Consolidate lazy-load observers by credod · Pull Request #59807 · WebKit/WebKit

credod · 2026-03-03T17:33:45Z

https://bugs.webkit.org/show_bug.cgi?id=309078

Reviewed by NOBODY (OOPS!).

Consolidates LazyLoadImageObserver, LazyLoadFrameObserver, and LazyLoadModelObserver to a single LazyLoadElementObserver.

* Source/WebCore/Modules/model-element/HTMLModelElement.cpp: (WebCore::HTMLModelElement::~HTMLModelElement):
(WebCore::HTMLModelElement::stop):
(WebCore::HTMLModelElement::insertedIntoAncestor): (WebCore::HTMLModelElement::removedFromAncestor):
(WebCore::HTMLModelElement::lazyLoadIntersectionCallbackInvoked):
* Source/WebCore/Modules/model-element/HTMLModelElement.h:
* Source/WebCore/Modules/model-element/LazyLoadModelObserver.cpp: Removed.
* Source/WebCore/Modules/model-element/LazyLoadModelObserver.h: Removed.
* Source/WebCore/SaferCPPExpectations/UncheckedCallArgsCheckerExpectations:
* Source/WebCore/SaferCPPExpectations/UncountedCallArgsCheckerExpectations:
* Source/WebCore/Sources.txt:
* Source/WebCore/WebCore.xcodeproj/project.pbxproj:
* Source/WebCore/dom/Document.cpp: (WebCore::Document::lazyLoadElementObserver):
(WebCore::Document::lazyLoadImageObserver): Deleted. (WebCore::Document::lazyLoadModelObserver): Deleted.
* Source/WebCore/dom/Document.h:
* Source/WebCore/html/HTMLIFrameElement.cpp: (WebCore::HTMLIFrameElement::attributeChanged):
(WebCore::HTMLIFrameElement::referrerPolicy const): (WebCore::HTMLIFrameElement::shouldLoadFrameLazily): (WebCore::HTMLIFrameElement::isLazyLoadObserverActive const): (WebCore::HTMLIFrameElement::loadDeferredFrame):
(WebCore::HTMLIFrameElement::lazyLoadIntersectionCallbackInvoked): (WebCore::HTMLIFrameElement::lazyLoadFrameObserver): Deleted.
* Source/WebCore/html/HTMLIFrameElement.h:
* Source/WebCore/html/HTMLImageElement.cpp: (WebCore::HTMLImageElement::lazyLoadIntersectionCallbackInvoked):
* Source/WebCore/html/HTMLImageElement.h:
* Source/WebCore/html/LazyLoadElementObserver.cpp: Renamed from Source/WebCore/html/LazyLoadImageObserver.cpp. (WebCore::LazyLoadElementObserver::observe):
(WebCore::LazyLoadElementObserver::unobserve):
(WebCore::LazyLoadElementObserver::intersectionObserver): (WebCore::LazyLoadElementObserver::isObserved const):
* Source/WebCore/html/LazyLoadElementObserver.h: Renamed from Source/WebCore/html/LazyLoadImageObserver.h.
* Source/WebCore/html/LazyLoadFrameObserver.cpp: Removed.
* Source/WebCore/html/LazyLoadFrameObserver.h: Removed.
* Source/WebCore/html/Origin.cpp:
* Source/WebCore/html/shadow/ProgressShadowElement.cpp:
* Source/WebCore/loader/ImageLoader.cpp: (WebCore::ImageLoader::didUpdateCachedImage):
(WebCore::ImageLoader::notifyFinished):
(WebCore::ImageLoader::resetLazyImageLoading):

583d2f0

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

webkit-early-warning-system · 2026-03-03T17:33:51Z

EWS run on previous version of this PR (hash 95e1fb2)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	❌ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	❌ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

credod · 2026-03-03T17:40:23Z

Source/WebCore/html/LazyLoadElementObserver.cpp

    if (!m_observer) {
-        auto callback = LazyImageLoadIntersectionObserverCallback::create(document);
+        auto callback = LazyLoadIntersectionObserverCallback::create(document);
        static NeverDestroyed<const String> lazyLoadingScrollMarginFallback(MAKE_STATIC_STRING_IMPL("100%"));


One thing to call out here is that the lazy loading behavior for <iframe> will change. LazyLoadFrameObserver didn't previously specify custom scrollMargin, meaning that <iframe> elements would only "intersect" when they entered the viewport. Here, we are setting this value to be 100%, which is what was done for LazyLoadImageObserver and LazyLoadModelObserver.

The HTML spec suggests that we should be reusing the lazy load observer instance across <img> and <iframe>:

For img and iframe elements that will lazy load, these steps are run from the lazy load intersection observer's callback or when their lazy loading attribute is set to the Eager state. This causes the element to continue loading.

Therefore, this change would ensure that Webkit is following this standard outlined by the spec but I'm curious to know what people think about this behavioral change.

Seems OK, but I'd like the behavior change to be confirmed by a new test (or a newly passing test). Are there any WPT for iframe lazy loading that use scroll-margin?

WPT tests typically seem to allow generous scroll margins so that browsers can implement lazy-loading to their liking. I did run existing WPT tests against this patch and seems like this implementation matches existing behavior, and additionally gets us passing a few more tests actually:

<iframe> loading tests in Safari <iframe> loading tests in MiniBrowser (with changes from this patch)

smfr · 2026-03-03T18:47:35Z

Source/WebCore/html/LazyLoadElementObserver.cpp

    if (!m_observer) {
-        auto callback = LazyImageLoadIntersectionObserverCallback::create(document);
+        auto callback = LazyLoadIntersectionObserverCallback::create(document);
        static NeverDestroyed<const String> lazyLoadingScrollMarginFallback(MAKE_STATIC_STRING_IMPL("100%"));


Seems OK, but I'd like the behavior change to be confirmed by a new test (or a newly passing test). Are there any WPT for iframe lazy loading that use scroll-margin?

smfr · 2026-03-03T18:57:39Z

Source/WebCore/html/LazyLoadElementObserver.cpp

-                element->document().lazyLoadImageObserver().unobserve(*element, element->document());
-            }
+            if (RefPtr element = dynamicDowncast<HTMLImageElement>(entry->target()))
+                element->lazyLoadIntersectionCallbackInvoked(entry->isIntersecting());


Maybe Element could have a virtual lazyLoadIntersectionCallbackInvoked, so you don't need to dynamicDowncast here

That could certainly clean things up here, but it kind of feels like overkill for Element to be aware of this, since it only impacts a few specific elements for now. However, I'm happy to make this change if we think this is a better approach!

smfr · 2026-03-03T19:18:16Z

Source/WebCore/html/LazyLoadElementObserver.cpp

-                element->document().lazyLoadImageObserver().unobserve(*element, element->document());
-            }
+            if (RefPtr element = dynamicDowncast<HTMLImageElement>(entry->target()))
+                element->lazyLoadIntersectionCallbackInvoked(entry->isIntersecting());


Maybe Element could have a virtual lazyLoadIntersectionCallbackInvoked, so you don't need to dynamicDowncast here

webkit-ews-buildbot · 2026-03-03T20:31:51Z

macOS Safer C++ Build #83729 (`95e1fb2`)

❌ Found 2 failing files with 8 issues. Please address these issues before landing. See WebKit Guidelines for Safer C++ Programming.
(cc @rniwa)

webkit-ews-buildbot · 2026-03-03T20:36:43Z

iOS Safer C++ Build #2019 (`95e1fb2`)

❌ Found 3 failing files with 9 issues. Please address these issues before landing. See WebKit Guidelines for Safer C++ Programming.
(cc @rniwa)

webkit-early-warning-system · 2026-03-03T22:17:47Z

EWS run on previous version of this PR (hash d7bb612)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	❌ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

webkit-ews-buildbot · 2026-03-04T00:25:33Z

macOS Safer C++ Build #83792 (`d7bb612`)

⚠️ Found 1 fixed file! Please update expectations in Source/[Project]/SaferCPPExpectations by running the following command and update your pull request:

Tools/Scripts/update-safer-cpp-expectations -p WebCore --UncheckedCallArgsChecker html/LazyLoadElementObserver.cpp --platform macOS

webkit-ews-buildbot · 2026-03-04T01:50:31Z

iOS Safer C++ Build #2082 (`d7bb612`)

❌ Found 1 failing file with 1 issue. Please address these issues before landing. See WebKit Guidelines for Safer C++ Programming.
(cc @rniwa)

⚠️ Found 1 fixed file! Please update expectations in Source/[Project]/SaferCPPExpectations by running the following command and update your pull request:

Tools/Scripts/update-safer-cpp-expectations -p WebCore --UncheckedCallArgsChecker html/LazyLoadElementObserver.cpp --platform iOS

Source/WebCore/Modules/model-element/HTMLModelElement.cpp

webkit-early-warning-system · 2026-03-04T16:29:38Z

EWS run on previous version of this PR (hash aa6db59)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	~~🛠 win~~
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	~~🧪 win-tests~~
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

weinig · 2026-03-04T16:40:46Z

Thanks for doing the cleanup!

webkit-ews-buildbot · 2026-03-04T19:02:37Z

macOS Safer C++ Build #83945 (`aa6db59`)

⚠️ Found 1 fixed file! Please update expectations in Source/[Project]/SaferCPPExpectations by running the following command and update your pull request:

Tools/Scripts/update-safer-cpp-expectations -p WebCore --NoDeleteChecker Modules/webtransport/WebTransportDatagramsWritable.cpp --platform macOS

https://bugs.webkit.org/show_bug.cgi?id=309078 Reviewed by NOBODY (OOPS!). Consolidates LazyLoadImageObserver, LazyLoadFrameObserver, and LazyLoadModelObserver to a single LazyLoadElementObserver. * Source/WebCore/Modules/model-element/HTMLModelElement.cpp: (WebCore::HTMLModelElement::~HTMLModelElement): (WebCore::HTMLModelElement::stop): (WebCore::HTMLModelElement::insertedIntoAncestor): (WebCore::HTMLModelElement::removedFromAncestor): (WebCore::HTMLModelElement::lazyLoadIntersectionCallbackInvoked): (WebCore::HTMLModelElement::viewportIntersectionChanged): Deleted. * Source/WebCore/Modules/model-element/HTMLModelElement.h: * Source/WebCore/Modules/model-element/LazyLoadModelObserver.cpp: Removed. * Source/WebCore/Modules/model-element/LazyLoadModelObserver.h: Removed. * Source/WebCore/Modules/webtransport/WebTransportDatagramsWritable.h: * Source/WebCore/SaferCPPExpectations/NoDeleteCheckerExpectations: * Source/WebCore/SaferCPPExpectations/UncheckedCallArgsCheckerExpectations: * Source/WebCore/SaferCPPExpectations/UncountedCallArgsCheckerExpectations: * Source/WebCore/Sources.txt: * Source/WebCore/WebCore.xcodeproj/project.pbxproj: * Source/WebCore/dom/Document.cpp: (WebCore::Document::lazyLoadElementObserver): (WebCore::Document::lazyLoadImageObserver): Deleted. (WebCore::Document::lazyLoadModelObserver): Deleted. * Source/WebCore/dom/Document.h: * Source/WebCore/html/HTMLIFrameElement.cpp: (WebCore::HTMLIFrameElement::attributeChanged): (WebCore::HTMLIFrameElement::referrerPolicy const): (WebCore::HTMLIFrameElement::shouldLoadFrameLazily): (WebCore::HTMLIFrameElement::isLazyLoadObserverActive const): (WebCore::HTMLIFrameElement::loadDeferredFrame): (WebCore::HTMLIFrameElement::lazyLoadIntersectionCallbackInvoked): (WebCore::HTMLIFrameElement::lazyLoadFrameObserver): Deleted. * Source/WebCore/html/HTMLIFrameElement.h: * Source/WebCore/html/HTMLImageElement.cpp: (WebCore::HTMLImageElement::lazyLoadIntersectionCallbackInvoked): * Source/WebCore/html/HTMLImageElement.h: * Source/WebCore/html/LazyLoadElementObserver.cpp: Renamed from Source/WebCore/html/LazyLoadImageObserver.cpp. (WebCore::LazyLoadElementObserver::observe): (WebCore::LazyLoadElementObserver::unobserve): (WebCore::LazyLoadElementObserver::intersectionObserver): (WebCore::LazyLoadElementObserver::isObserved const): * Source/WebCore/html/LazyLoadElementObserver.h: Renamed from Source/WebCore/html/LazyLoadImageObserver.h. * Source/WebCore/html/LazyLoadFrameObserver.cpp: Removed. * Source/WebCore/html/LazyLoadFrameObserver.h: Removed. * Source/WebCore/html/Origin.cpp: * Source/WebCore/html/shadow/ProgressShadowElement.cpp: * Source/WebCore/loader/ImageLoader.cpp: (WebCore::ImageLoader::didUpdateCachedImage): (WebCore::ImageLoader::notifyFinished): (WebCore::ImageLoader::resetLazyImageLoading):

webkit-early-warning-system · 2026-03-04T19:40:49Z

EWS run on current version of this PR (hash 583d2f0)

Details

Misc	iOS, visionOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 win
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 win-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 api-mac-debug	✅ 🛠 gtk3-libwebrtc
	✅ 🧪 api-ios	✅ 🧪 mac-wk1	✅ 🛠 gtk
	✅ 🛠 ios-safer-cpp	✅ 🧪 mac-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 vision	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 api-gtk
	✅ 🛠 vision-sim	✅ 🧪 mac-wk2-stress	~~🛠 playstation~~
	✅ 🧪 vision-wk2	✅ 🧪 mac-intel-wk2
	✅ 🛠 tv	✅ 🛠 mac-safer-cpp
	✅ 🛠 tv-sim
	✅ 🛠 watch
	✅ 🛠 watch-sim

credod requested review from cdumez, etiennesegonzac, mwyrzykowski and rniwa as code owners March 3, 2026 17:33

credod commented Mar 3, 2026

View reviewed changes

credod mentioned this pull request Mar 3, 2026

Implement HTML video and audio element lazy-loading via the loading attribute #58220

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smfr approved these changes Mar 3, 2026

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webkit-ews-buildbot added the merging-blocked Applied to prevent a change from being merged label Mar 3, 2026

credod force-pushed the eng/Consolidate-lazy-load-observers branch from 95e1fb2 to d7bb612 Compare March 3, 2026 22:17

weinig reviewed Mar 4, 2026

View reviewed changes

Source/WebCore/Modules/model-element/HTMLModelElement.cpp Outdated Show resolved Hide resolved

credod force-pushed the eng/Consolidate-lazy-load-observers branch from d7bb612 to aa6db59 Compare March 4, 2026 16:29

weinig approved these changes Mar 4, 2026

View reviewed changes

credod force-pushed the eng/Consolidate-lazy-load-observers branch from aa6db59 to 583d2f0 Compare March 4, 2026 19:40

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webkit-ews-buildbot commented Mar 3, 2026

macOS Safer C++ Build #83729 (95e1fb2)

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webkit-ews-buildbot commented Mar 3, 2026

iOS Safer C++ Build #2019 (95e1fb2)

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macOS Safer C++ Build #83792 (d7bb612)

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iOS Safer C++ Build #2082 (d7bb612)

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macOS Safer C++ Build #83945 (aa6db59)

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credod commented Mar 3, 2026 •

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webkit-early-warning-system commented Mar 3, 2026 •

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macOS Safer C++ Build #83729 (`95e1fb2`)

iOS Safer C++ Build #2019 (`95e1fb2`)

webkit-early-warning-system commented Mar 3, 2026 •

edited

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macOS Safer C++ Build #83792 (`d7bb612`)

iOS Safer C++ Build #2082 (`d7bb612`)

webkit-early-warning-system commented Mar 4, 2026 •

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macOS Safer C++ Build #83945 (`aa6db59`)

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