mdiff: don't emit a diff header for empty trivial deltas
An empty trivial delta, coded as (0, 0, 0) makes the delta application
do nothing, but still takes 12 bytes, while skipping it altogether works
as much, without taking any space at all.
Create a test repository:
$ hg init repo
$ cd repo
$ touch a ; hg add a ; hg ci -ma
$ touch b ; hg add b ; hg ci -mb
$ touch c ; hg add c ; hg ci -mc
$ hg bundle --base 0 --rev tip bundle.hg -v --type v1
2 changesets found
uncompressed size of bundle content:
332 (changelog)
282 (manifests)
93 b
93 c
Terse output:
$ hg debugbundle bundle.hg
0e067c57feba1a5694ca4844f05588bb1bf82342
991a3460af53952d10ec8a295d3d2cc2e5fa9690
Verbose output:
$ hg debugbundle --all bundle.hg
format: id, p1, p2, cset, delta base, len(delta)
changelog
0e067c57feba1a5694ca4844f05588bb1bf82342 3903775176ed42b1458a6281db4a0ccf4d9f287a 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 3903775176ed42b1458a6281db4a0ccf4d9f287a 80
991a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0e067c57feba1a5694ca4844f05588bb1bf82342 80
manifest
686dbf0aeca417636fa26a9121c681eabbb15a20 8515d4bfda768e04af4c13a69a72e28c7effbea7 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 8515d4bfda768e04af4c13a69a72e28c7effbea7 55
ae25a31b30b3490a981e7b96a3238cc69583fda1 686dbf0aeca417636fa26a9121c681eabbb15a20 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 686dbf0aeca417636fa26a9121c681eabbb15a20 55
b
b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 0e067c57feba1a5694ca4844f05588bb1bf82342 0000000000000000000000000000000000000000 0
c
b80de5d138758541c5f05265ad144ab9fa86d1db 0000000000000000000000000000000000000000 0000000000000000000000000000000000000000 991a3460af53952d10ec8a295d3d2cc2e5fa9690 0000000000000000000000000000000000000000 0
$ cd ..