Add a warning for Timer nodes with very low wait times

Very low wait times behave in unpredictable ways depending on the
rendered frame rate. This is because the timeout signal is only emitted
once per rendered frame (or physics frame, depending on the timer's
process mode).

doc/classes/Timer.xml

@@ -51,7 +51,8 @@
 			[b]Note:[/b] You cannot set this value. To change the timer's remaining time, use [method start].
 		</member>
 		<member name="wait_time" type="float" setter="set_wait_time" getter="get_wait_time" default="1.0">
-			Wait time in seconds.
+			The wait time in seconds.
+			[b]Note:[/b] Timers can only emit once per rendered frame at most (or once per physics frame if [member process_mode] is [constant TIMER_PROCESS_PHYSICS]). This means very low wait times (lower than 0.05 seconds) will behave in significantly different ways depending on the rendered framerate. For very low wait times, it is recommended to use a process loop in a script instead of using a Timer node.
 		</member>
 	</members>
 	<signals>

scene/main/timer.cpp

@@ -84,6 +84,7 @@ void Timer::_notification(int p_what) {
 void Timer::set_wait_time(float p_time) {
 	ERR_FAIL_COND_MSG(p_time <= 0, "Time should be greater than zero.");
 	wait_time = p_time;
+	update_configuration_warning();
 }
 float Timer::get_wait_time() const {
 	return wait_time;
@@ -178,6 +179,19 @@ void Timer::_set_process(bool p_process, bool p_force) {
 	processing = p_process;
 }
 
+String Timer::get_configuration_warning() const {
+	String warning = Node::get_configuration_warning();
+
+	if (wait_time < 0.05 - CMP_EPSILON) {
+		if (warning != String()) {
+			warning += "\n\n";
+		}
+		warning += TTR("Very low timer wait times (< 0.05 seconds) may behave in significantly different ways depending on the rendered or physics frame rate.\nConsider using a script's process loop instead of relying on a Timer for very low wait times.");
+	}
+
+	return warning;
+}
+
 void Timer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_wait_time", "time_sec"), &Timer::set_wait_time);
 	ClassDB::bind_method(D_METHOD("get_wait_time"), &Timer::get_wait_time);

scene/main/timer.h

@@ -73,6 +73,8 @@ public:
 
 	float get_time_left() const;
 
+	String get_configuration_warning() const;
+
 	void set_timer_process_mode(TimerProcessMode p_mode);
 	TimerProcessMode get_timer_process_mode() const;
 	Timer();