gptel-transient: Commands to act on region

gptel.el (gptel): When calling `gptel' with a selected region, insert it
into a new session.

gptel-transient.el (gptel--suffix-send-existing,
gptel--suffix-send-new): Transient suffixes available when a region is
selected.  These send the text as a prompt in a existing or new gptel
session.

gptel-transient.el

@@ -25,6 +25,7 @@
 ;;
 
 ;;; Code:
+(eval-when-compile (require 'cl-lib))
 (require 'gptel)
 (require 'transient)
 
@@ -163,8 +164,35 @@ will get progressively longer!"
              (read-from-minibuffer "Set temperature (0.0-2.0, leave empty for default): "
               (number-to-string gptel--temperature))))
 
+(transient-define-suffix gptel--suffix-send-existing ()
+  "Send query in existing chat session."
+  :if (lambda () (use-region-p))
+  :key "E"
+  :description "Send in existing session"
+  (interactive)
+  (when-let* ((this (buffer-name))
+              (prompt (buffer-substring (region-beginning)
+                                       (region-end)))
+              (buf
+               (completing-read
+                "Send query in buffer: " (mapcar #'buffer-name (buffer-list))
+                (lambda (buf) (and (buffer-local-value 'gptel-mode (get-buffer buf))
+                              (not (equal this buf)))))))
+    (with-current-buffer buf
+      (goto-char (point-max))
+      (insert prompt)
+      (pop-to-buffer buf))))
+
+(transient-define-suffix gptel--suffix-send-new ()
+  "Send query in new session."
+  :if (lambda () (use-region-p))
+  :description "Send in new session"
+  :key "N"
+  (interactive)
+  (let ((current-prefix-arg t)) (call-interactively #'gptel)))
+
 (transient-define-suffix gptel--suffix-system-message ()
-  "Set Establishing message sent to ChatGPT."
+  "Set directives sent to ChatGPT."
   :transient nil
   :description "Set custom directives"
   :key "h"

gptel.el

@@ -286,18 +286,23 @@ Return the message received."
     map))
 
 ;;;###autoload
-(defun gptel (name &optional api-key)
+(defun gptel (name &optional api-key initial)
   "Switch to or start ChatGPT session with NAME.
 
 With a prefix arg, query for a (new) session name.
 
-Ask for API-KEY if `gptel-api-key' is unset."
+Ask for API-KEY if `gptel-api-key' is unset.
+
+If region is active, use it as the INITIAL prompt."
   (interactive (list (if current-prefix-arg
                          (read-string "Session name: " (generate-new-buffer-name gptel-default-session))
                        gptel-default-session)
                      (or gptel-api-key
                          (setq gptel-api-key
-                               (read-passwd "OpenAI API key: ")))))
+                               (read-passwd "OpenAI API key: ")))
+                     (and (use-region-p)
+                          (buffer-substring (region-beginning)
+                                            (region-end)))))
   (unless api-key
     (user-error "No API key available"))
   (with-current-buffer (get-buffer-create name)
@@ -308,7 +313,7 @@ Ask for API-KEY if `gptel-api-key' is unset."
       (visual-line-mode 1))
      (t (funcall gptel-default-mode)))
     (unless gptel-mode (gptel-mode 1))
-    (if (bobp) (insert gptel-prompt-string))
+    (if (bobp) (insert (or initial gptel-prompt-string)))
     (pop-to-buffer (current-buffer))
     (goto-char (point-max))
     (skip-chars-backward "\t\r\n")