tor-browser

commit bf0542d5275f3b66542f13a55e8fea141450cf2a
parent e34292a5fd10a52530f19d4d0f21d50e4013e2fa
Author: Emilio Cobos Álvarez <emilio@crisal.io>
Date:   Thu,  2 Oct 2025 17:43:50 +0000

Bug 1992124 - Ignore invalid @position-try rules. r=layout-anchor-positioning-reviewers,layout-reviewers,dshin

Tested as part of bug 1992124.

Differential Revision: https://phabricator.services.mozilla.com/D267230

Diffstat:
M
layout/generic/AbsoluteContainingBlock.cpp
 | 
71
++++++++++++++++++++++++++++++++++++++++++++++++-----------------------

1 file changed, 48 insertions(+), 23 deletions(-)
diff --git a/layout/generic/AbsoluteContainingBlock.cpp b/layout/generic/AbsoluteContainingBlock.cpp
@@ -893,13 +893,47 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
       }
     }
   }
-  do {
-    const StylePositionTryFallbacksItem* currentFallback = nullptr;
-    RefPtr<ComputedStyle> currentFallbackStyle;
-    if (currentFallbackIndex) {
-      currentFallback = &fallbacks[*currentFallbackIndex];
+  const StylePositionTryFallbacksItem* currentFallback = nullptr;
+  RefPtr<ComputedStyle> currentFallbackStyle;
+
+  auto TryAdvanceFallback = [&]() -> bool {
+    if (fallbacks.IsEmpty()) {
+      return false;
+    }
+    uint32_t nextFallbackIndex =
+        currentFallbackIndex ? *currentFallbackIndex + 1 : 0;
+    if (nextFallbackIndex >= fallbacks.Length()) {
+      return false;
+    }
+    const StylePositionTryFallbacksItem* nextFallback;
+    RefPtr<ComputedStyle> nextFallbackStyle;
+    while (true) {
+      nextFallback = &fallbacks[nextFallbackIndex];
+      if (nextFallback->IsIdentAndOrTactic()) {
+        auto* ident = nextFallback->AsIdentAndOrTactic().ident.AsAtom();
+        if (!ident->IsEmpty()) {
+          nextFallbackStyle = aPresContext->StyleSet()->ResolvePositionTry(
+              *aKidFrame->GetContent()->AsElement(), *aKidFrame->Style(),
+              ident);
+          if (!nextFallbackStyle) {
+            // No @position-try rule for this name was found, per spec we should
+            // skip it.
+            nextFallbackIndex++;
+            if (nextFallbackIndex >= fallbacks.Length()) {
+              return false;
+            }
+          }
+        }
+      }
+      break;
     }
+    currentFallbackIndex = Some(nextFallbackIndex);
+    currentFallback = nextFallback;
+    currentFallbackStyle = std::move(nextFallbackStyle);
+    return true;
+  };
 
+  do {
     const nsRect usedCb = [&] {
       if (isGrid) {
         // TODO(emilio): how does position-area interact with grid?
@@ -911,14 +945,8 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
       if (currentFallback) {
         if (currentFallback->IsIdentAndOrTactic()) {
           const auto& item = currentFallback->AsIdentAndOrTactic();
-          if (!item.ident.AsAtom()->IsEmpty()) {
-            currentFallbackStyle = aPresContext->StyleSet()->ResolvePositionTry(
-                *aKidFrame->GetContent()->AsElement(), *aKidFrame->Style(),
-                item.ident.AsAtom());
-            if (currentFallbackStyle) {
-              positionArea =
-                  currentFallbackStyle->StylePosition()->mPositionArea;
-            }
+          if (currentFallbackStyle) {
+            positionArea = currentFallbackStyle->StylePosition()->mPositionArea;
           }
           tactic = &item.try_tactic;
         } else {
@@ -1159,21 +1187,18 @@ void AbsoluteContainingBlock::ReflowAbsoluteFrame(
 
     aKidFrame->DidReflow(aPresContext, &kidReflowInput);
 
-    if (fallbacks.IsEmpty() ||
-        (currentFallbackIndex &&
-         *currentFallbackIndex >= fallbacks.Length() - 1) ||
-        (usedCb.Contains(aKidFrame->GetRect()) && aStatus.IsComplete())) {
-      // If there are no further fallbacks, or we don't overflow, we're done.
+    if (usedCb.Contains(aKidFrame->GetRect()) && aStatus.IsComplete()) {
+      // We don't overflow our CB, no further fallback needed.
+      break;
+    }
+
+    if (!TryAdvanceFallback()) {
+      // If there are no further fallbacks, we're done.
       break;
     }
 
     // Try with the next  fallback.
     aKidFrame->AddStateBits(NS_FRAME_IS_DIRTY);
-    if (currentFallbackIndex) {
-      (*currentFallbackIndex)++;
-    } else {
-      currentFallbackIndex.emplace(0);
-    }
     aStatus.Reset();
   } while (true);