tests/test-issue612

convert/svn: make sink recover gracefully from empty changeset

Otherwise when processing a changeset that in fact changes no files
(perhaps due to bug in import from CVS) can get something like:
  unexpected svn output:
  abort: unable to cope with svn output

Bug report and patch draft by Jesse Glick <[e-mail]>

#!/bin/sh

mkdir t
cd t

hg init
mkdir src
echo a > src/a.c
hg ci -Ama -d "10000000 0"

hg mv src source
hg ci -Ammove -d "1000000 0"

hg co -C 0
echo new > src/a.c
echo compiled > src/a.o
hg ci -mupdate -d "1000000 0"

hg st

hg merge

hg st