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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.AxisInfo;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.NodeInfo;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.pattern.AnyNodeTest;
import net.sf.saxon.pattern.NodeKindTest;
import net.sf.saxon.pattern.NodeTestPattern;
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.*;
/**
* An expression whose value is always a set of nodes containing a single node,
* the document root. This corresponds to the XPath Expression "/", including the implicit
* "/" at the start of a path expression with a leading "/".
*/
public class RootExpression extends Expression {
private boolean contextMaybeUndefined = true;
private boolean doneWarnings = false;
public RootExpression() {
}
/**
* Type-check the expression.
*/
/*@NotNull*/
@Override
public Expression typeCheck(ExpressionVisitor visitor, /*@Nullable*/ ContextItemStaticInfo contextInfo) throws XPathException {
TypeHierarchy th = visitor.getConfiguration().getTypeHierarchy();
if (contextInfo == null || contextInfo.getItemType() == null || contextInfo.getItemType().equals(ErrorType.getInstance())) {
XPathException err = new XPathException(noContextMessage() + ": the context item is absent");
err.setErrorCode("XPDY0002");
err.setIsTypeError(true);
err.setLocation(getLocation());
throw err;
} else if (!doneWarnings && contextInfo.isParentless()
&& th.relationship(contextInfo.getItemType(),NodeKindTest.DOCUMENT) == Affinity.DISJOINT) {
visitor.issueWarning(noContextMessage() + ": the context item is parentless and is not a document node", getLocation());
doneWarnings = true;
}
contextMaybeUndefined = contextInfo.isPossiblyAbsent();
if (th.isSubType(contextInfo.getItemType(), NodeKindTest.DOCUMENT)) {
// this rewrite is important for streamability analysis
ContextItemExpression cie = new ContextItemExpression();
ExpressionTool.copyLocationInfo(this, cie);
cie.setStaticInfo(contextInfo);
return cie;
}
Affinity relation = th.relationship(contextInfo.getItemType(), AnyNodeTest.getInstance());
if (relation == Affinity.DISJOINT) {
XPathException err = new XPathException(noContextMessage() + ": the context item is not a node");
err.setErrorCode("XPTY0020");
err.setIsTypeError(true);
err.setLocation(getLocation());
throw err;
}
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 net.sf.saxon.trans.XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
@Override
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException {
// repeat the check: in XSLT insufficient information is available the first time
return typeCheck(visitor, contextItemType);
}
@Override
protected int computeSpecialProperties() {
return StaticProperty.ORDERED_NODESET |
StaticProperty.CONTEXT_DOCUMENT_NODESET |
StaticProperty.SINGLE_DOCUMENT_NODESET |
StaticProperty.NO_NODES_NEWLY_CREATED;
}
/**
* Ask whether there is a possibility that the context item will be undefined
*
* @return true if this is a possibility
*/
public boolean isContextPossiblyUndefined() {
return contextMaybeUndefined;
}
/**
* Customize the error message on type checking
* @return a suitable error message
*/
protected String noContextMessage() {
return "Leading '/' selects nothing";
}
/**
* Is this expression the same as another expression?
*/
public boolean equals(Object other) {
return other instanceof RootExpression;
}
/**
* Specify that the expression returns a singleton
*/
@Override
protected final int computeCardinality() {
return StaticProperty.EXACTLY_ONE;
}
/**
* Determine the data type of the items returned by this expression
*
* @return Type.NODE
*/
/*@NotNull*/
@Override
public ItemType getItemType() {
return NodeKindTest.DOCUMENT;
}
/**
* Get the static type of the expression as a UType, following precisely the type
* inference rules defined in the XSLT 3.0 specification.
*
* @return the static item type of the expression according to the XSLT 3.0 defined rules
*/
@Override
public UType getStaticUType(UType contextItemType) {
return UType.DOCUMENT;
}
/**
* An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
* This method indicates which of these methods is provided directly. The other methods will always be available
* indirectly, using an implementation that relies on one of the other methods.
*
* @return the implementation method, for example {@link #ITERATE_METHOD} or {@link #EVALUATE_METHOD} or
* {@link #PROCESS_METHOD}
*/
@Override
public int getImplementationMethod() {
return EVALUATE_METHOD;
}
/**
* get HashCode for comparing two expressions
*/
@Override
protected int computeHashCode() {
return "RootExpression".hashCode();
}
/**
* Return the first element selected by this Expression
*
* @param context The evaluation context
* @return the NodeInfo of the first selected element, or null if no element
* is selected
* @throws XPathException for dynamic errors (no context item, context item is not a node, context node
* not rooted at a document node)
*/
/*@Nullable*/
public NodeInfo getNode(XPathContext context) throws XPathException {
Item current = context.getContextItem();
if (current == null) {
dynamicError("Finding root of tree: the context item is absent", "XPDY0002", context);
}
if (current instanceof NodeInfo) {
NodeInfo doc = ((NodeInfo) current).getRoot();
if (doc.getNodeKind() != Type.DOCUMENT) {
dynamicError("The root of the tree containing the context item is not a document node", "XPDY0050", context);
}
return doc;
}
typeError("Finding root of tree: the context item is not a node", "XPTY0020", context);
// dummy return; we never get here
return null;
}
/**
* Determine which aspects of the context the expression depends on. The result is
* a bitwise-or'ed value composed from constants such as StaticProperty.VARIABLES and
* StaticProperty.CURRENT_NODE
*/
@Override
public int getIntrinsicDependencies() {
return StaticProperty.DEPENDS_ON_CONTEXT_DOCUMENT;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
* @param rebindings variables that need to be re-bound
*/
/*@NotNull*/
@Override
public Expression copy(RebindingMap rebindings) {
RootExpression exp = new RootExpression();
ExpressionTool.copyLocationInfo(this, exp);
return exp;
}
/**
* 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 new NodeTestPattern(NodeKindTest.DOCUMENT);
}
/**
* 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.
*
* @return the pathMapNode representing the focus established by this expression, in the case where this
* expression is the first operand of a path expression or filter expression
*/
@Override
public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) {
if (pathMapNodeSet == null) {
ContextItemExpression cie = new ContextItemExpression();
ExpressionTool.copyLocationInfo(this, cie);
pathMapNodeSet = new PathMap.PathMapNodeSet(pathMap.makeNewRoot(cie));
}
return pathMapNodeSet.createArc(AxisInfo.ANCESTOR_OR_SELF, NodeKindTest.DOCUMENT);
}
/**
* 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 "(/)";
}
@Override
public String getExpressionName() {
return "root";
}
/**
* 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("root", this);
destination.endElement();
}
/**
* Evaluate the expression in a given context to return an iterator
*
* @param context the evaluation context
*/
/*@NotNull*/
@Override
public SequenceIterator iterate(XPathContext context) throws XPathException {
return SingletonIterator.makeIterator(getNode(context));
}
@Override
public NodeInfo evaluateItem(XPathContext context) throws XPathException {
return getNode(context);
}
@Override
public boolean effectiveBooleanValue(XPathContext context) throws XPathException {
return getNode(context) != null;
}
/**
* 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 "RootExpression";
}
}