Fibers start with error_reporting = 0 when the error_reporting INI directive is not set

[diolektor]

Description

Since PHP 8.6.0 (tested on 8.6.0RC2, and present on the current PHP-8.6 and master branches), a new Fiber starts with error_reporting set to 0 whenever the error_reporting INI directive has no value. That is the default: without a php.ini (e.g. the official Docker images, or php -n), the directive is unset. All diagnostics raised inside the fiber are then silently suppressed. Outside the fiber, error_reporting() is E_ALL as expected.

The following code:

<?php
echo error_reporting(), "\n";
(new Fiber(function () {
    echo error_reporting(), "\n";
    echo $undefined;
    echo "after\n";
}))->start();

Run as php -n -d display_errors=1 test.php, it resulted in this output:

30719
0
after

But I expected this output instead (what PHP 8.5 prints):

30719
30719

Warning: Undefined variable $undefined in /test.php on line 5
after

Behaviour matrix, error_reporting() as seen inside the fiber (same results on NTS and ZTS builds):

Setup	8.5	8.6.0RC2
no php.ini (official image)	30719	0
php -n	30719	0
-d error_reporting=0	0	0
-d error_reporting=E_ALL	30719	30719
error_reporting(E_ALL) called at runtime before the fiber, directive unset	30719	0

Cause

Introduced by cd75300 (#21146).

zend_fiber_execute() seeds the fiber's EG(error_reporting) from the directive, falling back to E_ALL when the directive is unset:

/* Determine the current error_reporting ini setting. */
zend_long error_reporting = zend_ini_long_literal("error_reporting");
/* If error_reporting is 0 and not explicitly set to 0, zend_ini_str returns a null pointer. */
if (!error_reporting && !zend_ini_str_literal("error_reporting")) {
	error_reporting = E_ALL;
}

That commit ("Audit INI functions and macros, and replace them with better alternatives") replaced INI_INT()/INI_STR() with zend_ini_long_literal()/zend_ini_str_literal(). The old INI_STR() expanded to zend_ini_string_ex(name, len, 0, NULL), which returns NULL when the entry exists but has no value. error_reporting is registered with a NULL default in Zend/zend.c. The new zend_ini_str() returns ZSTR_EMPTY_ALLOC() in that case and returns NULL only when the directive does not exist at all. So the !zend_ini_str_literal(...) check is never true for error_reporting, and the E_ALL fallback is dead code. The comment above it still describes the old behaviour.

zend_ini_string() has the same empty-string mapping, so it is not a drop-in fix either. zend_ini_str_ex() keeps the old semantics:

if (!error_reporting && !zend_ini_str_ex("error_reporting", sizeof("error_reporting") - 1, false, NULL)) {
	error_reporting = E_ALL;
}

I grepped PHP-8.6 for other callers that null-check the result of zend_ini_str() / zend_ini_str_literal(). The only other ones (ext/com_dotnet, ext/standard/basic_functions.c) use NULL to mean "directive does not exist", which the new function still reports correctly. zend_fibers.c appears to be the only affected site. The "Unset directive" behaviour change of zend_ini_str() is not mentioned in UPGRADING.INTERNALS, so third-party code that migrated INI_STR() the same way may have the same issue.

PHP Version

PHP 8.6.0RC2 (also present on PHP-8.6 at 6f49ae8 and master at 99c2dba). Not affected: PHP 8.5.

Operating System

Alpine Linux 3.23 (official php:8.6.0RC2-cli-alpine and php:8.6.0RC2-zts-alpine3.23 images); not OS-specific.

[Girgias]

I'm trying to figure out why we couldn't jut do zend_long error_reporting = EG(error_reporting); instead of parsing the raw INI setting.