fix: powershell WindmillClient module loading on Windows workers

[rubenfiszel]

Summary

• Fix stale module cache detection: get_module_versions() previously returned ["unknown"] for empty/corrupted module directories, causing check_module_installed() to treat them as installed. Now verifies .psd1/.psm1 files actually exist in version subdirectories before considering a module cached.
• Fix Import-Module regex: RE_POWERSHELL_IMPORTS used ^Import-Module which skipped indented imports. Changed to ^\s*Import-Module — the old behavior was masked by caching (module only needed to be detected once), but became visible when the cache path changed in 1.650.0.
• Fix catch block formatting: Write-Output $_ was merged onto the same line as the closing " of the previous Write-Output due to a Rust line-continuation bug, causing PowerShell to parse $_ as an argument rather than a separate command. This is why error output showed the literal text Write-Output in the error message.

Regression introduced in: 1.650.0 (424ca59dfe — make WINDMILL_DIR configurable), which moved the Windows PowerShell cache from /tmp/windmill/cache/powershell to {temp_dir}/windmill/cache/powershell. The old cache was abandoned, and the bugs in module detection/regex prevented recovery.

Test plan

• Windows worker: run a PowerShell script with Import-Module WindmillClient and verify it installs and loads correctly
• Windows worker: run with indented Import-Module WindmillClient (inside function body or with leading spaces)
• Verify error output no longer shows literal Write-Output text when a script fails
• Delete the powershell cache directory and verify modules are re-downloaded on next run

🤖 Generated with Claude Code

[claude]

Claude finished @rubenfiszel's task in 54s —— View job

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Code Review: PR #8370

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Overall: Clean, well-targeted bugfix addressing a regression from 1.650.0. All three changes are correct and the PR description is excellent — clear root cause analysis with the originating commit identified.

Fix 1: Regex for indented Import-Module (line 21)

-r#"^Import-Module\s+..."#
+r#"^\s*Import-Module\s+..."#

Correct fix. ^\s* allows leading whitespace so Import-Module inside function bodies or indented blocks is properly detected. No concerns.

Fix 2: Stale module cache detection (lines 199–213)

The old code pushed "unknown" when no version subdirectories were found, which made check_module_installed think the module was present. Now it verifies .psd1/.psm1 files actually exist before considering a version valid, and returns an empty vec for empty/corrupted directories.

This is the right approach — it's better to re-download than silently use a broken cache. One minor observation: the fs::read_dir + iterator chain is synchronous I/O on a tokio async context. This is fine in practice since this is a cache directory scan with very few entries, so blocking is negligible. No change needed.

Fix 3: Catch block formatting (lines 476–478)

-            Write-Output \"An error occurred:\n\"\
-            Write-Output $_
+            Write-Output \"An error occurred:\"\n\
+            Write-Output $_\n\

This is the most subtle fix. In the old code:

• Line ending :\n\"\ — the \ at end of the Rust string literal continues to the next line, merging Write-Output "An error occurred:\n" with Write-Output $_ into a single line. PowerShell then interprets $_ as an argument to the first Write-Output rather than a separate command.
• The fix correctly places \n\ (newline + line continuation) after each statement.

Correct and well-explained in the PR description.

No issues found

All three fixes are sound. The changes are minimal, focused, and address the root cause rather than symptoms.

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Reproduction Instructions for Testing

On a Windows worker running Windmill 1.650.0+, create a new PowerShell script (Scripts > New Script > PowerShell). Write a script that uses Import-Module WindmillClient — both at the top level and indented inside a function body. First, delete any existing powershell cache directory under the worker's temp dir to start fresh. Run the script and verify: (1) WindmillClient installs and loads successfully, (2) indented Import-Module statements are detected, (3) if you intentionally throw an error, the error output shows the actual error message rather than literal Write-Output text in the catch block. Re-run the script to confirm the module is found in cache on subsequent runs.

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