Function generatePattern

packages/vite/src/node/plugins/define.ts:30–101

(environment: Environment)

  }

  function generatePattern(environment: Environment) {
    const isBundled = environment.config.isBundled
    const keepProcessEnv = environment.config.keepProcessEnv

    // during dev, import.meta properties are handled by importAnalysis plugin.
    const importMetaKeys: Record<string, string> = {}
    const importMetaEnvKeys: Record<string, string> = {}
    const importMetaFallbackKeys: Record<string, string> = {}
    if (isBuild) {
      importMetaKeys['import.meta.hot'] = `undefined`
    }
    if (isBundled) {
      for (const key in config.env) {
        const val = JSON.stringify(config.env[key])
        importMetaKeys[`import.meta.env.${key}`] = val
        importMetaEnvKeys[key] = val
      }
      // these will be set to a proper value below
      importMetaKeys['import.meta.env.SSR'] = `undefined`
      importMetaFallbackKeys['import.meta.env'] = `undefined`
    }

    const userDefine: Record<string, string> = {}
    const userDefineEnv: Record<string, any> = {}
    for (const key in environment.config.define) {
      userDefine[key] = handleDefineValue(environment.config.define[key])

      // make sure `import.meta.env` object has user define properties
      if (isBuild && key.startsWith('import.meta.env.')) {
        userDefineEnv[key.slice(16)] = environment.config.define[key]
      }
    }

    const define: Record<string, string> = {
      ...(keepProcessEnv ? {} : processEnv),
      ...importMetaKeys,
      ...userDefine,
      ...importMetaFallbackKeys,
    }

    // Additional define fixes based on `ssr` value
    const ssr = environment.config.consumer === 'server'

    if ('import.meta.env.SSR' in define) {
      define['import.meta.env.SSR'] = ssr + ''
    }

    const importMetaEnvVal = serializeDefine({
      ...importMetaEnvKeys,
      SSR: ssr + '',
      ...userDefineEnv,
    })

    // Create regex pattern as a fast check before running esbuild
    const patternKeys = Object.keys(userDefine)
    if (!keepProcessEnv && Object.keys(processEnv).length) {
      patternKeys.push('process.env')
    }