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Fixed an issue with nested contexts unwinding when server rendering. Issue #12984 #12985

Merged
merged 8 commits into from Jun 11, 2018
Expand Up @@ -191,5 +191,33 @@ describe('ReactDOMServerIntegration', () => {
expect(e.querySelector('#theme').textContent).toBe('light');
expect(e.querySelector('#language').textContent).toBe('english');
});

itRenders(
'nested context unwinding',
async render => {
const Theme = React.createContext('dark');
const Language = React.createContext('french');

const App = () => (
<div>
<Theme.Provider value="light">
<Language.Provider>
<Theme.Provider value="dark">
<Theme.Consumer>
{theme => <div id="theme1">{theme}</div>}
</Theme.Consumer>
</Theme.Provider>
<Theme.Consumer>
{theme => <div id="theme2">{theme}</div>}
</Theme.Consumer>
</Language.Provider>
</Theme.Provider>
</div>
);
let e = await render(<App />);
expect(e.querySelector('#theme1').textContent).toBe('dark');
expect(e.querySelector('#theme2').textContent).toBe('light');
},
);
});
});
23 changes: 14 additions & 9 deletions packages/react-dom/src/server/ReactPartialRenderer.js
Expand Up @@ -641,7 +641,7 @@ class ReactDOMServerRenderer {
previousWasTextNode: boolean;
makeStaticMarkup: boolean;

providerStack: Array<?ReactProvider<any>>;
providerStack: Array<ReactProvider<any>>;
providerIndex: number;

constructor(children: mixed, makeStaticMarkup: boolean) {
Expand Down Expand Up @@ -686,17 +686,22 @@ class ReactDOMServerRenderer {
'Unexpected pop.',
);
}
this.providerStack[this.providerIndex] = null;
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What does .length assignment do in V8? I'd like to make sure it doesn't think the array length change is likely to "stay" because it changes all the time. I think just using null is more straightforward and less surprising to the engine (even though the typing isn't as nice for us).

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OK. But, going back to using null seems to require testing for null when accessing array items by index, since Flow has been told that null and undefined are expected array item values. Or, is there an alternate Flow syntax that allows us to remove the explicit checks?

this.providerStack.length = this.providerIndex;
this.providerIndex -= 1;
const context: ReactContext<any> = provider.type._context;
if (this.providerIndex < 0) {
context._currentValue = context._defaultValue;
} else {
// We assume this type is correct because of the index check above.
const previousProvider: ReactProvider<any> = (this.providerStack[
this.providerIndex
]: any);
// find the correct previous provider based on type
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This comment is redundant, IMO the code speaks for itself

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OK

let previousProvider = null;
for (let i = this.providerIndex; i >= 0; i--) {
// We assume this Flow type is correct because of the index check above.
if ((this.providerStack[i]: ReactProvider<any>).type === provider.type) {
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Please read this.providerStack[i] once. (Move it to a constant.)

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Yep.

previousProvider = this.providerStack[i];
break;
}
}
if (previousProvider !== null) {
context._currentValue = previousProvider.props.value;
} else {
context._currentValue = context._defaultValue;
}
}

Expand Down