fibers: fix GH-23921 (Fibers start with error_reporting = 0 when the error_reporting INI directive is not set)

The way zend_fiber_execute() queries the error_reporting level is rather rather strange.

It cannot rely on the value of EG(error_reporting) as the @ silence operator may change it and this it would leak into the body of a fiber.
However, we can simply query the underlying value of the INI setting to get the correct error_reporting value as this is not modified by the @ operator.

Fixes an additional bug where the error_reporting value within a fiber was always E_ALL if the @ operator was used.

Closes GH-23930

Author: Girgias

NEWS

@@ -15,6 +15,8 @@ PHP                                                                        NEWS
     state. (Ilia Alshanetsky)
   . Fixed OSS-Fuzz #552682112 (assertion failure wrt
     zp_arg_must_be_sent_by_ref()). (ndossche)
+  . Fixed GH-23921 (Fibers start with error_reporting = 0 when the
+    error_reporting INI directive is not set). (Girgias)
 
 - FFI:
   . Fixed crashes with FFI callbacks created from __call() trampolines

Zend/tests/fibers/gh23921.phpt

@@ -0,0 +1,17 @@
+--TEST--
+GH-23921 (Fibers start with error_reporting = 0 when the error_reporting INI directive is not set)
+--FILE--
+<?php
+echo error_reporting(), "\n";
+(new Fiber(function () {
+    echo error_reporting(), "\n";
+    echo $undefined;
+    echo "after\n";
+}))->start();
+?>
+--EXPECTF--
+30719
+30719
+
+Warning: Undefined variable $undefined in %s on line 5
+after

Zend/tests/fibers/silence-operator-outside-fiber-should-no-widen-error-reporting.phpt

@@ -0,0 +1,18 @@
+--TEST--
+Silence operator must not change the error_reporting value within the fiber
+--FILE--
+<?php
+
+error_reporting(E_WARNING);
+
+@(new Fiber(function () {
+	var_dump(E_ALL);
+	var_dump(E_WARNING);
+    var_dump(error_reporting());
+}))->start();
+
+?>
+--EXPECT--
+int(30719)
+int(2)
+int(2)

Zend/zend_fibers.c

@@ -570,12 +570,9 @@ static ZEND_STACK_ALIGNED void zend_fiber_execute(zend_fiber_transfer *transfer)
 
 	zend_fiber *fiber = EG(active_fiber);
 
-	/* Determine the current error_reporting ini setting. */
+	/* We cannot rely on EG(error_reporting) as a silence operator @ may modify the executor global error_reporting
+	 * value without changing the underlying INI value */
 	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;
-	}
 
 	EG(vm_stack) = NULL;