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An OSGi bundle for Saxon-HE
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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.expr.instruct;
import net.sf.saxon.Configuration;
import net.sf.saxon.Controller;
import net.sf.saxon.event.SequenceOutputter;
import net.sf.saxon.event.SequenceReceiver;
import net.sf.saxon.expr.Expression;
import net.sf.saxon.expr.StaticProperty;
import net.sf.saxon.expr.XPathContext;
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.om.StandardNames;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.EmptyIterator;
import net.sf.saxon.tree.iter.SingletonIterator;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.Type;
import net.sf.saxon.type.TypeHierarchy;
import javax.xml.transform.SourceLocator;
/**
* Abstract superclass for all instructions in the compiled stylesheet.
* This represents a compiled instruction, and as such, the minimum information is
* retained from the original stylesheet.
* Note: this class implements SourceLocator: that is, it can identify where in the stylesheet
* the source instruction was located.
*/
public abstract class Instruction extends Expression implements SourceLocator, TailCallReturner {
/**
* Constructor
*/
public Instruction() {}
/**
* An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
* This method indicates which of these methods is prefered. For instructions this is the process() method.
*/
public int getImplementationMethod() {
return Expression.PROCESS_METHOD;
}
/**
* Get the namecode of the instruction for use in diagnostics
* @return a code identifying the instruction: typically but not always
* the fingerprint of a name in the XSLT namespace
*/
public int getInstructionNameCode() {
return -1;
}
/**
* Get a name identifying the kind of instruction, in terms meaningful to a user. This method
* is not used in the case where the instruction name code is a standard name (<1024).
* @return a name identifying the kind of instruction, 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 instruction.
*/
public String getInstructionName() {
return getClass().getName();
}
/**
* 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.
*/
public String getExpressionName() {
int code = getInstructionNameCode();
if (code < 0) {
return getClass().getName();
}
if (code < 1024) {
return StandardNames.getDisplayName(code);
} else {
return getInstructionName();
}
}
/**
* Get the item type of the items returned by evaluating this instruction
* @return the static item type of the instruction
* @param th the type hierarchy cache
*/
/*@NotNull*/
public ItemType getItemType(TypeHierarchy th) {
return Type.ITEM_TYPE;
}
/**
* Get the cardinality of the sequence returned by evaluating this instruction
* @return the static cardinality
*/
public int computeCardinality() {
return StaticProperty.ALLOWS_ZERO_OR_MORE;
}
/**
* ProcessLeavingTail: called to do the real work of this instruction. This method
* must be implemented in each subclass. The results of the instruction are written
* to the current Receiver, which can be obtained via the Controller.
* @param context The dynamic context of the transformation, giving access to the current node,
* the current variables, etc.
* @return null if the instruction has completed execution; or a TailCall indicating
* a function call or template call that is delegated to the caller, to be made after the stack has
* been unwound so as to save stack space.
*/
public abstract TailCall processLeavingTail(XPathContext context) throws XPathException;
/**
* 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 {
try {
TailCall tc = processLeavingTail(context);
while (tc != null) {
tc = tc.processLeavingTail();
}
} catch (XPathException err) {
err.maybeSetLocation(this);
throw err;
}
}
/**
* Get a SourceLocator identifying the location of this instruction
* @return the location of this instruction in the source stylesheet or query
*/
public SourceLocator getSourceLocator() {
return this;
}
/**
* Construct an exception with diagnostic information. Note that this method
* returns the exception, it does not throw it: that is up to the caller.
* @param loc the location of the error
* @param error The exception containing information about the error
* @param context The controller of the transformation
* @return an exception based on the supplied exception, but with location information
* added relating to this instruction
*/
protected static XPathException dynamicError(SourceLocator loc, XPathException error, XPathContext context) {
if (error instanceof TerminationException) {
return error;
}
error.maybeSetLocation(loc);
error.maybeSetContext(context);
return error;
}
/**
* Assemble a ParameterSet. Method used by instructions that have xsl:with-param
* children. This method is used for the non-tunnel parameters.
* @param context the XPath dynamic context
* @param actualParams the set of with-param parameters that specify tunnel="no"
* @return a ParameterSet
* @throws net.sf.saxon.trans.XPathException if an error occurs evaluating one of the
* parameters
*/
public static ParameterSet assembleParams(XPathContext context,
WithParam[] actualParams)
throws XPathException {
if (actualParams == null || actualParams.length == 0) {
return null;
}
ParameterSet params = new ParameterSet(actualParams.length);
for (WithParam actualParam : actualParams) {
params.put(actualParam.getParameterId(),
actualParam.getSelectValue(context),
actualParam.isTypeChecked());
}
return params;
}
/**
* Assemble a ParameterSet. Method used by instructions that have xsl:with-param
* children. This method is used for the tunnel parameters.
* @param context the XPath dynamic context
* @param actualParams the set of with-param parameters that specify tunnel="yes"
* @return a ParameterSet
* @throws net.sf.saxon.trans.XPathException if an error occurs evaluating one of the
* tunnel parameters
*/
public static ParameterSet assembleTunnelParams(XPathContext context,
WithParam[] actualParams)
throws XPathException {
ParameterSet existingParams = context.getTunnelParameters();
if (existingParams == null) {
return assembleParams(context, actualParams);
}
ParameterSet newParams = new ParameterSet(existingParams, (actualParams==null ? 0 : actualParams.length));
if (actualParams == null || actualParams.length == 0) {
return newParams;
}
for (WithParam actualParam : actualParams) {
newParams.put(actualParam.getParameterId(),
actualParam.getSelectValue(context),
false);
}
return newParams;
}
/**
* Simplify an expression. This performs any static optimization (by rewriting the expression
* as a different expression). The default implementation does nothing.
*
* @exception net.sf.saxon.trans.XPathException if an error is discovered during expression
* rewriting
* @return the simplified expression
* @param visitor an expression visitor
*/
/*@NotNull*/
public abstract Expression simplify(ExpressionVisitor visitor) throws XPathException;
/**
* 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 int computeSpecialProperties() {
int p = super.computeSpecialProperties();
if (createsNewNodes()) {
return p;
} else {
return p | StaticProperty.NON_CREATIVE;
}
}
/**
* Determine whether this instruction creates new nodes.
* This implementation returns a default value of false
* @return true if the instruction creates new nodes (or if it can't be proved that it doesn't)
*/
public boolean createsNewNodes() {
return false;
}
/**
* Handle promotion offers, that is, non-local tree rewrites.
* @param offer The type of rewrite being offered
* @throws XPathException if an error occurs
*/
protected void promoteInst(PromotionOffer offer) throws XPathException {
}
/**
* 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.
* 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 the parent of the subexpression
* @exception net.sf.saxon.trans.XPathException if any error is detected
* @return if the offer is not accepted, return this expression unchanged.
* Otherwise return the result of rewriting the expression to promote
* this subexpression
*/
public Expression promote(PromotionOffer offer, Expression parent) throws XPathException {
Expression exp = offer.accept(parent, this);
if (exp!=null) {
return exp;
} else {
promoteInst(offer);
return this;
}
}
/**
* 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
* @exception XPathException if any dynamic error occurs evaluating the
* expression
* @return the node or atomic value that results from evaluating the
* expression; or null to indicate that the result is an empty
* sequence
*/
public Item evaluateItem(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & EVALUATE_METHOD) != 0) {
throw new AssertionError(
"evaluateItem() is not implemented in the subclass " + getClass());
} else if ((m & ITERATE_METHOD) != 0) {
return iterate(context).next();
} else {
Controller controller = context.getController();
assert controller != null;
SequenceReceiver saved = context.getReceiver();
SequenceOutputter seq = controller.allocateSequenceOutputter(1);
seq.getPipelineConfiguration().setHostLanguage(getHostLanguage());
context.setReceiver(seq);
process(context);
context.setReceiver(saved);
seq.close();
Item result = seq.getFirstItem();
seq.reset();
return result;
}
}
/**
* 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.
*
* @exception XPathException if any dynamic error occurs evaluating the
* expression
* @param context supplies the context for evaluation
* @return a SequenceIterator that can be used to iterate over the result
* of the expression
*/
/*@NotNull*/
public SequenceIterator iterate(XPathContext context) throws XPathException {
int m = getImplementationMethod();
if ((m & EVALUATE_METHOD) != 0) {
Item item = evaluateItem(context);
if (item==null) {
return EmptyIterator.emptyIterator();
} else {
return SingletonIterator.makeIterator(item);
}
} else if ((m & ITERATE_METHOD) != 0) {
throw new AssertionError("iterate() is not implemented in the subclass " + getClass());
} else {
return getIteratorFromProcessMethod(context);
}
}
/**
* Helper method to construct an iterator over the results of the expression when all that
* the expression itself offers is a process() method. This builds the entire results of the
* expression as a sequence in memory and then iterates over it.
* @param context the dynamic evaluation context
* @return an iterator over the results of the expression
* @throws XPathException if a dynamic error occurs
*/
final protected SequenceIterator getIteratorFromProcessMethod(XPathContext context) throws XPathException {
// TODO: this fragment of code appears in many places - reuse it!
Controller controller = context.getController();
assert controller != null;
SequenceReceiver saved = context.getReceiver();
SequenceOutputter seq = controller.allocateSequenceOutputter(20);
seq.getPipelineConfiguration().setHostLanguage(getHostLanguage());
context.setReceiver(seq);
process(context);
context.setReceiver(saved);
seq.close();
return seq.iterate();
}
/**
* 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.
*
* @exception net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the
* expression
* @exception java.lang.ClassCastException if the result type of the
* expression is not xs:string?
* @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 "".
*/
public final CharSequence evaluateAsString(XPathContext context) throws XPathException {
Item item = evaluateItem(context);
if (item==null) {
return "";
} else {
return item.getStringValue();
}
}
/**
* Get the type of this expression for use in tracing and diagnostics
*
* @return the type of expression, as enumerated in class {@link net.sf.saxon.trace.Location}
*/
public int getConstructType() {
return getInstructionNameCode();
}
/**
* Establish whether this is an XSLT instruction or an XQuery instruction
* (used to produce appropriate diagnostics)
* @return true for XSLT, false for XQuery
*/
public boolean isXSLT() {
return getHostLanguage() == Configuration.XSLT;
}
}