gecko-dev/layout/style/CSSVariableResolver.cpp

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* object that resolves CSS variables using specified and inherited variable
* values
*/
#include "CSSVariableResolver.h"
#include "CSSVariableDeclarations.h"
#include "CSSVariableValues.h"
#include "mozilla/PodOperations.h"
#include "mozilla/UniquePtr.h"
#include <algorithm>
namespace mozilla {
/**
* Data used by the EnumerateVariableReferences callback. Reset must be called
* on it before it is used.
*/
class EnumerateVariableReferencesData
{
public:
explicit EnumerateVariableReferencesData(CSSVariableResolver& aResolver)
: mResolver(aResolver)
, mReferences(MakeUnique<bool[]>(aResolver.mVariables.Length()))
{
}
/**
* Resets the data so that it can be passed to another call of
* EnumerateVariableReferences for a different variable.
*/
void Reset()
{
PodZero(mReferences.get(), mResolver.mVariables.Length());
mReferencesNonExistentVariable = false;
}
void RecordVariableReference(const nsAString& aVariableName)
{
size_t id;
if (mResolver.mVariableIDs.Get(aVariableName, &id)) {
mReferences[id] = true;
} else {
mReferencesNonExistentVariable = true;
}
}
bool HasReferenceToVariable(size_t aID) const
{
return mReferences[aID];
}
bool ReferencesNonExistentVariable() const
{
return mReferencesNonExistentVariable;
}
private:
CSSVariableResolver& mResolver;
// Array of booleans, where each index is a variable ID. If an element is
// true, it indicates that the variable we have called
// EnumerateVariableReferences for has a reference to the variable with
// that ID.
const UniquePtr<bool[]> mReferences;
// Whether the variable we have called EnumerateVariableReferences for
// references a variable that does not exist in the resolver.
bool mReferencesNonExistentVariable;
};
static void
RecordVariableReference(const nsAString& aVariableName,
void* aData)
{
static_cast<EnumerateVariableReferencesData*>(aData)->
RecordVariableReference(aVariableName);
}
void
CSSVariableResolver::RemoveCycles(size_t v)
{
mVariables[v].mIndex = mNextIndex;
mVariables[v].mLowLink = mNextIndex;
mVariables[v].mInStack = true;
mStack.AppendElement(v);
mNextIndex++;
for (size_t i = 0, n = mReferences[v].Length(); i < n; i++) {
size_t w = mReferences[v][i];
if (!mVariables[w].mIndex) {
RemoveCycles(w);
mVariables[v].mLowLink = std::min(mVariables[v].mLowLink,
mVariables[w].mLowLink);
} else if (mVariables[w].mInStack) {
mVariables[v].mLowLink = std::min(mVariables[v].mLowLink,
mVariables[w].mIndex);
}
}
if (mVariables[v].mLowLink == mVariables[v].mIndex) {
if (mStack.LastElement() == v) {
// A strongly connected component consisting of a single variable is not
// necessarily invalid. We handle variables that reference themselves
// earlier, in CSSVariableResolver::Resolve.
mVariables[mStack.LastElement()].mInStack = false;
mStack.TruncateLength(mStack.Length() - 1);
} else {
size_t w;
do {
w = mStack.LastElement();
mVariables[w].mValue.Truncate(0);
mVariables[w].mInStack = false;
mStack.TruncateLength(mStack.Length() - 1);
} while (w != v);
}
}
}
void
CSSVariableResolver::ResolveVariable(size_t aID)
{
if (mVariables[aID].mValue.IsEmpty() || mVariables[aID].mWasInherited) {
// The variable is invalid or was inherited. We can just copy the value
// and its first/last token information across.
mOutput->Put(mVariables[aID].mVariableName,
mVariables[aID].mValue,
mVariables[aID].mFirstToken,
mVariables[aID].mLastToken);
} else {
// Otherwise we need to resolve the variable references, after resolving
// all of our dependencies first. We do this even for variables that we
// know do not reference other variables so that we can find their
// first/last token.
//
// XXX We might want to do this first/last token finding during
// EnumerateVariableReferences, so that we can avoid calling
// ResolveVariableValue and parsing the value again.
for (size_t i = 0, n = mReferences[aID].Length(); i < n; i++) {
size_t j = mReferences[aID][i];
if (aID != j && !mVariables[j].mResolved) {
ResolveVariable(j);
}
}
nsString resolvedValue;
nsCSSTokenSerializationType firstToken, lastToken;
if (mParser.ResolveVariableValue(mVariables[aID].mValue, mOutput,
resolvedValue, firstToken, lastToken)) {
mOutput->Put(mVariables[aID].mVariableName, resolvedValue,
firstToken, lastToken);
} else {
mOutput->Put(mVariables[aID].mVariableName, EmptyString(),
eCSSTokenSerialization_Nothing, eCSSTokenSerialization_Nothing);
}
}
mVariables[aID].mResolved = true;
}
void
CSSVariableResolver::Resolve(const CSSVariableValues* aInherited,
const CSSVariableDeclarations* aSpecified)
{
MOZ_ASSERT(!mResolved);
// The only time we would be worried about having a null aInherited is
// for the root, but in that case nsRuleNode::ComputeVariablesData will
// happen to pass in whatever we're using as mOutput for aInherited,
// which will initially be empty.
MOZ_ASSERT(aInherited);
MOZ_ASSERT(aSpecified);
aInherited->AddVariablesToResolver(this);
aSpecified->AddVariablesToResolver(this);
// First we look at each variable's value and record which other variables
// it references.
size_t n = mVariables.Length();
mReferences.SetLength(n);
EnumerateVariableReferencesData data(*this);
for (size_t id = 0; id < n; id++) {
data.Reset();
if (!mVariables[id].mWasInherited &&
!mVariables[id].mValue.IsEmpty()) {
if (mParser.EnumerateVariableReferences(mVariables[id].mValue,
RecordVariableReference,
&data)) {
// Convert the boolean array of dependencies in |data| to a list
// of dependencies.
for (size_t i = 0; i < n; i++) {
if (data.HasReferenceToVariable(i)) {
mReferences[id].AppendElement(i);
}
}
// If a variable references itself, it is invalid. (RemoveCycles
// does not check for cycles consisting of a single variable, so we
// check here.)
if (data.HasReferenceToVariable(id)) {
mVariables[id].mValue.Truncate();
}
// Also record whether it referenced any variables that don't exist
// in the resolver, so that we can ensure we still resolve its value
// in ResolveVariable, even though its mReferences list is empty.
mVariables[id].mReferencesNonExistentVariable =
data.ReferencesNonExistentVariable();
} else {
MOZ_ASSERT(false, "EnumerateVariableReferences should not have failed "
"if we previously parsed the specified value");
mVariables[id].mValue.Truncate(0);
}
}
}
// Next we remove any cycles in variable references using Tarjan's strongly
// connected components finding algorithm, setting variables in cycles to
// have an invalid value.
mNextIndex = 1;
for (size_t id = 0; id < n; id++) {
if (!mVariables[id].mIndex) {
RemoveCycles(id);
MOZ_ASSERT(mStack.IsEmpty());
}
}
// Finally we construct the computed value for the variable by substituting
// any variable references.
for (size_t id = 0; id < n; id++) {
if (!mVariables[id].mResolved) {
ResolveVariable(id);
}
}
#ifdef DEBUG
mResolved = true;
#endif
}
void
CSSVariableResolver::Put(const nsAString& aVariableName,
nsString aValue,
nsCSSTokenSerializationType aFirstToken,
nsCSSTokenSerializationType aLastToken,
bool aWasInherited)
{
MOZ_ASSERT(!mResolved);
size_t id;
if (mVariableIDs.Get(aVariableName, &id)) {
MOZ_ASSERT(mVariables[id].mWasInherited && !aWasInherited,
"should only overwrite inherited variables with specified "
"variables");
mVariables[id].mValue = aValue;
mVariables[id].mFirstToken = aFirstToken;
mVariables[id].mLastToken = aLastToken;
mVariables[id].mWasInherited = aWasInherited;
} else {
id = mVariables.Length();
mVariableIDs.Put(aVariableName, id);
mVariables.AppendElement(Variable(aVariableName, aValue,
aFirstToken, aLastToken, aWasInherited));
}
}
} // namespace mozilla