[Bug 1899076] [NEW] "import readline" crashes after loading an extension linked against libedit

[Colin Watson]

Public bug reported:

The Launchpad test suite segfaults on Python 3.6 in bionic when its
stdout is not a tty.  This is currently visible as
http://lpbuildbot.canonical.com/builders/lp-devel-bionic-
py3/builds/4/steps/shell_7/logs/stdio, though I'm not sure how long that
link will continue to exist before buildbot garbage-collects it, so the
relevant bit is:

  No entry for terminal type "unknown";
  using dumb terminal settings.
  bind: Invalid command `enable-meta-key'.
  No entry for terminal type "unknown";
  using dumb terminal settings.
  No entry for terminal type "unknown";
  using dumb terminal settings.
  Segmentation fault

After considerable effort I tracked this down as far as this upstream
bug report:

  https://bugs.python.org/issue38634

A reduced reproduction recipe (requiring "apt install gir1.2-gtk-3.0
python3-gi xvfb") is:

  xvfb-run python3 -c 'from gi.repository import Gtk; import readline'

While we may be able to work around this somehow in our test suite, it's
going to be very cumbersome and it looks as though it will have to
involve not importing readline anywhere, which is going to be pretty
fragile, or maybe stubbing readline.  Would you consider please
backporting the upstream change in
https://github.com/python/cpython/pull/16986/files, which looks as
though it should fix this properly?  (I also commented on the upstream
bug report remarking on how this isn't necessarily a rare case.)

** Affects: python3.6 (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1899076

Title:
  "import readline" crashes after loading an extension linked against
  libedit

Status in python3.6 package in Ubuntu:
  New

Bug description:
  The Launchpad test suite segfaults on Python 3.6 in bionic when its
  stdout is not a tty.  This is currently visible as
  http://lpbuildbot.canonical.com/builders/lp-devel-bionic-
  py3/builds/4/steps/shell_7/logs/stdio, though I'm not sure how long
  that link will continue to exist before buildbot garbage-collects it,
  so the relevant bit is:

    No entry for terminal type "unknown";
    using dumb terminal settings.
    bind: Invalid command `enable-meta-key'.
    No entry for terminal type "unknown";
    using dumb terminal settings.
    No entry for terminal type "unknown";
    using dumb terminal settings.
    Segmentation fault

  After considerable effort I tracked this down as far as this upstream
  bug report:

    https://bugs.python.org/issue38634

  A reduced reproduction recipe (requiring "apt install gir1.2-gtk-3.0
  python3-gi xvfb") is:

    xvfb-run python3 -c 'from gi.repository import Gtk; import readline'

  While we may be able to work around this somehow in our test suite,
  it's going to be very cumbersome and it looks as though it will have
  to involve not importing readline anywhere, which is going to be
  pretty fragile, or maybe stubbing readline.  Would you consider please
  backporting the upstream change in
  https://github.com/python/cpython/pull/16986/files, which looks as
  though it should fix this properly?  (I also commented on the upstream
  bug report remarking on how this isn't necessarily a rare case.)

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