Adding Acorn plugins to Snowpack workflow

rollup-acorn-conf.js

"use strict";

// https://stackoverflow.com/a/64501702/1768303

module.exports = function plugin(snowpackConfig, pluginOptions) {
  const name = "rollup-acorn-conf";

  snowpackConfig.installOptions = snowpackConfig.installOptions ?? {};
  snowpackConfig.installOptions.rollup = snowpackConfig.installOptions.rollup ?? {};
  snowpackConfig.installOptions.rollup.plugins = snowpackConfig.installOptions.rollup.plugins ?? [];

  snowpackConfig.installOptions.rollup.plugins.push({
    name,

    options: rollupOpts => { 
      console.log("Enabling 'acorn-stage3'...");
      rollupOpts.acorn = rollupOpts.acorn ?? {};
      rollupOpts.acorn.ecmaVersion = 2020;
      rollupOpts.acornInjectPlugins = rollupOpts.acornInjectPlugins ?? [];
      rollupOpts.acornInjectPlugins.push(require('acorn-stage3'));
      return rollupOpts;
    }
  });

  return { name };
};