Function detectPolyfills

packages/plugin-legacy/src/index.ts:827–871

(
  code: string,
  targets: any,
  assumptions: Record<string, boolean>,
  list: Set<string>,
)

}

export async function detectPolyfills(
  code: string,
  targets: any,
  assumptions: Record<string, boolean>,
  list: Set<string>,
): Promise<void> {
  const babel = await loadBabel()
  const result = babel.transform(code, {
    ast: true,
    code: false,
    babelrc: false,
    configFile: false,
    compact: false,
    targets,
    assumptions,
    browserslistConfigFile: false,
    plugins: [
      [
        (await import('babel-plugin-polyfill-corejs3')).default,
        {
          method: 'usage-global',
          version: _require('core-js/package.json').version,
          shippedProposals: true,
        },
      ],
      [
        (await import('babel-plugin-polyfill-regenerator')).default,
        {
          method: 'usage-global',
        },
      ],
    ],
  })
  for (const node of result!.ast!.program.body) {
    if (node.type === 'ImportDeclaration') {
      const source = node.source.value
      if (
        source.startsWith('core-js/') ||
        source.startsWith('regenerator-runtime/')
      ) {
        list.add(source)
      }
    }
  }
}

async function buildPolyfillChunk(
  ctx: Rollup.PluginContext,