rebase: always check if rebasing onto an applied mq patch.

Previously, it only checked for an mq patch if the user explicitly
passed -d/--dest.  But rebasing onto an mq patch is a bad idea
regardless of how we determine the rebase destination.

hgext/rebase.py

@@ -440,10 +440,14 b' def buildstate(repo, dest, src, base, de'
         branch = repo[None].branch()
         dest = repo[branch].rev()
     else:
+        dest = repo[dest].rev()
+
+    # This check isn't strictly necessary, since mq detects commits over an
+    # applied patch. But it prevents messing up the working directory when
+    # a partially completed rebase is blocked by mq.
         if 'qtip' in repo.tags() and (repo[dest].hex() in
                                 [s.rev for s in repo.mq.applied]):
             raise util.Abort(_('cannot rebase onto an applied mq patch'))
-        dest = repo[dest].rev()
 
     if src:
         commonbase = repo[src].ancestor(repo[dest])

tests/test-rebase-mq

@@ -45,6 +45,12 b" echo '% Rebase - try to rebase on an app"
 hg rebase -s 1 -d 3
 
 echo
+echo '% Rebase - same thing, but mq patch is default dest'
+hg update -q 1
+hg rebase
+hg update -q qtip
+
+echo
 echo '% Rebase - generate a conflict'
 hg rebase -s 2 -d 1
 

tests/test-rebase-mq.out

@@ -11,6 +11,9 b' o 0 C1 tags: qparent'
 % Rebase - try to rebase on an applied mq patch
 abort: cannot rebase onto an applied mq patch
 
+% Rebase - same thing, but mq patch is default dest
+abort: cannot rebase onto an applied mq patch
+
 % Rebase - generate a conflict
 merging f
 warning: conflicts during merge.