1. For singular, the location of the dynamic library needs to be communicated to the sage runtime.

   We add a configuration variable SINGULAR_SO to sage_conf.py.in.

   The filename can be found from src/Singular/libSingular.la (currently not installed):

# The name that we can dlopen(3).
dlname='libSingular-4.1.1.dylib'
...
# Directory that this library needs to be installed in:
libdir='/Users/mkoeppe/s/sage/sage-rebasing/worktree-algebraic-2018-spring/local/lib'

This will:

• reduce the need for downstream patching (see for example https://salsa.debian.org/science-team/sagemath/-/blob/master/debian/patches/d0-singular.patch),

• enable venv builds of sagelib (Add src/requirements.txt for installation of sagelib in a venv #30578, Add configure option --with-sage-venv=SAGE_VENV to create venv there instead of in SAGE_LOCAL #29013) -- for which _get_shared_lib_filename is wrong

• provide preparation for adding an spkg-configure.m4 for singular.

2. src/bin/sage-env unconditionally sets environment variable SINGULARPATH="$SAGE_LOCAL/share/singular"

   If SINGULARPATH is already set by the user, perhaps the directory in $SAGE_LOCAL should be prepended instead of overwriting it.

   (After Obtain singular.hlp location via libsingular_resources #32254, SINGULARPATH is only used by qepcad -- this last use should be removed in QEPCAD: improve installation locations #31275.)

3. src/bin/sage-env unconditionally sets environment variable SINGULAR_EXECUTABLE="$SAGE_LOCAL/bin/Singular".

   It should be investigated whether this is actually needed in any supported configuration. If not, remove.

   (Removed in Drop SINGULAR_EXECUTABLE from src/bin/sage-env #32302.)

4. src/sage/interfaces/singular.py tries to use SINGULARPATH as if it is a directory name (it is a colon-separated list of directories):

singular_docdir = SINGULARPATH + "/../info/"

This should be fixed so that it works when SINGULARPATH is set by a user to a colon-separated list.

(Solved in #32254 - Obtain singular.hlp location via libsingular_resources)

Upstream: Reported upstream. No feedback yet.

CC: @dimpase @kiwifb @slel @isuruf @orlitzky @tobiasdiez @antonio-rojas @dkwo

Component: build: configure

Keywords: sd111

Author: Michael Orlitzky, Samuel Lelièvre

Branch: f01ff1f

Reviewer: Dima Pasechnik, Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/29024