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BACKEND_GENERATION_SCRIPT ?= config.status

A traditional rule would look like this:

backend.%:

@echo do stuff

But with -j<n>, and multiple items in BUILD_BACKEND_FILES, the command would

run multiple times in parallel.

"Fortunately", make has some weird semantics for pattern rules: if there are

multiple targets in a pattern rule and each of them is matched at most once,

the command will only run once. So:

backend%RecursiveMakeBackend backend%FasterMakeBackend:

@echo do stuff

backend: backend.RecursiveMakeBackend backend.FasterMakeBackend

would only execute the command once.

Credit where due: http://stackoverflow.com/questions/2973445/gnu-makefile-rule-generating-a-few-targets-from-a-single-source-file/3077254#3077254

$(subst .,%,$(BUILD_BACKEND_FILES)): @echo 'Build configuration changed. Regenerating backend.' $(PYTHON) $(BACKEND_GENERATION_SCRIPT)

define build_backend_rule $(1): $$(wildcard $$(shell cat $(1).in))

endef $(foreach file,$(BUILD_BACKEND_FILES),$(eval $(call build_backend_rule,$(file))))