siyuan-note/siyuan · error

duplicate variable

Error message

duplicate variable %q

What it means

validateMCPServerEnvironment rejects a server whose explicit Env map contains the same variable name twice. Keys in the Go map are already unique, so this triggers when two names normalize to the same environmentKey — i.e. on Windows, names differing only by case (PATH vs Path). Explicitly setting the same variable twice is ambiguous, so it fails fast.

Solutions

1. Open the MCP server settings and remove one of the duplicated environment entries
2. On Windows, check for case-only variants (PATH vs Path) and keep a single entry
3. If the duplicate originates from an imported config, deduplicate the env object keys in conf.json and restart the server connection

Example fix

// before (Windows)
server.Env["PATH"] = "C:\\tools"
server.Env["Path"] = "C:\\other"
// after
server.Env["PATH"] = "C:\\tools;C:\\other"

// normalize keys case-insensitively on Windows before building Env
key := name
if runtime.GOOS == "windows" { key = strings.ToUpper(name) }
if _, dup := envByKey[key]; dup { return fmt.Errorf("duplicate env %q", name) }
envByKey[key] = value

When it happens

Trigger: conf.MCPServer.Env has two keys that map to the same environmentKey (case-insensitive match on Windows) when ValidateMCPServerEnvironment runs or a stdio server is launched.

Common situations: On Windows, adding both 'Path' and 'PATH' as explicit env entries; a config merge/import producing near-duplicate keys; hand-editing conf.json with case-variant duplicates.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

• duplicate inherited variable
• invalid name
• variable contains NUL
• attr must be a string or null (got %T)
• command is required for stdio server

AI-assisted analysis of siyuan-note/siyuan@9f775e8a12 (2026-09-19). Data as JSON: /api/errors/2c73085ae2fa5eda. Report an issue: GitHub.

Appendix: source

Thrown at kernel/mcp/client/mcp.go:568

			return err
		}
		key := environmentKey(name, goos)
		if inherited[key] {
			return fmt.Errorf("duplicate inherited variable %q", name)
		}
		inherited[key] = true
	}
	explicit := map[string]bool{}
	for name, value := range server.Env {
		if err := validateEnvironmentName(name); err != nil {
			return err
		}
		if strings.ContainsRune(value, '\x00') {
			return fmt.Errorf("variable %q contains NUL", name)
		}
		key := environmentKey(name, goos)
		if explicit[key] {
			return fmt.Errorf("duplicate variable %q", name)
		}
		explicit[key] = true
	}
	return nil
}

// ValidateMCPServerEnvironment 校验当前平台上的 stdio 环境变量配置。
func ValidateMCPServerEnvironment(server conf.MCPServer) error {
	return validateMCPServerEnvironment(server, runtime.GOOS)
}

func defaultMCPEnvironmentNames(goos string) []string {
	if goos == "windows" {
		return []string{"APPDATA", "HOMEDRIVE", "HOMEPATH", "LOCALAPPDATA", "PATH", "PATHEXT",
			"PROCESSOR_ARCHITECTURE", "PROGRAMFILES", "SYSTEMDRIVE", "SYSTEMROOT", "TEMP", "USERNAME", "USERPROFILE"}
	}
	return []string{"HOME", "LOGNAME", "PATH", "SHELL", "TERM"}
}

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