Order-only Prerequisite Bug or User Error?

[Davidson, Josh]

I am experiencing a weird issue with order-only prerequisites in GNU Make v3.8.  My expectation is based on the following statement from section 4.2 Types of Prerequisites of the GNU Make manual: “Also, you may still declare multiple lines of prerequisites for the same target: they are appended appropriately.”

 

Consider this dumbed down example (as viewed from a terminal):

 

-------------------Begin Example-------------------------------

%> cat Makefile.mk

 

d := temp

obj_$(d) := $(d)/obj

 

include Blah.mk

 

d := wtf

obj_$(d) := $(d)/obj

 

include Blah.mk

 

%> cat Blah.mk

 

VPATH := $(VPATH) $(d)

 

#This doesn't work

$(obj_$(d))/%.o: | $(obj_$(d))

$(obj_$(d))/%.o: %.c

            touch $@

 

#This does work

#$(obj_$(d))/%.o: %.c | $(obj_$(d))

#          touch $@

 

 

$(obj_$(d)):

            mkdir $@

 

%> mkdir temp

%> mkdir wtf

%> touch temp/blah.c

%> gmake –f Makefile.mk temp/obj/blah.o

Touch temp/obj/blah.o

Cannot create temp/obj/blah.o: No such file or directory

gmake: ***[temp/obj/blah.o] Error 1

 

-------------------End Example-------------------------------

 

If you’ll notice, the Blah.mk that is being included from the main makefile has a section commented out where the order-only prerequisite is combined with the implicit rule.  That works as expected.  From my interpretation of the manual, it what is currently uncommented and failing should also work.  I should note that most of the time this does work correctly.  Not sure is it has to do with simply expanded variables or what the deal is.

 

Josh