Mercurial > hg
view rust/README.rst @ 47315:825d5a5907b4
exewrapper: avoid directly linking against python3X.dll
Subsequent code calls `LoadLibrary()` to attempt to load the DLL, but because of
this symbol reference, there is an attempt to load the DLL used during the build
prior to `_main()` running. This causes the whole process to fail if the DLL
isn't in the standard search path. That also means it will never load the DLL
for HackableMercurial. (Maybe we should get rid of that for py3, since you can
install python for a user without admin rights?)
This could also be resolved by calling `GetProcAddress()` on the symbol and
dereferencing it, but using the environment variable is consistent with the
*.bat file since fc8a5c9ecee0. (The environment variable persists after the
interpreter is initialized.)
Far more concerning is somehow I've gotten my system into a state where setting
the flag causes any output to the pager to be lost (as if it wasn't set at all)
in MSYS, cmd.exe, WSL, and PowerShell using py3.9.0, but the environment
variable works properly. I'm sure this flag worked on some versions of py3, so
I'm not sure what's going on here. This is might be related to init config
related changes in 3.8[1], since it works with 3.7.8, but fails with 3.8.1.
Somebody who understands encoding issues better than I do should give some
thought to if we need to make some changes to our encoding strategy on Windows
with py3.
With or without the flag/envvar, there is proper output if the command is
directly paged by piping to `more.com` (in any environment) or `less` (in MSYS
and WSL), or if paging is disabled with `--pager=no`. Legacy mode is required
though when Mercurial decides to spin up a pager.
[1] https://bugs.python.org/issue41941
Differential Revision: https://phab.mercurial-scm.org/D10756
author | Matt Harbison <matt_harbison@yahoo.com> |
---|---|
date | Tue, 11 May 2021 01:05:38 -0400 |
parents | ec14c37958ec |
children | 4ee6b8b40787 |
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=================== Mercurial Rust Code =================== This directory contains various Rust code for the Mercurial project. Rust is not required to use (or build) Mercurial, but using it improves performance in some areas. There are currently three independent rust projects: - chg. An implementation of chg, in rust instead of C. - hgcli. A project that provide a (mostly) self-contained "hg" binary, for ease of deployment and a bit of speed, using PyOxidizer. See hgcli/README.md. - hg-core (and hg-cpython): implementation of some functionality of mercurial in rust, e.g. ancestry computations in revision graphs, status or pull discovery. The top-level ``Cargo.toml`` file defines a workspace containing these crates. Using Rust code =============== Local use (you need to clean previous build artifacts if you have built without rust previously):: $ make PURE=--rust local # to use ./hg $ ./tests/run-tests.py --rust # to run all tests $ ./hg debuginstall | grep -i rust # to validate rust is in use checking Rust extensions (installed) checking module policy (rust+c-allow) If the environment variable ``HGWITHRUSTEXT=cpython`` is set, the Rust extension will be used by default unless ``--no-rust``. One day we may use this environment variable to switch to new experimental binding crates like a hypothetical ``HGWITHRUSTEXT=hpy``. Special features ================ You might want to check the `features` section in ``hg-cpython/Cargo.toml``. It may contain features that might be interesting to try out. To use features from the Makefile, use the `HG_RUST_FEATURES` environment variable: for instance `HG_RUST_FEATURES="some-feature other-feature"` Profiling ========= Setting the environment variable ``RUST_LOG=trace`` will make hg print a few high level rust-related performance numbers. It can also indicate why the rust code cannot be used (say, using lookarounds in hgignore). Creating a ``.cargo/config`` file with the following content enables debug information in optimized builds. This make profiles more informative with source file name and line number for Rust stack frames and (in some cases) stack frames for Rust functions that have been inlined. [profile.release] debug = true ``py-spy`` (https://github.com/benfred/py-spy) can be used to construct a single profile with rust functions and python functions (as opposed to ``hg --profile``, which attributes time spent in rust to some unlucky python code running shortly after the rust code, and as opposed to tools for native code like ``perf``, which attribute time to the python interpreter instead of python functions). Example usage: $ make PURE=--rust local # Don't forget to recompile after a code change $ py-spy record --native --output /tmp/profile.svg -- ./hg ... Developing Rust =============== The current version of Rust in use is ``1.41.1``, because it's what Debian stable has. You can use ``rustup override set 1.41.1`` at the root of the repo to make it easier on you. Go to the ``hg-cpython`` folder:: $ cd rust/hg-cpython Or, only the ``hg-core`` folder. Be careful not to break compatibility:: $ cd rust/hg-core Simply run:: $ cargo build --release It is possible to build without ``--release``, but it is not recommended if performance is of any interest: there can be an order of magnitude of degradation when removing ``--release``. For faster builds, you may want to skip code generation:: $ cargo check For even faster typing:: $ cargo c You can run only the rust-specific tests (as opposed to tests of mercurial as a whole) with:: $ cargo test --all Formatting the code ------------------- We use ``rustfmt`` to keep the code formatted at all times. For now, we are using the nightly version because it has been stable enough and provides comment folding. To format the entire Rust workspace:: $ cargo +nightly fmt This requires you to have the nightly toolchain installed.