view tests/test-contrib.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

Set vars:

  $ CONTRIBDIR="$TESTDIR/../contrib"

Test simplemerge command:

  $ cp "$CONTRIBDIR/simplemerge" .
  $ echo base > base
  $ echo local > local
  $ cat base >> local
  $ cp local orig
  $ cat base > other
  $ echo other >> other

changing local directly

  $ "$PYTHON" simplemerge local base other && echo "merge succeeded"
  merge succeeded
  $ cat local
  local
  base
  other
  $ cp orig local

printing to stdout

  $ "$PYTHON" simplemerge -p local base other
  local
  base
  other

local:

  $ cat local
  local
  base

conflicts

  $ cp base conflict-local
  $ cp other conflict-other
  $ echo not other >> conflict-local
  $ echo end >> conflict-local
  $ echo end >> conflict-other

  $ "$PYTHON" simplemerge -p conflict-local base conflict-other
  base
  <<<<<<< conflict-local
  not other
  =======
  other
  >>>>>>> conflict-other
  end
  [1]

1 label

  $ "$PYTHON" simplemerge -p -L foo conflict-local base conflict-other
  base
  <<<<<<< foo
  not other
  =======
  other
  >>>>>>> conflict-other
  end
  [1]

2 labels

  $ "$PYTHON" simplemerge -p -L foo -L bar conflict-local base conflict-other
  base
  <<<<<<< foo
  not other
  =======
  other
  >>>>>>> bar
  end
  [1]

3 labels

  $ "$PYTHON" simplemerge -p -L foo -L bar -L base conflict-local base conflict-other
  base
  <<<<<<< foo
  not other
  end
  ||||||| base
  =======
  other
  end
  >>>>>>> bar
  [1]

too many labels

  $ "$PYTHON" simplemerge -p -L foo -L bar -L baz -L buz conflict-local base conflict-other
  abort: can only specify three labels.
  [255]

binary file

  $ "$PYTHON" -c "f = open('binary-local', 'w'); f.write('\x00'); f.close()"
  $ cat orig >> binary-local
  $ "$PYTHON" simplemerge -p binary-local base other
  warning: binary-local looks like a binary file.
  [1]

binary file --text

  $ "$PYTHON" simplemerge -a -p binary-local base other 2>&1
  warning: binary-local looks like a binary file.
  \x00local (esc)
  base
  other

help

  $ "$PYTHON" simplemerge --help
  simplemerge [OPTS] LOCAL BASE OTHER
  
      Simple three-way file merge utility with a minimal feature set.
  
      Apply to LOCAL the changes necessary to go from BASE to OTHER.
  
      By default, LOCAL is overwritten with the results of this operation.
  
  options:
   -L --label       labels to use on conflict markers
   -a --text        treat all files as text
   -p --print       print results instead of overwriting LOCAL
      --no-minimal  no effect (DEPRECATED)
   -h --help        display help and exit
   -q --quiet       suppress output

wrong number of arguments

  $ "$PYTHON" simplemerge
  simplemerge: wrong number of arguments
  simplemerge [OPTS] LOCAL BASE OTHER
  
      Simple three-way file merge utility with a minimal feature set.
  
      Apply to LOCAL the changes necessary to go from BASE to OTHER.
  
      By default, LOCAL is overwritten with the results of this operation.
  
  options:
   -L --label       labels to use on conflict markers
   -a --text        treat all files as text
   -p --print       print results instead of overwriting LOCAL
      --no-minimal  no effect (DEPRECATED)
   -h --help        display help and exit
   -q --quiet       suppress output
  [1]

bad option

  $ "$PYTHON" simplemerge --foo -p local base other
  simplemerge: option --foo not recognized
  simplemerge [OPTS] LOCAL BASE OTHER
  
      Simple three-way file merge utility with a minimal feature set.
  
      Apply to LOCAL the changes necessary to go from BASE to OTHER.
  
      By default, LOCAL is overwritten with the results of this operation.
  
  options:
   -L --label       labels to use on conflict markers
   -a --text        treat all files as text
   -p --print       print results instead of overwriting LOCAL
      --no-minimal  no effect (DEPRECATED)
   -h --help        display help and exit
   -q --quiet       suppress output
  [1]