instanceof redundant for class, but not for interface

[donquixote]

psalm is inconsistent in when it says "RedundantCondition" on instanceof checks.

https://psalm.dev/r/377cb86ce7

interface I {}
class C {}

/**
 * @param I $o
 */
function fI(I $o): void {
    // Not redundant?
    if ($o instanceof I) {
        print 'yes';
    }
}

/**
 * @param C $o
 */
function fC(C $o): void {
    // ERROR: RedundantCondition - 20:9 - Type C for $o is always C
    if ($o instanceof C) {
        print 'yes';
    }
}

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/377cb86ce7

<?php

interface I {}
class C {}

/**
 * @param I $o
 */
function fI(I $o): void {
    // Not redundant?
    if ($o instanceof I) {
        print 'yes';
    }
}

/**
 * @param C $o
 */
function fC(C $o): void {
    // ERROR: RedundantCondition - 20:9 - Type C for $o is always C
    if ($o instanceof C) {
        print 'yes';
    }
}

Psalm output (using commit 762ef8d):

ERROR: RedundantCondition - 21:9 - Type C for $o is always C

[orklah]

The difference is here:

psalm/src/Psalm/Internal/Type/AssertionReconciler.php

Line 504 in a53b521

&& !$new_type_has_interface

In your snippet, it doesn't matter that much, but the RedundantCondition is a false positive because of this: https://psalm.dev/r/3bd23090dd

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3bd23090dd

<?php

interface I {}
class C {}
class B extends C{}
class D extends C{}

class A{
    /**
     * @param C $o
     * @param class-string<C> $c
     */
    public static function C(C $o, string $c): void {
        // ERROR: RedundantCondition - 20:9 - Type C for $o is always C
        if ($o instanceof $c) {
            print 'yes';
        }
    }
}

$b = new B();

A::C($b, D::class);

Psalm output (using commit b941078):

ERROR: RedundantCondition - 15:13 - Type C for $o is always C

[orklah]

I actually worked on a very similar issue very close to this code: #6739

In fact, when dropping the && !$new_type_has_interface I linked above, it's my test that fails...

Not sure why there are two conditions