next.js/packages/next/src/server/lib/experimental/ppr.ts

/**
 * If set to `incremental`, only those leaf pages that export
 * `experimental_ppr = true` will have partial prerendering enabled. If any
 * page exports this value as `false` or does not export it at all will not
 * have partial prerendering enabled. If set to a boolean, the options for
 * `experimental_ppr` will be ignored.
 */

export type ExperimentalPPRConfig = boolean | 'incremental'

/**
 * Returns true if partial prerendering is enabled for the application. It does
 * not tell you if a given route has PPR enabled, as that requires analysis of
 * the route's configuration.
 *
 * @see {@link checkIsRoutePPREnabled} - for checking if a specific route has PPR enabled.
 */
export function checkIsAppPPREnabled(
  config: ExperimentalPPRConfig | undefined
): boolean {
  // If the config is undefined, partial prerendering is disabled.
  if (typeof config === 'undefined') return false

  // If the config is a boolean, use it directly.
  if (typeof config === 'boolean') return config

  // If the config is a string, it must be 'incremental' to enable partial
  // prerendering.
  if (config === 'incremental') return true

  return false
}

/**
 * Returns true if partial prerendering is supported for the current page with
 * the provided app configuration. If the application doesn't have partial
 * prerendering enabled, this function will always return false. If you want to
 * check if the application has partial prerendering enabled
 *
 * @see {@link checkIsAppPPREnabled} for checking if the application has PPR enabled.
 */
export function checkIsRoutePPREnabled(
  config: ExperimentalPPRConfig | undefined,
  appConfig: {
    experimental_ppr?: boolean
  }
): boolean {
  // If the config is undefined, partial prerendering is disabled.
  if (typeof config === 'undefined') return false

  // If the config is a boolean, use it directly.
  if (typeof config === 'boolean') return config

  // If the config is a string, it must be 'incremental' to enable partial
  // prerendering.
  if (config === 'incremental' && appConfig.experimental_ppr === true) {
    return true
  }

  return false
}