ob-R, ob-julia: Do not force-start session in Org Src buffers

* lisp/ob-R.el (org-babel-R-associate-session): Set
`ess-gen-proc-buffer-name-function' to associate the right session
buffer if user requests session interaction from inside Org Src edit
buffer.
(org-babel-edit-prep:R): Remove in favor of
`org-babel-R-associate-session'.
* lisp/ob-julia.el (org-babel-julia-associate-session): Implement
analogous functionality.
(org-babel-edit-prep:julia): Remove in favor of
`org-babel-julia-associate-session'.
* etc/ORG-NEWS (~org-edit-special~ no longer force-starts session in R
and Julia source blocks): Document the change.
* lisp/org-src.el (org-src-associate-babel-session): Run
org-babel-<lang>-associate-session even when session is not yet
initiated.

Link: https://orgmode.org/list/87r0ir2ln8.fsf@gmail.com

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-edit-special~ no longer force-starts session in R and Julia source blocks
+
+Previously, when R/Julia source block had =:session= header argument
+set to a session name with "earmuffs" (like =*session-name*=),
+~org-edit-special~ always started a session, if it does not exist.
+
+Now, ~org-edit-special~ arranges that a new session with correct name
+is initiated only when user explicitly executes R/Julia-mode commands
+that trigger session interactions (requires ESS 24.01.0 or newer).
+The same session will remain available in the context of Org babel.
+
 *** It is no longer allowed to tangle into the same file as Org source
 
 Previously, =file.org= with the following contents

lisp/ob-R.el

@@ -91,17 +91,6 @@ this variable.")
   :version "24.1"
   :type 'string)
 
-(defvar ess-current-process-name) ; dynamically scoped
-(defvar ess-local-process-name)   ; dynamically scoped
-(defun org-babel-edit-prep:R (info)
-  "Initiate R session for Org edit buffer, as needed.
-The session name is taken from INFO."
-  (let ((session (cdr (assq :session (nth 2 info)))))
-    (when (and session
-	       (string-prefix-p "*"  session)
-	       (string-suffix-p "*" session))
-      (org-babel-R-initiate-session session nil))))
-
 ;; The usage of utils::read.table() ensures that the command
 ;; read.table() can be found even in circumstances when the utils
 ;; package is not in the search path from R.
@@ -264,6 +253,8 @@ Retrieve variables from PARAMS."
 	  (t                (format "%s <- %S" name (prin1-to-string value))))))
 
 
+(defvar ess-current-process-name) ; dynamically scoped
+(defvar ess-local-process-name)   ; dynamically scoped
 (defvar ess-ask-for-ess-directory) ; dynamically scoped
 (defvar ess-gen-proc-buffer-name-function) ; defined in ess-inf.el
 (defun org-babel-R-initiate-session (session params)
@@ -296,9 +287,10 @@ Use PARAMS to set default directory when creating a new session."
   "Associate R code buffer with an R session.
 Make SESSION be the inferior ESS process associated with the
 current code buffer."
-  (setq ess-local-process-name
-	(process-name (get-buffer-process session)))
-  (ess-make-buffer-current))
+  (when-let ((process (get-buffer-process session)))
+    (setq ess-local-process-name (process-name process))
+    (ess-make-buffer-current))
+  (setq-local ess-gen-proc-buffer-name-function (lambda (_) session)))
 
 (defvar org-babel-R-graphics-devices
   '((:bmp "bmp" "filename")

lisp/ob-julia.el

@@ -70,12 +70,15 @@
 (defvar ess-local-process-name)   ; dynamically scoped
 (defvar ess-eval-visibly-p)       ; dynamically scoped
 (defvar ess-local-customize-alist); dynamically scoped
-(defun org-babel-edit-prep:julia (info)
-  (let ((session (cdr (assq :session (nth 2 info)))))
-    (when (and session
-	       (string-prefix-p "*"  session)
-	       (string-suffix-p "*" session))
-      (org-babel-julia-initiate-session session nil))))
+(defvar ess-gen-proc-buffer-name-function) ; defined in ess-inf.el
+(defun org-babel-julia-associate-session (session)
+  "Associate R code buffer with an R session.
+Make SESSION be the inferior ESS process associated with the
+current code buffer."
+  (when-let ((process (get-buffer-process session)))
+    (setq ess-local-process-name (process-name process))
+    (ess-make-buffer-current))
+  (setq-local ess-gen-proc-buffer-name-function (lambda (_) session)))
 
 (defun org-babel-expand-body:julia (body params &optional _graphics-file)
   "Expand BODY according to PARAMS, return the expanded body."
@@ -178,7 +181,6 @@ end"
     (format "%s = %s" name (org-babel-julia-quote-csv-field value))))
 
 (defvar ess-ask-for-ess-directory) ; dynamically scoped
-(defvar ess-gen-proc-buffer-name-function) ; defined in ess-inf.el
 (defun org-babel-julia-initiate-session (session params)
   "If there is not a current julia process then create one."
   (unless (string= session "none")

lisp/org-src.el

@@ -925,7 +925,6 @@ INFO should be a list similar in format to the return value of
   (interactive)
   (let ((session (cdr (assq :session (nth 2 info)))))
     (and session (not (string= session "none"))
-	 (org-babel-comint-buffer-livep session)
 	 (let ((f (intern (format "org-babel-%s-associate-session"
                                   (nth 0 info)))))
            (and (fboundp f) (funcall f session))))))