virtual_sdcard: Define a default for on_gcode_error

If on_gcode_error is not specified, default to running the
TURN_OFF_HEATERS command.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Config_Changes.md

@@ -8,6 +8,12 @@ All dates in this document are approximate.
 
 ## Changes
 
+20240415: The `on_error_gcode` parameter in the `[virtual_sdcard]`
+config section now has a default. If this parameter is not specified
+it now defaults to `TURN_OFF_HEATERS`. If the previous behavior is
+desired (take no default action on an error during a virtual_sdcard
+print) then define `on_error_gcode` with an empty value.
+
 20240313: The `max_accel_to_decel` parameter in the `[printer]` config
 section has been deprecated. The `ACCEL_TO_DECEL` parameter of the
 `SET_VELOCITY_LIMIT` command has been deprecated. The

docs/Config_Reference.md

@@ -1472,7 +1472,8 @@ path:
 #   be provided.
 #on_error_gcode:
 #   A list of G-Code commands to execute when an error is reported.
-
+#   See docs/Command_Templates.md for G-Code format. The default is to
+#   run TURN_OFF_HEATERS.
 ```
 
 ### [sdcard_loop]

klippy/extras/virtual_sdcard.py

@@ -7,6 +7,12 @@
 
 VALID_GCODE_EXTS = ['gcode', 'g', 'gco']
 
+DEFAULT_ERROR_GCODE = """
+{% if 'heaters' in printer %}
+   TURN_OFF_HEATERS
+{% endif %}
+"""
+
 class VirtualSD:
     def __init__(self, config):
         self.printer = config.get_printer()
@@ -27,7 +33,7 @@ def __init__(self, config):
         # Error handling
         gcode_macro = self.printer.load_object(config, 'gcode_macro')
         self.on_error_gcode = gcode_macro.load_template(
-            config, 'on_error_gcode', '')
+            config, 'on_error_gcode', DEFAULT_ERROR_GCODE)
         # Register commands
         self.gcode = self.printer.lookup_object('gcode')
         for cmd in ['M20', 'M21', 'M23', 'M24', 'M25', 'M26', 'M27']: