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rhg: Add support for automatic fallback to Python...
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

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testing.rs
72 lines | 1.7 KiB | application/rls-services+xml | RustLexer
// testing.rs
//
// Copyright 2018 Georges Racinet <georges.racinet@octobus.net>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.
use crate::{Graph, GraphError, Revision, NULL_REVISION};
/// A stub `Graph`, same as the one from `test-ancestor.py`
///
/// o 13
/// |
/// | o 12
/// | |
/// | | o 11
/// | | |\
/// | | | | o 10
/// | | | | |
/// | o---+ | 9
/// | | | | |
/// o | | | | 8
/// / / / /
/// | | o | 7
/// | | | |
/// o---+ | 6
/// / / /
/// | | o 5
/// | |/
/// | o 4
/// | |
/// o | 3
/// | |
/// | o 2
/// |/
/// o 1
/// |
/// o 0
#[derive(Clone, Debug)]
pub struct SampleGraph;
impl Graph for SampleGraph {
fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
match rev {
0 => Ok([NULL_REVISION, NULL_REVISION]),
1 => Ok([0, NULL_REVISION]),
2 => Ok([1, NULL_REVISION]),
3 => Ok([1, NULL_REVISION]),
4 => Ok([2, NULL_REVISION]),
5 => Ok([4, NULL_REVISION]),
6 => Ok([4, NULL_REVISION]),
7 => Ok([4, NULL_REVISION]),
8 => Ok([NULL_REVISION, NULL_REVISION]),
9 => Ok([6, 7]),
10 => Ok([5, NULL_REVISION]),
11 => Ok([3, 7]),
12 => Ok([9, NULL_REVISION]),
13 => Ok([8, NULL_REVISION]),
r => Err(GraphError::ParentOutOfRange(r)),
}
}
}
// A Graph represented by a vector whose indices are revisions
// and values are parents of the revisions
pub type VecGraph = Vec<[Revision; 2]>;
impl Graph for VecGraph {
fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
Ok(self[rev as usize])
}
}