Change Request: Option to allow config fallback

[btmills]

ESLint version

v8.25.0

What problem do you want to solve?

I usually work with files that are not part of a project. They are just files on the fly on my machine.

Since I like to use the "standard" rule, I have installed it globally and added the option "overrideConfigFile" to vscode eslint extension. This way I don't have to install "standard" and any other plugins every single time.

The problem comes when I have to work on a project with its own eslint rules. If I use "overrideConfigFile", it will cause some problems, like a plugin is not found or the project itself is not using "standard".

To solve this problem, I just have to open vscode "settings.json" file and comment out "overrideConfigFile" option.

What do you think is the correct solution?

Skip the manual process of commenting out "overrideConfigFile" in vscode settings by following the next:

If any eslint config or config file is not found on root and up directories, use the file declared in "overrideConfigFile" option (or a new option name).

Participation

• [ ] I am willing to submit a pull request for this change.

Additional comments

I'm opening the request over here instead of vscode eslint extension repository because while I was looking for a solution to this problem, I found out they rely entirely on the features you add: https://github.com/microsoft/vscode-eslint/issues/482#issuecomment-395336940

So I understand if this feature is added on a new version, it would be available on vscode eslint extension as well.

[mayil-ai[bot]]

To implement the fallback configuration feature in ESLint, follow these steps:

• Introduce a new command-line option --fallback-config in lib/cli.js. This option will allow users to specify a path to a fallback configuration file.

  // lib/cli.js
  // Add new CLI option
  program.option('--fallback-config <path>', 'Path to a fallback configuration file');

• Update the configuration resolution logic in lib/eslint/legacy-eslint.js. This logic should now check for the --fallback-config option when no other configuration is found. If the fallback configuration file exists, it should be used as the configuration file.

  // lib/eslint/legacy-eslint.js
  // Modify processOptions function to include fallbackConfigFile
  function processOptions({
    // ... existing parameters
    fallbackConfigFile = null, // Add new parameter for fallback config
    // ... rest of the parameters
  }) {
    // ... existing logic
  
    // Modify the logic to use fallbackConfigFile when no configFile is found
    if (!configFile && fallbackConfigFile) {
        try {
            if (fs.existsSync(fallbackConfigFile)) {
                configFile = fallbackConfigFile;
            } else {
                throw new Error(`Fallback configuration file not found: ${fallbackConfigFile}`);
            }
        } catch (error) {
            // Handle file not found or other errors
            console.error(error.message);
            process.exit(1);
        }
    }
  
    // ... rest of the function
  }

• Enhance the ESLint documentation to explain the new --fallback-config option. This should be done in docs/src/use/configure/configuration-files.md. Include a new section under "Configuration File Resolution" detailing how the fallback configuration works and provide usage examples.

  Ensure that the new documentation section is clear, concise, and includes necessary examples for users to understand how to use the --fallback-config option effectively.

Code snippets to check

• lib/eslint/legacy-eslint.js:163-707 | Contains 'overrideConfigFile' option handling, relevant to the issue of conflicting ESLint configurations.

• lib/eslint/eslint-helpers.js:1-727 | The function 'processOptions' handles various configuration options including 'overrideConfigFile', which is directly relevant for implementing the fallback configuration feature.