revlog: generate trivial deltas against null revision To avoid extra memory usage and performance issues with large files, generate a trivial delta header for deltas against the null revision rather than calling the usual delta generator. We append the delta header to meta rather than prepending it to data to avoid a large allocate and copy.

adding a
adding b/a
a
b/a
644 a
644 b/a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 b/a
a
a
b/a
a
b/a
% should fail
abort: unknown revision '2'!
abort: please specify just one revision
a
b/a