RE: highlight failed part of isearch input

[Drew Adams]

> > I find that this minor tweak to `isearch-message' helps a good deal when
> > using Isearch. It highlights, within your Isearch input, the
> > part that fails to match.
>
> As you can see in the original `isearch-message', it already highlights
> the part that fails to match, but only when this part contains trailing
> spaces.

Yes. That's probably where I got the idea; I don't remember.

> Your patch overwrites it with a new face.  I think these two
> features could be merged.

Sure. Unless someone thinks we should differentiate failure with trailing
space from other failure. (I see no reason to differentiate them,
personally.)

> Also I think it would be annoying to highlight
> the whole search string when it fails (like when repeating the search with
> the string from the search ring).  It could do this only during typing the
> search string character by character.

I don't agree about that. It lets you know right away what you've done. For
example, perhaps you changed buffers, so the previous search string is no
longer pertinent. The slight color change is enough to signal what's
happening, without your needing to really examine the minibuffer text and
process the "Failing" message mentally.

I do think it's important to use a face that is subdued, however, rather
than the red-foreground face that is the default for trailing space
highlighting. This should be something gently noticeable, not a blazing
warning of imminent danger.

If you haven't already, please give it a try, and see if you really find it
annoying for letting you know that the entire search string is a non-match.