fix: fix memoization

[ehmicky]

This fixes memoization of getNextConfig().

Note: the tests seem to be failing. Work in progress.

[jlengstorf]

🎉

[jlengstorf]

I'm thinking this test failure is due to the addition of a defaultFailBuild — the test can't override utils now, so it's throwing an actual error

[jlengstorf]

my new theory is that the memoization means the different next configs used in testing are no longer loaded due to returning the same promise

I started debugging this, but I ran into an issue where tests failed due to promises never resolving

I've run out of time to keep working on this, but for the record, here's where I ended up (tests still fail at this point)

first, I disabled memoization during tests:

  // Memoizes `nextConfig` except during test runs
  if (nextConfigPromise !== undefined && process.env.NODE_ENV !== 'test') {
    return await nextConfigPromise
  }

the code also moved the await out of the try/catch, so errors weren't throwing as expected. I moved it back in:

  let config
  try {
    nextConfigPromise = loadConfig(PHASE_PRODUCTION_BUILD, resolve('.'))
    config = await nextConfigPromise
  } catch (error) {
    return failBuild('Error loading your next.config.js.', { error })
  }

  return config

the tests at this point are failing with:

  ●  Cannot log after tests are done. Did you forget to wait for something async in your test?
    Attempted to log "warn  - Detected next.config.js, no exported configuration found. https://err.sh/vercel/next.js/empty-configuration".

so I'm either doing something very obviously wrong (quite possible) or there's something tricky happening here that we haven't found yet

[ehmicky]

Thanks for the additional debugging @jlengstorf, this really helped!
It turns out the problem was that:

• When the promise returned by loadConfig() was rejected, memoized calls would not be wrapped by the try/catch block. In other words, the try/catch block should have covered the whole function, including the memoized if block.
• Rejected promises should not be memoized.

I fixed those by using a proper memoization library instead, which correctly handles async functions. Tests are now passing 🎉

[ehmicky]

Needed by moize (otherwise, it throws).

[ehmicky]

maxSize is required by moize@6. 1 would work in our case since the function has no arguments, but I used 1e3 so it covers future usage where we might add more arguments to this function.

[jlengstorf]

nice! I'm adding this to my list of things to look at and figure out why your original solution didn't work