Hi Steve,

On 9/27/19 4:03 PM, Steve Kobes wrote:
Hi Emilio,

My recollection is that scroll anchoring was, in fact, a mess.  I do not personally have any opinion about whether scroll anchoring should be removed from Gecko.

We (Chrome) decided to accept some compat issues for the sake of launching the feature.  This was a judgment call and could reasonably have gone the other way.

Right, my concern is that taking compat fallout with Chrome's market share may be acceptable, because people will likely fix their websites if they misbehave.

But web developers may not take the same time to fix their site if it's broken on Firefox for Android, for example, which in turn drives Firefox users away (and you know this is a vicious cycle, the less users you have, the less people will care about fixing their websites in your browser).

That being said, more generally, I care about being interoperable / predictable here for web developers, and seems like that ship may have sailed if we need to fix some Gecko-specific issues by tweaking our heuristics, but Chromium / Blink doesn't change them in the same way (which is understandable, I guess, though I've filed spec issues for our reasoning behind these changes, which I think would apply to Chrome as well).

 -- Emilio

On Fri, 27 Sep 2019 at 09:09, Emilio Cobos Álvarez <emi...@mozilla.com <mailto:emi...@mozilla.com>> wrote:

    And, to be clear, we _can_ fix these compat issues, some way or another.

    One thought is to limit the amount of scroll adjustments without user
    scrolling or stuff like that, which would prevent the "you get stuck on
    the page".

    Making anchoring opt-in rather than opt-out is another option, but that
    defeats most of the purpose of the feature, I guess.

    See also some of the Chromium docs on the compat issues they found[1]
    and how were they trying to fix them before adding the
    "layout-affecting-property changed" heuristic, which is what is on the
    spec right now and what they implement.

    I just think that these are very hacky heuristics that are just
    going to
    bring a lot of compat pain and developer confusion.

    It doesn't help that all these things can break or not depending on the
    speed at which the user scrolls, the amount of scroll events that the
    user dispatches, the timing of these events relative to other
    events, etc...

       -- Emilio


    On 9/27/19 2:23 PM, Emilio Cobos Álvarez wrote:
     > Hi,
     > (cc'ing webkit-dev@ and blink-dev@ in case they have feedback or
     > opinions, as WebKit is the only engine which does not implement
     > anchoring, though I don't know if they plan to, and Blink is the
     > other engine that does implement it. Please reply to
    dev-platform@ though.)
     > TLDR: Scroll anchoring is really a mess.
     > I didn't do the initial implementation of the feature in Gecko,
    but I've
     > done a ton of work over the last few months to fix compat issues
    in our
     > implementation (see all the bugs blocking [1]).
     > At this point, our implementation is mostly compatible with
    Blink, but
     > even with a bug-for-bug compatible implementation, we did get compat
     > issues because of different content being served for different
     > or because our anti-tracking protections changing the final
    content of
     > the page slightly ([2] is an example of bug which only reproduces
     > ETP enabled only, but whose reduced test-case renders the site
     > in Chrome as well).
     > If you hit one of the broken cases as a user you think the
    browser is
     > completely broken, and the site is just unusable.
     > I've fixed those by tweaking the heuristics Gecko uses. Those extra
     > heuristics have also caused other compat issues, like [3], reported
     > today, which will require other adjustments to the heuristics, etc...
     > On top of that, the spec is not in a good state, with ton of open
     > without feedback from the editors [4].
     > So right now I'm at a stage where I think that the feature is
    just not
     > worth it. It doesn't behave predictably enough for developers,
    and you
     > have no guarantee of it behaving consistently unless you test a
     > particular browser, with a particular content in a particular
     > size... That's not great given the current dominant position of
     > Chromium-based browsers.
     > On top, issues with scroll anchoring are pretty hard to diagnose
     > you're aware of the feature.
     > All in all, it doesn't seem like the kind of feature that benefits a
     > diverse web (nor web developers for that matter), and I think we
     > remove the feature from Gecko.
     > Does anyone have strong opinions against removing scroll
    anchoring from
     > Gecko, based on the above?
     > Thanks,
     >   -- Emilio
     > [1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1519644
     > [2]: https://bugzilla.mozilla.org/show_bug.cgi?id=1561450
     > [3]: https://bugzilla.mozilla.org/show_bug.cgi?id=1584499
     > [4]:
     > _______________________________________________
     > dev-platform mailing list
     > dev-platf...@lists.mozilla.org
     > https://lists.mozilla.org/listinfo/dev-platform

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