spkg-configure.m4 for singular

[mkoeppe]

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 (#30578, #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 #32254, SINGULARPATH is only used by qepcad -- this last use should be removed in #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 #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)

[mkoeppe]

Which versions of singular are good?

[gh-mwageringel]

Replying to mkoeppe:

Which versions of singular are good?

Sage does not currently work correctly with any version of Singular, see #25993.

[dimpase]

well, Debian does have a Singular version which is compatible with their Sage package (v8.6 or so, I guess).

[mkoeppe]

Thanks for the info. I'll check back when #25993 is done.

[gh-thierry-FreeBSD]

This ticket should be listed in #27330 (ATM singular is listed in "No Tickets yet").

[mkoeppe]

Replying to gh-thierry-FreeBSD:

This ticket should be listed in #27330 (ATM singular is listed in "No Tickets yet").

I've added it

[gh-thierry-FreeBSD]

spkg-configure.m4 to be put under /build/pkgs/singular/

[gh-thierry-FreeBSD]

[Copying elements from #29024]

• my 1st problem was a build failure with Singular taken from an external package: to solve it, Singular must be built --with-ntl: it would be fine to add this check to spkg-configure.m4 (but I do not know how!)

• my 2nd error was when building dochtml: NameError: Singular library 'freegb.lib' not found. To solve it, src/sage/env.py and src/bin/sage-env must be modified so that SINGULARPATH is set to singlar's share dir (and not SAGE_SHARE / DESTDIR), and SINGULAR_EXECUTABLE is set to the real Singular and not under the DESTDIR directory.

Now it is OK for me (on FreeBSD).

[dimpase]

the error message

        raise RuntimeError(
            "libSingular not found--a working Singular install in $SAGE_LOCAL "
            "is required for Sage to work")

should be modified, too. Perhaps just remove in $SAGE_LOCAL

[mkoeppe]

Moving this ticket forward is great, but note that it is unrelated to the build problem on homebrew reported on sage-devel... and it is also unlikely that the homebrew version of singular actually works for us (homebrew does not like to patch).

As I explained in ​https://groups.google.com/d/msg/sage-devel/KXK_zxzfhIQ/RO3FryYWAwAJ, on the reporter's system the computed order of -I options is wrong -- something that I was not able reproduce on my system.

[dimpase]

Replying to gh-thierry-FreeBSD:

[Copying elements from #29024]

• my 1st problem was a build failure with Singular taken from an external package: to solve it, Singular must be built --with-ntl: it would be fine to add this check to spkg-configure.m4 (but I do not know how!)

• my 2nd error was when building dochtml: NameError: Singular library 'freegb.lib' not found. To solve it, src/sage/env.py and src/bin/sage-env must be modified so that SINGULARPATH is set to singlar's share dir (and not SAGE_SHARE / DESTDIR), and SINGULAR_EXECUTABLE is set to the real Singular and not under the DESTDIR directory.

Now it is OK for me (on FreeBSD).

The fix in SageMath needs some programming - specifically, the code in singular.pyx calls dlopen on SINGULAR_SO, which is computed by _get_shared_lib_filename dynamically in env.py, and assuming that it is in SAGE_LOCAL. So this probably can instead by handled using cython_aliases from the same module (which does compute all the needed info for Singular, it seems). Or by fixing _get_shared_lib_filename so that it also searches elsewhere.

[mkoeppe]

Is it known whether this comment added in 2009 to singular.pyx is still valid:

    This initializes the SINGULAR library. This is a hack to some
    extent.

    SINGULAR has a concept of compiled extension modules similar to
    Sage. For this, the compiled modules need to see the symbols from
    the main program. However, SINGULAR is a shared library in this
    context these symbols are not known globally. The work around so
    far is to load the library again and to specify ``RTLD_GLOBAL``.

[dimpase]

Someone working on innards of Singular might know. (I'd be surprised if it was changed).

Singular is not alone - this hack is also applied to libgap. I'm inclined to fix _get_shared_lib_filename so that it can accept other libdirs, not only SAGE_LOCAL/lib

[mkoeppe]

Replying to dimpase:

I'm inclined to fix _get_shared_lib_filename so that it can accept other libdirs, not only SAGE_LOCAL/lib

Yes, this function certainly would need changing if we continue to use it. For example, sysconfig.get_config_var('LIBDIR') gives a directory of the system python, not of the current venv.

But I think better solution would be to wrap loading of modules that are linked to singular by ​sys.setdlopenflags.

This is what pytorch does when it has to use RTLD_GLOBAL (see ​https://github.com/pytorch/pytorch/blob/master/torch/__init__.py#L132)

[mkoeppe]

Same at ​https://github.com/tensorflow/tensorflow/blob/9590c4c32dd4346ea5c35673336f5912c6072bf2/tensorflow/python/pywrap_dlopen_global_flags.py and ​https://github.com/tensorflow/tensorflow/blob/9590c4c32dd4346ea5c35673336f5912c6072bf2/tensorflow/python/pywrap_tensorflow.py

[mkoeppe]

I have opened #30561 for this

[mkoeppe]

Hoping we can make progress on this ticket this week - ​https://wiki.sagemath.org/days111

[mkoeppe]

Sage development has entered the release candidate phase for 9.3. Setting a new milestone for this ticket based on a cursory review of ticket status, priority, and last modification date.

[mkoeppe]

With #31642 taking us to a released version of Singular, it is time to work on an spkg-configure.m4 for using system singular. Arch already has the latest version (​https://repology.org/project/singular/versions)

[mjo]

The SINGULARPATH is being used to find the singular's docdir so that sage can manually parse its GNU info file and retrieve the docstring for Singular functions.

Currently the help file is mis-named (​https://github.com/Singular/Singular/issues/1107), but even so, there's a much more reliable way to get this information without parsing the file ourselves (and therefore, without SINGULARPATH):

$ info "(singular.hlp)align" | tail -n+2

5.1.1 align
-----------

`*Syntax:*'
     `align (' vector_expression, int_expression `)'
     `align (' module_expression, int_expression `)'

`*Type:*'
     type of the first argument

`*Purpose:*'
     maps module generators `gen(i)' to `gen(i+s)' for all i.

`*Example:*'
            ring r=0,(x,y,z),(c,dp);
            align([1,2,3],3);
          ==> [0,0,0,1,2,3]
            align([0,0,1,2,3],-1);
          ==> [0,1,2,3]
            align(freemodule(2),1);
          ==> _[1]=[0,1]
          ==> _[2]=[0,0,1]

[mjo]

This branch is only half-baked, but it already eliminates problems 2, 3, and 4 from the description at the cost of requiring GNU Info to be installed.

Can the first issue be avoided as well? Why are we using dlopen to load SINGULAR_SO instead of just linking to it?

[mkoeppe]

Replying to mjo:

Why are we using dlopen to load SINGULAR_SO instead of just linking to it?

See #30561

[mjo]

I've left the dlopen() alone because I don't feel like trying to eliminate it. This branch uses autoconf to find out the extension of shared libraries on the system (SHLIBEXT), and then tries to dlopen("libSingular.$SHLIBEXT"). If it works, we use the system copy, and use the same dlopen() strategy in singular.pyx. Otherwise we fall back to the SPKG and pass the full SAGE_LOCAL path to dlopen(). Works well enough on Gentoo.

---

New commits:

​5fa1125	Trac #32302: drop SINGULAR_EXECUTABLE from src/bin/sage-env.
​5395116	Trac #32243: look for cddlib-0.94m headers in the right place.
​ea42a9b	Trac #32243: patch gfan to look for cddlib headers in new location.
​c0340b3	Trac #29024: put the shared library extension in sage_conf.
​3919061	Trac #29024: new spkg-configure.m4 for singular.
​fc4dc8c	Trac #29024: don't set SINGULARPATH in sage-env.
​ae26f76	Trac #29024: use SINGULAR_LIB_BASE and SHLIBEXT to replace SINGULAR_SO.
​a3b5983	Trac #29024: add Gentoo package information.

[dimpase]

by the way, why there is no hint for pkgconfig in build/pkgs/pkgconfig/distros/gentoo.txt (and for many other obvious distros)?

I only notices as Gentoo's emerge was telling be about the switch to dev-util/pkgconf.

[dimpase]

OK, what's this:

[dochtml] make doc-inventory--Bug
[dochtml] cd /mnt/opt/Sage/sage-dev && ./sage --docbuild --no-pdf-links Bug inventory 
[dochtml] Bug >>Could not get expanded executable from "libSingular.so"<< at feResource.cc:434
[dochtml] 'Bug' is not a recognized document. Type 'sage --docbuild -D' for a list
[dochtml] of documents, or 'sage --docbuild --help' for more help.
[dochtml] make[5]: *** [Makefile:20: doc-inventory--Bug] Error 1

also,

$ ./sage
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 9.4.rc2, Release Date: 2021-08-12                 │
│ Using Python 3.8.9. Type "help()" for help.                        │
└────────────────────────────────────────────────────────────────────┘
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ Warning: this is a prerelease version, and it may be unstable.     ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
Bug >>Could not get expanded executable from "libSingular.so"<< at feResource.cc:434
sage: 2+2                                                                                                                            
4
sage:           

[dimpase]

Can this be coming from Gentoo's Singular install? Weird.

[mjo]

Replying to dimpase:

Can this be coming from Gentoo's Singular install? Weird.

Oh, right, I saw that too. Singular is trying to guess the path of its own executable and is failing. It doesn't hurt anything (that I noticed...), and is an upstream bug like the message says. I'll dig deeper as this gets closer to being merged and figure out what to report upstream.

[mjo]

Replying to dimpase:

by the way, why there is no hint for pkgconfig in build/pkgs/pkgconfig/distros/gentoo.txt (and for many other obvious distros)?

I only notices as Gentoo's emerge was telling be about the switch to dev-util/pkgconf.

The Sage "pkgconfig" package is a python module and not the tool itself. There's nothing we can do with it yet, but eventually it's dev-python/pkgconfig.

[mjo]

You can make the BUG warning go away with,

$ SINGULAR_BIN_DIR=$(dirname $(type -P Singular)) sage

but hopefully that is not needed long-term.

[mjo]

Upstream bug: ​https://github.com/Singular/Singular/issues/1113

[mkoeppe]

Replying to mjo:

The Sage "pkgconfig" package is a python module and not the tool itself. There's nothing we can do with it yet, but eventually it's dev-python/pkgconfig.

build/pkgs/pkgconf/distros also does not have an entry for gentoo (and neither for arch)

[mkoeppe]

build/pkgs/singular/distros looks like it needs more entries for some distributions

[mjo]

Replying to mkoeppe:

Replying to mjo:

The Sage "pkgconfig" package is a python module and not the tool itself. There's nothing we can do with it yet, but eventually it's dev-python/pkgconfig.

build/pkgs/pkgconf/distros also does not have an entry for gentoo (and neither for arch)

You can't bootstrap without pkgconf and you would be hard-pressed to find a Gentoo machine without it (being source-based), but it certainly can't hurt. The message that Dima saw says that we are getting rid of the old implementation, so now there's only dev-util/pkgconf to put in gentoo.txt.

[slelievre]

Here are Singular distro files for Arch Linux, Cygwin and Fedora.

Revert to your branch if those are not helping.

---

New commits:

​a5cfcec

29024: Add Singular distro info

[mkoeppe]

-# As of 2021-03-20, build of homebrew's singular from source fails
+# [2021-03-20] building from source with Homebrew's singular fails

this rewording changes the meaning. What failed at this time was really the from-source build of the homebrew package (via brew install -s, or implied when using brew with a non-standard prefix)

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​fe67a21

29024: Add Singular distro info

[mkoeppe]

Replying to dimpase:

OK, what's this:

[dochtml] make doc-inventory--Bug

This is likely caused by unexpected output (on stdout!) from the command ./sage --docbuild --all-documents reference

[dimpase]

We probably also need to do something with SINGULARPATH, a variable hold, if needed, paths to Singular's .lib files, something that may be installed by Sage's optional packages - it is done e.g. by p_group_cohomology. So to make the latter work with system-wide Singular one needs to export SINGULARPATH=$SAGE_LOCAL/share/singular/LIB.

[mjo]

Replying to dimpase:

We probably also need to do something with SINGULARPATH, a variable hold, if needed, paths to Singular's .lib files, something that may be installed by Sage's optional packages - it is done e.g. by p_group_cohomology. So to make the latter work with system-wide Singular one needs to export SINGULARPATH=$SAGE_LOCAL/share/singular/LIB.

What we really need is a system for optional packages to set their own environment variables, so we don't have to set every possible environment variable (for an unknowable number of optional packages) in sage-env. Of course Gentoo and everyone else already figured this out 20 years ago. We can have sage-env source any files in local/etc/env.d, and then tell optional packages to install what they need (e.g. a script that exports SINGULARPATH) there.

I guess I will waste my time reimplementing that so that some day I can stop wasting my time rebuilding the same copy of singular that I already have installed.

[mkoeppe]

Best to plan to move away from any such dependence on setting environment variables.

Instead, it should be set at runtime when initializing the singular interface / libsingular.

[mkoeppe]

(see #30818, #21707)

[mkoeppe]

In fact, do we actually install any custom Singular packages in SAGE_LOCAL/share/singular/LIB? I don't think we do.

src/sage/rings/function_field/function_field.py uses the correct approach -- it loads its custom Singular library using a fully qualified path to the library, which is just in the installed package data of the Sage library.

If the p_group_cohomology Sage code relies on SINGULARPATH, it should be changed so it uses the same approach.

[dimpase]

Replying to mkoeppe:

In fact, do we actually install any custom Singular packages in SAGE_LOCAL/share/singular/LIB? I don't think we do.

Not sure what "we" is here, but p_group_cohomology does install a custom Singular lib, called dickson.lib, and it ends up in $SAGE_LOCAL/share/singular/LIB, as spkg-install has

sdh_install singular_helper/dickson.lib "$SAGE_SHARE/singular/LIB/"

• which is fine if Singular is built by Sage, but not with the external Singular.

src/sage/rings/function_field/function_field.py uses the correct approach -- it loads its custom Singular library using a fully qualified path to the library, which is just in the installed package data of the Sage library.

If the p_group_cohomology Sage code relies on SINGULARPATH, it should be changed so it uses the same approach.

It doesn't rely on SINGULARPATH is seems to me. SINGULARPATH can be used by Singular, and system-wide Singular doesn't know about $SAGE_LOCAL/share/singular/LIB, obviously, unless something is done.

Should p_group_cohomology be using $SAGE_SHARE/singular/LIB/ to install dickson.lib, or some other location?

Regarding src/sage/ext_data/singular/function_field/core.lib, one sees

            from sage.env import SAGE_EXTCODE
            lib(SAGE_EXTCODE + '/singular/function_field/core.lib')

but

$ find . -name core.lib
./pkgs/sagemath-standard/build/lib.linux-x86_64-3.8/sage/ext_data/singular/function_field/core.lib
./src/sage/ext_data/singular/function_field/core.lib
./local/lib/python3.8/site-packages/sage/ext_data/singular/function_field/core.lib

so it also gets installed into site-packages. Is it a bug?

[mkoeppe]

Replying to dimpase:

Regarding src/sage/ext_data/singular/function_field/core.lib, one sees

            from sage.env import SAGE_EXTCODE
            lib(SAGE_EXTCODE + '/singular/function_field/core.lib')

but

$ find . -name core.lib
./pkgs/sagemath-standard/build/lib.linux-x86_64-3.8/sage/ext_data/singular/function_field/core.lib
./src/sage/ext_data/singular/function_field/core.lib
./local/lib/python3.8/site-packages/sage/ext_data/singular/function_field/core.lib

so it also gets installed into site-packages.

core.lib is package_data of the distribution package sagemath-standard. As such it gets installed alongside the Python files, in site-packages.

This works as designed.

[mkoeppe]

Replying to dimpase:

Replying to mkoeppe:

In fact, do we actually install any custom Singular packages in SAGE_LOCAL/share/singular/LIB? I don't think we do.

Not sure what "we" is here

... any package in the Sage distribution ...

Should p_group_cohomology be using $SAGE_SHARE/singular/LIB/ to install dickson.lib, or some other location?

As I said, this should be changed to follow the same model as src/sage/ext_data/singular/function_field/core.lib

[mkoeppe]

Is there any code that actually loads dickson.lib?

[dimpase]

Replying to mkoeppe:

Is there any code that actually loads dickson.lib?

sage -t src/sage/tests/modular_group_cohomology.py will trigger loading it, if p_group_cohomology is installed.

[dimpase]

Replying to mkoeppe:

Replying to dimpase:

Replying to mkoeppe:

In fact, do we actually install any custom Singular packages in SAGE_LOCAL/share/singular/LIB? I don't think we do.

Not sure what "we" is here

... any package in the Sage distribution ...

Should p_group_cohomology be using $SAGE_SHARE/singular/LIB/ to install dickson.lib, or some other location?

As I said, this should be changed to follow the same model as src/sage/ext_data/singular/function_field/core.lib

I've opened ​https://github.com/sagemath/p_group_cohomology/issues/5 for this

[mkoeppe]

As p_group_cohomology is broken since Sage 9.4 anyway (​https://github.com/sagemath/p_group_cohomology/issues/4), I think we can proceed here on the ticket without worrying about SINGULARPATH.

[dimpase]

So are we waiting for the upstream fix here, or proceed with making sure that

export SINGULAR_BIN_DIR=$(dirname $(type -P Singular))

is added at the correct place?

[mjo]

I think we'll have to add it. Upstream started to work on the issue but we're nowhere near having a complete fix in a released version of Singular. The BUG warning is harmless I think; but if we don't hide it, we're going to have to deal with a million bug reports about it.

I'll add the workaround and create a ticket to remove it whenever the fix is in an upstream release.

[mjo]

Actually, I just looked at the upstream issue and see that I missed a notification about a new commit. Let me go test it. We may still want to add the workaround for a few months until a new release is made and distros catch up.

[mkoeppe]

Replying to dimpase:

So are we waiting for the upstream fix here, or proceed with making sure that

export SINGULAR_BIN_DIR=$(dirname $(type -P Singular))

is added at the correct place?

Can we put this environment setting in src/sage/libs/singular/singular.pyx (init_libsingular)?

[mjo]

Replying to mkoeppe:

Replying to dimpase:

So are we waiting for the upstream fix here, or proceed with making sure that

export SINGULAR_BIN_DIR=$(dirname $(type -P Singular))

is added at the correct place?

Can we put this environment setting in src/sage/libs/singular/singular.pyx (init_libsingular)?

Both type -P and command -v are shell built-ins on my system, making them a bit hard to use from python code. Does putting it in sage-env cause a problem I've overlooked, or are you just thinking it would be more appropriate in init_singular()? I don't disagree -- but considering that this is a temporary workaround, it might just be easier to add the one line in sage-env instead of the python code to launch a full-blown shell and parse its output.

[mkoeppe]

Replying to mjo:

Does putting it in sage-env cause a problem I've overlooked

Yes, we are working on making sage pip-installable and importable into normal Python environments (import sage.all), and for this depending on sage-env needs to be removed

[mkoeppe]

Replying to mjo:

temporary workaround

Well, versions of singular that need this workaround may be in relevant distributions for years...

[mkoeppe]

And I think this just ​https://docs.python.org/3/library/shutil.html#shutil.which

[mjo]

Replying to mkoeppe:

And I think this just ​https://docs.python.org/3/library/shutil.html#shutil.which

Yep, here's an untested branch. It's going to take me all night to rebuild sage after the rebase but I'll make sure it works in the morning. And report back to upstream... that last commit looks strange to me.

---

New commits:

​28837b9	Trac #29024: put the shared library extension in sage_conf.
​c383777	Trac #29024: new spkg-configure.m4 for singular.
​8e80875	Trac #29024: don't set SINGULARPATH in sage-env.
​9b8244f	Trac #29024: use SINGULAR_LIB_BASE and SHLIBEXT to replace SINGULAR_SO.
​f6e4f89	Trac #29024: add Gentoo package information.
​1055247	29024: Add Singular distro info
​3cebd4f	Trac #29024: work around Singular issue 1113 in init_libsingular().

[mjo]

It works.

[mkoeppe]

Ready for review?

[mkoeppe]

This will need a GH Actions run

[dimpase]

I've started ​https://github.com/sagemath/sagetrac-mirror/actions/runs/1240853423

[mkoeppe]

Doesn't accept singular on cygwin-standard (​https://github.com/mkoeppe/sage/runs/3625055086)

-----------------------------------------------------------------------------
Checking whether SageMath should install SPKG singular...
checking whether any of gmp mpir ntl flint readline mpfr cddlib is installed as or will be installed as SPKG... no
checking for Singular... /usr/bin/Singular
checking for SINGULAR... no
checking if we can dlopen(libSingular.dll)... configure: no suitable system package found for SPKG singular

[mkoeppe]

Works OK on archlinux-latest-standard (​https://github.com/mkoeppe/sage/runs/3625059112)

----------------------------------------------------------------------------
Checking whether SageMath should install SPKG singular...
checking whether any of gmp mpir ntl flint readline mpfr cddlib is installed as or will be installed as SPKG... no
checking for Singular... /usr/sbin/Singular
checking for SINGULAR... yes
checking if we can dlopen(libSingular.so)... configure: will use system package and not install SPKG singular

(but looks like an AC_MSG_RESULT is missing)

[mkoeppe]

Also OK (as expected) on gentoo-standard

No luck on debian, fedora, and homebrew because of the cddlib dependency. It works correctly but does not accept system singular.

[mjo]

Replying to mkoeppe:

Doesn't accept singular on cygwin-standard (​https://github.com/mkoeppe/sage/runs/3625055086)

I think that's expected, since it has an older version of Singular than the pkg-config test looks for.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​d8118ac

Trac #29024: add missing AC_MSG_RESULTs in singular/spkg-configure.m4.

[mkoeppe]

Actually this needs more work on Cygwin: ​https://github.com/mkoeppe/sage/runs/3638292833?check_suite_focus=true

./sage -t -p --all --logfile=logs/ptest.log
no stored timings available
Running doctests with ID 2021-09-18-08-09-52-cb78f982.
Git branch: HEAD
Using --optional=build,cygwin,dochtml,pip,sage,sage_spkg
Doctesting entire Sage library.
Sorting sources by runtime so that slower doctests are run first....
Doctesting 4363 files using 3 threads.
Traceback (most recent call last):
  File "/cygdrive/d/a/sage/sage/src/bin/sage-runtests", line 144, in <module>
    err = DC.run()
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/doctest/control.py", line 1207, in run
    self.run_doctests()
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/doctest/control.py", line 904, in run_doctests
    self.dispatcher = DocTestDispatcher(self)
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/doctest/forker.py", line 1624, in __init__
    init_sage(controller)
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/doctest/forker.py", line 192, in init_sage
    controller.load_environment()
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/doctest/control.py", line 525, in load_environment
    return import_module(self.options.environment)
  File "/usr/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 848, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/repl/ipython_kernel/all_jupyter.py", line 5, in <module>
    from sage.all_cmdline import *
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/all_cmdline.py", line 19, in <module>
    from sage.all import *
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/all.py", line 141, in <module>
    from sage.rings.all      import *
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/rings/all.py", line 83, in <module>
    from .polynomial.all import *
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/rings/polynomial/all.py", line 42, in <module>
    from sage.rings.polynomial.laurent_polynomial_ring import LaurentPolynomialRing
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/rings/polynomial/laurent_polynomial_ring.py", line 50, in <module>
    from sage.rings.polynomial.laurent_polynomial import LaurentPolynomial_mpair, LaurentPolynomial_univariate
  File "sage/rings/polynomial/laurent_polynomial.pyx", line 1, in init sage.rings.polynomial.laurent_polynomial (build/cythonized/sage/rings/polynomial/laurent_polynomial.c:40817)
  File "sage/matrix/matrix0.pyx", line 28, in init sage.matrix.matrix0 (build/cythonized/sage/matrix/matrix0.c:44570)
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/modules/free_module.py", line 167, in <module>
    import sage.matrix.matrix_space
  File "/opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/python3.8/site-packages/sage/matrix/matrix_space.py", line 55, in <module>
    from . import matrix_mpolynomial_dense
  File "sage/matrix/matrix_mpolynomial_dense.pyx", line 1, in init sage.matrix.matrix_mpolynomial_dense (build/cythonized/sage/matrix/matrix_mpolynomial_dense.cpp:8666)
  File "sage/rings/polynomial/multi_polynomial_libsingular.pyx", line 1, in init sage.rings.polynomial.multi_polynomial_libsingular (build/cythonized/sage/rings/polynomial/multi_polynomial_libsingular.cpp:49840)
  File "sage/libs/singular/singular.pyx", line 808, in init sage.libs.singular.singular (build/cythonized/sage/libs/singular/singular.cpp:11287)
  File "sage/libs/singular/singular.pyx", line 785, in sage.libs.singular.singular.init_libsingular (build/cythonized/sage/libs/singular/singular.cpp:8697)
ImportError: cannot load Singular library from /opt/sage-032178416da49f83f86c3b8ce2797134fbb97bd8/lib/libSingular.dll (b'No such file or directory')
make: *** [Makefile:233: ptest-nodoc] Error 1

Note that on cygwin, dlls are installed in bin/, not in lib/

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​fbf01c4	Trac #29024: support libdir substitutions in sage_conf.
​fc2adfb	Trac #29024: use new SAGE_LIBDIR substitution for libSingular.so.
​da802ef	Trac #29024: clarify a comment in singular's spkg-configure.

[mjo]

I think that will fix it. I thought about eliminating SINGULAR_LIB_BASE entirely, but I can't say for sure that we won't encounter a platform where dlopen() does not search the library path, so I've left it in and invented a way to reference the libdir.

The hacks in sage_conf are starting to pile up, so I've opened #32540 with a proposal to refactor things.

[mkoeppe]

Have you tested this on Cygwin?

[mkoeppe]

Asking because the situation with DLLs on Cygwin is not really related to anything "LIBDIR". Only the naked DLLs end up in bin/ on the platform, but lib/ is still used for .a and .dll.a files

[dimpase]

Homebrew's Singular needs some fixes; 1st of all,

.homebrew-build-env

@@ -23 +23 @@
 LIBRARY_PATH="$HOMEBREW/lib$LIBRARY_PATH"
 [ -z "$CPATH" ] || CPATH=":${CPATH}"
 CPATH="$HOMEBREW/include$CPATH"
-for l in readline bzip2 ntl; do
+for l in readline bzip2 ntl singular; do
     if [ -d "$HOMEBREW/opt/$l/lib" ]; then
         LIBRARY_PATH="$HOMEBREW/opt/$l/lib:$LIBRARY_PATH"
     fi

Then, it appears that dlopen() call in singular.pyx needs a full path to .dylib on macOS. (it might be a Cython bug, or the plarform limitation, I don't know). That is, if I make sure that

SINGULAR_LIB_BASE = "/usr/local/opt/singular/lib/libSingular"

in sage_conf.py then everything works. I am not sure how to achieve the latter automatically. One way might be to export a special env. var. in .homebrew-build-env and use it to set up the proper SINGULAR_LIB_BASE in spkg-configure.m4 - but there could be a better way.

[dimpase]

Once the latter is fixed, we should apply

build/pkgs/singular/distros/homebrew.txt

@@ -1 @@
-# [2021-03-20] Homebrew's Singular can be built from source
-# (via `brew install -s`, or implied when using `brew` with
-# a non-standard prefix), but that currently fails.
-
-#singular
+singular

[arojas]

This breaks distro installs without sage_conf. Please keep the old _get_shared_lib_path code path as a fallback in case sage_conf gives an ImportError.

[dimpase]

Replying to arojas:

This breaks distro installs without sage_conf. Please keep the old _get_shared_lib_path code path as a fallback in case sage_conf gives an ImportError.

Do distros use env. vars from env.py? (That's where the change was, the env. var. there is not computed any more.

[arojas]

Replying to dimpase:

Replying to arojas:

This breaks distro installs without sage_conf. Please keep the old _get_shared_lib_path code path as a fallback in case sage_conf gives an ImportError.

Do distros use env. vars from env.py? (That's where the change was, the env. var. there is not computed any more.

Yes, env.py is part of sagelib. Actually, a simple fallback to SINGULAR_LIB_PATH="libSingular.so" would be fine for me (if any distro modifies the default library name, I guess it's their job to patch sage accordingly or provide a custom sage_conf)

[mjo]

Replying to mkoeppe:

Asking because the situation with DLLs on Cygwin is not really related to anything "LIBDIR". Only the naked DLLs end up in bin/ on the platform, but lib/ is still used for .a and .dll.a files

No, I haven't tested yet. I'll have to run it on GH.

Even if $libdir isn't being used... at some point, the build system is deciding to put those dlls into a $directory, and $directory=bin on cygwin while $directory=lib everywhere else, no? I don't suppose you know where that decision is made?

[mjo]

Replying to dimpase:

Then, it appears that dlopen() call in singular.pyx needs a full path to .dylib on macOS. (it might be a Cython bug, or the plarform limitation, I don't know).

This was a conscious choice, as da802ef now makes explicit. POSIX doesn't say what will happen if you use a filename without a path in dlopen(), so the SPKG is still used as a fallback on systems where it doesn't work.

There are a couple options to improve this, of varying difficulty:

• We could try to get the libdir from Singular itself. The feResource.cc file provides a bunch of other configuration information, but not the bare libdir at the moment. We could provide a patch upstream that lets us obtain its libdir. (However, the cygwin discussion is suggesting that libdir may not always be the right place?)
• We can eliminate the dlopen(), if possible. We already link directly to libSingular and that's easy to do portably with -lSingular. I'm not entirely sure why dlopen() is needed, but the init_libsingular() documentation says

  """                                                                                                                                                                      
  This initializes the SINGULAR library. This is a hack to some                                                                                                            
  extent.                                                                                                                                                                  
                                                                                                                                                                               
  SINGULAR has a concept of compiled extension modules similar to                                                                                                          
  Sage. For this, the compiled modules need to see the symbols from                                                                                                        
  the main program. However, SINGULAR is a shared library in this                                                                                                          
  context these symbols are not known globally. The work around so                                                                                                         
  far is to load the library again and to specify ``RTLD_GLOBAL``.                                                                                                         
  """
  

• We can invent some hacks that guess the right location on most of the platforms we support.

[dimpase]

Replying to mjo:

Even if $libdir isn't being used... at some point, the build system is deciding to put those dlls into a $directory, and $directory=bin on cygwin while $directory=lib everywhere else, no? I don't suppose you know where that decision is made?

I think it has to do with cygwin fork() design, Windows address space, rebasing... DLL needs to get a fixed memory address allocation, for fork() to work), and so bin/ is what's beging scanned by the corresponding Cygwin utility rebaseall.

Not running away screaming yet?

[dimpase]

Replying to mjo:

Replying to dimpase:

Then, it appears that dlopen() call in singular.pyx needs a full path to .dylib on macOS. (it might be a Cython bug, or the plarform limitation, I don't know).

This was a conscious choice, as da802ef now makes explicit. POSIX doesn't say what will happen if you use a filename without a path in dlopen(), so the SPKG is still used as a fallback on systems where it doesn't work.

This does not explain why no-full-path dlopen() succeeds in the test

configure:40299: checking if we can dlopen(libSingular.dylib)
configure:40330: gcc -o conftest -g -O2   -Ddarwin -I/usr/local/opt/gmp/include  -I/usr/local/Cellar/ecl/21.2.1/include  conftest.c -lmpfi -lmpc -lnauty -lglpk -lpari -lncurses -lcurl -lcddgmp -lbz2 -larb -lflint -lmpfr -lgmp -lm  -lntl  -lppl -lgmpxx -lgmp -ldl >&5
configure:40330: $? = 0
configure:40330: ./conftest
configure:40330: $? = 0
configure:40333: result: yes

but fails in singular.pyx.

[mjo]

Replying to dimpase:

Replying to mjo:

Even if $libdir isn't being used... at some point, the build system is deciding to put those dlls into a $directory, and $directory=bin on cygwin while $directory=lib everywhere else, no? I don't suppose you know where that decision is made?

I think it has to do with cygwin fork() design, Windows address space, rebasing... DLL needs to get a fixed memory address allocation, for fork() to work), and so bin/ is what's beging scanned by the corresponding Cygwin utility rebaseall.

Not running away screaming yet?

Is that an option? Can I wrap the whole thing in if [ $(whoami) = "mjo" ]?

The rebaseall thing makes some amount of sense to me (I used cygwin back when Windows XP was around), but I'm still not sure exactly when the dlls either get installed directly to bin, or moved from lib to bin.

[mjo]

Replying to dimpase:

This does not explain why no-full-path dlopen() succeeds in the test... but fails in singular.pyx.

Oh, no. That's interesting. What error message does it give you?

[dimpase]

Replying to mjo:

Replying to dimpase:

This does not explain why no-full-path dlopen() succeeds in the test... but fails in singular.pyx.

Oh, no. That's interesting. What error message does it give you?

...
--> 808 init_libsingular()
...
    782     handle = dlopen(lib, RTLD_GLOBAL|RTLD_LAZY)
    783     if not handle:
    784         err = dlerror()
--> 785         raise ImportError(f"cannot load Singular library from {SINGULAR_LIB_PATH} ({err})")
        global ImportError = undefined
    786 
    787     # load SINGULAR
    788     siInit(lib)
    789 
...
ImportError: cannot load Singular library from libSingular.dylib (b'dlopen(libSingular.dylib, 9): image not found')

I tried setting LD_LIBRARY_PATH or DYLD_FALLBACK_LIBRARY_PATH (cf. Apple's manpage on dlopen()), to no effect.

PS. related reading ​https://developer.apple.com/forums/thread/13161 sounds as if Apple broke the latter stuff in the name of "security"...

[mjo]

The cygwin magic happens in libtool.m4:

cygwin* | mingw* | pw32* | cegcc*)
...
  # DLL is installed to $(libdir)/../bin by postinstall_cmds                                                                                                               
  postinstall_cmds='base_file=`basename \$file`~
    dlpath=`$SHELL 2>&1 -c '\''. $dir/'\''\$base_file'\''i; echo \$dlname'\''`~
    dldir=$destdir/`dirname \$dlpath`~
    test -d \$dldir || mkdir -p \$dldir~
    $install_prog $dir/$dlname \$dldir/$dlname~
    chmod a+x \$dldir/$dlname~
    if test -n '\''$stripme'\'' && test -n '\''$striplib'\''; then
      eval '\''$striplib \$dldir/$dlname'\'' || exit \$?;
    fi'

I guess I'll just undo the last few commits and special-case cygwin*.

[dimpase]

As far as I know, on Cygwin dlopen() looks up things in $PATH rather than $LD_..., so this appears to be good as it is, no?

Although Conda and macOS still need an action.

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​c3e635a	Trac #29024: clarify a comment in singular's spkg-configure.
​8cd60dd	Trac #29024: fix libSingular path on Cygwin.

[mjo]

On cygwin the SPKG will always be used because its Singular is too old. But even that was failing, because the absolute path involving "lib" was wrong. It should be fixed now.

Remaining questions:

1. Do I need to use "cygSingular" as the library name on Cygwin?
2. WTF is happening on macOS?

[dimpase]

Replying to mjo:

On cygwin the SPKG will always be used because its Singular is too old.

I've asked for an update: ​https://cygwin.com/pipermail/cygwin/2021-September/249449.html

But even that was failing, because the absolute path involving "lib" was wrong. It should be fixed now.

Remaining questions:

1. Do I need to use "cygSingular" as the library name on Cygwin?

Yes, I think so.

2. WTF is happening on macOS?

I suppose we need to supply the full path to DLL (.e.g. .dylib), via an env. var in .homebrew-build-env and forget about it. (Not sure about Conda).

One discrepancy I noticed is that that singular.pyx is compiled as C++, while the test in spkg-configure is done with plain C; I tried with C++, saw no difference.

[dimpase]

Homebrew fix

---

New commits:

​f72df45

macOS dlopen() prefers full path sometimes

[mkoeppe]

This is not a good change.

--- a/.homebrew-build-env
+++ b/.homebrew-build-env
@@ -23,7 +23,7 @@ export PKG_CONFIG_PATH
 LIBRARY_PATH="$HOMEBREW/lib$LIBRARY_PATH"
 [ -z "$CPATH" ] || CPATH=":${CPATH}"
 CPATH="$HOMEBREW/include$CPATH"
-for l in readline bzip2 ntl; do
+for l in readline bzip2 ntl singular; do
     if [ -d "$HOMEBREW/opt/$l/lib" ]; then
         LIBRARY_PATH="$HOMEBREW/opt/$l/lib:$LIBRARY_PATH"
     fi

Adding to LIBRARY_PATH is only needed for "keg-only" packages. singular is a regular package, linked into /usr/local.

@@ -45,3 +45,5 @@ for l in gettext; do
     fi
 done
 export ACLOCAL_PATH
+SINGULAR_HOMEBREW_LIBDIR="$HOMEBREW/opt/singular/lib/"
+export SINGULAR_HOMEBREW_LIBDIR

Pretty sure you can find the information you need during configure using pkg-config.

[dimpase]

Indeed, we can instead call PKG_CHECK_VAR([SINGULAR_LIBDIR], [Singular], [libdir]) to get SINGULAR_LIBDIR. I suppose, to be on the safe side we should prepend it to SINGULAR_LIB_BASE unconditionally, not only on macOS.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​f11791b

pkg-config to get the libdir, properly nest tests

[mjo]

I was working on this at the same time =(

​https://git.sagemath.org/sage.git/commit/?h=u/mjo/ticket/29024&id=5a494d5a6b96949c5744239a0c8f866f3c2d9ac2

I've simplified the variables a bit, so the "base" and extension are no longer separate. I also added the special-case for cygwin into the system-singular code branch.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​e6c41f7

Fedora needs devel pkg

[dimpase]

Replying to mjo:

I was working on this at the same time =(

​https://git.sagemath.org/sage.git/commit/?h=u/mjo/ticket/29024&id=5a494d5a6b96949c5744239a0c8f866f3c2d9ac2

I've simplified the variables a bit, so the "base" and extension are no longer separate. I also added the special-case for cygwin into the system-singular code branch.

I'll try to merge your improvements

[dimpase]

there is also #32549 removing mpir spkg, so mpir should disappear in spkg-config.m4

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. Last 10 new commits:

​d5b8ac8	Trac #29024: add Gentoo package information.
​9589a1d	29024: Add Singular distro info
​c76a975	Trac #29024: work around Singular issue 1113 in init_libsingular().
​3730d72	Trac #29024: add missing AC_MSG_RESULTs in singular/spkg-configure.m4.
​30e7fd6	Trac #29024: clarify a comment in singular's spkg-configure.
​f64594c	Trac #29024: fix libSingular path on Cygwin.
​73d301d	macOS dlopen() prefers full path sometimes
​604b0c4	pkg-config to get the libdir, properly nest tests
​ca4aa03	Fedora needs devel pkg
​3404652	dependance on gmp/mpir already covered by mpfr

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. Last 10 new commits:

​a61b3a5	Trac #29024: add Gentoo package information.
​fa65fa5	29024: Add Singular distro info
​0846173	Trac #29024: work around Singular issue 1113 in init_libsingular().
​dd69ac1	Trac #29024: add missing AC_MSG_RESULTs in singular/spkg-configure.m4.
​9d6080f	Trac #29024: clarify a comment in singular's spkg-configure.
​e0c0e05	Trac #29024: fix libSingular path on Cygwin.
​93b2f47	macOS dlopen() prefers full path sometimes
​dca5125	pkg-config to get the libdir, properly nest tests
​f85d09c	Fedora needs devel pkg
​d8db64b	dependance on gmp/mpir already covered by mpfr

[dimpase]

so what's exactly is different in functionality in the current ticket branch, u/dimpase/ticket/29024 vs u/mjo/ticket/29024 ?

[mjo]

Now that we're just asking pkg-config for the correct location, the two variables SINGULAR_LIB_BASE and SINGULAR_LIB_FILE are redundant. (The "base" variable would be left empty in the past to let dlopen() search for the library.) I think the main difference in my branch is that I've refactored things to use only a single variable, LIBSINGULAR_PATH. The rest should be cosmetic.

[dimpase]

you do non-nested calls where they can and should be nested. slows down ./configure for no reason.

[mjo]

Replying to dimpase:

you do non-nested calls where they can and should be nested. slows down ./configure for no reason.

I find the logic much easier to understand when the "else" branch of a test is not separated from the test by an entire page. Ideally I would be able to put something like return; after each sage_spkg_install_singular=yes, but I don't know of a reliable way to accomplish that.

Running "make" takes many hours, so an extra second or two on systems without Singular didn't seem like a huge problem. And those of us who work on the build system and run ./configure repeatedly should be clever enough to install it. But I could still nest them if that's a deal-breaker for you.

[dimpase]

Replying to mjo:

Replying to dimpase:

you do non-nested calls where they can and should be nested. slows down ./configure for no reason.

I find the logic much easier to understand when the "else" branch of a test is not separated from the test by an entire page.

Do some coding in Lisp, then, for the training purposes ;-)

Ideally I would be able to put something like return; after each sage_spkg_install_singular=yes, but I don't know of a reliable way to accomplish that.

Running "make" takes many hours, so an extra second or two on systems without Singular didn't seem like a huge problem. And those of us who work on the build system and run ./configure repeatedly should be clever enough to install it. But I could still nest them if that's a deal-breaker for you.

Also, nesting makes sure that the output in case of errors is meaningful - it just errors on the 1st failing place, and that's it.

[dimpase]

I'm willing to review a branch with nesting - or, you can review my branch...

[mjo]

Here it is fully nested. I cherry-picked your fix for fedora.txt, but I left "gmp" in the DEPCHECK because it's easier to just list them all than it is to try to keep track of which DEPCHECKs need to be modified when e.g. mpfr loses a dependency.

---

Last 10 new commits:

​dfb5860	Trac #29024: add Gentoo package information.
​175e6f6	29024: Add Singular distro info
​dc1dcc3	Trac #29024: work around Singular issue 1113 in init_libsingular().
​ef79af8	Trac #29024: add missing AC_MSG_RESULTs in singular/spkg-configure.m4.
​2f32b69	Trac #29024: clarify a comment in singular's spkg-configure.
​8ec888a	Trac #29024: fix libSingular path on Cygwin.
​62065de	Trac #29024: always obtain the absolute path to libSingular.
​2aa55e7	Trac #29024: fully nest tests in Singular's spkg-configure.m4.
​eecd43c	Fedora needs devel pkg
​eb3b4e5	Trac #29024: drop "mpir" from singular's DEPCHECK.

[dimpase]

build/pkgs/singular/distros/homebrew.txt should be like in my branch:

build/pkgs/singular/distros/homebrew.txt

@@ -1 @@
-# [2021-03-20] Homebrew's Singular can be built from source
-# (via `brew install -s`, or implied when using `brew` with
-# a non-standard prefix), but that currently fails.
-
-#singular
+singular

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​a3c5305

Trac #29024: re-enable the system singular hint on homebrew.

[dimpase]

lgtm

[arojas]

comment:95 hasn't been addressed. This breaks sage_conf-less installs.

[dimpase]

Replying to arojas:

comment:95 hasn't been addressed. This breaks sage_conf-less installs.

Please open a followup ticket. It's not clear to me how or what exactly needs to be be fixed.

[mkoeppe]

Replying to git:

Branch pushed to git repo; I updated commit sha1. New commits:

​a3c5305

Trac #29024: re-enable the system singular hint on homebrew.

This needs testing on GH Actions.

[dimpase]

needs work ? On what exactly?

[dimpase]

I suggest we run tests on the followup ticket for sage_conf-less installs.

The most one might need to adjust here is the list of distros on which this works.

[arojas]

Replying to dimpase:

It's not clear to me how or what exactly needs to be be fixed.

This unconditionally imports sage_conf so it breaks on systems without it. As I said in comment:97 adding a simple fallback should fix it, here is a patch that works for me

src/sage/libs/singular/singular.pyx

@@ -768 +768 @@
 
     cdef void *handle = NULL
 
-    from sage_conf import LIBSINGULAR_PATH
+    try:
+        from sage_conf import LIBSINGULAR_PATH
+    except ImportError:
+    # No sage_conf, assume everything is properly set up by the distro
+        LIBSINGULAR_PATH="libSingular.so"
     lib = str_to_bytes(LIBSINGULAR_PATH, FS_ENCODING, "surrogateescape")
 
     # This is a workaround for https://github.com/Singular/Singular/issues/1113

[dimpase]

see ​https://github.com/sagemath/sagetrac-mirror/actions/runs/1360343429

[mkoeppe]

Replying to arojas:

Replying to dimpase:

It's not clear to me how or what exactly needs to be be fixed.

This unconditionally imports sage_conf so it breaks on systems without it. As I said in comment:97 adding a simple fallback should fix it, here is a patch that works for me

src/sage/libs/singular/singular.pyx

@@ -768 +768 @@
 
     cdef void *handle = NULL
 
-    from sage_conf import LIBSINGULAR_PATH
+    try:
+        from sage_conf import LIBSINGULAR_PATH
+    except ImportError:
+    # No sage_conf, assume everything is properly set up by the distro
+        LIBSINGULAR_PATH="libSingular.so"
     lib = str_to_bytes(LIBSINGULAR_PATH, FS_ENCODING, "surrogateescape")
 
     # This is a workaround for https://github.com/Singular/Singular/issues/1113

Actually this should be rewritten so that it goes through a variable declared in sage.env instead of using sage_conf directly.

sage.env already takes care of conditional import from sage_conf.