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Warn about conflicting style values during updates
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This is one of the most insidious quirks of React DOM that people run into. Now we warn when we think an update is dangerous.

We still allow rendering `{background, backgroundSize}` with unchanging values, for example. But once you remove either one or change `background` (without changing `backgroundSize` at the same time), that's bad news. So we warn.

Fixes facebook#6348.
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@sophiebits
sophiebits committed Nov 9, 2018
1 parent 2dd4ba1 commit 84bcf8c
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141 changes: 141 additions & 0 deletions packages/react-dom/src/__tests__/ReactDOMComponent-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,147 @@ describe('ReactDOMComponent', () => {
}
});

it('should warn for conflicting CSS shorthand updates', () => {
const container = document.createElement('div');
ReactDOM.render(
<div style={{font: 'foo', fontStyle: 'bar'}} />,
container,
);
expect(() =>
ReactDOM.render(<div style={{font: 'foo'}} />, container),
).toWarnDev(
'Warning: Removing a style property during rerender (fontStyle) ' +
'when a conflicting property is set (font) can lead to styling ' +
"bugs. To avoid this, don't mix shorthand and non-shorthand " +
'properties for the same value; instead, replace the shorthand ' +
'with separate values.' +
'\n in div (at **)',
);

// These updates are OK and don't warn:
ReactDOM.render(
<div style={{font: 'qux', fontStyle: 'bar'}} />,
container,
);
ReactDOM.render(
<div style={{font: 'foo', fontStyle: 'baz'}} />,
container,
);

expect(() =>
ReactDOM.render(
<div style={{font: 'qux', fontStyle: 'baz'}} />,
container,
),
).toWarnDev(
'Warning: Updating a style property during rerender (font) when ' +
'a conflicting property is set (fontStyle) can lead to styling ' +
"bugs. To avoid this, don't mix shorthand and non-shorthand " +
'properties for the same value; instead, replace the shorthand ' +
'with separate values.' +
'\n in div (at **)',
);
expect(() =>
ReactDOM.render(<div style={{fontStyle: 'baz'}} />, container),
).toWarnDev(
'Warning: Removing a style property during rerender (font) when ' +
'a conflicting property is set (fontStyle) can lead to styling ' +
"bugs. To avoid this, don't mix shorthand and non-shorthand " +
'properties for the same value; instead, replace the shorthand ' +
'with separate values.' +
'\n in div (at **)',
);

// A bit of a special case: backgroundPosition isn't technically longhand
// (it expands to backgroundPosition{X,Y} but so does background)
ReactDOM.render(
<div style={{background: 'yellow', backgroundPosition: 'center'}} />,
container,
);
expect(() =>
ReactDOM.render(<div style={{background: 'yellow'}} />, container),
).toWarnDev(
'Warning: Removing a style property during rerender ' +
'(backgroundPosition) when a conflicting property is set ' +
"(background) can lead to styling bugs. To avoid this, don't mix " +
'shorthand and non-shorthand properties for the same value; ' +
'instead, replace the shorthand with separate values.' +
'\n in div (at **)',
);
ReactDOM.render(
<div style={{background: 'yellow', backgroundPosition: 'center'}} />,
container,
);
// But setting them at the same time is OK:
ReactDOM.render(
<div style={{background: 'green', backgroundPosition: 'top'}} />,
container,
);
expect(() =>
ReactDOM.render(
<div style={{backgroundPosition: 'top'}} />,
container,
),
).toWarnDev(
'Warning: Removing a style property during rerender (background) ' +
'when a conflicting property is set (backgroundPosition) can lead ' +
"to styling bugs. To avoid this, don't mix shorthand and " +
'non-shorthand properties for the same value; instead, replace the ' +
'shorthand with separate values.' +
'\n in div (at **)',
);

// A bit of an even more special case: borderLeft and borderStyle overlap.
ReactDOM.render(
<div style={{borderStyle: 'dotted', borderLeft: '1px solid red'}} />,
container,
);
expect(() =>
ReactDOM.render(
<div style={{borderLeft: '1px solid red'}} />,
container,
),
).toWarnDev(
'Warning: Removing a style property during rerender (borderStyle) ' +
'when a conflicting property is set (borderLeft) can lead to ' +
"styling bugs. To avoid this, don't mix shorthand and " +
'non-shorthand properties for the same value; instead, replace the ' +
'shorthand with separate values.' +
'\n in div (at **)',
);
expect(() =>
ReactDOM.render(
<div style={{borderStyle: 'dashed', borderLeft: '1px solid red'}} />,
container,
),
).toWarnDev(
'Warning: Updating a style property during rerender (borderStyle) ' +
'when a conflicting property is set (borderLeft) can lead to ' +
"styling bugs. To avoid this, don't mix shorthand and " +
'non-shorthand properties for the same value; instead, replace the ' +
'shorthand with separate values.' +
'\n in div (at **)',
);
// But setting them at the same time is OK:
ReactDOM.render(
<div style={{borderStyle: 'dotted', borderLeft: '2px solid red'}} />,
container,
);
expect(() =>
ReactDOM.render(
<div style={{borderStyle: 'dotted'}} />,
container,
),
).toWarnDev(
'Warning: Removing a style property during rerender (borderLeft) ' +
'when a conflicting property is set (borderStyle) can lead to ' +
"styling bugs. To avoid this, don't mix shorthand and " +
'non-shorthand properties for the same value; instead, replace the ' +
'shorthand with separate values.' +
'\n in div (at **)',
);
});

it('should warn for unknown prop', () => {
const container = document.createElement('div');
expect(() =>
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3 changes: 3 additions & 0 deletions packages/react-dom/src/client/ReactDOMComponent.js
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Original file line number Diff line number Diff line change
Expand Up @@ -766,6 +766,9 @@ export function diffProperties(
}
}
if (styleUpdates) {
if (__DEV__) {
CSSPropertyOperations.validateShorthandPropertyCollisionInDev(styleUpdates, nextProps[STYLE]);
}
(updatePayload = updatePayload || []).push(STYLE, styleUpdates);
}
return updatePayload;
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107 changes: 107 additions & 0 deletions packages/react-dom/src/shared/CSSPropertyOperations.js
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Original file line number Diff line number Diff line change
Expand Up @@ -5,9 +5,16 @@
* LICENSE file in the root directory of this source tree.
*/

import {
overlappingShorthandsInDev,
longhandToShorthandInDev,
shorthandToLonghandInDev,
} from './CSSShorthandProperty';

import dangerousStyleValue from './dangerousStyleValue';
import hyphenateStyleName from './hyphenateStyleName';
import warnValidStyle from './warnValidStyle';
import warning from 'shared/warning';

/**
* Operations for dealing with CSS properties.
Expand Down Expand Up @@ -78,3 +85,103 @@ export function setValueForStyles(node, styles) {
}
}
}

function isValueEmpty(value) {
return value == null || typeof value === 'boolean' || value === '';
}

/**
* When mixing shorthand and longhand property names, we warn during updates if
* we expect an incorrect result to occur. In particular, we warn for:
*
* Updating a shorthand property (longhand gets overwritten):
* {font: 'foo', fontVariant: 'bar'} -> {font: 'baz', fontVariant: 'bar'}
* becomes .style.font = 'baz'
* Removing a shorthand property (longhand gets lost too):
* {font: 'foo', fontVariant: 'bar'} -> {fontVariant: 'bar'}
* becomes .style.font = ''
* Removing a longhand property (should revert to shorthand; doesn't):
* {font: 'foo', fontVariant: 'bar'} -> {font: 'foo'}
* becomes .style.fontVariant = ''
*/
export function validateShorthandPropertyCollisionInDev(
styleUpdates,
nextStyles,
) {
if (!nextStyles) {
return;
}

// Map from each individual property to which shorthand defined it.
// For example, styleUpdates = {flex: 'a', flexBasis: 'b'} gives
// expandedUpdates = {
// flexBasis: 'flexBasis',
// flexGrow: 'flex',
// flexShrink: 'flex',
// }
var expandedUpdates = {};
for (const key in styleUpdates) {
const longhands = shorthandToLonghandInDev[key];
}

for (var key in styleUpdates) {
const isEmpty = isValueEmpty(styleUpdates[key]);
if (isEmpty) {
// Property removal; check if we're removing a longhand property
const shorthands = longhandToShorthandInDev[key];
if (shorthands) {
const conflicting = shorthands.filter(
s => !isValueEmpty(nextStyles[s]),
);
if (conflicting.length) {
warning(
false,
'Removing a style property during rerender (%s) when a ' +
'conflicting property is set (%s) can lead to styling bugs. To ' +
"avoid this, don't mix shorthand and non-shorthand properties " +
'for the same value; instead, replace the shorthand with ' +
'separate values.',
key,
conflicting.join(', '),
);
}
}
}

// Updating or removing a property; check if it's a shorthand property
const longhands = shorthandToLonghandInDev[key];
const overlapping = overlappingShorthandsInDev[key];
var conflicting = new Set();
if (longhands) {
longhands.forEach(l => {
if (isValueEmpty(styleUpdates[l]) && !isValueEmpty(nextStyles[l])) {
// ex: key = 'font', l = 'fontStyle'
conflicting.add(l);
}
});
}
if (overlapping) {
overlapping.forEach(l => {
if (isValueEmpty(styleUpdates[l]) && !isValueEmpty(nextStyles[l])) {
// ex: key = 'borderLeft', l = 'borderStyle'
conflicting.add(l);
}
});
}
if (conflicting.size) {
warning(
false,
'%s a style property during rerender (%s) when a ' +
'conflicting property is set (%s) can lead to styling bugs. To ' +
"avoid this, don't mix shorthand and non-shorthand properties " +
'for the same value; instead, replace the shorthand with ' +
'separate values.',
isEmpty ? 'Removing' : 'Updating',
key,
Array.from(conflicting)
.sort()
.join(', '),
);
}
}
}
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