Add counter for :empty failing for white-space only.

If we are changing :empty to match when there are whitespace children,
we need to know to what extent this affects existing content.

Bug: 447880
Change-Id: I53906fe6295f42cdc72d5ca6d6e58e1aa60786c3
Reviewed-on: https://chromium-review.googlesource.com/c/1326003
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606443}

third_party/blink/public/platform/web_feature.mojom

@@ -2073,6 +2073,7 @@ enum WebFeature {
   kAdClick = 2621,
   kUpdateWithoutShippingOptionOnShippingAddressChange = 2622,
   kUpdateWithoutShippingOptionOnShippingOptionChange = 2623,
+  kCSSSelectorEmptyWhitespaceOnlyFail = 2624,
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.
   // Also, run update_use_counter_feature_enum.py in

third_party/blink/renderer/core/css/selector_checker.cc

@@ -761,6 +761,7 @@ bool SelectorChecker::CheckPseudoClass(const SelectorCheckingContext& context,
       return CheckPseudoNot(context, result);
     case CSSSelector::kPseudoEmpty: {
       bool result = true;
+      bool has_whitespace = false;
       for (Node* n = element.firstChild(); n; n = n->nextSibling()) {
         if (n->IsElementNode()) {
           result = false;
@@ -769,11 +770,20 @@ bool SelectorChecker::CheckPseudoClass(const SelectorCheckingContext& context,
         if (n->IsTextNode()) {
           Text* text_node = ToText(n);
           if (!text_node->data().IsEmpty()) {
+            if (text_node->ContainsOnlyWhitespaceOrEmpty()) {
+              has_whitespace = true;
+            } else {
               result = false;
               break;
             }
           }
         }
+      }
+      if (result && has_whitespace) {
+        UseCounter::Count(context.element->GetDocument(),
+                          WebFeature::kCSSSelectorEmptyWhitespaceOnlyFail);
+        result = false;
+      }
       if (mode_ == kResolvingStyle)
         element.SetStyleAffectedByEmpty();
       return result;

third_party/blink/renderer/core/css/style_engine_test.cc

@@ -26,6 +26,7 @@
 #include "third_party/blink/renderer/core/frame/frame_test_helpers.h"
 #include "third_party/blink/renderer/core/frame/local_frame_view.h"
 #include "third_party/blink/renderer/core/frame/viewport_data.h"
+#include "third_party/blink/renderer/core/html/html_collection.h"
 #include "third_party/blink/renderer/core/html/html_element.h"
 #include "third_party/blink/renderer/core/html/html_span_element.h"
 #include "third_party/blink/renderer/core/html/html_style_element.h"
@@ -1658,4 +1659,37 @@ TEST_F(StyleEngineTest, InitialDataCreation) {
   EXPECT_NE(data1, GetStyleEngine().MaybeCreateAndGetInitialData());
 }
 
+TEST_F(StyleEngineTest, CSSSelectorEmptyWhitespaceOnlyFail) {
+  GetDocument().body()->SetInnerHTMLFromString(R"HTML(
+    <style>.match:empty { background-color: red }</style>
+    <div></div>
+    <div> <span></span></div>
+    <div> <!-- -->X</div>
+    <div></div>
+    <div> <!-- --></div>
+  )HTML");
+  GetDocument().View()->UpdateAllLifecyclePhases();
+
+  EXPECT_FALSE(UseCounter::IsCounted(
+      GetDocument(), WebFeature::kCSSSelectorEmptyWhitespaceOnlyFail));
+
+  auto* div_elements = GetDocument().getElementsByTagName("div");
+  ASSERT_TRUE(div_elements);
+  ASSERT_EQ(5u, div_elements->length());
+
+  auto is_counted = [](Element* element) {
+    element->setAttribute(blink::html_names::kClassAttr, "match");
+    element->GetDocument().View()->UpdateAllLifecyclePhases();
+    return UseCounter::IsCounted(
+        element->GetDocument(),
+        WebFeature::kCSSSelectorEmptyWhitespaceOnlyFail);
+  };
+
+  EXPECT_FALSE(is_counted(div_elements->item(0)));
+  EXPECT_FALSE(is_counted(div_elements->item(1)));
+  EXPECT_FALSE(is_counted(div_elements->item(2)));
+  EXPECT_FALSE(is_counted(div_elements->item(3)));
+  EXPECT_TRUE(is_counted(div_elements->item(4)));
+}
+
 }  // namespace blink

tools/metrics/histograms/enums.xml

@@ -20680,6 +20680,7 @@ Called by update_net_error_codes.py.-->
   <int value="2621" label="AdClick"/>
   <int value="2622" label="UpdateWithoutShippingOptionOnShippingAddressChange"/>
   <int value="2623" label="UpdateWithoutShippingOptionOnShippingOptionChange"/>
+  <int value="2624" label="CSSSelectorEmptyWhitespaceOnlyFail"/>
 </enum>
 
 <enum name="FeaturePolicyFeature">