                                                  commandRedirection, context);
                }

                var cmdletInfo = commandProcessor?.CommandInfo as CmdletInfo;
                if (cmdletInfo?.ImplementingType == typeof(OutNullCommand))
                {
                    var commandsCount = pipelineProcessor.Commands.Count;
                    if (commandsCount == 1)
                    {
                        // Out-Null is the only command, bail without running anything
                        return;
                    }

                    // Out-Null is the last command, rewrite command before Out-Null to a null pipe, but
                    // only if it didn't redirect anything, e.g. `Get-Stuff > o.txt | Out-Null`
                    var nextToLastCommand = pipelineProcessor.Commands[commandsCount - 2];
                    if (!nextToLastCommand.CommandRuntime.OutputPipe.IsRedirected)
                    {
                        pipelineProcessor.Commands.RemoveAt(commandsCount - 1);
                        commandProcessor = nextToLastCommand;
                        nextToLastCommand.CommandRuntime.OutputPipe = new Pipe { NullPipe = true };
                    }
                }

                if (commandProcessor != null && !commandProcessor.CommandRuntime.OutputPipe.IsRedirected)
                {
                    pipelineProcessor.LinkPipelineSuccessOutput(outputPipe ?? new Pipe(new List<object>()));

                    // Fix up merge redirection bindings on last command processor.
                    if (commandRedirection != null)
                    {
                        foreach (CommandRedirection redirection in commandRedirection)
                        {
                            if (redirection is MergingRedirection)
                            {
                                redirection.Bind(pipelineProcessor, commandProcessor, context);
                            }
                        }
                    }
                }

                context.PushPipelineProcessor(pipelineProcessor);
                try
                {
                    pipelineProcessor.SynchronousExecuteEnumerate(input);
                }
                finally
                {
                    context.PopPipelineProcessor(false);
                }
            }
            finally
            {
                context.QuestionMarkVariableValue = !pipelineProcessor.ExecutionFailed;
                pipelineProcessor.Dispose();
            }
        }

        internal static void InvokePipelineInBackground(
                                            PipelineAst pipelineAst,
                                            FunctionContext funcContext)
        {
            PipelineProcessor pipelineProcessor = new PipelineProcessor();
            ExecutionContext context = funcContext._executionContext;
            Pipe outputPipe = funcContext._outputPipe;

            try
            {
                if (context.Events != null)
                {
                    context.Events.ProcessPendingActions();
                }

                CommandProcessorBase commandProcessor = null;

                // For background jobs rewrite the pipeline as a Start-Job command
                var scriptblockBodyString = pipelineAst.Extent.Text;
                var pipelineOffset = pipelineAst.Extent.StartOffset;
                var variables = pipelineAst.FindAll(x => x is VariableExpressionAst, true);
                // Used to make sure that the job runs in the current directory
                const string cmdPrefix = @"Microsoft.PowerShell.Management\Set-Location -LiteralPath $using:pwd ; ";
                // Minimize allocations by initializing the stringbuilder to the size of the source string + prefix + space for ${using:} * 2
                System.Text.StringBuilder updatedScriptblock = new System.Text.StringBuilder(cmdPrefix.Length + scriptblockBodyString.Length + 18);
                updatedScriptblock.Append(cmdPrefix);
                int position = 0;
                // Prefix variables in the scriptblock with $using:
                foreach (var v in variables)
                {
                    var vName = ((VariableExpressionAst)v).VariablePath.UserPath;
                    // Skip variables that don't exist
                    if (funcContext._executionContext.EngineSessionState.GetVariable(vName) == null)
                        continue;
                    // Skip PowerShell magic variables
                    if (Regex.Match(vName,
                            "^(global:){0,1}(PID|PSVersionTable|PSEdition|PSHOME|HOST|TRUE|FALSE|NULL)$",
                                RegexOptions.IgnoreCase | RegexOptions.CultureInvariant).Success == false
                    )
                    {
                        updatedScriptblock.Append(scriptblockBodyString.Substring(position, v.Extent.StartOffset - pipelineOffset - position));
                        updatedScriptblock.Append("${using:");
                        updatedScriptblock.Append(CodeGeneration.EscapeVariableName(vName));
                        updatedScriptblock.Append('}');
                        position = v.Extent.EndOffset - pipelineOffset;
                    }
                }

                updatedScriptblock.Append(scriptblockBodyString.Substring(position));
                var sb = ScriptBlock.Create(updatedScriptblock.ToString());
                var commandInfo = new CmdletInfo("Start-Job", typeof(StartJobCommand));
                commandProcessor = context.CommandDiscovery.LookupCommandProcessor(
                    commandInfo, CommandOrigin.Internal, false, context.EngineSessionState);
                var parameter = CommandParameterInternal.CreateParameterWithArgument(
                    /*parameterAst*/pipelineAst, "ScriptBlock", null,
                    /*argumentAst*/pipelineAst, sb,
                    false);
                commandProcessor.AddParameter(parameter);
                pipelineProcessor.Add(commandProcessor);
                pipelineProcessor.LinkPipelineSuccessOutput(outputPipe ?? new Pipe(new List<object>()));

                context.PushPipelineProcessor(pipelineProcessor);
                try
                {
                    pipelineProcessor.SynchronousExecuteEnumerate(AutomationNull.Value);
                }
                finally
                {
                    context.PopPipelineProcessor(false);
                }
            }
            finally
            {
                context.QuestionMarkVariableValue = !pipelineProcessor.ExecutionFailed;
                pipelineProcessor.Dispose();
            }
        }

        private static void AddNoopCommandProcessor(PipelineProcessor pipelineProcessor, ExecutionContext context)
        {
            var commandInfo = new CmdletInfo("Out-Null", typeof(OutNullCommand));
            var commandProcessor = context.CommandDiscovery.LookupCommandProcessor(commandInfo,
                                                                                   context.EngineSessionState.CurrentScope.ScopeOrigin,
                                                                                   useLocalScope: false,
                                                                                   sessionState: null);
            pipelineProcessor.Add(commandProcessor);
        }

        internal static object CheckAutomationNullInCommandArgument(object obj)
        {
            if (obj == AutomationNull.Value)
            {
                return null;
            }

            var objAsArray = obj as object[];
            return objAsArray != null ? CheckAutomationNullInCommandArgumentArray(objAsArray) : obj;
        }

        internal static object[] CheckAutomationNullInCommandArgumentArray(object[] objArray)
        {
            if (objArray != null)
            {
                for (int i = 0; i < objArray.Length; ++i)
                {
                    if (objArray[i] == AutomationNull.Value)
                    {
                        objArray[i] = null;
                    }
                }
            }

            return objArray;
        }

        internal static SteppablePipeline GetSteppablePipeline(PipelineAst pipelineAst, CommandOrigin commandOrigin, ScriptBlock scriptBlock, object[] args)
        {
            var pipelineProcessor = new PipelineProcessor();
            var commandTuples = new List<Tuple<CommandAst, List<CommandParameterInternal>, List<CommandRedirection>>>();

            ExecutionContext context = LocalPipeline.GetExecutionContextFromTLS();
            if (context == null)
            {
                // If ExecutionContext from TLS is null then we are not in powershell engine thread.
                string scriptText = scriptBlock.ToString();
                scriptText = ErrorCategoryInfo.Ellipsize(CultureInfo.CurrentUICulture, scriptText);

                PSInvalidOperationException e = PSTraceSource.NewInvalidOperationException(
                    ParserStrings.GetSteppablePipelineFromWrongThread,
                    scriptText);

                e.SetErrorId("GetSteppablePipelineFromWrongThread");
                throw e;
            }

            // We try binding the parameter when following conditions are satisfied:
            //   * Arguments are provided
            //   * The ScriptBlock has parameters
            // If the script block has no parameter, RuntimeDefinedParameters.Data will be set to RuntimeDefinedParameterDictionary.EmptyParameterArray
            bool useParameter = (args != null && args.Length > 0) &&
                                scriptBlock.RuntimeDefinedParameters.Data !=
                                RuntimeDefinedParameterDictionary.EmptyParameterArray;
            try
            {
                if (useParameter)
                {
                    // If any parameters are used, we create a new scope and bind the parameters.

                    var newScope = context.EngineSessionState.NewScope(false);
                    context.EngineSessionState.CurrentScope = newScope;
                    context.EngineSessionState.CurrentScope.ScopeOrigin = CommandOrigin.Internal;

                    var locals = MutableTuple.MakeTuple(Compiler.DottedLocalsTupleType,
                                                        Compiler.DottedLocalsNameIndexMap);
                    object[] remainingArgs =
                        ScriptBlock.BindArgumentsForScriptblockInvoke(
                            (RuntimeDefinedParameter[])scriptBlock.RuntimeDefinedParameters.Data,
                            args, context, false, null, locals);
                    locals.SetAutomaticVariable(AutomaticVariable.Args, remainingArgs, context);
                    newScope.LocalsTuple = locals;
                }

                // GetSteppablePipeline() is called on an arbitrary script block with the intention
                // of invoking it. So the trustworthiness is defined by the trustworthiness of the
                // script block's language mode.
                bool isTrusted = scriptBlock.LanguageMode == PSLanguageMode.FullLanguage;

                foreach (var commandAst in pipelineAst.PipelineElements.Cast<CommandAst>())
                {
                    var commandParameters = new List<CommandParameterInternal>();
                    foreach (var commandElement in commandAst.CommandElements)
                    {
                        var commandParameterAst = commandElement as CommandParameterAst;
                        if (commandParameterAst != null)
                        {
                            commandParameters.Add(GetCommandParameter(commandParameterAst, isTrusted, context));
                            continue;
                        }

                        var exprAst = (ExpressionAst)commandElement;
                        var argument = Compiler.GetExpressionValue(exprAst, isTrusted, context);
                        var splatting = (exprAst is VariableExpressionAst && ((VariableExpressionAst)exprAst).Splatted);
                        commandParameters.Add(CommandParameterInternal.CreateArgument(argument, exprAst, splatting));
                    }

                    var redirections = new List<CommandRedirection>();
                    foreach (var redirection in commandAst.Redirections)
                    {
                        redirections.Add(GetCommandRedirection(redirection, isTrusted, context));
                    }

                    commandTuples.Add(Tuple.Create(commandAst, commandParameters, redirections));
                }
            }
            finally
            {
                if (useParameter)
                {
                    context.EngineSessionState.RemoveScope(context.EngineSessionState.CurrentScope);
                }
            }

            foreach (var commandTuple in commandTuples)
            {
                var commandProcessor = AddCommand(pipelineProcessor, commandTuple.Item2.ToArray(), commandTuple.Item1, commandTuple.Item3.ToArray(), context);
                commandProcessor.Command.CommandOriginInternal = commandOrigin;
                commandProcessor.CommandScope.ScopeOrigin = commandOrigin;
                commandProcessor.Command.MyInvocation.CommandOrigin = commandOrigin;

                // For nicer error reporting, we want to make it look like errors in the steppable pipeline point back to
                // the caller of the proxy.  We don't want errors pointing to the script block created in the proxy.
                // Here we assume (in a safe way) that GetSteppablePipeline is called from script.  If that isn't the case,
                // we won't crash, but the error reporting might be a little misleading.
                var callStack = context.Debugger.GetCallStack().ToArray();
                if (callStack.Length > 0 && Regex.IsMatch(callStack[0].Position.Text, "GetSteppablePipeline", RegexOptions.IgnoreCase))
                {
                    var myInvocation = commandProcessor.Command.MyInvocation;
                    myInvocation.InvocationName = callStack[0].InvocationInfo.InvocationName;
                    if (callStack.Length > 1)
                    {
                        var displayPosition = callStack[1].Position;
                        if (displayPosition != null && displayPosition != PositionUtilities.EmptyExtent)
                        {
                            myInvocation.DisplayScriptPosition = displayPosition;
                        }
                    }
                }

                // Set the data stream merge properties based on ExecutionContext.
                if (context.CurrentCommandProcessor != null && context.CurrentCommandProcessor.CommandRuntime != null)
                {
                    commandProcessor.CommandRuntime.SetMergeFromRuntime(context.CurrentCommandProcessor.CommandRuntime);
                }
            }

            return new SteppablePipeline(context, pipelineProcessor);
        }

        private static CommandParameterInternal GetCommandParameter(CommandParameterAst commandParameterAst, bool isTrusted, ExecutionContext context)
        {
            var argumentAst = commandParameterAst.Argument;
            var errorPos = commandParameterAst.ErrorPosition;

            if (argumentAst == null)
            {
                return CommandParameterInternal.CreateParameter(commandParameterAst.ParameterName, errorPos.Text, commandParameterAst);
            }

            object argumentValue = Compiler.GetExpressionValue(argumentAst, isTrusted, context);
            bool spaceAfterParameter = (errorPos.EndLineNumber != argumentAst.Extent.StartLineNumber ||
                                        errorPos.EndColumnNumber != argumentAst.Extent.StartColumnNumber);
            return CommandParameterInternal.CreateParameterWithArgument(commandParameterAst, commandParameterAst.ParameterName,
                                                                        errorPos.Text, argumentAst, argumentValue,
                                                                        spaceAfterParameter);
        }

        private static CommandRedirection GetCommandRedirection(RedirectionAst redirectionAst, bool isTrusted, ExecutionContext context)
        {
            var fileRedirection = redirectionAst as FileRedirectionAst;
            if (fileRedirection != null)
            {
                object fileName = Compiler.GetExpressionValue(fileRedirection.Location, isTrusted, context);
                return new FileRedirection(fileRedirection.FromStream, fileRedirection.Append, fileName.ToString());
            }

            var mergingRedirectionAst = (MergingRedirectionAst)redirectionAst;
            return new MergingRedirection(mergingRedirectionAst.FromStream, mergingRedirectionAst.ToStream);
        }

        internal static object PipelineResult(List<object> resultList)
        {
            var resultCount = resultList.Count;
            if (resultCount == 0)
            {
                return AutomationNull.Value;
            }

            var result = resultCount == 1 ? resultList[0] : resultList.ToArray();
            // Clear the array list so that we don't write the results of the pipe when flushing the pipe.
            resultList.Clear();
            return result;
        }

        internal static void FlushPipe(Pipe oldPipe, List<object> resultList)
        {
            for (int i = 0; i < resultList.Count; i++)
            {
                oldPipe.Add(resultList[i]);
            }
        }

        internal static void ClearPipe(List<object> resultList)
        {
            resultList.Clear();
        }

        internal static ExitException GetExitException(object exitCodeObj)
        {
            int exitCode = 0;

            try
            {
                if (!LanguagePrimitives.IsNull(exitCodeObj))
                {
                    exitCode = ParserOps.ConvertTo<int>(exitCodeObj, PositionUtilities.EmptyExtent);
                }
            }
            catch (Exception) // ignore non-severe exceptions
            {
            }

            return new ExitException(exitCode);
        }

        internal static void CheckForInterrupts(ExecutionContext context)
        {
            if (context.Events != null)
            {
                context.Events.ProcessPendingActions();
            }

            if (context.CurrentPipelineStopping)
            {
                throw new PipelineStoppedException();
            }
        }

        // This is to work around a DLR problem with gotos in try/catch to the end of a lambda.
        internal static void Nop() { }
    }

    #region Redirections

    internal abstract class CommandRedirection
    {
        protected CommandRedirection(RedirectionStream from)
        {
            this.FromStream = from;
        }

        internal RedirectionStream FromStream { get; private set; }

        internal abstract void Bind(PipelineProcessor pipelineProcessor, CommandProcessorBase commandProcessor, ExecutionContext context);

        internal void UnbindForExpression(FunctionContext funcContext, Pipe[] pipes)
        {
            if (pipes == null)
            {
                // The pipes can be null if there was an exception (ideally we'd just call unbind
                // from a fault, but that isn't supported in a clr dynamic method.
                return;
            }

            var context = funcContext._executionContext;
            switch (FromStream)
            {
                case RedirectionStream.All:
                    funcContext._outputPipe = pipes[(int)RedirectionStream.Output];
                    context.ShellFunctionErrorOutputPipe = pipes[(int)RedirectionStream.Error];
                    context.ExpressionWarningOutputPipe = pipes[(int)RedirectionStream.Warning];
                    context.ExpressionVerboseOutputPipe = pipes[(int)RedirectionStream.Verbose];
                    context.ExpressionDebugOutputPipe = pipes[(int)RedirectionStream.Debug];
                    context.ExpressionInformationOutputPipe = pipes[(int)RedirectionStream.Information];
                    break;
                case RedirectionStream.Output:
                    funcContext._outputPipe = pipes[(int)RedirectionStream.Output];
                    break;
                case RedirectionStream.Error:
                    context.ShellFunctionErrorOutputPipe = pipes[(int)FromStream];
                    break;
                case RedirectionStream.Warning:
                    context.ExpressionWarningOutputPipe = pipes[(int)FromStream];
                    break;
                case RedirectionStream.Verbose:
                    context.ExpressionVerboseOutputPipe = pipes[(int)FromStream];
                    break;
                case RedirectionStream.Debug:
                    context.ExpressionDebugOutputPipe = pipes[(int)FromStream];
                    break;
                case RedirectionStream.Information:
                    context.ExpressionInformationOutputPipe = pipes[(int)FromStream];
                    break;
            }
        }
    }

    internal class MergingRedirection : CommandRedirection
    {
        internal MergingRedirection(RedirectionStream from, RedirectionStream to)
            : base(from)
        {
            if (to != RedirectionStream.Output)
            {
                throw InterpreterError.NewInterpreterException(to, typeof(ArgumentException),
                                               null, "RedirectionStreamCanOnlyMergeToOutputStream",
                                               ParserStrings.RedirectionStreamCanOnlyMergeToOutputStream);
            }

            // this.ToStream = to;
        }

        public override string ToString()
        {
            return FromStream == RedirectionStream.All
                       ? "*>&1"
                       : string.Format(CultureInfo.InvariantCulture, "{0}>&1", (int)FromStream);
        }

        // private RedirectionStream ToStream { get; set; }

        // Handle merging redirections for commands, like:
        //   dir 2>&1
        // A more realistic example:
        //   dir 2>&1 > out
        internal override void Bind(PipelineProcessor pipelineProcessor, CommandProcessorBase commandProcessor, ExecutionContext context)
        {
            Pipe pipe = commandProcessor.CommandRuntime.OutputPipe;

            switch (FromStream)
            {
                case RedirectionStream.All:
                    commandProcessor.CommandRuntime.ErrorMergeTo = MshCommandRuntime.MergeDataStream.Output;
                    commandProcessor.CommandRuntime.WarningOutputPipe = pipe;
                    commandProcessor.CommandRuntime.VerboseOutputPipe = pipe;
                    commandProcessor.CommandRuntime.DebugOutputPipe = pipe;
                    commandProcessor.CommandRuntime.InformationOutputPipe = pipe;
                    break;
                case RedirectionStream.Output:
                    break;
                case RedirectionStream.Error:
                    commandProcessor.CommandRuntime.ErrorMergeTo = MshCommandRuntime.MergeDataStream.Output;
                    break;
                case RedirectionStream.Warning:
                    commandProcessor.CommandRuntime.WarningOutputPipe = pipe;
                    break;
                case RedirectionStream.Verbose:
                    commandProcessor.CommandRuntime.VerboseOutputPipe = pipe;
                    break;
                case RedirectionStream.Debug:
                    commandProcessor.CommandRuntime.DebugOutputPipe = pipe;
                    break;
                case RedirectionStream.Information:
                    commandProcessor.CommandRuntime.InformationOutputPipe = pipe;
                    break;
            }
        }

        // Handle merging redirections for expressions, like:
        //   $(write-error) 2>&1
        // A more realistic example:
        //   $(write-error) 2>&1 > out
        internal Pipe[] BindForExpression(ExecutionContext context, FunctionContext funcContext)
        {
            Pipe[] oldPipes = new Pipe[(int)RedirectionStream.Information + 1];
            Pipe pipe = funcContext._outputPipe;

            // We set the redirection pipe directly in Context because there is no command processor
            // (which indirectly does the same thing as this code.)

            switch (FromStream)
            {
                case RedirectionStream.All:
                    oldPipes[(int)RedirectionStream.Output] = funcContext._outputPipe;
                    oldPipes[(int)RedirectionStream.Error] = context.ShellFunctionErrorOutputPipe;
                    context.ShellFunctionErrorOutputPipe = pipe;
                    oldPipes[(int)RedirectionStream.Warning] = context.ExpressionWarningOutputPipe;
                    context.ExpressionWarningOutputPipe = pipe;
                    oldPipes[(int)RedirectionStream.Verbose] = context.ExpressionVerboseOutputPipe;
                    context.ExpressionVerboseOutputPipe = pipe;
                    oldPipes[(int)RedirectionStream.Debug] = context.ExpressionDebugOutputPipe;
                    context.ExpressionDebugOutputPipe = pipe;
                    oldPipes[(int)RedirectionStream.Information] = context.ExpressionInformationOutputPipe;
                    context.ExpressionInformationOutputPipe = pipe;
                    break;
                case RedirectionStream.Output:
                    oldPipes[(int)RedirectionStream.Output] = funcContext._outputPipe;
                    break;
                case RedirectionStream.Error:
                    oldPipes[(int)FromStream] = context.ShellFunctionErrorOutputPipe;
                    context.ShellFunctionErrorOutputPipe = pipe;
                    break;
                case RedirectionStream.Warning:
                    oldPipes[(int)FromStream] = context.ExpressionWarningOutputPipe;
                    context.ExpressionWarningOutputPipe = pipe;
                    break;
                case RedirectionStream.Verbose:
                    oldPipes[(int)FromStream] = context.ExpressionVerboseOutputPipe;
                    context.ExpressionVerboseOutputPipe = pipe;
                    break;
                case RedirectionStream.Debug:
                    oldPipes[(int)FromStream] = context.ExpressionDebugOutputPipe;
                    context.ExpressionDebugOutputPipe = pipe;
                    break;
                case RedirectionStream.Information:
                    oldPipes[(int)FromStream] = context.ExpressionInformationOutputPipe;
                    context.ExpressionInformationOutputPipe = pipe;
                    break;
            }

            return oldPipes;
        }
    }