view tests/test-check-pylint.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 test-repo pylint hg10

Run pylint for known rules we care about.
-----------------------------------------

There should be no recorded failures; fix the codebase before introducing a
new check.

Current checks:
- W0102: no mutable default argument

  $ touch $TESTTMP/fakerc
  $ pylint --rcfile=$TESTTMP/fakerc --disable=all \
  >   --enable=W0102,C0321 \
  >   --reports=no \
  >   --ignore=thirdparty \
  >   mercurial hgdemandimport hgext hgext3rd | sed 's/\r$//'
  Using config file *fakerc (glob) (?)
   (?)
  ------------------------------------* (glob) (?)
  Your code has been rated at 10.00/10* (glob) (?)
   (?)