Completely remove disabled functions from function table

Currently, disabling a function only replaces the internal
function handler with one that throws a warning, and a few
places in the engine special-case such functions, such as
function_exists. This leaves us with a Schrödinger's function,
which both does not exist (function_exists returns false) and
does exist (you cannot define a function with the same name).
In particular, this prevents the implementation of robust
polyfills, as reported in https://bugs.php.net/bug.php?id=79382:

    if (!function_exists('getallheaders')) {
        function getallheaders(...) { ... }
    }

If getallheaders() is a disabled function, this code will break.

This patch changes disable_functions to remove the functions from
the function table completely. For all intents and purposes, it
will look like the function does not exist.

This also renders two bits of PHP functionality obsolete and thus
deprecated:

 * ReflectionFunction::isDisabled(), as it will no longer be
   possible to construct the ReflectionFunction of a disabled
   function in the first place.
 * get_defined_functions() with $exclude_disabled=false, as
   get_defined_functions() now never returns disabled functions.

Fixed bug #79382.

Closes GH-5473.

1 files changed, 7 insertions, 3 deletions

diff --git a/tests/basic/bug31875.phpt b/tests/basic/bug31875.phpt
index 65f68b9af3..c8ad25ec9f 100644
--- a/tests/basic/bug31875.phpt
+++ b/tests/basic/bug31875.phpt
@@ -8,6 +8,8 @@ disable_functions=dl
 <?php
 $disabled_function = 'dl';
 
+/* exclude_disabled parameters is harded to true */
+
 $functions = get_defined_functions();
 var_dump(in_array($disabled_function, $functions['internal']));
 
@@ -17,7 +19,9 @@ var_dump(in_array($disabled_function, $functions['internal']));
 $functions = get_defined_functions(true);
 var_dump(in_array($disabled_function, $functions['internal']));
 ?>
---EXPECT--
-bool(true)
-bool(true)
+--EXPECTF--
+bool(false)
+
+Deprecated: get_defined_functions(): Setting $exclude_disabled to false has no effect in %s on line %d
+bool(false)
 bool(false)