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# Visitors are used to traverse the Sass parse tree.
# Visitors should extend {Visitors::Base},
# which provides a small amount of scaffolding for traversal.
module Sass::Tree::Visitors
# The abstract base class for Sass visitors.
# Visitors should extend this class,
# then implement `visit_*` methods for each node they care about
# (e.g. `visit_rule` for {RuleNode} or `visit_for` for {ForNode}).
# These methods take the node in question as argument.
# They may `yield` to visit the child nodes of the current node.
#
# *Note*: due to the unusual nature of {Sass::Tree::IfNode},
# special care must be taken to ensure that it is properly handled.
# In particular, there is no built-in scaffolding
# for dealing with the return value of `@else` nodes.
#
# @abstract
class Base
# Runs the visitor on a tree.
#
# @param root [Tree::Node] The root node of the Sass tree.
# @return [Object] The return value of \{#visit} for the root node.
def self.visit(root)
new.send(:visit, root)
end
protected
# Runs the visitor on the given node.
# This can be overridden by subclasses that need to do something for each node.
#
# @param node [Tree::Node] The node to visit.
# @return [Object] The return value of the `visit_*` method for this node.
def visit(node)
if respond_to?(node.class.visit_method, true)
send(node.class.visit_method, node) {visit_children(node)}
else
visit_children(node)
end
end
# Visit the child nodes for a given node.
# This can be overridden by subclasses that need to do something
# with the child nodes' return values.
#
# This method is run when `visit_*` methods `yield`,
# and its return value is returned from the `yield`.
#
# @param parent [Tree::Node] The parent node of the children to visit.
# @return [Array<Object>] The return values of the `visit_*` methods for the children.
def visit_children(parent)
parent.children.map {|c| visit(c)}
end
# Returns the name of a node as used in the `visit_*` method.
#
# @param [Tree::Node] node The node.
# @return [String] The name.
def self.node_name(node)
Sass::Util.deprecated(self, "Call node.class.node_name instead.")
node.class.node_name
end
# `yield`s, then runs the visitor on the `@else` clause if the node has one.
# This exists to ensure that the contents of the `@else` clause get visited.
def visit_if(node)
yield
visit(node.else) if node.else
node
end
end
end
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