[Unhandled Error] [UriError]: cannot call joinPath on URI without path — workspaceExtensionsConfig / mcpToolRegistration

[vs-code-engineering]

Error Message

[UriError]: cannot call joinPath on URI without path

Stack Trace

    at a.joinPath (./src/vs/base/common/uri.ts:362:9)
    at uce.joinPath (./src/vs/base/common/resources.ts:186:13)
    at joinPath (./src/vs/platform/workspace/common/workspace.ts:435:0)
    at (anonymous) (./src/vs/workbench/services/extensionRecommendations/common/workspaceExtensionsConfig.ts:64:0)
    at Iye.value (./src/vs/workbench/services/extensionRecommendations/common/workspaceExtensionsConfig.ts:64:0)
    at E._deliver (./src/vs/base/common/event.ts:1354:12)
    at E._deliverQueue (./src/vs/base/common/event.ts:1365:8)
    at E.fire (./src/vs/base/common/event.ts:1389:8)
    at Iye.value (./src/vs/platform/files/common/fileService.ts:74:0)
    at E._deliver (./src/vs/base/common/event.ts:1354:12)
    at E.fire (./src/vs/base/common/event.ts:1385:8)
    at Iye.value (./src/vs/workbench/contrib/preferences/common/settingsFilesystemProvider.ts:40:25)
    at E._deliver (./src/vs/base/common/event.ts:1354:12)
    at E.fire (./src/vs/base/common/event.ts:1385:8)
    at ooi.registerSchemaAssociation (./src/vs/platform/jsonschemas/common/jsonContributionRegistry.ts:99:39)
    at XN.registerToolData (./src/vs/workbench/contrib/chat/browser/tools/languageModelToolsService.ts:284:0)
    at XN.registerTool (./src/vs/workbench/contrib/chat/browser/tools/languageModelToolsService.ts:327:0)
    at u (./src/vs/workbench/contrib/mcp/common/mcpLanguageModelToolContribution.ts:119:0)
    at registerTool (./src/vs/workbench/contrib/mcp/common/mcpLanguageModelToolContribution.ts:172:0)
    at fn (./src/vs/workbench/contrib/mcp/common/mcpLanguageModelToolContribution.ts:186:0)

Raw Stack Trace (minified)

Error: [UriError]: cannot call joinPath on URI without path     at a.joinPath (out/vs/sessions/sessions.desktop.main.js:406:59221)     at uce.joinPath (out/vs/sessions/sessions.desktop.main.js:406:68517)     at x5.toResource (out/vs/sessions/sessions.desktop.main.js:852:88845)     at out/vs/sessions/sessions.desktop.main.js:1434:6594     at Array.some (<anonymous>)     at Iye.value (out/vs/sessions/sessions.desktop.main.js:1434:6574)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3066)     at E._deliverQueue (out/vs/sessions/sessions.desktop.main.js:405:3155)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3490)     at Iye.value (out/vs/sessions/sessions.desktop.main.js:4167:27961)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3066)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3385)     at Iye.value (out/vs/sessions/sessions.desktop.main.js:1441:10149)     at E._deliver (out/vs/sessions/sessions.desktop.main.js:405:3066)     at E.fire (out/vs/sessions/sessions.desktop.main.js:405:3385)     at ooi.registerSchemaAssociation (out/vs/sessions/sessions.desktop.main.js:434:15716)     at XN.registerToolData (out/vs/sessions/sessions.desktop.main.js:3131:4799)     at XN.registerTool (out/vs/sessions/sessions.desktop.main.js:3131:5556)     at u (out/vs/sessions/sessions.desktop.main.js:3148:55693)     at out/vs/sessions/sessions.desktop.main.js:3148:56665     at MV._runFn (out/vs/sessions/sessions.desktop.main.js:3148:56790)     at MV._run (out/vs/sessions/sessions.desktop.main.js:407:6694)     at MV.endUpdate (out/vs/sessions/sessions.desktop.main.js:407:7325)     at Sb.endUpdate (out/vs/sessions/sessions.desktop.main.js:407:13497)     at Sb.endUpdate (out/vs/sessions/sessions.desktop.main.js:407:13497)     at xO.finish (out/vs/sessions/sessions.desktop.main.js:406:109976)     at Ni (out/vs/sessions/sessions.desktop.main.js:406:109176)     at out/vs/sessions/sessions.desktop.main.js:407:17058

Details

Property	Value
Bucket ID	d5d6e746-cf26-830d-fd36-00be78e3ea75
Version	1.116.0-insider
Commit	fc6d18c3
Last Seen	Wed Apr 08 2026 23:47:18 GMT+0000 (Coordinated Universal Time)
Platforms	Windows, Mac, Linux
Product	Agents

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This issue was automatically created from the VS Code Errors Dashboard

[vs-code-engineering]

Regression Details

• Product: Agents
• Regression type: New error
• Last release without this error: 1.115.0
• First release with this error: 1.116.0-insider
• Commit range: 41dd792b...fc6d18c3

Related Error Buckets

This error ([UriError]: cannot call joinPath on URI without path) is triggered through multiple call paths. All share the same root cause — joinPath called on a URI without a path, likely from workspace folder URIs in the sessions workspace context service.

Bucket	Hits	Call Path
d5d6e746	464	workspaceExtensionsConfig → mcpLanguageModelToolContribution
8f04cb06	50	promptFilesLocator → customizationCounts
59422771	50	promptFilesLocator → aiCustomizationShortcutsWidget
63292b4e	45	sessionsConfigurationService → copilotChatSessionsProvider
ddc6acb6	41	snippetsService → workspaceContextService
25b5723f	41	debug configurationManager → selectConfiguration
249ac59c	41	debug configurationManager → initLaunches
bb65995c	28	preferencesActionsContribution → workspaceContextService

Total: 760 hits across 26 users on 1.116.0-insider, affecting all platforms (Windows, Mac, Linux).

Generated by errors-agents-regression-scan · ◷

[vs-code-engineering]

🔍 Error Investigation

Summary

The error [UriError]: cannot call joinPath on URI without path is thrown when URI.joinPath is called on a workspace folder whose URI (unknown://) has no path component. This occurs in the Agents (sessions) product when an active session has no repository metadata — the AgentSessionAdapter._buildWorkspace() method uses URI.parse('unknown://') as a fallback, which is then added as a workspace folder. Any subsequent file-change event (e.g., triggered by MCP tool registration → JSON schema association) causes multiple listeners to call folder.toResource() → joinPath(), which throws. This affects 760 hits across 26 users on all platforms through 8 different call paths.

Culprit Commit

No single culprit commit was identified. The commit range 41dd792b...fc6d18c3 spans a diverged branch comparison (1.115.0 release vs 1.116.0-insider) with ~4,108 commits, making bisection impractical. The root cause code (URI.parse('unknown://') fallback in _buildWorkspace) exists in both the last-good and first-bad commits, suggesting the regression may be caused by a change in session lifecycle (e.g., sessions without repos becoming active more frequently) or MCP tool registration timing.

Code Flow

sequenceDiagram
    participant MCP as MCP Tool Registration
    participant Schema as JSON Schema Registry
    participant Settings as Settings FS Provider
    participant FileService as File Service
    participant ExtConfig as Workspace Extensions Config
    participant Folder as WorkspaceFolder
    participant URI as URI.joinPath

    MCP->>Schema: registerSchemaAssociation()
    Schema->>Settings: onDidChangeSchemaAssociations
    Settings->>FileService: onDidChangeFile (synthetic)
    FileService->>ExtConfig: onDidFilesChange
    ExtConfig->>Folder: folder.toResource('.vscode/extensions.json')
    Folder->>URI: joinPath(URI.parse('unknown://'), ...)
    Note over URI: 💥 Error: cannot call<br/>joinPath on URI without path
    Note over ExtConfig: ⚠️ Root cause: workspace folder<br/>has URI with no path component

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Affected Files

File	Role
src/vs/sessions/contrib/copilotChatSessions/browser/copilotChatSessionsProvider.ts	Root cause — _buildWorkspace() (line ~977) uses URI.parse('unknown://') (no path) as fallback when session has no repository metadata
src/vs/sessions/contrib/workspace/browser/workspaceFolderManagement.ts	Data flow — getActiveSessionFolderData() passes the unknown:// URI through as a workspace folder URI without validating it has a path
src/vs/workbench/services/extensionRecommendations/common/workspaceExtensionsConfig.ts	Crash site — line 64 calls folder.toResource(EXTENSIONS_CONFIG) on all workspace folders in onDidFilesChange handler
src/vs/platform/workspace/common/workspace.ts	Crash site — WorkspaceFolder.toResource() calls joinPath(this.uri, ...) which throws
src/vs/base/common/uri.ts	Throw site — URI.joinPath() line 362 throws when URI has no path

Repro Steps

1. Open the VS Code Agents (sessions) application
2. Have an active session whose metadata does not include repository information (no repositoryPath, workingDirectoryPath, or cloud repo metadata)
3. Any MCP tool with an input schema gets registered (triggers JSON schema association event)
4. The file change event propagates to workspaceExtensionsConfig.ts, which iterates workspace folders and calls toResource() on the folder with unknown:// URI
5. URI.joinPath throws because unknown:// has no path component

The error is deterministic once a session without repo metadata becomes the active session — it triggers on every schema association change.

Fix Proposal

Fix location: src/vs/sessions/contrib/copilotChatSessions/browser/copilotChatSessionsProvider.ts → AgentSessionAdapter._buildWorkspace()

Approach: When repoUri is undefined (no repository metadata available), _buildWorkspace should return undefined instead of creating a workspace with a pathless URI.parse('unknown://'). The method signature already allows returning undefined (ISessionWorkspace | undefined), but the current implementation never does. This will prevent WorkspaceFolderManagementContribution from adding a workspace folder without a valid URI.

Alternatively, if sessions without repos still need a workspace representation, change the fallback URI to include a root path: URI.from({ scheme: 'unknown', path: '/' }). This ensures joinPath can operate on the URI without throwing.

A defensive guard in WorkspaceFolderManagementContribution.getActiveSessionFolderData() could also be added to reject URIs without a path (if (!repository.path) return undefined), preventing any pathless URI from becoming a workspace folder.

Recommended Owner

@sandy081 — Primary maintainer of copilotChatSessionsProvider.ts (8 of last 20 commits) and the sessions management layer. The root cause is in the AgentSessionAdapter._buildWorkspace() method which was likely introduced as part of the sessions decoupling work.

Generated by errors-investigate · ◷