René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"PrepareRename throws NullReferenceException when an LSP client omits the `rename` capability (v4.6.0)","articleBody":"## Summary\n\nIn PSES `v4.6.0`, an LSP `initialize` whose `capabilities.textDocument` **omits**\n`rename` leaves the prepare-rename handler dereferencing a null client\n`RenameCapability`. Observed effect: the server never returns an `initialize`\nresponse (the handshake hangs) and the PSES log records a `NullReferenceException`\non the rename-handler path.\n\nDeclaring even a **minimal** `rename` capability avoids it and the handshake\ncompletes normally. This inverts the usual expectation that omitting an optional\nclient capability is always safe, so it is easy to hit from a minimal or hand-rolled\nLSP client.\n\n## Environment\n\n- PSES: `v4.6.0` (GitHub release asset `PowerShellEditorServices.zip`)\n- Host: PowerShell 7.6.2 (`pwsh`) and Windows PowerShell 5.1 -- reproduced on both\n- OS: Windows 11\n- Transport: `Start-EditorServices.ps1 -Stdio`\n\n## Steps to reproduce\n\n1. Launch PSES over stdio (paths trimmed for readability):\n\n   ```\n   pwsh -NoLogo -NoProfile -ExecutionPolicy Bypass -File \u003cPSES\u003e/Start-EditorServices.ps1 \\\n     -HostName repro -HostProfileId repro -HostVersion 1.0.0 -Stdio \\\n     -BundledModulesPath \u003cbundle\u003e -LogPath \u003clog\u003e -LogLevel Diagnostic \\\n     -SessionDetailsPath \u003csession.json\u003e\n   ```\n\n2. Send an LSP `initialize` whose `textDocument` capabilities cover the usual\n   entries but **omit** `rename`:\n\n   ```json\n   {\n     \"capabilities\": {\n       \"textDocument\": {\n         \"synchronization\": { \"didSave\": true },\n         \"publishDiagnostics\": { \"relatedInformation\": true },\n         \"hover\": {},\n         \"definition\": {}\n       }\n     }\n   }\n   ```\n\n3. Observe: no `initialize` **response** is returned (the handshake hangs), and the\n   PSES log shows a `NullReferenceException` in the rename-handler path.\n\n## The one-line delta that proves the cause\n\nRe-send `initialize` with a minimal `rename` capability declared and nothing else\nchanged:\n\n```json\n{\n  \"capabilities\": {\n    \"textDocument\": {\n      \"synchronization\": { \"didSave\": true },\n      \"publishDiagnostics\": { \"relatedInformation\": true },\n      \"hover\": {},\n      \"definition\": {},\n      \"rename\": { \"prepareSupport\": false }\n    }\n  }\n}\n```\n\nThe handshake now completes and diagnostics flow. The only difference is the\npresence of the `rename` capability object.\n\n## Expected\n\nOmitting the optional `rename` capability must not break `initialize`. The\nprepare-rename handler should null-guard the client `RenameCapability` (treat absent\nas \"client does not support rename\") rather than dereferencing it.\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 now declares a\nminimal `rename` capability specifically to dodge this, but the root cause should be\nfixed for any client that legitimately omits it.\n","author":{"url":"https://github.com/manderse21","@type":"Person","name":"manderse21"},"datePublished":"2026-06-06T19:53:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/2297/PowerShellEditorServices/issues/2297"}