view tests/test-contrib-check-commit.t @ 35569:964212780daf

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 the 'check-commit' script
==============================

A fine patch:

  $ cat > patch-with-long-header.diff << EOF
  > # HG changeset patch
  > # User timeless <[e-mail]>
  > # Date 1448911706 0
  > #      Mon Nov 30 19:28:26 2015 +0000
  > # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
  > # Parent  42aa0e570eaa364a622bc4443b0bcb79b1100a58
  > # ClownJoke This is a veryly long header that should not be warned about because its not the description
  > bundle2: use Oxford comma (issue123) (BC)
  > 
  > diff --git a/hgext/transplant.py b/hgext/transplant.py
  > --- a/hgext/transplant.py
  > +++ b/hgext/transplant.py
  > @@ -599,7 +599,7 @@
  >              return
  >          if not (opts.get('source') or revs or
  >                  opts.get('merge') or opts.get('branch')):
  > -            raise error.Abort(_('no source URL, branch revision or revision '
  > +            raise error.Abort(_('no source URL, branch revision, or revision '
  >                                 'list provided'))
  >          if opts.get('all'):
  > 
  > + def blahblah(x):
  > +     pass
  > EOF
  $ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit

This would normally be against the rules, but it's okay because that's
what tagging and signing looks like:

  $ cat > creates-a-tag.diff << EOF
  > # HG changeset patch
  > # User Augie Fackler <[e-mail]>
  > # Date 1484787778 18000
  > #      Wed Jan 18 20:02:58 2017 -0500
  > # Branch stable
  > # Node ID c177635e4acf52923bc3aa9f72a5b1ad1197b173
  > # Parent  a1dd2c0c479e0550040542e392e87bc91262517e
  > Added tag 4.1-rc for changeset a1dd2c0c479e
  > 
  > diff --git a/.hgtags b/.hgtags
  > --- a/.hgtags
  > +++ b/.hgtags
  > @@ -150,3 +150,4 @@ 438173c415874f6ac653efc1099dec9c9150e90f
  >  eab27446995210c334c3d06f1a659e3b9b5da769 4.0
  >  b3b1ae98f6a0e14c1e1ba806a6c18e193b6dae5c 4.0.1
  >  e69874dc1f4e142746ff3df91e678a09c6fc208c 4.0.2
  > +a1dd2c0c479e0550040542e392e87bc91262517e 4.1-rc
  > EOF
  $ $TESTDIR/../contrib/check-commit < creates-a-tag.diff

A patch with lots of errors:

  $ cat > patch-with-long-header.diff << EOF
  > # HG changeset patch
  > # User timeless
  > # Date 1448911706 0
  > #      Mon Nov 30 19:28:26 2015 +0000
  > # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
  > # Parent  42aa0e570eaa364a622bc4443b0bcb79b1100a58
  > # ClownJoke This is a veryly long header that should not be warned about because its not the description
  > transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
  > 
  > diff --git a/hgext/transplant.py b/hgext/transplant.py
  > --- a/hgext/transplant.py
  > +++ b/hgext/transplant.py
  > @@ -599,7 +599,7 @@
  >              return
  >          if not (opts.get('source') or revs or
  >                  opts.get('merge') or opts.get('branch')):
  > -            raise error.Abort(_('no source URL, branch revision or revision '
  > +            raise error.Abort(_('no source URL, branch revision, or revision '
  >                                 'list provided'))
  >          if opts.get('all'):
  > EOF
  $ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
  1: username is not an email address
   # User timeless
  7: summary keyword should be most user-relevant one-word command or topic
   transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
  7: (BC) needs to be uppercase
   transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
  7: use (issueDDDD) instead of bug
   transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
  7: no space allowed between issue and number
   transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
  7: summary line too long (limit is 78)
   transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
  [1]

A patch with other errors:

  $ cat > patch-with-long-header.diff << EOF
  > # HG changeset patch
  > # User timeless
  > # Date 1448911706 0
  > #      Mon Nov 30 19:28:26 2015 +0000
  > # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
  > # Parent  42aa0e570eaa364a622bc4443b0bcb79b1100a58
  > # ClownJoke This is a veryly long header that should not be warned about because its not the description
  > This has no topic and ends with a period.
  > 
  > diff --git a/hgext/transplant.py b/hgext/transplant.py
  > --- a/hgext/transplant.py
  > +++ b/hgext/transplant.py
  > @@ -599,7 +599,7 @@
  >          if opts.get('all'):
  >  
  > 
  > +
  > + some = otherjunk
  > +
  > +
  > + def blah_blah(x):
  > +     pass
  > +
  >  
  > EOF
  $ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
  1: username is not an email address
   # User timeless
  7: don't capitalize summary lines
   This has no topic and ends with a period.
  7: summary line doesn't start with 'topic: '
   This has no topic and ends with a period.
  7: don't add trailing period on summary line
   This has no topic and ends with a period.
  19: adds double empty line
   +
  20: adds a function with foo_bar naming
   + def blah_blah(x):
  23: adds double empty line
   +
  [1]