system/Validation/Rules.php
public function required_with($str = null, string $fields, array $data): bool
	{
		$fields = explode(',', $fields);

		// If the field is present we can safely assume that
		// the field is here, no matter whether the corresponding
		// search field is present or not.
		$present = $this->required($str ?? '');

		if ($present)
		{
			return true;
		}

		// Still here? Then we fail this test if
		// any of the fields are present in $data
		// as $fields is the lis
		$requiredFields = [];

		foreach ($fields as $field)
		{
			if (array_key_exists($field, $data))
			{
				$requiredFields[] = $field;
			}
		}

		// Remove any keys with empty values since, that means they
		// weren't truly there, as far as this is concerned.
		$requiredFields = array_filter($requiredFields, function ($item) use ($data) {
			return ! empty($data[$item]);
		});

		return empty($requiredFields);
	}
public function required_with($str = null, string $fields, array $data): bool
	{
		$fields = explode(',', $fields);

		// If the field is present we can safely assume that
		// the field is here, no matter whether the corresponding
		// search field is present or not.
		$present = $this->required($str ?? '');

		if ($present)
		{
			return true;
		}

		// Still here? Then we fail this test if
		// any of the fields are present in $data
		// as $fields is the lis
		$requiredFields = [];

		foreach ($fields as $field)
		{
			if (array_key_exists($field, $data))
			{
				$requiredFields[] = $field;
			}
		}

		// Remove any keys with empty values since, that means they
		// weren't truly there, as far as this is concerned.
		$requiredFields = array_filter($requiredFields, function ($item) use ($data) {
			return ! empty($data[$item]);
		});

		return empty($requiredFields);
	}
The field is required when any of the other required fields are present
in the data.

Example (field is required when the password field is present):

required_with[password]

@param $str
@param string $fields List of fields that we should check if present
@param array  $data   Complete list of fields from the form

@return boolean