[Bug 2058388] Re: urwid 2.6.4-1 exception when rendering an empty Pile or Columns as a flow widget

[Olivier Gayot]

** Patch added: "1-2.6.4-1__2.6.4-1ubuntu1.debdiff"
   https://bugs.launchpad.net/debian/+source/urwid/+bug/2058388/+attachment/5757228/+files/1-2.6.4-1__2.6.4-1ubuntu1.debdiff

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https://bugs.launchpad.net/bugs/2058388

Title:
  urwid 2.6.4-1 exception when rendering an empty Pile or Columns as a
  flow widget

Status in subiquity:
  Invalid
Status in urwid package in Ubuntu:
  In Progress
Status in urwid package in Debian:
  Unknown

Bug description:
  When attempting to render an empty Pile or Columns as a flow widget
  using urwid 2.6.4-1, it fails with the following exception:

    File "/usr/lib/python3/dist-packages/urwid/widget/widget.py", line 112, in cached_render
      canv = fn(self, size, focus=focus)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/urwid/widget/pile.py", line 822, in render
      _widths, heights, size_args = self.get_rows_sizes(size, focus)
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/urwid/widget/pile.py", line 730, in get_rows_sizes
      heights.append(w.pack(w_h_arg, item_focus)[1])
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/urwid/widget/pile.py", line 744, in pack
      return super().pack(size, focus)
             ^^^^^^^^^^^^^^^^^^^^^^^^^
    File "/usr/lib/python3/dist-packages/urwid/widget/widget.py", line 401, in pack
      raise WidgetError(f"Cannot pack (maxcol,) size, this is not a flow widget: {self!r}")
  urwid.widget.widget.WidgetError: Cannot pack (maxcol,) size, this is not a flow widget: <Pile widget>

  Minimal code to reproduce:

  ```python
  from urwid import Pile

  Pile([
      ("pack", Pile([])),
  ]).render((10,))
  ```

  This looks like a regression in 2.6.4-1 since the same code was not
  failing on 2.1.2-4

  There is an upstream fix [1] that is released in urwid 2.6.5.

   https://github.com/urwid/urwid/pull/843

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