[Request] [+++ ] D11808: docs: add documentation about Rust

[Alphare (Raphaël Gomès)]

Alphare created this revision.
Alphare added a comment.
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  Pending CI refresh

REVISION SUMMARY
  This makes the features more discoverable for users.

REPOSITORY
  rHG Mercurial

BRANCH
  default

REVISION DETAIL
  https://phab.mercurial-scm.org/D11808

AFFECTED FILES
  mercurial/help.py
  mercurial/helptext/rust.txt

CHANGE DETAILS

diff --git a/mercurial/helptext/rust.txt b/mercurial/helptext/rust.txt
new file mode 100644
--- /dev/null
+++ b/mercurial/helptext/rust.txt
@@ -0,0 +1,94 @@
+Mercurial can be augmented with Rust extensions for speeding up certain
+operations.
+
+Compatibility
+=============
+
+Though the Rust extensions are only tested by the project under Linux, users of
+MacOS, FreeBSD, other UNIX-likes have been using the Rust extensions. Your
+mileage may vary, but by all means do give us feedback or signal your interest
+for better support.
+
+No Rust extensions are available for Windows at this time.
+
+Features
+========
+
+The following operations are sped up when using Rust:
+    - discovery of differences between repositories (pull/push)
+    - nodemap (see :hg:`help config.format.use-persistent-nodemap`)
+    - all commands using the dirstate (status, commit, diff, add, update, etc.)
+    - dirstate-v2 (see :hg:`help config.format.exp-rc-dirstate-v2`)
+    - iteration over ancestors in a graph
+
+More features are in the works, and improvements on the above listed are still
+in progress. For more experimental work see the "rhg" section.
+
+Checking for Rust
+=================
+
+You may already have the Rust extensions depending on how you get Mercurial.
+
+  $ hg debuginstall | grep -i rust
+  checking Rust extensions (installed)
+  checking module policy (rust+c-allow)
+
+If those lines don't even exist, you're using an old version of `hg` which does
+not have any Rust extensions yet. 
+
+Installing
+==========
+
+You will need `cargo` to be in your `$PATH`. See the "MSRV" section for which
+version to use.
+
+Using pip
+---------
+
+Users of `pip` can install the Rust extensions with the following command:
+
+  $ pip install mercurial --global-option --rust --no-use-pep517
+
+`--no-use-pep517` is here to tell `pip` to preserve backwards compatibility with
+the legacy `setup.py` system. Mercurial has not yet migrated its complex setup
+to the new system, so we still need this to add compiled extensions.
+
+This might take a couple of minutes because you're compiling everything.
+
+See the "Checking for Rust" section to see if the install succeeded.
+
+From your distribution
+----------------------
+
+Some distributions are shipping Mercurial with Rust extensions enabled and
+pre-compiled (meaning you won't have to install `cargo`), or allow you to
+specify an install flag. Check with your specific distribution for how to do
+that, or ask their team to add support for hg+Rust!
+
+From source
+-----------
+
+Please refer to the `rust/README.rst` file in the Mercurial repository for
+instructions on how to install from source.
+
+MSRV
+====
+
+The minimum supported Rust version is currently 1.48.0. The project's policy is
+to follow the version from Debian stable, to make the distributions' job easier.
+
+rhg
+===
+
+There exists an experimental pure-Rust version of Mercurial called `rhg` with a
+fallback mechanism for unsupported invocations. It allows for much faster
+execution of certain commands while adding no discernable overhead for the rest.
+
+The only way of trying it out is by building it from source. Please refer to
+`rust/README.rst` in the Mercurial repository.
+
+Contributing
+============
+
+If you would like to help the Rust endeavor, please refer to `rust/README.rst`
+in the Mercurial repository.
diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -484,6 +484,15 @@
             TOPIC_CATEGORY_IDS,
         ),
         (
+            [
+                b'rust',
+                b'rustext',
+            ],
+            _(b'Rust in Mercurial'),
+            loaddoc(b'rust'),
+            TOPIC_CATEGORY_CONFIG,
+        ),
+        (
             [b'filesets', b'fileset'],
             _(b"Specifying File Sets"),
             loaddoc(b'filesets'),



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