$ NO_FALLBACK="env RHG_ON_UNSUPPORTED=abort"

  $ cat << EOF >> $HGRCPATH

  > [format]

  > sparse-revlog = no

  > EOF

  $ hg init repo --config format.generaldelta=no --config format.usegeneraldelta=no

  $ cd repo

  $ (echo header; seq.py 20) > f

  $ hg commit -q -Am initial

  $ (echo header; seq.py 20; echo footer) > f

  $ hg commit -q -Am x

  $ hg update ".^"

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ (seq.py 20; echo footer) > f

  $ hg commit -q -Am y

  $ hg debugdeltachain f --template '{rev} {prevrev} {deltatype}\n'

  0 -1 base

  1 0 prev

  2 1 prev

rhg works on non-generaldelta revlogs:

  $ $NO_FALLBACK hg cat f -r .

  1

  2

  3

  4

  5

  6

  7

  8

  9

  10

  11

  12

  13

  14

  15

  16

  17

  18

  19

  20

  footer