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[Fizz] Implement New Context (#21255)
* Add NewContext module This implements a reverse linked list tree containing the previous contexts. * Implement recursive algorithm This algorithm pops the contexts back to a shared ancestor on the way down the stack and then pushes new contexts in reverse order up the stack. * Move isPrimaryRenderer to ServerFormatConfig This is primarily intended to be used to support renderToString with a separate build than the main one. This allows them to be nested. * Wire up more element type matchers * Wire up Context Provider type * Wire up Context Consumer * Test * Implement reader in class * Update error codez
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/** | ||
* Copyright (c) Facebook, Inc. and its affiliates. | ||
* | ||
* This source code is licensed under the MIT license found in the | ||
* LICENSE file in the root directory of this source tree. | ||
* | ||
* @flow | ||
*/ | ||
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import type {ReactContext} from 'shared/ReactTypes'; | ||
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import {isPrimaryRenderer} from './ReactServerFormatConfig'; | ||
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import invariant from 'shared/invariant'; | ||
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let rendererSigil; | ||
if (__DEV__) { | ||
// Use this to detect multiple renderers using the same context | ||
rendererSigil = {}; | ||
} | ||
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// Used to store the parent path of all context overrides in a shared linked list. | ||
// Forming a reverse tree. | ||
type ContextNode<T> = { | ||
parent: null | ContextNode<any>, | ||
depth: number, // Short hand to compute the depth of the tree at this node. | ||
context: ReactContext<T>, | ||
parentValue: T, | ||
value: T, | ||
}; | ||
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// The structure of a context snapshot is an implementation of this file. | ||
// Currently, it's implemented as tracking the current active node. | ||
export opaque type ContextSnapshot = null | ContextNode<any>; | ||
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export const rootContextSnapshot: ContextSnapshot = null; | ||
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// We assume that this runtime owns the "current" field on all ReactContext instances. | ||
// This global (actually thread local) state represents what state all those "current", | ||
// fields are currently in. | ||
let currentActiveSnapshot: ContextSnapshot = null; | ||
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function popNode(prev: ContextNode<any>): void { | ||
if (isPrimaryRenderer) { | ||
prev.context._currentValue = prev.parentValue; | ||
} else { | ||
prev.context._currentValue2 = prev.parentValue; | ||
} | ||
} | ||
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function pushNode(next: ContextNode<any>): void { | ||
if (isPrimaryRenderer) { | ||
next.context._currentValue = next.value; | ||
} else { | ||
next.context._currentValue2 = next.value; | ||
} | ||
} | ||
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function popToNearestCommonAncestor( | ||
prev: ContextNode<any>, | ||
next: ContextNode<any>, | ||
): void { | ||
if (prev === next) { | ||
// We've found a shared ancestor. We don't need to pop nor reapply this one or anything above. | ||
} else { | ||
popNode(prev); | ||
const parentPrev = prev.parent; | ||
const parentNext = next.parent; | ||
if (parentPrev === null) { | ||
invariant( | ||
parentNext === null, | ||
'The stacks must reach the root at the same time. This is a bug in React.', | ||
); | ||
} else { | ||
invariant( | ||
parentNext !== null, | ||
'The stacks must reach the root at the same time. This is a bug in React.', | ||
); | ||
popToNearestCommonAncestor(parentPrev, parentNext); | ||
// On the way back, we push the new ones that weren't common. | ||
pushNode(next); | ||
} | ||
} | ||
} | ||
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function popAllPrevious(prev: ContextNode<any>): void { | ||
popNode(prev); | ||
const parentPrev = prev.parent; | ||
if (parentPrev !== null) { | ||
popAllPrevious(parentPrev); | ||
} | ||
} | ||
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function pushAllNext(next: ContextNode<any>): void { | ||
const parentNext = next.parent; | ||
if (parentNext !== null) { | ||
pushAllNext(parentNext); | ||
} | ||
pushNode(next); | ||
} | ||
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function popPreviousToCommonLevel( | ||
prev: ContextNode<any>, | ||
next: ContextNode<any>, | ||
): void { | ||
popNode(prev); | ||
const parentPrev = prev.parent; | ||
invariant( | ||
parentPrev !== null, | ||
'The depth must equal at least at zero before reaching the root. This is a bug in React.', | ||
); | ||
if (parentPrev.depth === next.depth) { | ||
// We found the same level. Now we just need to find a shared ancestor. | ||
popToNearestCommonAncestor(parentPrev, next); | ||
} else { | ||
// We must still be deeper. | ||
popPreviousToCommonLevel(parentPrev, next); | ||
} | ||
} | ||
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function popNextToCommonLevel( | ||
prev: ContextNode<any>, | ||
next: ContextNode<any>, | ||
): void { | ||
const parentNext = next.parent; | ||
invariant( | ||
parentNext !== null, | ||
'The depth must equal at least at zero before reaching the root. This is a bug in React.', | ||
); | ||
if (prev.depth === parentNext.depth) { | ||
// We found the same level. Now we just need to find a shared ancestor. | ||
popToNearestCommonAncestor(prev, parentNext); | ||
} else { | ||
// We must still be deeper. | ||
popNextToCommonLevel(prev, parentNext); | ||
} | ||
pushNode(next); | ||
} | ||
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// Perform context switching to the new snapshot. | ||
// To make it cheap to read many contexts, while not suspending, we make the switch eagerly by | ||
// updating all the context's current values. That way reads, always just read the current value. | ||
// At the cost of updating contexts even if they're never read by this subtree. | ||
export function switchContext(newSnapshot: ContextSnapshot): void { | ||
// The basic algorithm we need to do is to pop back any contexts that are no longer on the stack. | ||
// We also need to update any new contexts that are now on the stack with the deepest value. | ||
// The easiest way to update new contexts is to just reapply them in reverse order from the | ||
// perspective of the backpointers. To avoid allocating a lot when switching, we use the stack | ||
// for that. Therefore this algorithm is recursive. | ||
// 1) First we pop which ever snapshot tree was deepest. Popping old contexts as we go. | ||
// 2) Then we find the nearest common ancestor from there. Popping old contexts as we go. | ||
// 3) Then we reapply new contexts on the way back up the stack. | ||
const prev = currentActiveSnapshot; | ||
const next = newSnapshot; | ||
if (prev !== next) { | ||
if (prev === null) { | ||
// $FlowFixMe: This has to be non-null since it's not equal to prev. | ||
pushAllNext(next); | ||
} else if (next === null) { | ||
popAllPrevious(prev); | ||
} else if (prev.depth === next.depth) { | ||
popToNearestCommonAncestor(prev, next); | ||
} else if (prev.depth > next.depth) { | ||
popPreviousToCommonLevel(prev, next); | ||
} else { | ||
popNextToCommonLevel(prev, next); | ||
} | ||
currentActiveSnapshot = next; | ||
} | ||
} | ||
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export function pushProvider<T>( | ||
context: ReactContext<T>, | ||
nextValue: T, | ||
): ContextSnapshot { | ||
let prevValue; | ||
if (isPrimaryRenderer) { | ||
prevValue = context._currentValue; | ||
context._currentValue = nextValue; | ||
if (__DEV__) { | ||
if ( | ||
context._currentRenderer !== undefined && | ||
context._currentRenderer !== null && | ||
context._currentRenderer !== rendererSigil | ||
) { | ||
console.error( | ||
'Detected multiple renderers concurrently rendering the ' + | ||
'same context provider. This is currently unsupported.', | ||
); | ||
} | ||
context._currentRenderer = rendererSigil; | ||
} | ||
} else { | ||
prevValue = context._currentValue2; | ||
context._currentValue2 = nextValue; | ||
if (__DEV__) { | ||
if ( | ||
context._currentRenderer2 !== undefined && | ||
context._currentRenderer2 !== null && | ||
context._currentRenderer2 !== rendererSigil | ||
) { | ||
console.error( | ||
'Detected multiple renderers concurrently rendering the ' + | ||
'same context provider. This is currently unsupported.', | ||
); | ||
} | ||
context._currentRenderer2 = rendererSigil; | ||
} | ||
} | ||
const prevNode = currentActiveSnapshot; | ||
const newNode: ContextNode<T> = { | ||
parent: prevNode, | ||
depth: prevNode === null ? 0 : prevNode.depth + 1, | ||
context: context, | ||
parentValue: prevValue, | ||
value: nextValue, | ||
}; | ||
currentActiveSnapshot = newNode; | ||
return newNode; | ||
} | ||
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export function popProvider<T>(context: ReactContext<T>): ContextSnapshot { | ||
const prevSnapshot = currentActiveSnapshot; | ||
invariant( | ||
prevSnapshot !== null, | ||
'Tried to pop a Context at the root of the app. This is a bug in React.', | ||
); | ||
if (__DEV__) { | ||
if (prevSnapshot.context !== context) { | ||
console.error( | ||
'The parent context is not the expected context. This is probably a bug in React.', | ||
); | ||
} | ||
} | ||
if (isPrimaryRenderer) { | ||
prevSnapshot.context._currentValue = prevSnapshot.parentValue; | ||
if (__DEV__) { | ||
if ( | ||
context._currentRenderer !== undefined && | ||
context._currentRenderer !== null && | ||
context._currentRenderer !== rendererSigil | ||
) { | ||
console.error( | ||
'Detected multiple renderers concurrently rendering the ' + | ||
'same context provider. This is currently unsupported.', | ||
); | ||
} | ||
context._currentRenderer = rendererSigil; | ||
} | ||
} else { | ||
prevSnapshot.context._currentValue2 = prevSnapshot.parentValue; | ||
if (__DEV__) { | ||
if ( | ||
context._currentRenderer2 !== undefined && | ||
context._currentRenderer2 !== null && | ||
context._currentRenderer2 !== rendererSigil | ||
) { | ||
console.error( | ||
'Detected multiple renderers concurrently rendering the ' + | ||
'same context provider. This is currently unsupported.', | ||
); | ||
} | ||
context._currentRenderer2 = rendererSigil; | ||
} | ||
} | ||
return (currentActiveSnapshot = prevSnapshot.parent); | ||
} | ||
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export function getActiveContext(): ContextSnapshot { | ||
return currentActiveSnapshot; | ||
} | ||
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export function readContext<T>(context: ReactContext<T>): T { | ||
const value = isPrimaryRenderer | ||
? context._currentValue | ||
: context._currentValue2; | ||
return value; | ||
} |
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