A string after strlen > 0 check should be a non-empty-string

[MauricioFauth]

https://psalm.dev/r/ca291dd273

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/ca291dd273

<?php

/**
 * @return non-empty-string
 */
function nonEmptyString(string $str): string {
    return strlen($str) > 0 ? $str : 'string';
}

/**
 * @return non-empty-string
 */
function nonEmptyMbString(string $str): string {
    return mb_strlen($str) > 0 ? $str : 'string';
}

Psalm output (using commit f439d65):

INFO: LessSpecificReturnStatement - 7:12 - The type 'string' is more general than the declared return type 'non-empty-string' for nonEmptyString

INFO: MoreSpecificReturnType - 4:12 - The declared return type 'non-empty-string' for nonEmptyString is more specific than the inferred return type 'string'

INFO: LessSpecificReturnStatement - 14:12 - The type 'string' is more general than the declared return type 'non-empty-string' for nonEmptyMbString

INFO: MoreSpecificReturnType - 11:12 - The declared return type 'non-empty-string' for nonEmptyMbString is more specific than the inferred return type 'string'

[orklah]

Good idea!

This is handled in AssertionFinder. The role of this class is to find any hint it can use to refine a variable type. For example if(!empty($a)) will generate an assertion !empty. That way, once we enter the AssertionReconciler, we'll be able to refine the type of $a (previously stdClass|null) into stdClass.

AssertionFinder has 4 main methods:
getGreaterAssertions (for cases like $a > 5)
getLesserAssertions (for $a < 5)
scrapeInequalityAssertions (for $a !== 5)
scrapeEqualityAssertions (for $a === 5)
So every case must be taken into account for (mb_?)strlen

What you want to do is actually closer to what we already have with count (for example in if(count($arr) > 0), so you need something similar to that.

the count() case is handled here for getGreaterAssertions:

psalm/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php

Line 3736 in e7bc6f2

$count_inequality_position = self::hasLessThanCountEqualityCheck($conditional, $max_count);

The method we call must detect when count() > 5 is used, and then extract an assertion from that

In your case, you'll want to detect any strlen used on a string and then deduct if you can infer something from it.
Here are the assertions you should use:

• strlen($a) > 5 should create an assertion !empty (to transform string into non-empty-string
• strlen($a) == 1 should create an assertion !empty
• strlen($a) != 0 should create an assertion !empty

So this means you don't have to change anything in getLesserAssertions.

Don't hesitate to ask questions or to ping me for more help or explanations!

[theodorejb]

Should this be closed now?

[weirdan]

The PR implementing this has been reverted, so I'm reopening the issue.