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Forwardport diffing fix #4976

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Merged
JoviDeCroock merged 1 commit into from
Dec 16, 2025
+135 −101
Merged

Forwardport diffing fix #4976

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1 change: 1 addition & 0 deletions src/diff/children.js
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Original file line number Diff line number Diff line change
Expand Up @@ -239,6 +239,7 @@ function constructNewChildrenArray(
remainingOldChildren
));

oldVNode = NULL;
if (matchingIndex != -1) {
oldVNode = oldChildren[matchingIndex];
remainingOldChildren--;
Expand Down
235 changes: 134 additions & 101 deletions test/browser/keys.test.jsx
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Original file line number Diff line number Diff line change
Expand Up @@ -179,9 +179,11 @@ describe('keys', () => {
render({ children, busy }) {
return (
<div class={busy ? 'busy' : ''}>
{children && children.length
? children
: <div class="busy-placeholder" />}
{children && children.length ? (
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@JoviDeCroock JoviDeCroock Dec 16, 2025

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hmm, odd that the pre-commit reformats this

children
) : (
<div class="busy-placeholder" />
)}
<div class="indicator">
<div>indicator</div>
<div>indicator</div>
Expand Down Expand Up @@ -566,19 +568,21 @@ describe('keys', () => {
let Stateful2MovedRef;

function Foo({ moved }) {
return moved
? <div>
<div>1</div>
<Stateful1 key="c" ref={c => (Stateful1MovedRef = c)} />
<div>2</div>
<Stateful2 key="d" ref={c => (Stateful2MovedRef = c)} />
</div>
: <div>
<div>1</div>
<Stateful1 key="a" ref={c => (Stateful1Ref = c)} />
<div>2</div>
<Stateful2 key="b" ref={c => (Stateful2Ref = c)} />
</div>;
return moved ? (
<div>
<div>1</div>
<Stateful1 key="c" ref={c => (Stateful1MovedRef = c)} />
<div>2</div>
<Stateful2 key="d" ref={c => (Stateful2MovedRef = c)} />
</div>
) : (
<div>
<div>1</div>
<Stateful1 key="a" ref={c => (Stateful1Ref = c)} />
<div>2</div>
<Stateful2 key="b" ref={c => (Stateful2Ref = c)} />
</div>
);
}

const expectedHtml = div([
Expand Down Expand Up @@ -635,31 +639,27 @@ describe('keys', () => {
let Stateful2MovedRef;

function Foo({ moved }) {
return moved
? <div>
<div>1</div>
<Stateful2
key="b"
ref={c => (c ? (Stateful2MovedRef = c) : undefined)}
/>
<div>2</div>
<Stateful1
key="a"
ref={c => (c ? (Stateful1MovedRef = c) : undefined)}
/>
</div>
: <div>
<div>1</div>
<Stateful1
key="a"
ref={c => (c ? (Stateful1Ref = c) : undefined)}
/>
<div>2</div>
<Stateful2
key="b"
ref={c => (c ? (Stateful2Ref = c) : undefined)}
/>
</div>;
return moved ? (
<div>
<div>1</div>
<Stateful2
key="b"
ref={c => (c ? (Stateful2MovedRef = c) : undefined)}
/>
<div>2</div>
<Stateful1
key="a"
ref={c => (c ? (Stateful1MovedRef = c) : undefined)}
/>
</div>
) : (
<div>
<div>1</div>
<Stateful1 key="a" ref={c => (c ? (Stateful1Ref = c) : undefined)} />
<div>2</div>
<Stateful2 key="b" ref={c => (c ? (Stateful2Ref = c) : undefined)} />
</div>
);
}

const htmlForFalse = div([
Expand Down Expand Up @@ -841,19 +841,21 @@ describe('keys', () => {
let Stateful2MovedRef;

function Foo({ unkeyed }) {
return unkeyed
? <div>
<div>1</div>
<Stateful1 ref={c => (Stateful2MovedRef = c)} />
<div>2</div>
<Stateful2 ref={c => (Stateful1MovedRef = c)} />
</div>
: <div>
<div>1</div>
<Stateful1 key="a" ref={c => (Stateful1Ref = c)} />
<div>2</div>
<Stateful2 key="b" ref={c => (Stateful2Ref = c)} />
</div>;
return unkeyed ? (
<div>
<div>1</div>
<Stateful1 ref={c => (Stateful2MovedRef = c)} />
<div>2</div>
<Stateful2 ref={c => (Stateful1MovedRef = c)} />
</div>
) : (
<div>
<div>1</div>
<Stateful1 key="a" ref={c => (Stateful1Ref = c)} />
<div>2</div>
<Stateful2 key="b" ref={c => (Stateful2Ref = c)} />
</div>
);
}

const expectedHtml = div([
Expand Down Expand Up @@ -1007,18 +1009,20 @@ describe('keys', () => {
}

const App = props => {
return props.y === '2'
? <div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
: <div>
{null}
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>;
return props.y === '2' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
{null}
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
);
};

render(<App y="1" />, scratch);
Expand All @@ -1040,17 +1044,19 @@ describe('keys', () => {
}

const App = props => {
return props.y === '1'
? <div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
: <div>
<Comp key={1} i={1} />
{null}
<Comp key={3} i={3} />
</div>;
return props.y === '1' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
<Comp key={1} i={1} />
{null}
<Comp key={3} i={3} />
</div>
);
};

render(<App y="1" />, scratch);
Expand Down Expand Up @@ -1080,18 +1086,20 @@ describe('keys', () => {
}

const App = props => {
return props.y === '2'
? <div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
: <div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
{null}
<Comp key={3} i={3} />
</div>;
return props.y === '2' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
{null}
<Comp key={3} i={3} />
</div>
);
};

render(<App y="1" />, scratch);
Expand All @@ -1113,18 +1121,20 @@ describe('keys', () => {
}

const App = props => {
return props.y === '2'
? <div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
: <div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
{null}
</div>;
return props.y === '2' ? (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
</div>
) : (
<div>
<Comp key={1} i={1} />
<Comp key={2} i={2} />
<Comp key={3} i={3} />
{null}
</div>
);
};

render(<App y="1" />, scratch);
Expand All @@ -1133,4 +1143,27 @@ describe('keys', () => {
render(<App y="2" />, scratch);
expect(actions).to.deep.equal(['mounted 1', 'mounted 2', 'mounted 3']);
});

// Issue #4973: Test growing list diff
it('should correctly diff a growing list of keyed children', () => {
let values = [0, 1, 2, 3, 4];

render(<List values={values} />, scratch);
expect(scratch.textContent).to.equal('01234');

values = [2, 3, 4, 5, 6];
clearLog();

render(<List values={values} />, scratch);
expect(scratch.textContent).to.equal('23456');

expect(getLog()).to.deep.equal([
'<li>0.remove()',
'<li>1.remove()',
'<li>.appendChild(#text)',
'<ol>234.appendChild(<li>5)',
'<li>.appendChild(#text)',
'<ol>2345.appendChild(<li>6)'
]);
});
});
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