bug#14847: 24.1; gdb-mi.el does not handle backslashes as quotes

[Sergio Durigan Junior <sergiodj@riseup.net>]

If you start gdb-mi.el (on Emacs 24.1), and try to use backslashes to
quote/break long lines, it is not handled correctly.  For example,
suppose your program being debugged inside GDB takes 3 arguments.  You
could run it with:

    (gdb) file myprogram
    Reading symbols from myprogram...done.
    (gdb) run \
    first_arg \
    second_arg \
    third_arg

GDB should correctly run the binary using the 3 args.  However, inside
Emacs, you receive an error:

    Undefined command: "third_arg".  Try "help".

This is because gdb-mi.el is not handling the backslashes correctly.
The error is specifically on the function `gdb_send', and the patch
inlined in this message fixes this.  The patch can also be seen on:

<https://lists.gnu.org/archive/html/emacs-devel/2013-07/msg00423.html>

And there is also a GDB bug related to this issue:

<http://sourceware.org/bugzilla/show_bug.cgi?id=15596>

Thanks.

lisp/ChangeLog:
2013-07-12  Sergio Durigan Junior  <sergiodj@riseup.net>

	* progmodes/gdb-mi.el (gdb-strip-string-backslash): New function.
	(gdb-send): Correctly handle continuation strings with
	backslashes, and properly set the last command typed.

diff --git a/lisp/progmodes/gdb-mi.el b/lisp/progmodes/gdb-mi.el
index 2c4d6a0..87c5f98 100644
--- a/lisp/progmodes/gdb-mi.el
+++ b/lisp/progmodes/gdb-mi.el
@@ -1759,6 +1759,9 @@ static char *magick[] = {
 As long as GDB is in the recursive reading loop, it does not expect
 commands to be prefixed by \"-interpreter-exec console\".")
 
+(defun gdb-strip-string-backslash (string)
+  (replace-regexp-in-string "\\\\$" "" string))
+
 (defun gdb-send (proc string)
   "A comint send filter for gdb."
   (with-current-buffer gud-comint-buffer
@@ -1766,8 +1769,13 @@ commands to be prefixed by \"-interpreter-exec console\".")
       (remove-text-properties (point-min) (point-max) '(face))))
   ;; mimic <RET> key to repeat previous command in GDB
   (if (not (string= "" string))
-      (setq gdb-last-command string)
-    (if gdb-last-command (setq string gdb-last-command)))
+      (if gdb-continuation
+	  (setq gdb-last-command (concat gdb-continuation
+					 (gdb-strip-string-backslash string)
+					 " "))
+	(setq gdb-last-command (gdb-strip-string-backslash string)))
+    (if gdb-last-command (setq string gdb-last-command))
+    (setq gdb-continuation nil))
   (if (or (string-match "^-" string)
 	  (> gdb-control-level 0))
       ;; Either MI command or we are feeding GDB's recursive reading loop.
@@ -1779,10 +1787,13 @@ commands to be prefixed by \"-interpreter-exec console\".")
 	    (setq gdb-control-level (1- gdb-control-level))))
     ;; CLI command
     (if (string-match "\\\\$" string)
-	(setq gdb-continuation (concat gdb-continuation string "\n"))
+	(setq gdb-continuation
+	      (concat gdb-continuation (gdb-strip-string-backslash
+					string)
+		      " "))
       (setq gdb-first-done-or-error t)
       (let ((to-send (concat "-interpreter-exec console "
-                             (gdb-mi-quote string)
+                             (gdb-mi-quote (concat gdb-continuation string " "))
                              "\n")))
         (if gdb-enable-debug
             (push (cons 'mi-send to-send) gdb-debug-log))