Bug Description

When I either set a devtool config value to hidden-source-map-debugids or use a webpack.SourceMapDevToolPlugin with a configuration matching hidden-source-map-debugids, the debug ID appended to the generated .js file is corrupted – it looks like //# debugId=<hash>false instead of //debugId=<hash>.

Link to Minimal Reproduction and step to reproduce

https://github.com/in-doge-we-trust/webpack-debugids-append-issue-repro

Case #1 (webpack.SourceMapDevToolPlugin is used manually) steps:

1. Run npm install
2. Run npm run build

Case #2 (devtool set to hidden-source-map-debugids) steps:

1. Run npm run clear (optional)
2. Run npm run build

Expected Behavior

debugId value in the source-map file matches the value in //# debugId=<hash> comment appended to the generated .js.

Actual Behavior

debugId value in the source-map file is correct, while //# debugId=<hash> comment has false appended to the end and looks like this – //# debugId=<hash>false.

Environment

Binaries:
    Node: 22.18.0
    npm: 10.9.3
Packages:
    webpack: 5.102.1 => 5.102.1
    webpack-cli: 6.0.1 => 6.0.1

Is this a regression?

No

Last Working Version

No response

Additional Context

As a temporary workaround, developers can force the append to be a new line character:

// webpack.config.js
const config = {
  // --snip--

  plugins: [
    new webpack.SourceMapDevToolPlugin({
      filename: "[file].map",

      debugIds: true,
      append: '\n', // force append value

      module: true,
      columns: true,
    }),
  ],
};

export default config;

In that case, append doesn't corrupt the injected debugId, so it looks correct.