I am trying to modify the AOSP build system to run a script after 'make dist'
I have code that does what I want it to.... but I don't really understand it and would love an explanation and what is happening. The file I am looking at is:
https://android.googlesource.com/platform/build.git/+/master/core/distdir.mk
.PHONY: dist
dist: ;
dist_goal := $(strip $(filter dist,$(MAKECMDGOALS)))
MAKECMDGOALS := $(strip $(filter-out dist,$(MAKECMDGOALS)))
ifeq (,$(strip $(filter-out $(INTERNAL_MODIFIER_TARGETS),$(MAKECMDGOALS))))
# The commandline was something like "make dist" or "make dist showcommands".
# Add a dependency on a real target.
dist: $(DEFAULT_GOAL)
endif
The part that is confusing me is how there are two definitions for dist: but no warnings. If I had a recipe on to the second dist: target it will generate a warning about dist being redefined. What is the point of this second target?
dist: ;
just says, "to update dist target, do nothing". Without this, if the second part were not present, Make would not know what how to make dist. (In fact the "empty recipe" here ; is not really needed - it is only needed for specific situations, and this is not one of them - without it, you would still be doing "nothing" here)
If the second part is present:
dist: $(DEFAULT_GOAL)
that means, "to update dist target, update $(DEFAULT_GOAL)
If both parts are present, we update $(DEFAULT_GOAL) and then do nothing more.
In general, you can have one explicit rule for a target with a recipe present (here, the recipe is just ;), and then you can have other rules without recipes, they just establish additional dependencies as they are noted. There is no ambiguity which recipe to execute and Make is happy.