tests/test-rename-rev.t

nodemap: gate the feature behind a new requirement

Now that the feature is working smoothly, a question was still open, should we
gate the feature behind a new requirement or just treat it as a cache to be
warmed by those who can and ignored by other.

The advantage of using the cache approach is a transparent upgrade/downgrade
story, making the feature easier to move to. However having out of date cache
can come with a significant performance hit for process who expect an up to
date cache but found none. In this case the file needs to be stored under
`.hg/cache`.

The "requirement" approach guarantee that the persistent nodemap is up to date.
However, it comes with a less flexible activation story since an explicite
upgrade is required. In this case the file can be stored in `.hg/store`.

This wiki page is relevant to this questions:

  https://www.mercurial-scm.org/wiki/ComputedIndexPlan

So which one should we take? Another element came into plan, the persistent
nodemap use the `add` method of the transaction, it is used to keep track of a
file content before a transaction in case we need to rollback it back. It turns
out that the `transaction.add` API does not support file stored anywhere than
`.hg/store`. Making it support file stored elsewhere is possible, require a
change in on disk transaction format. Updating on disk file requires…
introducing a new requirements.

As a result, we pick the second option "gating the persistent nodemap behind a
new requirements".

Differential Revision: https://phab.mercurial-scm.org/D8417

  $ hg init
  $ mkdir d1 d1/d11 d2
  $ echo d1/a > d1/a
  $ echo d1/ba > d1/ba
  $ echo d1/a1 > d1/d11/a1
  $ echo d1/b > d1/b
  $ echo d2/b > d2/b
  $ hg add d1/a d1/b d1/ba d1/d11/a1 d2/b
  $ hg commit -m "intial"


Test single file

# One recoded copy, one copy to record after commit
  $ hg cp d1/b d1/c
  $ cp d1/b d1/d
  $ hg add d1/d
  $ hg ci -m 'copy d1/b to d1/c and d1/d'
  $ hg st -C --change .
  A d1/c
    d1/b
  A d1/d
# Errors out without --after for now
  $ hg cp --at-rev . d1/b d1/d
  abort: --at-rev requires --after
  [255]
# Errors out with non-existent destination
  $ hg cp -A --at-rev . d1/b d1/non-existent
  abort: d1/non-existent: copy destination does not exist in 8a9d70fa20c9
  [255]
# Successful invocation
  $ hg cp -A --at-rev . d1/b d1/d
  saved backup bundle to $TESTTMP/.hg/strip-backup/8a9d70fa20c9-973ae357-copy.hg
# New copy is recorded, and previously recorded copy is also still there
  $ hg st -C --change .
  A d1/c
    d1/b
  A d1/d
    d1/b

Test using directory as destination

  $ hg co 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ cp -R d1 d3
  $ hg add d3
  adding d3/a
  adding d3/b
  adding d3/ba
  adding d3/d11/a1
  $ hg ci -m 'copy d1/ to d3/'
  created new head
  $ hg cp -A --at-rev . d1 d3
  abort: d3: --at-rev does not support a directory as destination
  [255]