-include .check.cmd

comma   := ,
quote   := "
squote  := '
empty   :=
space   := $(empty) $(empty)
space_escape := _-_SPACE_-_
pound := \#

quiet_cmd_a = A
cmd_a = echo "doing a"
quiet_cmd_b = B
cmd_b = echo "doing b"

###
# Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
dot-target = $(dir $@).$(notdir $@)

###
# Escape single quote for use in echo statements
escsq = $(subst $(squote),'\$(squote)',$1)

ifneq ($(KBUILD_NOCMDDEP),1)
# Check if both arguments are the same including their order. Result is empty
# string if equal. User may override this check using make KBUILD_NOCMDDEP=1
arg-check = $(filter-out $(subst $(space),$(space_escape),$(strip $(cmd_$@))), \
                         $(subst $(space),$(space_escape),$(strip $(cmd_$1))))
else
arg-check = $(if $(strip $(cmd_$@)),,1)
endif

# Replace >$< with >$$< to preserve $ when reloading the .cmd file
# (needed for make)
# Replace >#< with >$(pound)< to avoid starting a comment in the .cmd file
# (needed for make)
# Replace >'< with >'\''< to be able to enclose the whole string in '...'
# (needed for the shell)
make-cmd = $(call escsq,$(subst $(pound),$$(pound),$(subst $$,$$$$,$(cmd_$(1)))))

# Find any prerequisites that is newer than target or that does not exist.
# PHONY targets skipped in both cases.
any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)

quiet = quiet_
# echo command.
# Short version is used, if $(quiet) equals `quiet_', otherwise full one.
echo-cmd = $(if $($(quiet)cmd_$(1)),\
	echo '  $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)

cmd = @$(echo-cmd) $(cmd_$(1))

# Execute command if command has changed or prerequisite(s) are updated.
if_changed = $(if $(filter-out undefined,$(origin if_changed_cnt)),          \
	@set -e;                                                             \
	echo "Warning: $@: multiple use of if_changed!" >&2; ,               \
	@set -e $(eval $@: if_changed_cnt := 1) ; )                          \
        $(if $(strip $(any-prereq) $(arg-check)),                            \
	$(echo-cmd) $(cmd_$(1));                                             \
	printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, :)

PHONY += FORCE
FORCE:

a.o: Makefile
	@printf 'if_change_cnt: -%s-\n' '$(origin if_change_cnt)'
	@touch a.o

check: a.o FORCE
	$(call if_changed,a)
	$(call if_changed,b)
	@touch check