Class AstNode

  • All Implemented Interfaces:
    Comparable<AstNode>, Iterable<Node>
    Direct Known Subclasses:
    ArrayLiteral, Block, CatchClause, Comment, ConditionalExpression, ElementGet, EmptyExpression, EmptyStatement, ErrorNode, ExpressionStatement, FunctionCall, IfStatement, InfixExpression, Jump, KeywordLiteral, LabeledStatement, Name, NumberLiteral, ObjectLiteral, ParenthesizedExpression, RegExpLiteral, ReturnStatement, StringLiteral, SwitchCase, ThrowStatement, TryStatement, UnaryExpression, VariableDeclaration, VariableInitializer, WithStatement, XmlFragment, XmlLiteral, XmlRef, Yield

    public abstract class AstNode
    extends Node
    implements Comparable<AstNode>
    Base class for AST node types. The goal of the AST is to represent the physical source code, to make it useful for code-processing tools such as IDEs or pretty-printers. The parser must not rewrite the parse tree when producing this representation.

    The AstNode hierarchy sits atop the older Node class, which was designed for code generation. The Node class is a flexible, weakly-typed class suitable for creating and rewriting code trees, but using it requires you to remember the exact ordering of the child nodes, which are kept in a linked list. The AstNode hierarchy is a strongly-typed facade with named accessors for children and common properties, but under the hood it's still using a linked list of child nodes. It isn't a very good idea to use the child list directly unless you know exactly what you're doing.

    Note that AstNode records additional information, including the node's position, length, and parent node. Also, some AstNode subclasses record some of their child nodes in instance members, since they are not needed for code generation. In a nutshell, only the code generator should be mixing and matching AstNode and Node objects.

    All offset fields in all subclasses of AstNode are relative to their parent. For things like paren, bracket and keyword positions, the position is relative to the current node. The node start position is relative to the parent node.

    During the actual parsing, node positions are absolute; adding the node to its parent fixes up the offsets to be relative. By the time you see the AST (e.g. using the Visitor interface), the offsets are relative.

    AstNode objects have property lists accessible via the Node.getProp(int) and Node.putProp(int, java.lang.Object) methods. The property lists are integer-keyed with arbitrary Object values. For the most part the parser generating the AST avoids using properties, preferring fields for elements that are always set. Property lists are intended for user-defined annotations to the tree. The Rhino code generator acts as a client and uses node properties extensively. You are welcome to use the property-list API for anything your client needs.

    This hierarchy does not have separate branches for expressions and statements, as the distinction in JavaScript is not as clear-cut as in Java or C++.

    • Constructor Detail

      • AstNode

        public AstNode()
      • AstNode

        public AstNode​(int pos)
        Constructs a new AstNode
        pos - the start position
      • AstNode

        public AstNode​(int pos,
                       int len)
        Constructs a new AstNode
        pos - the start position
        len - the number of characters spanned by the node in the source text
    • Method Detail

      • getPosition

        public int getPosition()
        Returns relative position in parent
      • setPosition

        public void setPosition​(int position)
        Sets relative position in parent
      • getAbsolutePosition

        public int getAbsolutePosition()
        Returns the absolute document position of the node. Computes it by adding the node's relative position to the relative positions of all its parents.
      • getLength

        public int getLength()
        Returns node length
      • setLength

        public void setLength​(int length)
        Sets node length
      • setBounds

        public void setBounds​(int position,
                              int end)
        Sets the node start and end positions. Computes the length as (end - position).
      • setRelative

        public void setRelative​(int parentPosition)
        Make this node's position relative to a parent. Typically only used by the parser when constructing the node.
        parentPosition - the absolute parent position; the current node position is assumed to be absolute and is decremented by parentPosition.
      • getParent

        public AstNode getParent()
        Returns the node parent, or null if it has none
      • setParent

        public void setParent​(AstNode parent)
        Sets the node parent. This method automatically adjusts the current node's start position to be relative to the new parent.
        parent - the new parent. Can be null.
      • addChild

        public void addChild​(AstNode kid)
        Adds a child or function to the end of the block. Sets the parent of the child to this node, and fixes up the start position of the child to be relative to this node. Sets the length of this node to include the new child.
        kid - the child
        IllegalArgumentException - if kid is null
      • getAstRoot

        public AstRoot getAstRoot()
        Returns the root of the tree containing this node.
        the AstRoot at the root of this node's parent chain, or null if the topmost parent is not an AstRoot.
      • toSource

        public abstract String toSource​(int depth)
        Emits source code for this node. Callee is responsible for calling this function recursively on children, incrementing indent as appropriate.

        Note: if the parser was in error-recovery mode, some AST nodes may have null children that are expected to be non-null when no errors are present. In this situation, the behavior of the toSource method is undefined: toSource implementations may assume that the AST node is error-free, since it is intended to be invoked only at runtime after a successful parse.

        depth - the current recursion depth, typically beginning at 0 when called on the root node.
      • toSource

        public String toSource()
        Prints the source indented to depth 0.
      • makeIndent

        public String makeIndent​(int indent)
        Constructs an indentation string.
        indent - the number of indentation steps
      • shortName

        public String shortName()
        Returns a short, descriptive name for the node, such as "ArrayComprehension".
      • operatorToString

        public static String operatorToString​(int op)
        Returns the string name for this operator.
        op - the token type, e.g. Token.ADD or Token.TYPEOF
        the source operator string, such as "+" or "typeof"
      • visit

        public abstract void visit​(NodeVisitor visitor)
        Visits this node and its children in an arbitrary order.

        It's up to each node subclass to decide the order for processing its children. The subclass also decides (and should document) which child nodes are not passed to the NodeVisitor. For instance, nodes representing keywords like each or in may not be passed to the visitor object. The visitor can simply query the current node for these children if desired.

        Generally speaking, the order will be deterministic; the order is whatever order is decided by each child node. Normally child nodes will try to visit their children in lexical order, but there may be exceptions to this rule.

        visitor - the object to call with this node and its children
      • hasSideEffects

        public boolean hasSideEffects()
        hasSideEffects in class Node
      • getEnclosingFunction

        public FunctionNode getEnclosingFunction()
        Returns the innermost enclosing function, or null if not in a function. Begins the search with this node's parent.
        the FunctionNode enclosing this node, else null
      • getEnclosingScope

        public Scope getEnclosingScope()
        Returns the innermost enclosing Scope node, or null if we're not nested in a scope. Begins the search with this node's parent. Note that this is not the same as the defining scope for a Name.
        the Scope enclosing this node, else null
      • compareTo

        public int compareTo​(AstNode other)
        Permits AST nodes to be sorted based on start position and length. This makes it easy to sort Comment and Error nodes into a set of other AST nodes: just put them all into a SortedSet, for instance.
        Specified by:
        compareTo in interface Comparable<AstNode>
        other - another node
        -1 if this node's start position is less than other's start position. If tied, -1 if this node's length is less than other's length. If the lengths are equal, sorts abitrarily on hashcode unless the nodes are the same per Object.equals(java.lang.Object).
      • depth

        public int depth()
        Returns the depth of this node. The root is depth 0, its children are depth 1, and so on.
        the node depth in the tree
      • getLineno

        public int getLineno()
        Return the line number recorded for this node. If no line number was recorded, searches the parent chain.
        getLineno in class Node
        the nearest line number, or -1 if none was found
      • debugPrint

        public String debugPrint()
        Returns a debugging representation of the parse tree starting at this node.
        a very verbose indented printout of the tree. The format of each line is: abs-pos name position length [identifier]