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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 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.pattern;
import net.sf.saxon.Configuration;
import net.sf.saxon.expr.*;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.expr.parser.PromotionOffer;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.SingletonIterator;
import net.sf.saxon.type.BuiltInAtomicType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.SchemaType;
import net.sf.saxon.type.TypeHierarchy;
import net.sf.saxon.value.BooleanValue;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
/**
* The PatternSponsor class allows a Pattern to be treated like an expression. Although
* patterns are not evaluated at run-time in the same way as expressions, they need to
* be manipulated in much the same way as expressions at compile time: for example variables
* need to be bound, dependencies need to be analyzed, and so on. This is especially true
* of patterns appearing in the xsl:number and xsl:for-each-group instructions (less so for
* the more common match patterns in xsl:template).
*
* This class implements the Expression interface, so that an Expression can have a
* PatternSponsor as a subexpression; it wraps a Pattern.
*
* A Pattern is treated as a boolean expression that returns true if the pattern matches
* the context node. It is evaluated in that way only when obtained through the s9api
* {@link net.sf.saxon.s9api.XPathCompiler#compilePattern(String)} method.
*/
public class PatternSponsor extends Expression {
private Pattern pattern;
/**
* Create a sponsor expression for a pattern
* @param pattern the pattern being wrapped
*/
public PatternSponsor(Pattern pattern) {
this.pattern = pattern;
}
/**
* Get the wrapped pattern
* @return the wrapped pattern
*/
public Pattern getPattern() {
return pattern;
}
/**
* 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.
*/
public int getImplementationMethod() {
return EVALUATE_METHOD;
}
/**
* Simplify an expression. This performs any static optimization (by rewriting the expression
* as a different expression). The default implementation does nothing.
*
* @return the simplified expression
* @throws XPathException if an error is discovered during expression
* rewriting
* @param visitor an expression visitor
*/
/*@NotNull*/
public Expression simplify(ExpressionVisitor visitor) throws XPathException {
pattern = pattern.simplify(visitor);
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*/
public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
return this;
}
/**
* Perform type checking of an expression and its subexpressions.
*
* This checks statically that the operands of the expression have
* the correct type; if necessary it generates code to do run-time type checking or type
* conversion. A static type error is reported only if execution cannot possibly succeed, that
* is, if a run-time type error is inevitable. The call may return a modified form of the expression.
*
* This method is called after all references to functions and variables have been resolved
* to the declaration of the function or variable. However, the types of such functions and
* variables may not be accurately known if they have not been explicitly declared.
*
* @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 to perform necessary
* run-time type checks, and to perform other type-related
* optimizations
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
pattern = pattern.analyze(visitor, contextItemType);
return this;
}
protected int computeCardinality() {
return StaticProperty.ALLOWS_ZERO_OR_MORE;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
*/
/*@NotNull*/
public Expression copy() {
throw new UnsupportedOperationException("PatternSponsor.copy()");
}
/**
* Offer promotion for this subexpression. The offer will be accepted if the subexpression
* is not dependent on the factors (e.g. the context item) identified in the PromotionOffer.
* By default the offer is not accepted - this is appropriate in the case of simple expressions
* such as constant values and variable references where promotion would give no performance
* advantage. This method is always called at compile time.
*
* @param offer details of the offer, for example the offer to move
* expressions that don't depend on the context to an outer level in
* the containing expression
* @param parent
* @return if the offer is not accepted, return this expression unchanged.
* Otherwise return the result of rewriting the expression to promote
* this subexpression
* @throws net.sf.saxon.trans.XPathException
* if any error is detected
*/
public Expression promote(PromotionOffer offer, Expression parent) throws XPathException {
pattern.promote(offer, this);
return this;
}
/**
* Determine the static cardinality of the expression. This establishes how many items
* there will be in the result of the expression, at compile time (i.e., without
* actually evaluating the result.
*
* This method should always return a result, though it may be the best approximation
* that is available at the time.
*
* @return one of the values {@link StaticProperty#ALLOWS_ONE},
* {@link StaticProperty#ALLOWS_ZERO_OR_MORE}, {@link StaticProperty#ALLOWS_ZERO_OR_ONE},
* {@link StaticProperty#ALLOWS_ONE_OR_MORE}, {@link StaticProperty#EMPTY}.
*/
public int getCardinality() {
return StaticProperty.EXACTLY_ONE;
}
/**
* Determine the data type of the expression, if possible. All expression return
* sequences, in general; this method determines the type of the items within the
* sequence, assuming that (a) this is known in advance, and (b) it is the same for
* all items in the sequence.
*
* This method should always return a result, though it may be the best approximation
* that is available at the time.
*
* @return a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER,
* Type.NODE, or Type.ITEM (meaning not known at compile time)
* @param th the type hierarchy cache
*/
/*@NotNull*/
public ItemType getItemType(TypeHierarchy th) {
return BuiltInAtomicType.BOOLEAN;
}
/**
* Determine which aspects of the context the expression depends on. The result is
* a bitwise-or'ed value composed from constants such as {@link net.sf.saxon.expr.StaticProperty#DEPENDS_ON_CONTEXT_ITEM} and
* {@link net.sf.saxon.expr.StaticProperty#DEPENDS_ON_CURRENT_ITEM}. The default implementation combines the intrinsic
* dependencies of this expression with the dependencies of the subexpressions,
* computed recursively. This is overridden for expressions such as FilterExpression
* where a subexpression's dependencies are not necessarily inherited by the parent
* expression.
*
* @return a set of bit-significant flags identifying the dependencies of
* the expression
*/
public int getDependencies() {
return pattern.getDependencies();
}
/**
* Get the immediate sub-expressions of this expression. Default implementation
* returns a zero-length array, appropriate for an expression that has no
* sub-expressions.
*
* @return an iterator containing the sub-expressions of this expression
*/
/*@NotNull*/
public Iterator iterateSubExpressions() {
return pattern.iterateSubExpressions();
}
/**
* Get the immediate sub-expressions of this expression, with information about the relationship
* of each expression to its parent expression. Default implementation
* works off the results of iterateSubExpressions()
*
* @return an iterator containing the sub-expressions of this expression
*/
/*@NotNull*/
public Iterator iterateSubExpressionInfo() {
// default implementation
List list = new ArrayList();
for (Iterator kids = iterateSubExpressions(); kids.hasNext(); ) {
list.add(new SubExpressionInfo(kids.next(), true, true, NAVIGATION_CONTEXT));
}
return list.iterator();
}
/**
* Replace one subexpression by a replacement subexpression
* @param original the original subexpression
* @param replacement the replacement subexpression
* @return true if the original subexpression is found
*/
public boolean replaceSubExpression(Expression original, Expression replacement) {
return pattern.replaceSubExpression(original, replacement);
}
/**
* Get the container that immediately contains this expression. This method
* returns null for an outermost expression; it also return null in the case
* of literal values. For an XPath expression occurring within an XSLT stylesheet,
* this method returns the XSLT instruction containing the XPath expression.
*
* @return the expression that contains this expression, if known; return null
* if there is no containing expression or if the containing expression is unknown.
*/
public Container getContainer() {
return pattern;
}
/**
* Convert this expression to an equivalent XSLT pattern
*
* @param config the Saxon configuration
* @param is30 true if this is XSLT 3.0
* @return the equivalent pattern
* @throws net.sf.saxon.trans.XPathException
* if conversion is not possible
*/
@Override
public Pattern toPattern(Configuration config, boolean is30) throws XPathException {
return pattern;
}
/**
* Evaluate an expression as a single item. This always returns either a single Item or
* null (denoting the empty sequence). No conversion is done. This method should not be
* used unless the static type of the expression is a subtype of "item" or "item?": that is,
* it should not be called if the expression may return a sequence. There is no guarantee that
* this condition will be detected.
*
* @param context The context in which the expression is to be evaluated
* @return the node or atomic value that results from evaluating the
* expression; or null to indicate that the result is an empty
* sequence
* @throws net.sf.saxon.trans.XPathException
* if any dynamic error occurs evaluating the
* expression
*/
public Item evaluateItem(XPathContext context) throws XPathException {
return BooleanValue.get(effectiveBooleanValue(context));
}
/**
* Return an Iterator to iterate over the values of a sequence. The value of every
* expression can be regarded as a sequence, so this method is supported for all
* expressions. This default implementation handles iteration for expressions that
* return singleton values: for non-singleton expressions, the subclass must
* provide its own implementation.
*
* @param context supplies the context for evaluation
* @return a SequenceIterator that can be used to iterate over the result
* of the expression
* @throws net.sf.saxon.trans.XPathException
* if any dynamic error occurs evaluating the
* expression
*/
/*@NotNull*/
public SequenceIterator iterate(XPathContext context) throws XPathException {
return SingletonIterator.makeIterator(evaluateItem(context));
}
/**
* Get the effective boolean value of the expression. Returns true if the underlying
* pattern matches the context node, otherwise false.
*
* @param context The context in which the expression is to be evaluated
* @return the effective boolean value
* @throws net.sf.saxon.trans.XPathException
* if any dynamic error occurs evaluating the
* expression
*/
public boolean effectiveBooleanValue(XPathContext context) throws XPathException {
return pattern.matches(context.getContextItem(), context);
}
/**
* Evaluate an expression as a String. This function must only be called in contexts
* where it is known that the expression will return a single string (or where an empty sequence
* is to be treated as a zero-length string). Implementations should not attempt to convert
* the result to a string, other than converting () to "". This method is used mainly to
* evaluate expressions produced by compiling an attribute value template.
*
* @param context The context in which the expression is to be evaluated
* @return the value of the expression, evaluated in the current context.
* The expression must return a string or (); if the value of the
* expression is (), this method returns "".
* @throws net.sf.saxon.trans.XPathException
* if any dynamic error occurs evaluating the
* expression
* @throws ClassCastException if the result type of the
* expression is not xs:string?
*/
public CharSequence evaluateAsString(XPathContext context) throws XPathException {
return evaluateItem(context).getStringValueCS();
}
/**
* Process the instruction, without returning any tail calls
*
* @param context The dynamic context, giving access to the current node,
* the current variables, etc.
*/
public void process(XPathContext context) throws XPathException {
throw new UnsupportedOperationException("Patterns cannot be evaluated in push mode");
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*/
public void explain(ExpressionPresenter out) {
out.startElement("pattern");
out.emitAttribute("match", pattern.toString());
out.endElement();
}
/**
* Check statically that the results of the expression are capable of constructing the content
* of a given schema type.
*
* @param parentType The schema type
* @param env the static context
* @param whole true if this expression is expected to make the whole content of the type, false
* if it is expected to make up only a part
* @throws net.sf.saxon.trans.XPathException
* if the expression doesn't match the required content type
*/
public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException {
throw new UnsupportedOperationException("checkPermittedContents() is not applicable to a pattern");
}
}