Remove strict requirement for libreadline when building python3

[mkoeppe]

Given that IPython is using prompt_toolkit for terminal interactions, we can probably remove the hard requirement for readline from the build of python3.

This would eliminate the build failures that we see reported occasionally related to ncurses/readline ("undefined symbol: UP", #31267).

[mkoeppe]

Moving this ticket to 9.4, as it seems unlikely that it will be merged in 9.3, which is in the release candidate stage

[mkoeppe]

New commits:

​de25ce5

build/pkgs/python3/spkg-build.in, spkg-configure.m4: Do not check for the readline module

[dimpase]

Does this mean we potentially will build Python without readline support (if this is possible at all)

[mkoeppe]

Yes

[dimpase]

OK

[mkoeppe]

Thanks.

[tscrim]

I think because of this I am now no longer able to build R:

checking for rl_callback_read_char in -lreadline... no
configure: error: --with-readline=yes (default) and headers/libs are not available

I couldn't get past the Python3 build without this ticket.

[mkoeppe]

It is unlikely that this is connected. R does not use Python. If R does not build, you can use ./configure --disable-r to disable it.

[tscrim]

Ah, okay. Thank you. Sorry for the noise.

[tscrim]

Perhaps this is related?

uqtscrim@SMP-36PQ8T2:~/sage-build$ ./sage -t src/sage/algebras/weyl_algebra.py 
too few successful tests, not using stored timings
Running doctests with ID 2021-06-28-16-35-50-d69fb13c.
Git branch: public/new_fmatrix-30423
Using --optional=build,debian,dochtml,pip,sage,sage_spkg
Doctesting 1 file.
Traceback (most recent call last):
  File "/home/uqtscrim/sage-build/src/bin/sage-runtests", line 144, in <module>
    err = DC.run()
  File "/home/uqtscrim/sage-build/local/lib/python3.9/site-packages/sage/doctest/control.py", line 1207, in run
    self.run_doctests()
  File "/home/uqtscrim/sage-build/local/lib/python3.9/site-packages/sage/doctest/control.py", line 904, in run_doctests
    self.dispatcher = DocTestDispatcher(self)
  File "/home/uqtscrim/sage-build/local/lib/python3.9/site-packages/sage/doctest/forker.py", line 1658, in __init__
    init_sage(controller)
  File "/home/uqtscrim/sage-build/local/lib/python3.9/site-packages/sage/doctest/forker.py", line 234, in init_sage
    import readline
ModuleNotFoundError: No module named 'readline'

[mkoeppe]

Yes, this one is...

[git]

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

​6df6144

src/sage/doctest/forker.py: Do not crash if readline cannot be imported

[mkoeppe]

Try with this fix please

[tscrim]

This now fixes the doctester. Thank you. Although now I am wondering why we even need that import there. Can't we just remove it, especially considering #32073?

[tscrim]

Replying to tscrim:

Can't we just remove it, especially considering #32073?

I guess we need to check that we don't have a regression to #14289.

[mkoeppe]

I commented out this import, and it does not seem to make a difference with current versions of Python and macOS.

However, I haven't really used sage -t --debug before and I don't really understand its interface (sometimes I'm getting pdb prompts, sometimes sage prompts?), so it is quite possible that I am missing something

[tscrim]

I think since this is needed in order for me to build Sage (hence, the blocker upgrade) and this makes the situation no worse for a secondary feature, we can just leave it in for now. Although that is equally a reason to just simply comment that one line with leaving a note...but perhaps best for a followup.

[mkoeppe]

Thanks. I agree.