Fix Singular configure so it accepts NTL installed in nonstandard locations

[mkoeppe]

As observed in #29104, Singular's configure may fail to find NTL even if Sage finds a system NTL. It continues to build, but the result is broken.

The details:

NTL's spkg-configure.m4 (from #27265/#27822) uses AC_CHECK_HEADER/AC_LINK_IFELSE/AC_RUN_IFELSE and therefore is able to find NTL in an environment where the user has set CPPFLAGS and LDFLAGS accordingly.
In that case, it sets AC_SUBST(SAGE_NTL_PREFIX, [''])

Then build/bin/sage-build-env-config.in does:

# This is usually blank if the system NTL is used, or $SAGE_LOCAL otherwise
export SAGE_NTL_PREFIX="@SAGE_NTL_PREFIX@"
if [ -n "$SAGE_NTL_PREFIX" ]; then
    # Many packages that depend on NTL accept a --with-ntl=<prefix> flag to
    # their ./configure scripts.  When using the system's NTL this is not
    # generally necessary, but when using the NTL package installed in
    # SAGE_LOCAL it is useful to pass it.
    export SAGE_CONFIGURE_NTL="--with-ntl=$SAGE_NTL_PREFIX"
fi

But Singular's configure (via its m4/ntl-check.m4) insists to find the headers in NTL_HOME_PATH, which defaults to DEFAULT_CHECKING_PATH="/usr /usr/local /sw /opt/local", which can of course be quite wrong.

On this ticket, we use a simple patch that modifies Singular's NTL detection code to make it similar to its GMP and FLINT detection codes.

An alternative solution would be to always provide the --with-ntl=PREFIX option to Singular.
We should also make it an error if Singular's configure cannot find NTL.

See also: #25993 - Upgrade Singular

CC: @dimpase @embray @kiwifb @mwageringel @antonio-rojas

Component: build: configure

Author: Matthias Koeppe

Branch/Commit: 50f62c7

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29335

[mkoeppe]

comment:1

Singular's checks for GMP and FLINT are almost as bad, but because the check for the header file is commented out, it happens to accept the libraries that are accessible via CPPFLAGS and LDFLAGS.

[mkoeppe]

Branch: u/mkoeppe/always_find_sage_ntl_prefix_and_call_singular_configure_with_it

[mkoeppe]

New commits:

50f62c7

build/pkgs/singular: Add patches to accept system NTL in nonstandard locations

[mkoeppe]

Commit: 50f62c7

[mkoeppe]

Author: Matthias Koeppe

[kiwifb]

comment:6

Those detections are a bit better in newer versions of singular, but still a bit off. My pull request to sanitize the new flint detection code has been accepted but that's not the only thing that should be sanitized. Singular/Singular#981

[mkoeppe]

comment:7

Glad to hear that upstream accepts build cleanup patches!

[mkoeppe]

comment:8

The fix on this ticket works (see #29104 / https://github.com/mkoeppe/sage/runs/508693083) - but it turns out that homebrew's NTL is not suitable:

  [singular-4.1.1p2.p0]   ld: illegal thread local variable reference to regular symbol __ZN3NTL13ErrorCallbackE for architecture x86_64
  [singular-4.1.1p2.p0]   clang: error: linker command failed with exit code 1 (use -v to see invocation)
  [singular-4.1.1p2.p0]   make[8]: *** [libSingular.la] Error 1

This is something that our ntl/spkg-configure.m4 should be checking. (This is #29339.)

[mkoeppe]

comment:10

Ready for review

[dimpase]

comment:11

what's going on in ./configure with NTL headers? Why is it there, and not in the corresponding spkg-configure.m4 ?

Why one cannot just use AC_CHECK_HEADER(S)(), instead of a dodgy loop?

[mkoeppe]

comment:12

Making upstream singular configuration non-dodgy is beyond the scope of this ticket.

[dimpase]

comment:13

oops, sorry, I have not realised that's Singular's ./configure
(stress and jetlag :-( )

how about we just pass it what's Sage already knows about NTL headers, i.e.
SAGE_NTL_PREFIX ?

[mkoeppe]

comment:14

The problem is that we do not really determine SAGE_NTL_PREFIX. It is empty if the system package is used.

[mkoeppe]

comment:15

(see ticket description)

[dimpase]

comment:16

Replying to @mkoeppe:

The problem is that we do not really determine SAGE_NTL_PREFIX. It is empty if the system package is used.

But we can, as we call AC_CHECK_HEADER, and it sets ac_cv_header_
so we can easily store it somewhere.

[mkoeppe]

comment:17

ac_cv_header_NTL_ZZ_h=yes

[dimpase]

comment:18

OK, but we can use AX_ABSOLUTE_HEADER() - as used in MPIR's spkg-configure.m4
to get the absolute path.

IMHO this way we don't have to patch Singular at all, right? Just pass the value, whatever it is.

[mkoeppe]

comment:19

I wouldn't consider use of this terrible macro an improvement.

[mkoeppe]

comment:20

In particular, reconstructing an install prefix from the location of a header file is NOT a good technical solution.

[dimpase]

comment:21

if you don't want a terrible macro, you can parse NTL/config_log.h to get the value of DEF_PREFIX, which is exactly the prefix we're after. If it's not defined, one can look forPREFIX, which would amount for the same thing. Finally, if neither are defined,
the prefix is /usr/local.
Cf. https://www.shoup.net/ntl/doc/tour-unix.html

[mkoeppe]

comment:22

Sorry, none of these are improvements over the simple patch.

[dimpase]

comment:23

OK. Upstream really needs to get this stuff fixed.

[dimpase]

Reviewer: Dima Pasechnik

[mkoeppe]

comment:24

Thanks.

[vbraun]

Changed branch from u/mkoeppe/always_find_sage_ntl_prefix_and_call_singular_configure_with_it to 50f62c7