Mercurial > hg
view tests/test-diff-issue2761.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
author | Simon Sapin <simon.sapin@octobus.net> |
---|---|
date | Mon, 01 Mar 2021 20:36:06 +0100 |
parents | 73e3e368bd42 |
children | 55c6ebd11cb9 |
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Test issue2761 $ hg init $ touch to-be-deleted $ hg add adding to-be-deleted $ hg ci -m first $ echo a > to-be-deleted $ hg ci -m second $ rm to-be-deleted $ hg diff -r 0 Same issue, different code path $ hg up -C 1 files updated, 0 files merged, 0 files removed, 0 files unresolved $ touch does-not-exist-in-1 $ hg add adding does-not-exist-in-1 $ hg ci -m third $ rm does-not-exist-in-1 $ hg diff -r 1