util.join() doesn't handle absolute path on Windows correctly

[mutoo]

We use the Webpack pipeline on Windows with sass-loader, postcss-loader, and css-loader. Then we found the generated source paths went crazy: F:\Projects\web-project-boilerplate\src\scss\index.scss just becomes F:/Projects/web-project-boilerplate/src/scss/F:/Projects/web-project-boilerplate/src/scss/F:/Projects/web-project-boilerplate/src/scss/index.scss.

As I followed the codebase in the pipeline, I noticed that the sass-loader use relative path, then the postcss-loader and css-loader turn to use absolute path for "sources" field in the sourceMap. In addition, the absolute path on Windows starts with a symbol of the disk driver, e.g. F: in our case. When it comes to sourceMap's util.join(), it only detects absolute path starts with /

source-map/lib/util.js

Line 228 in c3a8f5a

const joined = aPath.charAt(0) === "/"

So it joins multiple paths across the loaders.

Also, the util.isAbsolute doesn't deal with the Windows absolute path as well.

source-map/lib/util.js

Line 241 in c3a8f5a

return aPath.charAt(0) === "/" || urlRegexp.test(aPath);

Appendix:
Here is a case of how expressjs test the absolute path:

exports.isAbsolute = function(path){
  if ('/' === path[0]) return true;
  if (':' === path[1] && ('\\' === path[2] || '/' === path[2])) return true; // Windows device path
  if ('\\\\' === path.substring(0, 2)) return true; // Microsoft Azure absolute path
};

I'm not sure we need to handle the azure absolute path, but I would be better if we had window device path included.

Thanks

[jkrems]

Generally source maps operate on URLs, not file system paths. But it's unclear if tools like webpack will migrate or if the past of least resistance would be to allow on-the-fly conversions from file system paths in the API. Leaving open as a feature request for file system path support.