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Don’t error when returning an empty Fragment #12966

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merged 4 commits into from Jun 11, 2018
Merged

Don’t error when returning an empty Fragment #12966

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931bc7d
Don’t error when returning an empty Fragment
philipp-spiess Jun 2, 2018
4de2539
Test the update path as well
philipp-spiess Jun 2, 2018
697bd71
Reuse existing code path
gaearon Jun 11, 2018
6d8c3f5
An even more explicit solution that also fixes Flow
gaearon Jun 11, 2018
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25 changes: 25 additions & 0 deletions packages/react-dom/src/__tests__/ReactDOMFiber-test.js
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Expand Up @@ -171,6 +171,31 @@ describe('ReactDOMFiber', () => {
expect(firstNode.tagName).toBe('DIV');
});

it('renders an empty fragment', () => {
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No idea if that is the right place for the test :)

const Div = () => <div />;
const EmptyFragment = () => <React.Fragment />;
const NonEmptyFragment = () => (
<React.Fragment>
<Div />
</React.Fragment>
);

ReactDOM.render(<EmptyFragment />, container);
expect(container.firstChild).toBe(null);

ReactDOM.render(<NonEmptyFragment />, container);
expect(container.firstChild.tagName).toBe('DIV');

ReactDOM.render(<EmptyFragment />, container);
expect(container.firstChild).toBe(null);

ReactDOM.render(<Div />, container);
expect(container.firstChild.tagName).toBe('DIV');

ReactDOM.render(<EmptyFragment />, container);
expect(container.firstChild).toBe(null);
});

let svgEls, htmlEls, mathEls;
const expectSVG = {ref: el => svgEls.push(el)};
const expectHTML = {ref: el => htmlEls.push(el)};
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8 changes: 4 additions & 4 deletions packages/react-reconciler/src/ReactChildFiber.js
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Expand Up @@ -1208,12 +1208,12 @@ function ChildReconciler(shouldTrackSideEffects) {
// Handle top level unkeyed fragments as if they were arrays.
// This leads to an ambiguity between <>{[...]}</> and <>...</>.
// We treat the ambiguous cases above the same.
if (
const isUnkeyedTopLevelFragment =
typeof newChild === 'object' &&
newChild !== null &&
newChild.type === REACT_FRAGMENT_TYPE &&
newChild.key === null
) {
newChild.key === null;
if (isUnkeyedTopLevelFragment) {
newChild = newChild.props.children;
}

Expand Down Expand Up @@ -1281,7 +1281,7 @@ function ChildReconciler(shouldTrackSideEffects) {
warnOnFunctionType();
}
}
if (typeof newChild === 'undefined') {
if (typeof newChild === 'undefined' && !isUnkeyedTopLevelFragment) {
// If the new child is undefined, and the return fiber is a composite
// component, throw an error. If Fiber return types are disabled,
// we already threw above.
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