rust/README.rst

packaging: stage files and dynamically generate WiX installer

Like we did for Inno, we want to make the WiX installer
"dumb" and simply consume source files from a directory
tree rather than have to define every single file in
installer files. This will greatly decrease the amount of
effort required to maintain the WiX installer since we don't
have to think that much about keeping files in sync.

This commit changes the WiX packager to populate a staging
directory as part of packaging. After it does so, it scans
that directory and dynamically generates WiX XML defining the
content within.

The IDs and GUIDs being generated are deterministic. So,
upgrades should work as expected in Windows Installer land.
(WiX has a "heat" tool that can generate XML by walking the
filesystem but it doesn't have this deterministic property,
sadly.)

As part of this change, GUIDs are now effectively reset.
So the next upgrade should be a complete wipe and replace.
This could potentially cause issues. But in my local testing,
I was able to upgrade an existing 5.1.2 install without
issue.

Compared to the previous commit, the installed files differ
in the following:

* A ReleaseNotes.txt file is now included
* A hgrc.d/editor.rc file is now generated (mercurial.rc has been
  updated to reflect this logical change to the content source)
* All files are marked as read-only. Previously, only a subset
  of files were. This should help prevent unwanted tampering.
  Although we may want to consider use cases like modifying
  template files...

This change also means that Inno and WiX are now using very
similar code for managing the install layout. This means
that on disk both packages are nearly identical. The
differences in install layout are as follows:

* Inno has a Copying.txt vs a COPYING.rtf for WiX.
  (The WiX installer wants to use RTF.)
* Inno has a Mercurial.url file that is an internet shortcut
  to www.mercurial-scm.org. (This could potentially be
  removed.)
* Inno includes msvc[mpr]90.dll files and WiX does not.
  (WiX installs the MSVC runtime via merge modules.)
* Inno includes unins000.{dat,exe} files. (WiX's state is
  managed by Windows Installer, which places things elsewhere.)

Because file lists are dynamically generated now, the test
ensuring things remain in sync has been deleted. Good riddance.

While this is a huge step towards unifying the Windows installers,
there's still some improvements that can be made. But I think
it is worth celebrating the milestone of getting both Inno
and WiX to essentially share core packaging code and workflows.
That should make it much easier to change the installers going
forward. This will aid support of Python 3.

Differential Revision: https://phab.mercurial-scm.org/D7173

===================
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.