facebook/flow · error · Error

Unsupported .flowconfig option `log.file`. The VS Code exten

Error message

Unsupported .flowconfig option `log.file`. The VS Code extension does not support this option.

What it means

On activation, flow-for-vscode reads the project's .flowconfig and rejects it if it contains a `log.file` option (regex /^log\.file/m). The extension's logging integration cannot work while flow also writes a log file, so assertNoLogFileOption throws.

Source

Thrown at packages/flow-for-vscode/src/utils/assertNoLogFileOption.ts:10

/**
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */

export default function assertNoLogFileOption(flowconfig: string): void {
  if (/^log\.file/mu.test(flowconfig)) {
    throw new Error(
      'Unsupported .flowconfig option `log.file`. The VS Code extension does not support this option.',
    );
  }
}

View on GitHub (pinned to d1341dac89)

Solutions

1. Remove or comment out the `log.file` line in the workspace's .flowconfig (check all flowconfig variants)
2. Use the extension's output channel / VS Code developer tools for logging instead
3. Keep a separate flowconfig (e.g. .flowconfig-cli) for CLI runs that need file logs, selected via --flowconfig-name

Example fix

# before (.flowconfig)
[options]
log.file=./flow.log

# after (.flowconfig)
[options]
# log.file removed; use the extension's output panel

const hasLogFileOption = (flowconfig: string): boolean => /^log\.file/mu.test(flowconfig);

const contents = fs.readFileSync(flowconfigPath, 'utf8');
if (hasLogFileOption(contents)) {
  // strip or warn before the extension activation path runs
}

function isSupportedFlowconfig(flowconfig: string): boolean {
  return !/^log\.file/mu.test(flowconfig);
}

When it happens

Trigger: Starting the Flow VS Code extension on a workspace whose .flowconfig (any section) contains a `log.file=...` line.

Common situations: Configs copied from CLI-heavy setups where flow logs to a file for debugging; debug flowconfigs from CI reused locally; team-shared flowconfig that includes logging for batch runs.

Related errors

• Flow version ${version} doesn't support 'flow lsp'. Please u
• Flow not found
• '${command}' not found
• Unexpected function parameter ${param.type}
• updatePendingStatements: Variable for dependency "${dep}" no

AI-assisted analysis of facebook/flow@d1341dac89 (2026-08-17). Data as JSON: /api/errors/48067f693d22832b. Report an issue: GitHub.