bug#20699: bug#37499: Wrong location of deps directory when using AC_SUBST

[Karl Berry]

Hi Hans-Bernhard - you wrote recently, in connection with bug#37499:

    This may actually be related to my ancient bug entry #20699.

Comparing this bug (https://bugs.gnu.org/20699) with 37499, yeah,
perhaps they are related, but I tend to think not, since the OP in 37499
is not using subdir-objects, which seems to be the key point here.

Looking at 20699, as usual, I'm confused. Sorry. It seems like Automake
is just following instructions. The docs/Makefile.am declares a
dependency on ../src/main.c, so it removes ../src/*.o. How could it
guess otherwise? I feel like I'm missing some basic point.

And, even if it was refined to remove only ../src/main.o (and using *.o
is surely intentional, so I'd be disinclined to make such a change even
if I could figure out how), I gather that wouldn't solve your problem.

It does not seem feasible or desirable to somehow compute that
./src/whatever is not technically a "subdirectory" and therefore have
subdir-objects do nothing with those files. And only for the clean
targets? I can't wrap my head around this.

Let me step back and ask more generally: Is there some behavior in
current Automake (1.16.3) which is affecting current Gnuplot adversely?
If there is a practical problem that can be fixed, I want to fix it, but
making sweeping changes to how subdir-objects behaves doesn't sound like
a good idea.

As for your remark:

  the tool complains that the subdir-objects is about to be forced on me
  soon. That doesn't bode well.

Well, I agree, but:

1) what tool? Automake? And "forced" how?

2) as far as I'm concerned, Automake is not going to "force" anything
new on anyone in the future. I deplore changes that gratuitously break
code that has worked perfectly well for many years, and don't want to
make any such changes. So if current automake works well enough for you,
it shouldn't break in the future. At least until someone other than me
starts working on it.

Best regards,
Karl