Support update existing `.config/[name].[ext]`

[Yizack]

Describe the feature

Hello! This issue is related to the updateConfig util

I think it'd be nice to support updating existing files in the .config/ folder using the .config/[name].[ext] format, as described here.

For example, let's say I have a config file at .config/foo.ts and I want to update this existing config, I would typically set the configFile property to 'foo.config', so that foo.config.ts is created at the project's root if no config file is detected. However, the problem is that .config/foo.ts isn't being detected because of this line:

https://github.com/unjs/c12/blob/26c97080c5ab06e32686d7f3f93f59c5ee3471c5/src/update.ts#L25

It currently expects the file to be .config/foo.config.ts, thus it doesn't detect the existing .config/foo.ts file.

Implementation

I don't know if this implementation is right for performance, and I apologize if it's not or if this is already a work in progress upstream. Adding these lines would make it work without breaking the current support

let configFile =
  (await _tryResolve(
    `./${opts.configFile}`,
    opts.cwd,
    SUPPORTED_EXTENSIONS,
  )) ||
  (await _tryResolve(
    `./.config/${opts.configFile}`,
    opts.cwd,
    SUPPORTED_EXTENSIONS,
+ )) ||
+ (await _tryResolve(
+   `./.config/${opts.configFile.split(".")[0]}`,
+   opts.cwd, 
+   SUPPORTED_EXTENSIONS,
+ ));

I forked it, pushed my changes here https://github.com/unjs/c12/compare/main...Yizack:c12:main, and added a test case that creates a config file before in case you want to take a look.

Best wishes!

Additional information

• [X] Would you be willing to help implement this feature?