Highlighting text in open (displayed) buffers/windows -- searching for text from one buffer in another

Question

Right now, I have my Emacs frame vertically split, and am looking at two different buffers in the two windows.

I'd like to go to a word in one buffer, hit some keys, and have the ocurrences of that word (if any) highlighted in the other buffer, scrolling to it if necessary.

Is there a way to do that?

In the screenshot above, with my cursor just before "bar" in the left buffer, I'd like to be able to <do something> and quickly see where "bar" is in the right buffer.

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Note: This is related to How do I find text across multiple open buffers? in the sense that, if I could do an isearch across the "other" buffer, it would do what I want. But none of the answers there are exactly what I want:

• The occur based solutions open a new window that shows matching lines, while I'd like to keep my two windows still displayed -- I'm actually going to be looking in the other buffer for context around the match, so showing only the matching line is not very helpful.
• multi-isearch-buffers requires me to specify the list of buffers every time I want to do this search (a lot of times), instead of automatically picking it up as the two displayed buffers. More importantly, when I start from one window and perform the isearch, when it finds the match in the other buffer it displays that buffer in this window, so that both windows display the same (other) buffer. Then C-g puts everything back, and I can't see the word highlighted in the other buffer any more.
• icicle-search has so many features that one of them may be able to do this, but I wasn't able to find anything after a cursory look at the documentation.

Answer 1

You can use a package called highlight-global that's available from github but not on Melpa (as of writing this).

The highlight-frame-toggle function defined in this pacakge will highlight the word at point or the selected region everywhere in the frame (in all the buffers). This, though, would not do the autoscroll to the highlighted word that you need. It picks a different highlighting color as you highlight more words without clearing the earlier hightlights.

Here is a screenshot of what it looks like:

Click for better view of the screenshot

Answer 2

helm has interfaces that can accomplish this goal, I've recorded a Gifcast to demonstrate the helm-swoop package:

After starting the helm-swoop search I can either narrow down to less candidates by entering further space-separated tokens or hit C-p and C-n to switch to the next one and scroll in the target buffer at the same time.

Answer 3

How about using highlight-regexp to highlight the current symbol (or word, region, etc) in the other window?

Here's a couple functions that could work. The first one will find the symbol at point, then jump to the other window and highlight it. The second one jumps to the other window and removes the highlights.

 (require 'thingatpt)

 (defun highlight-other-window ()
   (interactive)
   (let ((match (thing-at-point 'symbol t)))
     (when match
       (save-excursion
         (other-window 1)
         (highlight-regexp (regexp-quote match))
         (other-window 1)))))

 (defun unhighlight-other-window ()
   (interactive)
   (save-excursion
     (other-window 1)
     (unhighlight-regexp t) 
     (other-window 1)))

In both cases this jumps back so the current window remains active at the end. Not sure if that's what you want, otherwise leave off the final other-window call.

These functions could also be improved by checking for and matching the active region; dealing with the case where there is no other window visible; etc.