René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"An attempt to modify a collection while it is being enumerated doesn't always result in an error","articleBody":"### Prerequisites\r\n\r\n- [X] Write a descriptive title.\r\n- [X] Make sure you are able to repro it on the [latest released version](https://github.com/PowerShell/PowerShell/releases)\r\n- [X] Search the existing issues.\r\n- [X] Refer to the [FAQ](https://github.com/PowerShell/PowerShell/blob/master/docs/FAQ.md).\r\n- [X] Refer to [Differences between Windows PowerShell 5.1 and PowerShell](https://learn.microsoft.com/powershell/scripting/whats-new/differences-from-windows-powershell).\r\n\r\n### Steps to reproduce\r\n\r\nAttempting modification of a collection while it is being enumerated should result in an _error_:\r\n* `An error occurred while enumerating through a collection: Collection was modified; enumeration operation may not execute.`\r\n\r\nThis error isn't consistently surfaced - note that this is a regression from Windows PowerShell:\r\n\r\n```powershell\r\n# OK: Reports an error for the attempt to modify the collection being enumerated.\r\n'--- foreach'\r\n$l = [System.Collections.Generic.List[string]] @('one', 'two')\r\nforeach ($e in $l) { $l.Remove($e) }\r\n\r\n# !! Fails QUIETLY in PS CORE as of v7.4.0-preview.5\r\n'--- pipeline'\r\n$l = [System.Collections.Generic.List[string]] @('one', 'two')\r\n$l | ForEach-Object { $l.Remove($_) }\r\n```\r\n\r\n**Important**: The quiet failure only occurs when the code is executed _via a script file_; if you paste the last two statements into an _interactive_ console, the error does surface.\r\n\r\n**[_Update_: NOT PowerShell's fault - see [below](https://github.com/PowerShell/PowerShell/issues/20181#issuecomment-1699515501)]** The following WinForms example affects Windows PowerShell too (both interactively and in a script):\r\n\r\n```powershell\r\nusing namespace System.Windows.Forms\r\nAdd-Type -Assembly System.Windows.Forms\r\n\r\n$f = [Form]::new()\r\n$f.Controls.AddRange((\r\n  [CheckBox]::new(),\r\n  [CheckBox]::new()\r\n))\r\n\r\n# !! Should fail with an error message, but quietly aborts after the first .Remove() call.\r\n$f.Controls | ForEach-Object { $f.Controls.Remove($_) }\r\n\r\n$f.Controls.Count # !! still nonzero\r\n```\r\n\r\n\r\n\r\n\r\n\r\n### Expected behavior\r\n\r\nFirst snippet:\r\n\r\n* Both the `foreach` and the `ForEach-Object` statement should report the expected error.\r\n\r\nSecond snippet:\r\n\r\n* The expected error should occur.\r\n\r\n\r\n### Actual behavior\r\n\r\nFirst snippet:\r\n\r\n* The `ForEach-Object` statement doesn't report an error and quietly aborts the pipeline after the first `.Remove()` call\r\n\r\nSecond snippet:\r\n\r\n* The expected error doesn't occur; quietly aborts the pipeline after the first `.Remove()` call.\r\n\r\n### Error details\r\n\r\n_No response_\r\n\r\n### Environment data\r\n\r\n```powershell\r\nPowerShell 7.4.0-preview.5\r\n```\r\n\r\n\r\n### Visuals\r\n\r\n_No response_","author":{"url":"https://github.com/mklement0","@type":"Person","name":"mklement0"},"datePublished":"2023-08-29T22:29:22.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/20181/PowerShell/issues/20181"}