py/py.mk: Add check that any specified USER_C_MODULES folder exists.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

py/py.mk

@@ -33,6 +33,8 @@ ifneq ($(USER_C_MODULES),)
 # pre-define USERMOD variables as expanded so that variables are immediate
 # expanded as they're added to them
 
+$(if $(wildcard $(USER_C_MODULES)/.),,$(error USER_C_MODULES doesn't exist: $(abspath $(USER_C_MODULES))))
+
 # C/C++ files that are included in the QSTR/module build
 SRC_USERMOD_C :=
 SRC_USERMOD_CXX :=