[php] Allow testing if an object is SWIG-wrapped

Since the switch to wrapping classes using PHP's C API, we now
internally need to be able to tell if a PHP object is of or derived
from a class that is wrapped by SWIG so we know if we can offset the
zend_object pointer to get to the swig_object_wrapper.  If we try to
do this to an object which isn't wrapped by SWIG then we invoke C/C++
undefined behaviour (and typically get a segmentation fault).

This check is implemented by having a SWIG\wrapped empty interface which
we make all SWIG-wrapped classes implement simply so we can test for it
to detect such classes.

Fixes #2125

Examples/test-suite/php/overload_simple_runme.php

@@ -187,8 +187,9 @@ check("' 11 '", 'char *');
 
 # Check TypeError is thrown when the wrong type is passed.
 check("array()", NULL);
-# FIXME: These need fixing
-#check("function(){}", NULL);
-#check("new stdClass()", NULL);
+check("function(){}", NULL);
+check("new stdClass()", NULL);
+class NotASwigWrappedClass { };
+check("new NotASwigWrappedClass()", NULL);
 
 check::done();

Lib/php/phprun.swg

@@ -93,6 +93,12 @@ static int default_error_code = E_ERROR;
 #define SWIG_GetModule(clientdata) SWIG_Php_GetModule()
 #define SWIG_SetModule(clientdata, pointer) SWIG_Php_SetModule(pointer, *(int*)clientdata)
 
+static zend_class_entry SWIG_Php_swig_wrapped_interface_ce;
+
+#if PHP_MAJOR_VERSION == 7
+# define zend_class_implements_interface(C, I) instanceof_function_ex(C, I, 1)
+#endif
+
 /* used to wrap returned objects in so we know whether they are newobject
    and need freeing, or not */
 typedef struct {
@@ -156,7 +162,18 @@ SWIG_ConvertPtrAndOwn(zval *z, void **ptr, swig_type_info *ty, int flags, swig_o
 
   switch (Z_TYPE_P(z)) {
     case IS_OBJECT: {
-      swig_object_wrapper *value = SWIG_Z_FETCH_OBJ_P(z);
+      zend_object *obj = Z_OBJ_P(z);
+      swig_object_wrapper *value;
+      if (ty && ty->clientdata == (void*)obj->ce) {
+	// Object is exactly the class asked for - this handles common cases cheaply,
+	// and in particular the PHP classes we use to wrap a pointer to a non-class.
+      } else if (!zend_class_implements_interface(obj->ce, &SWIG_Php_swig_wrapped_interface_ce)) {
+	// Not an object we've wrapped.
+	return -1;
+      }
+
+      /* convert and cast value->ptr from value->type to ptr as ty. */
+      value = swig_php_fetch_object(obj);
       if (!ty) {
 	/* They don't care about the target type, so just pass on the pointer! */
 	*ptr = value->ptr;

Source/Modules/php.cxx

@@ -87,6 +87,15 @@ static String *fake_class_name() {
   return result;
 }
 
+static String *swig_wrapped_interface_ce() {
+  static String *result = NULL;
+  if (!result) {
+    result = NewStringf("SWIG_Php_swig_wrapped_interface_ce");
+    Printf(s_oinit, "  INIT_CLASS_ENTRY(%s, \"SWIG\\\\wrapped\", NULL);\n", result);
+  }
+  return result;
+}
+
 /* To reduce code size (generated and compiled) we only want to emit each
  * different arginfo once, so we need to track which have been used.
  */
@@ -163,12 +172,14 @@ static void SwigPHP_emit_pointer_type_registrations() {
   while (ki.key) {
     String *type = ki.key;
 
+    String *swig_wrapped = swig_wrapped_interface_ce();
     Printf(s_creation, "/* class entry for pointer to %s */\n", type);
     Printf(s_creation, "static zend_class_entry *SWIG_Php_ce_%s;\n\n", type);
 
     Printf(s_oinit, "  INIT_CLASS_ENTRY(internal_ce, \"%s\\\\%s\", NULL);\n", "SWIG", type);
     Printf(s_oinit, "  SWIG_Php_ce_%s = zend_register_internal_class(&internal_ce);\n", type);
     Printf(s_oinit, "  SWIG_Php_ce_%s->create_object = swig_ptr_object_new;\n", type);
+    Printv(s_oinit, "  zend_do_implement_interface(SWIG_Php_ce_", type, ", &", swig_wrapped, ");\n", NIL);
     Printf(s_oinit, "  SWIG_TypeClientData(SWIGTYPE%s,SWIG_Php_ce_%s);\n", type, type);
     Printf(s_oinit, "\n");
 
@@ -1633,6 +1644,8 @@ public:
     if (Getattr(n, "abstracts") && !GetFlag(n, "feature:notabstract")) {
       Printf(s_oinit, "  SWIG_Php_ce_%s->ce_flags |= ZEND_ACC_EXPLICIT_ABSTRACT_CLASS;\n", class_name);
     }
+    String *swig_wrapped = swig_wrapped_interface_ce();
+    Printv(s_oinit, "  zend_do_implement_interface(SWIG_Php_ce_", class_name, ", &", swig_wrapped, ");\n", NIL);
 
     {
       Node *node = NewHash();