tor-browser

commit 9eddd6cafcab999967709d9ec3e5a6e4e40b8397
parent 2ade44471efb1e2d65ee81c5c112bee7547c823c
Author: Ting-Yu Lin <tlin@mozilla.com>
Date:   Mon, 15 Dec 2025 18:21:48 +0000

Bug 2005918 - Correct reflow flag and remove an overflow area special case when reflowing fixed pos children in PageContentFrame. r=layout-reviewers,emilio

* Remove the special case at the beginning of
  `AbsoluteContainingBlock::Reflow()`. `PageContentFrame` now calls
  `AbsoluteContainingBlock::Reflow()` directly with a null overflow-area pointer
  so that replicated fixed-pos children do not contribute to page overflow.

* We also stop using `AbsPosReflowFlag::AllowFragmentation`, since fixed pos children
  is replicated rather than fragmented. This does not change
  behavior with the current code, but becomes important once bug 1994346 starts
  adjusting the available block-size based on that flag.

Differential Revision: https://phabricator.services.mozilla.com/D276361

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
8
--------
M
layout/generic/nsPageContentFrame.cpp
 | 
27
+++++++++++++++++++++++++--

2 files changed, 25 insertions(+), 10 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -252,14 +252,6 @@ void AbsoluteContainingBlock::Reflow(nsContainerFrame* aDelegatingFrame,
                                      const nsRect& aContainingBlock,
                                      AbsPosReflowFlags aFlags,
                                      OverflowAreas* aOverflowAreas) {
-  // PageContentFrame replicates fixed pos children so we really don't want
-  // them contributing to overflow areas because that means we'll create new
-  // pages ad infinitum if one of them overflows the page.
-  if (aDelegatingFrame->IsPageContentFrame()) {
-    MOZ_ASSERT(mChildListID == FrameChildListID::Fixed);
-    aOverflowAreas = nullptr;
-  }
-
   const auto scrollableContainingBlock = [&]() -> nsRect {
     switch (aDelegatingFrame->Style()->GetPseudoType()) {
       case PseudoStyleType::scrolledContent:
diff --git a/layout/generic/nsPageContentFrame.cpp b/layout/generic/nsPageContentFrame.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "nsPageContentFrame.h"
 
+#include "mozilla/AbsoluteContainingBlock.h"
 #include "mozilla/PresShell.h"
 #include "mozilla/PresShellInlines.h"
 #include "mozilla/StaticPrefs_layout.h"
@@ -135,9 +136,31 @@ void nsPageContentFrame::Reflow(nsPresContext* aPresContext,
 
   FinishAndStoreOverflow(&aReflowOutput);
 
-  // Reflow our fixed frames
+  // Reflow any fixed-pos children. Note that we don't need to call
+  // PrepareAbsoluteFrames() because the fixed pos frames cannot split.
   nsReflowStatus fixedStatus;
-  ReflowAbsoluteFrames(aPresContext, aReflowOutput, aReflowInput, fixedStatus);
+  if (auto* absCB = GetAbsoluteContainingBlock();
+      absCB && absCB->HasAbsoluteFrames()) {
+    // The containing block for the fixed-pos children is formed by our padding
+    // edge.
+    const auto wm = GetWritingMode();
+    LogicalRect cbRect(wm, LogicalPoint(wm), aReflowOutput.Size(wm));
+    cbRect.Deflate(wm, GetLogicalUsedBorder(wm).ApplySkipSides(
+                           PreReflowBlockLevelLogicalSkipSides()));
+
+    // XXX: To optimize the performance, set the flags only when the CB width or
+    // height actually changes.
+    AbsPosReflowFlags flags{AbsPosReflowFlag::CBWidthChanged,
+                            AbsPosReflowFlag::CBHeightChanged};
+
+    // PageContentFrame replicates fixed-pos children, so we really don't want
+    // them contributing to overflow areas; otherwise we'll create new pages ad
+    // infinitum if one of them overflows the page.
+    absCB->Reflow(this, aPresContext, aReflowInput, fixedStatus,
+                  cbRect.GetPhysicalRect(wm, aReflowOutput.PhysicalSize()),
+                  flags,
+                  /* aOverflowAreas */ nullptr);
+  }
   NS_ASSERTION(fixedStatus.IsComplete(),
                "fixed frames can be truncated, but not incomplete");