Bug 1353312 - Don't use conditions when caching a struct with no rules. r=dbaron

MozReview-Commit-ID: 2Q1xWcDY10T

layout/style/RuleNodeCacheConditions.h

@@ -95,6 +95,11 @@ public:
     mBits |= eUncacheable;
   }
 
+  void Clear()
+  {
+    *this = RuleNodeCacheConditions();
+  }
+
   bool Cacheable() const
   {
     return !(mBits & eUncacheable);

layout/style/nsRuleNode.cpp

@@ -2678,6 +2678,42 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
              "not forcing detail to eRulePartialMixed just below is no "
              "longer valid");
 
+  if (detail == eRuleNone && isReset) {
+    // We specified absolutely no rule information for a reset struct, and we
+    // may or may not have found a parent rule in the tree that specified all
+    // the rule information.  Regardless, we don't need to use any cache
+    // conditions if we cache this struct in the rule tree.
+    //
+    // Normally ruleData.mConditions would already indicate that the struct
+    // is cacheable without conditions if detail is eRuleNone, but because
+    // of the UnsetPropertiesWithoutFlags call above, we may have encountered
+    // some rules with dependencies, which we then cleared out of ruleData.
+    //
+    // ruleData.mConditions could also indicate we are not cacheable at all,
+    // such as when AnimValuesStyleRule prevents us from caching structs
+    // when attempting to apply animations to pseudos.
+    //
+    // So if we we are uncacheable, we leave it, but if we are cacheable
+    // with dependencies, we convert that to cacheable without dependencies.
+    if (ruleData.mConditions.CacheableWithDependencies()) {
+      MOZ_ASSERT(pseudoRestriction,
+                 "should only be cacheable with dependencies if we had a "
+                 "pseudo restriction");
+      ruleData.mConditions.Clear();
+    } else {
+      // XXXheycam We shouldn't have `|| GetLevel() == SheetType::Transition`
+      // in the assertion condition, but rule nodes created by
+      // ResolveStyleByAddingRules don't call SetIsAnimationRule().
+      MOZ_ASSERT(ruleData.mConditions.CacheableWithoutDependencies() ||
+                 ((HasAnimationData() ||
+                   GetLevel() == SheetType::Transition) &&
+                  aContext->GetParent() &&
+                  aContext->GetParent()->HasPseudoElementData()),
+                 "should only be uncacheable if we had an animation rule "
+                 "and we're inside a pseudo");
+    }
+  }
+
   if (!ruleData.mConditions.CacheableWithoutDependencies() &&
       aSID != eStyleStruct_Variables) {
     // Treat as though some data is specified to avoid the optimizations and

layout/style/nsRuleNode.h

@@ -193,6 +193,7 @@ public:
     MOZ_ASSERT(!(mConditionalBits & GetBitForSID(aSID)),
                "rule node should not have unconditional and conditional style "
                "data for a given struct");
+    mConditionalBits &= ~GetBitForSID(aSID);
     mEntries[aSID] = aStyleStruct;
   }
 
@@ -200,13 +201,17 @@ public:
                     nsPresContext* aPresContext,
                     void* aStyleStruct,
                     const mozilla::RuleNodeCacheConditions& aConditions) {
-    MOZ_ASSERT((mConditionalBits & GetBitForSID(aSID)) ||
-               !mEntries[aSID],
-               "rule node should not have unconditional and conditional style "
-               "data for a given struct");
+    if (!(mConditionalBits & GetBitForSID(aSID))) {
+      MOZ_ASSERT(!mEntries[aSID],
+                 "rule node should not have unconditional and conditional "
+                 "style data for a given struct");
+      mEntries[aSID] = nullptr;
+    }
+
     MOZ_ASSERT(aConditions.CacheableWithDependencies(),
                "don't call SetStyleData with a cache key that has no "
                "conditions or is uncacheable");
+
 #ifdef DEBUG
     for (Entry* e = static_cast<Entry*>(mEntries[aSID]); e; e = e->mNext) {
       NS_WARNING_ASSERTION(e->mConditions != aConditions,