view tests/test-unamend.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 for command `hg unamend` which lives in uncommit extension
===============================================================

  $ cat >> $HGRCPATH << EOF
  > [alias]
  > glog = log -G -T '{rev}:{node|short}  {desc}'
  > [experimental]
  > evolution = createmarkers, allowunstable
  > [extensions]
  > rebase =
  > amend =
  > uncommit =
  > EOF

Repo Setup

  $ hg init repo
  $ cd repo
  $ for ch in a b c d e f g h; do touch $ch; echo "foo" >> $ch; hg ci -Aqm "Added "$ch; done

  $ hg glog
  @  7:ec2426147f0e  Added h
  |
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
Trying to unamend when there was no amend done

  $ hg unamend
  abort: changeset must have one predecessor, found 0 predecessors
  [255]

Unamend on clean wdir and tip

  $ echo "bar" >> h
  $ hg amend

  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID c9fa1a715c1b7661c0fafb362a9f30bd75878d7d
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r c9fa1a715c1b h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar

  $ hg glog --hidden
  @  8:c9fa1a715c1b  Added h
  |
  | x  7:ec2426147f0e  Added h
  |/
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg unamend
  $ hg glog --hidden
  @  9:46d02d47eec6  Added h
  |
  | x  8:c9fa1a715c1b  Added h
  |/
  | x  7:ec2426147f0e  Added h
  |/
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg diff
  diff -r 46d02d47eec6 h
  --- a/h	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo
  +bar

  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 46d02d47eec6ca096b8dcab3f8f5579c40c3dd9a
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r 46d02d47eec6 h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +foo

  $ hg status
  M h

  $ hg log -r . -T '{extras % "{extra}\n"}' --config alias.log=log
  branch=default
  unamend_source=c9fa1a715c1b7661c0fafb362a9f30bd75878d7d

Using unamend to undo an unamed (intentional)

  $ hg unamend
  $ hg exp
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 850ddfc1bc662997ec6094ada958f01f0cc8070a
  # Parent  87d6d66763085b629e6d7ed56778c79827273022
  Added h
  
  diff -r 87d6d6676308 -r 850ddfc1bc66 h
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/h	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar
  $ hg diff

Unamend on a dirty working directory

  $ echo "bar" >> a
  $ hg amend
  $ echo "foobar" >> a
  $ echo "bar" >> b
  $ hg status
  M a
  M b

  $ hg unamend

  $ hg status
  M a
  M b

  $ hg diff
  diff -r ec338db45d51 a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,3 @@
   foo
  +bar
  +foobar
  diff -r ec338db45d51 b
  --- a/b	Thu Jan 01 00:00:00 1970 +0000
  +++ b/b	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,2 @@
   foo
  +bar

Unamending an added file

  $ hg ci -m "Added things to a and b"
  $ echo foo > bar
  $ hg add bar
  $ hg amend

  $ hg unamend
  $ hg status
  A bar

  $ hg revert --all
  forgetting bar

Unamending a removed file

  $ hg remove a
  $ hg amend

  $ hg unamend
  $ hg status
  R a
  ? bar

  $ hg revert --all
  undeleting a

Unamending an added file with dirty wdir status

  $ hg add bar
  $ hg amend
  $ echo bar >> bar
  $ hg status
  M bar

  $ hg unamend
  $ hg status
  A bar
  $ hg diff
  diff -r 7f79409af972 bar
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/bar	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +foo
  +bar

  $ hg revert --all
  forgetting bar

Unamending in middle of a stack

  $ hg glog
  @  19:7f79409af972  Added things to a and b
  |
  o  12:ec338db45d51  Added h
  |
  o  6:87d6d6676308  Added g
  |
  o  5:825660c69f0c  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  
  $ hg up 5
  2 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo bar >> f
  $ hg amend
  $ hg rebase -s 6 -d . -q

  $ hg glog
  o  23:03ddd6fc5af1  Added things to a and b
  |
  o  22:3e7b64ee157b  Added h
  |
  o  21:49635b68477e  Added g
  |
  @  20:93f0e8ffab32  Added f
  |
  o  4:aa98ab95a928  Added e
  |
  o  3:62615734edd5  Added d
  |
  o  2:28ad74487de9  Added c
  |
  o  1:29becc82797a  Added b
  |
  o  0:18d04c59bb5d  Added a
  

  $ hg --config experimental.evolution=createmarkers unamend
  abort: cannot unamend changeset with children
  [255]

  $ hg unamend

Trying to unamend a public changeset

  $ hg up -C 23
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg phase -r . -p
  $ hg unamend
  abort: cannot unamend public changesets
  (see 'hg help phases' for details)
  [255]

Testing whether unamend retains copies or not

  $ hg status
  ? bar

  $ hg mv a foo

  $ hg ci -m "Moved a to foo"
  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID cfef290346fbee5126313d7e1aab51d877679b09
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo

  $ hg mv b foobar
  $ hg diff --git
  diff --git a/b b/foobar
  rename from b
  rename to foobar
  $ hg amend

  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID eca050985275bb271ce3092b54e56ea5c85d29a3
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo
  diff --git a/b b/foobar
  rename from b
  rename to foobar

  $ hg mv c wat
  $ hg unamend

Retained copies in new prdecessor commit

  $ hg exp --git
  # HG changeset patch
  # User test
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID 552e3af4f01f620f88ca27be1f898316235b736a
  # Parent  03ddd6fc5af19e028c44a2fd6d790dd22712f231
  Moved a to foo
  
  diff --git a/a b/foo
  rename from a
  rename to foo

Retained copies in working directoy

  $ hg diff --git
  diff --git a/b b/foobar
  rename from b
  rename to foobar
  diff --git a/c b/wat
  rename from c
  rename to wat