Bug 1289701 - Find the root style context by walkng up the style context tree instead of calling ResolveStyleFor or getting it from root element's primary frame. r=dbaron

The only call site of CalcLengthWith() with a null style context is
CalcLengthWithInitialFont(). CalcLengthWithInitialFont() calls
CalcLengthWith() with a valid nsStyleFont and aUseProvidedRootEmSize
true, so we can get the rem unit font size from the nsStyleFont when called
from CalcLengthWithInitialFont().

MozReview-Commit-ID: A9LKfQEozaB

layout/style/nsRuleNode.cpp

@@ -442,6 +442,11 @@ static nsSize CalcViewportUnitsScale(nsPresContext* aPresContext)
   return viewportSize;
 }
 
+// If |aStyleFont| is nullptr, aStyleContext->StyleFont() is used.
+//
+// In case that |aValue| is rem unit, if |aStyleContext| is null, callers must
+// specify a valid |aStyleFont| and |aUseProvidedRootEmSize| must be true so
+// that we can get the length from |aStyleFont|.
 static nscoord CalcLengthWith(const nsCSSValue& aValue,
                               nscoord aFontSize,
                               const nsStyleFont* aStyleFont,
@@ -458,8 +463,8 @@ static nscoord CalcLengthWith(const nsCSSValue& aValue,
                "not a length or calc unit");
   NS_ASSERTION(aStyleFont || aStyleContext,
                "Must have style data");
-  NS_ASSERTION(!aStyleFont || !aStyleContext,
-               "Duplicate sources of data");
+  NS_ASSERTION(aStyleContext || aUseProvidedRootEmSize,
+               "Must have style context or specify aUseProvidedRootEmSize");
   NS_ASSERTION(aPresContext, "Must have prescontext");
 
   if (aValue.IsFixedLengthUnit()) {
@@ -554,21 +559,12 @@ static nscoord CalcLengthWith(const nsCSSValue& aValue,
       } else {
         // This is not the root element or we are calculating something other
         // than font size, so rem is relative to the root element's font size.
-        RefPtr<nsStyleContext> rootStyle;
-        const nsStyleFont *rootStyleFont = styleFont;
-        Element* docElement = aPresContext->Document()->GetRootElement();
-
-        if (docElement) {
-          nsIFrame* rootFrame = docElement->GetPrimaryFrame();
-          if (rootFrame) {
-            rootStyle = rootFrame->StyleContext();
-          } else {
-            rootStyle = aPresContext->StyleSet()->AsGecko()->ResolveStyleFor(docElement,
-                                                                             nullptr);
-          }
-          rootStyleFont = rootStyle->StyleFont();
+        // Find the root style context by walking up the style context tree.
+        nsStyleContext* rootStyle = aStyleContext;
+        while (rootStyle->GetParent()) {
+          rootStyle = rootStyle->GetParent();
         }
-
+        const nsStyleFont *rootStyleFont = rootStyle->StyleFont();
         rootFontSize = rootStyleFont->mFont.size;
       }
 
@@ -3323,15 +3319,19 @@ struct SetFontSizeCalcOps : public css::BasicCoordCalcOps,
   const nscoord mParentSize;
   const nsStyleFont* const mParentFont;
   nsPresContext* const mPresContext;
+  nsStyleContext* const mStyleContext;
   const bool mAtRoot;
   RuleNodeCacheConditions& mConditions;
 
   SetFontSizeCalcOps(nscoord aParentSize, const nsStyleFont* aParentFont,
-                     nsPresContext* aPresContext, bool aAtRoot,
+                     nsPresContext* aPresContext,
+                     nsStyleContext* aStyleContext,
+                     bool aAtRoot,
                      RuleNodeCacheConditions& aConditions)
     : mParentSize(aParentSize),
       mParentFont(aParentFont),
       mPresContext(aPresContext),
+      mStyleContext(aStyleContext),
       mAtRoot(aAtRoot),
       mConditions(aConditions)
   {
@@ -3346,7 +3346,7 @@ struct SetFontSizeCalcOps : public css::BasicCoordCalcOps,
       // between us and the parent is simply ignored.
       size = CalcLengthWith(aValue, mParentSize,
                             mParentFont,
-                            nullptr, mPresContext, mAtRoot,
+                            mStyleContext, mPresContext, mAtRoot,
                             true, mConditions);
       if (!aValue.IsRelativeLengthUnit() && mParentFont->mAllowZoom) {
         size = nsStyleFont::ZoomText(mPresContext, size);
@@ -3370,6 +3370,7 @@ struct SetFontSizeCalcOps : public css::BasicCoordCalcOps,
 
 /* static */ void
 nsRuleNode::SetFontSize(nsPresContext* aPresContext,
+                        nsStyleContext* aContext,
                         const nsRuleData* aRuleData,
                         const nsStyleFont* aFont,
                         const nsStyleFont* aParentFont,
@@ -3436,7 +3437,8 @@ nsRuleNode::SetFontSize(nsPresContext* aPresContext,
            sizeValue->GetUnit() == eCSSUnit_Percent ||
            sizeValue->IsCalcUnit()) {
     SetFontSizeCalcOps ops(aParentSize, aParentFont,
-                           aPresContext, aAtRoot,
+                           aPresContext, aContext,
+                           aAtRoot,
                            aConditions);
     *aSize = css::ComputeCalc(*sizeValue, ops);
     if (*aSize < 0) {
@@ -3782,7 +3784,7 @@ nsRuleNode::SetFont(nsPresContext* aPresContext, nsStyleContext* aContext,
     aFont->mScriptMinSize =
       CalcLengthWith(*scriptMinSizeValue, aParentFont->mSize,
                      aParentFont,
-                     nullptr, aPresContext, atRoot, true,
+                     aContext, aPresContext, atRoot, true /* aUseUserFontSet */,
                      aConditions);
   }
 
@@ -4024,7 +4026,8 @@ nsRuleNode::SetFont(nsPresContext* aPresContext, nsStyleContext* aContext,
     scriptLevelAdjustedParentSize !=
       scriptLevelAdjustedUnconstrainedParentSize;
 
-  SetFontSize(aPresContext, aRuleData, aFont, aParentFont,
+  SetFontSize(aPresContext, aContext,
+              aRuleData, aFont, aParentFont,
               &aFont->mSize,
               systemFont, aParentFont->mSize, scriptLevelAdjustedParentSize,
               aUsedStartStruct, atRoot, aConditions);
@@ -4054,7 +4057,8 @@ nsRuleNode::SetFont(nsPresContext* aPresContext, nsStyleContext* aContext,
     // already called SetUncacheable.
     RuleNodeCacheConditions unconstrainedConditions;
 
-    SetFontSize(aPresContext, aRuleData, aFont, aParentFont,
+    SetFontSize(aPresContext, aContext,
+                aRuleData, aFont, aParentFont,
                 &aFont->mScriptUnconstrainedSize,
                 systemFont, aParentFont->mScriptUnconstrainedSize,
                 scriptLevelAdjustedUnconstrainedParentSize,

layout/style/nsRuleNode.h

@@ -755,6 +755,7 @@ protected:
 
   // helpers for |ComputeFontData| that need access to |mNoneBits|:
   static void SetFontSize(nsPresContext* aPresContext,
+                          nsStyleContext* aContext,
                           const nsRuleData* aRuleData,
                           const nsStyleFont* aFont,
                           const nsStyleFont* aParentFont,