tests/test-journal-exists.t

revlog: add the glue to use the Rust `InnerRevlog` from Python

The performance of this has been looked at for quite some time, and some
workflows are actually quite a bit faster than with the Python + C code.

However, we are still (up to 20%) slower in some crucial places like cloning
certain repos, log, cat, which makes this an incomplete rewrite. This is
mostly due to the high amount of overhead in Python <-> Rust FFI, especially
around the VFS code. A future patch series will rewrite the VFS code in
pure Rust, which should hopefully get us up to par with current perfomance,
if not better in all important cases.

This is a "save state" of sorts, as this is a ton of code, and I don't want
to pile up even more things in a single review.

Continuing to try to match the current performance will take an extremely
long time, if it's not impossible, without the aforementioned VFS work.

  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg ci -Am0
  adding a

  $ hg -q clone . foo

  $ touch .hg/store/journal

  $ echo foo > a
  $ hg ci -Am0
  abort: abandoned transaction found
  (run 'hg recover' to clean up transaction)
  [255]

  $ hg recover
  rolling back interrupted transaction
  (verify step skipped, run `hg verify` to check your repository content)

recover, explicit verify

  $ touch .hg/store/journal
  $ hg ci -Am0
  abort: abandoned transaction found
  (run 'hg recover' to clean up transaction)
  [255]
  $ hg recover --verify  -q

recover, no verify

  $ touch .hg/store/journal
  $ hg ci -Am0
  abort: abandoned transaction found
  (run 'hg recover' to clean up transaction)
  [255]
  $ hg recover --no-verify
  rolling back interrupted transaction
  (verify step skipped, run `hg verify` to check your repository content)


Check that zero-size journals are correctly aborted:

#if unix-permissions no-root
  $ hg bundle -qa repo.hg
  $ chmod -w foo/.hg/store/00changelog.i

#if rust
  $ hg -R foo unbundle repo.hg
  adding changesets
  transaction abort!
  rollback completed
  abort: failed to call opener: [Errno 13] $EACCES$: b'$TESTTMP/repo/foo/.hg/store/.00changelog.i-*' (glob)
  [50]
#else
  $ hg -R foo unbundle repo.hg
  adding changesets
  transaction abort!
  rollback completed
  abort: $EACCES$: '$TESTTMP/repo/foo/.hg/store/.00changelog.i-*' (glob)
  [255]
#endif

  $ if test -f foo/.hg/store/journal; then echo 'journal exists :-('; fi
#endif