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[Bug] TypeError: Cannot read properties of undefined (reading 'filter') #428
Description
Environment
- OS: Windows
- Eclipse Version: 2026-06 (4.40.0)
- Plugin Version: 0.21.0.202608060743
Describe the bug
The following error occurs in the Agent mode when there is no project in the workspace:
!ENTRY org.eclipse.lsp4e 4 0 2026-08-26 07:45:09.023
!MESSAGE [LS:GitHub Copilot Language Server][Error] [chat] Error processing turn 72df12fd-e941-4394-adb4-2b5917d14ed7 TypeError: Cannot read properties of undefined (reading 'filter') (at tsx element AgentPrompt > UserMessage > SubagentListPrompt)
at y0.collect (C:\snapshot\copilot-language-server-internal\dist\main.js:2411:12762)
at t.listCustomAgents (C:\snapshot\copilot-language-server-internal\dist\main.js:2411:23507)
at async $de.getAgents (C:\snapshot\copilot-language-server-internal\dist\main.js:3333:954)
at async $de.getAgentsForModelDispatch (C:\snapshot\copilot-language-server-internal\dist\main.js:3333:1202)
at async Itt.renderCopilot (C:\snapshot\copilot-language-server-internal\dist\main.js:3333:3037)
at async annotateError (C:\snapshot\copilot-language-server-internal\dist\main.js:69:4311)
at async C:\snapshot\copilot-language-server-internal\dist\main.js:67:29695
at async Promise.all (index 0)
at async jZe._processPromptPieces (C:\snapshot\copilot-language-server-internal\dist\main.js:67:29606)
at async jZe._processPromptRenderPiece (C:\snapshot\copilot-language-server-internal\dist\main.js:67:30200)
!ENTRY org.eclipse.lsp4e 4 0 2026-08-26 07:45:09.024
!MESSAGE [LS:GitHub Copilot Language Server][Error] [agenticTurnProcessor] Error in processing turn 72df12fd-e941-4394-adb4-2b5917d14ed7 TypeError: Cannot read properties of undefined (reading 'filter') (at tsx element AgentPrompt > UserMessage > SubagentListPrompt)
at y0.collect (C:\snapshot\copilot-language-server-internal\dist\main.js:2411:12762)
at t.listCustomAgents (C:\snapshot\copilot-language-server-internal\dist\main.js:2411:23507)
at async $de.getAgents (C:\snapshot\copilot-language-server-internal\dist\main.js:3333:954)
at async $de.getAgentsForModelDispatch (C:\snapshot\copilot-language-server-internal\dist\main.js:3333:1202)
at async Itt.renderCopilot (C:\snapshot\copilot-language-server-internal\dist\main.js:3333:3037)
at async annotateError (C:\snapshot\copilot-language-server-internal\dist\main.js:69:4311)
at async C:\snapshot\copilot-language-server-internal\dist\main.js:67:29695
at async Promise.all (index 0)
at async jZe._processPromptPieces (C:\snapshot\copilot-language-server-internal\dist\main.js:67:29606)
at async jZe._processPromptRenderPiece (C:\snapshot\copilot-language-server-internal\dist\main.js:67:30200)
To Reproduce
Steps to reproduce the behavior:
- Open a new empty workspace with no project imported into it
- Ensure on the Chat window Agent mode is selected
- Ask a question to Copilot e.g: "What day is today?"
- See error
Expected behavior
No error should appear
Screenshots
Additional context
The problem does not occur if Ask mode is selected
Activity
amvalente commentedon Sep 2, 2026
This appears to be the same underlying problem reported in #403. In my case, it occurs in an Eclipse RCP application whose workspace has no standard Eclipse project.
I can also provide the following regression test:
0.21.0.202608060743: issue reproduced0.21.0.202608261610_nightly: issue still reproduced0.20.0: works correctly in the same application and workspaceWith both 0.21 builds, Agent mode fails with:
Cannot read properties of undefined (reading 'filter') (at tsx element AgentPrompt > UserMessage > SubagentListPrompt)After downgrading to 0.20.0, Agent mode works without creating or importing a project. A locally configured MCP server is also discovered and its tools can be invoked successfully.
No application, workspace, or MCP configuration changes were made between the tests. Only the Copilot Eclipse plug-in version changed.
Given the
SubagentListPromptstack location, could this regression be related to the sub-agent enablement changes introduced by #349?tamasmiklossy commentedon Sep 2, 2026
Antonio Valente (@amvalente): seems these two issues are about the same problem, good catch!