Re: How to track down "No heading for this item in buffer or region."?

[Nick Dokos <nicholas.dokos@hp.com>]

Bastien <bzg@altern.org> wrote:

> Nick Dokos <nicholas.dokos@hp.com> writes:
> 
> > to try to reproduce Rainer's problem, when I first construct the agenda,
> > I get *both* the TODO and the no-heading message: text properties are not
> > active. If I then visit the file (e.g. RET on the TODO item) and construct
> > the agenda again, neither the TODO nor the no-heading message
> > appears.
> 
> I see -- it was not obvious to me you were trying without opening the
> file in a buffer.  With my patch, I can reproduce the error, but only
> the TODO (which appears instead of being skipped, not with the
> timestamp line.  Yes, seems related to properties.  I'll digg further.
> 

Not quite: the file *is* opened in a buffer (the agenda code opens all the
files, I presume with find-file-noselect), but the text properties are
not up to date. It's only when I explicitly visit the buffer
that they get updated.

E.g. if you evaluate

--8<---------------cut here---------------start------------->8---
(setq buf (find-file-noselect "/path/to/test.org"))
(with-current-buffer buf
  (setq s (buffer-substring 1 2)))
--8<---------------cut here---------------end--------------->8---

the echo area shows

,----
| #("#" 0 1 (fontified nil))
`----

But if you visit the buffer with C-x b test.org RET and then
evaluate the second form again, you get 

,----
| #("#" 0 1 (fontified t font-lock-fontified t face font-lock-comment-face))
`----

There is a section on lazy properties in the elisp manual but I don't
know how to use the mechanism described there: there are no examples in
current emacs code, some half-hearted experiments failed for unknown
reasons, and googling a bit found only one relevant thread in the emacs
group from 2004 - quoting Stefan Monnier from that thread:

#+BEGIN_QUOTE
  I think the lazy text properties that you refer to (i.e. variable
  buffer-access-fontify-functions) are a sadly perfect example of C code
  implemented before we knew what we needed.  It's implemented,
  documented, and 100% unused.
#+END_QUOTE

AFAICT, nothing has been done in this area since then.

Nick

PS. Here's the trivial test.org again for completeness:

--8<---------------cut here---------------start------------->8---
# timestamp: <2013-01-24 Thu>

* TODO foo
#  SCHEDULED: <2013-01-24 Thu>
--8<---------------cut here---------------end--------------->8---