content: # Copyright 2015 Google Inc. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  """Generic visitor pattern for pytrees.
  
  The lib2to3 parser produces a "pytree" - syntax tree consisting of Node
  and Leaf types. This module implements a visitor pattern for such trees.
  
  It also exports a basic "dumping" visitor that dumps a textual representation of
  a pytree into a stream.
  
    PyTreeVisitor: a generic visitor pattern for pytrees.
    PyTreeDumper: a configurable "dumper" for displaying pytrees.
    DumpPyTree(): a convenience function to dump a pytree.
  """
  
  import sys
  
  from yapf_third_party._ylib2to3 import pytree
  
  from yapf.pytree import pytree_utils
  
  
  class PyTreeVisitor(object):
    """Visitor pattern for pytree trees.
  
    Methods named Visit_XXX will be invoked when a node with type XXX is
    encountered in the tree. The type is either a token type (for Leaf nodes) or
    grammar symbols (for Node nodes). The return value of Visit_XXX methods is
    ignored by the visitor.
  
    Visitors can modify node contents but must not change the tree structure
    (e.g. add/remove children and move nodes around).
  
    This is a very common visitor pattern in Python code; it's also used in the
    Python standard library ast module for providing AST visitors.
  
    Note: this makes names that aren't style conformant, so such visitor methods
    need to be marked with # pylint: disable=invalid-name We don't have a choice
    here, because lib2to3 nodes have under_separated names.
  
    For more complex behavior, the visit, DefaultNodeVisit and DefaultLeafVisit
    methods can be overridden. Don't forget to invoke DefaultNodeVisit for nodes
    that may have children - otherwise the children will not be visited.
    """
  
    def Visit(self, node):
      """Visit a node."""
      method = 'Visit_{0}'.format(pytree_utils.NodeName(node))
      if hasattr(self, method):
        # Found a specific visitor for this node
        getattr(self, method)(node)
      else:
        if isinstance(node, pytree.Leaf):
          self.DefaultLeafVisit(node)
        else:
          self.DefaultNodeVisit(node)
  
    def DefaultNodeVisit(self, node):
      """Default visitor for Node: visits the node's children depth-first.
  
      This method is invoked when no specific visitor for the node is defined.
  
      Arguments:
        node: the node to visit
      """
      for child in node.children:
        self.Visit(child)
  
    def DefaultLeafVisit(self, leaf):
      """Default visitor for Leaf: no-op.
  
      This method is invoked when no specific visitor for the leaf is defined.
  
      Arguments:
        leaf: the leaf to visit
      """
      pass
  
  
  def DumpPyTree(tree, target_stream=sys.stdout):
    """Convenience function for dumping a given pytree.
  
    This function presents a very minimal interface. For more configurability (for
    example, controlling how specific node types are displayed), use PyTreeDumper
    directly.
  
    Arguments:
      tree: the tree to dump.
      target_stream: the stream to dump the tree to. A file-like object. By
        default will dump into stdout.
    """
    dumper = PyTreeDumper(target_stream)
    dumper.Visit(tree)
  
  
  class PyTreeDumper(PyTreeVisitor):
    """Visitor that dumps the tree to a stream.
  
    Implements the PyTreeVisitor interface.
    """
  
    def __init__(self, target_stream=sys.stdout):
      """Create a tree dumper.
  
      Arguments:
        target_stream: the stream to dump the tree to. A file-like object. By
          default will dump into stdout.
      """
      self._target_stream = target_stream
      self._current_indent = 0
  
    def _DumpString(self, s):
      self._target_stream.write('{0}{1}\n'.format(' ' * self._current_indent, s))
  
    def DefaultNodeVisit(self, node):
      # Dump information about the current node, and then use the generic
      # DefaultNodeVisit visitor to dump each of its children.
      self._DumpString(pytree_utils.DumpNodeToString(node))
      self._current_indent += 2
      super(PyTreeDumper, self).DefaultNodeVisit(node)
      self._current_indent -= 2
  
    def DefaultLeafVisit(self, leaf):
      self._DumpString(pytree_utils.DumpNodeToString(leaf))
  