/**
 * Creates a PathExpr using the given txExprLexer
 * @param lexer the txExprLexer for retrieving Tokens
 */
nsresult
txExprParser::createUnionExpr(txExprLexer& lexer, txIParseContext* aContext,
                              Expr** aResult)
{
    *aResult = nullptr;

    nsAutoPtr<Expr> expr;
    nsresult rv = createPathExpr(lexer, aContext, getter_Transfers(expr));
    NS_ENSURE_SUCCESS(rv, rv);
    
    if (lexer.peek()->mType != Token::UNION_OP) {
        *aResult = expr.forget();
        return NS_OK;
    }

    nsAutoPtr<UnionExpr> unionExpr(new UnionExpr());

    rv = unionExpr->addExpr(expr);
    NS_ENSURE_SUCCESS(rv, rv);

    expr.forget();

    while (lexer.peek()->mType == Token::UNION_OP) {
        lexer.nextToken(); //-- eat token

        rv = createPathExpr(lexer, aContext, getter_Transfers(expr));
        NS_ENSURE_SUCCESS(rv, rv);

        rv = unionExpr->addExpr(expr.forget());
        NS_ENSURE_SUCCESS(rv, rv);
    }

    *aResult = unionExpr.forget();
    return NS_OK;
}

/**
 * Using the given lexer, parses the tokens if they represent a parameter list
 * If an error occurs a non-zero String pointer will be returned containing the
 * error message.
 * @param list, the List to add parameter expressions to
 * @param lexer the txExprLexer to use for parsing tokens
 * @return NS_OK if successful, or another rv otherwise
 */
nsresult
txExprParser::parseParameters(FunctionCall* aFnCall, txExprLexer& lexer,
                              txIParseContext* aContext)
{
    if (lexer.peek()->mType == Token::R_PAREN) {
        lexer.nextToken();
        return NS_OK;
    }

    nsAutoPtr<Expr> expr;
    nsresult rv = NS_OK;
    while (1) {
        rv = createExpr(lexer, aContext, getter_Transfers(expr));
        NS_ENSURE_SUCCESS(rv, rv);

        if (aFnCall) {
            rv = aFnCall->addParam(expr.forget());
            NS_ENSURE_SUCCESS(rv, rv);
        }
                    
        switch (lexer.peek()->mType) {
            case Token::R_PAREN :
                lexer.nextToken();
                return NS_OK;
            case Token::COMMA: //-- param separator
                lexer.nextToken();
                break;
            default:
                return NS_ERROR_XPATH_PAREN_EXPECTED;
        }
    }

    NS_NOTREACHED("internal xpath parser error");
    return NS_ERROR_UNEXPECTED;
}

nsresult txPatternParser::createUnionPattern(txExprLexer& aLexer,
                                             txIParseContext* aContext,
                                             txPattern*& aPattern)
{
    nsresult rv = NS_OK;
    txPattern* locPath = 0;

    rv = createLocPathPattern(aLexer, aContext, locPath);
    if (NS_FAILED(rv))
        return rv;

    Token::Type type = aLexer.peek()->mType;
    if (type == Token::END) {
        aPattern = locPath;
        return NS_OK;
    }

    if (type != Token::UNION_OP) {
        delete locPath;
        return NS_ERROR_XPATH_PARSE_FAILURE;
    }

    txUnionPattern* unionPattern = new txUnionPattern();
    rv = unionPattern->addPattern(locPath);
#if 0 // XXX addPattern can't fail yet, it doesn't check for mem
    if (NS_FAILED(rv)) {
        delete unionPattern;
        delete locPath;
        return rv;
    }
#endif

    aLexer.nextToken();
    do {
        rv = createLocPathPattern(aLexer, aContext, locPath);
        if (NS_FAILED(rv)) {
            delete unionPattern;
            return rv;
        }
        rv = unionPattern->addPattern(locPath);
#if 0 // XXX addPattern can't fail yet, it doesn't check for mem
        if (NS_FAILED(rv)) {
            delete unionPattern;
            delete locPath;
            return rv;
        }
#endif
        type = aLexer.nextToken()->mType;
    } while (type == Token::UNION_OP);

    if (type != Token::END) {
        delete unionPattern;
        return NS_ERROR_XPATH_PARSE_FAILURE;
    }

    aPattern = unionPattern;
    return NS_OK;
}

nsresult txPatternParser::createStepPattern(txExprLexer& aLexer,
                                            txIParseContext* aContext,
                                            txPattern*& aPattern)
{
    nsresult rv = NS_OK;
    bool isAttr = false;
    Token* tok = aLexer.peek();
    if (tok->mType == Token::AXIS_IDENTIFIER) {
        if (TX_StringEqualsAtom(tok->Value(), nsGkAtoms::attribute)) {
            isAttr = true;
        }
        else if (!TX_StringEqualsAtom(tok->Value(), nsGkAtoms::child)) {
            // all done already for CHILD_AXIS, for all others
            // XXX report unexpected axis error
            return NS_ERROR_XPATH_PARSE_FAILURE;
        }
        aLexer.nextToken();
    }
    else if (tok->mType == Token::AT_SIGN) {
        aLexer.nextToken();
        isAttr = true;
    }

    txNodeTest* nodeTest;
    if (aLexer.peek()->mType == Token::CNAME) {
        tok = aLexer.nextToken();

        // resolve QName
        RefPtr<nsAtom> prefix, lName;
        int32_t nspace;
        rv = resolveQName(tok->Value(), getter_AddRefs(prefix), aContext,
                          getter_AddRefs(lName), nspace, true);
        if (NS_FAILED(rv)) {
            // XXX error report namespace resolve failed
            return rv;
        }

        uint16_t nodeType = isAttr ?
                            (uint16_t)txXPathNodeType::ATTRIBUTE_NODE :
                            (uint16_t)txXPathNodeType::ELEMENT_NODE;
        nodeTest = new txNameTest(prefix, lName, nspace, nodeType);
    }
    else {
        rv = createNodeTypeTest(aLexer, &nodeTest);
        NS_ENSURE_SUCCESS(rv, rv);
    }

    nsAutoPtr<txStepPattern> step(new txStepPattern(nodeTest, isAttr));
    rv = parsePredicates(step, aLexer, aContext);
    NS_ENSURE_SUCCESS(rv, rv);

    aPattern = step.forget();

    return NS_OK;
}

nsresult txPatternParser::createIdPattern(txExprLexer& aLexer,
                                          txPattern*& aPattern) {
  // check for '(' Literal ')'
  if (aLexer.peek()->mType != Token::LITERAL)
    return NS_ERROR_XPATH_PARSE_FAILURE;
  const nsDependentSubstring& value = aLexer.nextToken()->Value();
  if (aLexer.nextToken()->mType != Token::R_PAREN)
    return NS_ERROR_XPATH_PARSE_FAILURE;
  aPattern = new txIdPattern(value);
  return NS_OK;
}

nsresult
txExprParser::createFunctionCall(txExprLexer& lexer, txIParseContext* aContext,
                                 Expr** aResult)
{
    *aResult = nsnull;

    nsAutoPtr<FunctionCall> fnCall;

    Token* tok = lexer.nextToken();
    NS_ASSERTION(tok->mType == Token::FUNCTION_NAME_AND_PAREN,
                 "FunctionCall expected");

    //-- compare function names
    nsCOMPtr<nsIAtom> prefix, lName;
    PRInt32 namespaceID;
    nsresult rv = resolveQName(tok->Value(), getter_AddRefs(prefix), aContext,
                               getter_AddRefs(lName), namespaceID);
    NS_ENSURE_SUCCESS(rv, rv);

    txCoreFunctionCall::eType type;
    if (namespaceID == kNameSpaceID_None &&
        txCoreFunctionCall::getTypeFromAtom(lName, type)) {
        // It is a known built-in function.
        fnCall = new txCoreFunctionCall(type);
        NS_ENSURE_TRUE(fnCall, NS_ERROR_OUT_OF_MEMORY);
    }

    // check extension functions and xslt
    if (!fnCall) {
        rv = aContext->resolveFunctionCall(lName, namespaceID,
                                           getter_Transfers(fnCall));

        if (rv == NS_ERROR_NOT_IMPLEMENTED) {
            // this should just happen for unparsed-entity-uri()
            NS_ASSERTION(!fnCall, "Now is it implemented or not?");
            rv = parseParameters(0, lexer, aContext);
            NS_ENSURE_SUCCESS(rv, rv);

            *aResult = new txLiteralExpr(tok->Value() +
                                         NS_LITERAL_STRING(" not implemented."));
            NS_ENSURE_TRUE(*aResult, NS_ERROR_OUT_OF_MEMORY);

            return NS_OK;
        }

        NS_ENSURE_SUCCESS(rv, rv);
    }

    //-- handle parametes
    rv = parseParameters(fnCall, lexer, aContext);
    NS_ENSURE_SUCCESS(rv, rv);

    *aResult = fnCall.forget();
    return NS_OK;
}

nsresult txPatternParser::createKeyPattern(txExprLexer& aLexer,
                                           txIParseContext* aContext,
                                           txPattern*& aPattern)
{
    // check for '(' Literal, Literal ')'
    if (aLexer.peek()->mType != Token::LITERAL)
        return NS_ERROR_XPATH_PARSE_FAILURE;
    const nsDependentSubstring& key =
        aLexer.nextToken()->Value();
    if (aLexer.nextToken()->mType != Token::COMMA &&
        aLexer.peek()->mType != Token::LITERAL)
        return NS_ERROR_XPATH_PARSE_FAILURE;
    const nsDependentSubstring& value =
        aLexer.nextToken()->Value();
    if (aLexer.nextToken()->mType != Token::R_PAREN)
        return NS_ERROR_XPATH_PARSE_FAILURE;

    if (!aContext->allowed(txIParseContext::KEY_FUNCTION))
        return NS_ERROR_XSLT_CALL_TO_KEY_NOT_ALLOWED;

    const char16_t* colon;
    if (!XMLUtils::isValidQName(key, &colon)) {
        return NS_ERROR_XPATH_PARSE_FAILURE;
    }
    RefPtr<nsAtom> prefix, localName;
    int32_t namespaceID;
    nsresult rv = resolveQName(key, getter_AddRefs(prefix), aContext,
                               getter_AddRefs(localName), namespaceID);
    if (NS_FAILED(rv))
        return rv;

    aPattern  = new txKeyPattern(prefix, localName, namespaceID, value);
    return NS_OK;
}

nsresult txPatternParser::createKeyPattern(txExprLexer& aLexer,
                                           txIParseContext* aContext,
                                           txPattern*& aPattern)
{
    // check for '(' Literal, Literal ')'
    if (aLexer.peek()->mType != Token::LITERAL)
        return NS_ERROR_XPATH_PARSE_FAILURE;
    const nsDependentSubstring& key =
        aLexer.nextToken()->Value();
    if (aLexer.nextToken()->mType != Token::COMMA && 
        aLexer.peek()->mType != Token::LITERAL)
        return NS_ERROR_XPATH_PARSE_FAILURE;
    const nsDependentSubstring& value =
        aLexer.nextToken()->Value();
    if (aLexer.nextToken()->mType != Token::R_PAREN)
        return NS_ERROR_XPATH_PARSE_FAILURE;

    const PRUnichar* colon;
    if (!XMLUtils::isValidQName(PromiseFlatString(key), &colon))
        return NS_ERROR_XPATH_PARSE_FAILURE;
    nsCOMPtr<nsIAtom> prefix, localName;
    PRInt32 namespaceID;
    nsresult rv = resolveQName(key, getter_AddRefs(prefix), aContext,
                               getter_AddRefs(localName), namespaceID);
    if (NS_FAILED(rv))
        return rv;

    aPattern  = new txKeyPattern(prefix, localName, namespaceID, value);

    return aPattern ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
}

/**
 * This method only handles comment(), text(), processing-instructing()
 * and node()
 */
nsresult
txExprParser::createNodeTypeTest(txExprLexer& lexer, txNodeTest** aTest)
{
    *aTest = 0;
    nsAutoPtr<txNodeTypeTest> nodeTest;

    Token* nodeTok = lexer.peek();

    switch (nodeTok->mType) {
        case Token::COMMENT_AND_PAREN:
            lexer.nextToken();
            nodeTest = new txNodeTypeTest(txNodeTypeTest::COMMENT_TYPE);
            break;
        case Token::NODE_AND_PAREN:
            lexer.nextToken();
            nodeTest = new txNodeTypeTest(txNodeTypeTest::NODE_TYPE);
            break;
        case Token::PROC_INST_AND_PAREN:
            lexer.nextToken();
            nodeTest = new txNodeTypeTest(txNodeTypeTest::PI_TYPE);
            break;
        case Token::TEXT_AND_PAREN:
            lexer.nextToken();
            nodeTest = new txNodeTypeTest(txNodeTypeTest::TEXT_TYPE);
            break;
        default:
            return NS_ERROR_XPATH_NO_NODE_TYPE_TEST;
    }

    NS_ENSURE_TRUE(nodeTest, NS_ERROR_OUT_OF_MEMORY);

    if (nodeTok->mType == Token::PROC_INST_AND_PAREN &&
        lexer.peek()->mType == Token::LITERAL) {
        Token* tok = lexer.nextToken();
        nodeTest->setNodeName(tok->Value());
    }
    if (lexer.peek()->mType != Token::R_PAREN) {
        return NS_ERROR_XPATH_PAREN_EXPECTED;
    }
    lexer.nextToken();

    *aTest = nodeTest.forget();
    return NS_OK;
}

nsresult
txExprParser::createExpr(txExprLexer& lexer, txIParseContext* aContext,
                         Expr** aResult)
{
    *aResult = nsnull;

    nsresult rv = NS_OK;
    MBool done = MB_FALSE;

    nsAutoPtr<Expr> expr;

    txStack exprs;
    txStack ops;

    while (!done) {

        MBool unary = MB_FALSE;
        while (lexer.peek()->mType == Token::SUBTRACTION_OP) {
            unary = !unary;
            lexer.nextToken();
        }

        rv = createUnionExpr(lexer, aContext, getter_Transfers(expr));
        if (NS_FAILED(rv)) {
            break;
        }

        if (unary) {
            Expr* unaryExpr = new UnaryExpr(expr);
            if (!unaryExpr) {
                rv = NS_ERROR_OUT_OF_MEMORY;
                break;
            }
            
            expr.forget();
            expr = unaryExpr;
        }

        Token* tok = lexer.nextToken();
        short tokPrecedence = precedence(tok);
        if (tokPrecedence != 0) {
            while (!exprs.isEmpty() && tokPrecedence
                   <= precedence(static_cast<Token*>(ops.peek()))) {
                // can't use expr as argument due to order of evaluation
                nsAutoPtr<Expr> left(static_cast<Expr*>(exprs.pop()));
                nsAutoPtr<Expr> right(expr);
                rv = createBinaryExpr(left, right,
                                      static_cast<Token*>(ops.pop()),
                                      getter_Transfers(expr));
                if (NS_FAILED(rv)) {
                    done = PR_TRUE;
                    break;
                }
            }
            exprs.push(expr.forget());
            ops.push(tok);
        }
        else {
            lexer.pushBack();
            done = PR_TRUE;
        }
    }

    while (NS_SUCCEEDED(rv) && !exprs.isEmpty()) {
        nsAutoPtr<Expr> left(static_cast<Expr*>(exprs.pop()));
        nsAutoPtr<Expr> right(expr);
        rv = createBinaryExpr(left, right, static_cast<Token*>(ops.pop()),
                              getter_Transfers(expr));
    }
    // clean up on error
    while (!exprs.isEmpty()) {
        delete static_cast<Expr*>(exprs.pop());
    }
    NS_ENSURE_SUCCESS(rv, rv);

    *aResult = expr.forget();
    return NS_OK;
}

nsresult txPatternParser::createLocPathPattern(txExprLexer& aLexer,
                                               txIParseContext* aContext,
                                               txPattern*& aPattern)
{
    nsresult rv = NS_OK;

    bool isChild = true;
    bool isAbsolute = false;
    txPattern* stepPattern = 0;
    txLocPathPattern* pathPattern = 0;

    Token::Type type = aLexer.peek()->mType;
    switch (type) {
        case Token::ANCESTOR_OP:
            isChild = false;
            isAbsolute = true;
            aLexer.nextToken();
            break;
        case Token::PARENT_OP:
            aLexer.nextToken();
            isAbsolute = true;
            if (aLexer.peek()->mType == Token::END ||
                aLexer.peek()->mType == Token::UNION_OP) {
                aPattern = new txRootPattern();
                return NS_OK;
            }
            break;
        case Token::FUNCTION_NAME_AND_PAREN:
            // id(Literal) or key(Literal, Literal)
            {
                RefPtr<nsAtom> nameAtom =
                    NS_Atomize(aLexer.nextToken()->Value());
                if (nameAtom == nsGkAtoms::id) {
                    rv = createIdPattern(aLexer, stepPattern);
                }
                else if (nameAtom == nsGkAtoms::key) {
                    rv = createKeyPattern(aLexer, aContext, stepPattern);
                }
                if (NS_FAILED(rv))
                    return rv;
            }
            break;
        default:
            break;
    }
    if (!stepPattern) {
        rv = createStepPattern(aLexer, aContext, stepPattern);
        if (NS_FAILED(rv))
            return rv;
    }

    type = aLexer.peek()->mType;
    if (!isAbsolute && type != Token::PARENT_OP
        && type != Token::ANCESTOR_OP) {
        aPattern = stepPattern;
        return NS_OK;
    }

    pathPattern = new txLocPathPattern();
    if (isAbsolute) {
        txRootPattern* root = new txRootPattern();
#ifdef TX_TO_STRING
        root->setSerialize(false);
#endif

        rv = pathPattern->addStep(root, isChild);
        if (NS_FAILED(rv)) {
            delete stepPattern;
            delete pathPattern;
            delete root;
            return NS_ERROR_OUT_OF_MEMORY;
        }
    }

    rv = pathPattern->addStep(stepPattern, isChild);
    if (NS_FAILED(rv)) {
        delete stepPattern;
        delete pathPattern;
        return NS_ERROR_OUT_OF_MEMORY;
    }
    stepPattern = 0; // stepPattern is part of pathPattern now

    while (type == Token::PARENT_OP || type == Token::ANCESTOR_OP) {
        isChild = type == Token::PARENT_OP;
        aLexer.nextToken();
        rv = createStepPattern(aLexer, aContext, stepPattern);
        if (NS_FAILED(rv)) {
            delete pathPattern;
            return rv;
        }
        rv = pathPattern->addStep(stepPattern, isChild);
        if (NS_FAILED(rv)) {
            delete stepPattern;
            delete pathPattern;
            return NS_ERROR_OUT_OF_MEMORY;
        }
        stepPattern = 0; // stepPattern is part of pathPattern now
        type = aLexer.peek()->mType;
    }
    aPattern = pathPattern;
//.........这里部分代码省略.........

nsresult txPatternParser::createStepPattern(txExprLexer& aLexer,
                                            txIParseContext* aContext,
                                            txPattern*& aPattern)
{
    nsresult rv = NS_OK;
    MBool isAttr = MB_FALSE;
    Token* tok = aLexer.peek();
    if (tok->mType == Token::AXIS_IDENTIFIER) {
        if (TX_StringEqualsAtom(tok->Value(), txXPathAtoms::attribute)) {
            isAttr = MB_TRUE;
        }
        else if (!TX_StringEqualsAtom(tok->Value(), txXPathAtoms::child)) {
            // all done already for CHILD_AXIS, for all others
            // XXX report unexpected axis error
            return NS_ERROR_XPATH_PARSE_FAILURE;
        }
        aLexer.nextToken();
    }
    else if (tok->mType == Token::AT_SIGN) {
        aLexer.nextToken();
        isAttr = MB_TRUE;
    }
    tok = aLexer.nextToken();

    txNodeTest* nodeTest;
    if (tok->mType == Token::CNAME) {
        // resolve QName
        nsCOMPtr<nsIAtom> prefix, lName;
        PRInt32 nspace;
        rv = resolveQName(tok->Value(), getter_AddRefs(prefix), aContext,
                          getter_AddRefs(lName), nspace, PR_TRUE);
        if (NS_FAILED(rv)) {
            // XXX error report namespace resolve failed
            return rv;
        }

        PRUint16 nodeType = isAttr ?
                            (PRUint16)txXPathNodeType::ATTRIBUTE_NODE :
                            (PRUint16)txXPathNodeType::ELEMENT_NODE;
        nodeTest = new txNameTest(prefix, lName, nspace, nodeType);
        if (!nodeTest) {
            return NS_ERROR_OUT_OF_MEMORY;
        }
    }
    else {
        aLexer.pushBack();
        rv = createNodeTypeTest(aLexer, &nodeTest);
        NS_ENSURE_SUCCESS(rv, rv);
    }

    nsAutoPtr<txStepPattern> step(new txStepPattern(nodeTest, isAttr));
    if (!step) {
        delete nodeTest;
        return NS_ERROR_OUT_OF_MEMORY;
    }

    rv = parsePredicates(step, aLexer, aContext);
    NS_ENSURE_SUCCESS(rv, rv);

    aPattern = step.forget();

    return NS_OK;
}

nsresult
txExprParser::createFilterOrStep(txExprLexer& lexer, txIParseContext* aContext,
                                 Expr** aResult)
{
    *aResult = nullptr;

    nsresult rv = NS_OK;
    Token* tok = lexer.peek();

    nsAutoPtr<Expr> expr;
    switch (tok->mType) {
        case Token::FUNCTION_NAME_AND_PAREN:
            rv = createFunctionCall(lexer, aContext, getter_Transfers(expr));
            NS_ENSURE_SUCCESS(rv, rv);
            break;
        case Token::VAR_REFERENCE :
            lexer.nextToken();
            {
                nsCOMPtr<nsIAtom> prefix, lName;
                int32_t nspace;
                nsresult rv = resolveQName(tok->Value(), getter_AddRefs(prefix),
                                           aContext, getter_AddRefs(lName),
                                           nspace);
                NS_ENSURE_SUCCESS(rv, rv);
                expr = new VariableRefExpr(prefix, lName, nspace);
            }
            break;
        case Token::L_PAREN:
            lexer.nextToken();
            rv = createExpr(lexer, aContext, getter_Transfers(expr));
            NS_ENSURE_SUCCESS(rv, rv);

            if (lexer.peek()->mType != Token::R_PAREN) {
                return NS_ERROR_XPATH_PAREN_EXPECTED;
            }
            lexer.nextToken();
            break;
        case Token::LITERAL :
            lexer.nextToken();
            expr = new txLiteralExpr(tok->Value());
            break;
        case Token::NUMBER:
        {
            lexer.nextToken();
            expr = new txLiteralExpr(txDouble::toDouble(tok->Value()));
            break;
        }
        default:
            return createLocationStep(lexer, aContext, aResult);
    }

    if (lexer.peek()->mType == Token::L_BRACKET) {
        nsAutoPtr<FilterExpr> filterExpr(new FilterExpr(expr));

        expr.forget();

        //-- handle predicates
        rv = parsePredicates(filterExpr, lexer, aContext);
        NS_ENSURE_SUCCESS(rv, rv);
        expr = filterExpr.forget();
    }

    *aResult = expr.forget();
    return NS_OK;
}

/**
 * Creates a PathExpr using the given txExprLexer
 * @param lexer the txExprLexer for retrieving Tokens
 */
nsresult
txExprParser::createPathExpr(txExprLexer& lexer, txIParseContext* aContext,
                             Expr** aResult)
{
    *aResult = nullptr;

    nsAutoPtr<Expr> expr;

    Token* tok = lexer.peek();

    // is this a root expression?
    if (tok->mType == Token::PARENT_OP) {
        if (!isLocationStepToken(lexer.peekAhead())) {
            lexer.nextToken();
            *aResult = new RootExpr();
            return NS_OK;
        }
    }

    // parse first step (possibly a FilterExpr)
    nsresult rv = NS_OK;
    if (tok->mType != Token::PARENT_OP &&
        tok->mType != Token::ANCESTOR_OP) {
        rv = createFilterOrStep(lexer, aContext, getter_Transfers(expr));
        NS_ENSURE_SUCCESS(rv, rv);

        // is this a singlestep path expression?
        tok = lexer.peek();
        if (tok->mType != Token::PARENT_OP &&
            tok->mType != Token::ANCESTOR_OP) {
            *aResult = expr.forget();
            return NS_OK;
        }
    }
    else {
        expr = new RootExpr();

#ifdef TX_TO_STRING
        static_cast<RootExpr*>(expr.get())->setSerialize(false);
#endif
    }
    
    // We have a PathExpr containing several steps
    nsAutoPtr<PathExpr> pathExpr(new PathExpr());

    rv = pathExpr->addExpr(expr, PathExpr::RELATIVE_OP);
    NS_ENSURE_SUCCESS(rv, rv);

    expr.forget();

    // this is ugly
    while (1) {
        PathExpr::PathOperator pathOp;
        switch (lexer.peek()->mType) {
            case Token::ANCESTOR_OP :
                pathOp = PathExpr::DESCENDANT_OP;
                break;
            case Token::PARENT_OP :
                pathOp = PathExpr::RELATIVE_OP;
                break;
            default:
                *aResult = pathExpr.forget();
                return NS_OK;
        }
        lexer.nextToken();

        rv = createLocationStep(lexer, aContext, getter_Transfers(expr));
        NS_ENSURE_SUCCESS(rv, rv);

        rv = pathExpr->addExpr(expr, pathOp);
        NS_ENSURE_SUCCESS(rv, rv);

        expr.forget();
    }
    NS_NOTREACHED("internal xpath parser error");
    return NS_ERROR_UNEXPECTED;
}

nsresult
txExprParser::createLocationStep(txExprLexer& lexer, txIParseContext* aContext,
                                 Expr** aExpr)
{
    *aExpr = nullptr;

    //-- child axis is default
    LocationStep::LocationStepType axisIdentifier = LocationStep::CHILD_AXIS;
    nsAutoPtr<txNodeTest> nodeTest;

    //-- get Axis Identifier or AbbreviatedStep, if present
    Token* tok = lexer.peek();
    switch (tok->mType) {
        case Token::AXIS_IDENTIFIER:
        {
            //-- eat token
            lexer.nextToken();
            nsCOMPtr<nsIAtom> axis = do_GetAtom(tok->Value());
            if (axis == nsGkAtoms::ancestor) {
                axisIdentifier = LocationStep::ANCESTOR_AXIS;
            }
            else if (axis == nsGkAtoms::ancestorOrSelf) {
                axisIdentifier = LocationStep::ANCESTOR_OR_SELF_AXIS;
            }
            else if (axis == nsGkAtoms::attribute) {
                axisIdentifier = LocationStep::ATTRIBUTE_AXIS;
            }
            else if (axis == nsGkAtoms::child) {
                axisIdentifier = LocationStep::CHILD_AXIS;
            }
            else if (axis == nsGkAtoms::descendant) {
                axisIdentifier = LocationStep::DESCENDANT_AXIS;
            }
            else if (axis == nsGkAtoms::descendantOrSelf) {
                axisIdentifier = LocationStep::DESCENDANT_OR_SELF_AXIS;
            }
            else if (axis == nsGkAtoms::following) {
                axisIdentifier = LocationStep::FOLLOWING_AXIS;
            }
            else if (axis == nsGkAtoms::followingSibling) {
                axisIdentifier = LocationStep::FOLLOWING_SIBLING_AXIS;
            }
            else if (axis == nsGkAtoms::_namespace) {
                axisIdentifier = LocationStep::NAMESPACE_AXIS;
            }
            else if (axis == nsGkAtoms::parent) {
                axisIdentifier = LocationStep::PARENT_AXIS;
            }
            else if (axis == nsGkAtoms::preceding) {
                axisIdentifier = LocationStep::PRECEDING_AXIS;
            }
            else if (axis == nsGkAtoms::precedingSibling) {
                axisIdentifier = LocationStep::PRECEDING_SIBLING_AXIS;
            }
            else if (axis == nsGkAtoms::self) {
                axisIdentifier = LocationStep::SELF_AXIS;
            }
            else {
                return NS_ERROR_XPATH_INVALID_AXIS;
            }
            break;
        }
        case Token::AT_SIGN:
            //-- eat token
            lexer.nextToken();
            axisIdentifier = LocationStep::ATTRIBUTE_AXIS;
            break;
        case Token::PARENT_NODE :
            //-- eat token
            lexer.nextToken();
            axisIdentifier = LocationStep::PARENT_AXIS;
            nodeTest = new txNodeTypeTest(txNodeTypeTest::NODE_TYPE);
            break;
        case Token::SELF_NODE :
            //-- eat token
            lexer.nextToken();
            axisIdentifier = LocationStep::SELF_AXIS;
            nodeTest = new txNodeTypeTest(txNodeTypeTest::NODE_TYPE);
            break;
        default:
            break;
    }

    //-- get NodeTest unless an AbbreviatedStep was found
    nsresult rv = NS_OK;
    if (!nodeTest) {
        tok = lexer.peek();

        if (tok->mType == Token::CNAME) {
            lexer.nextToken();
            // resolve QName
            nsCOMPtr<nsIAtom> prefix, lName;
            int32_t nspace;
            rv = resolveQName(tok->Value(), getter_AddRefs(prefix),
                              aContext, getter_AddRefs(lName),
                              nspace, true);
            NS_ENSURE_SUCCESS(rv, rv);

            nodeTest =
              new txNameTest(prefix, lName, nspace,
//.........这里部分代码省略.........