[@container] Walk ancestry if ::first-line style is null

HasPseudoElementStyle may return true even if the element does not
currently apply any ::first-line rules because we
SetHasPseudoElementStyle when only container queries fail.

If we get a null ComputedStyle for an element which returns true for
HasPseudoElementStyle(kPseudoIdFirstLine), continue to walk ancestors to
look for the ::first-line style.

Bug: 1273913
Change-Id: I87b7f9c04f818f2d9c82c6eb417b81465f15d913
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3629362
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1001435}

third_party/blink/renderer/core/layout/layout_block.cc

@@ -43,7 +43,6 @@
 #include "third_party/blink/renderer/core/frame/local_frame_view.h"
 #include "third_party/blink/renderer/core/frame/settings.h"
 #include "third_party/blink/renderer/core/html/html_marquee_element.h"
-#include "third_party/blink/renderer/core/html/shadow/shadow_element_names.h"
 #include "third_party/blink/renderer/core/html_names.h"
 #include "third_party/blink/renderer/core/layout/api/line_layout_box.h"
 #include "third_party/blink/renderer/core/layout/api/line_layout_item.h"
@@ -2085,40 +2084,32 @@ LayoutUnit LayoutBlock::InlineBlockBaseline(
   return LayoutUnit(-1);
 }
 
-const LayoutBlock* LayoutBlock::EnclosingFirstLineStyleBlock() const {
+const LayoutBlock* LayoutBlock::FirstLineStyleParentBlock() const {
   NOT_DESTROYED();
-  auto* element = DynamicTo<Element>(GetNode());
-  if (element && element->ShadowPseudoId() ==
-                     shadow_element_names::kPseudoInternalInputSuggested) {
-    // Disable ::first-line style for autofill previews. See
-    // crbug.com/1227170.
-    return nullptr;
-  }
   const LayoutBlock* first_line_block = this;
-  bool has_pseudo = false;
-  while (true) {
-    has_pseudo =
-        first_line_block->StyleRef().HasPseudoElementStyle(kPseudoIdFirstLine);
-    if (has_pseudo)
-      break;
-    LayoutObject* parent_block = first_line_block->Parent();
-    if (first_line_block->IsAtomicInlineLevel() ||
-        first_line_block->IsFloatingOrOutOfFlowPositioned() || !parent_block ||
-        !parent_block->BehavesLikeBlockContainer())
-      break;
-    auto* parent_layout_block = DynamicTo<LayoutBlock>(parent_block);
-    const LayoutObject* first_child = parent_layout_block->FirstChild();
-    while (first_child->IsFloatingOrOutOfFlowPositioned())
-      first_child = first_child->NextSibling();
-    if (first_child != first_line_block)
-      break;
-    first_line_block = parent_layout_block;
-  }
+  // Inline blocks do not get ::first-line style from its containing blocks.
+  if (IsAtomicInlineLevel())
+    return nullptr;
+  // Floats and out of flow blocks do not get ::first-line style from its
+  // containing blocks.
+  if (IsFloatingOrOutOfFlowPositioned())
+    return nullptr;
+
+  LayoutObject* parent_block = first_line_block->Parent();
+  if (!parent_block || !parent_block->BehavesLikeBlockContainer())
+    return nullptr;
+
+  const LayoutBlock* parent_layout_block = To<LayoutBlock>(parent_block);
 
-  if (!has_pseudo)
+  // If we are not the first in-flow child of our parent, we cannot get
+  // ::first-line style from our ancestors.
+  const LayoutObject* first_child = parent_layout_block->FirstChild();
+  while (first_child->IsFloatingOrOutOfFlowPositioned())
+    first_child = first_child->NextSibling();
+  if (first_child != first_line_block)
     return nullptr;
 
-  return first_line_block;
+  return parent_layout_block;
 }
 
 LayoutBlockFlow* LayoutBlock::NearestInnerBlockWithFirstLine() {

third_party/blink/renderer/core/layout/layout_block.h

@@ -409,9 +409,10 @@ class CORE_EXPORT LayoutBlock : public LayoutBox {
   //   </div>
   // </div>
 
-  // Returns the nearest enclosing block (including this block) that contributes
-  // a first-line style to our first line.
-  const LayoutBlock* EnclosingFirstLineStyleBlock() const;
+  // Return the parent LayoutObject if it can contribute to our ::first-line
+  // style.
+  const LayoutBlock* FirstLineStyleParentBlock() const;
+
   // Returns this block or the nearest inner block containing the actual first
   // line.
   LayoutBlockFlow* NearestInnerBlockWithFirstLine();

third_party/blink/renderer/core/layout/layout_object.cc

@@ -63,6 +63,7 @@
 #include "third_party/blink/renderer/core/html/html_table_cell_element.h"
 #include "third_party/blink/renderer/core/html/html_table_element.h"
 #include "third_party/blink/renderer/core/html/image_document.h"
+#include "third_party/blink/renderer/core/html/shadow/shadow_element_names.h"
 #include "third_party/blink/renderer/core/input/event_handler.h"
 #include "third_party/blink/renderer/core/inspector/inspector_trace_events.h"
 #include "third_party/blink/renderer/core/intersection_observer/element_intersection_observer_data.h"
@@ -3937,14 +3938,32 @@ const ComputedStyle* LayoutObject::FirstLineStyleWithoutFallback() const {
 
   if (BehavesLikeBlockContainer()) {
     if (const ComputedStyle* cached =
-            StyleRef().GetCachedPseudoElementStyle(kPseudoIdFirstLine))
+            StyleRef().GetCachedPseudoElementStyle(kPseudoIdFirstLine)) {
       return cached;
+    }
+
+    if (Element* element = DynamicTo<Element>(GetNode())) {
+      if (element->ShadowPseudoId() ==
+          shadow_element_names::kPseudoInternalInputSuggested) {
+        // Disable ::first-line style for autofill previews. See
+        // crbug.com/1227170.
+        return nullptr;
+      }
+    }
 
-    if (const LayoutBlock* first_line_block =
-            To<LayoutBlock>(this)->EnclosingFirstLineStyleBlock()) {
-      if (first_line_block->Style() == Style()) {
-        return first_line_block->GetCachedPseudoElementStyle(
-            kPseudoIdFirstLine);
+    for (const LayoutBlock* first_line_block = To<LayoutBlock>(this);
+         first_line_block;
+         first_line_block = first_line_block->FirstLineStyleParentBlock()) {
+      const ComputedStyle& style = first_line_block->StyleRef();
+      if (!style.HasPseudoElementStyle(kPseudoIdFirstLine))
+        continue;
+      if (first_line_block == this) {
+        if (const ComputedStyle* cached =
+                first_line_block->GetCachedPseudoElementStyle(
+                    kPseudoIdFirstLine)) {
+          return cached;
+        }
+        continue;
       }
 
       // We can't use first_line_block->GetCachedPseudoElementStyle() because

third_party/blink/renderer/core/layout/layout_object.h

@@ -3726,8 +3726,8 @@ class CORE_EXPORT LayoutObject : public GarbageCollected<LayoutObject>,
       AncestorSkipInfo* = nullptr) const;
 
   // Returns the first line style declared in CSS. The style may be declared on
-  // an ancestor block (see EnclosingFirstLineStyleBlock()) that applies to this
-  // object. Returns nullptr if there is no applicable first line style.
+  // an ancestor block (see LayoutBlock::FirstLineStyleParentBlock) that applies
+  // to this object. Returns nullptr if there is no applicable first line style.
   // Whether the style applies is based on CSS rules, regardless of whether this
   // object is really in the first line which is unknown before layout.
   const ComputedStyle* FirstLineStyleWithoutFallback() const;

third_party/blink/web_tests/external/wpt/css/css-contain/container-queries/inner-first-line-non-matching-ref.html

@@ -0,0 +1,3 @@
+<!doctype html>
+<title>CSS Test Reference</title>
+<div style="color:green">This text should be green.</div>

third_party/blink/web_tests/external/wpt/css/css-contain/container-queries/inner-first-line-non-matching.html

@@ -0,0 +1,13 @@
+<!doctype html>
+<title>CSS Container Queries Test: Non-matching ::first-line in @container</title>
+<link rel="help" href="https://drafts.csswg.org/css-contain-3/#container-queries">
+<link rel="match" href="inner-first-line-non-matching-ref.html">
+<style>
+  #outer::first-line { color: green }
+  @container (width > 99999px) {
+    #inner::first-line { color: red }
+  }
+</style>
+<div id="outer">
+  <div id="inner">This text should be green.</div>
+</div>