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

[Juri Linkov <juri@jurta.org>]

> I think replace-regexp-lax-whitespace is needed while the Isearch
> counterpart (isearch-regexp-lax-whitespace) exists, if you want to
> support the option I was asking for, whereby the lax-whitespace
> settings in query-replace[-regexp] are "connected" (or "redirected")
> to the Isearch counterparts.
>
> And IMO this option is important, for a consistent user-experience.

The reason why replace-regexp-lax-whitespace is important to have
is not just for consistency but because replace-lax-whitespace
should not affect regexp replacements.  But currently its value applies
to regexp replacements because it depends on calls from isearch that has
a separate variable for regexp that starts a lax-whitespace regexp replacement
to replace the same regexp matches as in isearch.  So actually a lax-whitespace
regexp replacement feature exists in replace.el implicitly.  A clean way to
fix this problem is to add a new option replace-regexp-lax-whitespace:

=== modified file 'lisp/replace.el'
--- lisp/replace.el	2012-09-06 09:12:16 +0000
+++ lisp/replace.el	2012-09-07 09:27:35 +0000
@@ -35,7 +35,15 @@ (defcustom case-replace t
 
 (defcustom replace-lax-whitespace nil
   "Non-nil means `query-replace' matches a sequence of whitespace chars.
-When you enter a space or spaces in the strings or regexps to be replaced,
+When you enter a space or spaces in the strings to be replaced,
+it will match any sequence matched by the regexp `search-whitespace-regexp'."
+  :type 'boolean
+  :group 'matching
+  :version "24.3")
+
+(defcustom replace-regexp-lax-whitespace nil
+  "Non-nil means `query-replace-regexp' matches a sequence of whitespace chars.
+When you enter a space or spaces in the regexps to be replaced,
 it will match any sequence matched by the regexp `search-whitespace-regexp'."
   :type 'boolean
   :group 'matching
@@ -282,7 +290,7 @@ (defun query-replace-regexp (regexp to-s
 all caps, or capitalized, then its replacement is upcased or
 capitalized.)
 
-If `replace-lax-whitespace' is non-nil, a space or spaces in the regexp
+If `replace-regexp-lax-whitespace' is non-nil, a space or spaces in the regexp
 to be replaced will match a sequence of whitespace chars defined by the
 regexp in `search-whitespace-regexp'.
 
@@ -362,7 +370,7 @@ (defun query-replace-regexp-eval (regexp
 Preserves case in each replacement if `case-replace' and `case-fold-search'
 are non-nil and REGEXP has no uppercase letters.
 
-If `replace-lax-whitespace' is non-nil, a space or spaces in the regexp
+If `replace-regexp-lax-whitespace' is non-nil, a space or spaces in the regexp
 to be replaced will match a sequence of whitespace chars defined by the
 regexp in `search-whitespace-regexp'.
 
@@ -499,7 +507,7 @@ (defun replace-regexp (regexp to-string
 Preserve case in each match if `case-replace' and `case-fold-search'
 are non-nil and REGEXP has no uppercase letters.
 
-If `replace-lax-whitespace' is non-nil, a space or spaces in the regexp
+If `replace-regexp-lax-whitespace' is non-nil, a space or spaces in the regexp
 to be replaced will match a sequence of whitespace chars defined by the
 regexp in `search-whitespace-regexp'.
 
@@ -1790,9 +1798,9 @@ (defun perform-replace (from-string repl
 	      (let ((isearch-regexp regexp-flag)
 		    (isearch-word delimited-flag)
 		    (isearch-lax-whitespace
-		     (and replace-lax-whitespace (not regexp-flag)))
+		     replace-lax-whitespace)
 		    (isearch-regexp-lax-whitespace
-		     (and replace-lax-whitespace regexp-flag))
+		     replace-regexp-lax-whitespace)
 		    (isearch-case-fold-search case-fold-search)
 		    (isearch-forward t))
 		(isearch-search-fun))))
@@ -2151,9 +2159,9 @@ (defun replace-highlight (match-beg matc
 	    (isearch-regexp regexp-flag)
 	    (isearch-word delimited-flag)
 	    (isearch-lax-whitespace
-	     (and replace-lax-whitespace (not regexp-flag)))
+	     replace-lax-whitespace)
 	    (isearch-regexp-lax-whitespace
-	     (and replace-lax-whitespace regexp-flag))
+	     replace-regexp-lax-whitespace)
 	    (isearch-case-fold-search case-fold-search)
 	    (isearch-forward t)
 	    (isearch-error nil))

=== modified file 'lisp/isearch.el'
--- lisp/isearch.el	2012-09-06 09:12:16 +0000
+++ lisp/isearch.el	2012-09-07 09:27:42 +0000
@@ -1613,10 +1613,9 @@ (defun isearch-query-replace (&optional
 	;; `isearch-no-upper-case-p' in `perform-replace'
 	(search-upper-case nil)
 	(replace-lax-whitespace
-	 (and search-whitespace-regexp
-	      (if isearch-regexp
-		  isearch-regexp-lax-whitespace
-		isearch-lax-whitespace)))
+	 isearch-lax-whitespace)
+	(replace-regexp-lax-whitespace
+	 isearch-regexp-lax-whitespace)
 	;; Set `isearch-recursive-edit' to nil to prevent calling
 	;; `exit-recursive-edit' in `isearch-done' that terminates
 	;; the execution of this command when it is non-nil.