Assertion failure in xdisp.c

[Stefan]

src/emacs -Q lisp/gnus/mm-util.el -f outline-minor-mode -f reveal-mode
C-u 1000 M-x hide-sublevels RET  [ this hides all the function bodies. ]
C-e                              [ shows the previously hidden file header ]
C-a M->                          [ The first line show not visible any more ]
M-<                              [ Back on the first line, the copyright
                                   notice should be hidden again.  If not
                                   try M-> M-< a few more times. ]
C-e

This last C-e (which should re-show the header with the copyright notice)
aborts.  It aborts inside `find_first_unchanged_at_end_row' at the test:

          if (!row->enabled_p || !MATRIX_ROW_DISPLAYS_TEXT_P (row))
            abort ();

On my Mac OS X machine, catching this abort in the debugger leads to
a confusing stack trace (GDB tells me I'm in try_window_id called from
try_window_id, and doesn't mention find_first_unchanged_at_end_row).
Replacing the above by

          eassert (row->enabled_p && MATRIX_ROW_DISPLAYS_TEXT_P (row));

helped a great deal.

If I remove the assertion, everything works just dandy.  Is the assertion
still correct (and thus some bug needs to be fixed) or should the assertion
be fixed/eliminated?


        Stefan