Instanceof interface breaks type inference.

[tanzanite777]

Type: Bug

Code sample to explain the issue:

interface I {
    function i() : void;
}

class B {
    function b() : void {}
}

class C extends B implements I {
    function c() : void {}
    function i() : void {}
}

function bug(B $b) {
    if($b instanceof I) {
        // BUG: $b stopped being an instance of B
        $b->b(); // invalid issue: Call to unknown method: I::b() PHP(PHP0418)
        $b->c(); // correct issue: Call to unknown method: I::c() PHP(PHP0418)
        $b->i();
    }
}

$c = new C();
if($c instanceof I) {
    // BUG: $c stopped being an instance of C (and B)
    $c->b(); // invalid issue: Call to unknown method: I::b() PHP(PHP0418)
    $c->c(); // invalid issue: Call to unknown method: I::c() PHP(PHP0418)
    $c->i();
}

Extension version: 1.56.16884
VS Code version: Code 1.97.2 (e54c774e0add60467559eb0d1e229c6452cf8447, 2025-02-12T23:20:35.343Z)
OS version: Windows_NT x64 10.0.19045
Modes:

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz (8 x 3600)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	undefined
Memory (System)	15.88GB (5.53GB free)
Process Argv	--crash-reporter-id adf79977-8c83-4303-918e-a7dfc5f31bf1
Screen Reader	no
VM	0%

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[jakubmisek]

@tanzanite777 thank you for the test case!

I've improved the instanceof type inferring, so it treats interfaces as you suggested.

The feature will be available in the next update. If you have anything else, please let us know!