bug#40216: 28.0.50; Misinformation in isearch char-fold

[Robert Pluim]

>>>>> On Wed, 25 Mar 2020 22:29:29 +0200, Juri Linkov <juri@linkov.net> said:

    >> Out of curiosity, what were you searching for that resulted in such a
    >> large regexp?

    Juri> Sometimes I pull a few of lines (usually 1-3 lines, not more)
    Juri> from the buffer into the search string to confirm that the same lines
    Juri> exist in more places in the same buffer ignoring the differences 
defined
    Juri> by folding rules.  But after pulling 2 lines into the search string,
    Juri> the generated regexp becomes so long that the regexp search fails
    Juri> with the error "Regular expression too big".  Currently it silently
    Juri> switches to literal search without notification that it doesn't follow
    Juri> the folding rules anymore.  With the patch it informs about switching
    Juri> to literal search.

Ah, I hadn't considered that use case. Do we need an option to
char-fold-regexp that says 'only apply char-folding to non-ascii
characters'? That would reduce the size of the regexp considerably.

Robert