RE: suppress "target '*' given more than once in the same rule"

[Cook, Malcolm]

> -----Original Message-----
> From: help-make-bounces+mec=stowers.org@gnu.org <help-make-
> bounces+mec=stowers.org@gnu.org> On Behalf Of Belliveau, Fran - 0666 -
> MITLL
> Sent: Tuesday, June 25, 2024 11:03 AM
> To: help-make@gnu.org
> Subject: suppress "target '*' given more than once in the same rule"
> 
> I have a setup where I use include directives to access makefile content used
> by multiple “make” situations throughout a large project.
> 
> As I try to replace a bunch of (heavily simplified) things like:
> 
> FOO_DIR?=fd
> BAH_DIR?=bd
> ####
> $(FOO_DIR)/foo: $(F_HDRS)
> mkdir -p $(FOO_DIR)
> genF $@
> 
> $(BAH_DIR)/foo: $(B_HDRS)
> mkdir -p $(BAH_DIR)
> genB $@
> 
> with a something like
> 
> ####
> $(FOO_DIR) $(BAH_DIR):
> mkdir -p $@
> 
> $(FOO_DIR)/foo: $(HDRS) | $(FOO_DIR)
> gen $@
> 
> $(BAH_DIR)/bah: $(B_HDRS) | $(BAH_DIR)
> genB $@
> 
> I run into “make complaints” when multiple directory variables actually point
> to the same directory.
> This may just be a warning, but it looks like an error to those who do not 
> know
> what is going on.
> 
> I am wondering if there is a way to suppress this with a directive of some 
> sort?
> Is there a function call I might be able to make like $(unique $(FOO_DIR)
> $(BAH_DIR)): ?

Sort removes duplicates also, so perhaps 

$(sort $(FOO_DIR) $(BAH_DIR)): 

However, you might consider entirely changing your approach to auto make any 
directory, as follows:

.SECONDEXPANSION:
.SECONDARY: %/
%/:
## PURPOSE: auto make any directory!!!  IT IS CONSIDERED A "BAD
## PRACTICE" (at least in some circles!) to have directories be
## themselves the direct precondition of a rule.  However, it is VERY
## CONVENIENT, at least when directory paths (with trailing "/") are
## only used as *order-only* prerequisitive (e.g. introduced with a
## vertical bar "|") to rules that target files within them.  Notably,
## when using .SECONDEXPANSION:, $${@D}/ can be used to idiomatically
## & generically refer to the current rule's directory.
        mkdir -p $@

The result of your Makefile could then be written as:

FOO_DIR?=fd
BAH_DIR?=bd

$(FOO_DIR)/foo: $(HDRS) | $${@D}
        gen $@ 

$(BAH_DIR)/bah: $(B_HDRS) | $${@D}
        genB $@

It is not clear to if there are other useful abstractions to additionally be 
factored out.  Your example is short on detail. I can't guess what FOO and BAH 
and their respective HDRS and gen procedure are doing, especially since neither 
HDRS nor B_HDRS variables are used in the recipe.

> 
> 
> Francis Belliveau
> Consultant
> Lincoln Laboratory, Massachusetts Institute of Technology
> 244 Wood Street
> Lexington, MA 02421-6426
> 
>