🔧 Allow float Z_PROBE_LOW_POINT (MarlinFirmware#26711)

Author: petaflot

Marlin/src/inc/SanityCheck.h

@@ -1508,9 +1508,7 @@ static_assert(NUM_SERVOS <= NUM_SERVO_PLUGS, "NUM_SERVOS (or some servo index) i
     #endif
   #endif
 
-  #if Z_PROBE_LOW_POINT > 0
-    #error "Z_PROBE_LOW_POINT must be less than or equal to 0."
-  #endif
+  static_assert(Z_PROBE_LOW_POINT <= 0, "Z_PROBE_LOW_POINT must be less than or equal to 0.");
 
   #if ENABLED(PROBE_ACTIVATION_SWITCH)
     #ifndef PROBE_ACTIVATION_SWITCH_STATE

Marlin/src/module/probe.cpp

@@ -1010,6 +1010,10 @@ float Probe::probe_at_point(const_float_t rx, const_float_t ry, const ProbePtRai
 
     // If any error occurred stow the probe and set an alert
     if (isnan(measured_z)) {
+      // TODO: Disable steppers (unless G29_RETRY_AND_RECOVER or G29_HALT_ON_FAILURE are set).
+      // Something definitely went wrong at this point, so it might be a good idea to release the steppers.
+      // The user may want to quickly move the carriage or bed by hand to avoid bed damage from the (hot) nozzle.
+      // This would also benefit from the contemplated "Audio Alerts" feature.
       stow();
       LCD_MESSAGE(MSG_LCD_PROBING_FAILED);
       #if DISABLED(G29_RETRY_AND_RECOVER)