RE: Gnus + emacs.stackexchange

[Drew Adams <drew.adams@oracle.com>]

> >>> (wrong-type-argument char-or-string-p nil) in
> >>> tabulated-list-print
> >>
> >> Ok, would you be willing to produce a backtrace?
> >> (with M-x toggle-debug-on-error)
> >
> > This is what it says for `sx-search':
> >
> >     Debugger entered--Lisp error: (wrong-type-argument char-or-
> >                                    string-p nil)
> >       tabulated-list-print-fake-header()
> >       tabulated-list-print(remember)
> 
> Ok. It looks like something is setting your
> `tabulated-list-use-header-line' variable to nil *between* the
> buffer initialization and the list printing. So the
> `tabulated-list--header-string' variable doesn't get set (it's
> normally set during buffer initialization), but when it's time to
> print, the variable is expected to be a string.
> I think that's a bug in tabulated-list-mode (which I'll try to get
> fixed now), but do you have any hooks or advices that may be causing
> that?

Check where you call the major (derived) mode, which calls
`tabulated-list-mode'.  If it calls it after you have already
inserted the header line then that line will be removed when
`tabulated-list-mode' (calls `special-mode' which) kills all
local variables.

IMO, the `tabulated-list-mode' doc is not clear about such
things.  Put differently, the design of `tabulated-list-mode'
seems to be a bit fragile.  You need to do things in a specific
order, which is not well documented.

Caveat: I'm no expert on `tabulated-list-mode'.  Just starting
to wade through it myself, actually - which is why I think I
recognize the above error.  When I understand it better I will
perhaps file a bug report or two - doc or otherwise.