False positive NoValue

[mrsuh]

Hi.
Psalm 5.7.1
I got this error on a simple example.

<?php

$str = $argv[1] ?? '';
if(empty($str) || strlen($str) < 3) {
    exit(1);
}

echo $str; // ERROR: [NoValue](https://psalm.dev/179) - 8:6 - All possible types for this argument were invalidated - This may be dead code

https://psalm.dev/r/f12fbc1db8

The error disappeared when I removed the unnecessary "empty" check.

<?php

$str = $argv[1] ?? '';
if(strlen($str) < 3) {
    exit(1);
}

echo $str;

https://psalm.dev/r/a0bf807db5

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/f12fbc1db8

<?php

$str = $argv[1] ?? '';
if(empty($str) || strlen($str) < 3) {
    exit(1);
}

echo $str;

Psalm output (using commit 589fee7):

ERROR: NoValue - 8:6 - All possible types for this argument were invalidated - This may be dead code

https://psalm.dev/r/a0bf807db5

<?php

$str = $argv[1] ?? '';
if(strlen($str) < 3) {
    exit(1);
}

echo $str;

Psalm output (using commit 589fee7):

No issues!

[piotrekkr]

Same with:

<?php
class CodeReader
{
    public function read(string $code): ?string
    {
        if (empty($code) || strlen($code) < 32) {
            return null;
        }

        $code = substr($code, 3);
        
        return $code;
    }
}

https://psalm.dev/r/a99bcc7c07

works without empty

<?php
class CodeReader
{
    public function read(string $code): ?string
    {
        if (strlen($code) < 32) {
            return null;
        }

        $code = substr($code, 3);
        
        return $code;
    }
}

https://psalm.dev/r/1fbf4fbcfc

Error is shown in wrong line imho. Should be something like unnecessary empty() check or something.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/a99bcc7c07

<?php

class CodeReader
{
    public function read(string $code): ?string
    {
        if (empty($code) || strlen($code) < 32) {
            return null;
        }

        $code = substr($code, 3);
        
        return $code;
    }
}

Psalm output (using commit 589fee7):

ERROR: NoValue - 11:24 - All possible types for this argument were invalidated - This may be dead code

https://psalm.dev/r/1fbf4fbcfc

<?php
class CodeReader
{
    public function read(string $code): ?string
    {
        if (strlen($code) < 32) {
            return null;
        }

        $code = substr($code, 3);
        
        return $code;
    }
}

Psalm output (using commit 589fee7):

No issues!

[weirdan]

/cc: @LeoVie

[jacekkarczmarczyk]

slighly different usecase with different error, but I guess underlying issue is the same

https://psalm.dev/r/01a80b3670

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/01a80b3670

<?php
function test(string $s): void {
	if (!$s || strlen($s) !== 9) {
        throw new Exception();
    }
}

Psalm output (using commit 589fee7):

ERROR: TypeDoesNotContainType - 3:13 - Type non-falsy-string for $s is always !non-empty

[jack-worman]

Here is another false-positive example: https://psalm.dev/r/b72669f3a0

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b72669f3a0

<?php

/** @var string $a */
if (strlen($a) === 7) {
    return $a;
} elseif (strlen($a) === 10) {
    return $a;
}

Psalm output (using commit 471a8c6):

ERROR: NoValue - 7:5 - All possible types for this return were invalidated - This may be dead code

[weirdan]

Thanks @jack-worman, this is probably the clearest example out of all posted here.

With traces: https://psalm.dev/r/8b1462cca9

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/8b1462cca9

<?php

/** @var string $a */
if (strlen($a) === 7) {
    return $a;
} else {
    /** @psalm-trace $a */; 
    if (strlen($a) === 10) {
        return $a;
    }
}

Psalm output (using commit 471a8c6):

INFO: Trace - 7:27 - $a: ''|'0'

ERROR: NoValue - 9:9 - All possible types for this return were invalidated - This may be dead code