Mercurial > hg
view rust/rhg/README.md @ 48275:1ea289e34c70 stable
tests: better determinism in test-chg.t
chg tests fail pretty often with "Sample count: *" line disappearing.
It disappears because the sample count is zero, in which case a custom message is printed.
This commit makes the test succeed in that case.
Differential Revision: https://phab.mercurial-scm.org/D11716
author | Arseniy Alekseyev <aalekseyev@janestreet.com> |
---|---|
date | Wed, 20 Oct 2021 18:44:26 +0100 |
parents | 6df528ed47a9 |
children | b1c20e41098f |
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# `rhg` The `rhg` executable implements a subset of the functionnality of `hg` using only Rust, to avoid the startup cost of a Python interpreter. This subset is initially small but grows over time as `rhg` is improved. When fallback to the Python implementation is configured (see below), `rhg` aims to be a drop-in replacement for `hg` that should behave the same, except that some commands run faster. ## Building To compile `rhg`, either run `cargo build --release` from this `rust/rhg/` directory, or run `make build-rhg` from the repository root. The executable can then be found at `rust/target/release/rhg`. ## Mercurial configuration `rhg` reads Mercurial configuration from the usual sources: the user’s `~/.hgrc`, a repository’s `.hg/hgrc`, command line `--config`, etc. It has some specific configuration in the `[rhg]` section: * `on-unsupported` governs the behavior of `rhg` when it encounters something that it does not support but “full” `hg` possibly does. This can be in configuration, on the command line, or in a repository. - `abort`, the default value, makes `rhg` print a message to stderr to explain what is not supported, then terminate with a 252 exit code. - `abort-silent` makes it terminate with the same exit code, but without printing anything. - `fallback` makes it silently call a (presumably Python-based) `hg` subprocess with the same command-line parameters. The `rhg.fallback-executable` configuration must be set. * `fallback-executable`: path to the executable to run in a sub-process when falling back to a Python implementation of Mercurial. * `allowed-extensions`: a list of extension names that `rhg` can ignore. Mercurial extensions can modify the behavior of existing `hg` sub-commands, including those that `rhg` otherwise supports. Because it cannot load Python extensions, finding them enabled in configuration is considered “unsupported” (see above). A few exceptions are made for extensions that `rhg` does know about, with the Rust implementation duplicating their behavior. This configuration makes additional exceptions: `rhg` will proceed even if those extensions are enabled. ## Installation and configuration example For example, to install `rhg` as `hg` for the current user with fallback to the system-wide install of Mercurial, and allow it to run even though the `rebase` and `absorb` extensions are enabled, on a Unix-like platform: * Build `rhg` (see above) * Make sure the `~/.local/bin` exists and is in `$PATH` * From the repository root, make a symbolic link with `ln -s rust/target/release/rhg ~/.local/bin/hg` * Configure `~/.hgrc` with: ``` [rhg] on-unsupported = fallback fallback-executable = /usr/bin/hg allowed-extensions = rebase, absorb ``` * Check that the output of running `hg notarealsubcommand` starts with `hg: unknown command`, which indicates fallback. * Check that the output of running `hg notarealsubcommand --config rhg.on-unsupported=abort` starts with `unsupported feature:`.