Regression in 1.17.0: artisan tinker fails with RuntimeException from PsySH stream_select() in Laravel/K8s environments

[jwadhams]

Summary

DDTrace 1.17.0 introduces a regression that breaks php artisan tinker in Laravel applications running in Kubernetes environments. 1.15.2 works correctly; 1.17.0 does not.

Symptom

Running artisan tinker immediately throws:

RuntimeException

Error waiting for execution loop: file_get_contents(.env): Failed to open stream: No such file or directory

Environment

• PHP: 8.3.14
• Laravel: 12.x
• PsySH: via laravel/tinker
• OS: Alpine Linux 3.19 (Kubernetes pod)
• DDTrace broken: 1.17.0
• DDTrace working: 1.15.2 (and 1.13.0)

Root Cause Analysis

PsySH's ProcessForker (vendor/psy/psysh/src/ExecutionLoop/ProcessForker.php) forks via pcntl_fork() and the parent process waits on a Unix socket pair using @stream_select(). If stream_select() returns false, PsySH reads error_get_last() and throws:

throw new \RuntimeException('Error waiting for execution loop: ' . $err['message']);

In Kubernetes environments, there is no .env file — all config is injected via environment variables. Laravel's bootstrap calls vlucas/phpdotenv, which attempts @file_get_contents('/var/www/html/.env'). The @ suppresses the error display but still sets error_get_last() to:

file_get_contents(/var/www/html/.env): Failed to open stream: No such file or directory

This has always happened at bootstrap, but PsySH's execution loop only surfaces it when stream_select() returns false. With DDTrace 1.15.2, stream_select() succeeds normally. With 1.17.0, it returns false (likely due to a hook into PHP's socket/stream or pcntl internals), causing the stale error_get_last() value to bubble up as the exception message.

Reproduction

1. Run a Laravel 12 app in a Kubernetes pod (no .env file; config from env vars)
2. Install DDTrace 1.17.0 via datadog-setup.php
3. Run php artisan tinker
4. Observe RuntimeException: Error waiting for execution loop: file_get_contents(.env): ...

Downgrade to 1.15.2 — issue disappears.

Workaround

Pin DDTrace to 1.15.2 in your Dockerfile:

RUN php -r "readfile('https://github.com/DataDog/dd-trace-php/releases/download/1.15.2/datadog-setup.php');" | php -- --php-bin=all --enable-profiling

[bwoebi]

Hm @jwadhams, I wonder, is this a signal which gets delivered? The tracer does in fact not hook stream_select.

It's really odd that stream_select does not set error_get_last(). Do you have any idea why?

Is it possible for you to run this under strace to check whether there was a specific return value (like EINTR)?

Thanks!

[bwoebi]

Or , alternatively @jwadhams:

https://s3.us-east-1.amazonaws.com/dd-trace-php-builds/1.18.0%2B9a2f5deb5c00c029a629362d4d882cd28d01983b/datadog-setup.php

Try this setup script instead - it blocks the sidecar-communication signal for the duration of stream_select(). Maybe that helps.

Try it please, and tell me!