Bug Report

AddInstanceofAssertForNullableInstanceRector repeatedly inserts the same assertInstanceOf() call when processing a public test method in a trait. This happens within a single Rector invocation, not just across subsequent CLI runs. Rector never reaches a stable result.

I reproduced this with a fresh installation of rector/rector:2.8.3 and only this rule enabled. The input uses PHP's built-in Throwable interface and contains no project-specific code.

Minimal PHP Code Causing Issue

input.php:

<?php
trait T
{
    function test(Throwable $e)
    {
        $p = $e->getPrevious();
        $p->getMessage();
    }
}

rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\PHPUnit\CodeQuality\Rector\ClassMethod\AddInstanceofAssertForNullableInstanceRector;
use Rector\ValueObject\PhpVersion;

return RectorConfig::configure()
    ->withRules([
        AddInstanceofAssertForNullableInstanceRector::class,
    ]);

Run with a hard deadline to avoid leaving the process running indefinitely:

vendor/bin/rector --version
# Rector 2.8.3

timeout -s KILL 10 vendor/bin/rector process input.php \
    --config=rector.php \
    --dry-run --debug --no-progress-bar --clear-cache

The uninstrumented run did not finish before the deadline and was killed with exit code 137.

Expected Behaviour

Rector should add a single assertion before $p->getMessage() and terminate:

$p = $e->getPrevious();
$this->assertInstanceOf(\Throwable::class, $p);
$p->getMessage();

The transformation should be idempotent: processing the transformed code again should not insert another identical assertion.