build/rebuild-backend.mk

   1 # This Source Code Form is subject to the terms of the Mozilla Public
   2 # License, v. 2.0. If a copy of the MPL was not distributed with this
   3 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
   4
   5 BACKEND_GENERATION_SCRIPT ?= config.status
   6
   7 # A traditional rule would look like this:
   8 #    backend.%:
   9 #        @echo do stuff
  10 #
  11 # But with -j<n>, and multiple items in BUILD_BACKEND_FILES, the command would
  12 # run multiple times in parallel.
  13 #
  14 # "Fortunately", make has some weird semantics for pattern rules: if there are
  15 # multiple targets in a pattern rule and each of them is matched at most once,
  16 # the command will only run once. So:
  17 #     backend%RecursiveMakeBackend backend%FasterMakeBackend:
  18 #         @echo do stuff
  19 #     backend: backend.RecursiveMakeBackend backend.FasterMakeBackend
  20 # would only execute the command once.
  21 #
  22 # Credit where due: http://stackoverflow.com/questions/2973445/gnu-makefile-rule-generating-a-few-targets-from-a-single-source-file/3077254#3077254
  23 $(subst .,%,$(BUILD_BACKEND_FILES)):
  24         @echo 'Build configuration changed. Regenerating backend.'
  25         $(PYTHON) $(BACKEND_GENERATION_SCRIPT)
  26
  27 define build_backend_rule
  28 $(1): $$(wildcard $$(shell cat $(1).in))
  29
  30 endef
  31 $(foreach file,$(BUILD_BACKEND_FILES),$(eval $(call build_backend_rule,$(file))))