When developing in an RSC environment, you should be able to work in a
single environment as if it was a unified environment. With thrown
errors we already serialize them and then rethrow them on the client.
Since by default we log them via onError both in Flight and Fizz, you
can get the same log in the RSC runtime, the SSR runtime and on the
client.
With console logs made in SSR renders, you typically replay the same
code during hydration on the client. So for example warnings already
show up both in the SSR logs and on the client (although not guaranteed
to be the same). You could just spend your time in the client and you'd
be fine.
Previously, RSC logs would not be replayed because they don't hydrate.
So it's easy to miss warnings for example.
With this approach, we replay RSC logs both during SSR so they end up in
the SSR logs and on the client. That way you can just stay in the
browser window during normal development cycles. You shouldn't have to
care if your component is a server or client component when working on
logical things or iterating on a product.
With this change, you probably should mostly ignore the Flight log
stream and just look at the client or maybe the SSR one. Unless you're
digging into something specific. In particular if you just naively run
both Flight and Fizz in the same terminal you get duplicates. I like to
run out fixtures `yarn dev:region` and `yarn dev:global` in two separate
terminals.
Console logs may contain complex objects which can be inspected. Ideally
a DevTools inspector could reach into the RSC server and remotely
inspect objects using the remote inspection protocol. That way complex
objects can be loaded on demand as you expand into them. However, that
is a complex environment to set up and the server might not even be
alive anymore by the time you inspect the objects. Therefore, I do a
best effort to serialize the objects using the RSC protocol but limit
the depth that can be rendered.
This feature is only own in dev mode since it can be expensive.
In a follow up, I'll give the logs a special styling treatment to
clearly differentiate them from logs coming from the client. As well as
deal with stacks.
Stacked on #26557
Supporting Float methods such as ReactDOM.preload() are challenging for
flight because it does not have an easy means to convey direct
executions in other environments. Because the flight wire format is a
JSON-like serialization that is expected to be rendered it currently
only describes renderable elements. We need a way to convey a function
invocation that gets run in the context of the client environment
whether that is Fizz or Fiber.
Fiber is somewhat straightforward because the HostDispatcher is always
active and we can just have the FlightClient dispatch the serialized
directive.
Fizz is much more challenging becaue the dispatcher is always scoped but
the specific request the dispatch belongs to is not readily available.
Environments that support AsyncLocalStorage (or in the future
AsyncContext) we will use this to be able to resolve directives in Fizz
to the appropriate Request. For other environments directives will be
elided. Right now this is pragmatic and non-breaking because all
directives are opportunistic and non-critical. If this changes in the
future we will need to reconsider how widespread support for async
context tracking is.
For Flight, if AsyncLocalStorage is available Float methods can be
called before and after await points and be expected to work. If
AsyncLocalStorage is not available float methods called in the sync
phase of a component render will be captured but anything after an await
point will be a noop. If a float call is dropped in this manner a DEV
warning should help you realize your code may need to be modified.
This PR also introduces a way for resources (Fizz) and hints (Flight) to
flush even if there is not active task being worked on. This will help
when Float methods are called in between async points within a function
execution but the task is blocked on the entire function finishing.
This PR also introduces deduping of Hints in Flight using the same
resource keys used in Fizz. This will help shrink payload sizes when the
same hint is attempted to emit over and over again
Sebastian MarkbågeandGitHub
Josh StoryandGitHub