Support windows paths on windows, both absolute and relative

[cspotcode]

Trying to get this working for cspotcode/node-source-map-support#38, and hitting issues where it cannot handle Windows paths on Windows.

When pulling sourcemaps from source files, I need to resolve their sourcemap URLs relative to the file's path. For example, I get C:\foo\bar.js as a path, I read the file contents and parse out the source-map comment, then use resolve-uri to resolve that source-map comment relative to the windows path.

require('resolve-uri')('foo.js.map', 'C:\\foo.js')
// Would also like to support
require('resolve-uri')('C:\\foo.js.map', 'C:\\foo.js')

// Currently, a naive replacement of \ with / also fails
require('@jridgewell/resolve-uri')('C:/foo.js.map', 'C:/foo.js')
// C:/C:/foo.js.map

Per the readme, I believe this should be supported. Is this something we can get working?

[jridgewell]

I aim to resolve URLs, and URL-like paths (basically posix, foo/bar like you'd get out of a location.pathname). You could convert to an absolute beforehand:

function toUrl(str) {
  if (str.indexOf('\\') === -1) return str;

  str = str.replace(/\\/g, '/');
  if (/^[a-z]:/i.test(str)) str = 'file:///' + str;
  return str;
}

function toWindows(str) {
  if (str.startsWith('file:///')) str = str.slice('file:///'.length);
  return str.replace(/\//g, '\\');
}


const resolve = require('@jridgewell/resolve-uri');
const resolved = resolve(toUrl('c:\\foo.js.map'), toUrl('C:\\foo.js'));
console.log(toWindows(resolved));
// c:\foo.js.map

I could try adding helpers to the library to handle this.

[cspotcode]

The problem for this project is that the resolved output needs to match the format/style of the input. If the input is a windows path, the output should also be a windows path in that same style. For CommonJS modules on nodejs, this means backslashes, without file://.

When we rewrite a stack frame, the input we get may look like this:

Error
  at foo (D:\project\dist\path.js:1:1)

So we should mimic that style through the remapping:

Error
  at foo (D:\project\src\path.ts:1:1)

This is what you'd get from node if you really were natively executing path.ts as a CommonJS file, and it's also what you get from node's native --enable-sourcemaps flag.

[cspotcode]

To achieve this, I've avoided using resolve-uri when the base is an absolute path and the URL is neither a protocol-relative nor absolute URL. In these cases I use path.resolve(path.dirname())

To do this, I copied isAbsoluteUrl and isSchemeRelativeUrl into my code since they're not exposed by resolve-uri. Would be great to have that functionality exposed in some form.