Restrict allowed usages of $GLOBALS

This restricts allowed usage of $GLOBALS, with the effect that
plain PHP arrays can no longer contain INDIRECT elements.

RFC: https://wiki.php.net/rfc/restrict_globals_usage

Closes GH-6487.

Author: nikic

UPGRADING

@@ -19,6 +19,15 @@ PHP 8.1 UPGRADE NOTES
 1. Backward Incompatible Changes
 ========================================
 
+- Core:
+  . Access to the $GLOBALS array is now subject to a number of restrictions.
+    Read and write access to individual array elements like $GLOBALS['var']
+    continues to work as-is. Read-only access to the entire $GLOBALS array also
+    continues to be supported. However, write access to the entire $GLOBALS
+    array is no longer supported. For example, array_pop($GLOBALS) will result
+    in an error.
+    RFC: https://wiki.php.net/rfc/restrict_globals_usage
+
 - Fileinfo:
   . The fileinfo functions now accept and return, respectively, finfo objects
     instead of resources.

Zend/tests/array_self_add_globals.phpt

@@ -2,7 +2,6 @@
 Add $GLOBALS to itself
 --FILE--
 <?php
-$GLOBALS += $GLOBALS;
 $x = $GLOBALS + $GLOBALS;
 ?>
 ===DONE===

Zend/tests/bug71539_6.phpt

@@ -29,6 +29,6 @@ string(%d) "%s"
 Warning: Undefined array key "PHP_SELF" in %s on line %d
 NULL
 
-Warning: Undefined variable $_SERVER in %s on line %d
+Warning: Undefined global variable $_SERVER in %s on line %d
 NULL
 Done

Zend/tests/bug71695.phpt

@@ -32,6 +32,6 @@ string(%d) "%s"
 Warning: Undefined array key "PHP_SELF" in %s on line %d
 NULL
 
-Warning: Undefined variable $_SERVER in %s on line %d
+Warning: Undefined global variable $_SERVER in %s on line %d
 NULL
 Done

Zend/tests/gc_010.phpt

@@ -38,6 +38,6 @@ string(%d) "%s"
 Warning: Undefined array key "PHP_SELF" in %s on line %d
 NULL
 
-Warning: Undefined variable $_SERVER in %s on line %d
+Warning: Undefined global variable $_SERVER in %s on line %d
 NULL
 Done

Zend/tests/globals_001.phpt

@@ -23,6 +23,6 @@ string(%d) "%s"
 Warning: Undefined array key "PHP_SELF" in %s on line %d
 NULL
 
-Warning: Undefined variable $_SERVER in %s on line %d
+Warning: Undefined global variable $_SERVER in %s on line %d
 NULL
 Done

Zend/tests/globals_002.phpt

@@ -0,0 +1,11 @@
+--TEST--
+$GLOBALS no longer contains 'GLOBALS'
+--FILE--
+<?php
+
+$g = $GLOBALS;
+var_dump(isset($g['GLOBALS']));
+
+?>
+--EXPECT--
+bool(false)