Fix #79749: Converting FFI instances to bool fails

Casting objects to bool is supposed to yield `true`.  Since the
`cast_object` handler is required now, we have to implement the
`_IS_BOOL` conversion there.

NEWS

@@ -1,6 +1,11 @@
 PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
-?? ??? ????, PHP 8.0.0alpha1
+?? ??? ????, PHP 8.0.0alpha2
+
+- FFI:
+  . Fixed bug #79749 (Converting FFI instances to bool fails). (cmb)
+
+25 Jun 2020, PHP 8.0.0alpha1
 
 - Core:
   . Removed the pdo_odbc.db2_instance_name php.ini directive. (Kalle)

ext/ffi/ffi.c

@@ -1096,6 +1096,9 @@ again:
 		}
 		convert_to_string(writeobj);
 		return SUCCESS;
+	} else if (type == _IS_BOOL) {
+		ZVAL_TRUE(writeobj);
+		return SUCCESS;
 	}
 
 	return FAILURE;
@@ -4642,7 +4645,13 @@ static HashTable *zend_fake_get_gc(zend_object *ob, zval **table, int *n) /* {{{
 
 static int zend_fake_cast_object(zend_object *obj, zval *result, int type)
 {
-	return FAILURE;
+	switch (type) {
+		case _IS_BOOL:
+			ZVAL_TRUE(result);
+			return SUCCESS;
+		default:
+			return FAILURE;
+	}
 }
 
 static ZEND_COLD zend_never_inline void zend_ffi_use_after_free(void) /* {{{ */

ext/ffi/tests/bug79749.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Bug #79749 (Converting FFI instances to bool fails)
+--SKIPIF--
+<?php
+if (!extension_loaded('ffi')) die('skip ffi extension not available');
+?>
+--FILE--
+<?php
+$ffi = FFI::cdef('typedef int dummy;');
+var_dump((bool) $ffi);
+var_dump((bool) FFI::type('int'));
+var_dump((bool) FFI::new('int'));
+?>
+--EXPECT--
+bool(true)
+bool(true)
+bool(true)