René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"CompleteInput fails when passed an empty string/AST","articleBody":"\u003c!--\r\n\r\nFor Windows PowerShell 5.1 issues, suggestions, or feature requests please use the following link instead:\r\n- Windows PowerShell [UserVoice](https://windowsserver.uservoice.com/forums/301869-powershell)\r\n\r\nIf it is a bug report:\r\n- make sure you are able to repro it on the latest released version. \r\nYou can install the latest version from https://github.com/PowerShell/PowerShell/releases\r\n- Search the existing issues.\r\n- Refer to the [FAQ](https://github.com/PowerShell/PowerShell/blob/master/docs/FAQ.md).\r\n- Refer to the [known issues](https://github.com/PowerShell/PowerShell/blob/master/docs/KNOWNISSUES.md).\r\n- Fill out the following repro template:\r\n\r\nIf it's not a bug, please remove the template and elaborate the issue in your own words.\r\n--\u003e\r\n\r\nSteps to reproduce\r\n------------------\r\n\r\n```powershell\r\n[System.Management.Automation.CommandCompletion]::CompleteInput('', 0, @{})\r\n```\r\n\r\nOr\r\n\r\n```powershell\r\n[System.Management.Automation.CommandCompletion]::CompleteInput(\r\n\t{}.Ast,\r\n\t@(),\r\n\t{}.Ast.Extent.StartScriptPosition,\r\n\t@{})\r\n```\r\n\r\nExpected behavior\r\n-----------------\r\n\r\n```none\r\nCurrentMatchIndex ReplacementIndex ReplacementLength CompletionMatches\r\n----------------- ---------------- ----------------- -----------------\r\n               -1                0                 0 {}\r\n```\r\n\r\nAlternatively if throwing is a design choice, throw an `ArgumentException` instead of letting `Enumerable.Last` fail.\r\n\r\nActual behavior\r\n---------------\r\n\r\n```none\r\n\u003e [System.Management.Automation.CommandCompletion]::CompleteInput('', 0, @{})\r\nException calling \"CompleteInput\" with \"3\" argument(s): \"Sequence contains no elements\"\r\nAt line:1 char:1\r\n+ [System.Management.Automation.CommandCompletion]::CompleteInput('', 0 ...\r\n+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r\n+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException\r\n+ FullyQualifiedErrorId : InvalidOperationException\r\n\r\n\u003e $Error[0].Exception.InnerException | Format-List * -Force\r\nMessage        : Sequence contains no elements\r\nData           : {}\r\nInnerException :\r\nTargetSite     : TSource Last[TSource](System.Collections.Generic.IEnumerable`1[TSource])\r\nStackTrace     :    at System.Linq.Enumerable.Last[TSource](IEnumerable`1 source)\r\n                    at\r\n                 System.Management.Automation.CompletionAnalysis.InitializeCompletionContext(TypeInferenceContext\r\n                 typeInferenceContext)\r\n                    at System.Management.Automation.CompletionAnalysis.GetResults(PowerShell powerShell, Int32\u0026\r\n                 replacementIndex, Int32\u0026 replacementLength)\r\n                    at System.Management.Automation.CommandCompletion.CompleteInputImpl(Ast ast, Token[] tokens,\r\n                 IScriptPosition positionOfCursor, Hashtable options)\r\n                    at System.Management.Automation.CommandCompletion.CompleteInput(String input, Int32 cursorIndex,\r\n                 Hashtable options)\r\n                    at CallSite.Target(Closure , CallSite , Type , String , Int32 , Hashtable )\r\nHelpLink       :\r\nSource         : System.Linq\r\nHResult        : -2146233079\r\n```\r\n\r\nEnvironment data\r\n----------------\r\n\r\n\u003c!-- provide the output of $PSVersionTable --\u003e\r\n\r\n```powershell\r\n\u003e $PSVersionTable\r\nName                           Value\r\n----                           -----\r\nPSVersion                      6.0.0-rc.2\r\nPSEdition                      Core\r\nGitCommitId                    v6.0.0-rc.2\r\nOS                             Microsoft Windows 10.0.15063\r\nPlatform                       Win32NT\r\nPSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}\r\nPSRemotingProtocolVersion      2.3\r\nSerializationVersion           1.1.0.1\r\nWSManStackVersion              3.0\r\n```\r\n","author":{"url":"https://github.com/SeeminglyScience","@type":"Person","name":"SeeminglyScience"},"datePublished":"2017-12-24T20:46:53.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/5743/PowerShell/issues/5743"}