gcode_macro: Add the ability to define custom g-code macros

Add the ability to add a custom g-code command that in turn executes
one or more configured g-code commands.

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

klippy/extras/gcode_macro.py

@@ -0,0 +1,29 @@
+# Add ability to define custom g-code macros
+#
+# Copyright (C) 2018  Kevin O'Connor <kevin@koconnor.net>
+#
+# This file may be distributed under the terms of the GNU GPLv3 license.
+
+class GCodeMacro:
+    def __init__(self, config):
+        self.alias = config.get_name().split()[1].upper()
+        self.script = config.get('gcode')
+        printer = config.get_printer()
+        self.gcode = printer.lookup_object('gcode')
+        try:
+            self.gcode.register_command(self.alias, self.cmd, desc=self.cmd_desc)
+        except self.gcode.error as e:
+            raise config.error(str(e))
+        self.in_script = False
+    cmd_desc = "G-Code macro"
+    def cmd(self, params):
+        if self.in_script:
+            raise self.gcode.error("Macro %s called recursively" % (self.alias,))
+        self.in_script = True
+        try:
+            self.gcode.run_script(self.script)
+        finally:
+            self.in_script = False
+
+def load_config_prefix(config):
+    return GCodeMacro(config)