CaRMtl/org/mozilla/javascript/Node.java

/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Rhino code, released
 * May 6, 1999.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1997-1999
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Norris Boyd
 *   Roshan James
 *   Roger Lawrence
 *   Mike McCabe
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License Version 2 or later (the "GPL"), in which
 * case the provisions of the GPL are applicable instead of those above. If
 * you wish to allow use of your version of this file only under the terms of
 * the GPL and not to allow others to use your version of this file under the
 * MPL, indicate your decision by deleting the provisions above and replacing
 * them with the notice and other provisions required by the GPL. If you do
 * not delete the provisions above, a recipient may use your version of this
 * file under either the MPL or the GPL.
 *
 * ***** END LICENSE BLOCK ***** */

package org.mozilla.javascript;

import java.util.Map;
import java.util.LinkedHashMap;
import java.util.Iterator;
import java.util.Collections;

/**
 * This class implements the root of the intermediate representation.
 *
 * @author Norris Boyd
 * @author Mike McCabe
 */

public class Node
{
    public static final int
        FUNCTION_PROP      =  1,
        LOCAL_PROP         =  2,
        LOCAL_BLOCK_PROP   =  3,
        REGEXP_PROP        =  4,
        CASEARRAY_PROP     =  5,
    /*
        the following properties are defined and manipulated by the
        optimizer -
        TARGETBLOCK_PROP - the block referenced by a branch node
        VARIABLE_PROP - the variable referenced by a BIND or NAME node
        ISNUMBER_PROP - this node generates code on Number children and
                        delivers a Number result (as opposed to Objects)
        DIRECTCALL_PROP - this call node should emit code to test the function
                          object against the known class and call direct if it
                          matches.
    */

        TARGETBLOCK_PROP   =  6,
        VARIABLE_PROP      =  7,
        ISNUMBER_PROP      =  8,
        DIRECTCALL_PROP    =  9,
        SPECIALCALL_PROP   = 10,
        SKIP_INDEXES_PROP  = 11, // array of skipped indexes of array literal
        OBJECT_IDS_PROP    = 12, // array of properties for object literal
        INCRDECR_PROP      = 13, // pre or post type of increment/decrement
        CATCH_SCOPE_PROP   = 14, // index of catch scope block in catch
        LABEL_ID_PROP      = 15, // label id: code generation uses it
        MEMBER_TYPE_PROP   = 16, // type of element access operation
        NAME_PROP          = 17, // property name
        CONTROL_BLOCK_PROP = 18, // flags a control block that can drop off
        PARENTHESIZED_PROP = 19, // expression is parenthesized
        GENERATOR_END_PROP = 20,
        DESTRUCTURING_ARRAY_LENGTH = 21,
        DESTRUCTURING_NAMES= 22,
        LAST_PROP          = 22;

    // values of ISNUMBER_PROP to specify
    // which of the children are Number types
    public static final int
        BOTH = 0,
        LEFT = 1,
        RIGHT = 2;

    public static final int    // values for SPECIALCALL_PROP
        NON_SPECIALCALL  = 0,
        SPECIALCALL_EVAL = 1,
        SPECIALCALL_WITH = 2;

    public static final int   // flags for INCRDECR_PROP
        DECR_FLAG = 0x1,
        POST_FLAG = 0x2;

    public static final int   // flags for MEMBER_TYPE_PROP
        PROPERTY_FLAG    = 0x1, // property access: element is valid name
        ATTRIBUTE_FLAG   = 0x2, // x.@y or x..@y
        DESCENDANTS_FLAG = 0x4; // x..y or x..@i

    private static class NumberNode extends Node
    {
        NumberNode(double number)
        {
            super(Token.NUMBER);
            this.number = number;
        }

        double number;
    }

    private static class StringNode extends Node
    {
        StringNode(int type, String str) {
            super(type);
            this.str = str;
        }

        String str;
        Node.Scope scope;
    }

    public static class Jump extends Node
    {
        public Jump(int type)
        {
            super(type);
        }

        Jump(int type, int lineno)
        {
            super(type, lineno);
        }

        Jump(int type, Node child)
        {
            super(type, child);
        }

        Jump(int type, Node child, int lineno)
        {
            super(type, child, lineno);
        }

        public final Jump getJumpStatement()
        {
            if (!(type == Token.BREAK || type == Token.CONTINUE)) Kit.codeBug();
            return jumpNode;
        }

        public final void setJumpStatement(Jump jumpStatement)
        {
            if (!(type == Token.BREAK || type == Token.CONTINUE)) Kit.codeBug();
            if (jumpStatement == null) Kit.codeBug();
            if (this.jumpNode != null) Kit.codeBug(); //only once
            this.jumpNode = jumpStatement;
        }

        public final Node getDefault()
        {
            if (!(type == Token.SWITCH)) Kit.codeBug();
            return target2;
        }

        public final void setDefault(Node defaultTarget)
        {
            if (!(type == Token.SWITCH)) Kit.codeBug();
            if (defaultTarget.type != Token.TARGET) Kit.codeBug();
            if (target2 != null) Kit.codeBug(); //only once
            target2 = defaultTarget;
        }

        public final Node getFinally()
        {
            if (!(type == Token.TRY)) Kit.codeBug();
            return target2;
        }

        public final void setFinally(Node finallyTarget)
        {
            if (!(type == Token.TRY)) Kit.codeBug();
            if (finallyTarget.type != Token.TARGET) Kit.codeBug();
            if (target2 != null) Kit.codeBug(); //only once
            target2 = finallyTarget;
        }

        public final Jump getLoop()
        {
            if (!(type == Token.LABEL)) Kit.codeBug();
            return jumpNode;
        }

        public final void setLoop(Jump loop)
        {
            if (!(type == Token.LABEL)) Kit.codeBug();
            if (loop == null) Kit.codeBug();
            if (jumpNode != null) Kit.codeBug(); //only once
            jumpNode = loop;
        }

        public final Node getContinue()
        {
            if (type != Token.LOOP) Kit.codeBug();
            return target2;
        }

        public final void setContinue(Node continueTarget)
        {
            if (type != Token.LOOP) Kit.codeBug();
            if (continueTarget.type != Token.TARGET) Kit.codeBug();
            if (target2 != null) Kit.codeBug(); //only once
            target2 = continueTarget;
        }

        public Node target;
        private Node target2;
        private Jump jumpNode;
    }
    
    static class Symbol {
        Symbol(int declType, String name) {
            this.declType = declType;
            this.name = name;
            this.index = -1;
        }
        /**
         * One of Token.FUNCTION, Token.LP (for parameters), Token.VAR, 
         * Token.LET, or Token.CONST
         */
        int declType;
        int index;
        String name;
        Node.Scope containingTable;
    }
    
    static class Scope extends Jump {
        public Scope(int nodeType) {
            super(nodeType);
        }
        
        public Scope(int nodeType, int lineno) {
            super(nodeType, lineno);
        }
        
        public Scope(int nodeType, Node n, int lineno) {
            super(nodeType, n, lineno);
        }
        
        /*
         * Creates a new scope node, moving symbol table information
         * from "scope" to the new node, and making "scope" a nested
         * scope contained by the new node.
         * Useful for injecting a new scope in a scope chain.
         */
        public static Scope splitScope(Scope scope) {
            Scope result = new Scope(scope.getType());
            result.symbolTable = scope.symbolTable;
            scope.symbolTable = null;
            result.parent = scope.parent;
            scope.parent = result;
            result.top = scope.top;
            return result;
        }

        public static void joinScopes(Scope source, Scope dest) {
            source.ensureSymbolTable();
            dest.ensureSymbolTable();
            if (!Collections.disjoint(source.symbolTable.keySet(),
                                      dest.symbolTable.keySet()))
            {
                throw Kit.codeBug();
            }
            dest.symbolTable.putAll(source.symbolTable);
        }
        
        public void setParent(Scope parent) {
            this.parent = parent;
            this.top = parent == null ? (ScriptOrFnNode)this : parent.top;
        }
        
        public Scope getParentScope() {
            return parent;
        }
  
        public Scope getDefiningScope(String name) {
            for (Scope sn=this; sn != null; sn = sn.parent) {
                if (sn.symbolTable == null)
                    continue;
                if (sn.symbolTable.containsKey(name))
                    return sn;
            }
            return null;
        }
        
        public Symbol getSymbol(String name) {
            return symbolTable == null ? null : symbolTable.get(name);
        }
        
        public void putSymbol(String name, Symbol symbol) {
            ensureSymbolTable();
            symbolTable.put(name, symbol);
            symbol.containingTable = this;
            top.addSymbol(symbol);
        }
        
        public Map<String,Symbol> getSymbolTable() {
            return symbolTable;
        }
        
        private void ensureSymbolTable() {
            if (symbolTable == null) {
                symbolTable = new LinkedHashMap<String,Symbol>(5);
            }
        }
  
        // Use LinkedHashMap so that the iteration order is the insertion order
        protected LinkedHashMap<String,Symbol> symbolTable;
        private Scope parent;
        private ScriptOrFnNode top;
    }

    private static class PropListItem
    {
        PropListItem next;
        int type;
        int intValue;
        Object objectValue;
    }


    public Node(int nodeType) {
        type = nodeType;
    }

    public Node(int nodeType, Node child) {
        type = nodeType;
        first = last = child;
        child.next = null;
    }

    public Node(int nodeType, Node left, Node right) {
        type = nodeType;
        first = left;
        last = right;
        left.next = right;
        right.next = null;
    }

    public Node(int nodeType, Node left, Node mid, Node right) {
        type = nodeType;
        first = left;
        last = right;
        left.next = mid;
        mid.next = right;
        right.next = null;
    }

    public Node(int nodeType, int line) {
        type = nodeType;
        lineno = line;
    }

    public Node(int nodeType, Node child, int line) {
        this(nodeType, child);
        lineno = line;
    }

    public Node(int nodeType, Node left, Node right, int line) {
        this(nodeType, left, right);
        lineno = line;
    }

    public Node(int nodeType, Node left, Node mid, Node right, int line) {
        this(nodeType, left, mid, right);
        lineno = line;
    }

    public static Node newNumber(double number) {
        return new NumberNode(number);
    }

    public static Node newString(String str) {
        return new StringNode(Token.STRING, str);
    }

    public static Node newString(int type, String str) {
        return new StringNode(type, str);
    }

    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    public boolean hasChildren() {
        return first != null;
    }

    public Node getFirstChild() {
        return first;
    }

    public Node getLastChild() {
        return last;
    }

    public Node getNext() {
        return next;
    }

    public Node getChildBefore(Node child) {
        if (child == first)
            return null;
        Node n = first;
        while (n.next != child) {
            n = n.next;
            if (n == null)
                throw new RuntimeException("node is not a child");
        }
        return n;
    }

    public Node getLastSibling() {
        Node n = this;
        while (n.next != null) {
            n = n.next;
        }
        return n;
    }

    public void addChildToFront(Node child) {
        child.next = first;
        first = child;
        if (last == null) {
            last = child;
        }
    }

    public void addChildToBack(Node child) {
        child.next = null;
        if (last == null) {
            first = last = child;
            return;
        }
        last.next = child;
        last = child;
    }

    public void addChildrenToFront(Node children) {
        Node lastSib = children.getLastSibling();
        lastSib.next = first;
        first = children;
        if (last == null) {
            last = lastSib;
        }
    }

    public void addChildrenToBack(Node children) {
        if (last != null) {
            last.next = children;
        }
        last = children.getLastSibling();
        if (first == null) {
            first = children;
        }
    }

    /**
     * Add 'child' before 'node'.
     */
    public void addChildBefore(Node newChild, Node node) {
        if (newChild.next != null)
            throw new RuntimeException(
                      "newChild had siblings in addChildBefore");
        if (first == node) {
            newChild.next = first;
            first = newChild;
            return;
        }
        Node prev = getChildBefore(node);
        addChildAfter(newChild, prev);
    }

    /**
     * Add 'child' after 'node'.
     */
    public void addChildAfter(Node newChild, Node node) {
        if (newChild.next != null)
            throw new RuntimeException(
                      "newChild had siblings in addChildAfter");
        newChild.next = node.next;
        node.next = newChild;
        if (last == node)
            last = newChild;
    }

    public void removeChild(Node child) {
        Node prev = getChildBefore(child);
        if (prev == null)
            first = first.next;
        else
            prev.next = child.next;
        if (child == last) last = prev;
        child.next = null;
    }

    public void replaceChild(Node child, Node newChild) {
        newChild.next = child.next;
        if (child == first) {
            first = newChild;
        } else {
            Node prev = getChildBefore(child);
            prev.next = newChild;
        }
        if (child == last)
            last = newChild;
        child.next = null;
    }

    public void replaceChildAfter(Node prevChild, Node newChild) {
        Node child = prevChild.next;
        newChild.next = child.next;
        prevChild.next = newChild;
        if (child == last)
            last = newChild;
        child.next = null;
    }

    private static final String propToString(int propType)
    {
        if (Token.printTrees) {
            // If Context.printTrees is false, the compiler
            // can remove all these strings.
            switch (propType) {
                case FUNCTION_PROP:      return "function";
                case LOCAL_PROP:         return "local";
                case LOCAL_BLOCK_PROP:   return "local_block";
                case REGEXP_PROP:        return "regexp";
                case CASEARRAY_PROP:     return "casearray";

                case TARGETBLOCK_PROP:   return "targetblock";
                case VARIABLE_PROP:      return "variable";
                case ISNUMBER_PROP:      return "isnumber";
                case DIRECTCALL_PROP:    return "directcall";

                case SPECIALCALL_PROP:   return "specialcall";
                case SKIP_INDEXES_PROP:  return "skip_indexes";
                case OBJECT_IDS_PROP:    return "object_ids_prop";
                case INCRDECR_PROP:      return "incrdecr_prop";
                case CATCH_SCOPE_PROP:   return "catch_scope_prop";
                case LABEL_ID_PROP:      return "label_id_prop";
                case MEMBER_TYPE_PROP:   return "member_type_prop";
                case NAME_PROP:          return "name_prop";
                case CONTROL_BLOCK_PROP: return "control_block_prop";
                case PARENTHESIZED_PROP: return "parenthesized_prop";
                case GENERATOR_END_PROP: return "generator_end";
                case DESTRUCTURING_ARRAY_LENGTH:
                                         return "destructuring_array_length";
                case DESTRUCTURING_NAMES:return "destructuring_names";

                default: Kit.codeBug();
            }
        }
        return null;
    }

    private PropListItem lookupProperty(int propType)
    {
        PropListItem x = propListHead;
        while (x != null && propType != x.type) {
            x = x.next;
        }
        return x;
    }

    private PropListItem ensureProperty(int propType)
    {
        PropListItem item = lookupProperty(propType);
        if (item == null) {
            item = new PropListItem();
            item.type = propType;
            item.next = propListHead;
            propListHead = item;
        }
        return item;
    }

    public void removeProp(int propType)
    {
        PropListItem x = propListHead;
        if (x != null) {
            PropListItem prev = null;
            while (x.type != propType) {
                prev = x;
                x = x.next;
                if (x == null) { return; }
            }
            if (prev == null) {
                propListHead = x.next;
            } else {
                prev.next = x.next;
            }
        }
    }

    public Object getProp(int propType)
    {
        PropListItem item = lookupProperty(propType);
        if (item == null) { return null; }
        return item.objectValue;
    }

    public int getIntProp(int propType, int defaultValue)
    {
        PropListItem item = lookupProperty(propType);
        if (item == null) { return defaultValue; }
        return item.intValue;
    }

    public int getExistingIntProp(int propType)
    {
        PropListItem item = lookupProperty(propType);
        if (item == null) { Kit.codeBug(); }
        return item.intValue;
    }

    public void putProp(int propType, Object prop)
    {
        if (prop == null) {
            removeProp(propType);
        } else {
            PropListItem item = ensureProperty(propType);
            item.objectValue = prop;
        }
    }

    public void putIntProp(int propType, int prop)
    {
        PropListItem item = ensureProperty(propType);
        item.intValue = prop;
    }

    public int getLineno() {
        return lineno;
    }

    /** Can only be called when <tt>getType() == Token.NUMBER</tt> */
    public final double getDouble() {
        return ((NumberNode)this).number;
    }

    public final void setDouble(double number) {
        ((NumberNode)this).number = number;
    }

    /** Can only be called when node has String context. */
    public final String getString() {
        return ((StringNode)this).str;
    }

    /** Can only be called when node has String context. */
    public final void setString(String s) {
        if (s == null) Kit.codeBug();
        ((StringNode)this).str = s;
    }
    
    /** Can only be called when node has String context. */
    public final Scope getScope() {
        return ((StringNode)this).scope;
    }

    /** Can only be called when node has String context. */
    public final void setScope(Scope s) {
        if (s == null) Kit.codeBug();
        if (!(this instanceof StringNode)) {
            throw Kit.codeBug();
        }
        ((StringNode)this).scope = s;
    }

    public static Node newTarget()
    {
        return new Node(Token.TARGET);
    }

    public final int labelId()
    {
        if (type != Token.TARGET && type != Token.YIELD) Kit.codeBug();
        return getIntProp(LABEL_ID_PROP, -1);
    }

    public void labelId(int labelId)
    {
        if (type != Token.TARGET  && type != Token.YIELD) Kit.codeBug();
        putIntProp(LABEL_ID_PROP, labelId);
    }
    

    /**
     * Does consistent-return analysis on the function body when strict mode is
     * enabled.
     *
     *   function (x) { return (x+1) }
     * is ok, but
     *   function (x) { if (x < 0) return (x+1); }
     * is not becuase the function can potentially return a value when the
     * condition is satisfied and if not, the function does not explicitly
     * return value.
     *
     * This extends to checking mismatches such as "return" and "return <value>"
     * used in the same function. Warnings are not emitted if inconsistent
     * returns exist in code that can be statically shown to be unreachable.
     * Ex.
     *   function (x) { while (true) { ... if (..) { return value } ... } }
     * emits no warning. However if the loop had a break statement, then a
     * warning would be emitted.
     *
     * The consistency analysis looks at control structures such as loops, ifs,
     * switch, try-catch-finally blocks, examines the reachable code paths and
     * warns the user about an inconsistent set of termination possibilities.
     *
     * Caveat: Since the parser flattens many control structures into almost
     * straight-line code with gotos, it makes such analysis hard. Hence this
     * analyser is written to taken advantage of patterns of code generated by
     * the parser (for loops, try blocks and such) and does not do a full
     * control flow analysis of the gotos and break/continue statements.
     * Future changes to the parser will affect this analysis.
     */

    /**
     * These flags enumerate the possible ways a statement/function can
     * terminate. These flags are used by endCheck() and by the Parser to
     * detect inconsistent return usage.
     *
     * END_UNREACHED is reserved for code paths that are assumed to always be
     * able to execute (example: throw, continue)
     *
     * END_DROPS_OFF indicates if the statement can transfer control to the
     * next one. Statement such as return dont. A compound statement may have
     * some branch that drops off control to the next statement.
     *
     * END_RETURNS indicates that the statement can return (without arguments)
     * END_RETURNS_VALUE indicates that the statement can return a value.
     *
     * A compound statement such as
     * if (condition) {
     *   return value;
     * }
     * Will be detected as (END_DROPS_OFF | END_RETURN_VALUE) by endCheck()
     */
    static final int END_UNREACHED = 0;
    static final int END_DROPS_OFF = 1;
    static final int END_RETURNS = 2;
    static final int END_RETURNS_VALUE = 4;
    static final int END_YIELDS = 8;

    /**
     * Checks that every return usage in a function body is consistent with the
     * requirements of strict-mode.
     * @return true if the function satisfies strict mode requirement.
     */
    public boolean hasConsistentReturnUsage()
    {
        int n = endCheck();
        return (n & END_RETURNS_VALUE) == 0 ||
               (n & (END_DROPS_OFF|END_RETURNS|END_YIELDS)) == 0;
    }

    /**
     * Returns in the then and else blocks must be consistent with each other.
     * If there is no else block, then the return statement can fall through.
     * @return logical OR of END_* flags
     */
    private int endCheckIf()
    {
        Node th, el;
        int rv = END_UNREACHED;

        th = next;
        el = ((Jump)this).target;

        rv = th.endCheck();

        if (el != null)
            rv |= el.endCheck();
        else
            rv |= END_DROPS_OFF;

        return rv;
    }

    /**
     * Consistency of return statements is checked between the case statements.
     * If there is no default, then the switch can fall through. If there is a
     * default,we check to see if all code paths in the default return or if
     * there is a code path that can fall through.
     * @return logical OR of END_* flags
     */
    private int endCheckSwitch()
    {
        Node n;
        int rv = END_UNREACHED;

        // examine the cases
        for (n = first.next; n != null; n = n.next)
        {
            if (n.type == Token.CASE) {
                rv |= ((Jump)n).target.endCheck();
            } else
                break;
        }

        // we don't care how the cases drop into each other
        rv &= ~END_DROPS_OFF;

        // examine the default
        n = ((Jump)this).getDefault();
        if (n != null)
            rv |= n.endCheck();
        else
            rv |= END_DROPS_OFF;

        // remove the switch block
        rv |= getIntProp(CONTROL_BLOCK_PROP, END_UNREACHED);

        return rv;
    }

    /**
     * If the block has a finally, return consistency is checked in the
     * finally block. If all code paths in the finally returns, then the
     * returns in the try-catch blocks don't matter. If there is a code path
     * that does not return or if there is no finally block, the returns
     * of the try and catch blocks are checked for mismatch.
     * @return logical OR of END_* flags
     */
    private int endCheckTry()
    {
        Node n;
        int rv = END_UNREACHED;

        // check the finally if it exists
        n = ((Jump)this).getFinally();
        if(n != null) {
            rv = n.next.first.endCheck();
        } else {
            rv = END_DROPS_OFF;
        }

        // if the finally block always returns, then none of the returns
        // in the try or catch blocks matter
        if ((rv & END_DROPS_OFF) != 0) {
            rv &= ~END_DROPS_OFF;

            // examine the try block
            rv |= first.endCheck();

            // check each catch block
            n = ((Jump)this).target;
            if (n != null)
            {
                // point to the first catch_scope
                for (n = n.next.first; n != null; n = n.next.next)
                {
                    // check the block of user code in the catch_scope
                    rv |= n.next.first.next.first.endCheck();
                }
            }
        }

        return rv;
    }

    /**
     * Return statement in the loop body must be consistent. The default
     * assumption for any kind of a loop is that it will eventually terminate.
     * The only exception is a loop with a constant true condition. Code that
     * follows such a loop is examined only if one can statically determine
     * that there is a break out of the loop.
     *  for(<> ; <>; <>) {}
     *  for(<> in <> ) {}
     *  while(<>) { }
     *  do { } while(<>)
     * @return logical OR of END_* flags
     */
    private int endCheckLoop()
    {
        Node n;
        int rv = END_UNREACHED;

        // To find the loop body, we look at the second to last node of the
        // loop node, which should be the predicate that the loop should
        // satisfy.
        // The target of the predicate is the loop-body for all 4 kinds of
        // loops.
        for (n = first; n.next != last; n = n.next) {
            /* skip */
        }
        if (n.type != Token.IFEQ)
            return END_DROPS_OFF;

        // The target's next is the loop body block
        rv = ((Jump)n).target.next.endCheck();

        // check to see if the loop condition is true
        if (n.first.type == Token.TRUE)
            rv &= ~END_DROPS_OFF;

        // look for effect of breaks
        rv |= getIntProp(CONTROL_BLOCK_PROP, END_UNREACHED);

        return rv;
    }


    /**
     * A general block of code is examined statement by statement. If any
     * statement (even compound ones) returns in all branches, then subsequent
     * statements are not examined.
     * @return logical OR of END_* flags
     */
    private int endCheckBlock()
    {
        Node n;
        int rv = END_DROPS_OFF;

        // check each statment and if the statement can continue onto the next
        // one, then check the next statement
        for (n=first; ((rv & END_DROPS_OFF) != 0) && n != null; n = n.next)
        {
            rv &= ~END_DROPS_OFF;
            rv |= n.endCheck();
        }
        return rv;
    }

    /**
     * A labelled statement implies that there maybe a break to the label. The
     * function processes the labelled statement and then checks the
     * CONTROL_BLOCK_PROP property to see if there is ever a break to the
     * particular label.
     * @return logical OR of END_* flags
     */
    private int endCheckLabel()
    {
        int rv = END_UNREACHED;

        rv = next.endCheck();
        rv |= getIntProp(CONTROL_BLOCK_PROP, END_UNREACHED);

        return rv;
    }

    /**
     * When a break is encountered annotate the statement being broken
     * out of by setting its CONTROL_BLOCK_PROP property.
     * @return logical OR of END_* flags
     */
    private int endCheckBreak()
    {
        Node n = ((Jump) this).jumpNode;
        n.putIntProp(CONTROL_BLOCK_PROP, END_DROPS_OFF);
        return END_UNREACHED;
    }

    /**
     * endCheck() examines the body of a function, doing a basic reachability
     * analysis and returns a combination of flags END_* flags that indicate
     * how the function execution can terminate. These constitute only the
     * pessimistic set of termination conditions. It is possible that at
     * runtime certain code paths will never be actually taken. Hence this
     * analysis will flag errors in cases where there may not be errors.
     * @return logical OR of END_* flags
     */
    private int endCheck()
    {
        switch(type)
        {
            case Token.BREAK:
                return endCheckBreak();

            case Token.EXPR_VOID:
                if (this.first != null)
                    return first.endCheck();
                return END_DROPS_OFF;

            case Token.YIELD:
                return END_YIELDS;

            case Token.CONTINUE:
            case Token.THROW:
                return END_UNREACHED;

            case Token.RETURN:
                if (this.first != null)
                    return END_RETURNS_VALUE;
                else
                    return END_RETURNS;

            case Token.TARGET:
                if (next != null)
                    return next.endCheck();
                else
                    return END_DROPS_OFF;

            case Token.LOOP:
                return endCheckLoop();

            case Token.LOCAL_BLOCK:
            case Token.BLOCK:
                // there are several special kinds of blocks
                if (first == null)
                    return END_DROPS_OFF;

                switch(first.type) {
                    case Token.LABEL:
                        return first.endCheckLabel();

                    case Token.IFNE:
                        return first.endCheckIf();

                    case Token.SWITCH:
                        return first.endCheckSwitch();

                    case Token.TRY:
                        return first.endCheckTry();

                    default:
                        return endCheckBlock();
                }

            default:
                return END_DROPS_OFF;
        }
    }

    public boolean hasSideEffects()
    {
        switch (type) {
          case Token.EXPR_VOID:
          case Token.COMMA:
            if (last != null)
                return last.hasSideEffects();
            else
                return true;

          case Token.HOOK:
            if (first == null ||
                first.next == null ||
                first.next.next == null)
                Kit.codeBug();
            return first.next.hasSideEffects() &&
                   first.next.next.hasSideEffects();

          case Token.AND:
          case Token.OR:
            if (first == null || last == null)
                Kit.codeBug();
            return first.hasSideEffects() || last.hasSideEffects();

          case Token.ERROR:         // Avoid cascaded error messages
          case Token.EXPR_RESULT:
          case Token.ASSIGN:
          case Token.ASSIGN_ADD:
          case Token.ASSIGN_SUB:
          case Token.ASSIGN_MUL:
          case Token.ASSIGN_DIV:
          case Token.ASSIGN_MOD:
          case Token.ASSIGN_BITOR:
          case Token.ASSIGN_BITXOR:
          case Token.ASSIGN_BITAND:
          case Token.ASSIGN_LSH:
          case Token.ASSIGN_RSH:
          case Token.ASSIGN_URSH:
          case Token.ENTERWITH:
          case Token.LEAVEWITH:
          case Token.RETURN:
          case Token.GOTO:
          case Token.IFEQ:
          case Token.IFNE:
          case Token.NEW:
          case Token.DELPROP:
          case Token.SETNAME:
          case Token.SETPROP:
          case Token.SETELEM:
          case Token.CALL:
          case Token.THROW:
          case Token.RETHROW:
          case Token.SETVAR:
          case Token.CATCH_SCOPE:
          case Token.RETURN_RESULT:
          case Token.SET_REF:
          case Token.DEL_REF:
          case Token.REF_CALL:
          case Token.TRY:
          case Token.SEMI:
          case Token.INC:
          case Token.DEC:
          case Token.EXPORT:
          case Token.IMPORT:
          case Token.IF:
          case Token.ELSE:
          case Token.SWITCH:
          case Token.WHILE:
          case Token.DO:
          case Token.FOR:
          case Token.BREAK:
          case Token.CONTINUE:
          case Token.VAR:
          case Token.CONST:
          case Token.LET:
          case Token.LETEXPR:
          case Token.WITH:
          case Token.WITHEXPR:
          case Token.CATCH:
          case Token.FINALLY:
          case Token.BLOCK:
          case Token.LABEL:
          case Token.TARGET:
          case Token.LOOP:
          case Token.JSR:
          case Token.SETPROP_OP:
          case Token.SETELEM_OP:
          case Token.LOCAL_BLOCK:
          case Token.SET_REF_OP:
          case Token.YIELD:
            return true;

          default:
            return false;
        }
    }

    @Override
    public String toString()
    {
        if (Token.printTrees) {
            StringBuffer sb = new StringBuffer();
            toString(new ObjToIntMap(), sb);
            return sb.toString();
        }
        return String.valueOf(type);
    }

    private void toString(ObjToIntMap printIds, StringBuffer sb)
    {
        if (Token.printTrees) {
            sb.append(Token.name(type));
            if (this instanceof StringNode) {
                sb.append(' ');
                sb.append(getString());
                Scope scope = getScope();
                if (scope != null) {
                    sb.append("[scope: ");
                    appendPrintId(scope, printIds, sb);
                    sb.append("]");
                }
            } else if (this instanceof Node.Scope) {
                if (this instanceof ScriptOrFnNode) {
                    ScriptOrFnNode sof = (ScriptOrFnNode)this;
                    if (this instanceof FunctionNode) {
                        FunctionNode fn = (FunctionNode)this;
                        sb.append(' ');
                        sb.append(fn.getFunctionName());
                    }
                    sb.append(" [source name: ");
                    sb.append(sof.getSourceName());
                    sb.append("] [encoded source length: ");
                    sb.append(sof.getEncodedSourceEnd()
                              - sof.getEncodedSourceStart());
                    sb.append("] [base line: ");
                    sb.append(sof.getBaseLineno());
                    sb.append("] [end line: ");
                    sb.append(sof.getEndLineno());
                    sb.append(']');
                }
                if (((Node.Scope)this).symbolTable != null) {
                    sb.append(" [scope ");
                    appendPrintId(this, printIds, sb);
                    sb.append(": ");
                    Iterator<String> iter =
                        ((Node.Scope) this).symbolTable.keySet().iterator();
                    while (iter.hasNext()) {
                        sb.append(iter.next());
                        sb.append(" ");
                    }
                    sb.append("]");
                }
            } else if (this instanceof Jump) {
                Jump jump = (Jump)this;
                if (type == Token.BREAK || type == Token.CONTINUE) {
                    sb.append(" [label: ");
                    appendPrintId(jump.getJumpStatement(), printIds, sb);
                    sb.append(']');
                } else if (type == Token.TRY) {
                    Node catchNode = jump.target;
                    Node finallyTarget = jump.getFinally();
                    if (catchNode != null) {
                        sb.append(" [catch: ");
                        appendPrintId(catchNode, printIds, sb);
                        sb.append(']');
                    }
                    if (finallyTarget != null) {
                        sb.append(" [finally: ");
                        appendPrintId(finallyTarget, printIds, sb);
                        sb.append(']');
                    }
                } else if (type == Token.LABEL || type == Token.LOOP
                           || type == Token.SWITCH)
                {
                    sb.append(" [break: ");
                    appendPrintId(jump.target, printIds, sb);
                    sb.append(']');
                    if (type == Token.LOOP) {
                        sb.append(" [continue: ");
                        appendPrintId(jump.getContinue(), printIds, sb);
                        sb.append(']');
                    }
                } else {
                    sb.append(" [target: ");
                    appendPrintId(jump.target, printIds, sb);
                    sb.append(']');
                }
            } else if (type == Token.NUMBER) {
                sb.append(' ');
                sb.append(getDouble());
            } else if (type == Token.TARGET) {
                sb.append(' ');
                appendPrintId(this, printIds, sb);
            }
            if (lineno != -1) {
                sb.append(' ');
                sb.append(lineno);
            }

            for (PropListItem x = propListHead; x != null; x = x.next) {
                int type = x.type;
                sb.append(" [");
                sb.append(propToString(type));
                sb.append(": ");
                String value;
                switch (type) {
                  case TARGETBLOCK_PROP : // can't add this as it recurses
                    value = "target block property";
                    break;
                  case LOCAL_BLOCK_PROP :     // can't add this as it is dull
                    value = "last local block";
                    break;
                  case ISNUMBER_PROP:
                    switch (x.intValue) {
                      case BOTH:
                        value = "both";
                        break;
                      case RIGHT:
                        value = "right";
                        break;
                      case LEFT:
                        value = "left";
                        break;
                      default:
                        throw Kit.codeBug();
                    }
                    break;
                  case SPECIALCALL_PROP:
                    switch (x.intValue) {
                      case SPECIALCALL_EVAL:
                        value = "eval";
                        break;
                      case SPECIALCALL_WITH:
                        value = "with";
                        break;
                      default:
                        // NON_SPECIALCALL should not be stored
                        throw Kit.codeBug();
                    }
                    break;
                  case OBJECT_IDS_PROP: {
                    Object[] a = (Object[]) x.objectValue;
                    value = "[";
                    for (int i=0; i < a.length; i++) {
                        value += a[i].toString();
                        if (i+1 < a.length)
                            value += ", ";
                    }
                    value += "]";
                    break;
                  }
                  default :
                    Object obj = x.objectValue;
                    if (obj != null) {
                        value = obj.toString();
                    } else {
                        value = String.valueOf(x.intValue);
                    }
                    break;
                }
                sb.append(value);
                sb.append(']');
            }
        }
    }

    public String toStringTree(ScriptOrFnNode treeTop) {
        if (Token.printTrees) {
            StringBuffer sb = new StringBuffer();
            toStringTreeHelper(treeTop, this, null, 0, sb);
            return sb.toString();
        }
        return null;
    }

    private static void toStringTreeHelper(ScriptOrFnNode treeTop, Node n,
                                           ObjToIntMap printIds,
                                           int level, StringBuffer sb)
    {
        if (Token.printTrees) {
            if (printIds == null) {
                printIds = new ObjToIntMap();
                generatePrintIds(treeTop, printIds);
            }
            for (int i = 0; i != level; ++i) {
                sb.append("    ");
            }
            n.toString(printIds, sb);
            sb.append('\n');
            for (Node cursor = n.getFirstChild(); cursor != null;
                 cursor = cursor.getNext())
            {
                if (cursor.getType() == Token.FUNCTION) {
                    int fnIndex = cursor.getExistingIntProp(Node.FUNCTION_PROP);
                    FunctionNode fn = treeTop.getFunctionNode(fnIndex);
                    toStringTreeHelper(fn, fn, null, level + 1, sb);
                } else {
                    toStringTreeHelper(treeTop, cursor, printIds, level + 1, sb);
                }
            }
        }
    }

    private static void generatePrintIds(Node n, ObjToIntMap map)
    {
        if (Token.printTrees) {
            map.put(n, map.size());
            for (Node cursor = n.getFirstChild(); cursor != null;
                 cursor = cursor.getNext())
            {
                generatePrintIds(cursor, map);
            }
        }
    }

    private static void appendPrintId(Node n, ObjToIntMap printIds,
                                      StringBuffer sb)
    {
        if (Token.printTrees) {
            if (n != null) {
                int id = printIds.get(n, -1);
                sb.append('#');
                if (id != -1) {
                    sb.append(id + 1);
                } else {
                    sb.append("<not_available>");
                }
            }
        }
    }

    int type;              // type of the node; Token.NAME for example
    Node next;             // next sibling
    private Node first;    // first element of a linked list of children
    private Node last;     // last element of a linked list of children
    protected int lineno = -1;

    /**
     * Linked list of properties. Since vast majority of nodes would have
     * no more then 2 properties, linked list saves memory and provides
     * fast lookup. If this does not holds, propListHead can be replaced
     * by UintMap.
     */
    private PropListItem propListHead;
}