zstd: vendor python-zstandard 0.5.0
As the commit message for the previous changeset says, we wish
for zstd to be a 1st class citizen in Mercurial. To make that
happen, we need to enable Python to talk to the zstd C API. And
that requires bindings.
This commit vendors a copy of existing Python bindings. Why do we
need to vendor? As the commit message of the previous commit says,
relying on systems in the wild to have the bindings or zstd present
is a losing proposition. By distributing the zstd and bindings with
Mercurial, we significantly increase our chances that zstd will
work. Since zstd will deliver a better end-user experience by
achieving better performance, this benefits our users. Another
reason is that the Python bindings still aren't stable and the
API is somewhat fluid. While Mercurial could be coded to target
multiple versions of the Python bindings, it is safer to bundle
an explicit, known working version.
The added Python bindings are mostly a fully-featured interface
to the zstd C API. They allow one-shot operations, streaming,
reading and writing from objects implements the file object
protocol, dictionary compression, control over low-level compression
parameters, and more. The Python bindings work on Python 2.6,
2.7, and 3.3+ and have been tested on Linux and Windows. There are
CFFI bindings, but they are lacking compared to the C extension.
Upstream work will be needed before we can support zstd with PyPy.
But it will be possible.
The files added in this commit come from Git commit
e637c1b214d5f869cf8116c550dcae23ec13b677 from
https://github.com/indygreg/python-zstandard and are added without
modifications. Some files from the upstream repository have been
omitted, namely files related to continuous integration.
In the spirit of full disclosure, I'm the maintainer of the
"python-zstandard" project and have authored 100% of the code
added in this commit. Unfortunately, the Python bindings have
not been formally code reviewed by anyone. While I've tested
much of the code thoroughly (I even have tests that fuzz APIs),
there's a good chance there are bugs, memory leaks, not well
thought out APIs, etc. If someone wants to review the code and
send feedback to the GitHub project, it would be greatly
appreciated.
Despite my involvement with both projects, my opinions of code
style differ from Mercurial's. The code in this commit introduces
numerous code style violations in Mercurial's linters. So, the code
is excluded from most lints. However, some violations I agree with.
These have been added to the known violations ignore list for now.
https://bz.mercurial-scm.org/1306
Initialize remote repo with branches:
$ hg init remote
$ cd remote
$ echo a > a
$ hg ci -Ama
adding a
$ hg branch br
marked working directory as branch br
(branches are permanent and global, did you want a bookmark?)
$ hg ci -Amb
$ echo c > c
$ hg ci -Amc
adding c
$ hg log
changeset: 2:ae3d9c30ec50
branch: br
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: c
changeset: 1:3f7f930ca414
branch: br
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: b
changeset: 0:cb9a9f314b8b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a
$ cd ..
Try cloning -r branch:
$ hg clone -rbr remote local1
adding changesets
adding manifests
adding file changes
added 3 changesets with 2 changes to 2 files
updating to branch br
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R local1 parents
changeset: 2:ae3d9c30ec50
branch: br
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: c
Try cloning -rother clone#branch:
$ hg clone -r0 remote#br local2
adding changesets
adding manifests
adding file changes
added 3 changesets with 2 changes to 2 files
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R local2 parents
changeset: 0:cb9a9f314b8b
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a
Try cloning -r1 clone#branch:
$ hg clone -r1 remote#br local3
adding changesets
adding manifests
adding file changes
added 3 changesets with 2 changes to 2 files
updating to branch br
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R local3 parents
changeset: 1:3f7f930ca414
branch: br
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: b