(In reply to Nick Alexander :nalexander [he/him] from comment #6)

bgrins, others -- if you'd like to do some initial experiments, a try push
with those patches should help.

Brendan started looking into this. It sounds like ifdefs through the tree wherever XBL service is used is the most straightforward approach so far.

(In reply to Brian Grinstead [:bgrins] from comment #8)

Brendan started looking into this. It sounds like ifdefs through the tree wherever XBL service is used is the most straightforward approach so far.

Note that Fennec will move to ESR 68:

https://docs.google.com/document/d/1oRPkwP3l7QzdQYj0Wn7d_3EfTZaakocA_i_pGKlG0dI/edit

There will be no Fennec 69 release or later, but we'll continue to support Fennec 68.x with ESR releases at least until mid-2020. We'll continue to ship GeckoView from mozilla-central/beta/release, but I assume GeckoView doesn't include any XBL code.

However, we will keep building and running tests on Fennec 69 and 70 until Fennec 68 ESR successfully ships to the Release channel. If there is a major problem with ESR 68, we will want Fennec 69-70 as a backup release option. So you can start ripping out Fennec code in the 71 Nightly cycle (starting 2019-09-02), but I would keep using #ifdefs until then.

(In reply to Chris Peterson [:cpeterson] from comment #9)

There will be no Fennec 69 release or later, but we'll continue to support Fennec 68.x with ESR releases at least until mid-2020. We'll continue to ship GeckoView from mozilla-central/beta/release, but I assume GeckoView doesn't include any XBL code.

GeckoView shouldn't have any XBL bindings, but all the platform code to support XBL is still there.

Hey bz, I wanted to get your feedback before going forward...

I have a patch working that adds a MOZ_XBL define which doesn't compile anything in the dom/xbl folder and #ifdefs XBL out of most of the places it's used in the tree. I also had to add some stubs in stylo. The gecko view tests are passing, but we have a number of other android failures because XBL is still needed there. My next steps will be to address those failures, but I first wanted to check with you and see if this is a sane approach going foward. Adding some 100+ ifdefs seems less than ideal, but it could be our first steps in removing XBL.

I agree that we're going to need something like this anyway for XBL removal, in the sense of having to do this audit at some point.

I don't have a problem with the number of ifdefs given that these are somewhat temporary (I know, famous last words).

Note that if we really wanted to, we could make GetAnonymousElementByAttribute completely conditional on MOZ_XBL instead of just stubbing it out ifndef MOZ_XBL. That would actually reduce the number of ifdefs a bit, I suspect, though would require preprocessing Document.webidl.

Defaults XBL to disabled on android, but still enabled for desktop.

When XBL is disabled, no code in dom/xbl will be built. Also, adds ifdefs
to remove any of the XBL related code elsewhere. There's definitely more
that can be done here, but I think it's better to wait to do the rest of
the cleanup when we actually remove the code.

Depends on D45612

Adds a feature "moz_xbl" that when disabled causes the XBL code in servo to
be stubbed out.

Depends on D45613

Adds a way for mochitest, reftest, and crashtests to skip XBL related
tests when XBL is disabled. Also, add an app constant so JS can
check whether XBL is enabled.

Depends on D45614

BL will be disabled on android, so these tests must be skipped.

Depends on D45615

https://hg.mozilla.org/mozilla-central/rev/36b84f0fb2d1
https://hg.mozilla.org/mozilla-central/rev/4a104e817b35
https://hg.mozilla.org/mozilla-central/rev/02740878ddd6
https://hg.mozilla.org/mozilla-central/rev/5a2309893b3a
https://hg.mozilla.org/mozilla-central/rev/75db6763ead5

firefox70=wontfix because we don't need to uplift these GeckoView XBL patches to Beta (70).

Hi Brendan!
Since this bug landed, artifact builds as well as windows aarch64 builds no longer have XBL enabled.
This makes try pushes using artifact builds a bit noisy, because several tests still using XBL are failing.
eg devtools/client/inspector/test/browser_inspector_highlighter-xbl.js, dom/base/test/chrome/test_bug683852.xul

Any idea how to fix this? Or should we just make sure that those tests are skipped if !xbl?

(edit: seems that skip-if = !xbl doesn't do the trick here, also some tests skipped if !xbl seem to pass on artifact builds, so not sure exactly what is wrong with artifact builds / xbl)

I think xbl is being disabled on artifact builds because of when='--enable-compile-environment' in config, but I don't understand why it's disabled for aarch64 builds. I'll be fixing this over in bug 1587662.