Andres Freund <andres@anarazel.de> writes:
> On 2021-05-11 14:30:10 -0400, Andrew Dunstan wrote:
>> I'm not aware of any other case where we generate an in-tree file from a
>> vpath, which is why it feels strange.
> Yea, it is a bit odd, agreed. We don't have many generated sources
> inside the git repo (vs in the tarball). The most prominent one is
> configure, obviously...
I think this is overly cute. As a counterexample, the rules to regenerate
gram.c and similar files don't bend over backwards like that to force the
output to be in the srcdir.
I haven't dug in the gmake manual to be sure, but I think that in a VPATH
build, $@ will refer to the file in the srcdir if the file exists there
but is out-of-date. So if you go with the straightforward use of $< and
$@, I believe it will in fact work. The only way to make it fail under
VPATH would be to do
rm path/to/srcdir/Gen_dummy_probes.pl; make Gen_dummy_probes.pl
which I think is sufficiently unlikely to not be a problem. In fact,
one could argue that building Gen_dummy_probes.pl in the VPATH dir
is exactly what the user is trying to make happen if she does this.
In short: don't be cuter than the longstanding bison/flex rules are.
regards, tom lane