view tests/test-remotefilelog-clone-tree.t @ 46667:93e9f448273c

rhg: Add support for automatic fallback to Python

`rhg` is a command-line application that can do a small subset of what
`hg` can. It is written entirely in Rust, which avoids the cost of starting
a Python interpreter and importing many Python modules.
In a script that runs many `hg` commands, this cost can add up.

However making users decide when to use `rhg` instead of `hg` is
not practical as we want the subset of supported functionality
to grow over time.

Instead we introduce "fallback" behavior where, when `rhg` encounters
something (a sub-command, a repository format, …) that is not implemented
in Rust-only, it does nothing but silently start a subprocess of
Python-based `hg` running the same command.
That way `rhg` becomes a drop-in replacement for `hg` that sometimes
goes faster. Whether Python is used should be an implementation detail
not apparent to users (other than through speed).

A new `fallback` value is added to the previously introduced
`rhg.on-unsupported` configuration key. When in this mode, the new
`rhg.fallback-executable` config is determine what command to use
to run a Python-based `hg`.

The previous `rhg.on-unsupported = abort-silent` configuration was designed
to let a wrapper script call `rhg` and then fall back to `hg` based on the
exit code. This is still available, but having fallback behavior built-in
in rhg might be easier for users instead of leaving that script "as an
exercise for the reader".

Using a subprocess like this is not idea, especially when `rhg` is to be
installed in `$PATH` as `hg`, since the other `hg.py` executable needs
to still be available… somewhere. Eventually this could be replaced
by using PyOxidizer to a have a single executable that embeds a Python
interpreter, but only starts it when needed.

Differential Revision: https://phab.mercurial-scm.org/D10093

#require no-windows

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

  $ hg init master
  $ cd master
  $ echo treemanifest >> .hg/requires
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > EOF
# uppercase directory name to test encoding
  $ mkdir -p A/B
  $ echo x > A/B/x
  $ hg commit -qAm x

  $ cd ..

# shallow clone from full

  $ hgcloneshallow ssh://user@dummy/master shallow --noupdate
  streaming all changes
  4 files to transfer, 449 bytes of data
  transferred 449 bytes in * seconds (*/sec) (glob)
  searching for changes
  no changes found
  $ cd shallow
  $ cat .hg/requires
  dotencode
  exp-remotefilelog-repo-req-1
  fncache
  generaldelta
  revlogv1
  sparserevlog
  store
  treemanifest
  $ find .hg/store/meta | sort
  .hg/store/meta
  .hg/store/meta/_a
  .hg/store/meta/_a/00manifest.i
  .hg/store/meta/_a/_b
  .hg/store/meta/_a/_b/00manifest.i

  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  1 files fetched over 1 fetches - (1 misses, 0.00% hit ratio) over *s (glob)

  $ cat A/B/x
  x

  $ ls .hg/store/data
  $ echo foo > A/B/F
  $ hg add A/B/F
  $ hg ci -m 'local content'
  $ ls .hg/store/data
  ca31988f085bfb945cb8115b78fabdee40f741aa

  $ cd ..

# shallow clone from shallow

  $ hgcloneshallow ssh://user@dummy/shallow shallow2  --noupdate
  streaming all changes
  5 files to transfer, 1008 bytes of data
  transferred 1008 bytes in * seconds (*/sec) (glob)
  searching for changes
  no changes found
  $ cd shallow2
  $ cat .hg/requires
  dotencode
  exp-remotefilelog-repo-req-1
  fncache
  generaldelta
  revlogv1
  sparserevlog
  store
  treemanifest
  $ ls .hg/store/data
  ca31988f085bfb945cb8115b78fabdee40f741aa

  $ hg update
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ cat A/B/x
  x

  $ cd ..

# full clone from shallow
# - send stderr to /dev/null because the order of stdout/err causes
#   flakiness here
  $ hg clone --noupdate ssh://user@dummy/shallow full 2>/dev/null
  streaming all changes
  [255]

# getbundle full clone

  $ printf '[server]\npreferuncompressed=False\n' >> master/.hg/hgrc
  $ hgcloneshallow ssh://user@dummy/master shallow3
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files
  new changesets 18d955ee7ba0
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ ls shallow3/.hg/store/data
  $ cat shallow3/.hg/requires
  dotencode
  exp-remotefilelog-repo-req-1
  fncache
  generaldelta
  revlogv1
  sparserevlog
  store
  treemanifest