bug#55025: Automake should allow one to enable POSIX make behavior

[Mike Frysinger]

On 13 Jan 2023 16:01, Karl Berry wrote:
> I am doubtful about blithely defining .POSIX unconditionally. I feel
> sure that will break existing Makefiles. I don't think we should do that.
> 
> Detecting .POSIX in an existing Makefile.am and moving it to the front
> sounds desirable, since that is clearly what the developer intended.
> 
> Another (not mutually exclusive) possibility is to add an Automake
> option (say, "make-posix") that outputs the .POSIX line. --thanks, karl.

i'd be amenable to a `no-make-posix` option, but imo forcing people to
opt-in to the right behavior is the wrong mental model.

i'm also a bit skeptical of the idea that we're breaking makefiles.  if
an implementation is POSIX compliant, then it already behaves as POSIX
defines make.  as it stands now, we, and our users, are generating files
that target an undefined standard that no one agrees on, cannot be tested
or asserted, and maybe they happen to work on the developer's desktop, but
not on random users of their own.  by defining .POSIX, we turn the state
from "usually works, but sometimes fails" to "either works or fails, but
it's the same everywhere".

i grok that not everyone is POSIX-compliant, and we sometimes try to add
support for such systems where reasonable, but that's a case-by-case, and
we can't keep bending over backwards to support decades old dead software
that no one uses.
-mike

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