After LazyCollection calls the unique method and then calls the isEmpty method, a piece of data will be lost.

[zishang520]

• Laravel Version: 6.20.34
• PHP Version: 7.4.2
• Database Driver & Version:
  mysql 5.7.34-log

Description:

After LazyCollection calls the unique method and then calls the isEmpty method, a piece of data will be lost.

Steps To Reproduce:

// The offending code snippet:
$items = \Illuminate\Support\LazyCollection::make(fn () => yield from [['id' => '1'], ['id' => '2'], ['id' => '4']]);
dump($items->toArray()); // Output: [['id' => '1'], ['id' => '2'], ['id' => '4']]
$unique_items = $items->unique('id');
// If the output is here, there is no problem, but `LazyCollection::isEmpty()` will return true.
// dump($unique_items->toArray()); // Output: [['id' => '1'], ['id' => '2'], ['id' => '4']]
if (!$unique_items->isEmpty()) {
    // When I judge whether it is a null value, I lost a value.
    dump($unique_items->toArray()); // Output: [['id' => '2'], ['id' => '4']]
}

// Everything is normal for this part of the code.
$items = \Illuminate\Support\Collection::make([['id' => '1'], ['id' => '2'], ['id' => '4']]);
dump($items->toArray());
$items = $items->unique('id');
if (!$items ->isEmpty()) {
    dump($items ->toArray());
}

[driesvints]

@JosephSilber I guess this works as expected but wanted to confirm with you.

[JosephSilber]

I guess this works as expected

It does not. It's broken.

You can see the problem more easily with this piece of code:

$items = LazyCollection::make(function () {
    yield 1;
    yield 2;
    yield 3;
});

$items
    ->unique()
    ->tap(fn ($collection) => $collection->take(2)->eager())
    ->dd(); // [3]

That call to take(2)->eager() consumed the first 2 items, so the subsequent enumeration is missing that.

That's not expected. Separate enumerations should never affect each other.

---

I'll work on a fix.

[driesvints]

Thanks @JosephSilber