Parcel: Parcel adds a / before sourcemap paths -> Firefox can't read them

[lhk]

🐛 bug report

I'm working on a webextension for Firefox. The code is written in Typescript.
But parcel generates sourcemap paths that are not parsed correctly by Firefox.
The paths look like this:
//# sourceMappingURL=/content2.map

without the slash in from of content2.map, the path can be read by Firefox.
This problem occurs only for sourcefiles within folders.

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

My configuration is minimal, just Typescript and Parcel. To let you reproduce the problem, I set up a git repository, see below.

🤔 Expected Behavior

Parcel shouldn't generate that slash.

😯 Current Behavior

Well, currently it generates it :P

💻 Code Sample

Here is a repository that can reproduce the problem:
https://github.com/lhk/nested_sourcemaps

This sample contains two scripts. One is in src/, the other is in src/content. Both scripts print something to the console, which makes them easy to find.
The master branch contains no parcel and shows you how the code works correctly:

git clone https://github.com/lhk/nested_sourcemaps
cd nested_sourcemaps
npm install
tsc

Now you can load src/manifest.json into Firefox. Open any website, open the developer console, reload the website, you will see two logs from the two scripts. Firefox automatically recognizes them as typescript :)

Now you switch to the parcel branch

git reset --hard
git clean -xdf
git checkout parcel_branch
npm install
parcel build src/manifest.json

Same procedure as above, load the plugin into Firefox. Now you have to use the manifest from dist/manifest.json.

Again, you can see two console logs. But for the script in src/content, the sourcemap can't be parsed.

If I edit this file manually and change the last line from:
//# sourceMappingURL=/content2.map
to
//# sourceMappingURL=content2.map
Then it works as expected.

🌍 Your Environment

| Software | Version(s) |
| ---------------- | ---------- |
| Parcel | 1.10.3
| Node | v8.12.0
| npm/Yarn | npm 6.4.1
| Operating System | ubuntu 18.04.01 64bit
| Firefox | 63

[lhk]

This is very similar to #1753

Curiously, in the other case the / is missing, while I want to get rid of it.

[DeMoorJasper]

@lhk use —public-url ./

_{Sent with GitHawk}

[lhk]

Thanks, that solves it.