org-babel-comint-with-output: Fix for edge case of `comint-prompt-regexp'

* lisp/ob-comint.el (org-babel-comint-with-output): Implement more
universal algorithm catching agglomerated prompts.  The new approach
works for regexps that match ^, but not as the first char in the
regexp string.
* testing/lisp/test-ob-octave.el (ob-octave/session-multiline): Add
new test.

Reported-by: Paul Stansell <paulstansell@gmail.com>
Link: https://orgmode.org/list/CAMJKaZwuTV-06pPz5nv87CNcoVcqCwFjEodubXTzXs15Q=OFug@mail.gmail.com

lisp/ob-comint.el

@@ -76,7 +76,10 @@ or user `keyboard-quit' during execution of body."
 	(remove-echo (nth 2 meta))
 	(full-body (nth 3 meta))
         (org-babel-comint-prompt-separator
-         "org-babel-comint-prompt-separator"))
+         ;; We need newline in case if we do progressive replacement
+         ;; of agglomerated comint prompts with `comint-prompt-regexp'
+         ;; containing ^.
+         "org-babel-comint-prompt-separator\n"))
     `(org-babel-comint-in-buffer ,buffer
        (let* ((string-buffer "")
 	      (comint-output-filter-functions
@@ -106,21 +109,20 @@ or user `keyboard-quit' during execution of body."
 	 (insert dangling-text)
 
          ;; Filter out prompts.
-         (setq string-buffer
-               (replace-regexp-in-string
-                ;; Sometimes, we get multiple agglomerated
-                ;; prompts together in a single output:
-                ;; "prompt prompt prompt output"
-                ;; Or even "<whitespace>prompt<whitespace>prompt ...>.
-                ;; Remove them progressively, so that
-                ;; possible "^" in the prompt regexp gets to
-                ;; work as we remove the heading prompt
-                ;; instance.
-                (if (string-prefix-p "^" comint-prompt-regexp)
-                    (format "^\\([ \t]*%s\\)+" (substring comint-prompt-regexp 1))
-                  comint-prompt-regexp)
-                ,org-babel-comint-prompt-separator
-                string-buffer))
+         (while (string-match-p comint-prompt-regexp string-buffer)
+           (setq string-buffer
+                 (replace-regexp-in-string
+                  ;; Sometimes, we get multiple agglomerated
+                  ;; prompts together in a single output:
+                  ;; "prompt prompt prompt output"
+                  ;; Or even "<whitespace>prompt<whitespace>prompt ...>.
+                  ;; Remove them progressively, so that
+                  ;; possible "^" in the prompt regexp gets to
+                  ;; work as we remove the heading prompt
+                  ;; instance.
+                  (format "\\(?:%s\\)?\\(?:%s\\)[ \t]*" ,org-babel-comint-prompt-separator comint-prompt-regexp)
+                  ,org-babel-comint-prompt-separator
+                  string-buffer)))
 	 ;; remove echo'd FULL-BODY from input
 	 (when (and ,remove-echo ,full-body
 		    (string-match

testing/lisp/test-ob-octave.el

@@ -122,5 +122,15 @@ sombrero;
       (when (get-buffer "*Org-Babel Error Output*")
         (kill-buffer "*Org-Babel Error Output*")))))
 
+(ert-deftest ob-octave/session-multiline ()
+  "Test multiline session input."
+  (dotimes (_ 3)
+    (org-test-with-temp-text
+        "#+begin_src octave :session oct2 :results output
+  x = 1;
+  x = 1;
+  x = 1
+#+end_src"
+      (should (equal "x = 1" (org-babel-execute-src-block))))))
 
 (provide 'test-ob-octave)