org-babel: New babel backend API function org-babel-session-buffer:<lang>

* lisp/ob-core.el (org-babel-session-buffer): New API function that
return session buffer, if such buffer exists and is live.
(org-babel-execute-src-block): Use `org-babel-session-buffer'.
* lisp/ob-lua.el (org-babel-session-buffer:lua):
* lisp/ob-python.el (org-babel-session-buffer:python): Provide API to
retrieve session buffer name.
(org-babel-python-initiate-session-by-key): Use
`org-babel-session-buffer:python'.
* etc/ORG-NEWS (Org babel backends are now expected to define an
additional API function ~org-babel-session-buffer:<lang>~): Declare
the API addition.

Link: https://orgmode.org/list/87r0hr9f3b.fsf@localhost

etc/ORG-NEWS

@@ -13,6 +13,17 @@ Please send Org bug reports to mailto:emacs-orgmode@gnu.org.
 
 * Version 9.7 (not released yet)
 ** Important announcements and breaking changes
+*** Org babel backends are now expected to define an additional API function ~org-babel-session-buffer:<lang>~
+
+Org babel now uses session buffer (if it exists) to retrieve
+~default-directory~ environment during src block evaluation.
+
+By default, buffer named like session is checked.  All the backends
+that create sessions inside buffers named differently should provide a
+function ~org-babel-session-buffer:<lang>~.  The function must accept
+two arguments - session name and info list (as returned by
+~org-babel-get-src-block-info~); and return the session buffer name.
+
 *** ~org-insert-subheading~ no longer inserts a sub-heading above current when point is at the beginning of line
 
 Previously, calling ~org-insert-subheading~ on

lisp/ob-core.el

@@ -767,8 +767,30 @@ When `:file-desc' is missing, return nil."
     (`(:file-desc) result)
     (`(:file-desc . ,(and (pred stringp) val)) val)))
 
-(defvar *this*) ; Dynamically bound in `org-babel-execute-src-block'
-                ; and `org-babel-read'
+(defvar *this*)
+;; Dynamically bound in `org-babel-execute-src-block'
+;; and `org-babel-read'
+
+(defun org-babel-session-buffer (&optional info)
+  "Return buffer name for session associated with current code block.
+Return nil when no such live buffer with process exists.
+When INFO is non-nil, it should be a list returned by
+`org-babel-get-src-block-info'.
+This function uses org-babel-session-buffer:<lang> function to
+retrieve backend-specific session buffer name."
+  (declare-function org-babel-comint-buffer-livep "ob-comint" (buffer))
+  (when-let* ((info (or info (org-babel-get-src-block-info 'no-eval)))
+              (lang (nth 0 info))
+              (session (cdr (assq :session (nth 2 info))))
+              (cmd (intern (concat "org-babel-session-buffer:" lang)))
+              (buffer-name
+               (if (fboundp cmd)
+                   (funcall cmd session info)
+                 ;; Use session name as buffer name by default.
+                 session)))
+    (require 'ob-comint)
+    (when (org-babel-comint-buffer-livep buffer-name)
+      buffer-name)))
 
 ;;;###autoload
 (defun org-babel-execute-src-block (&optional arg info params executor-type)
@@ -842,9 +864,8 @@ guess will be made."
 		 (default-directory
 		  (cond
 		   ((not dir) default-directory)
-                   ((when-let ((session (cdr (assq :session params))))
-                      (when (org-babel-comint-buffer-livep session)
-                        (buffer-local-value 'default-directory (get-buffer session)))))
+                   ((when-let ((session (org-babel-session-buffer info)))
+                      (buffer-local-value 'default-directory (get-buffer session))))
 		   ((member mkdirp '("no" "nil" nil))
 		    (file-name-as-directory (expand-file-name dir)))
 		   (t

lisp/ob-lua.el

@@ -184,6 +184,11 @@ Emacs-lisp table, otherwise return the results as a string."
 	name
       (format "*%s*" name))))
 
+(defun org-babel-session-buffer:lua (session &optional _)
+  "Return session buffer name for SESSION."
+  (or (org-babel-lua-session-buffer session)
+      (org-babel-lua-with-earmuffs session)))
+
 (defun org-babel-lua-without-earmuffs (session)
 "Remove stars around *SESSION*, leaving SESSION."
   (let ((name (if (stringp session) session (format "%s" session))))

lisp/ob-python.el

@@ -260,6 +260,11 @@ results as a string."
 	(substring name 1 (- (length name) 1))
       name)))
 
+(defun org-babel-session-buffer:python (session &optional _)
+  "Return session buffer name for SESSION."
+  (or (org-babel-python-session-buffer session)
+      (org-babel-python-with-earmuffs session)))
+
 (defun org-babel-python--python-util-comint-end-of-output-p ()
   "Return non-nil if the last prompt matches input prompt.
 Backport of `python-util-comint-end-of-output-p' to emacs28.  To
@@ -302,8 +307,7 @@ already been configured as such, do nothing.  Return the
 initialized session."
   (save-window-excursion
     (let* ((session (if session (intern session) :default))
-           (py-buffer (or (org-babel-python-session-buffer session)
-                          (org-babel-python-with-earmuffs session)))
+           (py-buffer (org-babel-session-buffer:python session))
            (python-shell-buffer-name
 	    (org-babel-python-without-earmuffs py-buffer))
            (existing-session-p (comint-check-proc py-buffer))