* Pass config.experimental.cpus to export during build
Currently, there is no way of specifying the number of worker threads of
`next export` when run as part of `next build`.
I suggest a sane default should be to just use the same amount of
workers that were used during the build process which currently seems to
be configured through `config.experimental.cpus`.
This setting is already respected in the two other places where
jest-workers are in use: The TerserPlugin and the staticCheckWorkers in
`next build`.
* Only enable worker threads if there is more than 1 worker
Multiple worker threads can cause problems when certain dependencies are
being used, see e.g. https://github.com/zeit/next.js/issues/7894
This patch allows disabling of worker threads by setting
`config.experimental.cpus = 1`.
The benefit of spawning 1 worker thread, if there is any at all, should
very limited anyways, so the workload can just as well be processed in
the main thread.
* Disable parallel build for firebase authentication example
* Add integration test to cover #7894
* Rename test suite and add worker_threads config
* Disable worker_threads by default
* Update index.test.js
* Use workerThreads config for TerserPlugin
* Update to use workerThreads config in
TerserPlugin for consistency
* Disable node 12 specific test
14ed867537