Fixing Windows and DOS command line argument quoting

[Daniel Colascione <dan.colascione@gmail.com>]

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As I explain in [1], many Windows programs get command line argument
quoting wrong.  Emacs is one of these programs.  The attached patch
resolves the issue, and if there are no objections, I'll apply it to
both the Emacs 23 branch and the trunk in the next few days.

[1]
http://blogs.msdn.com/b/twistylittlepassagesallalike/archive/2011/04/23/everyone-quotes-arguments-the-wrong-way.aspx


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=== modified file 'lisp/subr.el'
--- lisp/subr.el	2011-04-19 13:44:55 +0000
+++ lisp/subr.el	2011-04-25 02:05:07 +0000
@@ -2507,19 +2507,33 @@
   "Quote ARGUMENT for passing as argument to an inferior shell."
   (if (or (eq system-type 'ms-dos)
           (and (eq system-type 'windows-nt) (w32-shell-dos-semantics)))
-      ;; Quote using double quotes, but escape any existing quotes in
-      ;; the argument with backslashes.
-      (let ((result "")
-	    (start 0)
-	    end)
-	(if (or (null (string-match "[^\"]" argument))
-		(< (match-end 0) (length argument)))
-	    (while (string-match "[\"]" argument start)
-	      (setq end (match-beginning 0)
-		    result (concat result (substring argument start end)
-				   "\\" (substring argument end (1+ end)))
-		    start (1+ end))))
-	(concat "\"" result (substring argument start) "\""))
+      
+      ;; First, quote argument so that CommandLineToArgvW will
+      ;; understand it.  Inside an argument, 2n or 2n + 1 backslashes
+      ;; followed by a double quote produces n backslashes.  In the
+      ;; former case, we also ends the argument.  In the latter case,
+      ;; we also produce a double-quote character and end the
+      ;; argument.  Backslashes not followed by a quotation mark are
+      ;; left alone. See
+      ;; http://msdn.microsoft.com/en-us/library/17w5ykft%28v=vs.85%29.aspx
+      ;; After we perform that level of quoting, replace shell
+      ;; metacharacters so that cmd won't mangle our argument.
+
+      (replace-regexp-in-string
+       "\\([()\"<>&|^]\\)"
+       "^\\1"
+       (concat
+        "\""
+        ;; escape backslashes at end of string
+        (replace-regexp-in-string
+         "\\(\\\\*\\)$"
+         "\\1\\1"
+         ;; escape backslashes and quotes in string body
+         (replace-regexp-in-string
+          "\\(\\\\*\\)\""
+          "\\1\\1\\\\\""
+          argument))
+        "\""))
     (if (equal argument "")
         "''"
       ;; Quote everything except POSIX filename characters.


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