fix: node_modules relative paths in sourcemaps

[zachkirsch]

Fixes #3500

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

Taking a stab at fixing #3500.

The source maps published with blueprint are incorrect. For example:

app/node_modules/@blueprintjs/select/lib/css/blueprint-select.css.map
{
    "version":3,
    "sources":[
        "../../src/components/omnibar/_omnibar.scss",
        "../../../../node_modules/@blueprintjs/core/src/common/_react-transition.scss",
        ...

The resolved path of that second source is app/node_modules/node_modules/@blueprintjs/core/src/common/_react-transition.scss (notice the double node_modules). This leads to webpack errors like:

Failed to parse source map from '/Users/zachkirsch/Dropbox/Mac/Documents/trace-app/node_modules/node_modules/@blueprintjs/core/src/common/_react-transition.scss' file: Error: ENOENT: no such file or directory, open '/Users/zachkirsch/Dropbox/Mac/Documents/trace-app/node_modules/node_modules/@blueprintjs/core/src/common/_react-transition.scss'

Where does "../../../../node_modules come from?

When the sass is compiled, the path "~@blueprintjs/core/src/common/react-transition" is resolved to "node_modules/@blueprintjs/core/src/common/_react-transition.scss", and node_modules is 4 directories up, hence the final result of ../../../../node_modules/@blueprintjs/core/src/common/_react-transition.scss. Ideally node-sass-chokidar could resolve/follow the symlink to figure out that there's a more direct route to that file (../../../core/src/common/_react-transition.scss), but it doesn't seem like that's possible.

I tried moving to dart-sass since node-sass-chokidar is deprecated, but it looks like the source maps have the same issue (paths going through node_modules).

So this PR is a "cheap" solution - after writing the source maps files, convert the "roundabout" node_modules paths to more direct paths:

{
	"version": 3,
	"sources": [
		"../../src/components/omnibar/_omnibar.scss",
		"../../../core/src/common/_react-transition.scss",

Reviewers should focus on:

Is there a place I can add tests?

Screenshot

[adidahiya]

seems to work fine, I can view the remapped files in dev tools and set a debug breakpoint: