1447130 - [meta] Component-ify

Status: RESOLVED FIXED

(Firefox :: New Tab Page, enhancement)

Description

[Kate Hudson :k88hudson]

We will need to do this in order to support the Add-ons team removing support for boostrapped addons.

There are a few possible ways to do this which we discussed at the San Fran All Hands, including:

* migrating to a web extension
* migrating away from being a system add-on to being a regular Firefox component

Comment 1

[Dan Mosedale (:dmosedale, :dmose)]

When we talked in the SF, it was the case that loading as a web-extension would likely delay startup in some way, but that the WebExtensions team had bug 1378459 tracking that.  That bug just sprouted some proof-of-concept patches; linking to it here.

Comment 2

[Ed Lee :Mardak]

The "basic" steps of component-ify-ing is to replace the functionality provided by legacy bootstrap extensions -- in our case, mainly bootstrap.js and install.rdf. (Where we already have a bunch of custom packaging with jar.mn already.) Some functionality can just be removed as we don't need to support uninstalling/reinstalling/upgrading/downgrading a live extension.

I believe this is the current lifecycle:

1) activity-stream bootstrap.js is loaded very early as that's when extensions get loaded
- this does minimal startup work waiting for "sessionstore-windows-restored"
- https://searchfox.org/mozilla-central/source/browser/extensions/activity-stream/bootstrap.js
2) browser.js starts aboutNewTabService from delayedStartup
- https://searchfox.org/mozilla-central/rev/28daa2806c89684b3dfa4f0b551db1d099dda7c2/browser/base/content/browser.js#1438-1441
3) aboutNewTabService (on main process) loads/calls AboutNewTab.init()
- https://searchfox.org/mozilla-central/source/browser/components/newtab/aboutNewTabService.js
4) AboutNewTab.init() registers RemotePages
- this needs to happen early to catch the initial about:home/newtab
- https://searchfox.org/mozilla-central/source/browser/modules/AboutNewTab.jsm
5) "sessionstore-windows-restored" triggers a deferred activity stream startup
- this loads resource://activity-stream/lib/ActivityStream.jsm and the rest of activity stream
- this is deferred to avoid talos sessionrestore
- this also finds all potentially loaded modules to unload them on shutdown (so live upgrade of add-on can re-register)
6) activity stream INIT action and other stuff happens
- this also handles early about:newtab type pages that RemotePages noticed but ActivityStream.jsm wasn't ready yet
…
7) "quit-application-granted"
- aboutNewTabService calls its uninit and AboutNewTab.uninit (for main)
8) bootstrap.js shutdown
- call activityStream.uninit() to dispatch UNINIT action
- unload modules

We should be able to move bootstrap.js into AboutNewTab. Details: move (1) bootstrap.js startup related bits into (4) AboutNewTab.init to wait for "sessionstore-windows-restored" and move (5) deferred loading as part of AboutNewTab module. Similarly we can move (8) shutdown to be handled in (7) AboutNewTab.uninit().

I think we can break this transition into some steps by having both bootstrap.js and AboutNewTab coexisting without actually moving browser/extensions/activity-stream at the same time. If we have AboutNewTab handle `new ActivityStream()` and `activityStream.uninit()` as described above, we can leave other extension-specific stuff in bootstrap.js.

Comment 3

[Ed Lee :Mardak]

All dependent bugs resolved and successfully exported with bug 1478870!