iOS 17: History back sometimes scrolls to top of the page (with app b…

…anner)

https://bugs.webkit.org/show_bug.cgi?id=231563
rdar://117107620

Reviewed by Tim Horton.

Sometimes, navigating back to a page on iOS would fail to restore the scroll position to the correct
location. This happened when `WebPage::restorePageState()` hit the second mismatched
`minimumLayoutSizeInScrollViewCoordinates` clause, which made use of
`historyItem.unobscuredContentRect()`. This could happen when MobileSafari app banners were hidden
or shown. `historyItem.unobscuredContentRect()` had the wrong value in this case, containing a rect
that had a 0,0 location which triggered a scroll back to the top.

`historyItem.unobscuredContentRect()` was wrong because it was set in
`HistoryController::saveScrollPositionAndViewStateToItem()` which runs after we've reset the content
size in preparation for the navigation; note that this function uses
`frameView->cachedScrollPosition()`. So the fix is to cache `unobscuredContentRect()` and
`exposedContentRect()` in the same way.

This is messy; ScrollView shouldn't be in the business of storing caches related to page navigation,
but fixing that is out of scope for this change.

The API test navigates and goes back with a view size change, which triggers the bug.

Also add some release logging to help diagnose scroll restoration bugs.

* Source/WebCore/dom/Document.cpp:
(WebCore::Document::setBackForwardCacheState):
* Source/WebCore/loader/HistoryController.cpp:
(WebCore::FrameLoader::HistoryController::saveScrollPositionAndViewStateToItem):
* Source/WebCore/platform/ScrollView.cpp:
(WebCore::ScrollView::cacheCurrentScrollState):
* Source/WebCore/platform/ScrollView.h:
(WebCore::ScrollView::cachedUnobscuredContentRect const):
(WebCore::ScrollView::cachedExposedContentRect const):
(WebCore::ScrollView::cacheCurrentScrollPosition): Deleted.
* Tools/TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj:
* Tools/TestWebKitAPI/Tests/ios/ScrollViewInsetTests.mm:
(TestWebKitAPI::TEST):
* Tools/TestWebKitAPI/ios/scrollable-page.html: Added.

Canonical link: https://commits.webkit.org/269611@main

Source/WebCore/dom/Document.cpp

@@ -6099,7 +6099,7 @@ void Document::setBackForwardCacheState(BackForwardCacheState state)
             // called too early on in the process of a page exiting the cache for that work to be possible in this
             // function. It would be nice if there was more symmetry here.
             // https://bugs.webkit.org/show_bug.cgi?id=98698
-            frameView->cacheCurrentScrollPosition();
+            frameView->cacheCurrentScrollState();
             if (page && m_frame->isMainFrame()) {
                 frameView->resetScrollbarsAndClearContentsSize();
                 if (RefPtr scrollingCoordinator = page->scrollingCoordinator())

Source/WebCore/loader/HistoryController.cpp

@@ -75,17 +75,21 @@ void FrameLoader::HistoryController::saveScrollPositionAndViewStateToItem(Histor
     if (!item || !frameView)
         return;
 
-    if (m_frame.document()->backForwardCacheState() != Document::NotInBackForwardCache)
+    if (m_frame.document()->backForwardCacheState() != Document::NotInBackForwardCache) {
         item->setScrollPosition(frameView->cachedScrollPosition());
-    else
+#if PLATFORM(IOS_FAMILY)
+        item->setUnobscuredContentRect(frameView->cachedUnobscuredContentRect());
+        item->setExposedContentRect(frameView->cachedExposedContentRect());
+#endif
+    } else {
         item->setScrollPosition(frameView->scrollPosition());
-
 #if PLATFORM(IOS_FAMILY)
-    item->setExposedContentRect(frameView->exposedContentRect());
-    item->setUnobscuredContentRect(frameView->unobscuredContentRect());
+        item->setUnobscuredContentRect(frameView->unobscuredContentRect());
+        item->setExposedContentRect(frameView->exposedContentRect());
 #endif
+    }
 
-    Page* page = m_frame.page();
+    auto* page = m_frame.page();
     if (page && m_frame.isMainFrame()) {
         item->setPageScaleFactor(page->pageScaleFactor() / page->viewScaleFactor());
 #if PLATFORM(IOS_FAMILY)

Source/WebCore/platform/ScrollView.cpp

@@ -429,6 +429,15 @@ ScrollPosition ScrollView::adjustScrollPositionWithinRange(const ScrollPosition&
     return scrollPosition.constrainedBetween(minimumScrollPosition(), maximumScrollPosition());
 }
 
+void ScrollView::cacheCurrentScrollState()
+{
+    m_cachedScrollPosition = scrollPosition();
+#if PLATFORM(IOS_FAMILY)
+    m_cachedUnobscuredContentRect = unobscuredContentRect();
+    m_cachedExposedContentRect = exposedContentRect();
+#endif
+}
+
 ScrollPosition ScrollView::documentScrollPositionRelativeToViewOrigin() const
 {
     return scrollPosition() - IntSize(

Source/WebCore/platform/ScrollView.h

@@ -277,8 +277,12 @@ class ScrollView : public Widget, public ScrollableArea {
 
     IntSize overhangAmount() const final;
 
-    void cacheCurrentScrollPosition() { m_cachedScrollPosition = scrollPosition(); }
+    void cacheCurrentScrollState();
     ScrollPosition cachedScrollPosition() const { return m_cachedScrollPosition; }
+#if PLATFORM(IOS_FAMILY)
+    IntRect cachedUnobscuredContentRect() const { return m_cachedUnobscuredContentRect; }
+    FloatRect cachedExposedContentRect() const { return m_cachedExposedContentRect; }
+#endif
 
     // Functions for scrolling the view.
     virtual void setScrollPosition(const ScrollPosition&, const ScrollPositionChangeOptions& = ScrollPositionChangeOptions::createProgrammatic());
@@ -537,6 +541,10 @@ class ScrollView : public Widget, public ScrollableArea {
 #endif
     ScrollPosition m_scrollPosition;
     IntPoint m_cachedScrollPosition;
+#if PLATFORM(IOS_FAMILY)
+    IntRect m_cachedUnobscuredContentRect;
+    FloatRect m_cachedExposedContentRect;
+#endif
     IntSize m_fixedLayoutSize;
     IntSize m_contentsSize;
 

Source/WebKit/WebProcess/WebPage/ios/WebPageIOS.mm

@@ -527,6 +527,7 @@ static inline FloatRect adjustExposedRectForNewScale(const FloatRect& exposedRec
             scrollPosition = FloatPoint(historyItem.scrollPosition());
         }
 
+        RELEASE_LOG(Scrolling, "WebPage::restorePageState with matching minimumLayoutSize; historyItem.shouldRestoreScrollPosition %d, scrollPosition.y %d", historyItem.shouldRestoreScrollPosition(), historyItem.scrollPosition().y());
         send(Messages::WebPageProxy::RestorePageState(scrollPosition, frameView.scrollOrigin(), historyItem.obscuredInsets(), boundedScale));
     } else {
         IntSize oldContentSize = historyItem.contentSize();
@@ -543,6 +544,7 @@ static inline FloatRect adjustExposedRectForNewScale(const FloatRect& exposedRec
                 newCenter = FloatRect(historyItem.unobscuredContentRect()).center();
         }
 
+        RELEASE_LOG(Scrolling, "WebPage::restorePageState with mismatched minimumLayoutSize; historyItem.shouldRestoreScrollPosition %d, unobscured rect top %d, scale %.2f", historyItem.shouldRestoreScrollPosition(), historyItem.unobscuredContentRect().y(), newScale);
         scalePage(newScale, IntPoint());
         send(Messages::WebPageProxy::RestorePageCenterAndScale(newCenter, newScale));
     }

Tools/TestWebKitAPI/TestWebKitAPI.xcodeproj/project.pbxproj

@@ -87,6 +87,7 @@
 		0F5651F91FCE513500310FBC /* scroll-to-anchor.html in Copy Resources */ = {isa = PBXBuildFile; fileRef = 0F5651F81FCE50E800310FBC /* scroll-to-anchor.html */; };
 		0FEFAF64271FC2CD005704D7 /* ScrollingCoordinatorTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 0FEFAF63271FC2CD005704D7 /* ScrollingCoordinatorTests.mm */; };
 		0FF1134E22D68679009A81DA /* ScrollViewScrollabilityTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 0FF1134D22D68679009A81DA /* ScrollViewScrollabilityTests.mm */; };
+		0FF1F0CD2AE205F5006ECC4F /* scrollable-page.html in Copy Resources */ = {isa = PBXBuildFile; fileRef = 0FF1F0C52AE204C0006ECC4F /* scrollable-page.html */; };
 		0FF332932A0EFCCF00C048D8 /* HysteresisActivityTests.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 0FF3328B2A0EFCCF00C048D8 /* HysteresisActivityTests.cpp */; };
 		115EB3431EE0BA03003C2C0A /* ViewportSizeForViewportUnits.mm in Sources */ = {isa = PBXBuildFile; fileRef = 115EB3421EE0B720003C2C0A /* ViewportSizeForViewportUnits.mm */; };
 		1171B24F219F49CD00CB897D /* FirstMeaningfulPaintMilestone_Bundle.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 11B7FD21219F46DD0069B27F /* FirstMeaningfulPaintMilestone_Bundle.cpp */; };
@@ -1836,6 +1837,7 @@
 				1CE6FAC32320267C00E48F6E /* rich-color-filtered.html in Copy Resources */,
 				2E92B8F7216490D4005B64F0 /* rich-text-attributes.html in Copy Resources */,
 				0F5651F91FCE513500310FBC /* scroll-to-anchor.html in Copy Resources */,
+				0FF1F0CD2AE205F5006ECC4F /* scrollable-page.html in Copy Resources */,
 				F4E0A296211FC5FB00AF7C7F /* selected-text-and-textarea.html in Copy Resources */,
 				F4D65DA81F5E4704009D8C27 /* selected-text-image-link-and-editable.html in Copy Resources */,
 				7A66BDB81EAF18D500CCC924 /* set-long-title.html in Copy Resources */,
@@ -2042,6 +2044,7 @@
 		0FEAE3671B7D19CB00CE17F2 /* Condition.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Condition.cpp; sourceTree = "<group>"; };
 		0FEFAF63271FC2CD005704D7 /* ScrollingCoordinatorTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ScrollingCoordinatorTests.mm; sourceTree = "<group>"; };
 		0FF1134D22D68679009A81DA /* ScrollViewScrollabilityTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ScrollViewScrollabilityTests.mm; sourceTree = "<group>"; };
+		0FF1F0C52AE204C0006ECC4F /* scrollable-page.html */ = {isa = PBXFileReference; lastKnownFileType = text.html; name = "scrollable-page.html"; path = "ios/scrollable-page.html"; sourceTree = SOURCE_ROOT; };
 		0FF3328B2A0EFCCF00C048D8 /* HysteresisActivityTests.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = HysteresisActivityTests.cpp; sourceTree = "<group>"; };
 		0FFC45A41B73EBE20085BD62 /* Lock.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Lock.cpp; sourceTree = "<group>"; };
 		115EB3421EE0B720003C2C0A /* ViewportSizeForViewportUnits.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = ViewportSizeForViewportUnits.mm; sourceTree = "<group>"; };
@@ -4999,6 +5002,7 @@
 				A11E7D9F24A169E200026745 /* link-with-hover-menu.html */,
 				0F340777230382540060A1A0 /* overflow-scroll.html */,
 				A1C4FB721BACD1B7003742D0 /* pages.pages */,
+				0FF1F0C52AE204C0006ECC4F /* scrollable-page.html */,
 				CE6E81A320A933B800E2C80F /* set-timeout-function.html */,
 			);
 			name = Resources;

Tools/TestWebKitAPI/Tests/ios/ScrollViewInsetTests.mm

@@ -223,6 +223,38 @@ static void waitUntilInnerHeightIs(TestWKWebView *webView, CGFloat expectedValue
     EXPECT_EQ(-400, initialContentOffset.y);
 }
 
+TEST(ScrollViewInsetTests, RestoreContentOffsetAfterBackWithInsetChange)
+{
+    auto webView = adoptNS([[TestWKWebView alloc] initWithFrame:CGRectMake(0, 0, 320, viewHeight)]);
+    [webView scrollView].contentInset = UIEdgeInsetsMake(100, 0, 0, 0);
+
+    RetainPtr<NSURL> testURL = [[NSBundle mainBundle] URLForResource:@"scrollable-page" withExtension:@"html" subdirectory:@"TestWebKitAPI.resources"];
+    [webView loadRequest:[NSURLRequest requestWithURL:testURL.get()]];
+    [webView _test_waitForDidFinishNavigation];
+    [webView waitForNextPresentationUpdate];
+
+    [webView stringByEvaluatingJavaScript:@"scrollTo(0, 1000)"];
+    [webView waitForNextPresentationUpdate];
+
+    CGPoint contentOffsetAfterScrolling = [webView scrollView].contentOffset;
+    EXPECT_EQ(0, contentOffsetAfterScrolling.x);
+    EXPECT_EQ(1000, contentOffsetAfterScrolling.y);
+
+    RetainPtr<NSURL> secondPageURL = [[NSBundle mainBundle] URLForResource:@"composited" withExtension:@"html" subdirectory:@"TestWebKitAPI.resources"];
+    [webView loadRequest:[NSURLRequest requestWithURL:secondPageURL.get()]];
+    [webView _test_waitForDidFinishNavigation];
+    [webView waitForNextPresentationUpdate];
+
+    constexpr float additionalViewHeight = 20;
+    [webView goBack];
+    [webView setFrame:CGRectMake(0, 0, 320, viewHeight + additionalViewHeight)];
+    [webView _test_waitForDidFinishNavigation];
+
+    CGPoint contentOffsetAfterNavigation = [webView scrollView].contentOffset;
+    EXPECT_EQ(0, contentOffsetAfterNavigation.x);
+    EXPECT_EQ(1000 - additionalViewHeight / 2, contentOffsetAfterNavigation.y);
+}
+
 TEST(ScrollViewInsetTests, ChangeInsetWithoutAutomaticAdjustmentWhileWebProcessIsUnresponsive)
 {
     constexpr CGFloat initialTopInset = 100;

Tools/TestWebKitAPI/ios/scrollable-page.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <meta name="viewport" content="width=device-width">
+    <style>
+        body {
+            height: 5000px;
+        }
+    </style>
+</head>
+<body>
+</body>
+</html>