Convert Object::cast_to() to the static version

Currently we rely on some undefined behavior when Object->cast_to() gets
called with a Null pointer. This used to work fine with GCC < 6 but
newer versions of GCC remove all codepaths in which the this pointer is
Null. However, the non-static cast_to() was supposed to be null safe.

This patch makes cast_to() Null safe and removes the now redundant Null
checks where they existed.

It is explained in this article: https://www.viva64.com/en/b/0226/

5 files changed, 66 insertions, 75 deletions

diff --git a/modules/gdscript/gd_compiler.cpp b/modules/gdscript/gd_compiler.cpp
index c243f88b7a..2aa24e88a9 100644
--- a/modules/gdscript/gd_compiler.cpp
+++ b/modules/gdscript/gd_compiler.cpp
@@ -1971,7 +1971,7 @@ Error GDCompiler::_parse_class(GDScript *p_script, GDScript *p_owner, const GDPa
 					p_script->placeholders.erase(psi); //remove placeholder
 
 					GDInstance *instance = memnew(GDInstance);
-					instance->base_ref = E->get()->cast_to<Reference>();
+					instance->base_ref = Object::cast_to<Reference>(E->get());
 					instance->members.resize(p_script->member_indices.size());
 					instance->script = Ref<GDScript>(p_script);
 					instance->owner = E->get();
diff --git a/modules/gdscript/gd_editor.cpp b/modules/gdscript/gd_editor.cpp
index 863009f1a7..de9903fd70 100644
--- a/modules/gdscript/gd_editor.cpp
+++ b/modules/gdscript/gd_editor.cpp
@@ -372,8 +372,8 @@ static GDCompletionIdentifier _get_type_from_variant(const Variant &p_variant) {
 		Object *obj = p_variant;
 		if (obj) {
 			/*
-			if (obj->cast_to<GDNativeClass>()) {
-				t.obj_type=obj->cast_to<GDNativeClass>()->get_name();
+			if (Object::cast_to<GDNativeClass>(obj)) {
+				t.obj_type=Object::cast_to<GDNativeClass>(obj)->get_name();
 				t.value=Variant();
 			} else {
 			*/
@@ -597,8 +597,7 @@ static bool _guess_expression_type(GDCompletionContext &context, const GDParser:
 
 					if (id.operator String() == "new" && base.value.get_type() == Variant::OBJECT) {
 						Object *obj = base.value;
-						if (obj && obj->cast_to<GDNativeClass>()) {
-							GDNativeClass *gdnc = obj->cast_to<GDNativeClass>();
+						if (GDNativeClass *gdnc = Object::cast_to<GDNativeClass>(obj)) {
 							r_type.type = Variant::OBJECT;
 							r_type.value = Variant();
 							r_type.obj_type = gdnc->get_name();
@@ -1495,48 +1494,45 @@ static void _find_type_arguments(GDCompletionContext &context, const GDParser::N
 			if (id.value.get_type()) {
 				Object *obj = id.value;
 
-				if (obj) {
-
-					GDScript *scr = obj->cast_to<GDScript>();
-					if (scr) {
-						while (scr) {
+				GDScript *scr = Object::cast_to<GDScript>(obj);
+				if (scr) {
+					while (scr) {
 
-							for (const Map<StringName, GDFunction *>::Element *E = scr->get_member_functions().front(); E; E = E->next()) {
-								if (E->get()->is_static() && p_method == E->get()->get_name()) {
-									arghint = "static func " + String(p_method) + "(";
-									for (int i = 0; i < E->get()->get_argument_count(); i++) {
-										if (i > 0)
-											arghint += ", ";
-										else
-											arghint += " ";
-										if (i == p_argidx) {
-											arghint += String::chr(0xFFFF);
-										}
-										arghint += "var " + E->get()->get_argument_name(i);
-										int deffrom = E->get()->get_argument_count() - E->get()->get_default_argument_count();
-										if (i >= deffrom) {
-											int defidx = deffrom - i;
-											if (defidx >= 0 && defidx < E->get()->get_default_argument_count()) {
-												arghint += "=" + E->get()->get_default_argument(defidx).get_construct_string();
-											}
-										}
-										if (i == p_argidx) {
-											arghint += String::chr(0xFFFF);
+						for (const Map<StringName, GDFunction *>::Element *E = scr->get_member_functions().front(); E; E = E->next()) {
+							if (E->get()->is_static() && p_method == E->get()->get_name()) {
+								arghint = "static func " + String(p_method) + "(";
+								for (int i = 0; i < E->get()->get_argument_count(); i++) {
+									if (i > 0)
+										arghint += ", ";
+									else
+										arghint += " ";
+									if (i == p_argidx) {
+										arghint += String::chr(0xFFFF);
+									}
+									arghint += "var " + E->get()->get_argument_name(i);
+									int deffrom = E->get()->get_argument_count() - E->get()->get_default_argument_count();
+									if (i >= deffrom) {
+										int defidx = deffrom - i;
+										if (defidx >= 0 && defidx < E->get()->get_default_argument_count()) {
+											arghint += "=" + E->get()->get_default_argument(defidx).get_construct_string();
 										}
 									}
-									arghint += ")";
-									return; //found
+									if (i == p_argidx) {
+										arghint += String::chr(0xFFFF);
+									}
 								}
+								arghint += ")";
+								return; //found
 							}
-
-							if (scr->get_base().is_valid())
-								scr = scr->get_base().ptr();
-							else
-								scr = NULL;
 						}
-					} else {
-						on_script = obj->get_script();
+
+						if (scr->get_base().is_valid())
+							scr = scr->get_base().ptr();
+						else
+							scr = NULL;
 					}
+				} else {
+					on_script = obj->get_script();
 				}
 			}
 
@@ -2207,30 +2203,27 @@ Error GDScriptLanguage::complete_code(const String &p_code, const String &p_base
 					if (t.value.get_type()) {
 						Object *obj = t.value;
 
-						if (obj) {
-
-							GDScript *scr = obj->cast_to<GDScript>();
-							if (scr) {
-								while (scr) {
+						GDScript *scr = Object::cast_to<GDScript>(obj);
+						if (scr) {
+							while (scr) {
 
-									if (!isfunction) {
-										for (const Map<StringName, Variant>::Element *E = scr->get_constants().front(); E; E = E->next()) {
-											options.insert(E->key());
-										}
+								if (!isfunction) {
+									for (const Map<StringName, Variant>::Element *E = scr->get_constants().front(); E; E = E->next()) {
+										options.insert(E->key());
 									}
-									for (const Map<StringName, GDFunction *>::Element *E = scr->get_member_functions().front(); E; E = E->next()) {
-										if (E->get()->is_static())
-											options.insert(E->key());
-									}
-
-									if (scr->get_base().is_valid())
-										scr = scr->get_base().ptr();
-									else
-										scr = NULL;
 								}
-							} else {
-								on_script = obj->get_script();
+								for (const Map<StringName, GDFunction *>::Element *E = scr->get_member_functions().front(); E; E = E->next()) {
+									if (E->get()->is_static())
+										options.insert(E->key());
+								}
+
+								if (scr->get_base().is_valid())
+									scr = scr->get_base().ptr();
+								else
+									scr = NULL;
 							}
+						} else {
+							on_script = obj->get_script();
 						}
 					}
 
@@ -2822,9 +2815,9 @@ Error GDScriptLanguage::lookup_code(const String &p_code, const String &p_symbol
 							Object *obj = value;
 							if (obj) {
 
-								if (obj->cast_to<GDNativeClass>()) {
+								if (Object::cast_to<GDNativeClass>(obj)) {
 									r_result.type = ScriptLanguage::LookupResult::RESULT_CLASS;
-									r_result.class_name = obj->cast_to<GDNativeClass>()->get_name();
+									r_result.class_name = Object::cast_to<GDNativeClass>(obj)->get_name();
 
 								} else {
 									r_result.type = ScriptLanguage::LookupResult::RESULT_CLASS;
diff --git a/modules/gdscript/gd_function.cpp b/modules/gdscript/gd_function.cpp
index 13a7480a36..3b78573f58 100644
--- a/modules/gdscript/gd_function.cpp
+++ b/modules/gdscript/gd_function.cpp
@@ -371,7 +371,7 @@ Variant GDFunction::call(GDInstance *p_instance, const Variant **p_args, int p_a
 				Object *obj_A = *a;
 				Object *obj_B = *b;
 
-				GDScript *scr_B = obj_B->cast_to<GDScript>();
+				GDScript *scr_B = Object::cast_to<GDScript>(obj_B);
 
 				bool extends_ok = false;
 
@@ -397,7 +397,7 @@ Variant GDFunction::call(GDInstance *p_instance, const Variant **p_args, int p_a
 
 				} else {
 
-					GDNativeClass *nc = obj_B->cast_to<GDNativeClass>();
+					GDNativeClass *nc = Object::cast_to<GDNativeClass>(obj_B);
 
 					if (!nc) {
 
@@ -1434,7 +1434,7 @@ Variant GDFunctionState::_signal_callback(const Variant **p_args, int p_argcount
 	// If the return value is a GDFunctionState reference,
 	// then the function did yield again after resuming.
 	if (ret.is_ref()) {
-		GDFunctionState *gdfs = ret.operator Object *()->cast_to<GDFunctionState>();
+		GDFunctionState *gdfs = Object::cast_to<GDFunctionState>((Object *)&ret);
 		if (gdfs && gdfs->function == function)
 			completed = false;
 	}
@@ -1490,7 +1490,7 @@ Variant GDFunctionState::resume(const Variant &p_arg) {
 	// If the return value is a GDFunctionState reference,
 	// then the function did yield again after resuming.
 	if (ret.is_ref()) {
-		GDFunctionState *gdfs = ret.operator Object *()->cast_to<GDFunctionState>();
+		GDFunctionState *gdfs = Object::cast_to<GDFunctionState>((Object *)&ret);
 		if (gdfs && gdfs->function == function)
 			completed = false;
 	}
diff --git a/modules/gdscript/gd_parser.cpp b/modules/gdscript/gd_parser.cpp
index de8daedb8b..820304184e 100644
--- a/modules/gdscript/gd_parser.cpp
+++ b/modules/gdscript/gd_parser.cpp
@@ -3957,7 +3957,7 @@ void GDParser::_parse_class(ClassNode *p_class) {
 							member._export.usage |= PROPERTY_USAGE_SCRIPT_VARIABLE;
 							if (cn->value.get_type() == Variant::OBJECT) {
 								Object *obj = cn->value;
-								Resource *res = obj->cast_to<Resource>();
+								Resource *res = Object::cast_to<Resource>(obj);
 								if (res == NULL) {
 									_set_error("Exported constant not a type or resource.");
 									return;
diff --git a/modules/gdscript/gd_script.cpp b/modules/gdscript/gd_script.cpp
index fbc7816f91..68c1fb3635 100644
--- a/modules/gdscript/gd_script.cpp
+++ b/modules/gdscript/gd_script.cpp
@@ -73,7 +73,7 @@ Variant GDNativeClass::_new() {
 		ERR_FAIL_COND_V(!o, Variant());
 	}
 
-	Reference *ref = o->cast_to<Reference>();
+	Reference *ref = Object::cast_to<Reference>(o);
 	if (ref) {
 		return REF(ref);
 	} else {
@@ -161,7 +161,7 @@ Variant GDScript::_new(const Variant **p_args, int p_argcount, Variant::CallErro
 		owner = memnew(Reference); //by default, no base means use reference
 	}
 
-	Reference *r = owner->cast_to<Reference>();
+	Reference *r = Object::cast_to<Reference>(owner);
 	if (r) {
 		ref = REF(r);
 	}
@@ -397,7 +397,7 @@ ScriptInstance *GDScript::instance_create(Object *p_this) {
 	}
 
 	Variant::CallError unchecked_error;
-	return _create_instance(NULL, 0, p_this, p_this->cast_to<Reference>(), unchecked_error);
+	return _create_instance(NULL, 0, p_this, Object::cast_to<Reference>(p_this), unchecked_error);
 }
 bool GDScript::instance_has(const Object *p_this) const {
 
@@ -575,9 +575,7 @@ void GDScript::update_exports() {
 	//print_line("update exports for "+get_path()+" ic: "+itos(copy.size()));
 	for (Set<ObjectID>::Element *E = copy.front(); E; E = E->next()) {
 		Object *id = ObjectDB::get_instance(E->get());
-		if (!id)
-			continue;
-		GDScript *s = id->cast_to<GDScript>();
+		GDScript *s = Object::cast_to<GDScript>(id);
 		if (!s)
 			continue;
 		s->update_exports();
@@ -2006,11 +2004,11 @@ Error ResourceFormatSaverGDScript::save(const String &p_path, const RES &p_resou
 
 void ResourceFormatSaverGDScript::get_recognized_extensions(const RES &p_resource, List<String> *p_extensions) const {
 
-	if (p_resource->cast_to<GDScript>()) {
+	if (Object::cast_to<GDScript>(*p_resource)) {
 		p_extensions->push_back("gd");
 	}
 }
 bool ResourceFormatSaverGDScript::recognize(const RES &p_resource) const {
 
-	return p_resource->cast_to<GDScript>() != NULL;
+	return Object::cast_to<GDScript>(*p_resource) != NULL;
 }