How to paste with mouse middle click the text copied from Emacs or other applications?

I would like to:

Copy text from Emacs by highlighting it with a mouse (or copy from other applications with command+c).
Paste the copied text into Emacs with mouse middle click (or paste it into other applications with command+v).

How can I do this?

Copying from Emacs and then pasting into Emacs works OK.
But copying from other applications and pasting into Emacs with mouse middle click does not work. I have to use control+y instead.

I am using Emacs Version 30.1 from GNU Emacs For Mac OS X, running on MacBook Pro with Apple M1 Max chip, macOS Sequoia 15.4.1.

Notes

I also tried using the code below in my ~/.emacs file:

(setq select-active-regions nil)
(setq mouse-drag-copy-region t)
(global-set-key [mouse-2] 'mouse-yank-at-click)

But this code has a side effect described in this post: After cutting text, and then copying another text, the cut text is prepended to the copied text upon pasting - Emacs Stack Exchange. The issue described in that post still remains unsolved. I borrowed this code from this answer to this question: How to combine Emacs primary/clipboard copy and paste behavior on MS Windows? - Stack Overflow.

Solution

If you want to make mouse middle-click paste from the clipboard instead, regardless of whether the text came from Emacs or a macOS app, you can redefine the mouse-2 binding to yank from the clipboard, like this

Add this to your ~/.emacs

(defun my/mouse-yank-from-clipboard (event)
  "Paste text from the clipboard at mouse click."
  (interactive "e")
  (mouse-set-point event)
  (insert (gui-get-selection 'CLIPBOARD)))

(global-set-key [mouse-2] #'my/mouse-yank-from-clipboard)

This do as below

Moves point where you click.
Inserts text from the clipboard (which macOS Cmd+C sets).
Avoids the messy primary selection issue entirely.
Works cleanly with macOS and Emacs for Mac.

Below is what happen in Emacs

mouse-2 (mouse-yank-at-click) pastes from the primary selection.
On X11 systems (like Linux), selecting text with a mouse automatically sets the primary selection, but macOS doesn’t have this concept natively.
On macOS, when you copy text in another app (Cmd+C), it only goes to the clipboard, not the primary selection.
By default, Emacs on macOS integrates with the clipboard (for C-y and Cmd-v), but middle-click still tries to yank from the primary selection, which isn't getting updated from macOS apps.

Note

If you also want Emacs kill commands (like C-w, M-w) to copy to the system clipboard, add below.

(setq select-enable-clipboard t)

Update 1

Can you use below. The code is updated with If Emacs has a primary selection, use it else use the system clipboard.

(defun my/mouse-yank-smart (event)
  "Paste primary selection if available, otherwise paste from clipboard."
  (interactive "e")
  (mouse-set-point event)
  (if (and (fboundp 'gui-get-primary-selection)
           (gui-get-primary-selection))
      (insert (gui-get-primary-selection))
    (insert (gui-get-selection 'CLIPBOARD))))

(global-set-key [mouse-2] #'my/mouse-yank-smart)

Update 2

Can you try updated code below for last issues.

;; Make all Emacs copy/cut operations go to system clipboard
(setq select-enable-clipboard t)

;; Disable primary selection to avoid conflicts (no X11 primary selection on macOS)
(setq select-enable-primary nil)

;; Make mouse-dragging a region immediately copy it to clipboard
(setq mouse-drag-copy-region t)

;; Smart middle-click: paste active region if it exists, else paste from clipboard
(defun my/mouse-yank-smart (event)
  "Paste active region if available, otherwise paste from system clipboard."
  (interactive "e")
  (mouse-set-point event)
  (cond
   ;; If there's an active region, paste it
   ((use-region-p)
    (insert (buffer-substring-no-properties (region-beginning) (region-end))))
   ;; Else paste from macOS system clipboard
   (t
    (insert (gui-get-selection 'CLIPBOARD)))))

;; Bind middle-click to our smart paste function
(global-set-key [mouse-2] #'my/mouse-yank-smart)