Create is_countable() to check if it's safe to call count()

NEWS

@@ -20,6 +20,7 @@ PHP                                                                        NEWS
     php.exe). (Michele Locati)
   . Implemented "Convert numeric keys in object/array casts" RFC, fixes
     bugs #53838, #61655, #66173, #70925, #72254, etc. (Andrea)
+  . Added is_countable() to check if the parameter is safe to pass to count(). (Craig Duncan)
 
 - Date:
   . Fixed bug #69587 (DateInterval properties and isset). (jhdxr)

UPGRADING

@@ -77,6 +77,7 @@ PHP 7.2 UPGRADE NOTES
   . Simplified password hashing API updated to support Argon2i hashes when PHP is compiled with libargon2
     (https://wiki.php.net/rfc/argon2_password_hash).
   . proc_nice() is now supported on Windows platforms.
+  . Added is_countable() to check if the parameter is safe to pass to count().
 
 ========================================
 3. Changes in SAPI modules

ext/standard/array.c

@@ -773,6 +773,38 @@ PHPAPI zend_long php_count_recursive(zval *array, zend_long mode) /* {{{ */
 }
 /* }}} */
 
+/* {{{ proto bool is_countable(mixed var)
+   Returns true if variable is countable using count() */
+PHP_FUNCTION(is_countable)
+{
+	zval *array;
+
+	ZEND_PARSE_PARAMETERS_START(1, 1)
+		Z_PARAM_ZVAL(array)
+	ZEND_PARSE_PARAMETERS_END();
+
+	switch (Z_TYPE_P(array)) {
+		case IS_ARRAY:
+			RETURN_TRUE;
+			return;
+		case IS_OBJECT:
+			/* first, we check if the handler is defined */
+			if (Z_OBJ_HT_P(array)->count_elements) {
+				RETURN_TRUE;
+				return;
+			}
+			/* if not check if the object implements Countable */
+			if (instanceof_function(Z_OBJCE_P(array), spl_ce_Countable)) {
+				RETURN_TRUE;
+				return;
+			}
+		default:
+			RETURN_FALSE;
+			break;
+	}
+}
+/* }}} */
+
 /* {{{ proto int count(mixed var [, int mode])
    Count the number of elements in a variable (usually an array) */
 PHP_FUNCTION(count)

ext/standard/basic_functions.c

@@ -224,6 +224,10 @@ ZEND_BEGIN_ARG_INFO_EX(arginfo_ksort, 0, 0, 1)
 	ZEND_ARG_INFO(0, sort_flags)
 ZEND_END_ARG_INFO()
 
+ZEND_BEGIN_ARG_INFO(arginfo_is_countable, 0)
+	ZEND_ARG_INFO(0, var)
+ZEND_END_ARG_INFO()
+
 ZEND_BEGIN_ARG_INFO_EX(arginfo_count, 0, 0, 1)
 	ZEND_ARG_INFO(0, var)
 	ZEND_ARG_INFO(0, mode)
@@ -3311,6 +3315,7 @@ const zend_function_entry basic_functions[] = { /* {{{ */
 	PHP_FE(shuffle,															arginfo_shuffle)
 	PHP_FE(array_walk,														arginfo_array_walk)
 	PHP_FE(array_walk_recursive,											arginfo_array_walk_recursive)
+	PHP_FE(is_countable,													arginfo_is_countable)
 	PHP_FE(count,															arginfo_count)
 	PHP_FE(end,																arginfo_end)
 	PHP_FE(prev,															arginfo_prev)

ext/standard/php_array.h

@@ -40,6 +40,7 @@ PHP_FUNCTION(uasort);
 PHP_FUNCTION(uksort);
 PHP_FUNCTION(array_walk);
 PHP_FUNCTION(array_walk_recursive);
+PHP_FUNCTION(is_countable);
 PHP_FUNCTION(count);
 PHP_FUNCTION(end);
 PHP_FUNCTION(prev);

ext/standard/tests/array/is_countable.phpt

@@ -0,0 +1,36 @@
+--TEST--
+Check if variables can be counted
+--FILE--
+<?php
+
+$types = [
+    "array"     =>  [],
+    "null"      =>  null,
+    "string"    =>  "test",
+    "integer"   =>  123,
+    "float"     =>  3.14,
+    "true"      =>  true,
+    "false"     =>  false,
+    "object"    =>  (object) [],
+    "simplexml" =>  new ArrayObject(["one", "two", "three"]),
+    "countable" =>  new class implements Countable { function count() { return 1; }},
+];
+
+foreach ($types as $type => $value) {
+    echo "{$type}: ";
+    var_dump(is_countable($value));
+}
+
+?>
+--EXPECTF--
+
+array: bool(true)
+null: bool(false)
+string: bool(false)
+integer: bool(false)
+float: bool(false)
+true: bool(false)
+false: bool(false)
+object: bool(false)
+simplexml: bool(true)
+countable: bool(true)