Turn on rehydration based on config

[mansona]

This is something that we discussed in the weekly Fastboot meeting where I thought it would be useful to be able to turn on rehydration based on a config entry rather than using the environment variable.

This would allow you to create a PR with the change to turn on rehydration quite easily, and also would support most preview apps setups when using heroku or something like netlify if you're using prember

I have managed to get my little test passing, and if all the other tests pass then I'm pretty confident that this would be ok to merge but I guess that we should probably still discuss it at one of the Fastboot meetings before we do.

One interesting fact: this doesn't actually enable rehydration for prember 🙈 the issue is that prember is actually instantiating its own Fastboot instance so I would need to make a change in prember to enable passing the config to either the constructor of the instance or the visit function call 🙃

[xg-wang]

Suggestion: check input and throw a silent-error if not allowed values ("serialize")

[mansona]

yes that's probably a good idea, but to be honest I'm not even sure if renderMode is the right thing to be passing around 🤔 right now it can only have exactly one value and that is being used to turn a feature on... which makes me feel like a boolean would be better

maybe something quite explicit like turnOnRehydration or something but I don't know 🤷 I guess the question becomes: how likely is it that we will have more render modes? 😂

[xg-wang]

Yea I agree with you here renderMode is not the right public interface we expose.

renderMode is what ember-cli-fastboot passes to ember: when rehydration is enabled, it is serialize on server side, and rehydrate on client side. If rehydration is not enabled, ember will use undefined renderMode to use the default clientBuilder (see https://github.com/emberjs/ember.js/blob/4cb7da45fd6e4720daf7e769877b3d8868a3cf71/packages/%40ember/-internals/glimmer/lib/setup-registry.ts#L25-L38)

User should not be aware of these wirings, let's call it enableRehydration which people can set in environement.fastboot.enableRehydration.

The config will be picked up by your change here and set renderMode which ember/glimmer understand.

I'd like to deprecate the EXPERIMENTAL_RENDER_MODE_SERIALIZE with the PR to use the config flag instead.

For Prember if fastboot is upgraded to latest, rehydration will be enabled if the app is configured with enableRehydration.

[xg-wang]

Alternatively we can set it in fastboot.visit(path, { enableRehydration }), then per visit is allowed have different behavior. But I don't think it is necessary since user will have a single flag to control all visit behavior.

[mansona]

I already have a corresponding PR on Prember that I know works if you wanted to check it out ef4/prember#66

I totally agree with your suggestion for the public API and I'll get that done when I get a chance 👍

I hadn't actually thought about deprecating the environment variable 🤔 I guess it's a good idea so I'll add that to this PR too

While I agree that in my use case and in most use cases we would probably enable rehydration holistically for the whole app at once, @rwjblue did specifically ask that we expose a per-request API for people that didn't want to turn it on for everything or wanted to experiment with A/B tests for example. I have no preference on this particular point because I'm very much going to be enabling it for a full Prember run all at once so I can't really defend this position well since it's not my idea 🙈

[xg-wang]

We can start writing tests involving fastboot / ember-cli-fastboot in https://github.com/ember-fastboot/ember-cli-fastboot/blob/2a6ed5d76b00da2106a9ba10f048aa2bef989a80/test-packages/integration-tests/test/basic-test.js.
But we can land this PR and do another follow up to move later.

[mansona]

oh is this the new place that @kiwiupover has been working on? to be honest I wasn't sure and I just copy and pasted an existing test to get it to work. I would much prefer to do it the right way in this PR rather than fix it up in another one, I just don't exactly know how 😂

[xg-wang]

You can move the fixture app to test-packages, then assert result in test-packages/integration-tests/test/basic-test.js. But don't worry I can get a test when we figure out how we want to name the config flag.

[mansona]

@xg-wang regarding our discussion of the API of this change, here is me consuming the fastboot lib in prember: ef4/prember#66 which might be useful to see what the API looks like in the wild.

Let me know what you think, and we can probably discuss it in the weekly meeting too 👍