Re: History for query replace pairs

[Juri Linkov <juri@jurta.org>]

> The (not (equal (car preloaded-file-list) "replace")) test makes
> no sense.  Why don't we want to call char-displayable-p while
> pre-loading replace?  Shouldn't we instead test (fboundp 'char-displayable-p)
> or simply wrap the code in ignore-errors (if the problem is that
> char-displayable-p fails when run without a real frame at hand, which
> might also happen in daemon mode)?

I already tried (fboundp 'char-displayable-p) earlier but it
returns t while pre-loading because the problem was caused
by an attempt to autoload char-displayable-p.

Now I tried ignore-errors, and there are no problems with it:

=== modified file 'lisp/replace.el'
--- lisp/replace.el	2014-11-07 23:33:41 +0000
+++ lisp/replace.el	2014-11-09 22:58:25 +0000
@@ -67,11 +67,16 @@ (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")
 
-(defvar query-replace-from-to-separator
-  (propertize "\0"
-	      'display (propertize " \u2192 " 'face 'minibuffer-prompt)
-	      'separator t)
-  "String that separates FROM and TO in the history of replacement pairs.")
+(defcustom query-replace-from-to-separator
+  (propertize
+   (or (ignore-errors
+	 (if (char-displayable-p ?\u2192) " \u2192 " " -> "))
+       " -> ")
+   'face 'minibuffer-prompt)
+  "String that separates FROM and TO in the history of replacement pairs."
+  :group 'matching
+  :type 'sexp
+  :version "25.1")
 
 (defcustom query-replace-from-history-variable 'query-replace-history
   "History list to use for the FROM argument of `query-replace' commands.
@@ -137,19 +142,25 @@ (defun query-replace-read-from (prompt r
 wants to replace FROM with TO."
   (if query-replace-interactive
       (car (if regexp-flag regexp-search-ring search-ring))
+    (custom-reevaluate-setting 'query-replace-from-to-separator)
     (let* ((history-add-new-input nil)
+	   (separator
+	    (when query-replace-from-to-separator
+	      (propertize "\0"
+			  'display query-replace-from-to-separator
+			  'separator t)))
 	   (query-replace-from-to-history
 	    (append
-	     (when query-replace-from-to-separator
+	     (when separator
 	       (mapcar (lambda (from-to)
 			 (concat (query-replace-descr (car from-to))
-				 query-replace-from-to-separator
+				 separator
 				 (query-replace-descr (cdr from-to))))
 		       query-replace-defaults))
 	     (symbol-value query-replace-from-history-variable)))
 	   (minibuffer-allow-text-properties t) ; separator uses text-properties
 	   (prompt
-	    (if (and query-replace-defaults query-replace-from-to-separator)
+	    (if (and query-replace-defaults separator)
 		(format "%s (default %s): " prompt (car query-replace-from-to-history))
 	      (format "%s: " prompt)))
 	   (from
@@ -166,7 +177,7 @@ (defun query-replace-read-from (prompt r
 	  (cons (caar query-replace-defaults)
 		(query-replace-compile-replacement
 		 (cdar query-replace-defaults) regexp-flag))
-	(let* ((to (if (and (string-match query-replace-from-to-separator from)
+	(let* ((to (if (and (string-match separator from)
 			    (get-text-property (match-beginning 0) 'separator from))
 		       (query-replace-compile-replacement
 			(substring-no-properties from (match-end 0)) regexp-flag)))