bug#192: regexp does not work as documented

[Chong Yidong <cyd@stupidchicken.com>]

martin rudalics <rudalics@gmx.at> writes:

>> First I'll work on the hi-lock warning as I described below, then I'll
>> see about detecting and doing something helpful for additional
>> situations where multi-line won't work.
>
> Think of the following pathological case: Devise a regexp to highlight
> the first line of a buffer provided the buffer does not end with a
> newline.  Doing this with `font-lock-multiline' hardly makes any sense.

Ideally, highlight-regexp should work automagically, instead of forcing
users to do something extra to make their multi-line regexp work
properly.  The right way to do this is probably for hi-lock-mode to
process the buffer initially, setting up text properties to make
font-lock DTRT even for multi-line expressions.  But that's a big job.

As for making hi-lock-mode detect whether or not a regexp is multi-line,
isn't that a computationally non-trivial problem?

Maybe making hi-lock-mode turn on font-lock-multiline, while not
foolproof, works often enough to be satisfactory.