(comint-prompt-read-only): New variable.

(comint-output-filter): Implement it.

1 files changed, 24 insertions, 7 deletions

diff --git a/lisp/comint.el b/lisp/comint.el
index 7766307f156..52217fa8ad6 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -171,6 +171,14 @@ Good choices:
 
 This is a good thing to set in mode hooks.")
 
+(defcustom comint-prompt-read-only nil
+  "If non-nil, the comint prompt is read only.
+This does not affect existing prompts.
+Certain derived modes may override this option."
+  :type 'boolean
+  :group 'comint
+  :version "21.4")
+
 (defvar comint-delimiter-argument-list ()
   "List of characters to recognise as separate arguments in input.
 Strings comprising a character in this list will separate the arguments
@@ -1687,16 +1695,25 @@ Make backspaces delete the previous character."
               (let ((inhibit-read-only t))
                 (add-text-properties comint-last-output-start (point)
                                      '(rear-nonsticky t
-                                       field output
-                                       inhibit-line-move-field-capture t))))
+                                       field output
+                                       inhibit-line-move-field-capture t))))
 
             ;; Highlight the prompt, where we define `prompt' to mean
             ;; the most recent output that doesn't end with a newline.
-            (unless (and (bolp) (null comint-last-prompt-overlay))
-              ;; Need to create or move the prompt overlay (in the case
-              ;; where there is no prompt ((bolp) == t), we still do
-              ;; this if there's already an existing overlay).
-              (let ((prompt-start (save-excursion (forward-line 0) (point))))
+            (let ((prompt-start (save-excursion (forward-line 0) (point)))
+                  (inhibit-read-only t))
+              (when comint-prompt-read-only
+                (or (= (point-min) prompt-start)
+                    (get-text-property (1- prompt-start) 'read-only)
+                    (put-text-property
+                     (1- prompt-start) prompt-start 'read-only 'fence))
+                (add-text-properties
+                 prompt-start (point)
+                 '(read-only t rear-non-sticky t front-sticky (read-only))))
+              (unless (and (bolp) (null comint-last-prompt-overlay))
+                ;; Need to create or move the prompt overlay (in the case
+                ;; where there is no prompt ((bolp) == t), we still do
+                ;; this if there's already an existing overlay).
                 (if comint-last-prompt-overlay
                     ;; Just move an existing overlay
                     (move-overlay comint-last-prompt-overlay