bug#10885: Replace expressions: enhance functionality when searching in filled paragraphs

[Juri Linkov <juri@jurta.org>]

>> Would it make sense for replace-regexp/query-replace-regexp (and
>> other commands that read regexps from the user) to respect
>> search-whitespace-regexp, just like isearch?
>
> Good question.
>
> Quote from the docstring of `isearch-forward-regexp':
>
>  In regexp incremental searches, a space or spaces normally matches
>  any whitespace (the variable `search-whitespace-regexp' controls
>  precisely what that means).  If you want to search for a literal space
>  and nothing else, enter C-q SPC.
>
> Does anyone know why `query-replace-regexp' doesn't behave that way too?
>
> I think it should, i.e., `query-replace-regexp' should find the same
> matches that `isearch-forward-regexp' would find with the same search
> regexp.

Full agreement.  This patch for 24.2 brings query-replace closer to isearch:

=== modified file 'lisp/replace.el'
--- lisp/replace.el	2012-02-24 22:46:57 +0000
+++ lisp/replace.el	2012-02-28 10:38:58 +0000
@@ -1752,6 +1752,7 @@ (defun perform-replace (from-string repl
 	  (if (and case-fold-search search-upper-case)
 	      (isearch-no-upper-case-p from-string regexp-flag)
 	    case-fold-search))
+	 (search-spaces-regexp (if regexp-flag search-whitespace-regexp))
          (nocasify (not (and case-replace case-fold-search)))
          (literal (or (not regexp-flag) (eq regexp-flag 'literal)))
          (search-function
@@ -2117,9 +2115,8 @@ (defun replace-highlight (match-beg matc
   (if query-replace-lazy-highlight
       (let ((isearch-string string)
 	    (isearch-regexp regexp)
-	    (search-whitespace-regexp nil)
 	    (isearch-case-fold-search case-fold)
 	    (isearch-forward t)
 	    (isearch-error nil))