[ResizeObserver] The initial last reported size of ResizeObservation …

…should be -1x-1 which always notify observed elements

https://bugs.webkit.org/show_bug.cgi?id=251015

Reviewed by Oriol Brufau and Ryosuke Niwa.

This patch initializes the lastReportedSize of ResizeObservation to -1 x -1, which is the conclusion of [1],
it indicates that -1 x -1 is the initial size when first observing an element with ResizeObserver.

The previous change makes every ResizeObservation be delivered at least once, even if the target is a disconnected element.
When GC happens between observe and gather ResizeObservations, JSC::Weak<JSC::JSObject> m_callback inside JSCallbackDataWeak
could be released, and the element and JSResizeObserver might not be released, for they are not strong connected, this scenario
would trigger the ASSERT in ResizeObserver::deliverObservations. To fix it, this patch adds m_targetsWaitingForFirstObservation
to extend the life cycle of ResizeObserver to the first time of deliverObservations. The fix is similar to
what IntersectionObserver does in bug 231235.

The test6 of resize-observer/notify.html still fails in mac-wk1, because updaterendering is not triggered properly.
Filed [2] to track it.

[1] w3c/csswg-drafts#3664
[2] https://bugs.webkit.org/show_bug.cgi?id=250900

* LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe-expected.txt:
* LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt:
* LayoutTests/platform/mac-wk1/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt: Copied from LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt.
* LayoutTests/platform/mac/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt:
* Source/WebCore/page/ResizeObservation.cpp:
* Source/WebCore/page/ResizeObserver.cpp:
(WebCore::ResizeObserver::observe):
(WebCore::ResizeObserver::deliverObservations):
(WebCore::ResizeObserver::isReachableFromOpaqueRoots const):
(WebCore::ResizeObserver::removeAllTargets):
(WebCore::ResizeObserver::removeObservation):
* Source/WebCore/page/ResizeObserver.h:

Canonical link: https://commits.webkit.org/259673@main

LayoutTests/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt

@@ -2,17 +2,22 @@ ResizeObserver tests
 
 t1
 t2
-t3 inline
-
-Harness Error (TIMEOUT), message = null
+t3
+inline
 
 PASS ResizeObserver implemented
-NOTRUN guard
+PASS guard
 PASS test0: notification ordering
 PASS test1: display:none triggers notification
 PASS test2: remove/appendChild trigger notification
 PASS test3: dimensions match
 PASS test4: transform do not cause notifications
 PASS test5: moving an element does not trigger notifications
-FAIL test6: inline element notifies once with 0x0. assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
+PASS test6: inline element notifies once with 0x0.
+PASS test7: unobserve inside notify callback
+PASS test8: observe inside notify callback
+PASS test9: disconnect inside notify callback
+PASS test10: element notifies when parent removed
+PASS test11: display:none element should be notified
+PASS test12: element sized 0x0 should be notified
 

LayoutTests/imported/w3c/web-platform-tests/resize-observer/observe-expected.txt

@@ -19,7 +19,7 @@ PASS test12: no observation is fired after the change of writing mode when box's
 PASS test13: an observation is fired after the change of writing mode when box's specified size comes from physical size properties.
 PASS test14: observe the same target but using a different box should override the previous one
 PASS test15: an observation is fired with box dimensions 0 when element's display property is set to inline
-FAIL test16: observations fire once with 0x0 size for non-replaced inline elements assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
+PASS test16: observations fire once with 0x0 size for non-replaced inline elements
 PASS test17: Box sizing snd Resize Observer notifications
 FAIL test18: an observation is fired when device-pixel-content-box is being observed assert_unreached: Caught a throw, possible syntax error Reached unreachable code
 

LayoutTests/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt

@@ -19,5 +19,10 @@ PASS test7: observe svg:polyline
 PASS test8: observe svg:rect
 PASS test9: observe svg:text
 PASS test10: observe svg:svg, top/left is 0 even with padding
-FAIL test11: observe svg non-displayable element assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
+PASS test11: observe svg non-displayable element
+PASS test12: observe svg:rect content box
+PASS test13: observe svg:rect border box
+PASS test14: observe g:rect content and border box
+PASS test15: observe svg:text content and border box
+FAIL test16: observe g:rect content, border and device-pixel-content boxes assert_unreached: Caught a throw, possible syntax error Reached unreachable code
 

LayoutTests/platform/mac-wk1/imported/w3c/web-platform-tests/resize-observer/notify-expected.txt

@@ -0,0 +1,23 @@
+ResizeObserver tests
+
+t1
+t2
+t3
+inline
+
+PASS ResizeObserver implemented
+PASS guard
+PASS test0: notification ordering
+PASS test1: display:none triggers notification
+PASS test2: remove/appendChild trigger notification
+PASS test3: dimensions match
+PASS test4: transform do not cause notifications
+PASS test5: moving an element does not trigger notifications
+FAIL test6: inline element notifies once with 0x0. assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
+PASS test7: unobserve inside notify callback
+PASS test8: observe inside notify callback
+PASS test9: disconnect inside notify callback
+PASS test10: element notifies when parent removed
+PASS test11: display:none element should be notified
+PASS test12: element sized 0x0 should be notified
+

LayoutTests/platform/mac/imported/w3c/web-platform-tests/resize-observer/svg-expected.txt

@@ -19,5 +19,10 @@ PASS test7: observe svg:polyline
 PASS test8: observe svg:rect
 PASS test9: observe svg:text
 PASS test10: observe svg:svg, top/left is 0 even with padding
-FAIL test11: observe svg non-displayable element assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
+PASS test11: observe svg non-displayable element
+PASS test12: observe svg:rect content box
+PASS test13: observe svg:rect border box
+PASS test14: observe g:rect content and border box
+FAIL test15: observe svg:text content and border box assert_equals: expected 30 but got 30.015625
+FAIL test16: observe g:rect content, border and device-pixel-content boxes assert_unreached: Caught a throw, possible syntax error Reached unreachable code
 

Source/WebCore/page/ResizeObservation.cpp

@@ -41,6 +41,7 @@ Ref<ResizeObservation> ResizeObservation::create(Element& target, ResizeObserver
 
 ResizeObservation::ResizeObservation(Element& element, ResizeObserverBoxOptions observedBox)
     : m_target { element }
+    , m_lastObservationSizes { LayoutSize(-1, -1), LayoutSize(-1, -1), LayoutSize(-1, -1) }
     , m_observedBox { observedBox }
 {
 }

Source/WebCore/page/ResizeObserver.cpp

@@ -82,6 +82,11 @@ void ResizeObserver::observe(Element& target, const ResizeObserverOptions& optio
 
     m_observations.append(ResizeObservation::create(target, options.box));
 
+    // Per the specification, we should dispatch at least one observation for the target. For this reason, we make sure to keep the
+    // target alive until this first observation. This, in turn, will keep the ResizeObserver's JS wrapper alive via
+    // isReachableFromOpaqueRoots(), so the callback stays alive.
+    m_targetsWaitingForFirstObservation.append(target);
+
     if (m_document) {
         m_document->addResizeObserver(*this);
         m_document->scheduleRenderingUpdate(RenderingUpdateStep::ResizeObservations);
@@ -141,6 +146,8 @@ void ResizeObserver::deliverObservations()
     m_activeObservations.clear();
     auto activeObservationTargets = std::exchange(m_activeObservationTargets, { });
 
+    auto targetsWaitingForFirstObservation = std::exchange(m_targetsWaitingForFirstObservation, { });
+
     // FIXME: The JSResizeObserver wrapper should be kept alive as long as the resize observer can fire events.
     ASSERT(m_callback->hasCallback());
     if (!m_callback->hasCallback())
@@ -165,7 +172,7 @@ bool ResizeObserver::isReachableFromOpaqueRoots(JSC::AbstractSlotVisitor& visito
         if (containsWebCoreOpaqueRoot(visitor, target.get()))
             return true;
     }
-    return false;
+    return !m_targetsWaitingForFirstObservation.isEmpty();
 }
 
 bool ResizeObserver::removeTarget(Element& target)
@@ -186,11 +193,15 @@ void ResizeObserver::removeAllTargets()
     }
     m_activeObservationTargets.clear();
     m_activeObservations.clear();
+    m_targetsWaitingForFirstObservation.clear();
     m_observations.clear();
 }
 
 bool ResizeObserver::removeObservation(const Element& target)
 {
+    m_targetsWaitingForFirstObservation.removeFirstMatching([&target](auto& pendingTarget) {
+        return pendingTarget.ptr() == ⌖
+    });
     return m_observations.removeFirstMatching([&target](auto& observation) {
         return observation->target() == ⌖
     });

Source/WebCore/page/ResizeObserver.h

@@ -84,6 +84,8 @@ class ResizeObserver : public RefCounted<ResizeObserver>, public CanMakeWeakPtr<
 
     Vector<Ref<ResizeObservation>> m_activeObservations;
     Vector<GCReachableRef<Element>> m_activeObservationTargets;
+    Vector<GCReachableRef<Element>> m_targetsWaitingForFirstObservation;
+
     bool m_hasSkippedObservations { false };
 };