Removes support for using arbitrary promises as the type of a React
element. Instead, promises must be wrapped in React.lazy. This gives us
flexibility later if we need to change the protocol.
The reason is that promises do not provide a way to call their
constructor multiple times. For example:
const promiseForA = new Promise(resolve => {
fetchA(a => resolve(a));
});
Given a reference to `promiseForA`, there's no way to call `fetchA`
again. Calling `then` on the promise doesn't run the constructor again;
it only attaches another listener.
In the future we will likely introduce an API like `React.eager` that
is similar to `lazy` but eagerly calls the constructor. That gives us
the ability to call the constructor multiple times. E.g. to increase
the priority, or to retry if the first operation failed.
* pure
A higher-order component version of the `React.PureComponent` class.
During an update, the previous props are compared to the new props. If
they are the same, React will skip rendering the component and
its children.
Unlike userspace implementations, `pure` will not add an additional
fiber to the tree.
The first argument must be a functional component; it does not work
with classes.
`pure` uses shallow comparison by default, like `React.PureComponent`.
A custom comparison can be passed as the second argument.
Co-authored-by: Andrew Clark <acdlite@fb.com>
Co-authored-by: Sophie Alpert <sophiebits@fb.com>
* Warn if first argument is not a functional component
* fix: do not reconcile children that are iterable functions
* fix: remove fit
* Refactor comparison to exclude anything that isnt an object
* Remove redundant undefined check
Changed the API to match what we've been using in our latest discussions.
Our tentative plans are for <Placeholder> to automatically hide the timed-out
children, instead of removing them, so their state is not lost. This part is
not yet implemented. We'll likely have a lower level API that does not include
the hiding behavior. This is also not yet implemented.
* Timeout component
Adds Timeout component. If a promise is thrown from inside a Timeout component,
React will suspend the in-progress render from committing. When the promise
resolves, React will retry. If the render is suspended for longer than the
maximum threshold, the Timeout switches to a placeholder state.
The timeout threshold is defined as the minimum of:
- The expiration time of the current render
- The `ms` prop given to each Timeout component in the ancestor path of the
thrown promise.
* Add a test for nested fallbacks
Co-authored-by: Andrew Clark <acdlite@fb.com>
* Resume on promise rejection
React should resume rendering regardless of whether it resolves
or rejects.
* Wrap Suspense code in feature flag
* Children of a Timeout must be strict mode compatible
Async is not required for Suspense, but strict mode is.
* Simplify list of pending work
Some of this was added with "soft expiration" in mind, but now with our revised
model for how soft expiration will work, this isn't necessary.
It would be nice to remove more of this, but I think the list itself is inherent
because we need a way to track the start times, for <Timeout ms={ms} />.
* Only use the Timeout update queue to store promises, not for state
It already worked this way in practice.
* Wrap more Suspense-only paths in the feature flag
* Attach promise listener immediately on suspend
Instead of waiting for commit phase.
* Infer approximate start time using expiration time
* Remove list of pending priority levels
We can replicate almost all the functionality by tracking just five
separate levels: the highest/lowest priority pending levels, the
highest/lowest priority suspended levels, and the lowest pinged level.
We lose a bit of granularity, in that if there are multiple levels of
pending updates, only the first and last ones are known. But in practice
this likely isn't a big deal.
These heuristics are almost entirely isolated to a single module and
can be adjusted later, without API changes, if necessary.
Non-IO-bound work is not affected at all.
* ReactFiberPendingWork -> ReactFiberPendingPriority
* Renaming method names from "pending work" to "pending priority"
* Get rid of SuspenseThenable module
Idk why I thought this was neccessary
* Nits based on Sebastian's feedback
* More naming nits + comments
* Add test for hiding a suspended tree to unblock
* Revert change to expiration time rounding
This means you have to account for the start time approximation
heuristic when writing Suspense tests, but that's going to be
true regardless.
When updating the tests, I also made a fix related to offscreen
priority. We should never timeout inside a hidden tree.
* palceholder -> placeholder
Add a new component type, Profiler, that can be used to collect new render time metrics. Since this is a new, experimental API, it will be exported as React.unstable_Profiler initially.
Most of the functionality for this component has been added behind a feature flag, enableProfileModeMetrics. When the feature flag is disabled, the component will just render its children with no additional behavior. When the flag is enabled, React will also collect timing information and pass it to the onRender function (as described below).
* Replace unstable_AsyncComponent with Unstable_AsyncMode
Mirrors the StrictMode API and uses the new Mode type of work.
* internalContextTag -> mode
Change this now that we have a better name
* Unstable_ -> unstable_
* New context API
Introduces a declarative context API that propagates updates even when
shouldComponentUpdate returns false.
* Fuzz tester for context
* Use ReactElement for provider and consumer children
* Unify more branches in createFiberFromElement
* Compare context values using Object.is
Same semantics as PureComponent/shallowEqual.
* Add support for Provider and Consumer to server-side renderer
* Store providers on global stack
Rather than using a linked list stored on the context type. The global
stack can be reset in case of an interruption or error, whereas with the
linked list implementation, you'd need to keep track of every
context type.
* Put new context API behind a feature flag
We'll enable this in www only for now.
* Store nearest provider on context object
* Handle reentrancy in server renderer
Context stack should be per server renderer instance.
* Bailout of consumer updates using bitmask
The context type defines an optional function that compares two context
values, returning a bitfield. A consumer may specify the bits it needs
for rendering. If a provider's context changes, and the consumer's bits
do not intersect with the changed bits, we can skip the consumer.
This is similar to how selectors are used in Redux but fast enough to do
while scanning the tree. The only user code involved is the function
that computes the changed bits. But that's only called once per provider
update, not for every consumer.
* Store current value and changed bits on context object
There are fewer providers than consumers, so better to do this work
at the provider.
* Use maximum of 31 bits for bitmask
This is the largest integer size in V8 on 32-bit systems. Warn in
development if too large a number is used.
* ProviderComponent -> ContextProvider, ConsumerComponent -> ContextConsumer
* Inline Object.is
* Warn if multiple renderers concurrently render the same context provider
Let's see if we can get away with not supporting this for now. If it
turns out that it's needed, we can fall back to backtracking the
fiber return path.
* Nits that came up during review
Added new StrictMode component for enabling async warnings (without enabling async rendering). This component can be used in the future to help with other warnings (eg compilation, Fabric).
