rust: implementation of `hg`
This commit provides a mostly-working implementation of the
`hg` script in Rust along with scaffolding to support Rust in
the repository.
If you are familiar with Rust, the contents of the added rust/
directory should be pretty straightforward. We create an "hgcli"
package that implements a binary application to run Mercurial.
The output of this package is an "hg" binary.
Our Rust `hg` (henceforth "rhg") essentially is a port of the existing
`hg` Python script. The main difference is the creation of the embedded
CPython interpreter is handled by the binary itself instead of relying
on the shebang. In that sense, rhg is more similar to the "exe wrapper"
we currently use on Windows. However, unlike the exe wrapper, rhg does
not call the `hg` Python script. Instead, it uses the CPython APIs to
import mercurial modules and call appropriate functions. The amount of
code here is surprisingly small.
It is my intent to replace the existing C-based exe wrapper with rhg.
Preferably in the next Mercurial release. This should be achievable -
at least for some Mercurial distributions. The future/timeline for
rhg on other platforms is less clear. We already ship a hg.exe on
Windows. So if we get the quirks with Rust worked out, shipping a
Rust-based hg.exe should hopefully not be too contentious.
Now onto the implementation.
We're using python27-sys and the cpython crates for talking to the
CPython API. We currently don't use too much functionality of the
cpython crate and could have probably cut it out. However, it does
provide a reasonable abstraction over unsafe {} CPython function
calls. While we still have our fair share of those, at least we're
not dealing with too much refcounting, error checking, etc. So I
think the use of the cpython crate is justified. Plus, there is
not-yet-implemented functionality that could benefit from cpython. I
see our use of this crate only increasing.
The cpython and python27-sys crates are not without their issues.
The cpython crate didn't seem to account for the embedding use case
in its design. Instead, it seems to assume that you are building
a Python extension. It is making some questionable decisions around
certain CPython APIs. For example, it insists that
PyEval_ThreadsInitialized() is called and that the Python code
likely isn't the main thread in the underlying application. It
is also missing some functionality that is important for embedded
use cases (such as exporting the path to the Python interpreter
from its build script). After spending several hours trying to
wrangle python27-sys and cpython, I gave up and forked the project
on GitHub. Our Cargo.toml tracks this fork. I'm optimistic that
the upstream project will accept our contributions and we can
eventually unfork.
There is a non-trivial amount of code in our custom Cargo build
script. Our build.rs (which is called as part of building the hgcli
crate):
* Validates that the Python interpreter that was detected by the
python27-sys crate provides a shared library (we only support
shared library linking at this time - although this restriction
could be loosened).
* Validates that the Python is built with UCS-4 support. This ensures
maximum Unicode compatibility.
* Exports variables to the crate build allowing the built crate to e.g.
find the path to the Python interpreter.
The produced rhg should be considered alpha quality. There are several
known deficiencies. Many of these are documented with inline TODOs.
Probably the biggest limitation of rhg is that it assumes it is
running from the ./rust/target/<target> directory of a source
distribution. So, rhg is currently not very practical for real-world
use. But, if you can `cargo build` it, running the binary *should*
yield a working Mercurial CLI.
In order to support using rhg with the test harness, we needed to hack
up run-tests.py so the path to Mercurial's Python files is set properly.
The change is extremely hacky and is only intended to be a stop-gap
until the test harness gains first-class support for installing rhg.
This will likely occur after we support running rhg outside the
source directory.
Despite its officially alpha quality, rhg copes extremely well with
the test harness (at least on Linux). Using
`run-tests.py --with-hg ../rust/target/debug/hg`, I only encounter
the following failures:
* test-run-tests.t -- Warnings emitted about using an unexpected
Mercurial library. This is due to the hacky nature of setting the
Python directory when run-tests.py detected rhg.
* test-devel-warnings.t -- Expected stack trace missing frame for `hg`
(This is expected since we no longer have an `hg` script!)
* test-convert.t -- Test running `$PYTHON "$BINDIR"/hg`, which obviously
assumes `hg` is a Python script.
* test-merge-tools.t -- Same assumption about `hg` being executable with
Python.
* test-http-bad-server.t -- Seeing exit code 255 instead of 1 around
line 358.
* test-blackbox.t -- Exit code 255 instead of 1.
* test-basic.t -- Exit code 255 instead of 1.
It certainly looks like we have a bug around exit code handling. I
don't think it is severe enough to hold up review and landing of this
initial implementation. Perfect is the enemy of good.
Differential Revision: https://phab.mercurial-scm.org/D1581
Test basic functionality of url#rev syntax
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -qAm 'add a'
$ hg branch foo
marked working directory as branch foo
(branches are permanent and global, did you want a bookmark?)
$ echo >> a
$ hg ci -m 'change a'
$ cd ..
$ hg clone 'repo#foo' clone
adding changesets
adding manifests
adding file changes
added 2 changesets with 2 changes to 1 files
new changesets 1f0dee641bb7:cd2a86ecc814
updating to branch foo
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg --cwd clone heads
changeset: 1:cd2a86ecc814
branch: foo
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change a
changeset: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
$ hg --cwd clone parents
changeset: 1:cd2a86ecc814
branch: foo
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change a
$ cat clone/.hg/hgrc
# example repository config (see 'hg help config' for more info)
[paths]
default = $TESTTMP/repo#foo
# path aliases to other clones of this repo in URLs or filesystem paths
# (see 'hg help config.paths' for more info)
#
# default:pushurl = ssh://jdoe@example.net/hg/jdoes-fork
# my-fork = ssh://jdoe@example.net/hg/jdoes-fork
# my-clone = /home/jdoe/jdoes-clone
[ui]
# name and email (local to this repository, optional), e.g.
# username = Jane Doe <jdoe@example.com>
Changing original repo:
$ cd repo
$ echo >> a
$ hg ci -m 'new head of branch foo'
$ hg up -qC default
$ echo bar > bar
$ hg ci -qAm 'add bar'
$ hg log
changeset: 3:4cd725637392
tag: tip
parent: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add bar
changeset: 2:faba9097cad4
branch: foo
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: new head of branch foo
changeset: 1:cd2a86ecc814
branch: foo
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: change a
changeset: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
$ hg -q outgoing '../clone'
2:faba9097cad4
3:4cd725637392
$ hg summary --remote --config paths.default='../clone'
parent: 3:4cd725637392 tip
add bar
branch: default
commit: (clean)
update: (current)
phases: 4 draft
remote: 2 outgoing
$ hg -q outgoing '../clone#foo'
2:faba9097cad4
$ hg summary --remote --config paths.default='../clone#foo'
parent: 3:4cd725637392 tip
add bar
branch: default
commit: (clean)
update: (current)
phases: 4 draft
remote: 1 outgoing
$ hg -q --cwd ../clone incoming '../repo#foo'
2:faba9097cad4
$ hg --cwd ../clone summary --remote --config paths.default='../repo#foo'
parent: 1:cd2a86ecc814 tip
change a
branch: foo
commit: (clean)
update: (current)
remote: 1 or more incoming
$ hg -q push '../clone#foo'
$ hg --cwd ../clone heads
changeset: 2:faba9097cad4
branch: foo
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: new head of branch foo
changeset: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
$ hg -q --cwd ../clone incoming '../repo#foo'
[1]
$ hg --cwd ../clone summary --remote --config paths.default='../repo#foo'
parent: 1:cd2a86ecc814
change a
branch: foo
commit: (clean)
update: 1 new changesets (update)
remote: (synced)
$ cd ..
$ cd clone
$ hg rollback
repository tip rolled back to revision 1 (undo push)
$ hg -q incoming
2:faba9097cad4
$ hg -q pull
$ hg heads
changeset: 2:faba9097cad4
branch: foo
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: new head of branch foo
changeset: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
Pull should not have updated:
$ hg parents -q
1:cd2a86ecc814
Going back to the default branch:
$ hg up -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg parents
changeset: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add a
No new revs, no update:
$ hg pull -qu
$ hg parents -q
0:1f0dee641bb7
$ hg rollback
repository tip rolled back to revision 1 (undo pull)
$ hg parents -q
0:1f0dee641bb7
Pull -u takes us back to branch foo:
$ hg pull -qu
$ hg parents
changeset: 2:faba9097cad4
branch: foo
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: new head of branch foo
$ hg rollback
repository tip rolled back to revision 1 (undo pull)
working directory now based on revision 0
$ hg up -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg parents -q
0:1f0dee641bb7
$ hg heads -q
1:cd2a86ecc814
0:1f0dee641bb7
$ hg pull -qur default default
$ hg parents
changeset: 3:4cd725637392
tag: tip
parent: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add bar
$ hg heads
changeset: 3:4cd725637392
tag: tip
parent: 0:1f0dee641bb7
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add bar
changeset: 2:faba9097cad4
branch: foo
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: new head of branch foo
Test handling of invalid urls
$ hg id http://foo/?bar
abort: unsupported URL component: "bar"
[255]
$ cd ..
Test handling common incoming revisions between "default" and
"default-push"
$ hg -R clone rollback
repository tip rolled back to revision 1 (undo pull)
working directory now based on revision 0
$ cd repo
$ hg update -q -C default
$ echo modified >> bar
$ hg commit -m "new head to push current default head"
$ hg -q push -r ".^1" '../clone'
$ hg -q outgoing '../clone'
2:faba9097cad4
4:d515801a8f3d
$ hg summary --remote --config paths.default='../clone#default' --config paths.default-push='../clone#foo'
parent: 4:d515801a8f3d tip
new head to push current default head
branch: default
commit: (clean)
update: (current)
phases: 1 draft
remote: 1 outgoing
$ hg summary --remote --config paths.default='../clone#foo' --config paths.default-push='../clone'
parent: 4:d515801a8f3d tip
new head to push current default head
branch: default
commit: (clean)
update: (current)
phases: 1 draft
remote: 2 outgoing
$ hg summary --remote --config paths.default='../clone' --config paths.default-push='../clone#foo'
parent: 4:d515801a8f3d tip
new head to push current default head
branch: default
commit: (clean)
update: (current)
phases: 1 draft
remote: 1 outgoing
$ hg clone -q -r 0 . ../another
$ hg -q outgoing '../another#default'
3:4cd725637392
4:d515801a8f3d
$ hg summary --remote --config paths.default='../another#default' --config paths.default-push='../clone#default'
parent: 4:d515801a8f3d tip
new head to push current default head
branch: default
commit: (clean)
update: (current)
phases: 1 draft
remote: 1 outgoing
$ cd ..
Test url#rev syntax of local destination path, which should be taken as
a 'url#rev' path
$ hg clone repo '#foo'
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg root -R '#foo'
$TESTTMP/#foo