view tests/test-remotefilelog-tags.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
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > EOF
  $ echo x > foo
  $ echo y > bar
  $ hg commit -qAm one
  $ hg tag tag1
  $ cd ..

# clone with tags

  $ hg clone --shallow ssh://user@dummy/master shallow --noupdate --config remotefilelog.excludepattern=.hgtags
  streaming all changes
  3 files to transfer, 662 bytes of data
  transferred 662 bytes in * seconds (*/sec) (glob)
  searching for changes
  no changes found
  $ cat >> shallow/.hg/hgrc <<EOF
  > [remotefilelog]
  > cachepath=$PWD/hgcache
  > debug=True
  > reponame = master
  > excludepattern=.hgtags
  > [extensions]
  > remotefilelog=
  > EOF

  $ cd shallow
  $ ls .hg/store/data
  ~2ehgtags.i
  $ hg tags
  tip                                1:6ce44dcfda68
  tag1                               0:e0360bc0d9e1
  $ hg update
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  2 files fetched over 1 fetches - (2 misses, 0.00% hit ratio) over *s (glob)

# pull with tags

  $ cd ../master
  $ hg tag tag2
  $ cd ../shallow
  $ hg pull
  pulling from ssh://user@dummy/master
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files
  new changesets 6a22dfa4fd34
  (run 'hg update' to get a working copy)
  $ hg tags
  tip                                2:6a22dfa4fd34
  tag2                               1:6ce44dcfda68
  tag1                               0:e0360bc0d9e1
  $ hg update
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ ls .hg/store/data
  ~2ehgtags.i

  $ hg log -l 1 --stat
  changeset:   2:6a22dfa4fd34
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     Added tag tag2 for changeset 6ce44dcfda68
  
   .hgtags |  1 +
   1 files changed, 1 insertions(+), 0 deletions(-)