René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"NullReferenceException in OnInitialize on Linux when the initialize request includes workspaceFolders (v4.6.0)","articleBody":"On PSES `v4.6.0` running on Linux, an LSP `initialize` whose `params` include a\n`workspaceFolders` array throws a `NullReferenceException` inside the server's own\n`OnInitialize` handler, on the path that adds the workspace folders. The handshake\ndoes not complete -- no `initialize` response is returned -- so the server is unusable\nfor any client that sends `workspaceFolders` on this platform.\n\nThe same `initialize`, byte-for-byte, completes normally on Windows. Dropping\n`workspaceFolders` and relying on `rootUri` alone avoids the exception on Linux. The\nplatform asymmetry is the notable part: a client whose handshake is verified on\nWindows silently fails on Linux at exactly this step.\n\nThis is distinct from the rename-handler NRE (#2297 / PR #2299): different trigger\n(`workspaceFolders`, not an omitted `rename` capability), a different code path, and\nLinux-only rather than cross-platform.\n\n## Environment\n\n- PSES: `v4.6.0` (GitHub release asset `PowerShellEditorServices.zip`)\n- Host: PowerShell 7 (`pwsh`)\n- OS: Linux (reproduced on the GitHub Actions `ubuntu-latest` runner); **Windows is unaffected**\n- Transport: `Start-EditorServices.ps1 -Stdio`\n\n## Steps to reproduce\n\n1. Launch PSES over stdio on Linux with `-NoLogo -NoProfile`, logging to a file.\n\n2. Send an LSP `initialize` whose `params` include a `workspaceFolders` array, e.g.:\n\n   ```json\n   {\n     \"processId\": 12345,\n     \"clientInfo\": { \"name\": \"repro\", \"version\": \"1.0.0\" },\n     \"rootUri\": \"file:///home/runner/work/example\",\n     \"workspaceFolders\": [\n       { \"uri\": \"file:///home/runner/work/example\", \"name\": \"workspace\" }\n     ],\n     \"capabilities\": { \"textDocument\": { \"rename\": { \"prepareSupport\": false } } }\n   }\n   ```\n\n   (The `rename` capability is declared deliberately, to keep the separate v4.6.0\n   PrepareRename NRE -- #2297 -- out of the picture; this report is about\n   `workspaceFolders`.)\n\n3. Observe on Linux: no `initialize` **response** is returned, and the PSES log\n   records a `NullReferenceException` in the `OnInitialize` handler on the\n   workspace-folders add path. The NRE stack captured during debugging points at\n   `PsesLanguageServer.cs` around the `OnInitialize` workspaceFolders handling\n   (line numbers should be confirmed against the v4.6.0 source by a maintainer).\n\n## The one-line delta that proves the cause\n\nRe-send the same `initialize` with **`workspaceFolders` removed** and nothing else\nchanged:\n\n   ```json\n   {\n     \"processId\": 12345,\n     \"clientInfo\": { \"name\": \"repro\", \"version\": \"1.0.0\" },\n     \"rootUri\": \"file:///home/runner/work/example\",\n     \"capabilities\": { \"textDocument\": { \"rename\": { \"prepareSupport\": false } } }\n   }\n   ```\n\nOn Linux the handshake now completes and diagnostics flow. The only difference is the\npresence of the `workspaceFolders` array.\n\n## Expected\n\nSending `workspaceFolders` on `initialize` -- a standard, optional LSP field -- must\nnot throw inside `OnInitialize`. The workspace-folders add path should null-guard\nwhatever it dereferences (treat an empty/uninitialized collection as \"no folders yet\")\nrather than throwing, and it must behave the same on Linux as on Windows.\n\n## Context\n\nFound while building a Claude Code plugin that drives PSES over stdio\n(https://github.com/manderse21/claude-powershell-lsp). The plugin's Windows CI legs\nalways passed this handshake; only the Linux leg surfaced the NRE. The plugin now\nomits `workspaceFolders` to work around it (it opens each file explicitly via\n`didOpen`/`didChange`, so multi-root folders are not needed for diagnostics), but the\nroot cause should be fixed for any client that legitimately sends `workspaceFolders`\non Linux.\n","author":{"url":"https://github.com/manderse21","@type":"Person","name":"manderse21"},"datePublished":"2026-06-10T14:50:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/2300/PowerShellEditorServices/issues/2300"}