bookmarks: warn about bookmark names that unambiguously resolve to a node (BC) I just burned myself on this today because I left out the -r in my `hg bookmark` command, which then left me confused because I didn't notice the bookmark I created in the wrong place that was silently shadowing the revision I was trying to check out. Let's warn the user. This patch only enforces the check on bookmark names 4 characters long or longer. We can tweak that if we'd like, I selected that since that's the fewest characters shortest will use in the templater output. A previous version of this patch rejected such bookmarks. It was proposed during review (and I agree) that the behavior change for a bookmark named "cafe" or similar as history accumulated was a little too weird, but that the warning definitely has merit.

--- a/mercurial/commands.py	Thu May 04 11:51:07 2017 +0900
+++ b/mercurial/commands.py	Mon May 22 19:18:12 2017 -0400
@@ -968,6 +968,11 @@
             and not force):
             raise error.Abort(
                 _("a bookmark cannot have the name of an existing branch"))
+        if len(mark) > 3 and mark in repo and not force:
+            repo.ui.warn(
+                _("bookmark %s matches a changeset hash\n"
+                  "(did you leave a -r out of an 'hg bookmark' command?)\n") %
+                mark)
 
     if delete and rename:
         raise error.Abort(_("--delete and --rename are incompatible"))