Arr::dot() doesn't flatten empty arrays

[ropi-bc]

Laravel Version

12.26

PHP Version

8.3.9

Database Driver & Version

No response

Description

I have a Filament feature that finds differences between the before and after of a record after editing. I'm starting out with:

$data = array (
  'name' => 'láadwáldalwéáasmnlkadswwadwa',
  'description' => NULL,
  'dimension_values' => 
  array (
    1 => 1,
    2 => 15,
    3 => NULL,
    4 => 134,
    5 => 149,
  ),
)

$oldState = array (
  'id' => 78233,
  'name' => 'láadwáldalwéáasmnlkadsw',
  'created_at' => '2025-10-02T14:02:09.000000Z',
  'updated_at' => '2025-10-08T09:23:46.000000Z',
  'type' => 4,
  'description' => NULL,
  'tags' => 
  array (
  ),
  'dimension_values' => 
  array (
    1 => '1',
    2 => '15',
    3 => NULL,
    4 => '134',
    5 => '149',
  ),
)

I can't call array_diff() on these because both arrays are multi-dimensional, so I tried Arr::dot(), which works well for the most part, but what I see instead is that the empty array $oldState['tags'] remained untouched. This is problematic because the result still counts as a multi-dimensional array, which means that I still can't use it as input to array_diff().

Based on the description (Flatten a multi-dimensional associative array with dots.), I'd expect the output to be completely flattened.

Is this really the expected output of this function? I'd expect the output to be either:

  array (
    'id' => 78233,
    'name' => 'láadwáldalwéáasmnlkadswwa',
    'created_at' => '2025-10-02T14:02:09.000000Z',
    'updated_at' => '2025-10-08T12:14:38.000000Z',
    'type' => 4,
    'description' => NULL,
    'dimension_values.1' => '1',
    'dimension_values.2' => '15',
    'dimension_values.3' => NULL,
    'dimension_values.4' => '134',
    'dimension_values.5' => '149',
  )

Or:

  array (
    'id' => 78233,
    'name' => 'láadwáldalwéáasmnlkadswwa',
    'created_at' => '2025-10-02T14:02:09.000000Z',
    'updated_at' => '2025-10-08T12:14:38.000000Z',
    'type' => 4,
    'description' => NULL,
    'tags' => NULL,
    'dimension_values.1' => '1',
    'dimension_values.2' => '15',
    'dimension_values.3' => NULL,
    'dimension_values.4' => '134',
    'dimension_values.5' => '149',
  )

Steps To Reproduce

<?php

use Illuminate\Support\Collection;

it('after calling dot() on a collection, I should see no empty arrays', function () {
    $data = [
        'user' => [
            'name' => 'John',
            'address' => [
                'street' => 'Main St',
                'empty_array' => [],
                'city' => 'New York',
            ],
            'empty_array' => [],
        ],
    ];

    $dotted = collect($data)->dot();

    expect($dotted['user.address.empty_array'])->not->toBeArray();
    expect($dotted['user.empty_array'])->not->toBeArray();
});

[ropi-bc]

Filed a PR too, that should be the clearest way to describe what I'd expect to happen

[jmarble]

@ropi-bc Arr::dot() should not coalesce any value types... i.e. an empty array should not be transformed to null. But for your use case you could maybe do this:

$flatOld = collect($oldState)
    ->dot()
    ->map(fn($v) => is_array($v) && empty($v) ? null : $v);

$flatNew = collect($data)
    ->dot()
    ->map(fn($v) => is_array($v) && empty($v) ? null : $v);

$differences = $flatNew->diffAssoc($flatOld);

[johnstormentswe]

Took the backwards-compatible route - added an opt-in $preserveEmptyArrays = false flag rather than changing the default behavior, since (as @jmarble pointed out) Arr::dot() is type-preserving by contract and silently turning [] into null or dropping keys would break existing callers.
Usage: Arr::dot($data, '', INF, false);
Open to feedback if maintainers prefer a different approach (e.g. a separate Arr::dotFlat() helper, or renaming the flag).