Frame-local diff-hl-margin-mode?

[CyberShadow]

Thank you for this essential package!

I have a question: do you know if it's possible to make diff-hl-margin-mode frame-local? I.e. so that TTY frames have it on, but graphical frames have it off.

Use case: I access my Emacs server locally (graphically) and remotely (over SSH / TTY). Every time I switch, I have to nudge diff-hl to update margin mode (off locally, on remotely). I think ideally it would just be on for TTY frames, if that's possible.

I noticed that there is diff-hl-margin-local-mode, but I don't think that's quite it since that makes it buffer-local, but the same buffer can be open in both a graphical and TTY frame.

Thanks!

[dgutov]

We could do something like this:

diff --git a/diff-hl-margin.el b/diff-hl-margin.el
index c3fffde..a754a43 100644
--- a/diff-hl-margin.el
+++ b/diff-hl-margin.el
@@ -78,6 +78,10 @@
          (set-default symbol value)
          (setq diff-hl-margin-spec-cache nil)))
 
+(defcustom diff-hl-margin-nongraphic-only nil
+  "Only use the margin when a text-only terminal is used."
+  :type 'boolean)
+
 ;;;###autoload
 (define-minor-mode diff-hl-margin-mode
   "Toggle displaying `diff-hl-mode' highlights on the margin."
@@ -147,10 +151,13 @@ You probably shouldn't use this function directly."
                         ,(propertize char 'face
                                      (intern (format "diff-hl-margin-%s" type)))))))))
 
-(defun diff-hl-highlight-on-margin (ovl type _shape)
-  (let ((spec (cdr (assoc (cons type diff-hl-side)
-                          (diff-hl-margin-spec-cache)))))
-    (overlay-put ovl 'before-string spec)))
+(defun diff-hl-highlight-on-margin (ovl type shape)
+  (if (and diff-hl-margin-nongraphic-only
+           (display-graphic-p))
+      (funcall diff-hl-margin-old-highlight-function ovl type shape)
+    (let ((spec (cdr (assoc (cons type diff-hl-side)
+                            (diff-hl-margin-spec-cache)))))
+      (overlay-put ovl 'before-string spec))))
 
 (provide 'diff-hl-margin)
 

Apply the patch, change the variable to t and see the difference.

The only roadbump, I guess, is that the mode also changes the corresponding margin width (from 0 to 1, usually). But if you wanted to use the margin for something else, that shouldn't be a problem.

How make it frame-local isn't obvious, though I suppose the value could be changed on every update. Not sure if there will be any performance implications.