Re: confusing ifeq behavior

[John Graham-Cumming]

address@hidden wrote:
> ALL_BLOCKS        := a b c d e
> SOME_BLOCKS       := c d
>
> $(ALL_BLOCKS):
>       @echo "the target is ->$@<-"
> ifeq  ($@, $(filter $@, $(SOME_BLOCKS)))
>       @echo "yes ->$@<=>$(filter $@, $(SOME_BLOCKS))<-"
> else
>       @echo "no  ->$@<=>$(filter $@, $(SOME_BLOCKS))<-"
> endif

That's not going to work because ifeq is handled when the Makefile is 
parsed (not when the rule is when).  While the Makefile is being parsed 
$@ (and other automatic variables) are not set and hence you will not 
get the result you expect.

I think you have two choice: replace your ifeq with $(if) or use $(eval) 
(GNU Make 3.80 or above) to iterate through $(ALL_BLOCKS) and create 
each rule with the appropriate body programmatically.

The $(if) variant would look something like this (I used the GNU Make 
Standard Library to get its seq function):

include gmsl

ALL_BLOCKS        := a b c d e
SOME_BLOCKS       := c d

all: $(ALL_BLOCKS)

$(ALL_BLOCKS):
        @echo "the target is ->$@<-"
        $(if $(call seq,$@,$(filter $@,$(SOME_BLOCKS))),     \
      @echo "yes ->$@<=>$(filter $@, $(SOME_BLOCKS))<-",     \
      @echo "no  ->$@<=>$(filter $@, $(SOME_BLOCKS))<-")

(You could in fact simplify $(call seq,$@,$(filter $@,$(SOME_BLOCKS))) 
to just $(filter $@,$(SOME_BLOCKS)) and get the same result).

John.
--
John Graham-Cumming
address@hidden

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