tests/test-check-rust-format.t

hgdemandimport: bypass demandimport for _ast module (issue6407)

This is broken on Python 3.9rc1, and while it sounds like there may be
a fix in Python, we probably also should have this workaround in place
in hg. See the bug for more details (including on bugs at redhat and
b.p.o).

Differential Revision: https://phab.mercurial-scm.org/D9004

#require rustfmt test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"

  $ cd "$TESTDIR"/..
  $ RUSTFMT=$(rustup which --toolchain nightly rustfmt)
  $ for f in `testrepohg files 'glob:**/*.rs'` ; do
  >   $RUSTFMT --check --edition=2018 --unstable-features --color=never $f
  > done