% create subversion repo
Checked out revision 0.
A         src
A         src/alpha
A         externals
A         externals/other
Adding         externals
Adding         externals/other
Adding         src
Adding         src/alpha
Transmitting file data ..
Committed revision 1.
At revision 1.
property 'svn:externals' set on 'src'
Sending        src

Committed revision 2.
% create hg repo
% first revision, no sub
adding a
% add first svn sub
committing subrepository s
% debugsub
path s
 source   file:///root/svn-repo/src
 revision 2

% change file in svn and hg, commit
committing subrepository s
Sending        s/alpha
Transmitting file data .
Committed revision 3.

Fetching external item into 's/externals'
External at revision 1.

At revision 3.
path s
 source   file:///root/svn-repo/src
 revision 3

% should be empty despite change to s/a

% add a commit from svn
U    alpha

Fetching external item into 'externals'
A    externals/other
Updated external to revision 1.

Updated to revision 3.
property 'svn:mime-type' set on 'alpha'
Sending        src/alpha
Transmitting file data .
Committed revision 4.
% this commit from hg will fail
committing subrepository s
abort: svn: Commit failed (details follow):
svn: File '/src/alpha' is out of date
% this commit fails because of meta changes
property 'svn:mime-type' set on 's/alpha'
committing subrepository s
abort: svn: Commit failed (details follow):
svn: File '/src/alpha' is out of date
% this commit fails because of externals changes
committing subrepository s
abort: cannot commit svn externals
% this commit fails because of externals meta changes
property 'svn:mime-type' set on 's/externals/other'
committing subrepository s
abort: cannot commit svn externals

% clone
updating to branch default
A    s/alpha
 U   s

Fetching external item into 's/externals'
A    s/externals/other
Checked out external at revision 1.

Checked out revision 3.
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
% debugsub in clone
path s
 source   file:///root/svn-repo/src
 revision 3