I was trying to compile, with the linking of an external library, but the build variables (described in build.md) did not seem to have effect for libraries. I know the make process was reading them at some point from my myapp.mk file, because the INCLUDE_DIRS variable was read. Basically, it seemed when building a $(APP).elf file (a rule from module.mk), it never read the LIB_DIRS, LIBS, or LIB_DEPS from my myapp.mk file.
Eventually, I added a variable inside the $(TARGET_BASE).elf rule in model.mk of $(LIB_MINE):
$(VERBOSE)$(CPP) $(CFLAGS) $(ALLOBJ) --output $@ $(LDFLAGS) $(LIB_MINE)
and set $(LIB_MINE) in my makefile as such:
cd firmware/main && make all PLATFORM=photon APP=myapp LIB_MINE=/the/full/path/foo.a
This seems sloppy and something I will have to manually maintain. Any help would be appreciated.