Add a flag to make the connection automatically emit the source object.

core/object/object.cpp

@@ -1024,6 +1024,7 @@ Error Object::emit_signalp(const StringName &p_name, const Variant **p_args, int
 	OBJ_DEBUG_LOCK
 
 	Error err = OK;
+	Variant appended_self;
 
 	for (int i = 0; i < ssize; i++) {
 		const Connection &c = slot_map.getv(i).conn;
@@ -1037,6 +1038,18 @@ Error Object::emit_signalp(const StringName &p_name, const Variant **p_args, int
 		const Variant **args = p_args;
 		int argc = p_argcount;
 
+		if (c.flags & CONNECT_APPEND_SOURCE_OBJECT) {
+			argc += 1;
+			args = (const Variant **)alloca(sizeof(Variant *) * argc);
+			for (int j = 0; j < p_argcount; j++) {
+				args[j] = (const Variant *)p_args[j];
+			}
+			if (unlikely(appended_self.get_type() == Variant::NIL)) {
+				appended_self = this;
+			}
+			args[p_argcount] = &appended_self;
+		}
+
 		if (c.flags & CONNECT_DEFERRED) {
 			MessageQueue::get_singleton()->push_callablep(c.callable, args, argc, true);
 		} else {
@@ -1582,6 +1595,7 @@ void Object::_bind_methods() {
 	BIND_ENUM_CONSTANT(CONNECT_PERSIST);
 	BIND_ENUM_CONSTANT(CONNECT_ONE_SHOT);
 	BIND_ENUM_CONSTANT(CONNECT_REFERENCE_COUNTED);
+	BIND_ENUM_CONSTANT(CONNECT_APPEND_SOURCE_OBJECT);
 }
 
 void Object::set_deferred(const StringName &p_property, const Variant &p_value) {

core/object/object.h

@@ -553,10 +553,11 @@ class Object {
 public:
 	enum ConnectFlags {
 		CONNECT_DEFERRED = 1,
-		CONNECT_PERSIST = 2, // hint for scene to save this connection
+		CONNECT_PERSIST = 2, // Hint for scene to save this connection
 		CONNECT_ONE_SHOT = 4,
 		CONNECT_REFERENCE_COUNTED = 8,
 		CONNECT_INHERITED = 16, // Used in editor builds.
+		CONNECT_APPEND_SOURCE_OBJECT = 32, // Hint for the connection dialog to append the source object as the last call argument.
 	};
 
 	struct Connection {

doc/classes/Object.xml

@@ -955,5 +955,8 @@
 		<constant name="CONNECT_REFERENCE_COUNTED" value="8" enum="ConnectFlags">
 			Reference-counted connections can be assigned to the same [Callable] multiple times. Each disconnection decreases the internal counter. The signal fully disconnects only when the counter reaches 0.
 		</constant>
+		<constant name="CONNECT_APPEND_SOURCE_OBJECT" value="32" enum="ConnectFlags">
+			Automatically sends the source object when emitting the signal. Mainly used to improve the usability of the connection dialog. If this flag bit is enabled, the source object will be appended right after the original arguments of the signal.
+		</constant>
 	</constants>
 </class>

editor/connections_dialog.cpp

@@ -186,6 +186,8 @@ void ConnectDialog::_unbind_count_changed(double p_count) {
 			e->set_read_only(p_count > 0);
 		}
 	}
+
+	append_source->set_disabled(p_count > 0);
 }
 
 void ConnectDialog::_method_selected() {
@@ -532,6 +534,10 @@ bool ConnectDialog::get_one_shot() const {
 	return one_shot->is_pressed();
 }
 
+bool ConnectDialog::get_append_source() const {
+	return !append_source->is_disabled() && append_source->is_pressed();
+}
+
 /*
  * Returns true if ConnectDialog is being used to edit an existing connection.
  */
@@ -563,12 +569,13 @@ void ConnectDialog::init(const ConnectionData &p_cd, const PackedStringArray &p_
 
 	bool b_deferred = (p_cd.flags & CONNECT_DEFERRED) == CONNECT_DEFERRED;
 	bool b_oneshot = (p_cd.flags & CONNECT_ONE_SHOT) == CONNECT_ONE_SHOT;
+	bool b_append_source = (p_cd.flags & CONNECT_APPEND_SOURCE_OBJECT) == CONNECT_APPEND_SOURCE_OBJECT;
 
 	deferred->set_pressed(b_deferred);
 	one_shot->set_pressed(b_oneshot);
+	append_source->set_pressed(b_append_source);
 
 	unbind_count->set_max(p_signal_args.size());
-
 	unbind_count->set_value(p_cd.unbinds);
 	_unbind_count_changed(p_cd.unbinds);
 
@@ -783,6 +790,12 @@ ConnectDialog::ConnectDialog() {
 	one_shot->set_tooltip_text(TTR("Disconnects the signal after its first emission."));
 	hbox->add_child(one_shot);
 
+	append_source = memnew(CheckBox);
+	append_source->set_h_size_flags(0);
+	append_source->set_text(TTR("Append source"));
+	append_source->set_tooltip_text(TTR("The source object is automatically sent when the signal is emitted."));
+	vbc_right->add_child(append_source);
+
 	cdbinds = memnew(ConnectDialogBinds);
 
 	error = memnew(AcceptDialog);
@@ -855,7 +868,8 @@ void ConnectionsDock::_make_or_edit_connection() {
 	}
 	bool b_deferred = connect_dialog->get_deferred();
 	bool b_oneshot = connect_dialog->get_one_shot();
-	cd.flags = CONNECT_PERSIST | (b_deferred ? CONNECT_DEFERRED : 0) | (b_oneshot ? CONNECT_ONE_SHOT : 0);
+	bool b_append_source = connect_dialog->get_append_source();
+	cd.flags = CONNECT_PERSIST | (b_deferred ? CONNECT_DEFERRED : 0) | (b_oneshot ? CONNECT_ONE_SHOT : 0) | (b_append_source ? CONNECT_APPEND_SOURCE_OBJECT : 0);
 
 	// Conditions to add function: must have a script and must not have the method already
 	// (in the class, the script itself, or inherited).
@@ -888,6 +902,28 @@ void ConnectionsDock::_make_or_edit_connection() {
 	if (add_script_function) {
 		PackedStringArray script_function_args = connect_dialog->get_signal_args();
 		script_function_args.resize(script_function_args.size() - cd.unbinds);
+
+		// Append the source.
+		if (b_append_source) {
+			String class_name = cd.source->get_class();
+			bool found = false;
+
+			Ref<Script> source_script = cd.source->get_script();
+			if (source_script.is_valid()) {
+				found = source_script->has_script_signal(cd.signal);
+			}
+			if (!found) {
+				found = ClassDB::has_signal(class_name, cd.signal, true);
+			}
+
+			while (!found) {
+				class_name = ClassDB::get_parent_class(class_name);
+				found = ClassDB::has_signal(class_name, cd.signal, true);
+			}
+
+			script_function_args.push_back("source:" + class_name);
+		}
+
 		for (int i = 0; i < cd.binds.size(); i++) {
 			script_function_args.push_back("extra_arg_" + itos(i) + ":" + Variant::get_type_name(cd.binds[i].get_type()));
 		}
@@ -1365,6 +1401,9 @@ void ConnectionsDock::update_tree() {
 				if (cd.flags & CONNECT_ONE_SHOT) {
 					path += " (one-shot)";
 				}
+				if (cd.flags & CONNECT_APPEND_SOURCE_OBJECT) {
+					path += " (source)";
+				}
 				if (cd.unbinds > 0) {
 					path += " unbinds(" + itos(cd.unbinds) + ")";
 				} else if (!cd.binds.is_empty()) {

editor/connections_dialog.h

@@ -133,6 +133,7 @@ class ConnectDialog : public ConfirmationDialog {
 	OptionButton *type_list = nullptr;
 	CheckBox *deferred = nullptr;
 	CheckBox *one_shot = nullptr;
+	CheckBox *append_source = nullptr;
 	CheckButton *advanced = nullptr;
 	Vector<Control *> bind_controls;
 
@@ -178,6 +179,7 @@ class ConnectDialog : public ConfirmationDialog {
 
 	bool get_deferred() const;
 	bool get_one_shot() const;
+	bool get_append_source() const;
 	bool is_editing() const;
 
 	void init(const ConnectionData &p_cd, const PackedStringArray &p_signal_args, bool p_edit = false);