[ESS] what is font-lock-pre-idle-hook

[Stephen Eglen]

Stephen Eglen writes:
 > 
 >  > It has nothing to do with the ESS R buffer. i.e it has something to do
 >  > with loading .R files only. So if I load a .R file and I edited outside
 >  > the buffer (e.g. through pico or something) I get the message.
 >  > 
 >  > shortest example:
 >  > touch temp.R
 >  > xemacs temp.R
 >  > ls > temp.R # in gnome-terminal or something and go back to xemacs
 >  > Mx revert-buffer
 > 
 > Thanks for this - I can now reproduce the warning; will investigate
 > sometime - although it is a minor warning, it may have consequences
 > elsewhere.

Ok, looks to me like an XEmacs bug, as several other modes report same
problem.  Notably, ProofGeneral says the following:
http://proofgeneral.inf.ed.ac.uk/BUGS

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XEmacs font-lock problem in certain versions of XEmacs 21.4

When reloading (with C-x C-f) an already loaded script file that has
been changed on the file system you see the error:

(1) (warning/warning) Error caught in `font-lock-pre-idle-hook':
    (wrong-type-argument markerp nil)

As a result fontification, etc, fails. Workaround: use C-x C-v
instead. This problem has gone away since 21.4.12 or so.

Update: this has reappeared in version 21.4.15.
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So, sorry, no joy for fixing this one.

best wishes,
Stephen