nodetransformer.java

這是一個javascript 的 interpreter是了解 web browser的好材料

                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;
                } else {
                  // 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: {
                Node.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.NAME:
              case Token.SETNAME:
              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();
                Node.Scope defining = scope.getDefiningScope(name);
                if (defining != null) {
                    nameSource.setScope(defining);
                    if (type == Token.NAME) {
                        node.setType(Token.GETVAR);
                    } else if (type == Token.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 Node.Scope ? (Node.Scope)node : scope,
                createScopeObjects);
        }
    }

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

    protected void visitCall(Node node, ScriptOrFnNode 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<Object> list = new ArrayList<Object>();
            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
                    Node.Scope.joinScopes((Node.Scope)current,
                                          (Node.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((Node.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);
            } else {
                result.addChildToBack(new Node(Token.EXPR_VOID, newVars));
                scopeNode.setType(Token.BLOCK);
                result.addChildToBack(scopeNode);
                scopeNode.addChildrenToBack(body);
            }
        }
        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;
}