Rollup plugins with extra outputs

[mattsoulanille]

Is there a good way to make Bazel aware of extra outputs from rollup plugins in rollup_bundle. For example, rollup-plugin-visualizer generates an html page to show the contents of a bundle. It can be made to write the html page to the output directory by using a template, e.g.:

rollup_template.config.js

export default {
  plugins: [
    visualizer({
      sourcemap: true,
      filename: 'TEMPLATE_stats',
    })
  ]
}

some_build_rule.bzl

...
ctx.actions.expand_template(
    template = ctx.file.template, # The rollup template above
    output = ctx.outputs.config_file,
    substitutions = {
        "TEMPLATE_stats": "computed/path/to/where/stats/file/should/go.html",
    },
}
...

However, I haven't found a good way to declare that this html output file exists. Ideally, the rollup_bundle that uses an instance of the above template would declare it, but I don't think that's supported. Right now, I'm just not declaring it (since I don't have any downstream rules that need the html pages), and it still appears in the output tree as expected. This is not a blocker for me. I'm just wondering if there's a better solution.

[mattsoulanille]

I've learned some more about Bazel, and I believe (but haven't tried it yet) that one way to do this is to create a rule that wraps rollup_bundle and declares the extra output. I'll update this when / if I try this solution.