tests/test-remotefilelog-blame.t

rust-revlog: fix RevlogEntry.data() for NULL_REVISION

Before this change, the pseudo-entry returned by `Revlog.get_entry` for
`NULL_REVISION` would trigger errors in application code using it.

For example, this fixes a crash spotted with changelog data
while implementing RHGitaly: `Changelog.data_for_rev(-1)` was already
returning the pseudo content as expected, e.g., for `hg log`, but
`Changelog.entry_for_rev(-1).data()` would still crash with
"corrupted revlog, hash check failed for revision -1". There is
an added test for this scenario.

#require no-windows

  $ . "$TESTDIR/remotefilelog-library.sh"

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > EOF
  $ echo x > x
  $ hg commit -qAm x
  $ echo y >> x
  $ hg commit -qAm y
  $ echo z >> x
  $ hg commit -qAm z
  $ echo a > a
  $ hg commit -qAm a

  $ cd ..

  $ hgcloneshallow ssh://user@dummy/master shallow -q
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)
  $ cd shallow

Test blame

  $ hg blame x
  0: x
  1: y
  2: z
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)

Test grepping the working directory.

  $ hg grep --all-files x
  x:x
  $ echo foo >> x
  $ hg grep --all-files x
  x:x