core/scripts/trim-vapor-exports.js

// @ts-check

/**
 * runtime-core exports a number of internal helpers that are only used by
 * runtime-vapor, which should be only preserved in vapor / esm-bundler builds.
 * This plugin should be included as the first plugin for all other formats
 * other than vapor / esm-bundler.
 *
 * @param {string} format
 * @param {string} pkgName
 * @returns {import('rollup').Plugin[]}
 */
export function trimVaporExportsPlugin(format, pkgName) {
  if (
    format === 'vapor' ||
    format.startsWith('esm-bundler') ||
    pkgName === '@vue/runtime-vapor'
  ) {
    return []
  } else {
    return [
      {
        name: 'trim-vapor-exports',
        transform(code, id) {
          if (id.endsWith('runtime-core/src/index.ts')) {
            const index = code.lastIndexOf('// VAPOR ---')
            return code.slice(0, index)
          }
        },
      },
    ]
  }
}