Lazy Parse CSS

third_party/WebKit/Source/core/css/StyleRule.cpp

Index: third_party/WebKit/Source/core/css/StyleRule.cpp
diff --git a/third_party/WebKit/Source/core/css/StyleRule.cpp b/third_party/WebKit/Source/core/css/StyleRule.cpp
index ffc73fe80bc83c10d6dd96c826c9646bb7d9eb7e..c00747492f0799f84f56093f1e44caaa83daf0d2 100644
--- a/third_party/WebKit/Source/core/css/StyleRule.cpp
+++ b/third_party/WebKit/Source/core/css/StyleRule.cpp
@@ -212,15 +212,31 @@ unsigned StyleRule::averageSizeInBytes()
 
 StyleRule::StyleRule(CSSSelectorList selectorList, StylePropertySet* properties)
     : StyleRuleBase(Style)
+    , m_selectorList(std::move(selectorList))
     , m_properties(properties)
 {
-    m_selectorList = std::move(selectorList);
+}
+
+StyleRule::StyleRule(CSSSelectorList selectorList, std::unique_ptr<DeferredPropertiesClosure> deferredProperties)
+    : StyleRuleBase(Style)
+    , m_selectorList(std::move(selectorList))
+    , m_deferred(std::move(deferredProperties))
+{
+}
+
+const StylePropertySet& StyleRule::properties() const
+{
+    if (!m_properties) {
+        m_properties = (*m_deferred)();
+        m_deferred.reset();
+    }
+    return *m_properties;
 }
 
 StyleRule::StyleRule(const StyleRule& o)
     : StyleRuleBase(o)
-    , m_properties(o.m_properties->mutableCopy())
     , m_selectorList(o.m_selectorList.copy())
+    , m_properties(o.properties().mutableCopy())
 {
 }
 
@@ -230,11 +246,25 @@ StyleRule::~StyleRule()
 
 MutableStylePropertySet& StyleRule::mutableProperties()
 {
-    if (!m_properties->isMutable())
-        m_properties = m_properties->mutableCopy();
+    // Ensure m_properties is initialized.
+    const StylePropertySet& props = properties();

[Timothy Loh, 2016/09/27 05:15:45]

The style guide (blink.style/guide) says to avoid abbreviations. Maybe just call
properties() and then use m_properties?

[Charlie Harrison, 2016/09/27 13:22:00]

Done.

+    if (!props.isMutable())
+        m_properties = props.mutableCopy();
     return *toMutableStylePropertySet(m_properties.get());
 }
 
+bool StyleRule::propertiesHaveFailedOrCanceledSubresources() const
+{
+    return m_properties && m_properties->hasFailedOrCanceledSubresources();
+}
+
+bool StyleRule::hasEmptyProperties() const

[Timothy Loh, 2016/09/27 05:15:45]

Is this supposed to be called somewhere? It's not obvious to me what this is
for, and the below comment is wrong because you could have "a { }" or "a { not
valid : properties; garbage }", etc.

[Charlie Harrison, 2016/09/27 13:22:00]

My mistake, this is supposed to be called in
ElementRuleCollector::collectMatchingRulesForList. There is an optimization that
checks for empty properties to avoid checking matching.

You're right that there are cases where the lazy parsing can have empty
properties by having garbage, etc. I've changed the code so that these go
through anyways. If we find this optimization is really necessary we may be able
to match "{ }" cases during tokenizing. I haven't done that yet because I
imagine it will slow down the code a bit (like searching for attr()).

+{
+    // We only lazily parse if the property block has a nonzero amount of
+    // tokens. Thus, consider all lazily initialized properties to be non-empty.
+    return m_properties && m_properties->isEmpty();
+}
+
 DEFINE_TRACE_AFTER_DISPATCH(StyleRule)
 {
     visitor->trace(m_properties);