tests/test-repo-compengines.t

tests: duplicate test for pager for old extension and for in-core pager

When the old pager extension is enabled, I think we should try to be
as BC as reasonable. To help with that, this patch brings back
test-pager.t as of 65a3b4d67a65 (pager: add a test of --pager=no
functionality, 2017-02-06), but under the name test-pager-legacy.t
However, since the behavior has changed in a few cases (notably by no
longer respecting pager.attend), the file is modified to work with the
current version. We will recover some lost BC in coming patches.

Also, to make sure the in-core pager does not depend on the pager
extension being enabled, this patch disables the extension in
test-pager.t. It turns out that pager.attend-$cmd was only supported
when the pager extension was enabled, so the tests are updated to
reflect that. We will need to decide what to do with these.

A new repository uses zlib storage, which doesn't need a requirement

  $ hg init default
  $ cd default
  $ cat .hg/requires
  dotencode
  fncache
  generaldelta
  revlogv1
  store

  $ touch foo
  $ hg -q commit -A -m 'initial commit with a lot of repeated repeated repeated text to trigger compression'
  $ hg debugrevlog -c | grep 0x78
      0x78 (x)  :   1 (100.00%)
      0x78 (x)  : 110 (100.00%)

  $ cd ..

Unknown compression engine to format.compression aborts

  $ hg --config experimental.format.compression=unknown init unknown
  abort: compression engine unknown defined by experimental.format.compression not available
  (run "hg debuginstall" to list available compression engines)
  [255]

A requirement specifying an unknown compression engine results in bail

  $ hg init unknownrequirement
  $ cd unknownrequirement
  $ echo exp-compression-unknown >> .hg/requires
  $ hg log
  abort: repository requires features unknown to this Mercurial: exp-compression-unknown!
  (see https://mercurial-scm.org/wiki/MissingRequirement for more information)
  [255]

  $ cd ..

#if zstd

  $ hg --config experimental.format.compression=zstd init zstd
  $ cd zstd
  $ cat .hg/requires
  dotencode
  exp-compression-zstd
  fncache
  generaldelta
  revlogv1
  store

  $ touch foo
  $ hg -q commit -A -m 'initial commit with a lot of repeated repeated repeated text'

  $ hg debugrevlog -c | grep 0x28
      0x28      :  1 (100.00%)
      0x28      : 98 (100.00%)

  $ cd ..

Specifying a new format.compression on an existing repo won't introduce data
with that engine or a requirement

  $ cd default
  $ touch bar
  $ hg --config experimental.format.compression=zstd -q commit -A -m 'add bar with a lot of repeated repeated repeated text'

  $ cat .hg/requires
  dotencode
  fncache
  generaldelta
  revlogv1
  store

  $ hg debugrevlog -c | grep 0x78
      0x78 (x)  :   2 (100.00%)
      0x78 (x)  : 199 (100.00%)

#endif