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Warn about undefined return value for memo and forwardRef #19550

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Aug 6, 2020
Merged

Warn about undefined return value for memo and forwardRef #19550

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20 changes: 20 additions & 0 deletions packages/react-dom/src/__tests__/ReactEmptyComponent-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -316,4 +316,24 @@ describe('ReactEmptyComponent', () => {
const noscript2 = container.firstChild;
expect(noscript2).toBe(null);
});

it('should warn about React.forwardRef that returns undefined', () => {
const Empty = () => {};
const EmptyForwardRef = React.forwardRef(Empty);

expect(() => {
ReactTestUtils.renderIntoDocument(<EmptyForwardRef />);
}).toThrowError(
'ForwardRef(Empty)(...): Nothing was returned from render.',
);
});

it('should warn about React.memo that returns undefined', () => {
const Empty = () => {};
const EmptyMemo = React.memo(Empty);

expect(() => {
ReactTestUtils.renderIntoDocument(<EmptyMemo />);
}).toThrowError('Empty(...): Nothing was returned from render.');
});
});
10 changes: 7 additions & 3 deletions packages/react-reconciler/src/ReactChildFiber.new.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,9 @@ import {
ClassComponent,
HostText,
HostPortal,
ForwardRef,
Fragment,
SimpleMemoComponent,
Block,
} from './ReactWorkTags';
import invariant from 'shared/invariant';
Expand Down Expand Up @@ -1393,14 +1395,16 @@ function ChildReconciler(shouldTrackSideEffects) {
// Intentionally fall through to the next case, which handles both
// functions and classes
// eslint-disable-next-lined no-fallthrough
case FunctionComponent: {
const Component = returnFiber.type;
case Block:
case FunctionComponent:
case ForwardRef:
case SimpleMemoComponent: {
invariant(
false,
'%s(...): Nothing was returned from render. This usually means a ' +
'return statement is missing. Or, to render nothing, ' +
'return null.',
Component.displayName || Component.name || 'Component',
getComponentName(returnFiber.type) || 'Component',
);
}
}
Expand Down
10 changes: 7 additions & 3 deletions packages/react-reconciler/src/ReactChildFiber.old.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,9 @@ import {
ClassComponent,
HostText,
HostPortal,
ForwardRef,
Fragment,
SimpleMemoComponent,
Block,
} from './ReactWorkTags';
import invariant from 'shared/invariant';
Expand Down Expand Up @@ -1385,14 +1387,16 @@ function ChildReconciler(shouldTrackSideEffects) {
// Intentionally fall through to the next case, which handles both
// functions and classes
// eslint-disable-next-lined no-fallthrough
case FunctionComponent: {
const Component = returnFiber.type;
case Block:
case FunctionComponent:
case ForwardRef:
case SimpleMemoComponent: {
invariant(
false,
'%s(...): Nothing was returned from render. This usually means a ' +
'return statement is missing. Or, to render nothing, ' +
'return null.',
Component.displayName || Component.name || 'Component',
getComponentName(returnFiber.type) || 'Component',
);
}
}
Expand Down