Skeleton implementation of CSS Properties and Values API

third_party/WebKit/Source/core/style/ComputedStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 1442 matching lines @@
 void ComputedStyle::setVariable(const AtomicString& name, PassRefPtr<CSSVariableData> value)
 {
     RefPtr<StyleVariableData>& variables = m_rareInheritedData.access()->variables;
     if (!variables)
         variables = StyleVariableData::create();
     else if (!variables->hasOneRef())
         variables = variables->copy();
     variables->setVariable(name, value);
 }
 
+void ComputedStyle::setRegisteredInheritedProperty(const AtomicString& name, const CSSValue* parsedValue)
+{
+    RefPtr<StyleVariableData>& variables = m_rareInheritedData.access()->variables;
+    DCHECK(variables);
+    if (!variables->hasOneRef())
+        variables = variables->copy();
+    DCHECK(!!parsedValue == !!variables->getVariable(name));

[meade_UTC10, 2016/09/06 04:52:07]

I don't really understand what this check is for, both parsedValue and
getVariable(name) must be null, or both must be not null? Why?

+    DCHECK(!(parsedValue && variables->getVariable(name)->needsVariableResolution()));

[meade_UTC10, 2016/09/06 04:52:07]

Is this one "you can clear a variable that still needs resolution, but you can't
set a new one (yet)"?

[Timothy Loh, 2016/09/06 08:21:17]

Both dchecks are sanity checks about the relation between the token stream value
(CSSVariableData) and the parsed value (CSSValue). For these to work we need to
guarantee some ordering of setting, I chose to always set the CSSVariableData
first. These two are alternate representations of the same data so they need to
be in sync.

First dcheck - There's a CSSVariableData if and only if there's a CSSValue
Second dcheck - If we have a value, we've already resolved the var references.
Maybe clearer if I write DCHECK(!(variables->getVariable(name) &&
variables->getVariable(name)->needsVariableResolution()))?

+    variables->setRegisteredInheritedProperty(name, parsedValue);
+}
+
 void ComputedStyle::removeVariable(const AtomicString& name)
 {
     RefPtr<StyleVariableData>& variables = m_rareInheritedData.access()->variables;
     if (!variables)
         return;
     if (!variables->hasOneRef())
         variables = variables->copy();
     variables->removeVariable(name);
 }
 
@@ skipping 572 matching lines @@
         if (value < 0)
             fvalue -= 0.5f;
         else
             fvalue += 0.5f;
     }
 
     return roundForImpreciseConversion<int>(fvalue / zoomFactor);
 }
 
 } // namespace blink