On Mon, 2012-04-02 at 23:13 -0400, Brown, Ruben wrote:
> Is this behavior by design or an unfortunately long lived bug? If it
> is by design, what purpose does maintaining this behavior serve?
>
> ***Makefile***
> .PHONY: all A B
> all: A
> VAR := 0
> A: B
> A: VAR:= 1
> B:
> @echo VAR=$(VAR) @ B
> A:
> @echo VAR=$(VAR) @ A
>
> ***Observed Behavior***
> It appears that the dependent target B is always executed after the
> evaluation of VAR:=1, when target A is the entry point.
This is by design. See the GNU make manual definition of the
target-specific variables feature:
There is one more special feature of target-specific variables: when
you define a target-specific variable that variable value is also in
effect for all prerequisites of this target, and all their
prerequisites, etc. (unless those prerequisites override that variable
with their own target-specific variable value). So, for example, a
statement like this:
prog : CFLAGS = -g
prog : prog.o foo.o bar.o
will set `CFLAGS' to `-g' in the command script for `prog', but it will
also set `CFLAGS' to `-g' in the command scripts that create `prog.o',
`foo.o', and `bar.o', and any command scripts which create their
prerequisites.
The reason for it is seen in the example above. Another common use is
something like this:
all: <all targets>
debug: CFLAGS += -g
debug: all
Now if you run "make" or "make all", you get non-debug versions. If you
run "make debug" you get the extra -g flag added to every target.
This behavior is inherited from other versions of make, which
implemented the target-specific variable feature first.
In GNU make 3.82 you can use the "private" keyword to avoid this
behavior (see the section "Suppressing Inheritance").
--
-------------------------------------------------------------------------------
Paul D. Smith <psm...@gnu.org> Find some GNU make tips at:
http://www.gnu.org http://make.mad-scientist.net
"Please remain calm...I may be mad, but I am a professional." --Mad Scientist
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