tests/test-clone-pull-corruption.t

tests: add test for Rust formatting

We enforce formatting for Python and C. It makes sense to do it
for Rust as well.

Since our rustfmt.toml relies on unstable rustfmt features, we
need to use a Nightly rustfmt with --unstable-features in order
for it to work. This is a bit hacky and I would prefer we remove
this requirement. But for now, this commit assumes this is the
way things must be and we go out of our way to detect and use the
rustfmt from the "nightly" toolchain, as installed via rustup.

We had to add some environment variables to the tests to make
the Rust binaries happy. Otherwise when running rustfmt we get
an error about no default toolchain being installed.

Differential Revision: https://phab.mercurial-scm.org/D7579

Corrupt an hg repo with a pull started during an aborted commit
Create two repos, so that one of them can pull from the other one.

  $ hg init source
  $ cd source
  $ touch foo
  $ hg add foo
  $ hg ci -m 'add foo'
  $ hg clone . ../corrupted
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo >> foo
  $ hg ci -m 'change foo'

Add a hook to wait 5 seconds and then abort the commit

  $ cd ../corrupted
  $ echo "[hooks]" >> .hg/hgrc
  $ echo 'pretxncommit = sh -c "sleep 5; exit 1"' >> .hg/hgrc

start a commit...

  $ touch bar
  $ hg add bar
  $ hg ci -m 'add bar' &

... and start a pull while the commit is still running

  $ sleep 1
  $ hg pull ../source 2>/dev/null
  pulling from ../source
  transaction abort!
  rollback completed
  abort: pretxncommit hook exited with status 1
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets 52998019f625
  (run 'hg update' to get a working copy)

see what happened

  $ wait
  $ hg verify
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 2 changes to 1 files

  $ cd ..