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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"This apparently acyclic combination of Import-Module calls results in stack overflow","articleBody":"This came up after #12036 and #12014 while trying to implement [the proposed solution for those issues](https://github.com/PowerShell/PowerShell/issues/12036#issuecomment-595425489).  The solution to those issues will, ostensibly, involve liberal calls to `Import-Module` within modules during module loading to shadow the names of commands such that name resolution occurs in module and not global scope.  In practice I have found that there are scenarios where such liberal use of `Import-Module` causes stack overflows.  Some such stack overflows are the result of straightforward cyclic calls to `Import-Module`.  This one is slightly different as it is apparently acyclic.  \r\n\r\nOne module affected by this is (a later, internal version of) [StructuredResource](https://github.com/alx9r/StructuredResource).  The culprit seems to be [these lines which validate that the DSC resource module imports without error](https://github.com/alx9r/StructuredResource/blob/2efcdfceb4760b500344034e847accad9059d0bf/Functions/tests_.ps1#L194-L198).  A DSC resource that requires `StructuredResource` is also tested by and therefore imported by `StructuredResource`.  I suspect this is an unusual perhaps inadvisable use case, but I'd still like to understand what is happening so I can conclusively work around the stack overflow.\r\n\r\nThis leaves me with the following questions:\r\n\r\n1. Why isn't this acyclic?  Why does this cause a stack overflow?\r\n2. Is there some other way to cross-import without stack overflow?\r\n---\r\n\r\nReferring to the repro below, here is what I would have expected to happen:\r\n\r\n1. `p1` is called which results in imported module `p` then `p1` is invoked\r\n2. `p1` outputs `p1` then imports module `m` into `p1`'s scope\r\n3. import of module `m` includes a call to `Import-Module p` so module `p` is imported a second time, this time into module `m`'s scope\r\n4. the second import of module `p` does not result in any more imports or calls and the whole stack unwinds (*)\r\n\r\n(*) In (4) the call to `Import-Module m` is within the `p1` scriptblock and so should not be invoked by the module import.\r\n\r\nThis is not, however, what happens.  Stack overflow seems to occur after (3) but before (4) is reached.\r\n\r\n# Steps to reproduce\r\n\r\nCreate two well-formed modules `m` and `p` in `$Env:PSModulePath`:\r\n\r\n```powershell\r\n# m.psm1\r\nWrite-Host 'import m'\r\nImport-Module p\r\n```\r\n```powershell\r\n# p.psm1\r\nWrite-Host 'import p'\r\nfunction p1 { Write-Host 'p1'; Import-Module m}\r\n```\r\n\r\nInvoke the following:\r\n\r\n```PowerShell\r\np1\r\n```\r\n\r\n# Expected behavior\r\n\r\n```none\r\nimport p\r\np1\r\nimport m\r\nimport p\r\n```\r\n\r\n# Actual behavior\r\n\r\n```none\r\nimport p\r\np1\r\nimport m\r\nStack overflow.\r\n```\r\n![image](https://user-images.githubusercontent.com/11237922/76027623-cf7fc380-5ee5-11ea-887f-dd37cdb14041.png)\r\n\r\n\r\n# Environment data\r\n\r\n\u003c!-- provide the output of $PSVersionTable --\u003e\r\n\r\n```none\r\n\r\nName                           Value\r\n----                           -----\r\nPSVersion                      7.0.0\r\nPSEdition                      Core\r\nGitCommitId                    7.0.0\r\nOS                             Microsoft Windows 6.3.9600\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/alx9r","@type":"Person","name":"alx9r"},"datePublished":"2020-03-05T22:04:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/12039/PowerShell/issues/12039"}