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

[Juri Linkov <juri@jurta.org>]

> 1. Add a new defcustom like `case-replace' with a name e.g.
> `replace-lax-whitespace' and use it in `perform-replace'.
> When non-nil, spaces will match any whitespace in replacement.

This is implemented in the following patch:

=== modified file 'lisp/replace.el'
--- lisp/replace.el	2012-08-06 05:33:39 +0000
+++ lisp/replace.el	2012-09-02 11:27:15 +0000
@@ -33,6 +33,13 @@ (defcustom case-replace t
   :type 'boolean
   :group 'matching)
 
+(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,
+it will match any sequence matched by the regexp `search-whitespace-regexp'."
+  :type 'boolean
+  :group 'matching)
+
 (defvar query-replace-history nil
   "Default history list for query-replace commands.
 See `query-replace-from-history-variable' and
@@ -226,6 +233,10 @@ (defun query-replace (from-string to-str
 matched is all caps, or capitalized, then its replacement is upcased
 or capitalized.)
 
+If `replace-lax-whitespace' is non-nil, a space or spaces in the string
+to be replaced will match a sequence of whitespace chars defined by the
+regexp in `search-whitespace-regexp'.
+
 Third arg DELIMITED (prefix arg if interactive), if non-nil, means replace
 only matches surrounded by word boundaries.
 Fourth and fifth arg START and END specify the region to operate on.
@@ -270,6 +281,10 @@ (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
+to be replaced will match a sequence of whitespace chars defined by the
+regexp in `search-whitespace-regexp'.
+
 Third arg DELIMITED (prefix arg if interactive), if non-nil, means replace
 only matches surrounded by word boundaries.
 Fourth and fifth arg START and END specify the region to operate on.
@@ -346,6 +361,10 @@ (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
+to be replaced will match a sequence of whitespace chars defined by the
+regexp in `search-whitespace-regexp'.
+
 Third arg DELIMITED (prefix arg if interactive), if non-nil, means replace
 only matches that are surrounded by word boundaries.
 Fourth and fifth arg START and END specify the region to operate on."
@@ -437,6 +456,10 @@ (defun replace-string (from-string to-st
 \(Preserving case means that if the string matched is all caps, or capitalized,
 then its replacement is upcased or capitalized.)
 
+If `replace-lax-whitespace' is non-nil, a space or spaces in the string
+to be replaced will match a sequence of whitespace chars defined by the
+regexp in `search-whitespace-regexp'.
+
 In Transient Mark mode, if the mark is active, operate on the contents
 of the region.  Otherwise, operate from point to the end of the buffer.
 
@@ -475,6 +498,10 @@ (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
+to be replaced will match a sequence of whitespace chars defined by the
+regexp in `search-whitespace-regexp'.
+
 In Transient Mark mode, if the mark is active, operate on the contents
 of the region.  Otherwise, operate from point to the end of the buffer.
 
@@ -1717,12 +1745,12 @@ (defun replace-match-maybe-edit (newtext
   (replace-match newtext fixedcase literal)
   noedit)
 
-(defvar replace-search-function 'search-forward
+(defvar replace-search-function nil
   "Function to use when searching for strings to replace.
 It is used by `query-replace' and `replace-string', and is called
 with three arguments, as if it were `search-forward'.")
 
-(defvar replace-re-search-function 're-search-forward
+(defvar replace-re-search-function nil
   "Function to use when searching for regexps to replace.
 It is used by `query-replace-regexp', `replace-regexp',
 `query-replace-regexp-eval', and `map-query-replace-regexp'.
@@ -1755,9 +1783,16 @@ (defun perform-replace (from-string repl
          (nocasify (not (and case-replace case-fold-search)))
          (literal (or (not regexp-flag) (eq regexp-flag 'literal)))
          (search-function
-	  (if regexp-flag
-	      replace-re-search-function
-	    replace-search-function))
+	  (or (if regexp-flag
+		  replace-re-search-function
+		replace-search-function)
+	      (if replace-lax-whitespace
+		  (if regexp-flag
+		      #'re-search-forward-lax-whitespace
+		    #'search-forward-lax-whitespace)
+		(if regexp-flag
+		    #'re-search-forward
+		  #'search-forward))))
          (search-string from-string)
          (real-match-data nil)       ; The match data for the current match.
          (next-replacement nil)
@@ -2120,7 +2156,10 @@ (defun replace-highlight (match-beg matc
 	    ;; Set isearch-word to nil because word-replace is regexp-based,
 	    ;; so `isearch-search-fun' should not use `word-search-forward'.
 	    (isearch-word nil)
-	    (search-whitespace-regexp nil)
+	    (isearch-lax-whitespace
+	     (and replace-lax-whitespace (not regexp)))
+	    (isearch-regexp-lax-whitespace
+	     (and replace-lax-whitespace regexp))
 	    (isearch-case-fold-search case-fold)
 	    (isearch-forward t)
 	    (isearch-error nil))

=== modified file 'lisp/isearch.el'
--- lisp/isearch.el	2012-09-02 09:31:45 +0000
+++ lisp/isearch.el	2012-09-02 11:27:15 +0000
@@ -1579,14 +1612,11 @@ (defun isearch-query-replace (&optional
 	;; set `search-upper-case' to nil to not call
 	;; `isearch-no-upper-case-p' in `perform-replace'
 	(search-upper-case nil)
-	(replace-search-function
-	 (if (and isearch-lax-whitespace (not regexp-flag))
-	     #'search-forward-lax-whitespace
-	   replace-search-function))
-	(replace-re-search-function
-	 (if (and isearch-regexp-lax-whitespace regexp-flag)
-	     #'re-search-forward-lax-whitespace
-	   replace-re-search-function))
+	(replace-lax-whitespace
+	 (and search-whitespace-regexp
+	      (if isearch-regexp
+		  isearch-regexp-lax-whitespace
+		isearch-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.
@@ -2956,6 +3045,10 @@ (defun isearch-lazy-highlight-search ()
 	    (isearch-regexp isearch-lazy-highlight-regexp)
 	    (isearch-word isearch-lazy-highlight-word)
 	    (search-invisible nil)	; don't match invisible text
+	    (isearch-lax-whitespace
+	     isearch-lazy-highlight-lax-whitespace)
+	    (isearch-regexp-lax-whitespace
+	     isearch-lazy-highlight-regexp-lax-whitespace)
 	    (retry t)
 	    (success nil)
 	    (isearch-forward isearch-lazy-highlight-forward)