view tests/test-obsolete-checkheads.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

Check that obsolete properly strip heads
  $ cat >> $HGRCPATH << EOF
  > [phases]
  > # public changeset are not obsolete
  > publish=false
  > [ui]
  > logtemplate='{node|short} ({phase}) {desc|firstline}\n'
  > [experimental]
  > evolution.createmarkers=True
  > EOF
  $ mkcommit() {
  >    echo "$1" > "$1"
  >    hg add "$1"
  >    hg ci -m "add $1"
  > }
  $ getid() {
  >    hg id --debug -ir "desc('$1')"
  > }


  $ hg init remote
  $ cd remote
  $ mkcommit base
  $ hg phase --public .
  $ cd ..
  $ cp -R remote base
  $ hg clone remote local
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd local

New head replaces old head
==========================

setup
(we add the 1 flags to prevent bumped error during the test)

  $ mkcommit old
  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  $ hg up -q '.^'
  $ mkcommit new
  created new head
  $ hg debugobsolete --flags 1 `getid old` `getid new`
  obsoleted 1 changesets
  $ hg log -G --hidden
  @  71e3228bffe1 (draft) add new
  |
  | x  c70b08862e08 (draft) add old
  |/
  o  b4952fcf48cf (public) add base
  
  $ cp -R ../remote ../backup1

old exists remotely as draft. It is obsoleted by new that we now push.
Push should not warn about creating new head

  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)

old head is now public (public local version)
=============================================

setup

  $ rm -fr ../remote
  $ cp -R ../backup1 ../remote
  $ hg -R ../remote phase --public c70b08862e08
  $ hg pull -v
  pulling from $TESTTMP/remote
  searching for changes
  no changes found
  $ hg log -G --hidden
  @  71e3228bffe1 (draft) add new
  |
  | o  c70b08862e08 (public) add old
  |/
  o  b4952fcf48cf (public) add base
  

Abort: old will still be an head because it's public.

  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  abort: push creates new remote head 71e3228bffe1!
  (merge or see 'hg help push' for details about pushing new heads)
  [255]

old head is now public (public remote version)
==============================================

TODO: Not implemented yet.

# setup
#
#   $ rm -fr ../remote
#   $ cp -R ../backup1 ../remote
#   $ hg -R ../remote phase --public c70b08862e08
#   $ hg phase --draft --force c70b08862e08
#   $ hg log -G --hidden
#   @  71e3228bffe1 (draft) add new
#   |
#   | x  c70b08862e08 (draft) add old
#   |/
#   o  b4952fcf48cf (public) add base
#
#
#
# Abort: old will still be an head because it's public.
#
#   $ hg push
#   pushing to $TESTTMP/remote
#   searching for changes
#   abort: push creates new remote head 71e3228bffe1!
#   (merge or see 'hg help push' for details about pushing new heads)
#   [255]

old head is obsolete but replacement is not pushed
==================================================

setup

  $ rm -fr ../remote
  $ cp -R ../backup1 ../remote
  $ hg phase --draft --force '(0::) - 0'
  $ hg up -q '.^'
  $ mkcommit other
  created new head
  $ hg log -G --hidden
  @  d7d41ccbd4de (draft) add other
  |
  | o  71e3228bffe1 (draft) add new
  |/
  | x  c70b08862e08 (draft) add old
  |/
  o  b4952fcf48cf (public) add base
  

old exists remotely as draft. It is obsoleted by new but we don't push new.
Push should abort on new head

  $ hg push -r 'desc("other")'
  pushing to $TESTTMP/remote
  searching for changes
  abort: push creates new remote head d7d41ccbd4de!
  (merge or see 'hg help push' for details about pushing new heads)
  [255]



Both precursors and successors are already know remotely. Descendant adds heads
===============================================================================

setup. (The obsolete marker is known locally only

  $ cd ..
  $ rm -rf local
  $ hg clone remote local
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd local
  $ mkcommit old
  old already tracked!
  nothing changed
  [1]
  $ hg up -q '.^'
  $ mkcommit new
  created new head
  $ hg push -f
  pushing to $TESTTMP/remote
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  $ mkcommit desc1
  $ hg up -q '.^'
  $ mkcommit desc2
  created new head
  $ hg debugobsolete `getid old` `getid new`
  obsoleted 1 changesets
  $ hg log -G --hidden
  @  5fe37041cc2b (draft) add desc2
  |
  | o  a3ef1d111c5f (draft) add desc1
  |/
  o  71e3228bffe1 (draft) add new
  |
  | x  c70b08862e08 (draft) add old
  |/
  o  b4952fcf48cf (public) add base
  
  $ hg log -G --hidden -R ../remote
  o  71e3228bffe1 (draft) add new
  |
  | o  c70b08862e08 (draft) add old
  |/
  @  b4952fcf48cf (public) add base
  
  $ cp -R ../remote ../backup2

Push should not warn about adding new heads. We create one, but we'll delete
one anyway.

  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files (+1 heads)


Remote head is unknown but obsoleted by a local changeset
=========================================================

setup

  $ rm -fr ../remote
  $ cp -R ../backup1 ../remote
  $ cd ..
  $ rm -rf local
  $ hg clone remote local -r 0
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets b4952fcf48cf
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd local
  $ mkcommit new
  $ hg -R ../remote id --debug -r tip
  c70b08862e0838ea6d7c59c85da2f1ed6c8d67da tip
  $ hg  id --debug -r tip
  71e3228bffe1886550777233d6c97bb5a6b2a650 tip
  $ hg debugobsolete c70b08862e0838ea6d7c59c85da2f1ed6c8d67da 71e3228bffe1886550777233d6c97bb5a6b2a650
  $ hg log -G --hidden
  @  71e3228bffe1 (draft) add new
  |
  o  b4952fcf48cf (public) add base
  
  $ hg log -G --hidden -R ../remote
  o  c70b08862e08 (draft) add old
  |
  @  b4952fcf48cf (public) add base
  

We do not have enought data to take the right decision, we should fail

  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  remote has heads on branch 'default' that are not known locally: c70b08862e08
  abort: push creates new remote head 71e3228bffe1!
  (pull and merge or see 'hg help push' for details about pushing new heads)
  [255]

Pulling the missing data makes it work

  $ hg pull
  pulling from $TESTTMP/remote
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  (run 'hg heads' to see heads)
  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)

Old head is pruned without parent data and new unrelated head added
===================================================================

setup

  $ cd ..
  $ rm -R remote local
  $ cp -R backup1 remote
  $ hg clone remote local -qr c70b08862e08
  $ cd local
  $ hg up -q '.^'
  $ mkcommit new-unrelated
  created new head
  $ hg debugobsolete `getid old`
  obsoleted 1 changesets
  $ hg log -G --hidden
  @  350a93b716be (draft) add new-unrelated
  |
  | x  c70b08862e08 (draft) add old
  |/
  o  b4952fcf48cf (public) add base
  

  $ hg push
  pushing to $TESTTMP/remote
  searching for changes
  abort: push creates new remote head 350a93b716be!
  (merge or see 'hg help push' for details about pushing new heads)
  [255]