gecko/dom/xslt/xpath/txExpr.h

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* 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/. */

#ifndef TRANSFRMX_EXPR_H
#define TRANSFRMX_EXPR_H

#include "mozilla/Attributes.h"
#include "nsAutoPtr.h"
#include "txExprResult.h"
#include "txCore.h"
#include "nsString.h"
#include "txOwningArray.h"
#include "nsIAtom.h"

#ifdef DEBUG
#define TX_TO_STRING
#endif

/*
  XPath class definitions.
  Much of this code was ported from XSL:P.
*/

class nsIAtom;
class txIParseContext;
class txIMatchContext;
class txIEvalContext;
class txNodeSet;
class txXPathNode;

/**
 * A Base Class for all XSL Expressions
**/
class Expr
{
public:
    Expr()
    {
        MOZ_COUNT_CTOR(Expr);
    }
    virtual ~Expr()
    {
        MOZ_COUNT_DTOR(Expr);
    }

    /**
     * Evaluates this Expr based on the given context node and processor state
     * @param context the context node for evaluation of this Expr
     * @param ps the ContextState containing the stack information needed
     * for evaluation
     * @return the result of the evaluation
    **/
    virtual nsresult evaluate(txIEvalContext* aContext,
                              txAExprResult** aResult) = 0;


    /**
     * Returns the type of this expression.
     */
    enum ExprType {
        LOCATIONSTEP_EXPR,
        PATH_EXPR,
        UNION_EXPR,
        LITERAL_EXPR,
        OTHER_EXPR
    };
    virtual ExprType getType()
    {
      return OTHER_EXPR;
    }

    /**
     * Returns the type or types of results this Expr return.
     */
    typedef uint16_t ResultType;
    enum {
        NODESET_RESULT = 0x01,
        BOOLEAN_RESULT = 0x02,
        NUMBER_RESULT = 0x04,
        STRING_RESULT = 0x08,
        RTF_RESULT = 0x10,
        ANY_RESULT = 0xFFFF
    };
    virtual ResultType getReturnType() = 0;
    bool canReturnType(ResultType aType)
    {
        return (getReturnType() & aType) != 0;
    }

    typedef uint16_t ContextSensitivity;
    enum {
        NO_CONTEXT = 0x00,
        NODE_CONTEXT = 0x01,
        POSITION_CONTEXT = 0x02,
        SIZE_CONTEXT = 0x04,
        NODESET_CONTEXT = POSITION_CONTEXT | SIZE_CONTEXT,
        VARIABLES_CONTEXT = 0x08,
        PRIVATE_CONTEXT = 0x10,
        ANY_CONTEXT = 0xFFFF
    };

    /**
     * Returns true if this expression is sensitive to *any* of
     * the requested contexts in aContexts.
     */
    virtual bool isSensitiveTo(ContextSensitivity aContexts) = 0;

    /**
     * Returns sub-expression at given position
     */
    virtual Expr* getSubExprAt(uint32_t aPos) = 0;

    /**
     * Replace sub-expression at given position. Does not delete the old
     * expression, that is the responsibility of the caller.
     */
    virtual void setSubExprAt(uint32_t aPos, Expr* aExpr) = 0;

    virtual nsresult evaluateToBool(txIEvalContext* aContext,
                                    bool& aResult);

    virtual nsresult evaluateToString(txIEvalContext* aContext,
                                      nsString& aResult);

#ifdef TX_TO_STRING
    /**
     * Returns the String representation of this Expr.
     * @param dest the String to use when creating the String
     * representation. The String representation will be appended to
     * any data in the destination String, to allow cascading calls to
     * other #toString() methods for Expressions.
     * @return the String representation of this Expr.
    **/
    virtual void toString(nsAString& str) = 0;
#endif
}; //-- Expr

#ifdef TX_TO_STRING
#define TX_DECL_TOSTRING \
    void toString(nsAString& aDest);
#define TX_DECL_GETNAMEATOM \
    nsresult getNameAtom(nsIAtom** aAtom);
#else
#define TX_DECL_TOSTRING
#define TX_DECL_GETNAMEATOM
#endif

#define TX_DECL_EXPR_BASE \
    nsresult evaluate(txIEvalContext* aContext, txAExprResult** aResult); \
    ResultType getReturnType(); \
    bool isSensitiveTo(ContextSensitivity aContexts);

#define TX_DECL_EXPR \
    TX_DECL_EXPR_BASE \
    TX_DECL_TOSTRING \
    Expr* getSubExprAt(uint32_t aPos); \
    void setSubExprAt(uint32_t aPos, Expr* aExpr);

#define TX_DECL_OPTIMIZABLE_EXPR \
    TX_DECL_EXPR \
    ExprType getType();
    

#define TX_DECL_FUNCTION \
    TX_DECL_GETNAMEATOM \
    TX_DECL_EXPR_BASE

#define TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)          \
Expr::ResultType                                              \
_class::getReturnType()                                       \
{                                                             \
    return _ReturnType;                                       \
}

#define TX_IMPL_EXPR_STUBS_0(_class, _ReturnType)             \
TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                  \
Expr*                                                         \
_class::getSubExprAt(uint32_t aPos)                           \
{                                                             \
    return nullptr;                                            \
}                                                             \
void                                                          \
_class::setSubExprAt(uint32_t aPos, Expr* aExpr)              \
{                                                             \
    NS_NOTREACHED("setting bad subexpression index");         \
}

#define TX_IMPL_EXPR_STUBS_1(_class, _ReturnType, _Expr1)     \
TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                  \
Expr*                                                         \
_class::getSubExprAt(uint32_t aPos)                           \
{                                                             \
    if (aPos == 0) {                                          \
        return _Expr1;                                        \
    }                                                         \
    return nullptr;                                            \
}                                                             \
void                                                          \
_class::setSubExprAt(uint32_t aPos, Expr* aExpr)              \
{                                                             \
    NS_ASSERTION(aPos < 1, "setting bad subexpression index");\
    _Expr1.forget();                                          \
    _Expr1 = aExpr;                                           \
}

#define TX_IMPL_EXPR_STUBS_2(_class, _ReturnType, _Expr1, _Expr2) \
TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                  \
Expr*                                                         \
_class::getSubExprAt(uint32_t aPos)                           \
{                                                             \
    switch(aPos) {                                            \
        case 0:                                               \
            return _Expr1;                                    \
        case 1:                                               \
            return _Expr2;                                    \
        default:                                              \
            break;                                            \
    }                                                         \
    return nullptr;                                            \
}                                                             \
void                                                          \
_class::setSubExprAt(uint32_t aPos, Expr* aExpr)              \
{                                                             \
    NS_ASSERTION(aPos < 2, "setting bad subexpression index");\
    if (aPos == 0) {                                          \
        _Expr1.forget();                                      \
        _Expr1 = aExpr;                                       \
    }                                                         \
    else {                                                    \
        _Expr2.forget();                                      \
        _Expr2 = aExpr;                                       \
    }                                                         \
}

#define TX_IMPL_EXPR_STUBS_LIST(_class, _ReturnType, _ExprList) \
TX_IMPL_EXPR_STUBS_BASE(_class, _ReturnType)                  \
Expr*                                                         \
_class::getSubExprAt(uint32_t aPos)                           \
{                                                             \
    return _ExprList.SafeElementAt(aPos);                     \
}                                                             \
void                                                          \
_class::setSubExprAt(uint32_t aPos, Expr* aExpr)              \
{                                                             \
    NS_ASSERTION(aPos < _ExprList.Length(),                   \
                 "setting bad subexpression index");          \
    _ExprList[aPos] = aExpr;                                  \
}


/**
 * This class represents a FunctionCall as defined by the XPath 1.0
 * Recommendation.
**/
class FunctionCall : public Expr
{
public:
    /**
     * Adds the given parameter to this FunctionCall's parameter list.
     * The ownership of the given Expr is passed over to the FunctionCall,
     * even on failure.
     * @param aExpr the Expr to add to this FunctionCall's parameter list
     * @return nsresult indicating out of memory
     */
    nsresult addParam(Expr* aExpr)
    {
        return mParams.AppendElement(aExpr) ?
            NS_OK : NS_ERROR_OUT_OF_MEMORY;
    }

    /**
     * Check if the number of parameters falls within a range.
     *
     * @param aParamCountMin minimum number of required parameters.
     * @param aParamCountMax maximum number of parameters. If aParamCountMax
     *                       is negative the maximum number is not checked.
     * @return boolean representing whether the number of parameters falls
     *         within the expected range or not.
     *
     * XXX txIEvalContext should be txIParseContest, bug 143291
     */
    virtual bool requireParams(int32_t aParamCountMin,
                                 int32_t aParamCountMax,
                                 txIEvalContext* aContext);

    TX_DECL_TOSTRING
    Expr* getSubExprAt(uint32_t aPos) MOZ_OVERRIDE;
    void setSubExprAt(uint32_t aPos, Expr* aExpr) MOZ_OVERRIDE;

protected:

    txOwningArray<Expr> mParams;

    /*
     * Evaluates the given Expression and converts its result to a number.
     */
    static nsresult evaluateToNumber(Expr* aExpr, txIEvalContext* aContext,
                                     double* aResult);

    /*
     * Evaluates the given Expression and converts its result to a NodeSet.
     * If the result is not a NodeSet an error is returned.
     */
    static nsresult evaluateToNodeSet(Expr* aExpr, txIEvalContext* aContext,
                                      txNodeSet** aResult);

    /**
     * Returns true if any argument is sensitive to the given context.
     */
    bool argsSensitiveTo(ContextSensitivity aContexts);


#ifdef TX_TO_STRING
    /*
     * Returns the name of the function as an atom.
     */
    virtual nsresult getNameAtom(nsIAtom** aAtom) = 0;
#endif
};

class txCoreFunctionCall : public FunctionCall
{
public:

    // This must be ordered in the same order as descriptTable in
    // txCoreFunctionCall.cpp. If you change one, change the other.
    enum eType {
        COUNT = 0,         // count()
        ID,                // id()
        LAST,              // last()
        LOCAL_NAME,        // local-name()
        NAMESPACE_URI,     // namespace-uri()
        NAME,              // name()
        POSITION,          // position()

        CONCAT,            // concat()
        CONTAINS,          // contains()
        NORMALIZE_SPACE,   // normalize-space()
        STARTS_WITH,       // starts-with()
        STRING,            // string()
        STRING_LENGTH,     // string-length()
        SUBSTRING,         // substring()
        SUBSTRING_AFTER,   // substring-after()
        SUBSTRING_BEFORE,  // substring-before()
        TRANSLATE,         // translate()

        NUMBER,            // number()
        ROUND,             // round()
        FLOOR,             // floor()
        CEILING,           // ceiling()
        SUM,               // sum()

        BOOLEAN,           // boolean()
        _FALSE,            // false()
        LANG,              // lang()
        _NOT,              // not()
        _TRUE              // true()
    };

    /*
     * Creates a txCoreFunctionCall of the given type
     */
    txCoreFunctionCall(eType aType) : mType(aType)
    {
    }

    TX_DECL_FUNCTION

    static bool getTypeFromAtom(nsIAtom* aName, eType& aType);

private:
    eType mType;
};


/*
 * This class represents a NodeTest as defined by the XPath spec
 */
class txNodeTest
{
public:
    txNodeTest()
    {
        MOZ_COUNT_CTOR(txNodeTest);
    }
    virtual ~txNodeTest()
    {
        MOZ_COUNT_DTOR(txNodeTest);
    }

    /*
     * Virtual methods
     * pretty much a txPattern, but not supposed to be used 
     * standalone. The NodeTest node() is different to the
     * Pattern "node()" (document node isn't matched)
     */
    virtual bool matches(const txXPathNode& aNode,
                           txIMatchContext* aContext) = 0;
    virtual double getDefaultPriority() = 0;

    /**
     * Returns the type of this nodetest.
     */
    enum NodeTestType {
        NAME_TEST,
        NODETYPE_TEST,
        OTHER_TEST
    };
    virtual NodeTestType getType()
    {
      return OTHER_TEST;
    }

    /**
     * Returns true if this expression is sensitive to *any* of
     * the requested flags.
     */
    virtual bool isSensitiveTo(Expr::ContextSensitivity aContext) = 0;

#ifdef TX_TO_STRING
    virtual void toString(nsAString& aDest) = 0;
#endif
};

#define TX_DECL_NODE_TEST \
    TX_DECL_TOSTRING \
    bool matches(const txXPathNode& aNode, txIMatchContext* aContext); \
    double getDefaultPriority(); \
    bool isSensitiveTo(Expr::ContextSensitivity aContext);

/*
 * This class represents a NameTest as defined by the XPath spec
 */
class txNameTest : public txNodeTest
{
public:
    /*
     * Creates a new txNameTest with the given type and the given
     * principal node type
     */
    txNameTest(nsIAtom* aPrefix, nsIAtom* aLocalName, int32_t aNSID,
               uint16_t aNodeType);

    NodeTestType getType() MOZ_OVERRIDE;

    TX_DECL_NODE_TEST

    nsCOMPtr<nsIAtom> mPrefix;
    nsCOMPtr<nsIAtom> mLocalName;
    int32_t mNamespace;
private:
    uint16_t mNodeType;
};

/*
 * This class represents a NodeType as defined by the XPath spec
 */
class txNodeTypeTest : public txNodeTest
{
public:
    enum NodeType {
        COMMENT_TYPE,
        TEXT_TYPE,
        PI_TYPE,
        NODE_TYPE
    };

    /*
     * Creates a new txNodeTypeTest of the given type
     */
    txNodeTypeTest(NodeType aNodeType)
        : mNodeType(aNodeType)
    {
    }

    /*
     * Sets the name of the node to match. Only availible for pi nodes
     */
    void setNodeName(const nsAString& aName)
    {
        mNodeName = do_GetAtom(aName);
    }

    NodeType getNodeTestType()
    {
        return mNodeType;
    }

    NodeTestType getType() MOZ_OVERRIDE;

    TX_DECL_NODE_TEST

private:
    NodeType mNodeType;
    nsCOMPtr<nsIAtom> mNodeName;
};

/**
 * Class representing a nodetest combined with a predicate. May only be used
 * if the predicate is not sensitive to the context-nodelist.
 */
class txPredicatedNodeTest : public txNodeTest
{
public:
    txPredicatedNodeTest(txNodeTest* aNodeTest, Expr* aPredicate);
    TX_DECL_NODE_TEST

private:
    nsAutoPtr<txNodeTest> mNodeTest;
    nsAutoPtr<Expr> mPredicate;
};

/**
 * Represents an ordered list of Predicates,
 * for use with Step and Filter Expressions
**/
class PredicateList  {
public:
    /**
     * Adds the given Expr to the list.
     * The ownership of the given Expr is passed over the PredicateList,
     * even on failure.
     * @param aExpr the Expr to add to the list
     * @return nsresult indicating out of memory
     */
    nsresult add(Expr* aExpr)
    {
        NS_ASSERTION(aExpr, "missing expression");
        return mPredicates.AppendElement(aExpr) ?
            NS_OK : NS_ERROR_OUT_OF_MEMORY;
    }

    nsresult evaluatePredicates(txNodeSet* aNodes, txIMatchContext* aContext);

    /**
     * Drops the first predicate without deleting it.
     */
    void dropFirst()
    {
        mPredicates.RemoveElementAt(0);
    }

    /**
     * returns true if this predicate list is empty
    **/
    bool isEmpty()
    {
        return mPredicates.IsEmpty();
    }

#ifdef TX_TO_STRING
    /**
     * Returns the String representation of this PredicateList.
     * @param dest the String to use when creating the String
     * representation. The String representation will be appended to
     * any data in the destination String, to allow cascading calls to
     * other #toString() methods for Expressions.
     * @return the String representation of this PredicateList.
    **/
    void toString(nsAString& dest);
#endif

protected:
    bool isSensitiveTo(Expr::ContextSensitivity aContext);
    Expr* getSubExprAt(uint32_t aPos)
    {
        return mPredicates.SafeElementAt(aPos);
    }
    void setSubExprAt(uint32_t aPos, Expr* aExpr)
    {
        NS_ASSERTION(aPos < mPredicates.Length(),
                     "setting bad subexpression index");
        mPredicates[aPos] = aExpr;
    }

    //-- list of predicates
    txOwningArray<Expr> mPredicates;
}; //-- PredicateList

class LocationStep : public Expr,
                     public PredicateList
{
public:
    enum LocationStepType {
        ANCESTOR_AXIS = 0,
        ANCESTOR_OR_SELF_AXIS,
        ATTRIBUTE_AXIS,
        CHILD_AXIS,
        DESCENDANT_AXIS,
        DESCENDANT_OR_SELF_AXIS,
        FOLLOWING_AXIS,
        FOLLOWING_SIBLING_AXIS,
        NAMESPACE_AXIS,
        PARENT_AXIS,
        PRECEDING_AXIS,
        PRECEDING_SIBLING_AXIS,
        SELF_AXIS
    };

    /**
     * Creates a new LocationStep using the given NodeExpr and Axis Identifier
     * @param nodeExpr the NodeExpr to use when matching Nodes
     * @param axisIdentifier the Axis Identifier in which to search for nodes
    **/
    LocationStep(txNodeTest* aNodeTest,
                 LocationStepType aAxisIdentifier)
        : mNodeTest(aNodeTest),
          mAxisIdentifier(aAxisIdentifier)
    {
    }

    TX_DECL_OPTIMIZABLE_EXPR

    txNodeTest* getNodeTest()
    {
        return mNodeTest;
    }
    void setNodeTest(txNodeTest* aNodeTest)
    {
        mNodeTest.forget();
        mNodeTest = aNodeTest;
    }
    LocationStepType getAxisIdentifier()
    {
        return mAxisIdentifier;
    }
    void setAxisIdentifier(LocationStepType aAxisIdentifier)
    {
        mAxisIdentifier = aAxisIdentifier;
    }

private:
    void fromDescendants(const txXPathNode& aNode, txIMatchContext* aCs,
                         txNodeSet* aNodes);
    void fromDescendantsRev(const txXPathNode& aNode, txIMatchContext* aCs,
                            txNodeSet* aNodes);

    nsAutoPtr<txNodeTest> mNodeTest;
    LocationStepType mAxisIdentifier;
};

class FilterExpr : public Expr,
                   public PredicateList
{
public:

    /**
     * Creates a new FilterExpr using the given Expr
     * @param expr the Expr to use for evaluation
     */
    FilterExpr(Expr* aExpr)
        : expr(aExpr)
    {
    }

    TX_DECL_EXPR

private:
    nsAutoPtr<Expr> expr;

}; //-- FilterExpr


class txLiteralExpr : public Expr {
public:
    txLiteralExpr(double aDbl)
        : mValue(new NumberResult(aDbl, nullptr))
    {
    }
    txLiteralExpr(const nsAString& aStr)
        : mValue(new StringResult(aStr, nullptr))
    {
    }
    txLiteralExpr(txAExprResult* aValue)
        : mValue(aValue)
    {
    }

    TX_DECL_EXPR

private:
    nsRefPtr<txAExprResult> mValue;
};

/**
 * Represents an UnaryExpr. Returns the negative value of its expr.
**/
class UnaryExpr : public Expr {

public:

    UnaryExpr(Expr* aExpr)
        : expr(aExpr)
    {
    }

    TX_DECL_EXPR

private:
    nsAutoPtr<Expr> expr;
}; //-- UnaryExpr

/**
 * Represents a BooleanExpr, a binary expression that
 * performs a boolean operation between its lvalue and rvalue.
**/
class BooleanExpr : public Expr
{
public:

    //-- BooleanExpr Types
    enum _BooleanExprType { AND = 1, OR };

     BooleanExpr(Expr* aLeftExpr, Expr* aRightExpr, short aOp)
         : leftExpr(aLeftExpr),
           rightExpr(aRightExpr),
           op(aOp)
    {
    }

    TX_DECL_EXPR

private:
    nsAutoPtr<Expr> leftExpr, rightExpr;
    short op;
}; //-- BooleanExpr

/**
 * Represents a MultiplicativeExpr, a binary expression that
 * performs a multiplicative operation between its lvalue and rvalue:
 *  *   : multiply
 * mod  : modulus
 * div  : divide
 *
**/
class txNumberExpr : public Expr
{
public:

    enum eOp { ADD, SUBTRACT, DIVIDE, MULTIPLY, MODULUS };

    txNumberExpr(Expr* aLeftExpr, Expr* aRightExpr, eOp aOp)
        : mLeftExpr(aLeftExpr),
          mRightExpr(aRightExpr),
          mOp(aOp)
    {
    }

    TX_DECL_EXPR

private:
    nsAutoPtr<Expr> mLeftExpr, mRightExpr;
    eOp mOp;
}; //-- MultiplicativeExpr

/**
 * Represents a RelationalExpr, an expression that compares its lvalue
 * to its rvalue using:
 * =  : equal to
 * <  : less than
 * >  : greater than
 * <= : less than or equal to
 * >= : greater than or equal to
 *
**/
class RelationalExpr : public Expr
{
public:
    enum RelationalExprType {
        EQUAL,
        NOT_EQUAL,
        LESS_THAN,
        GREATER_THAN,
        LESS_OR_EQUAL,
        GREATER_OR_EQUAL
    };

    RelationalExpr(Expr* aLeftExpr, Expr* aRightExpr, RelationalExprType aOp)
        : mLeftExpr(aLeftExpr),
          mRightExpr(aRightExpr),
          mOp(aOp)
    {
    }


    TX_DECL_EXPR

private:
    bool compareResults(txIEvalContext* aContext, txAExprResult* aLeft,
                          txAExprResult* aRight);

    nsAutoPtr<Expr> mLeftExpr;
    nsAutoPtr<Expr> mRightExpr;
    RelationalExprType mOp;
};

/**
 * VariableRefExpr
 * Represents a variable reference ($refname)
**/
class VariableRefExpr : public Expr {

public:

    VariableRefExpr(nsIAtom* aPrefix, nsIAtom* aLocalName, int32_t aNSID);

    TX_DECL_EXPR

private:
    nsCOMPtr<nsIAtom> mPrefix;
    nsCOMPtr<nsIAtom> mLocalName;
    int32_t mNamespace;
};

/**
 *  Represents a PathExpr
**/
class PathExpr : public Expr {

public:

    //-- Path Operators
    //-- RELATIVE_OP is the default
    //-- LF, changed from static const short to enum
    enum PathOperator { RELATIVE_OP, DESCENDANT_OP };

    /**
     * Adds the Expr to this PathExpr
     * The ownership of the given Expr is passed over the PathExpr,
     * even on failure.
     * @param aExpr the Expr to add to this PathExpr
     * @return nsresult indicating out of memory
     */
    nsresult addExpr(Expr* aExpr, PathOperator pathOp);

    /**
     * Removes and deletes the expression at the given index.
     */
    void deleteExprAt(uint32_t aPos)
    {
        NS_ASSERTION(aPos < mItems.Length(),
                     "killing bad expression index");
        mItems.RemoveElementAt(aPos);
    }

    TX_DECL_OPTIMIZABLE_EXPR

    PathOperator getPathOpAt(uint32_t aPos)
    {
        NS_ASSERTION(aPos < mItems.Length(), "getting bad pathop index");
        return mItems[aPos].pathOp;
    }
    void setPathOpAt(uint32_t aPos, PathOperator aPathOp)
    {
        NS_ASSERTION(aPos < mItems.Length(), "setting bad pathop index");
        mItems[aPos].pathOp = aPathOp;
    }

private:
    class PathExprItem {
    public:
        nsAutoPtr<Expr> expr;
        PathOperator pathOp;
    };

    nsTArray<PathExprItem> mItems;

    /*
     * Selects from the descendants of the context node
     * all nodes that match the Expr
     */
    nsresult evalDescendants(Expr* aStep, const txXPathNode& aNode,
                             txIMatchContext* aContext,
                             txNodeSet* resNodes);
};

/**
 * This class represents a RootExpr, which only matches the Document node
**/
class RootExpr : public Expr {
public:
    /**
     * Creates a new RootExpr
     */
    RootExpr()
#ifdef TX_TO_STRING
        : mSerialize(true)
#endif
    {
    }

    TX_DECL_EXPR

#ifdef TX_TO_STRING
public:
    void setSerialize(bool aSerialize)
    {
        mSerialize = aSerialize;
    }

private:
    // When a RootExpr is used in a PathExpr it shouldn't be serialized
    bool mSerialize;
#endif
}; //-- RootExpr

/**
 *  Represents a UnionExpr
**/
class UnionExpr : public Expr {
public:
    /**
     * Adds the PathExpr to this UnionExpr
     * The ownership of the given Expr is passed over the UnionExpr,
     * even on failure.
     * @param aExpr the Expr to add to this UnionExpr
     * @return nsresult indicating out of memory
     */
    nsresult addExpr(Expr* aExpr)
    {
        return mExpressions.AppendElement(aExpr) ?
            NS_OK : NS_ERROR_OUT_OF_MEMORY;
    }

    /**
     * Removes and deletes the expression at the given index.
     */
    void deleteExprAt(uint32_t aPos)
    {
        NS_ASSERTION(aPos < mExpressions.Length(),
                     "killing bad expression index");

        delete mExpressions[aPos];
        mExpressions.RemoveElementAt(aPos);
    }

    TX_DECL_OPTIMIZABLE_EXPR

private:

   txOwningArray<Expr> mExpressions;

}; //-- UnionExpr

/**
 * Class specializing in executing expressions like "@foo" where we are
 * interested in different result-types, and expressions like "@foo = 'hi'"
 */
class txNamedAttributeStep : public Expr
{
public:
    txNamedAttributeStep(int32_t aNsID, nsIAtom* aPrefix,
                         nsIAtom* aLocalName);

    TX_DECL_EXPR

private:
    int32_t mNamespace;
    nsCOMPtr<nsIAtom> mPrefix;
    nsCOMPtr<nsIAtom> mLocalName;
};

/**
 *
 */
class txUnionNodeTest : public txNodeTest
{
public:
    nsresult addNodeTest(txNodeTest* aNodeTest)
    {
        return mNodeTests.AppendElement(aNodeTest) ?
            NS_OK : NS_ERROR_OUT_OF_MEMORY;
    }

    TX_DECL_NODE_TEST

private:
    txOwningArray<txNodeTest> mNodeTests;
};

/**
 *  Expression that failed to parse
 */
class txErrorExpr : public Expr
{
public:
#ifdef TX_TO_STRING
    txErrorExpr(const nsAString& aStr)
      : mStr(aStr)
    {
    }
#endif

    TX_DECL_EXPR

#ifdef TX_TO_STRING
private:
    nsString mStr;
#endif
};

#endif