@psalm-assert should assert type after passing all never-returning branches

[fluffycondor]

https://psalm.dev/r/4150a3c1a7

It's safe to assume the type from @psalm-assert for $bar after passing all never-returning branches.

Expected: no errors.
Got: LessSpecificReturnStatement and MoreSpecificReturnType.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/1e53bfa534

<?php

/**
 * @psalm-assert non-empty-string $bar
 * @return non-empty-string
 */
function foo(string $bar): string
{
    if (strlen($bar) < 4) {
        throw new RuntimeException();
    }
    
    // here $bar should be assumed as non-empty-string because of the @psalm-assert
    
    // of course one can do $bar = '' here, so assuming the type in the moment of returning it is unsafe
    // because the type a function asserts and the type the function returns can differ
    // but it's safe to assume the type from @psalm-assert for $bar after every never-returning branches 

    return $bar;
}

Psalm output (using commit a9bc87e):

INFO: LessSpecificReturnStatement - 19:12 - The type 'string' is more general than the declared return type 'non-empty-string' for foo

INFO: MoreSpecificReturnType - 5:12 - The declared return type 'non-empty-string' for foo is more specific than the inferred return type 'string'

[orklah]

the strlen check should let Psalm infer that $bar is non-empty.

Aside from that, it's Psalm's job to check, not to assume you didn't make mistakes. It would be weird to automatically consider that the type is the correct one (and it would lead to a whole new set of issues to be emitted in case you want to force a bool to be a string through an assertion for example).

Your snippet is pretty weird too, why would you return $bar without changing it after asserting its type?

[kkmuffme]

There is an issue for strlen already, see #7387.

The error is correct here, as it shouldn't make any assumptions. When checking for !== '' https://psalm.dev/r/97270ba09f

This issue can be closed.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/97270ba09f

<?php

/**
 * @psalm-assert non-empty-string $bar
 * @return non-empty-string
 */
function foo(string $bar): string
{
    if ($bar === '') {
        throw new RuntimeException();
    }
    
    // here $bar should be assumed as non-empty-string because of the @psalm-assert
    
    // of course one can do $bar = '' here, so assuming the type in the moment of returning it is unsafe
    // because the type a function asserts and the type the function returns can differ
    // but it's safe to assume the type from @psalm-assert for $bar after passing all never-returning branches 

    return $bar;
}

Psalm output (using commit bebce06):

No issues!