bug#61069: 30.0.50; comint-copy-old-input should include continuation lines

[Bob Rogers]

   From: Robert Pluim <rpluim@gmail.com>
   Date: Mon, 30 Jan 2023 09:25:19 +0100

   >>>>> On Fri, 27 Jan 2023 19:45:33 -0800, Bob Rogers <rogers@rgrjr.com> said:
      Bob> Then the following should fit the bill.  Given that this solution
       Bob> introduces a defcustom, I imagine it should also have a NEWS item as
       Bob> well . . .

   Yes. And a :version on the new defcustom itself.

Right.

       Bob>                                     -- Bob

       Bob> * lisp/shell.el (shell-get-old-input-include-continuation-lines): 
New
       Bob> defcustom (default nil).
       Bob> (shell-get-old-input): Like comint-get-old-input-default but include
       Bob> all continuation lines if the above is true.
       Bob> (shell-mode): Install shell-get-old-input. (bug#61069)

   Two spaces after '.'

Good; I prefer that as well.  (I see I chose a poor example as a commit
log message prototype.)

       Bob> +(defcustom shell-get-old-input-include-continuation-lines nil
       Bob> +  "If non-nil, shell-get-old-input-default includes \"\\\" lines."
       Bob> +  :type 'boolean
       Bob> +  :group 'shell)
       Bob> +

   "Whether `shell-get-old-input-default' includes \"\\\" lines."

Nice; I was wondering how to make that more concise.

       Bob> +(defun shell-get-old-input ()
       Bob> +  . . .
       Bob> +  (let (field-prop bof)
       Bob> +    (if (and (not comint-use-prompt-regexp)
       Bob> +             ;; Make sure we're in an input rather than output 
field.
       Bob> +             (not (setq field-prop (get-char-property
       Bob> +                                    (setq bof (field-beginning)) 
'field))))
       Bob> +   (field-string-no-properties bof)

   Emacs uses spaces only in elisp. We even have a .dir-locals.el
   enforcing that.

   Robert
   -- 

I hadn't noticed that, actually -- either the .dir-locals.el or the
policy.  FWIW, I think both of these tabs are from cutting-and-pasting
from comint.el.

                                        -- Bob

* lisp/shell.el (shell-get-old-input-include-continuation-lines): New
defcustom (default nil).
(shell-get-old-input): Like comint-get-old-input-default but include
all continuation lines if the above is true.
(shell-mode): Install shell-get-old-input.  (bug#61069)

diff --git a/lisp/shell.el b/lisp/shell.el
index 5cf108bfa3b..31fb98c0176 100644
--- a/lisp/shell.el
+++ b/lisp/shell.el
@@ -366,6 +366,12 @@ shell-has-auto-cd
   :group 'shell-directories
   :version "28.1")
 
+(defcustom shell-get-old-input-include-continuation-lines nil
+  "Whether shell-get-old-input-default includes \"\\\" lines."
+  :type 'boolean
+  :group 'shell
+  :version "30.1")
+
 (defcustom shell-kill-buffer-on-exit nil
   "Kill a shell buffer after the shell process terminates."
   :type 'boolean
@@ -506,6 +512,38 @@ shell--parse-pcomplete-arguments
           (push (mapconcat #'identity (nreverse arg) "") args)))
       (cons (nreverse args) (nreverse begins)))))
 
+(defun shell-get-old-input ()
+  "Default for `comint-get-old-input' in shell-mode.
+If `comint-use-prompt-regexp' is nil, then either
+return the current input field, if point is on an input field, or the
+current line, if point is on an output field.
+If `comint-use-prompt-regexp' is non-nil, then return
+the current line with any initial string matching the regexp
+`comint-prompt-regexp' removed.  In either case, if
+shell-get-old-input-include-continuation-lines is non-nil and the
+current line ends with a backslash, the next line is also included and
+examined for a backslash, ending with a final line without a backslash."
+  (let (field-prop bof)
+    (if (and (not comint-use-prompt-regexp)
+             ;; Make sure we're in an input rather than output field.
+             (not (setq field-prop (get-char-property
+                                    (setq bof (field-beginning)) 'field))))
+        (field-string-no-properties bof)
+      (comint-bol)
+      (let ((start (point)))
+        (cond ((or comint-use-prompt-regexp
+                   (eq field-prop 'output))
+               (goto-char (line-end-position))
+               (when shell-get-old-input-include-continuation-lines
+                 ;; Include continuation lines as long as the current
+                 ;; line ends with a backslash.
+                 (while (and (not (eobp))
+                             (= (char-before) ?\\))
+                   (goto-char (line-end-position 2)))))
+              (t
+               (goto-char (field-end))))
+        (buffer-substring-no-properties start (point))))))
+
 ;;;###autoload
 (defun split-string-shell-command (string)
   "Split STRING (a shell command) into a list of strings.
@@ -642,6 +680,7 @@ shell-mode
   (setq-local font-lock-defaults '(shell-font-lock-keywords t))
   (setq-local shell-dirstack nil)
   (setq-local shell-last-dir nil)
+  (setq-local comint-get-old-input #'shell-get-old-input)
   ;; People expect Shell mode to keep the last line of output at
   ;; window bottom.
   (setq-local scroll-conservatively 101)