Makefile: conditionals inside define

Question

I am trying to check that variable value is yes or no, but the following always fails:

FLAG1 ?= no
FLAG2 ?= yes
define check_
 ifneq ($(filter $(2),$($(1))),$($(1)))
 $(error Bad $(1) argument)
 endif
endef
$(call check_,FLAG1,yes no)
$(call check_,FLAG2,yes no)

What am I doing wrong?

• HardcoreHenry: For one, you add a space to the first parameter...

Answer 1

FLAG1 ?= no
FLAG2 ?= yes
define check_
 $(if $(filter $($(1)),$(2)),,$(error BAD $(1) argument))
endef
$(call check_,FLAG1,yes no)
$(call check_,FLAG2,yes no)

Notice that you added a space before FLAG1, which means $$(1) resolves to $( FLAG1), which in turn resolves to blank. The next part is that I'm not sure about is the use if ifneq inside of a define. You can use $(if ) instead

---- EDIT ------

Actually, it's a combination of the missing space and @MadScientists answer... The following also works:

define check_
 ifneq ($(filter $($(1)),$(2)),$($(1)))
 $$(error Bad $(1) argument [$($(1))] / [$(filter $($(1)),$(2))])
 endif
endef
$(eval $(call check_,FLAG1,yes no))

Thus ifneq can be used inside of a macro... (and as @MadScientist pointed out, you have to escape the $ in front of $(error) to prevent it from being expanded by call...)

• user2052436: Space was a typo, did not work without space either. Apparently, ifeq/ifneq do not work inside define, as you said.
• user2052436: The only issue with filter function is that make FLAG1="yes no" passes the test. Is there a simple fix?
• HardcoreHenry: You would have to do some trickery with $(words) like so: $(if $(filter-out $(2),$($(1)))$(filter-out 1,$(words $($(1)))),$(error blah)). This would fail for any FLAG1 with more than one word.
• user2052436: I came up with this: $(filter $(addsuffix s,$(addprefix p,$(2))),p$($(1))s)
• BUFU: Why do you not need to double the $ in front of filter and before the $(1) like so: ifneq ($$(filter $$($(1)),$(2)),$$($(1)))? Doesn't call remove one layer for everything but the $(1) $(2) etc it inserts?

Answer 2

You can't use plain call with a multi-line macro. You have to use $(eval $(call ...)) if the result of the call function consists of more than one line of makefile content.

You can use this:

define check_
 ifneq ($$(filter $(2),$$($(1))),$$($(1)))
 $$(error Bad $(1) argument)
 endif
endef

Basically, anything you want to be interpreted by the eval needs to be escaped so that call doesn't see it.

• user2052436: $(eval $(call ...)) did not help. Looks like inside check_ it translates $$(1) into 1ドル instead of $(FLAG1)
• MadScientist: If you use eval you need an extra level of escaping. I'll update the answer.