view tests/test-treediscovery-legacy.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

#require killdaemons

Tests discovery against servers without getbundle support:

  $ cat >> $HGRCPATH <<EOF
  > [ui]
  > logtemplate="{rev} {node|short}: {desc} {branches}\n"
  > EOF
  $ cp $HGRCPATH $HGRCPATH-withcap

  $ CAP="getbundle known changegroupsubset bundle2"
  $ . "$TESTDIR/notcapable"
  $ cp $HGRCPATH $HGRCPATH-nocap
  $ cp $HGRCPATH-withcap $HGRCPATH

Prep for test server without branchmap support

  $ CAP="branchmap"
  $ . "$TESTDIR/notcapable"
  $ cp $HGRCPATH $HGRCPATH-nocap-branchmap
  $ cp $HGRCPATH-withcap $HGRCPATH

Setup HTTP server control:

  $ remote=http://localhost:$HGPORT/
  $ export remote
  $ tstart() {
  >   echo '[web]' > $1/.hg/hgrc
  >   echo 'push_ssl = false' >> $1/.hg/hgrc
  >   echo 'allow_push = *' >> $1/.hg/hgrc
  >   cp $HGRCPATH-nocap $HGRCPATH
  >   hg serve -R $1 -p $HGPORT -d --pid-file=hg.pid -E errors.log
  >   cat hg.pid >> $DAEMON_PIDS
  > }
  $ tstop() {
  >   killdaemons.py
  >   cp $HGRCPATH-withcap $HGRCPATH
  > }

Both are empty:

  $ hg init empty1
  $ hg init empty2
  $ tstart empty2
  $ hg incoming -R empty1 $remote
  comparing with http://localhost:$HGPORT/
  no changes found
  [1]
  $ hg outgoing -R empty1 $remote
  comparing with http://localhost:$HGPORT/
  no changes found
  [1]
  $ hg pull -R empty1 $remote
  pulling from http://localhost:$HGPORT/
  no changes found
  $ hg push -R empty1 $remote
  pushing to http://localhost:$HGPORT/
  no changes found
  [1]
  $ tstop

Base repo:

  $ hg init main
  $ cd main
  $ hg debugbuilddag -mo '+2:tbase @name1 +3:thead1 <tbase @name2 +4:thead2 @both /thead1 +2:tmaintip'
  $ hg log -G
  o  11 a19bfa7e7328: r11 both
  |
  o  10 8b6bad1512e1: r10 both
  |
  o    9 025829e08038: r9 both
  |\
  | o  8 d8f638ac69e9: r8 name2
  | |
  | o  7 b6b4d315a2ac: r7 name2
  | |
  | o  6 6c6f5d5f3c11: r6 name2
  | |
  | o  5 70314b29987d: r5 name2
  | |
  o |  4 e71dbbc70e03: r4 name1
  | |
  o |  3 2c8d5d5ec612: r3 name1
  | |
  o |  2 a7892891da29: r2 name1
  |/
  o  1 0019a3b924fd: r1
  |
  o  0 d57206cc072a: r0
  
  $ cd ..
  $ tstart main

Full clone:

  $ hg clone main full
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd full
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg pull $remote
  pulling from http://localhost:$HGPORT/
  searching for changes
  no changes found
  $ hg push $remote
  pushing to http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ cd ..

Local is empty:

  $ cd empty1
  $ hg incoming $remote --rev name1
  comparing with http://localhost:$HGPORT/
  abort: cannot look up remote changes; remote repository does not support the 'changegroupsubset' capability!
  [255]
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  0 d57206cc072a: r0 
  1 0019a3b924fd: r1 
  2 a7892891da29: r2 name1
  3 2c8d5d5ec612: r3 name1
  4 e71dbbc70e03: r4 name1
  5 70314b29987d: r5 name2
  6 6c6f5d5f3c11: r6 name2
  7 b6b4d315a2ac: r7 name2
  8 d8f638ac69e9: r8 name2
  9 025829e08038: r9 both
  10 8b6bad1512e1: r10 both
  11 a19bfa7e7328: r11 both
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  no changes found
  [1]
  $ hg push $remote
  pushing to http://localhost:$HGPORT/
  no changes found
  [1]
  $ hg pull $remote
  pulling from http://localhost:$HGPORT/
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 12 changesets with 24 changes to 2 files
  new changesets d57206cc072a:a19bfa7e7328
  (run 'hg update' to get a working copy)
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ cd ..

Local is subset:

  $ cp $HGRCPATH-withcap $HGRCPATH
  $ hg clone main subset --rev name2 ; cd subset
  adding changesets
  adding manifests
  adding file changes
  added 6 changesets with 12 changes to 2 files
  new changesets d57206cc072a:d8f638ac69e9
  updating to branch name2
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cp $HGRCPATH-nocap $HGRCPATH
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  6 a7892891da29: r2 name1
  7 2c8d5d5ec612: r3 name1
  8 e71dbbc70e03: r4 name1
  9 025829e08038: r9 both
  10 8b6bad1512e1: r10 both
  11 a19bfa7e7328: r11 both
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg push $remote
  pushing to http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg pull $remote
  pulling from http://localhost:$HGPORT/
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 6 changesets with 12 changes to 2 files
  new changesets a7892891da29:a19bfa7e7328
  (run 'hg update' to get a working copy)
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ cd ..

Remote is empty:

  $ tstop ; tstart empty2
  $ cd main
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  0 d57206cc072a: r0 
  1 0019a3b924fd: r1 
  2 a7892891da29: r2 name1
  3 2c8d5d5ec612: r3 name1
  4 e71dbbc70e03: r4 name1
  5 70314b29987d: r5 name2
  6 6c6f5d5f3c11: r6 name2
  7 b6b4d315a2ac: r7 name2
  8 d8f638ac69e9: r8 name2
  9 025829e08038: r9 both
  10 8b6bad1512e1: r10 both
  11 a19bfa7e7328: r11 both
  $ hg pull $remote
  pulling from http://localhost:$HGPORT/
  searching for changes
  no changes found
  $ hg push $remote
  pushing to http://localhost:$HGPORT/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 12 changesets with 24 changes to 2 files
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ cd ..

Local is superset:

  $ tstop
  $ hg clone main subset2 --rev name2
  adding changesets
  adding manifests
  adding file changes
  added 6 changesets with 12 changes to 2 files
  new changesets d57206cc072a:d8f638ac69e9
  updating to branch name2
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ tstart subset2
  $ cd main
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  2 a7892891da29: r2 name1
  3 2c8d5d5ec612: r3 name1
  4 e71dbbc70e03: r4 name1
  9 025829e08038: r9 both
  10 8b6bad1512e1: r10 both
  11 a19bfa7e7328: r11 both
  $ hg pull $remote
  pulling from http://localhost:$HGPORT/
  searching for changes
  no changes found
  $ hg push $remote
  pushing to http://localhost:$HGPORT/
  searching for changes
  abort: push creates new remote branches: both, name1!
  (use 'hg push --new-branch' to create new remote branches)
  [255]
  $ hg push $remote --new-branch
  pushing to http://localhost:$HGPORT/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 6 changesets with 12 changes to 2 files
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ cd ..

Partial pull:

  $ tstop ; tstart main
  $ hg clone $remote partial --rev name2
  abort: partial pull cannot be done because other repository doesn't support changegroupsubset.
  [255]
  $ hg init partial; cd partial
  $ hg incoming $remote --rev name2
  comparing with http://localhost:$HGPORT/
  abort: cannot look up remote changes; remote repository does not support the 'changegroupsubset' capability!
  [255]
  $ hg pull $remote --rev name2
  pulling from http://localhost:$HGPORT/
  abort: partial pull cannot be done because other repository doesn't support changegroupsubset.
  [255]
  $ cd ..

  $ tstop

Exercise pushing to server without branchmap capability

  $ cp $HGRCPATH-nocap-branchmap $HGRCPATH-nocap
  $ hg init rlocal
  $ cd rlocal
  $ echo A > A
  $ hg ci -Am A
  adding A
  $ cd ..
  $ hg clone rlocal rremote
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd rlocal
  $ echo B > B
  $ hg ci -Am B
  adding B
  $ cd ..
  $ tstart rremote

  $ cd rlocal
  $ hg incoming $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  1 27547f69f254: B 
  $ hg pull $remote
  pulling from http://localhost:$HGPORT/
  searching for changes
  no changes found
  $ hg push $remote
  pushing to http://localhost:$HGPORT/
  searching for changes
  remote: adding changesets
  remote: adding manifests
  remote: adding file changes
  remote: added 1 changesets with 1 changes to 1 files
  $ hg outgoing $remote
  comparing with http://localhost:$HGPORT/
  searching for changes
  no changes found
  [1]
  $ cd ..

  $ tstop