Package: make
Version: 3.81-5
Severity: minor
Hi,
I ran into some odd behaviour yesterday thanks to a bug in one of my
makefiles, but this seems to have raised some questions about how make
actually should behave in that case. The initial problem was that a
rule was (inadvertantly) being composed something like this:
target: override FOO += bar
target: FOO += baz
Manoj and I discussed this on IRC, and he expressed the opinion that
it was intuitive and correct for all normal assignments after an
override to be ignored (as if that variable really was assigned on
the command line, even if it isn't). This isn't documented as such,
but I don't really disagree with that as being a fairly reasonable
interpretation -- and indeed in my case, the missing override on the
second line _was_ an accident and a bug in that makefile.
I do however have a couple of examples to share that don't behave
according to that interpretation, and which may be of interest (:
In this case, the target specific override appears to be ignored
completely if the variable is passed on the command line ...
override FOO += 1
FOO += 2
a: override BAR += 11
a: BAR += 12
a:
echo "got FOO = $(FOO), BAR = $(BAR)"
$ make -f a.mk
got FOO = 1, BAR = 11
$ make -f a.mk FOO=3 BAR=13
got FOO = 3 1, BAR = 13
This one is even more interesting, the second normal assignment of
BAR succeeds after the override, though the first does not:
override FOO += 1
FOO += 2
a: override BAR += 11
a: BAR += 12
a: BAR += zomg!
a:
@echo "got FOO = $(FOO), BAR = $(BAR)"
$ make -f a.mk
got FOO = 1, BAR = 11 zomg!
$ make -f a.mk FOO=3 BAR=13
got FOO = 3 1, BAR = 13
I don't really have a strong opinion as to how this should be resolved,
empirically the only reasonable assumption I can make at present is that
mixing overrides with normal assignments results in undefined behaviour,
and it wouldn't seem unreasonable to me to formally declare that as such.
OTOH maybe this reveals a glitch in the internal logic somewhere that
should be looked into. For that reason I thought this worth sharing.
Feel free to close it once any questions it raises for you guys are
resolved to your satisfaction.
Cheers,
Ron
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