patch: do not overwrite broken untracked symlinks

mercurial/patch.py

@@ -25,7 +25,7 b' class NoHunks(PatchError):'
 
 def copyfile(src, dst, basedir):
     abssrc, absdst = [util.canonpath(basedir, basedir, x) for x in [src, dst]]
-    if os.path.exists(absdst):
+    if os.path.lexists(absdst):
         raise util.Abort(_("cannot create %s: destination already exists") %
                          dst)
 

tests/test-mq-symlinks

@@ -66,3 +66,9 b' hg qnew movelink'
 hg qpop
 hg qpush
 $TESTDIR/readlink.py linkb
+echo '% check patch does not overwrite untracked symlinks'
+hg qpop
+ln -s linkbb linkb
+hg qpush
+
+true
  No newline at end of file

tests/test-mq-symlinks.out

@@ -35,3 +35,10 b' now at: link'
 applying movelink
 now at: movelink
 linkb -> linkb
+% check patch does not overwrite untracked symlinks
+popping movelink
+now at: link
+applying movelink
+patch failed, unable to continue (try -v)
+patch failed, rejects left in working dir
+errors during apply, please fix and refresh movelink