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[LiveComponent] Prevent LiveCollectionTrait from reusing removed indexes #3465

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[LiveComponent] Prevent LiveCollectionTrait from reusing removed indexes #3465

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3 changes: 3 additions & 0 deletions src/LiveComponent/CHANGELOG.md
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Expand Up @@ -3,6 +3,9 @@
## 3.1

- Use `aria-busy` attribute during component re-render
- Fix `LiveCollectionTrait::addCollectionItem()` reusing an index previously
freed by `removeCollectionItem()`, which caused a newly added item to be
rebound to the removed entity when used with a Doctrine collection.

## 3.0.0

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20 changes: 18 additions & 2 deletions src/LiveComponent/src/LiveCollectionTrait.php
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Expand Up @@ -14,6 +14,7 @@
use Symfony\Component\PropertyAccess\PropertyAccessorInterface;
use Symfony\UX\LiveComponent\Attribute\LiveAction;
use Symfony\UX\LiveComponent\Attribute\LiveArg;
use Symfony\UX\LiveComponent\Attribute\LiveProp;

/**
* @author Gábor Egyed <gabor.egyed@gmail.com>
Expand All @@ -22,6 +23,18 @@ trait LiveCollectionTrait
{
use ComponentWithFormTrait;

/**
* Tracks indexes removed from each collection so that newly added items
* never reuse a previously used index, which would make the form re-bind
* to a stale entity from the initial collection.
*
* Keyed by the collection field name passed to the add/remove actions.
*
* @var array<string, list<int>>
*/
#[LiveProp]
public array $liveCollectionRemovedKeys = [];
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@JacquesMougin JacquesMougin Apr 15, 2026

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@Amoifr Do you think this could be "private" instead of "public"? I can’t think of a case where it would be useful outside this context

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@Amoifr Amoifr Apr 15, 2026

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Good catch — I'd love to make it private, but Symfony's PropertyAccess (used by LiveComponentHydrator) can't read or write private properties without an accessor, so the dehydration/rehydration cycle would silently drop the tombstone. I verified it with a tiny repro:

class T {
    #[LiveProp] private array $privateArray = ['init' => 1];
    #[LiveProp] public  array $publicArray  = ['init' => 1];
}

$pa = PropertyAccess::createPropertyAccessor();
$pa->getValue(new T(), 'privateArray'); // ❌ "Can't get a way to read the property "privateArray"…"
$pa->getValue(new T(), 'publicArray');  // ✅

Every existing #[LiveProp] in the codebase (ComponentWithFormTrait::$formName, $formValues, $isValidated, $validatedFields, ValidatableComponentTrait::$isValidated, …) is public for the same reason. I'll keep public here to match that convention — let me know if you'd rather I add a private + getter/setter pair instead, happy to rework.

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@JacquesMougin JacquesMougin Apr 15, 2026

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@Amoifr Thanks a lot for the explanation, I didn’t dig deep enough to understand the full context !

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@Amoifr Amoifr Apr 15, 2026

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@JacquesMougin you're welcome ! I get to much pain in the first hours of the live component with this kind of things to remember about that 😄


#[LiveAction]
public function addCollectionItem(PropertyAccessorInterface $propertyAccessor, #[LiveArg] string $name): void
{
Expand All @@ -33,7 +46,8 @@ public function addCollectionItem(PropertyAccessorInterface $propertyAccessor, #
$data = [];
}

$index = [] !== $data ? max(array_keys($data)) + 1 : 0;
$usedKeys = array_merge(array_keys($data), $this->liveCollectionRemovedKeys[$name] ?? []);
$index = [] !== $usedKeys ? max($usedKeys) + 1 : 0;
$propertyAccessor->setValue($this->formValues, $propertyPath."[$index]", []);
}

Expand All @@ -44,6 +58,8 @@ public function removeCollectionItem(PropertyAccessorInterface $propertyAccessor
$data = $propertyAccessor->getValue($this->formValues, $propertyPath);
unset($data[$index]);
$propertyAccessor->setValue($this->formValues, $propertyPath, $data);

$this->liveCollectionRemovedKeys[$name][] = $index;
}

private function fieldNameToPropertyPath(string $collectionFieldName, string $rootFormName): string
Expand All @@ -60,4 +76,4 @@ private function fieldNameToPropertyPath(string $collectionFieldName, string $ro

return $propertyPath;
}
}
}
25 changes: 25 additions & 0 deletions src/LiveComponent/tests/Unit/LiveCollectionTraitTest.php
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Expand Up @@ -42,6 +42,31 @@ public function testRemoveCollectionItem(array $postedFormData, string $collecti
self::assertSame($expectedFormData[$component->formName], $component->formValues);
}

public function testAddCollectionItemDoesNotReusePreviouslyRemovedIndex()
{
$component = $this->createComponent([
'' => [
'items' => [
0 => [],
1 => [],
2 => [],
],
],
]);
$propertyAccessor = PropertyAccess::createPropertyAccessor();

$component->removeCollectionItem($propertyAccessor, 'items', 2);
$component->addCollectionItem($propertyAccessor, 'items');

self::assertSame([
'items' => [
0 => [],
1 => [],
3 => [],
],
], $component->formValues);
}

public static function provideAddedItems(): iterable
{
yield 'unnamed parent form' => [
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