Sourcemap url with multiple entrypoints

[mischnic]

🐛 bug report

The sourcemap url in Javascript bundles isn't respecting the subfolder of the corresponding bundle.

🎛 Configuration (.babelrc, package.json, cli command)

parcel build src/a/index.js src/b/index.js

🤔 Expected Behavior

The two output files should contains these sourcemap comments:
a/index.js: //# sourceMappingURL=/a/index.js.map
b/index.js: //# sourceMappingURL=/b/index.js.map

😯 Current Behavior

The two output files contain these sourcemap comments (the map files are emitted correctly though) :
a/index.js: //# sourceMappingURL=/index.js.map
b/index.js: //# sourceMappingURL=/index.js.map

💁 Possible Solution

This is the related code:

parcel/packages/core/parcel-bundler/src/packagers/JSPackager.js

Lines 238 to 245 in 791b4b8

	let mapBundle = this.bundle.siblingBundlesMap.get('map');
	if (mapBundle) {
	let mapUrl = urlJoin(
	this.options.publicURL,
	path.basename(mapBundle.name)
	);
	await this.write(`\n//# sourceMappingURL=${mapUrl}`);
	}

💻 Code Sample

// src/a/index.js
console.log("asd");

// src/b/index.js
console.log("asd");

🌍 Your Environment

Software	Version(s)
Parcel	master
Node	11
npm/Yarn
Operating System

[lustoykov]

@mischnic you mind me taking this one or you've already started working on it?

On a first thought

path.basename(mapBundle.name) -> path.relative(this.options.outDir, mapBundle.name)

might do it?

[mischnic]

Go ahead. I would say the publicUrl needs to be prepended as well?

[lustoykov]

yes, I had in mind:

let mapUrl = urlJoin( 
     this.options.publicURL, 
     path.basename(mapBundle.name) -> path.relative(this.options.outDir, mapBundle.name)
);

will give it a try

[lustoykov]

Can we close, @mischnic?