bug#10734: Proposal: comint-history-read-only

[Zachary Kanfer <zkanfer@gmail.com>]

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This patch proposes a new feature in comint mode. Currently, setting
comint-prompt-read-only to some non-nil value makes the prompt read-only,
but this only makes the prompt read-only. I don't find it useful to insert
text into the middle of a historical buffer, so I added a new variable
comint-history-read-only. If set to non-nil, this variable makes the entire
history read-only.

-Zachary Kanfer

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[-- Attachment #2: comint-history-read-only-2012-02-06.txt --]
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=== modified file 'lisp/comint.el'
*** lisp/comint.el	2011-11-20 07:30:16 +0000
--- lisp/comint.el	2012-02-06 07:25:40 +0000
*************** you might wish to use another binding fo
*** 194,199 ****
--- 194,204 ----
    :group 'comint
    :version "22.1")
  
+ (defcustom comint-history-read-only nil
+   "If non-nil, all comint history is read only."
+   :type 'boolean
+   :group 'comint)
+ 
  (defvar comint-delimiter-argument-list ()
    "List of characters to recognize as separate arguments in input.
  Strings comprising a character in this list will separate the arguments
*************** Make backspaces delete the previous char
*** 2022,2035 ****
  	    (let ((prompt-start (save-excursion (forward-line 0) (point)))
  		  (inhibit-read-only t)
  		  (inhibit-modification-hooks 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-nonsticky 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
--- 2027,2043 ----
  	    (let ((prompt-start (save-excursion (forward-line 0) (point)))
  		  (inhibit-read-only t)
  		  (inhibit-modification-hooks t))
!               (cond (comint-history-read-only
!                      (add-text-properties (point-min) (point)
!                                           '(read-only t front-sticky (read-only))))
!                     (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-nonsticky 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