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The XSLT and XQuery Processor
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2015 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.event.SequenceReceiver;
import net.sf.saxon.evpull.EmptyEventIterator;
import net.sf.saxon.evpull.EventIterator;
import net.sf.saxon.evpull.EventIteratorOverSequence;
import net.sf.saxon.evpull.SingletonEventIterator;
import net.sf.saxon.expr.parser.*;
import net.sf.saxon.functions.*;
import net.sf.saxon.lib.Logger;
import net.sf.saxon.om.*;
import net.sf.saxon.pattern.NodeKindTest;
import net.sf.saxon.pattern.NodeSetPattern;
import net.sf.saxon.pattern.NodeTest;
import net.sf.saxon.pattern.Pattern;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trace.LocationKind;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.SingletonIterator;
import net.sf.saxon.tree.util.FastStringBuffer;
import net.sf.saxon.type.AtomicType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.SchemaType;
import net.sf.saxon.value.*;
import net.sf.saxon.z.IntHashSet;
import net.sf.saxon.z.IntIterator;
import java.net.URI;
import java.util.*;
/**
* Interface supported by an XPath expression. This includes both compile-time
* and run-time methods.
*
* Two expressions are considered equal if they return the same result when evaluated in the
* same context.
*
* Expressions manage their own subexpressions but must observe certain conventions when doing
* so. Every expression must implement the methods operands() and getOperand(N) to access the
* operands of the expression; here N is an integer identifier for the subexpression which
* is unique among the subexpressions and whose allocation is a matter for each expression
* to determined. So a subexpression of an expression can change (during optimization rewrite,
* for example), then (a) the expression must implement the method setOperandExpression(N, expr)
* to effect the change, and (b) calling this method must cause a call on adoptChildExpression(N, expr)
* which is implemented in the expression class itself, and takes responsibility for maintaining
* the consistency of the tree, e.g. by invalidating cached information.
*
* The default implementations of methods such as operands() work for expressions that have
* no subexpressions.
*/
public abstract class Expression implements /*InstructionInfo,*/ IdentityComparable {
public static final int EVALUATE_METHOD = 1;
public static final int ITERATE_METHOD = 2;
public static final int PROCESS_METHOD = 4;
public static final int WATCH_METHOD = 8;
public static final int ITEM_FEED_METHOD = 16;
public static final int EFFECTIVE_BOOLEAN_VALUE = 32;
public static final int UPDATE_METHOD = 64;
protected int staticProperties = -1;
private Location location = ExplicitLocation.UNKNOWN_LOCATION;
private Expression parentExpression;
private RetainedStaticContext retainedStaticContext;
private int[] slotsUsed;
private int evaluationMethod;
// public int serial; // used to identify expressions for internal diagnostics
// private static int nextSerial = 0;
public Expression() {
//serial = nextSerial++;
}
/**
* 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 export() output displaying the expression.
*/
public String getExpressionName() {
return getClass().getName();
}
/**
* 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()
*
* If the expression is a Callable, then it is required that the order of the operands
* returned by this function is the same as the order of arguments supplied to the corresponding
* call() method.
*
* @return an iterator containing the sub-expressions of this expression
*/
/*@NotNull*/
public Iterable operands() {
return Collections.emptyList();
}
/**
* Get the immediate sub-expressions of this expression, verifying that the parent pointers
* in the child expressions are correct.
* @return the list of sub-expressions, in the same way as with the {@link #operands()} method,
* but with additional checking
*/
public final Iterable checkedOperands() {
Iterable ops = operands();
for (Operand o : ops) {
Expression child = o.getChildExpression();
if (child.getParentExpression() != this) {
System.err.println("*** Bad parent pointer found in " + child.toShortString() +
" at " + child.getLocation().getLineNumber() + " ***");
child.setParentExpression(Expression.this);
//throw new IllegalStateException("Bad parent pointer");
}
if (child.getRetainedStaticContext() == null) {
child.setRetainedStaticContext(getRetainedStaticContext());
}
}
return ops;
}
/**
* Helper method for subclasses to build a list of operands
* @param a the sequence of operands (which must all be non-null)
* @return a list of operands
*/
protected List operandList(Operand... a) {
return Arrays.asList(a);
}
/**
* Helper method for subclasses to build a list of operands
* @param a the sequence of operands; any null values in the list are ignored
* @return a list of operands
*/
protected List operandSparseList(Operand... a) {
List operanda = new ArrayList();
for (Operand o : a) {
if (o != null) {
operanda.add(o);
}
}
return operanda;
}
/**
* Get the parent expression of this expression in the expression tree.
* @return the parent expression. Null if at the root of the tree, for example,
* the expression representing the body of a function or template.
*/
public Expression getParentExpression() {
return parentExpression;
}
public String getSystemId() {
return getLocation().getSystemId();
}
/**
* Set the parent expression of this expression in the expression tree.
* @param parent the parent expression
*/
public void setParentExpression(Expression parent) {
// if (parent != null && parent != parentExpression) {
// System.err.println("Set parent of " + this.getClass() + serial + " to " + parent.getClass() + parent.serial);
// }
parentExpression = parent;
}
/**
* Verify that parent pointers are correct throughout the subtree rooted at this expression
* @throws IllegalStateException if invalid parent pointers are found
*/
// public Expression verifyParentPointers() throws IllegalStateException {
// for (Operand o : operands()) {
// Expression parent = o.getChildExpression().getParentExpression();
// if (parent != this) {
// throw new IllegalStateException("Invalid parent pointer in " +
// o.getChildExpression().getClass() + o.getChildExpression().serial + " -> " + parent.getClass() + parent.serial);
// }
// o.getChildExpression().verifyParentPointers();
// }
// return this;
// }
/**
* Restore parent pointers for the subtree rooted at this expression
*/
public void restoreParentPointers() {
for (Operand o : operands()) {
Expression child = o.getChildExpression();
child.setParentExpression(Expression.this);
child.restoreParentPointers();
}
}
/**
* 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}
*/
public abstract int getImplementationMethod();
// {
// if (Cardinality.allowsMany(getCardinality())) {
// return ITERATE_METHOD;
// } else {
// return EVALUATE_METHOD;
// }
// }
/**
* Determine whether this expression implements its own method for static type checking
*
* @return true if this expression has a non-trivial implementation of the staticTypeCheck()
* method
*/
public boolean implementsStaticTypeCheck() {
return false;
}
/**
* Ask whether this expression is, or contains, the binding of a given variable
* @param binding the variable binding
* @return true if this expression is the variable binding (for example a ForExpression
* or LetExpression) or if it is a FLWOR expression that binds the variable in one of its
* clauses.
*/
public boolean hasVariableBinding(Binding binding) {
return false;
}
/**
* Simplify an expression. This performs any static optimization (by rewriting the expression
* as a different expression). The default implementation simplifies its operands.
* @return the simplified expression (or the original if unchanged, or if modified in-situ)
* @throws net.sf.saxon.trans.XPathException
* if an error is discovered during expression
* rewriting
*/
/*@NotNull*/
public Expression simplify() throws XPathException {
simplifyChildren();
return Expression.this;
}
/**
* Simplify an expression. This performs any static optimization (by rewriting the expression
* as a different expression). The default implementation simplifies its operands.
* @return the simplified expression (or the original if unchanged, or if modified in-situ)
* @throws net.sf.saxon.trans.XPathException
* if an error is discovered during expression
* rewriting
*/
/*@NotNull*/
protected final void simplifyChildren() throws XPathException {
for (Operand o : operands()) {
if (o != null) {
Expression e = o.getChildExpression();
if (e != null) {
Expression f = e.simplify();
o.setChildExpression(f);
}
}
}
}
/**
* Set the retained static context
* @param rsc the static context to be retained
*/
public void setRetainedStaticContext(RetainedStaticContext rsc) {
retainedStaticContext = rsc;
for (Operand o : operands()) {
if (o != null) {
Expression child = o.getChildExpression();
if (child != null && child.retainedStaticContext == null) {
child.setRetainedStaticContext(rsc);
}
}
}
}
/**
* Set the parts of the static context that might be needed by the function, without
* passing them on to subexpressions. Used for dynamic function calls only.
*/
public void setRetainedStaticContextLocally(RetainedStaticContext rsc) {
retainedStaticContext = rsc;
}
/**
* Get the retained static context of the expression
* @return the retained static context
*/
public final RetainedStaticContext getRetainedStaticContext() {
if (retainedStaticContext == null) {
Expression parent = getParentExpression();
retainedStaticContext = parent == null ? null : parent.getRetainedStaticContext();
}
return retainedStaticContext;
}
/**
* Get the saved static base URI as a string
*
* @return the static base URI
*/
public String getStaticBaseURIString() {
return getRetainedStaticContext().getStaticBaseUriString();
}
/**
* Get the saved static base URI as a URI
*
* @return the static base URI as a URI
*/
public URI getStaticBaseURI() throws XPathException {
return getRetainedStaticContext().getStaticBaseUri();
}
/**
* Ask whether this expression is a call on a particular function
* @param function the implementation class of the function in question
*/
public boolean isCallOn(Class function) {
return false;
}
public boolean isCallOnSystemFunction(String localName) {
return false;
}
/**
* Perform type checking of an expression and its subexpressions. This is the second phase of
* static optimization.
*
* 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 contextInfo Information available statically about the context item: whether it is (possibly)
* absent; its static type; its streaming posture.
* @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,
ContextItemStaticInfo contextInfo) throws XPathException {
typeCheckChildren(visitor, contextInfo);
return Expression.this;
}
/**
* Perform type checking of the children of this expression (and their children, recursively)
* This method is provided as a helper for implementations of the
* {@link #typeCheck(net.sf.saxon.expr.parser.ExpressionVisitor, net.sf.saxon.expr.parser.ContextItemStaticInfo)}
* method, since checking the children is an inevitable part of checking the expression itse.f
*
* @param visitor an expression visitor
* @param contextInfo Information available statically about the context item: whether it is (possibly)
* absent; its static type; its streaming posture.
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
protected final void typeCheckChildren(ExpressionVisitor visitor,
ContextItemStaticInfo contextInfo) throws XPathException {
for (Operand o : checkedOperands()) {
o.typeCheck(visitor, contextInfo);
}
}
/**
* Static type checking of some expressions is delegated to the expression itself, by calling
* this method. The default implementation of the method throws UnsupportedOperationException.
* If there is a non-default implementation, then implementsStaticTypeCheck() will return true
*
*
* @param req the required type
* @param backwardsCompatible true if backwards compatibility mode applies
* @param role the role of the expression in relation to the required type
* @param visitor an expression visitor
* @return the expression after type checking (perhaps augmented with dynamic type checking code)
* @throws XPathException if failures occur, for example if the static type of one branch of the conditional
* is incompatible with the required type
*/
public Expression staticTypeCheck(SequenceType req,
boolean backwardsCompatible,
RoleDiagnostic role, ExpressionVisitor visitor)
throws XPathException {
throw new UnsupportedOperationException("staticTypeCheck");
}
/**
* Perform optimisation of an expression and its subexpressions. This is the third and final
* phase of static optimization.
*
* 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 contextInfo 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,
/*@Nullable*/ ContextItemStaticInfo contextInfo) throws XPathException {
optimizeChildren(visitor, contextInfo);
return Expression.this;
}
/**
* Perform optimization of the children of this expression (and their children, recursively)
* This method is provided as a helper for implementations of the
* {@link #optimize(net.sf.saxon.expr.parser.ExpressionVisitor, net.sf.saxon.expr.parser.ContextItemStaticInfo)}
* method, since optimizing the children is an inevitable part of optimizing the expression itself
*
* @param visitor an expression visitor
* @param contextInfo Information available statically about the context item: whether it is (possibly)
* absent; its static type; its streaming posture.
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
protected final void optimizeChildren(ExpressionVisitor visitor,
ContextItemStaticInfo contextInfo) throws XPathException {
for (Operand o : operands()) {
o.optimize(visitor, contextInfo);
}
}
/**
* Return the estimated cost of evaluating an expression. This is a very crude measure based
* on the syntactic form of the expression (we have no knowledge of data values). We take
* the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one),
* and we assume that a sequence has length 5. The resulting estimates may be used, for
* example, to reorder the predicates in a filter expression so cheaper predicates are
* evaluated first.
* @return an estimate of the gross cost of evaluating the expression, including the cost
* of evaluating its operands.
*/
public int getCost() {
int i = getNetCost();
for (Operand o : operands()) {
i += o.getChildExpression().getCost();
}
return i;
}
/**
* Return the net cost of evaluating this expression, excluding the cost of evaluating
* its operands. We take the cost of evaluating a simple scalar comparison or arithmetic
* expression as 1 (one).
* @return the intrinsic cost of this operation, excluding the costs of evaluating
* the operands
*/
protected int getNetCost() {
return 1;
}
/**
* 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 accepted. 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
* @return if the offer is not accepted, return this expression unchanged.
* Otherwise return the result of rewriting the expression to promote
* this subexpression
* @throws XPathException if any error is detected
*/
public Expression promote(PromotionOffer offer) throws XPathException {
Expression exp = offer.accept(Expression.this);
if (exp != null) {
return exp;
} else {
promoteChildren(offer);
return Expression.this;
}
}
/**
* Helper method for implementations of
* {@link #promote(net.sf.saxon.expr.parser.PromotionOffer)}
* to apply the requested promotion to all subexpressions
* @param offer the promotion offer
* @throws XPathException if any failure occurs
*/
protected void promoteChildren(PromotionOffer offer) throws XPathException {
if (offer.action == PromotionOffer.FOCUS_INDEPENDENT) {
for (Operand o : operands()) {
if (o.hasSameFocus()) {
o.setChildExpression(doPromotion(o.getChildExpression(), offer));
}
}
} else {
for (Operand o : operands()) {
o.setChildExpression(doPromotion(o.getChildExpression(), offer));
}
}
}
/**
* Promote a subexpression if possible, and if the expression was changed, carry out housekeeping
* to reset the static properties and correct the parent pointers in the tree
*
* @param subexpression the subexpression that is a candidate for promotion
* @param offer details of the promotion being considered @return the result of the promotion. This will be the current expression if no promotion
* actions have taken place
* @return the expression that results from doing the promotion as requested. Returns null if and only
* if the supplied subexpression is null.
* @throws net.sf.saxon.trans.XPathException
* if an error occurs
*/
public final Expression doPromotion(Expression subexpression, PromotionOffer offer)
throws XPathException {
if (subexpression == null) {
return null;
}
Expression e = subexpression.promote(offer);
if (e != subexpression) {
//e.restoreParentPointers();
adoptChildExpression(e);
} else if (offer.accepted) {
ExpressionTool.resetStaticProperties(e);
}
return e;
}
/**
* Replace this expression by a simpler expression that delivers the results without regard
* to order.
*
* @param retainAllNodes set to true if the result must contain exactly the same nodes as the
* original; set to false if the result can eliminate (or introduce) duplicates.
* @param forStreaming set to true if the result is to be optimized for streaming
* @return an expression that delivers the same nodes in a more convenient order
* @throws XPathException if the rewrite fails
*/
public Expression unordered(boolean retainAllNodes, boolean forStreaming) throws XPathException {
return Expression.this;
}
/**
* Get the static properties of this expression (other than its type). The result is
* bit-signficant. These properties are used for optimizations. In general, if
* property bit is set, it is true, but if it is unset, the value is unknown.
*
* @return a set of flags indicating static properties of this expression
*/
public final int getSpecialProperties() {
if (staticProperties == -1) {
computeStaticProperties();
}
return staticProperties & StaticProperty.SPECIAL_PROPERTY_MASK;
}
/**
* 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.
*
* @return one of the values Cardinality.ONE_OR_MORE,
* Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE,
* Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default
* implementation returns ZERO_OR_MORE (which effectively gives no
* information).
*/
public int getCardinality() {
if (staticProperties == -1) {
computeStaticProperties();
}
return staticProperties & StaticProperty.CARDINALITY_MASK;
}
/**
* 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)
*/
/*@NotNull*/
public abstract ItemType getItemType();
/**
* Determine which aspects of the context the expression depends on. The result is
* a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and
* XPathContext.CURRENT_NODE. 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() {
// Implemented as a memo function: we only compute the dependencies
// for each expression once
if (staticProperties == -1) {
computeStaticProperties();
}
return staticProperties & StaticProperty.DEPENDENCY_MASK;
}
/**
* For an expression that returns an integer or a sequence of integers, get
* a lower and upper bound on the values of the integers that may be returned, from
* static analysis. The default implementation returns null, meaning "unknown" or
* "not applicable". Other implementations return an array of two IntegerValue objects,
* representing the lower and upper bounds respectively. The values
* UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that
* the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH
* are used to indicate values limited by the size of a string or the size of a sequence.
*
* @return the lower and upper bounds of integer values in the result, or null to indicate
* unknown or not applicable.
*/
/*@Nullable*/
public IntegerValue[] getIntegerBounds() {
return null;
}
public static final IntegerValue UNBOUNDED_LOWER = (IntegerValue) IntegerValue.makeIntegerValue(new DoubleValue(-1e100));
public static final IntegerValue UNBOUNDED_UPPER = (IntegerValue) IntegerValue.makeIntegerValue(new DoubleValue(+1e100));
public static final IntegerValue MAX_STRING_LENGTH = Int64Value.makeIntegerValue(Integer.MAX_VALUE);
public static final IntegerValue MAX_SEQUENCE_LENGTH = Int64Value.makeIntegerValue(Integer.MAX_VALUE);
/**
* Mark an expression as being "flattened". This is a collective term that includes extracting the
* string value or typed value, or operations such as simple value construction that concatenate text
* nodes before atomizing. The implication of all of these is that although the expression might
* return nodes, the identity of the nodes has no significance. This is called during type checking
* of the parent expression.
*
* @param flattened set to true if the result of the expression is atomized or otherwise turned into
* an atomic value
*/
public void setFlattened(boolean flattened) {
// no action in general
}
/**
* Mark an expression as filtered: that is, it appears as the base expression in a filter expression.
* This notification currently has no effect except when the expression is a variable reference.
*
* @param filtered if true, marks this expression as the base of a filter expression
*/
public void setFiltered(boolean filtered) {
// default: do nothing
}
/**
* 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
*/
/*@Nullable*/
public Item evaluateItem(XPathContext context) throws XPathException {
return iterate(context).next();
}
/**
* 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 {
Item value = evaluateItem(context);
return SingletonIterator.makeIterator(value);
}
/**
* Deliver the result of the expression as a sequence of events.
*
* The events (of class {@link net.sf.saxon.evpull.PullEvent}) are either complete
* items, or one of startElement, endElement, startDocument, or endDocument, known
* as semi-nodes. The stream of events may also include a nested EventIterator.
* If a start-end pair exists in the sequence, then the events between
* this pair represent the content of the document or element. The content sequence will
* have been processed to the extent that any attribute and namespace nodes in the
* content sequence will have been merged into the startElement event. Namespace fixup
* will have been performed: that is, unique prefixes will have been allocated to element
* and attribute nodes, and all namespaces will be declared by means of a namespace node
* in the startElement event or in an outer startElement forming part of the sequence.
* However, duplicate namespaces may appear in the sequence.
* The content of an element or document may include adjacent or zero-length text nodes,
* atomic values, and nodes represented as nodes rather than broken down into events.
*
* @param context The dynamic evaluation context
* @return the result of the expression as an iterator over a sequence of PullEvent objects
* @throws XPathException if a dynamic error occurs during expression evaluation
*/
/*@Nullable*/
public EventIterator iterateEvents(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & EVALUATE_METHOD) != 0) {
Item item = evaluateItem(context);
if (item == null) {
return EmptyEventIterator.getInstance();
} else {
return new SingletonEventIterator(item);
}
} else {
return new EventIteratorOverSequence(iterate(context));
}
}
/**
* Get the effective boolean value of the expression. This returns false if the value
* is the empty sequence, a zero-length string, a number equal to zero, or the boolean
* false. Otherwise it returns true.
*
* @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 ExpressionTool.effectiveBooleanValue(iterate(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?, xs:untypedAtomic?, or xs:anyURI?
*/
public CharSequence evaluateAsString(XPathContext context) throws XPathException {
Item o = evaluateItem(context);
StringValue value = (StringValue) o; // the ClassCastException is deliberate
if (value == null) {
return "";
}
return value.getStringValueCS();
}
/**
* Process the instruction, without returning any tail calls
*
* @param context The dynamic context, giving access to the current node,
* the current variables, etc.
* @throws net.sf.saxon.trans.XPathException
* if a dynamic error occurs
*/
public void process(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & EVALUATE_METHOD) != 0) {
Item item = evaluateItem(context);
if (item != null) {
context.getReceiver().append(item, getLocation(), NodeInfo.ALL_NAMESPACES);
}
} else if ((m & ITERATE_METHOD) != 0) {
SequenceIterator iter = iterate(context);
SequenceReceiver out = context.getReceiver();
try {
Item it;
while ((it = iter.next()) != null) {
out.append(it, getLocation(), NodeInfo.ALL_NAMESPACES);
}
} catch (XPathException e) {
e.maybeSetLocation(getLocation());
e.maybeSetContext(context);
throw e;
}
} else {
throw new AssertionError("process() is not implemented in the subclass " + getClass());
}
}
/**
* Evaluate an updating expression, adding the results to a Pending Update List.
* The default implementation of this method, which is used for non-updating expressions,
* throws an UnsupportedOperationException
*
* @param context the XPath dynamic evaluation context
* @param pul the pending update list to which the results should be written
* @throws net.sf.saxon.trans.XPathException
* if evaluation fails
* @throws UnsupportedOperationException if the expression is not an updating expression
*/
public void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) throws XPathException {
if (isVacuousExpression()) {
iterate(context).next(); // typically, a call on fn:error
} else {
throw new UnsupportedOperationException("Expression " + getClass() + " is not an updating expression");
}
}
/**
* The toString() method for an expression attempts to give a representation of the expression
* in an XPath-like form.
*
* For subclasses of Expression that represent XPath expressions, the result should always be a string that
* parses as an XPath 3.0 expression. The expression produced should be equivalent to the original making certain
* assumptions about the static context. In general the expansion will make no assumptions about namespace bindings,
* except that (a) the prefix "xs" is used to refer to the XML Schema namespace, and (b) the default function namespace
* is assumed to be the "fn" namespace.
*
* In the case of XSLT instructions and XQuery expressions, the toString() method gives an abstracted view of the syntax
* that is not designed in general to be parseable.
*
* @return a representation of the expression as a string
*/
public String toString() {
// fallback implementation
FastStringBuffer buff = new FastStringBuffer(FastStringBuffer.C64);
String className = getClass().getName();
while (true) {
int dot = className.indexOf('.');
if (dot >= 0) {
className = className.substring(dot + 1);
} else {
break;
}
}
buff.append(className);
boolean first = true;
for (Operand o : operands()) {
buff.append(first ? "(" : ", ");
buff.append(o.getChildExpression().toString());
first = false;
}
if (!first) {
buff.append(")");
}
return buff.toString();
}
/**
* Produce a short string identifying the expression for use in error messages
* @return a short string, sufficient to identify the expression
*/
public String toShortString() {
// fallback implementation
return getExpressionName();
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*
* @param out the expression presenter used to display the structure
* @throws XPathException if the export fails, for example if an expression is found that won't work
* in the target environment.
*/
public abstract void export(ExpressionPresenter out) throws XPathException;
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied outputstream.
*
* @param out the expression presenter used to display the structure
*/
public final void explain(Logger out) {
ExpressionPresenter ep = new ExpressionPresenter(getConfiguration(), out);
try {
export(ep);
} catch (XPathException e) {
ep.startElement("failure");
ep.emitAttribute("message", e.getMessage());
ep.endElement();
}
ep.close();
}
/**
* Check that any elements and attributes constructed or returned by this expression are acceptable
* in the content model of a given complex type. It's always OK to say yes, since the check will be
* repeated at run-time. The process of checking element and attribute constructors against the content
* model of a complex type also registers the type of content expected of those constructors, so the
* static validation can continue recursively.
*
* @param parentType the "given complex type": the method is checking that the nodes returned by this
* expression are acceptable members of the content model of this type
* @param whole if true, we want to check that the value of this expression satisfies the content model
* as a whole; if false we want to check that the value of the expression is acceptable as one part
* of the content
* @throws XPathException if the value delivered by this expression cannot be part of the content model
* of the given type
*/
public void checkPermittedContents(SchemaType parentType, boolean whole) throws XPathException {
//
}
/**
* Set up a parent-child relationship between this expression and a given child expression.
*
* Note: many calls on this method are now redundant, but are kept in place for "belt-and-braces"
* reasons. The rule is that an implementation of simplify(), typeCheck(), or optimize() that returns
* a value other than "this" is required to set the location information and parent pointer in the new
* child expression. However, in the past this was often left to the caller, which did it by calling
* this method, either unconditionally on return from one of these methods, or after testing that the
* returned object was not the same as the original.
*
* @param child the child expression
*/
public void adoptChildExpression(Expression child) {
if (child == null) {
return;
}
// if (child.getParentExpression() != null && child.getParentExpression() != this) {
// for (Operand o : child.getParentExpression().operands()) {
// if (o.getChildExpression() == child) {
// o.detachChild();
// }
// }
// }
child.setParentExpression(Expression.this);
if (child.retainedStaticContext == null) {
child.retainedStaticContext = retainedStaticContext;
}
if (getLocation() == null || getLocation() == ExplicitLocation.UNKNOWN_LOCATION) {
ExpressionTool.copyLocationInfo(child, Expression.this);
} else if (child.getLocation() == null || child.getLocation() == ExplicitLocation.UNKNOWN_LOCATION) {
ExpressionTool.copyLocationInfo(Expression.this, child);
}
resetLocalStaticProperties();
}
/**
* Set the location on an expression.
*
* @param id the location
*/
public void setLocation(Location id) {
location = id;
}
/**
* Get the location of the expression
*
* @return a location identifier, which can be turned into real
* location information by reference to a location provider
*/
public final Location getLocation() {
return location;
}
/**
* Get the configuration containing this expression
*
* @return the containing Configuration
*/
public Configuration getConfiguration() {
try {
return getRetainedStaticContext().getConfiguration();
} catch (NullPointerException e) {
throw new NullPointerException("Internal error: expression " + toShortString() + " has no retained static context");
}
}
/**
* Get information about the containing package
* @return package data
*/
public PackageData getPackageData() {
try {
return getRetainedStaticContext().getPackageData();
} catch (NullPointerException e) {
throw new NullPointerException("Internal error: expression " + toShortString() + " has no retained static context");
}
}
/**
* Compute the static properties. This should only be done once for each
* expression.
*/
public final void computeStaticProperties() {
staticProperties =
computeDependencies() |
computeCardinality() |
computeSpecialProperties();
}
/**
* Reset the static properties of the expression to -1, so that they have to be recomputed
* next time they are used.
*/
public void resetLocalStaticProperties() {
staticProperties = -1;
}
/**
* Compute the static cardinality of this expression
*
* @return the computed cardinality, as one of the values {@link StaticProperty#ALLOWS_ZERO_OR_ONE},
* {@link StaticProperty#EXACTLY_ONE}, {@link StaticProperty#ALLOWS_ONE_OR_MORE},
* {@link StaticProperty#ALLOWS_ZERO_OR_MORE}
*/
protected abstract int computeCardinality();
/**
* Compute the special properties of this expression. These properties are denoted by a bit-significant
* integer, possible values are in class {@link StaticProperty}. The "special" properties are properties
* other than cardinality and dependencies, and most of them relate to properties of node sequences, for
* example whether the nodes are in document order.
*
* @return the special properties, as a bit-significant integer
*/
protected int computeSpecialProperties() {
return 0;
}
/**
* Compute the dependencies of an expression, as the union of the
* dependencies of its subexpressions. (This is overridden for path expressions
* and filter expressions, where the dependencies of a subexpression are not all
* propogated). This method should be called only once, to compute the dependencies;
* after that, getDependencies should be used.
*
* @return the depencies, as a bit-mask
*/
public int computeDependencies() {
int dependencies = getIntrinsicDependencies();
for (Operand o : operands()) {
if (o.hasSameFocus()) {
dependencies |= o.getChildExpression().getDependencies();
} else {
dependencies |= o.getChildExpression().getDependencies() & ~StaticProperty.DEPENDS_ON_FOCUS;
}
}
return dependencies;
}
/**
* Determine the intrinsic dependencies of an expression, that is, those which are not derived
* from the dependencies of its subexpressions. For example, position() has an intrinsic dependency
* on the context position, while (position()+1) does not. The default implementation
* of the method returns 0, indicating "no dependencies".
*
* @return a set of bit-significant flags identifying the "intrinsic"
* dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
*/
public int getIntrinsicDependencies() {
return 0;
}
/**
* Set a static property on an expression. Used when inlining functions to retain properties
* of the inlined function (though this is only partially successful because the properties
* can be recomputed later
* @param prop the property to be set
*/
public void setStaticProperty(int prop) {
if (staticProperties == -1) {
computeStaticProperties();
}
staticProperties |= prop;
}
/**
* Check to ensure that this expression does not contain any inappropriate updating subexpressions.
* This check is overridden for those expressions that permit updating subexpressions.
*
* @throws XPathException if the expression has a non-permitted updating subexpression
*/
public void checkForUpdatingSubexpressions() throws XPathException {
for (Operand o : operands()) {
Expression sub = o.getChildExpression();
if (sub == null) {
throw new NullPointerException();
}
sub.checkForUpdatingSubexpressions();
if (sub.isUpdatingExpression()) {
XPathException err = new XPathException(
"Updating expression appears in a context where it is not permitted", "XUST0001");
err.setLocation(sub.getLocation());
throw err;
}
}
}
/**
* Determine whether this is an updating expression as defined in the XQuery update specification
*
* @return true if this is an updating expression
*/
public boolean isUpdatingExpression() {
for (Operand o : operands()) {
if (o.getChildExpression().isUpdatingExpression()) {
return true;
}
}
return false;
}
/**
* Determine whether this is a vacuous expression as defined in the XQuery update specification
*
* @return true if this expression is vacuous
*/
public boolean isVacuousExpression() {
return false;
}
/**
* Copy an expression. This makes a deep copy.
*
* @return the copy of the original expression
* @param rebindings if a local variable is encountered whose binding is present in this
* map, then the binding will be replaced with a new binding.
*/
/*@NotNull*/
public abstract Expression copy(RebindingMap rebindings);
/**
* Suppress validation on contained element constructors, on the grounds that the parent element
* is already performing validation. The default implementation does nothing.
*
* @param parentValidationMode the kind of validation being performed on the parent expression
*/
public void suppressValidation(int parentValidationMode) {
// do nothing
}
/**
* Mark tail-recursive calls on stylesheet functions. For most expressions, this does nothing.
*
* @param qName the name of the function
* @param arity the arity (number of parameters) of the function
* @return {@link UserFunctionCall#NOT_TAIL_CALL} if no tail call was found;
* {@link UserFunctionCall#FOREIGN_TAIL_CALL} if a tail call on a different function was found;
* @link UserFunctionCall#SELF_TAIL_CALL} if a tail recursive call was found and if this call accounts for the whole of the value.
*/
public int markTailFunctionCalls(StructuredQName qName, int arity) {
return UserFunctionCall.NOT_TAIL_CALL;
}
/**
* 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 XPathException if conversion is not possible
*/
public Pattern toPattern(Configuration config, boolean is30) throws XPathException {
ItemType type = getItemType();
if (((getDependencies() & StaticProperty.DEPENDS_ON_NON_DOCUMENT_FOCUS) == 0) &&
(type instanceof NodeTest || this instanceof VariableReference)) {
return new NodeSetPattern(Expression.this);
}
if (isCallOn(KeyFn.class) || isCallOn(SuperId.class)) {
return new NodeSetPattern(Expression.this);
}
throw new XPathException("Cannot convert the expression {" + toString() + "} to a pattern");
}
/**
* Get the local variables (identified by their slot numbers) on which this expression depends.
* Should only be called if the caller has established that there is a dependency on local variables.
*
* @return an array of integers giving the slot numbers of the local variables referenced in this
* expression.
*/
public final synchronized int[] getSlotsUsed() {
// synchronized because it's calculated lazily at run-time the first time it's needed
if (slotsUsed != null) {
return slotsUsed;
}
IntHashSet slots = new IntHashSet(10);
gatherSlotsUsed(Expression.this, slots);
slotsUsed = new int[slots.size()];
int i = 0;
IntIterator iter = slots.iterator();
while (iter.hasNext()) {
slotsUsed[i++] = iter.next();
}
Arrays.sort(slotsUsed);
return slotsUsed;
}
private static void gatherSlotsUsed(Expression exp, IntHashSet slots) {
if (exp instanceof LocalVariableReference) {
slots.add(((LocalVariableReference)exp).getSlotNumber());
} else if (exp instanceof SuppliedParameterReference) {
int slot = ((SuppliedParameterReference) exp).getSlotNumber();
slots.add(slot);
} else {
for (Operand o : exp.operands()) {
gatherSlotsUsed(o.getChildExpression(), slots);
}
}
}
/**
* Method used in subclasses to signal a dynamic error
*
* @param message the error message
* @param code the error code
* @param context the XPath dynamic context
* @throws XPathException always thrown, to signal a dynamic error
*/
protected void dynamicError(String message, String code, XPathContext context) throws XPathException {
XPathException err = new XPathException(message, code, getLocation());
err.setXPathContext(context);
throw err;
}
/**
* Method used in subclasses to signal a runtime type error
*
* @param message the error message
* @param errorCode the error code
* @param context the XPath dynamic context
* @throws XPathException always thrown, to signal a dynamic error
*/
protected void typeError(String message, String errorCode, XPathContext context) throws XPathException {
XPathException e = new XPathException(message, errorCode, getLocation());
e.setIsTypeError(true);
e.setXPathContext(context);
throw e;
}
/**
* Get the type of this expression for use in tracing and diagnostics
*
* @return the type of expression, as enumerated in class {@link LocationKind}
*/
public int getConstructType() {
return LocationKind.XPATH_EXPRESSION;
}
/*@Nullable*/
public StructuredQName getObjectName() {
return null;
}
/*@Nullable*/
public Object getProperty(String name) {
if (name.equals("expression")) {
return Expression.this.getLocation();
} else {
return null;
}
}
/**
* Get an iterator over all the properties available. The values returned by the iterator
* will be of type String, and each string can be supplied as input to the getProperty()
* method to retrieve the value of the property. The iterator may return properties whose
* value is null.
*/
public Iterator getProperties() {
return new MonoIterator("expression");
}
/**
* Get the host language (XSLT, XQuery, XPath) used to implement the code in this container
*
* @return typically {@link net.sf.saxon.Configuration#XSLT} or {@link net.sf.saxon.Configuration#XQUERY}
*/
public int getHostLanguage() {
return getPackageData().getHostLanguage();
}
/**
* 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.
*/
/*@Nullable*/
public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, /*@Nullable*/ PathMap.PathMapNodeSet pathMapNodeSet) {
boolean dependsOnFocus = ExpressionTool.dependsOnFocus(Expression.this);
PathMap.PathMapNodeSet attachmentPoint;
if (pathMapNodeSet == null) {
if (dependsOnFocus) {
ContextItemExpression cie = new ContextItemExpression();
ExpressionTool.copyLocationInfo(Expression.this, cie);
pathMapNodeSet = new PathMap.PathMapNodeSet(pathMap.makeNewRoot(cie));
}
attachmentPoint = pathMapNodeSet;
} else {
attachmentPoint = dependsOnFocus ? pathMapNodeSet : null;
}
PathMap.PathMapNodeSet result = new PathMap.PathMapNodeSet();
for (Operand o : operands()) {
OperandUsage usage = o.getUsage();
Expression child = o.getChildExpression();
PathMap.PathMapNodeSet target = child.addToPathMap(pathMap, attachmentPoint);
if (usage == OperandUsage.NAVIGATION) {
// indicate that the function navigates to all elements in the document
target = target.createArc(AxisInfo.ANCESTOR_OR_SELF, NodeKindTest.ELEMENT);
target = target.createArc(AxisInfo.DESCENDANT, NodeKindTest.ELEMENT);
}
result.addNodeSet(target);
}
if (getItemType() instanceof AtomicType) {
// if expression returns an atomic value then any nodes accessed don't contribute to the result
return null;
} else {
return result;
}
}
/**
* 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.
*/
public boolean isSubtreeExpression() {
if (ExpressionTool.dependsOnFocus(Expression.this)) {
if ((getIntrinsicDependencies() & StaticProperty.DEPENDS_ON_FOCUS) != 0) {
return false;
} else {
for (Operand o : operands()) {
if (!o.getChildExpression().isSubtreeExpression()) {
return false;
}
}
return true;
}
} else {
return true;
}
}
public void setEvaluationMethod(int method) {
Expression.this.evaluationMethod = method;
}
public int getEvaluationMethod() {
return evaluationMethod;
}
/**
* Determine whether two IdentityComparable objects are identical. This is a stronger
* test than equality (even schema-equality); for example two dateTime values are not identical unless
* they are in the same timezone. In the case of expressions, we test object identity, since the normal
* equality test ignores the location of the expression.
*
* @param other the value to be compared with
* @return true if the two values are indentical, false otherwise
*/
public boolean isIdentical(IdentityComparable other) {
return this == other;
}
/**
* Get a hashCode that offers the guarantee that if A.isIdentical(B), then A.identityHashCode() == B.identityHashCode()
*
* @return a hashCode suitable for use when testing for identity.
*/
public int identityHashCode() {
return System.identityHashCode(Expression.this.getLocation());
}
//project:preconditions
public Expression optimizeForType(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException {
return Expression.this;
}
}
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