tests/test-dirstate-version-fallback.t

revlog: use a `reading` context in `_enforceinlinesize`

We are about to enforce reading context on various operation, so we make sure
top level method are in the right context.

In the future we might move the responsibility of opening the revlog for reading
higher in the call chain but lets limit the disruption for now.

  $ cat >> $HGRCPATH << EOF
  > [storage]
  > dirstate-v2.slow-path=allow
  > [format]
  > use-dirstate-v2=no
  > EOF

Set up a v1 repo

  $ hg init repo
  $ cd repo
  $ echo a > a
  $ touch file-with-somewhat-long-name-to-make-dirstate-v1-bigger-than-v2
  $ hg commit -Aqm a
  $ hg debugrequires | grep dirstate
  [1]
  $ ls -1 .hg/dirstate*
  .hg/dirstate

Copy v1 dirstate
  $ cp .hg/dirstate $TESTTMP/dirstate-v1-backup

Upgrade it to v2

  $ hg debugupgraderepo -q --config format.use-dirstate-v2=1 --run | grep -E 'added:|removed:'
     added: dirstate-v2
  $ hg debugrequires | grep dirstate
  dirstate-v2
  $ ls -1 .hg/dirstate*
  .hg/dirstate
  .hg/dirstate.* (glob)

Manually reset to dirstate v1 to simulate an incomplete dirstate-v2 upgrade

  $ rm .hg/dirstate*
  $ cp $TESTTMP/dirstate-v1-backup .hg/dirstate

There should be no errors, but a v2 dirstate should be written back to disk
  $ hg st
  $ ls -1 .hg/dirstate*
  .hg/dirstate
  .hg/dirstate.* (glob)

Corrupt the dirstate to see how the errors show up to the user
  $ echo "I ate your data" > .hg/dirstate

  $ hg st
  abort: working directory state appears damaged! (no-rhg !)
  (falling back to dirstate-v1 from v2 also failed) (no-rhg !)
  abort: Too little data for dirstate: 16 bytes. (rhg !)
  [255]