class Parser::TreeRewriter

{Parser::TreeRewriter} offers a basic API that makes it easy to rewrite existing ASTs. It's built on top of {Parser::AST::Processor} and {Parser::Source::TreeRewriter}

For example, assume you want to remove `do` tokens from a while statement. You can do this as following:

require 'parser/current'

class RemoveDo < Parser::TreeRewriter
  def on_while(node)
    # Check if the statement starts with "do"
    if node.location.begin.is?('do')
      remove(node.location.begin)
    end
  end
end

code = <<-EOF
while true do
  puts 'hello'
end
EOF

ast           = Parser::CurrentRuby.parse code
buffer        = Parser::Source::Buffer.new('(example)', source: code)
rewriter      = RemoveDo.new

# Rewrite the AST, returns a String with the new form.
puts rewriter.rewrite(buffer, ast)

This would result in the following Ruby code:

while true
  puts 'hello'
end

Keep in mind that {Parser::TreeRewriter} does not take care of indentation when inserting/replacing code so you'll have to do this yourself.

See also [a blog entry](whitequark.org/blog/2013/04/26/lets-play-with-ruby-code/) describing rewriters in greater detail.

@api public

Public Instance Methods

assignment?(node) click to toggle source

Returns `true` if the specified node is an assignment node, returns false otherwise.

@param [Parser::AST::Node] node @return [Boolean]

# File lib/parser/tree_rewriter.rb, line 79
def assignment?(node)
  [:lvasgn, :ivasgn, :gvasgn, :cvasgn, :casgn].include?(node.type)
end
insert_after(range, content) click to toggle source

Inserts new code after the given source range.

@param [Parser::Source::Range] range @param [String] content

# File lib/parser/tree_rewriter.rb, line 118
def insert_after(range, content)
  @source_rewriter.insert_after(range, content)
end
insert_before(range, content) click to toggle source

Inserts new code before the given source range.

@param [Parser::Source::Range] range @param [String] content

# File lib/parser/tree_rewriter.rb, line 108
def insert_before(range, content)
  @source_rewriter.insert_before(range, content)
end
remove(range) click to toggle source

Removes the source range.

@param [Parser::Source::Range] range

# File lib/parser/tree_rewriter.rb, line 88
def remove(range)
  @source_rewriter.remove(range)
end
replace(range, content) click to toggle source

Replaces the code of the source range `range` with `content`.

@param [Parser::Source::Range] range @param [String] content

# File lib/parser/tree_rewriter.rb, line 128
def replace(range, content)
  @source_rewriter.replace(range, content)
end
rewrite(source_buffer, ast, **policy) click to toggle source

Rewrites the AST/source buffer and returns a String containing the new version.

@param [Parser::Source::Buffer] source_buffer @param [Parser::AST::Node] ast @param [Symbol] crossing_deletions:, different_replacements:, swallowed_insertions:

policy arguments for TreeRewriter (optional)

@return [String]

# File lib/parser/tree_rewriter.rb, line 62
def rewrite(source_buffer,
            ast,
            **policy)
  @source_rewriter = Parser::Source::TreeRewriter.new(source_buffer, **policy)

  process(ast)

  @source_rewriter.process
end
wrap(range, before, after) click to toggle source

Wraps the given source range with the given values.

@param [Parser::Source::Range] range @param [String] content

# File lib/parser/tree_rewriter.rb, line 98
def wrap(range, before, after)
  @source_rewriter.wrap(range, before, after)
end