Re: Extensions Infrastructure Work

On Tue, Jun 21, 2011 at 7:40 AM, Jasper St. Pierre
<jstpierre mecheye net> wrote:
> On Tue, Jun 21, 2011 at 6:54 AM, ecyrbe <ecyrbe gmail com> wrote:
>> Thank you for the hard work you are providing. juste some first questions.
>> 2011/6/21 Jasper St. Pierre <jstpierre mecheye net>
>>> Hey guys, it's Jasper.
>>> As part of my work on SweetTooth[0], I'm planning on a bunch of
>>> changes to make the user experience for installing, enabling and
>>> disabling extensions better. Unfortunately, I'm gonna have to break
>>> some stuff unless someone can come up with a clever hack. These
>>> changes are not set in stone, but they're what I'm hacking on
>>> currently, and I'd like to discuss them to make sure I'm on the right
>>> track. Extension developers, I'm talking to you:
>>>  * I want live extension enabling and disabling. The user experience
>>> is "click a button on, it takes effect
>>> immediately".
>>>  * I want to make it safer and more usable for developers to import
>>> code and assets their extension directory.
>>>  * I want extensions to be smart about their dependencies. For
>>> instance, the systemMonitor extension depends on an introspectable
>>> GTop, which AFAIK is unreleased, and hasn't been packaged in F15. The
>>> only clue users have that something has gone wrong is the Errors tab
>>> in the LookingGlass.
>> Will it be needed to explicitly declare depedencies, or will it be automatic
>> when importing?
>> can it be dependant on another one, to ensure that it is loaded after?
>> (imagine an extension that requires theme to be enabled for exemple)
> Both of these are planned, but currently unimplemented, and I'm not
> comfortable telling people what it looks like when it's unimplemented.
> But my generic answers are "Yes" and "Yes". I'm unsure if I can do
> stuff to make PackageKit pop-up, or find the dependent extension
> install under the web-UI, we'll see.

I must have been really tired last night, these answers are useless.

Extension dependency management is tricky... first, for
auto-dependency-installation, they must be on the extensions web-site.
The harder part is versioning.

Extensions will need to explicitly list their dependencies. I don't
know enough about PackageKit, but I'd like to say, "can you look for a
GTop.typelib anywhere for the correct architecture", and hopefully it
will work, even if the package puts it somewhere un-standard, but
that's Richard's question to answer.

If it's not trivial, then nope, it's on the backburner for now.

>>> Unfortunately, in order to do these things, I need your cooperation.
>>> I'm going to break some stuff, and I'd like your involvement so that I
>>> don't make a wrong decision which means another API break. I'd rather
>>> break it all at once and do things right.
>>> Let's tackle item 1:
>>> == Enabling and Disabling ==
>>> I'm going to remove the main() method, and replace it with a new system.
>>> You still require one function: init(). It does everything the main()
>>> function usually does, except it cannot change *any* Shell state. This
>>> is here so that you can set up anything you need to, like gettext
>>> silly shell actors. It's guaranteed to be called at most once per
>>> shell session.
>> How does shell state modification will be prevented? i thought that it was
>> not possible to prevent code to mess with other shell part?
>> or did i missread you?
> I won't try to install code that prevents you from modifying the Shell
> init(). There's two other deterrents:
> One, I'm going on the nature that everybody will play nicely. What's
> the incentive for users to modify the Shell during init()?
> Two, if you don't do follow the rules, you won't pass review on the
> web-UI, which means you have to try harder for people to install your
> extension.
>>> So, what's used to change the Shell UI? We introduce two new methods:
>>> enable() and disable(). Here's some simple rules:
>>>  * The Shell will call init(), and then enable() if your extension is
>>> enabled when the shell starts up.
>>>  * The Shell may then call disable() and enable() again during the
>>> same session, but it should never call init() more than once, ever.
>>>  * The Shell will not call disable() if your extension is disabled at
>>> startup.
>>>  * Right now the Shell calls init() even for disabled extensions at
>>> startup, but I may change that so that it calls init(), then enable()
>>> at first enable. The simplest solution is to not rely on init() coming
>>> at the start of the Shell session.
>>> For those of you who would like something a bit more object-oriented,
>>> you're in luck: init() can also return a state object. All that
>>> requires is functions named "enable" and "disable" on that object, the
>>> type doesn't matter nor do any other fields. The shell won't touch
>>> that object except for calling 'enable()' or 'disable()' on it. If you
>>> don't return anything (or return a false-y object), it's assumed that
>>> enabl() and disable() are on the moduie itself. Here's a simple code
>>> example: For lack of better terms, I'm calling these extensions
>>> "stateful", and the module ones "stateless", even though that's a huge
>>> lie: both have state.
>>> Starting with an improved version of the stock "Hello, World!"
>>> extension in the old system[1], we can build a new extension in one of
>>> two ways:
>>>  1. We can simply rename the main() function to init(), and move the
>>> line of code that adds the actor to the Shell to a new enable()
>>> method, and add a disable() method that does the reverse.[2]
>>>  2. Or we can make the extension return an object that has enable()
>>> and disable() functions.[3]
>>> If you want your extension to be compatible for old versions of the
>>> shell, thankfully, it's very easy: just write a main() that calls
>>> init(), then enable(). For the extensions website, I may allow
>>> so-called "legacy" extensions with a special method that restarts the
>>> Shell, but it would break the user-experience a bit, and it's extra
>>> code that I don't think would get used.
>>> Checking out the code samples, you may notice an argument called
>>> "helper". That's a cliff-hanger for next time, when I want to talk
>>> about items 2 and 3. I'd like your feedback on the information I'd
>>> provided so far, and any questions on SweetTooth, the web site, or the
>>> modifications I'm making would be extremely appreciated.
>>>  Jasper
>> will the gnome extension infrastructure be officially supported by
>> gnome-shell?
> Yes. There's no point if it isn't or won't.
>> will there be a crypto system to sign your extensions to prevent them to be
>> added from unrecognised sources?
> I discussed it with Owen, but I think we both think it's not
> necessary: as long as we make the automatic system only work from
>, we should be safe. I don't want to prevent users
> from installing random extensions, just make it harder: a rogue Shell
> extension can (unfortunately) do a lot more than a Firefox/Chrome one
> right now, so I doubt I'll be making exceptions to that rule until
> that changes. If the extension is not on, users
> can unpack the extensions and restart the shell manually.
>> will there be an automatic update infrastructure?
> Yes. The Shell saves a "manifest" for every extension it installs,
> which is basically the metadata.json that the user uploaded along with
> the extension zipfile, plus some other stuff. It includes the UUID,
> among other things. This means that it can automatically update if
> there is a newer version compatible with the shell version.
>  Jasper

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