view tests/test-legacy-exit-code.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

Tests that the exit code is as expected when ui.detailed-exit-code is *not*
enabled.

  $ cat >> $HGRCPATH << EOF
  > [ui]
  > detailed-exit-code=no
  > EOF

  $ hg init
  $ echo a > a
Expect exit code 0 on success
  $ hg ci -Aqm initial

  $ hg co nonexistent
  abort: unknown revision 'nonexistent'
  [255]

  $ hg co 'none()'
  abort: empty revision set
  [255]

  $ hg co 'invalid('
  hg: parse error at 8: not a prefix: end
  (invalid(
           ^ here)
  [255]

  $ hg co 'invalid('
  hg: parse error at 8: not a prefix: end
  (invalid(
           ^ here)
  [255]

  $ hg continue
  abort: no operation in progress
  [255]

  $ hg st --config a=b
  abort: malformed --config option: 'a=b' (use --config section.name=value)
  [255]

  $ echo b > a
  $ hg ci -m second
  $ echo c > a
  $ hg ci -m third
  $ hg --config extensions.rebase= rebase -r . -d 0 -q
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see 'hg resolve', then 'hg rebase --continue')
  [1]