`SoftDeletes` should call `syncOriginal()` after UPDATE query execution

[mpyw]

• Laravel Version: 6.16.0
• PHP Version: 7.4

Description:

Currently models get dirty (isDirty() == true) after both force-deletion and soft-deletion.

Force-deletion

Correct behavior. After deletion, the model doesn't exist anymore: $exists = false. We cannot sync the latest attributes from database.

Soft-deletion

Wrong behavior. After deletion, the model still exists: $exists = true. We should be able to retrieve the latest attributes or immediately restore the data. Currently, immediate restore() call just after delete() has a broken behavior. SoftDeletes should call syncOriginal() after UPDATE query execution.

Steps To Reproduce:

$softDeletable->delete();
$softDeletable->restore(); // It does't execute any queries

$softDeletable->delete();
$softDeletable->refresh();
$softDeletable->restore(); // It works

[driesvints]

I can reproduce this but unsure what's causing this. Tried to dive into the internals but it's not clear why the deleted_at column isn't cleared in the database when restore is called.

[mpyw]

@driesvints

When we soft-delete models:

1. Model::delete()
2. SoftDeletes::runSoftDelete()
3. Model attributes have been set (Model::isDirty() returns true)
4. Builder::update()
5. Model::syncOriginal() should be called here but we are missing it

When we restore models:

    /**
     * Restore a soft-deleted model instance.
     *
     * @return bool|null
     */
    public function restore()
    {
        /* ... */

        // This revert the model attribute changes
        // `Model::isDirty()` returns false!!!!!!
        $this->{$this->getDeletedAtColumn()} = null;

        /* ... */

        $result = $this->save();

        /* ... */
    }

    /**
     * Save the model to the database.
     *
     * @param  array  $options
     * @return bool
     */
    public function save(array $options = [])
    {
        /* ... */

        if ($this->exists) {
            $saved = $this->isDirty() ?
                        $this->performUpdate($query) : true; // Model::performUpdate() won't be fired
        }

        /* ... */
    }

[danielsuguimoto]

@taylorotwell closed the PR, so I'm bringing the question here. Should we sync the timestamps fields only? See #31631 (comment)

[quetzyg]

Currently I'm running into issue #31823, due to the changes proposed here.