Implement custom first symbol value for @counter-style 'fixed' systems

Bug: 687225
Change-Id: I475aa0fb47961e8d3d50c5721522586359b3e565
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587701
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836890}

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

@@ -238,6 +238,9 @@ CounterStyle::CounterStyle(const StyleRuleCounterStyle& rule)
     if (system_ == CounterStyleSystem::kUnresolvedExtends) {
       const auto& second = To<CSSValuePair>(system)->Second();
       extends_name_ = To<CSSCustomIdentValue>(second).Value();
+    } else if (system_ == CounterStyleSystem::kFixed && system->IsValuePair()) {
+      const auto& second = To<CSSValuePair>(system)->Second();
+      first_symbol_value_ = To<CSSPrimitiveValue>(second).GetIntValue();
     }
   }
 
@@ -284,7 +287,7 @@ CounterStyle::CounterStyle(const StyleRuleCounterStyle& rule)
     }
   }
 
-  // TODO(crbug.com/687225): Implement and populate other fields.
+  // TODO(crbug.com/687225): Implement 'prefix', 'suffix' and 'speak-as'.
 }
 
 void CounterStyle::ResolveExtends(const CounterStyle& extended) {
@@ -293,6 +296,9 @@ void CounterStyle::ResolveExtends(const CounterStyle& extended) {
 
   system_ = extended.system_;
 
+  if (system_ == CounterStyleSystem::kFixed)
+    first_symbol_value_ = extended.first_symbol_value_;
+
   if (!style_rule_->GetFallback()) {
     fallback_name_ = extended.fallback_name_;
     fallback_style_ = nullptr;
@@ -315,7 +321,7 @@ void CounterStyle::ResolveExtends(const CounterStyle& extended) {
   if (!style_rule_->GetRange())
     range_ = extended.range_;
 
-  // TODO(crbug.com/687225): Implement and populate other fields.
+  // TODO(crbug.com/687225): Implement 'prefix', 'suffix' and 'speak-as'.
 }
 
 void CounterStyle::ResetExtends() {
@@ -425,8 +431,8 @@ String CounterStyle::GenerateInitialRepresentation(int value) const {
       symbol_indexes = CyclicAlgorithm(value, symbols_.size());
       break;
     case CounterStyleSystem::kFixed:
-      // TODO(crbug.com/687225): Implement non-default first symbol values.
-      symbol_indexes = FixedAlgorithm(value - 1, symbols_.size());
+      symbol_indexes =
+          FixedAlgorithm(value - first_symbol_value_, symbols_.size());
       break;
     case CounterStyleSystem::kNumeric:
       symbol_indexes = NumericAlgorithm(value, symbols_.size());

third_party/blink/renderer/core/css/counter_style.h

@@ -110,6 +110,9 @@ class CORE_EXPORT CounterStyle final : public GarbageCollected<CounterStyle> {
   String pad_symbol_;
   wtf_size_t pad_length_ = 0;
 
+  // First symbol value, for 'fixed' system only.
+  wtf_size_t first_symbol_value_ = 1;
+
   friend class CounterStyleMapTest;
 };
 

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

@@ -326,4 +326,34 @@ TEST_F(CounterStyleTest, AdditiveWithExtendedRange) {
   EXPECT_EQ("A", extended.GenerateRepresentation(1));
 }
 
+TEST_F(CounterStyleTest, CustomFirstSymbolValue) {
+  InsertStyleElement(R"CSS(
+    @counter-style base {
+      system: fixed 2;
+      symbols: A B C;
+    }
+
+    @counter-style extended {
+      system: extends base;
+    }
+  )CSS");
+  UpdateAllLifecyclePhasesForTest();
+
+  // Getting custom first symbol value directly from descriptor value.
+  const CounterStyle& base = GetCounterStyle("base");
+  EXPECT_EQ("1", base.GenerateRepresentation(1));
+  EXPECT_EQ("A", base.GenerateRepresentation(2));
+  EXPECT_EQ("B", base.GenerateRepresentation(3));
+  EXPECT_EQ("C", base.GenerateRepresentation(4));
+  EXPECT_EQ("5", base.GenerateRepresentation(5));
+
+  // Getting custom first symbol value indirectly using 'extends'.
+  const CounterStyle& extended = GetCounterStyle("extended");
+  EXPECT_EQ("1", extended.GenerateRepresentation(1));
+  EXPECT_EQ("A", extended.GenerateRepresentation(2));
+  EXPECT_EQ("B", extended.GenerateRepresentation(3));
+  EXPECT_EQ("C", extended.GenerateRepresentation(4));
+  EXPECT_EQ("5", extended.GenerateRepresentation(5));
+}
+
 }  // namespace blink