bug#8861: 24.0.50; Isearch: Repeating the last search

[Juri Linkov <juri@jurta.org>]

> I expect that, whenever Isearch is active, the search string will
> always be highlighted to reflect the matched and unmatched parts at
> every moment, regardless of how that string has been introduced
> (char by char, by copy&paste, by "C-s C-s",

Currently it's possible to reproduce the behavior you are asking for,
by copy&paste from the system clipboard into Emacs running in xterm
(it pastes char by char):

1. emacs -Q -nw
2. M-<
3. C-s S-Ins

When trying this, it seems it's worse than the default behavior because
treating the search string char by char is useful only when you are
typing it because highlighting the failed part helps to correct typos.
But when you want to search for the previous search string by `C-s C-s'
or by copy&paste from the clipboard/kill-ring it's more useful
to treat it as a whole.  For instance, often it's necessary to
put a string into the search ring (`C-s string RET') and search
its exact occurrence in another buffer (`C-x o C-s C-s').
It would be annoying when searching for e.g. "caterpillar"
will stop at "cat" and highlight it.

However, your idea is not completely useless.  Currently isearch mode
is interactively incremental but you propose to extend it it into
non-interactively incremental (i.e. incremental even when the search
string is not composed interactively).  Maybe a new option/mode
could do that but I think it should not be enabled by default.