bug#5961: 23.1 regression: vc-hg does not show 0 version number for 'added files

[Dan Nicolaescu]

After this change:

  Show working revision correctly for mercurial.
  * vc-hg.el (vc-hg-working-revision): Use hg parent instead of
  hg log as suggested by Alex Harsanyi <alexharsanyi@gmail.com>,


the mode-line show Hg@ instead of Hg@0 for files in the VC 'added state.  This 
is a regression from 23.1.

The problem is that the "hg parent " command does not distinguish
between the 'added and 'unregistered files.

Should the patch below go into the 23.2 branch?

=== modified file 'lisp/vc-hg.el'
--- lisp/vc-hg.el       2010-04-07 05:56:35 +0000
+++ lisp/vc-hg.el       2010-04-16 19:36:29 +0000
@@ -196,16 +196,16 @@ If nil, use the value of `vc-diff-switch
   (let*
       ((status nil)
        (default-directory (file-name-directory file))
+       ;; Avoid localization of messages so we can parse the output.
+       (avoid-local-env (append (list "TERM=dumb" "LANGUAGE=C" "HGRC=")
+                                    process-environment))
        (out
         (with-output-to-string
           (with-current-buffer
               standard-output
             (setq status
                   (condition-case nil
-                     (let ((process-environment
-                            ;; Avoid localization of messages so we can parse 
the output.
-                            (append (list "TERM=dumb" "LANGUAGE=C" "HGRC=")
-                                    process-environment)))
+                     (let ((process-environment avoid-local-env))
                        ;; Ignore all errors.
                        (process-file
                         "hg" nil t nil
@@ -213,7 +213,21 @@ If nil, use the value of `vc-diff-switch
                     ;; Some problem happened.  E.g. We can't find an `hg'
                     ;; executable.
                     (error nil)))))))
-    (when (eq 0 status) out)))
+    (if (eq 0 status)
+       out
+      ;; Check if the file is in the 'added state, the above hg
+      ;; command does not distinguish between 'added and 'unregistered.
+      (setq status
+           (condition-case nil
+               (let ((process-environment avoid-local-env))
+                 ;; Ignore all errors.
+                 (process-file
+                  "hg" nil nil nil
+                  "log" "-l1" (file-relative-name file)))
+             ;; Some problem happened.  E.g. We can't find an `hg'
+             ;; executable.
+             (error nil)))
+      (when (eq 0 status) "0"))))
 
 ;;; History functions