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    Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.

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    /* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * 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/. */

package org.mozilla.javascript;

import java.util.ArrayList;
import java.util.List;
import org.mozilla.javascript.ast.FunctionNode;
import org.mozilla.javascript.ast.Jump;
import org.mozilla.javascript.ast.Scope;
import org.mozilla.javascript.ast.ScriptNode;

/**
 * This class transforms a tree to a lower-level representation for codegen.
 *
 * @see Node
 * @author Norris Boyd
 */
public class NodeTransformer {

    public NodeTransformer() {}

    public final void transform(ScriptNode tree, CompilerEnvirons env) {
        transform(tree, false, env);
    }

    public final void transform(ScriptNode tree, boolean inStrictMode, CompilerEnvirons env) {
        boolean useStrictMode = inStrictMode;
        // Support strict mode inside a function only for "ES6" language level
        // and above. Otherwise, we will end up breaking backward compatibility for
        // many existing scripts.
        if ((env.getLanguageVersion() >= Context.VERSION_ES6) && tree.isInStrictMode()) {
            useStrictMode = true;
        }
        transformCompilationUnit(tree, useStrictMode);
        for (int i = 0; i != tree.getFunctionCount(); ++i) {
            FunctionNode fn = tree.getFunctionNode(i);
            transform(fn, useStrictMode, env);
        }
    }

    private void transformCompilationUnit(ScriptNode tree, boolean inStrictMode) {
        loops = new ObjArray();
        loopEnds = new ObjArray();

        // to save against upchecks if no finally blocks are used.
        hasFinally = false;

        // Flatten all only if we are not using scope objects for block scope
        boolean createScopeObjects =
                tree.getType() != Token.FUNCTION || ((FunctionNode) tree).requiresActivation();
        tree.flattenSymbolTable(!createScopeObjects);

        // uncomment to print tree before transformation
        if (Token.printTrees) System.out.println(tree.toStringTree(tree));
        transformCompilationUnit_r(tree, tree, tree, createScopeObjects, inStrictMode);
    }

    private void transformCompilationUnit_r(
            final ScriptNode tree,
            final Node parent,
            Scope scope,
            boolean createScopeObjects,
            boolean inStrictMode) {
        Node node = null;
        siblingLoop:
        for (; ; ) {
            Node previous = null;
            if (node == null) {
                node = parent.getFirstChild();
            } else {
                previous = node;
                node = node.getNext();
            }
            if (node == null) {
                break;
            }

            int type = node.getType();
            if (createScopeObjects
                    && (type == Token.BLOCK || type == Token.LOOP || type == Token.ARRAYCOMP)
                    && (node instanceof Scope)) {
                Scope newScope = (Scope) node;
                if (newScope.getSymbolTable() != null) {
                    // transform to let statement so we get a with statement
                    // created to contain scoped let variables
                    Node let = new Node(type == Token.ARRAYCOMP ? Token.LETEXPR : Token.LET);
                    Node innerLet = new Node(Token.LET);
                    let.addChildToBack(innerLet);
                    for (String name : newScope.getSymbolTable().keySet()) {
                        innerLet.addChildToBack(Node.newString(Token.NAME, name));
                    }
                    newScope.setSymbolTable(null); // so we don't transform again
                    Node oldNode = node;
                    node = replaceCurrent(parent, previous, node, let);
                    type = node.getType();
                    let.addChildToBack(oldNode);
                }
            }

            switch (type) {
                case Token.LABEL:
                case Token.SWITCH:
                case Token.LOOP:
                    loops.push(node);
                    loopEnds.push(((Jump) node).target);
                    break;

                case Token.WITH:
                    {
                        loops.push(node);
                        Node leave = node.getNext();
                        if (leave.getType() != Token.LEAVEWITH) {
                            Kit.codeBug();
                        }
                        loopEnds.push(leave);
                        break;
                    }

                case Token.TRY:
                    {
                        Jump jump = (Jump) node;
                        Node finallytarget = jump.getFinally();
                        if (finallytarget != null) {
                            hasFinally = true;
                            loops.push(node);
                            loopEnds.push(finallytarget);
                        }
                        break;
                    }

                case Token.TARGET:
                case Token.LEAVEWITH:
                    if (!loopEnds.isEmpty() && loopEnds.peek() == node) {
                        loopEnds.pop();
                        loops.pop();
                    }
                    break;

                case Token.YIELD:
                case Token.YIELD_STAR:
                    ((FunctionNode) tree).addResumptionPoint(node);
                    break;

                case Token.RETURN:
                    {
                        boolean isGenerator =
                                tree.getType() == Token.FUNCTION
                                        && ((FunctionNode) tree).isGenerator();
                        if (isGenerator) {
                            node.putIntProp(Node.GENERATOR_END_PROP, 1);
                        }
                        /* If we didn't support try/finally, it wouldn't be
                         * necessary to put LEAVEWITH nodes here... but as
                         * we do need a series of JSR FINALLY nodes before
                         * each RETURN, we need to ensure that each finally
                         * block gets the correct scope... which could mean
                         * that some LEAVEWITH nodes are necessary.
                         */
                        if (!hasFinally) break; // skip the whole mess.
                        Node unwindBlock = null;
                        for (int i = loops.size() - 1; i >= 0; i--) {
                            Node n = (Node) loops.get(i);
                            int elemtype = n.getType();
                            if (elemtype == Token.TRY || elemtype == Token.WITH) {
                                Node unwind;
                                if (elemtype == Token.TRY) {
                                    Jump jsrnode = new Jump(Token.JSR);
                                    jsrnode.target = ((Jump) n).getFinally();
                                    unwind = jsrnode;
                                } else {
                                    unwind = new Node(Token.LEAVEWITH);
                                }
                                if (unwindBlock == null) {
                                    unwindBlock = new Node(Token.BLOCK, node.getLineno());
                                }
                                unwindBlock.addChildToBack(unwind);
                            }
                        }
                        if (unwindBlock != null) {
                            Node returnNode = node;
                            Node returnExpr = returnNode.getFirstChild();
                            node = replaceCurrent(parent, previous, node, unwindBlock);
                            if (returnExpr == null || isGenerator) {
                                unwindBlock.addChildToBack(returnNode);
                            } else {
                                Node store = new Node(Token.EXPR_RESULT, returnExpr);
                                unwindBlock.addChildToFront(store);
                                returnNode = new Node(Token.RETURN_RESULT);
                                unwindBlock.addChildToBack(returnNode);
                                // transform return expression
                                transformCompilationUnit_r(
                                        tree, store, scope, createScopeObjects, inStrictMode);
                            }
                            // skip transformCompilationUnit_r to avoid infinite loop
                            continue siblingLoop;
                        }
                        break;
                    }

                case Token.BREAK:
                case Token.CONTINUE:
                    {
                        Jump jump = (Jump) node;
                        Jump jumpStatement = jump.getJumpStatement();
                        if (jumpStatement == null) Kit.codeBug();

                        for (int i = loops.size(); ; ) {
                            if (i == 0) {
                                // Parser/IRFactory ensure that break/continue
                                // always has a jump statement associated with it
                                // which should be found
                                throw Kit.codeBug();
                            }
                            --i;
                            Node n = (Node) loops.get(i);
                            if (n == jumpStatement) {
                                break;
                            }

                            int elemtype = n.getType();
                            if (elemtype == Token.WITH) {
                                Node leave = new Node(Token.LEAVEWITH);
                                previous = addBeforeCurrent(parent, previous, node, leave);
                            } else if (elemtype == Token.TRY) {
                                Jump tryNode = (Jump) n;
                                Jump jsrFinally = new Jump(Token.JSR);
                                jsrFinally.target = tryNode.getFinally();
                                previous = addBeforeCurrent(parent, previous, node, jsrFinally);
                            }
                        }

                        if (type == Token.BREAK) {
                            jump.target = jumpStatement.target;
                        } else {
                            jump.target = jumpStatement.getContinue();
                        }
                        jump.setType(Token.GOTO);

                        break;
                    }

                case Token.CALL:
                    visitCall(node, tree);
                    break;

                case Token.NEW:
                    visitNew(node, tree);
                    break;

                case Token.LETEXPR:
                case Token.LET:
                    {
                        Node child = node.getFirstChild();
                        if (child.getType() == Token.LET) {
                            // We have a let statement or expression rather than a
                            // let declaration
                            boolean createWith =
                                    tree.getType() != Token.FUNCTION
                                            || ((FunctionNode) tree).requiresActivation();
                            node = visitLet(createWith, parent, previous, node);
                            break;
                        }
                        // fall through to process let declaration...
                    }
                    /* fall through */
                case Token.CONST:
                case Token.VAR:
                    {
                        Node result = new Node(Token.BLOCK);
                        for (Node cursor = node.getFirstChild(); cursor != null; ) {
                            // Move cursor to next before createAssignment gets chance
                            // to change n.next
                            Node n = cursor;
                            cursor = cursor.getNext();
                            if (n.getType() == Token.NAME) {
                                if (!n.hasChildren()) continue;
                                Node init = n.getFirstChild();
                                n.removeChild(init);
                                n.setType(Token.BINDNAME);
                                n =
                                        new Node(
                                                type == Token.CONST
                                                        ? Token.SETCONST
                                                        : Token.SETNAME,
                                                n,
                                                init);
                            } else {
                                // May be a destructuring assignment already transformed
                                // to a LETEXPR
                                if (n.getType() != Token.LETEXPR) throw Kit.codeBug();
                            }
                            Node pop = new Node(Token.EXPR_VOID, n, node.getLineno());
                            result.addChildToBack(pop);
                        }
                        node = replaceCurrent(parent, previous, node, result);
                        break;
                    }

                case Token.TYPEOFNAME:
                    {
                        Scope defining = scope.getDefiningScope(node.getString());
                        if (defining != null) {
                            node.setScope(defining);
                        }
                    }
                    break;

                case Token.TYPEOF:
                case Token.IFNE:
                    {
                        /* We want to suppress warnings for undefined property o.p
                         * for the following constructs: typeof o.p, if (o.p),
                         * if (!o.p), if (o.p == undefined), if (undefined == o.p)
                         */
                        Node child = node.getFirstChild();
                        if (type == Token.IFNE) {
                            while (child.getType() == Token.NOT) {
                                child = child.getFirstChild();
                            }
                            if (child.getType() == Token.EQ || child.getType() == Token.NE) {
                                Node first = child.getFirstChild();
                                Node last = child.getLastChild();
                                if (first.getType() == Token.NAME
                                        && first.getString().equals("undefined")) {
                                    child = last;
                                } else if (last.getType() == Token.NAME
                                        && last.getString().equals("undefined")) {
                                    child = first;
                                }
                            }
                        }
                        if (child.getType() == Token.GETPROP) {
                            child.setType(Token.GETPROPNOWARN);
                        }
                        break;
                    }

                case Token.SETNAME:
                    if (inStrictMode) {
                        node.setType(Token.STRICT_SETNAME);
                    }
                    /* fall through */
                case Token.NAME:
                case Token.SETCONST:
                case Token.DELPROP:
                    {
                        // Turn name to var for faster access if possible
                        if (createScopeObjects) {
                            break;
                        }
                        Node nameSource;
                        if (type == Token.NAME) {
                            nameSource = node;
                        } else {
                            nameSource = node.getFirstChild();
                            if (nameSource.getType() != Token.BINDNAME) {
                                if (type == Token.DELPROP) {
                                    break;
                                }
                                throw Kit.codeBug();
                            }
                        }
                        if (nameSource.getScope() != null) {
                            break; // already have a scope set
                        }
                        String name = nameSource.getString();
                        Scope defining = scope.getDefiningScope(name);
                        if (defining != null) {
                            nameSource.setScope(defining);
                            if (type == Token.NAME) {
                                node.setType(Token.GETVAR);
                            } else if (type == Token.SETNAME || type == Token.STRICT_SETNAME) {
                                node.setType(Token.SETVAR);
                                nameSource.setType(Token.STRING);
                            } else if (type == Token.SETCONST) {
                                node.setType(Token.SETCONSTVAR);
                                nameSource.setType(Token.STRING);
                            } else if (type == Token.DELPROP) {
                                // Local variables are by definition permanent
                                Node n = new Node(Token.FALSE);
                                node = replaceCurrent(parent, previous, node, n);
                            } else {
                                throw Kit.codeBug();
                            }
                        }
                        break;
                    }
            }

            transformCompilationUnit_r(
                    tree,
                    node,
                    node instanceof Scope ? (Scope) node : scope,
                    createScopeObjects,
                    inStrictMode);
        }
    }

    protected void visitNew(Node node, ScriptNode tree) {}

    protected void visitCall(Node node, ScriptNode tree) {}

    protected Node visitLet(boolean createWith, Node parent, Node previous, Node scopeNode) {
        Node vars = scopeNode.getFirstChild();
        Node body = vars.getNext();
        scopeNode.removeChild(vars);
        scopeNode.removeChild(body);
        boolean isExpression = scopeNode.getType() == Token.LETEXPR;
        Node result;
        Node newVars;
        if (createWith) {
            result = new Node(isExpression ? Token.WITHEXPR : Token.BLOCK);
            result = replaceCurrent(parent, previous, scopeNode, result);
            ArrayList list = new ArrayList<>();
            Node objectLiteral = new Node(Token.OBJECTLIT);
            for (Node v = vars.getFirstChild(); v != null; v = v.getNext()) {
                Node current = v;
                if (current.getType() == Token.LETEXPR) {
                    // destructuring in let expr, e.g. let ([x, y] = [3, 4]) {}
                    List destructuringNames =
                            (List) current.getProp(Node.DESTRUCTURING_NAMES);
                    Node c = current.getFirstChild();
                    if (c.getType() != Token.LET) throw Kit.codeBug();
                    // Add initialization code to front of body
                    if (isExpression) {
                        body = new Node(Token.COMMA, c.getNext(), body);
                    } else {
                        body = new Node(Token.BLOCK, new Node(Token.EXPR_VOID, c.getNext()), body);
                    }
                    // Update "list" and "objectLiteral" for the variables
                    // defined in the destructuring assignment
                    if (destructuringNames != null) {
                        list.addAll(destructuringNames);
                        for (int i = 0; i < destructuringNames.size(); i++) {
                            objectLiteral.addChildToBack(new Node(Token.VOID, Node.newNumber(0.0)));
                        }
                    }
                    current = c.getFirstChild(); // should be a NAME, checked below
                }
                if (current.getType() != Token.NAME) throw Kit.codeBug();
                list.add(ScriptRuntime.getIndexObject(current.getString()));
                Node init = current.getFirstChild();
                if (init == null) {
                    init = new Node(Token.VOID, Node.newNumber(0.0));
                }
                objectLiteral.addChildToBack(init);
            }
            objectLiteral.putProp(Node.OBJECT_IDS_PROP, list.toArray());
            newVars = new Node(Token.ENTERWITH, objectLiteral);
            result.addChildToBack(newVars);
            result.addChildToBack(new Node(Token.WITH, body));
            result.addChildToBack(new Node(Token.LEAVEWITH));
        } else {
            result = new Node(isExpression ? Token.COMMA : Token.BLOCK);
            result = replaceCurrent(parent, previous, scopeNode, result);
            newVars = new Node(Token.COMMA);
            for (Node v = vars.getFirstChild(); v != null; v = v.getNext()) {
                Node current = v;
                if (current.getType() == Token.LETEXPR) {
                    // destructuring in let expr, e.g. let ([x, y] = [3, 4]) {}
                    Node c = current.getFirstChild();
                    if (c.getType() != Token.LET) throw Kit.codeBug();
                    // Add initialization code to front of body
                    if (isExpression) {
                        body = new Node(Token.COMMA, c.getNext(), body);
                    } else {
                        body = new Node(Token.BLOCK, new Node(Token.EXPR_VOID, c.getNext()), body);
                    }
                    // We're removing the LETEXPR, so move the symbols
                    Scope.joinScopes((Scope) current, (Scope) scopeNode);
                    current = c.getFirstChild(); // should be a NAME, checked below
                }
                if (current.getType() != Token.NAME) throw Kit.codeBug();
                Node stringNode = Node.newString(current.getString());
                stringNode.setScope((Scope) scopeNode);
                Node init = current.getFirstChild();
                if (init == null) {
                    init = new Node(Token.VOID, Node.newNumber(0.0));
                }
                newVars.addChildToBack(new Node(Token.SETVAR, stringNode, init));
            }
            if (isExpression) {
                result.addChildToBack(newVars);
                scopeNode.setType(Token.COMMA);
                result.addChildToBack(scopeNode);
                scopeNode.addChildToBack(body);
                if (body instanceof Scope) {
                    Scope scopeParent = ((Scope) body).getParentScope();
                    ((Scope) body).setParentScope((Scope) scopeNode);
                    ((Scope) scopeNode).setParentScope(scopeParent);
                }
            } else {
                result.addChildToBack(new Node(Token.EXPR_VOID, newVars));
                scopeNode.setType(Token.BLOCK);
                result.addChildToBack(scopeNode);
                scopeNode.addChildrenToBack(body);
                if (body instanceof Scope) {
                    Scope scopeParent = ((Scope) body).getParentScope();
                    ((Scope) body).setParentScope((Scope) scopeNode);
                    ((Scope) scopeNode).setParentScope(scopeParent);
                }
            }
        }
        return result;
    }

    private static Node addBeforeCurrent(Node parent, Node previous, Node current, Node toAdd) {
        if (previous == null) {
            if (!(current == parent.getFirstChild())) Kit.codeBug();
            parent.addChildToFront(toAdd);
        } else {
            if (!(current == previous.getNext())) Kit.codeBug();
            parent.addChildAfter(toAdd, previous);
        }
        return toAdd;
    }

    private static Node replaceCurrent(Node parent, Node previous, Node current, Node replacement) {
        if (previous == null) {
            if (!(current == parent.getFirstChild())) Kit.codeBug();
            parent.replaceChild(current, replacement);
        } else if (previous.next == current) {
            // Check cachedPrev.next == current is necessary due to possible
            // tree mutations
            parent.replaceChildAfter(previous, replacement);
        } else {
            parent.replaceChild(current, replacement);
        }
        return replacement;
    }

    private ObjArray loops;
    private ObjArray loopEnds;
    private boolean hasFinally;
}
    
    
    
    

    




    
    
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