Incorrect UnusedReturnValue for a recursive private method

[dabrowiecki]

If you have a private method used recursively and return type is used only in recursion, psalm incorrectly emits UnusedReturnValue.

Example code:

class A {
    private array $cache = [];
    public function a(): void {
        $this->buildCacheRecursively(6);
    }
    
    private function buildCacheRecursively(int $id): int
    {
        if ($id === 1) {
            return 1;
        }
        
        $this->cache[$id] = $id * $this->buildCacheRecursively($id-1);
        return $this->cache[$id];
    }
}

https://psalm.dev/r/029a1d1479

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/029a1d1479

<?php

/**
 * @psalm-api
 **/
final class A {
    private array $cache = [];
    public function a(): void {
        $this->buildCacheRecursively(6);
    }
    
    private function buildCacheRecursively(int $id): int
    {
        if ($id === 1) {
            return 1;
        }
        
        $this->cache[$id] = $id * $this->buildCacheRecursively($id-1);
        return $this->cache[$id];
    }
}

Psalm output (using commit cdceda0):

ERROR: UnusedReturnValue - 12:54 - The return value for this private method is never used