support Stringable objects

Author: staabm

src/Type/ObjectType.php

@@ -706,6 +706,10 @@ public function toArrayKey(): Type
 
 	public function toCoercedArgumentType(bool $strictTypes): Type
 	{
+		if (!$strictTypes) {
+			return TypeCombinator::union($this, $this->toString());
+		}
+
 		return $this;
 	}
 

tests/PHPStan/Analyser/nsrt/bug-12393b.php

@@ -534,3 +534,15 @@ public function doFoo(array $list): void
     }
 
 }
+
+class StringableFoo {
+    private string $foo;
+
+    public function doFoo(StringableFoo $foo): void {
+        $this->foo = $foo;
+        assertType('string', $this->foo);
+    }
+    public function __toString(): string {
+        return 'Foo';
+    }
+}