revlog: always enable generaldelta on version 2 revlogs
This commit starts the process of diverging version 2 revlogs
from version 1 revlogs.
generaldelta is a useful feature and has been enabled by
default for ages. I can't think of a good reason why the
feature should be disabled. Yes, it is true changelogs
today don't have generaldelta enabled. But that's because
they don't have delta chains enabled, so generaldelta makes
no sense there.
This commit makes generaldelta always enabled on version 2
revlogs.
As part of this, one-off code in changelog.py mucking with
revlog.version had to be made conditional on the revlog
version, as we don't want to change revlog feature
flags on version 2 revlogs. The fact this code exists
is horrible and stems from revlog options being shared by
the opener. We probably want a better API here. But that can
wait for another patch.
Differential Revision: https://phab.mercurial-scm.org/D5561
===================
Mercurial Rust Code
===================
This directory contains various Rust code for the Mercurial project.
The top-level ``Cargo.toml`` file defines a workspace containing
all primary Mercurial crates.
Building
========
To build the Rust components::
$ cargo build
If you prefer a non-debug / release configuration::
$ cargo build --release
Features
--------
The following Cargo features are available:
localdev (default)
Produce files that work with an in-source-tree build.
In this mode, the build finds and uses a ``python2.7`` binary from
``PATH``. The ``hg`` binary assumes it runs from ``rust/target/<target>hg``
and it finds Mercurial files at ``dirname($0)/../../../``.
Build Mechanism
---------------
The produced ``hg`` binary is *bound* to a CPython installation. The
binary links against and loads a CPython library that is discovered
at build time (by a ``build.rs`` Cargo build script). The Python
standard library defined by this CPython installation is also used.
Finding the appropriate CPython installation to use is done by
the ``python27-sys`` crate's ``build.rs``. Its search order is::
1. ``PYTHON_SYS_EXECUTABLE`` environment variable.
2. ``python`` executable on ``PATH``
3. ``python2`` executable on ``PATH``
4. ``python2.7`` executable on ``PATH``
Additional verification of the found Python will be performed by our
``build.rs`` to ensure it meets Mercurial's requirements.
Details about the build-time configured Python are built into the
produced ``hg`` binary. This means that a built ``hg`` binary is only
suitable for a specific, well-defined role. These roles are controlled
by Cargo features (see above).
Running
=======
The ``hgcli`` crate produces an ``hg`` binary. You can run this binary
via ``cargo run``::
$ cargo run --manifest-path hgcli/Cargo.toml
Or directly::
$ target/debug/hg
$ target/release/hg
You can also run the test harness with this binary::
$ ./run-tests.py --with-hg ../rust/target/debug/hg
.. note::
Integration with the test harness is still preliminary. Remember to
``cargo build`` after changes because the test harness doesn't yet
automatically build Rust code.