Yeah. That is probably the best solution.

The "Requirements" section of the index.html already lists some packages. It is probably not up-to-date. I didn't know this list existed and never added anything on to it (like e.g. `zstd`).

My previous change allows the _ctypes module to be built but I see the following messages in the build-python3 log file:

*** WARNING: renaming "_ctypes" since importing it failed: libffi.so.8: cannot open shared object file: No such file or directory

[...]

Following modules built successfully but were removed because they could not be imported:
_ctypes

If I pass "--without-system-ffi" to the configure command in build-python3.mk I see the same problem as above.

I don't know to fix that.  Maybe some LD_LIBRARY_PATH setting, but I'm not seeing how to make it work.

After looking at my build (not one of the buildbots) I noticed this problem in the build-python3 log file:

gcc -pthread -fPIC -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Werror=implicit-function-declaration -I/scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/Include/internal -I/scratch/build/mxe-octave-w64/default/usr/x86_64-w64-mingw32/include -I. -I/scratch/build/mxe-octave-w64/default/usr/include -IObjects -IPython -I/usr/include/x86_64-linux-gnu -I/usr/local/include -I/scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/Include -I/scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/.build -c /scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/Modules/_ctypes/_ctypes.c -o build/temp.linux-x86_64-3.8/scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/Modules/_ctypes/_ctypes.o
In file included from /scratch/build/mxe-octave-w64/default/usr/x86_64-w64-mingw32/include/corecrt.h:10,
                 from /scratch/build/mxe-octave-w64/default/usr/x86_64-w64-mingw32/include/crtdefs.h:10,
                 from /scratch/build/mxe-octave-w64/default/usr/x86_64-w64-mingw32/include/limits.h:6,
                 from /scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/Include/Python.h:11,
                 from /scratch/build/mxe-octave-w64/default/tmp-build-python3/Python-3.8.3/Modules/_ctypes/_ctypes.c:104:
/scratch/build/mxe-octave-w64/default/usr/x86_64-w64-mingw32/include/_mingw.h:272:2: error: #error Only Win32 target is supported!
  272 | #error Only Win32 target is supported!
      |  ^~~~~

I was not expecting to see "-I/scratch/build/mxe-octave-w64/default/usr/x86_64-w64-mingw32/include" in the compiler flags when building a native build tool.  If I understand correctly, this is happening because the python3 configure script is using the pkg-config program that we build to tell us what -I option we should use to find libffi headers.  But by default our pkg-config program looks for .pc files in directories that are appropriate for the cross built packages, not the native ones.  We try to fix that up in the build-*.mk files where needed by using "PKG_CONFIG_PATH='$(BUILD_PKG_CONFIG_PATH)'" on the configure command line, but the value of BUILD_PKG_CONFIG_PATH is set in the mxe-octave configure script before we build the build-pkg-config program.

I checked in the following change but I'm not sure it is the best solution.

https://hg.octave.org/mxe-octave/rev/4e1ae8cbc9ec

Let's see if this helps with the buildbots.  If not, I'll take another look.

And another one that adds build-libtool to the dependencies of build-libffi:
https://hg.octave.org/mxe-octave/rev/5cb9ea0261ba

Unfortunately, building those build tools seems to depend on which packages are installed on the build system. So it looks like it can fail on some build systems even if it works for me locally.
I hope we'll reach a point where this is working reliably (and less dependent on the build system) soon.

That should have read: "The buildbots are failing to compile build-markupsafe now."

The error looks very similar to the one that you saw on your new system.

Works for me so closing as fixed.  Thanks!

The change seems fine to me.  Go ahead and push it and I'll uninstall libffi-dev on my system and try another build.

I hit the following problem when doing an mxe-octave build on a new system:

[build]    build-markupsafe

Failed to build package build-markupsafe!
------------------------------------------------------------
make[2]: Entering directory '/scratch/build/mxe-octave-w64/default'
rm -rf   '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe' '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe-install'
mkdir -p '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe'
( cd '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe' &&  tar xzf '/share/mxe-octave/pkg-src/MarkupSafe-1.0.tar.gz' ) ||  false
test ! -d '/home/jwe/src/mxe-octave/src/build-markupsafe' || cp -a '/home/jwe/src/mxe-octave/src/build-markupsafe' '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe'
cd '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe/MarkupSafe-1.0'
cd '/scratch/build/mxe-octave-w64/default/tmp-build-markupsafe/MarkupSafe-1.0' && python3 setup.py install --prefix='/scratch/build/mxe-octave-w64/default/usr'
Traceback (most recent call last):
  File "setup.py", linlibffi-dee 6, in <module>
    from setuptools import setup, Extension, Feature
  File "/scratch/build/mxe-octave-w64/default/usr/lib/python3.8/site-packages/setuptools/__init__.py", line 20, in <module>
    from setuptools.dist import Distribution, Feature
  File "/scratch/build/mxe-octave-w64/default/usr/lib/python3.8/site-packages/setuptools/dist.py", line 35, in <module>
    from setuptools import windows_support
  File "/scratch/build/mxe-octave-w64/default/usr/lib/python3.8/site-packages/setuptools/windows_support.py", line 2, in <module>
    import ctypes
  File "/scratch/build/mxe-octave-w64/default/usr/lib/python3.8/ctypes/__init__.py", line 7, in <module>
    from _ctypes import Union, Structure, Array
ModuleNotFoundError: No module named '_ctypes'
make[2]: *** [/scratch/build/mxe-octave-w64/default/Makefile:977: build-only-build-markupsafe] Error 1

After installing libffi-dev on the build system and rebuilding the build-python3 package in mxe-octave, the problem is gone and the build-markupsafe package builds successfully.  But maybe we should have rules to build the libffi package as part of the mxe-octave build rules so we can control the version that is used and to avoid this problem in the future?