The original php method preg_split might return `string[][]` in some
situations, however this should never be the case for this library. By
adding an extra assert, we should be more safe.
Psalm flags this condition as redundant:
```
ERROR: RedundantCondition - src/DocBlock/Tags/Return_.php:62:48 - "" can never contain non-empty-lowercase-string (see https://psalm.dev/122)
return $type . ($description !== '' ? ($type !== '' ? ' ' : '') . $description : '');
```
Based on the statement in the line above - `$type = $this->type ? '' . $this->type : 'mixed';` -, Psalm is correct and the `$type` variable can never be an empty string.
Psalm flags these type casts as redundant:
```
ERROR: RedundantCastGivenDocblockType - src/DocBlock/Tags/Author.php:80:23 - Redundant cast to string given docblock-provided type (see https://psalm.dev/263)
$authorName = (string) $this->authorName;
ERROR: RedundantCastGivenDocblockType - src/DocBlock/Tags/Example.php:150:21 - Redundant cast to string given docblock-provided type (see https://psalm.dev/263)
$filePath = (string) $this->filePath;
ERROR: RedundantCastGivenDocblockType - src/DocBlock/Tags/Link.php:74:17 - Redundant cast to string given docblock-provided type (see https://psalm.dev/263)
$link = (string) $this->link;
ERROR: RedundantCastGivenDocblockType - src/DocBlock/Tags/Method.php:228:23 - Redundant cast to string given docblock-provided type (see https://psalm.dev/263)
$methodName = (string) $this->methodName;
```
I have verified each and can confirm that these are redundant. They are probably a left-over from the time when the `__construct()` method in these classes did not yet have type declarations.
Correctly flagged by Psalm:
```
ERROR: PossiblyNullArgument - src\Utils.php:50:53 - Argument 3 of preg_split cannot be null, possibly null value provided (see https://psalm.dev/078)
$parts = php_preg_split($pattern, $subject, $limit, $flags);
```
The `$limit` argument of the PHP native `preg_split()` function is not nullable.
Ref: https://www.php.net/manual/en/function.preg-split
PHPStan flags the code within the `Source::__toString()` method:
```
------ -------------------------------------------------------------------------------------------
Line DocBlock\Tags\Source.php
------ -------------------------------------------------------------------------------------------
111 Result of || is always true.
114 Result of || is always true.
114 Result of || is always true.
------ -------------------------------------------------------------------------------------------
```
I have investigated this and can confirm that these flags are correct.
1. `$this->startingLine` is cast to an integer in the `__construct()` method (line 45) and subsequently cast to a string in `__toString()` (line 105).
This means that it can only ever be a non-empty ("truthy") string or the string '0', so the `$startingLine || $startingLine === '0'` condition used in two places is redundant.
2. `$this->lineCount` is either an integer or `null` after the `__construct()` method (line 46).
In the `__toString()` method, if the `lineCount` is an integer, it is effectively cast to a string by the concatenation with an empty string on line 107, while if the `lineCount` was `null`, it is turned into an empty string.
By changing the concatenation from concatenating with an empty string to concatenating with a one-space string, we can remove the ternary in the `return` statement checking for `$lineCount` being empty.
The existing unit tests already cover this code and still pass after this change.