Re: RFC: a plugin architecture for git extensions?

From: Andreas Ericsson <ae@op5.se>
Date: Apr 27, 2011, 14:52 UTC
Message-ID: <4DB82D90.6060200@op5.se>
In-Reply-To: <BANLkTimUHrHqS-Ssj+mK=0T8QHKg34pkaw@mail.gmail.com>

On 04/27/2011 02:50 PM, Jon Seymour wrote:

Show 26 quoted lines

> On Wednesday, April 27, 2011, Andreas Ericsson  wrote:
>> On 04/27/2011 05:36 AM, Jon Seymour wrote:
>>> Has anyone ever given consideration to git supporting a plugin
>>> architecture for git extensions?
>>>
>>> The idea would be to provide a consistent way to install, and address
>>> extensions to the core git functionality in a manner that does not
>>> require the extension to actually be integrated into the git core.
>>>
>>
> 
>> Horrible idea. There are already as many package managers as there
>> are packages without us throwing another one into the mix.
>>
> 
> I agree that there are too many package managers. But do you know
> what? There isn't a single package manager that reliably works across
> platform. apt-get? great. Except you need something else for Mac,
> cywgin, or, um Fedora. Brew? Fine then you only need to worry about
> Linux and cygwin. Cygwin? ...
> 
> The platform for my extension is git. Not Mac. Not Debian. Not Fedora.
> Not cygwin. git.
> 
> The lowest common denominator across these environments is, um, git.
>

You're utterly horribly wrong. It'll work well enough for scripted languages but when you start mixing in compiler requirements and whatnot the scheme falls apart. Quickly. Binary packages are popular for (very good) reasons: They are simple, fast and there's a reasonable chance they've been tested fairly well with the rest of the system so nothing breaks horribly once you install it.

Perl, Ruby, Python and PHP all have their own extension installers. That makes perfect sense since the same code runs unchanged on all platforms (with some few exceptions).

Show 5 quoted lines

> I challenge the sceptIcs to specify a one line command script that
> works across all possible environment that is more succinct than:
> 
>     git pm install gitwork
>

That's not the point. Mac users supposedly already know about brew. Fedora users already know about yum. Cygwin users... well, I have no idea what they know about, but whatever it is, it's fairly safe to assume they already know about it. That means they'll turn to that familiar tool for managing packages when they want to install something new. What you're proposing would force users on *all* systems to have to learn a new one.

> It shouldn't be too hard. A tar command here, an enviroment  variable
> edit there. Perhaps a curl command or a browser download.
>

And what you get in the end is a f*cking mess of spaghetti shell code that works worse than the existing package managers.

And you're right. It's not too hard, so long as every extension manager maintains some short list of requirements in the proper format, which current package maintainers will have to learn if they want some modules to be part of the "default" system install, the way a whole bunch of Perl modules are.

> You have 4 words. Knock yourself out.
>

make install

Made it in 2. What you described is what the user does to get new extensions. What I described below is what developers have to do to make their extensions easy to install *without* a package manager even if the distro the user is on doesn't ship that particular extension.

Show 29 quoted lines

> 
>>> So, perhaps it won't be included in git. That's fine, I can build my
>>> own fork of git which includes the proposed extension [ indeed, this
>>> is how I originally developed it]. That's fine for
>>> me, but it isn't the most practical way to distribute it to others
>>> since I'll have to produce distribution packages for a variety of
>>> different distribution formats or fallback to tars and zips.
>>>
>>
>> What you can do is let your Makefile (or some other install-script)
>> take the destination path for "make install" (or equivalent) from
>> the output of "git --exec-path".
>>
>> That way, you can ship "git extadd" or whatever you want to call it
>> as a simple installer that installs executable and man-page in their
>> proper locations. If the commands you install require configuration
>> by default I'd say they're broken to begin with, but even that can
>> be remedied by running "git config --add key value" from the installer.
>>
>> So in a way, git is already its own pkg-config binary and anyone
>> clever enough to write useful scripts that enhances git will almost
>> certainly see that and use it from their favourite language quite
>> without having to learn some new magic format for package management.
>>
> 
> Those 3 paragraphs were substantially longer than 4 words. Again,
> there is a tar ball, let me know how I can install it across alll
> environments that got runs on. Make sure the man pages work.
>

So the complete description would be

  git clone git://somerepo/gitworks
  cd gitworks
  make install

and the rest is in developer hands. If you make the extension manager run *ONLY* those commands, you've made it fairly simple for extension developers and users both, but then the gain is so extremely small that it's hardly worth it anymore, although I agree it would be nifty to keep a list of popular extensions on a wiki somewhere so users can actually find them.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

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