Re: History for query replace pairs

[Juri Linkov <juri@jurta.org>]

> The widget library is definitely too heavy.  And I don't like the idea
> of making it read-only either.  Just use a special character/string, and
> give it a special appearance via text-properties (make sure the user
> can't delete just a part of it, so a single char is best, probably with
> a display property), so that the user can tell it's not just text and so
> that Elisp can reliably recognize it as well.
> E.g. (propertize "\0" 'display (propertize " -> " 'face 'my-face))

Currently there are two user variables `query-replace-from-history-variable'
and `query-replace-to-history-variable' by default both pointing
to the same history variable `query-replace-history'.  The simplest
solution would be to add another history variable named
`query-replace-from-to-history', so the users could easily customize
`query-replace-from-history-variable' either to the old value
`query-replace-history' to restore the current functionality,
or customize it to the new from-to pair history.

Below is a preliminary implementation.  However, there is a problem
that after saving it to the desktop or savehist, and restoring back
FROM-TO string pairs in the history lose text-properties.
If there is no way to save text properties then perhaps we should have
two history variables: one with cons pairs (FROM . TO) to save
in the desktop, and another with a list of strings "FROM<separator>TO"
to use in `read-from-minibuffer', and keep these two variables in sync.

=== modified file 'lisp/replace.el'
--- lisp/replace.el	2014-08-25 02:36:45 +0000
+++ lisp/replace.el	2014-10-25 20:48:10 +0000
@@ -54,10 +54,11 @@ (defvar query-replace-history nil
 See `query-replace-from-history-variable' and
 `query-replace-to-history-variable'.")
 
-(defvar query-replace-defaults nil
-  "Default values of FROM-STRING and TO-STRING for `query-replace'.
-This is a cons cell (FROM-STRING . TO-STRING), or nil if there is
-no default value.")
+(defvar query-replace-from-to-history nil
+  "Default history list of FROM-TO strings for `query-replace'.
+This is a list of string pairs of FROM-STRING and TO-STRING
+separated by `query-replace-from-to-separator', or nil
+if there is no history.  See `query-replace-from-history-variable'.")
 
 (defvar query-replace-interactive nil
   "Non-nil means `query-replace' uses the last search string.
@@ -67,14 +68,24 @@ (make-obsolete-variable 'query-replace-i
 to the minibuffer that reads the string to replace, or invoke replacements
 from Isearch by using a key sequence like `C-s C-s M-%'." "24.3")
 
-(defcustom query-replace-from-history-variable 'query-replace-history
+(defvar query-replace-from-to-separator
+  (propertize
+   "\0" 'display (propertize
+		  (if (char-displayable-p ?\u2192) " \u2192 " " -> ")
+		  'face 'minibuffer-prompt))
+  "String that separates FROM and TO in `query-replace-from-to-history'.")
+
+(defcustom query-replace-from-history-variable 'query-replace-from-to-history
   "History list to use for the FROM argument of `query-replace' commands.
 The value of this variable should be a symbol; that symbol
 is used as a variable to hold a history list for the strings
 or patterns to be replaced."
   :group 'matching
-  :type 'symbol
-  :version "20.3")
+  :type '(choice
+	  (const :tag "History of FROM-TO pairs" query-replace-from-to-history)
+	  (const :tag "History of FROM strings" query-replace-history)
+	  (symbol :tag "Your choice of history list"))
+  :version "24.5")
 
 (defcustom query-replace-to-history-variable 'query-replace-history
   "History list to use for the TO argument of `query-replace' commands.
@@ -132,11 +143,10 @@ (defun query-replace-read-from (prompt r
   (if query-replace-interactive
       (car (if regexp-flag regexp-search-ring search-ring))
     (let* ((history-add-new-input nil)
+	   (default (car query-replace-from-to-history))
 	   (prompt
-	    (if query-replace-defaults
-		(format "%s (default %s -> %s): " prompt
-			(query-replace-descr (car query-replace-defaults))
-			(query-replace-descr (cdr query-replace-defaults)))
+	    (if query-replace-from-to-history
+		(format "%s (default %s): " prompt default)
 	      (format "%s: " prompt)))
 	   (from
 	    ;; The save-excursion here is in case the user marks and copies
@@ -148,11 +158,25 @@ (defun query-replace-read-from (prompt r
 		(read-from-minibuffer
 		 prompt nil nil nil query-replace-from-history-variable
 		 (car (if regexp-flag regexp-search-ring search-ring)) t)))))
-      (if (and (zerop (length from)) query-replace-defaults)
-	  (cons (car query-replace-defaults)
+      (if (or
+	   ;; Default value
+	   (and (zerop (length from)) query-replace-from-to-history
+		(string-match query-replace-from-to-separator default))
+	   ;; History of FROM-TO pairs
+	   (and (eq query-replace-from-history-variable
+		    'query-replace-from-to-history)
+		(string-match query-replace-from-to-separator from)))
+	  (let ((from-string (substring (if (zerop (length from)) default from) 0 (match-beginning 0)))
+		(to-string (substring (if (zerop (length from)) default from) (match-end 0))))
+	    (unless (zerop (length from))
+	      (add-to-history query-replace-from-history-variable from nil t))
+	    (cons from-string
 		(query-replace-compile-replacement
-		 (cdr query-replace-defaults) regexp-flag))
-	(add-to-history query-replace-from-history-variable from nil t)
+		   to-string regexp-flag)))
+	;; Just FROM string
+	(unless (eq query-replace-from-history-variable
+		    'query-replace-from-to-history)
+	  (add-to-history query-replace-from-history-variable from nil t))
 	;; Warn if user types \n or \t, but don't reject the input.
 	(and regexp-flag
 	     (string-match "\\(\\`\\|[^\\]\\)\\(\\\\\\\\\\)*\\(\\\\[nt]\\)" from)
@@ -216,7 +240,9 @@ (defun query-replace-read-to (from promp
 		 nil nil nil
 		 query-replace-to-history-variable from t)))
        (add-to-history query-replace-to-history-variable to nil t)
-       (setq query-replace-defaults (cons from to))
+       (add-to-history 'query-replace-from-to-history
+		       (concat from query-replace-from-to-separator to)
+		       nil t)
        to))
    regexp-flag))