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The XSLT and XQuery Processor
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// 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/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr;
import net.sf.saxon.Configuration;
import net.sf.saxon.expr.parser.*;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.pattern.AnchorPattern;
import net.sf.saxon.pattern.Pattern;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.SingletonIterator;
import net.sf.saxon.type.AnyItemType;
import net.sf.saxon.type.ErrorType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.UType;
import net.sf.saxon.value.SequenceType;
/**
* This class represents the expression "(dot)", which always returns the context item.
* This may be a AtomicValue or a Node.
*/
public class ContextItemExpression extends Expression {
private ContextItemStaticInfo staticInfo = ContextItemStaticInfo.DEFAULT;
private String errorCodeForAbsentContext = "XPDY0002";
private boolean absentContextIsTypeError = false; // absurdly, but that's what the spec says
/**
* Create the expression
*/
public ContextItemExpression() {
}
/**
* Get a name identifying the kind of expression, in terms meaningful to a user.
*
* @return a name identifying the kind of expression, in terms meaningful to a user.
* The name will always be in the form of a lexical XML QName, and should match the name used
* in explain() output displaying the expression.
*/
@Override
public String getExpressionName() {
return "dot";
}
/**
* Create a clone copy of this expression
*
* @return a copy of this expression
* @param rebindings variables that must be re-bound
*/
/*@NotNull*/
@Override
public Expression copy(RebindingMap rebindings) {
ContextItemExpression cie2 = new ContextItemExpression();
cie2.staticInfo = staticInfo;
cie2.setErrorCodeForUndefinedContext(errorCodeForAbsentContext, false);
ExpressionTool.copyLocationInfo(this, cie2);
return cie2;
}
public void setErrorCodeForUndefinedContext(String errorCode, boolean isTypeError) {
errorCodeForAbsentContext = errorCode;
absentContextIsTypeError = isTypeError;
}
public String getErrorCodeForUndefinedContext() {
return errorCodeForAbsentContext;
}
/**
* Set static information about the context item
* @param info static information about the context item
*/
public void setStaticInfo(ContextItemStaticInfo info) {
staticInfo = info;
}
/**
* Type-check the expression.
*/
/*@NotNull*/
@Override
public Expression typeCheck(ExpressionVisitor visitor, /*@Nullable*/ ContextItemStaticInfo contextInfo) throws XPathException {
if (contextInfo.getItemType() == ErrorType.getInstance()) {
visitor.issueWarning("Evaluation will always fail: there is no context item", getLocation());
ErrorExpression ee = new ErrorExpression(
"There is no context item",
getErrorCodeForUndefinedContext(),
absentContextIsTypeError);
ee.setOriginalExpression(this);
ExpressionTool.copyLocationInfo(this, ee);
return ee;
} else {
staticInfo = contextInfo;
}
return this;
}
/**
* Perform optimisation of an expression and its subexpressions.
* This method is called after all references to functions and variables have been resolved
* to the declaration of the function or variable, and after all type checking has been done.
*
* @param visitor an expression visitor
* @param contextItemType the static type of "." at the point where this expression is invoked.
* The parameter is set to null if it is known statically that the context item will be undefined.
* If the type of the context item is not known statically, the argument is set to
* {@link net.sf.saxon.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
@Override
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException {
// In XSLT, we don't catch this error at the typeCheck() phase because it's done one XPath expression
// at a time. So we repeat the check here.
if (contextItemType == null) {
XPathException err = new XPathException("The context item is undefined at this point");
err.setErrorCode(getErrorCodeForUndefinedContext());
err.setIsTypeError(absentContextIsTypeError);
err.setLocation(getLocation());
throw err;
}
return this;
}
/**
* Determine the item type
*/
/*@NotNull*/
@Override
public ItemType getItemType() {
return staticInfo.getItemType();
}
/**
* Get the static type of the expression as a UType, following precisely the type
* inference rules defined in the XSLT 3.0 specification.
*
* @param contextItemType the static type of the context item
* @return the static item type of the expression according to the XSLT 3.0 defined rules
*/
@Override
public UType getStaticUType(UType contextItemType) {
return contextItemType;
}
/**
* Ask whether the context item may possibly be undefined
*
* @return true if it might be undefined
*/
public boolean isContextPossiblyUndefined() {
return staticInfo.isPossiblyAbsent();
}
/**
* Get the static cardinality
*/
@Override
protected int computeCardinality() {
return StaticProperty.EXACTLY_ONE;
}
/**
* Determine the special properties of this expression
*
* @return the value {@link StaticProperty#NO_NODES_NEWLY_CREATED}
*/
@Override
protected int computeSpecialProperties() {
int p = super.computeSpecialProperties();
return p | StaticProperty.NO_NODES_NEWLY_CREATED | StaticProperty.CONTEXT_DOCUMENT_NODESET;
}
@Override
public int getImplementationMethod() {
return EVALUATE_METHOD;
}
/**
* Is this expression the same as another expression?
*/
public boolean equals(Object other) {
return other instanceof ContextItemExpression;
}
/**
* get HashCode for comparing two expressions
*/
@Override
protected int computeHashCode() {
return "ContextItemExpression".hashCode();
}
@Override
public int getIntrinsicDependencies() {
return StaticProperty.DEPENDS_ON_CONTEXT_ITEM;
}
/**
* Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited
* by an expression in a source tree.
* The default implementation of this method assumes that an expression does no navigation other than
* the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the
* same context as the containing expression. The method must be overridden for any expression
* where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression,
* and RootExpression (because they perform navigation), and for the doc(), document(), and collection()
* functions because they create a new navigation root. Implementations also exist for PathExpression and
* FilterExpression because they have subexpressions that are evaluated in a different context from the
* calling expression.
*
* @param pathMap the PathMap to which the expression should be added
* @param pathMapNodeSet the PathMapNodeSet to which the paths embodied in this expression should be added
* @return the pathMapNodeSet representing the points in the source document that are both reachable by this
* expression, and that represent possible results of this expression. For an expression that does
* navigation, it represents the end of the arc in the path map that describes the navigation route. For other
* expressions, it is the same as the input pathMapNode.
*/
@Override
public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) {
if (pathMapNodeSet == null) {
pathMapNodeSet = new PathMap.PathMapNodeSet(pathMap.makeNewRoot(this));
}
return pathMapNodeSet;
}
/**
* Determine whether the expression can be evaluated without reference to the part of the context
* document outside the subtree rooted at the context node.
*
* @return true if the expression has no dependencies on the context node, or if the only dependencies
* on the context node are downward selections using the self, child, descendant, attribute, and namespace
* axes.
*/
@Override
public boolean isSubtreeExpression() {
return true;
}
@Override
public int getNetCost() {
return 0;
}
/**
* Convert this expression to an equivalent XSLT pattern
*
* @param config the Saxon configuration
* @return the equivalent pattern
* @throws net.sf.saxon.trans.XPathException
* if conversion is not possible
*/
@Override
public Pattern toPattern(Configuration config) throws XPathException {
return AnchorPattern.getInstance();
}
/**
* Get the (partial) name of a class that supports streaming of this kind of expression
*
* @return the partial name of a class that can be instantiated to provide streaming support in Saxon-EE,
* or null if there is no such class
*/
@Override
public String getStreamerName() {
return "ContextItemExpr";
}
/**
* Iterate over the value of the expression
*/
/*@NotNull*/
@Override
public SequenceIterator iterate(XPathContext context) throws XPathException {
Item item = context.getContextItem();
if (item == null) {
reportAbsentContext(context);
}
return SingletonIterator.makeIterator(item);
}
/**
* Evaluate the expression
*/
@Override
public Item evaluateItem(XPathContext context) throws XPathException {
Item item = context.getContextItem();
if (item == null) {
reportAbsentContext(context);
}
return item;
}
private void reportAbsentContext(XPathContext context) throws XPathException {
if (absentContextIsTypeError) {
typeError("The context item is absent", getErrorCodeForUndefinedContext(), context);
} else {
dynamicError("The context item is absent", getErrorCodeForUndefinedContext(), context);
}
}
/**
* The toString() method for an expression attempts to give a representation of the expression
* in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
* In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
*/
public String toString() {
return ".";
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
@Override
public void export(ExpressionPresenter destination) throws XPathException {
destination.startElement("dot", this);
ItemType type = getItemType();
if (!(type == AnyItemType.getInstance())) {
SequenceType st = SequenceType.makeSequenceType(type,StaticProperty.EXACTLY_ONE);
destination.emitAttribute("type", st.toAlphaCode());
}
if (staticInfo.isPossiblyAbsent()) {
destination.emitAttribute("flags", "a");
}
destination.endElement();
}
@Override
public String toShortString() {
return ".";
}
}