Re: My plans for Bison: simplify autotools use

[Paul Eggert]

On 2/13/19 2:29 PM, Eric S. Raymond wrote:
> > So, for a start, there is not one HAVE_ in Bison's code.
> Which is a pretty powerful*argument*  that the "bootstrap" and
> "configure" steps are useless weight.

But there are lots of "HAVE_"s in the Bison tarball that people use to 
build Bison. These "HAVE_"s may not be in the Bison git repository and 
they're not something the Bison maintainers have to think about, but 
they're pulled in by 'bootstrap' for porting to various platforms and 
although many of these platforms are no longer relevant (and I'd welcome 
pruning Gnulib to stop worrying about them), some platform variations 
still matter.

Plus, looking for HAVE_ does not suffice. One must look for all the 
symbols that configure.ac and/or m4/*.m4 potentially define, and they 
don't all begin with "HAVE_".

One way to get a handle on the porting issues involved, would be to look 
at the Gnulib modules that Bison uses (see bootstrap.conf's 
gnulib_modules), and then go to the Gnulib documentation to see what 
porting issues they address. One should take the transitive closure of 
the Gnulib modules explicitly listed in bootstrap.conf, together with 
all the Gnulib modules they depend on.

For example, bootstrap.conf lists obstack, and obstack depends on 
alignof, gettext-h, exitfail, stdint, and stdlib, which in turn depend 
on a bunch of other stuff. Much of this stuff is older and is irrelevant 
if we assume C99 and/or POSIX-2001 or later, but not all of it is. For 
starters, alignof is a C11-ism and it's still too soon to assume C11. 
And even C99's stdint has porting problems: 
<https://www.gnu.org/software/gnulib/manual/html_node/stdint_002eh.html> 
says that the Gnulib stdint module fixes some bugs in pre-C++-11 
compilers, and some other bugs in glibc 2.24 (2016), and these platforms 
(though not bleeding-edge) are still common enough to be of some 
practical porting concern.

I think Gnulib and Bison's configure.ac could stand a lot of pruning; I 
have little doubt that more than half could go. I'm not sure we could 
get rid of it all, though.