class RuboCop::NodePattern::Compiler

@private Builds Ruby code which implements a pattern

Constants

CLOSING
FUNCALL
IDENTIFIER
LITERAL
META
METHOD_NAME
NODE
NUMBER
PARAM
PARAM_NUMBER
PREDICATE
SEPARATORS
STRING
SYMBOL
TOKEN
TOKENS
WILDCARD

Attributes

match_code[R]

Public Class Methods

new(str, node_var = 'node0') click to toggle source
# File lib/rubocop/node_pattern.rb, line 124
def initialize(str, node_var = 'node0')
  @string   = str
  @root     = node_var

  @temps    = 0  # avoid name clashes between temp variables
  @captures = 0  # number of captures seen
  @unify    = {} # named wildcard -> temp variable number
  @params   = 0  # highest % (param) number seen

  run(node_var)
end

Public Instance Methods

compile_arg(token) click to toggle source
# File lib/rubocop/node_pattern.rb, line 394
def compile_arg(token)
  case token
  when WILDCARD  then
    name   = token[1..-1]
    number = @unify[name] || fail_due_to('invalid in arglist: ' + token)
    "temp#{number}"
  when LITERAL   then token
  when PARAM     then get_param(token[1..-1])
  when CLOSING   then fail_due_to("#{token} in invalid position")
  when nil       then fail_due_to('pattern ended prematurely')
  else fail_due_to("invalid token in arglist: #{token.inspect}")
  end
end
compile_args(tokens) click to toggle source
# File lib/rubocop/node_pattern.rb, line 387
def compile_args(tokens)
  args = []
  args << compile_arg(tokens.shift) until tokens.first == ')'
  tokens.shift # drop the )
  args
end
compile_ascend(tokens, cur_node, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 331
def compile_ascend(tokens, cur_node, seq_head)
  "(#{cur_node}.parent && " \
    "#{compile_expr(tokens, "#{cur_node}.parent", seq_head)})"
end
compile_capt_ellip(tokens, cur_node, terms, index) click to toggle source
# File lib/rubocop/node_pattern.rb, line 238
def compile_capt_ellip(tokens, cur_node, terms, index)
  capture = next_capture
  if (term = compile_seq_tail(tokens, "#{cur_node}.children.last"))
    terms << "(#{cur_node}.children.size > #{index})"
    terms << term
    terms << "(#{capture} = #{cur_node}.children[#{index}..-2])"
  else
    terms << "(#{cur_node}.children.size >= #{index})" if index > 0
    terms << "(#{capture} = #{cur_node}.children[#{index}..-1])"
  end
  terms
end
compile_capture(tokens, cur_node, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 322
def compile_capture(tokens, cur_node, seq_head)
  "(#{next_capture} = #{cur_node}#{'.type' if seq_head}; " \
    "#{compile_expr(tokens, cur_node, seq_head)})"
end
compile_ellipsis(tokens, cur_node, terms, index) click to toggle source
# File lib/rubocop/node_pattern.rb, line 228
def compile_ellipsis(tokens, cur_node, terms, index)
  if (term = compile_seq_tail(tokens, "#{cur_node}.children.last"))
    terms << "(#{cur_node}.children.size > #{index})"
    terms << term
  elsif index > 0
    terms << "(#{cur_node}.children.size >= #{index})"
  end
  terms
end
compile_expr(tokens, cur_node, seq_head) click to toggle source

rubocop:disable Metrics/MethodLength, Metrics/AbcSize

# File lib/rubocop/node_pattern.rb, line 146
def compile_expr(tokens, cur_node, seq_head)
  # read a single pattern-matching expression from the token stream,
  # return Ruby code which performs the corresponding matching operation
  # on 'cur_node' (which is Ruby code which evaluates to an AST node)
  #
  # the 'pattern-matching' expression may be a composite which
  # contains an arbitrary number of sub-expressions
  token = tokens.shift
  case token
  when '('       then compile_seq(tokens, cur_node, seq_head)
  when '{'       then compile_union(tokens, cur_node, seq_head)
  when '['       then compile_intersect(tokens, cur_node, seq_head)
  when '!'       then compile_negation(tokens, cur_node, seq_head)
  when '$'       then compile_capture(tokens, cur_node, seq_head)
  when '^'       then compile_ascend(tokens, cur_node, seq_head)
  when WILDCARD  then compile_wildcard(cur_node, token[1..-1], seq_head)
  when FUNCALL   then compile_funcall(tokens, cur_node, token, seq_head)
  when LITERAL   then compile_literal(cur_node, token, seq_head)
  when PREDICATE then compile_predicate(tokens, cur_node, token, seq_head)
  when NODE      then compile_nodetype(cur_node, token)
  when PARAM     then compile_param(cur_node, token[1..-1], seq_head)
  when CLOSING   then fail_due_to("#{token} in invalid position")
  when nil       then fail_due_to('pattern ended prematurely')
  else                fail_due_to("invalid token #{token.inspect}")
  end
end
compile_expr_with_capture_check(tokens, temp_node, seq_head, before, after) click to toggle source
# File lib/rubocop/node_pattern.rb, line 297
def compile_expr_with_capture_check(tokens, temp_node, seq_head, before,
                                    after)
  @captures = before
  expr = compile_expr(tokens, temp_node, seq_head)
  if @captures != after
    fail_due_to('each branch of {} must have same # of captures')
  end

  expr
end
compile_expr_with_captures(tokens, temp_node, seq_head) { |expr, captures_before, captures| ... } click to toggle source
# File lib/rubocop/node_pattern.rb, line 290
def compile_expr_with_captures(tokens, temp_node, seq_head)
  captures_before = @captures
  expr = compile_expr(tokens, temp_node, seq_head)

  yield expr, captures_before, @captures
end
compile_expr_with_index(tokens, cur_node, index) click to toggle source
# File lib/rubocop/node_pattern.rb, line 216
def compile_expr_with_index(tokens, cur_node, index)
  if index.nil?
    # in 'sequence head' position; some expressions are compiled
    # differently at 'sequence head' (notably 'node type' expressions)
    # grep for seq_head to see where it makes a difference
    [compile_expr(tokens, cur_node, true), 0]
  else
    child_node = "#{cur_node}.children[#{index}]"
    [compile_expr(tokens, child_node, false), index + 1]
  end
end
compile_funcall(tokens, cur_node, method, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 366
def compile_funcall(tokens, cur_node, method, seq_head)
  # call a method in the context which this pattern-matching
  # code is used in. pass target value as an argument
  method = method[1..-1] # drop the leading #
  if method.end_with?('(') # is there an arglist?
    args = compile_args(tokens)
    method = method[0..-2] # drop the trailing (
    "(#{method}(#{cur_node}#{'.type' if seq_head}),#{args.join(',')})"
  else
    "(#{method}(#{cur_node}#{'.type' if seq_head}))"
  end
end
compile_intersect(tokens, cur_node, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 308
def compile_intersect(tokens, cur_node, seq_head)
  fail_due_to('empty intersection') if tokens.first == ']'

  with_temp_node(cur_node) do |init, temp_node|
    terms = []
    until tokens.first == ']'
      terms << compile_expr(tokens, temp_node, seq_head)
    end
    tokens.shift

    join_terms(init, terms, ' && ')
  end
end
compile_literal(cur_node, literal, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 352
def compile_literal(cur_node, literal, seq_head)
  "(#{cur_node}#{'.type' if seq_head} == #{literal})"
end
compile_negation(tokens, cur_node, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 327
def compile_negation(tokens, cur_node, seq_head)
  "(!#{compile_expr(tokens, cur_node, seq_head)})"
end
compile_nodetype(cur_node, type) click to toggle source
# File lib/rubocop/node_pattern.rb, line 379
def compile_nodetype(cur_node, type)
  "(#{cur_node} && #{cur_node}.#{type.tr('-', '_')}_type?)"
end
compile_param(cur_node, number, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 383
def compile_param(cur_node, number, seq_head)
  "(#{cur_node}#{'.type' if seq_head} == #{get_param(number)})"
end
compile_predicate(tokens, cur_node, predicate, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 356
def compile_predicate(tokens, cur_node, predicate, seq_head)
  if predicate.end_with?('(') # is there an arglist?
    args = compile_args(tokens)
    predicate = predicate[0..-2] # drop the trailing (
    "(#{cur_node}#{'.type' if seq_head}.#{predicate}(#{args.join(',')}))"
  else
    "(#{cur_node}#{'.type' if seq_head}.#{predicate})"
  end
end
compile_seq(tokens, cur_node, seq_head) click to toggle source

rubocop:enable Metrics/MethodLength, Metrics/AbcSize

# File lib/rubocop/node_pattern.rb, line 174
def compile_seq(tokens, cur_node, seq_head)
  fail_due_to('empty parentheses') if tokens.first == ')'
  fail_due_to('parentheses at sequence head') if seq_head

  # 'cur_node' is a Ruby expression which evaluates to an AST node,
  # but we don't know how expensive it is
  # to be safe, cache the node in a temp variable and then use the
  # temp variable as 'cur_node'
  with_temp_node(cur_node) do |init, temp_node|
    terms = compile_seq_terms(tokens, temp_node)

    join_terms(init, terms, ' && ')
  end
end
compile_seq_tail(tokens, cur_node) click to toggle source
# File lib/rubocop/node_pattern.rb, line 251
def compile_seq_tail(tokens, cur_node)
  tokens.shift
  if tokens.first == ')'
    tokens.shift
    nil
  else
    expr = compile_expr(tokens, cur_node, false)
    fail_due_to('missing )') unless tokens.shift == ')'
    expr
  end
end
compile_seq_terms(tokens, cur_node) click to toggle source
# File lib/rubocop/node_pattern.rb, line 189
def compile_seq_terms(tokens, cur_node)
  ret, size =
    compile_seq_terms_with_size(tokens, cur_node) do |token, terms, index|
      case token
      when '...'.freeze
        return compile_ellipsis(tokens, cur_node, terms, index)
      when '$...'.freeze
        return compile_capt_ellip(tokens, cur_node, terms, index)
      end
    end

  ret << "(#{cur_node}.children.size == #{size})"
end
compile_seq_terms_with_size(tokens, cur_node) { |first, terms, index || 0| ... } click to toggle source
# File lib/rubocop/node_pattern.rb, line 203
def compile_seq_terms_with_size(tokens, cur_node)
  index = nil
  terms = []
  until tokens.first == ')'
    yield tokens.first, terms, index || 0
    term, index = compile_expr_with_index(tokens, cur_node, index)
    terms << term
  end

  tokens.shift # drop concluding )
  [terms, index]
end
compile_union(tokens, cur_node, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 263
def compile_union(tokens, cur_node, seq_head)
  fail_due_to('empty union') if tokens.first == '}'

  with_temp_node(cur_node) do |init, temp_node|
    terms = union_terms(tokens, temp_node, seq_head)
    join_terms(init, terms, ' || ')
  end
end
compile_wildcard(cur_node, name, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 336
def compile_wildcard(cur_node, name, seq_head)
  if name.empty?
    'true'
  elsif @unify.key?(name)
    # we have already seen a wildcard with this name before
    # so the value it matched the first time will already be stored
    # in a temp. check if this value matches the one stored in the temp
    "(#{cur_node}#{'.type' if seq_head} == temp#{@unify[name]})"
  else
    n = @unify[name] = next_temp_value
    # double assign to temp#{n} to avoid "assigned but unused variable"
    "(temp#{n} = #{cur_node}#{'.type' if seq_head}; " \
    "temp#{n} = temp#{n}; true)"
  end
end
emit_capture_list() click to toggle source
# File lib/rubocop/node_pattern.rb, line 422
def emit_capture_list
  (1..@captures).map { |n| "capture#{n}" }.join(',')
end
emit_guard_clause() click to toggle source
# File lib/rubocop/node_pattern.rb, line 445
      def emit_guard_clause
        <<-RUBY
          return unless node.is_a?(RuboCop::AST::Node)
        RUBY
      end
emit_method_code() click to toggle source
# File lib/rubocop/node_pattern.rb, line 451
      def emit_method_code
        <<-RUBY
          return unless #{@match_code}
          block_given? ? yield(#{emit_capture_list}) : (return #{emit_retval})
        RUBY
      end
emit_param_list() click to toggle source
# File lib/rubocop/node_pattern.rb, line 436
def emit_param_list
  (1..@params).map { |n| "param#{n}" }.join(',')
end
emit_retval() click to toggle source
# File lib/rubocop/node_pattern.rb, line 426
def emit_retval
  if @captures.zero?
    'true'
  elsif @captures == 1
    'capture1'
  else
    "[#{emit_capture_list}]"
  end
end
emit_trailing_params() click to toggle source
# File lib/rubocop/node_pattern.rb, line 440
def emit_trailing_params
  params = emit_param_list
  params.empty? ? '' : ",#{params}"
end
fail_due_to(message) click to toggle source
# File lib/rubocop/node_pattern.rb, line 458
def fail_due_to(message)
  raise Invalid, "Couldn't compile due to #{message}. Pattern: #{@string}"
end
get_param(number) click to toggle source
# File lib/rubocop/node_pattern.rb, line 412
def get_param(number)
  number = number.empty? ? 1 : Integer(number)
  @params = number if number > @params
  number.zero? ? @root : "param#{number}"
end
join_terms(init, terms, operator) click to toggle source
# File lib/rubocop/node_pattern.rb, line 418
def join_terms(init, terms, operator)
  "(#{init};#{terms.join(operator)})"
end
next_capture() click to toggle source
# File lib/rubocop/node_pattern.rb, line 408
def next_capture
  "capture#{@captures += 1}"
end
next_temp_value() click to toggle source
# File lib/rubocop/node_pattern.rb, line 473
def next_temp_value
  @temps += 1
end
run(node_var) click to toggle source
# File lib/rubocop/node_pattern.rb, line 136
def run(node_var)
  tokens =
    @string.scan(TOKEN).reject { |token| token =~ /\A#{SEPARATORS}\Z/ }

  @match_code = compile_expr(tokens, node_var, false)

  fail_due_to('unbalanced pattern') unless tokens.empty?
end
union_terms(tokens, temp_node, seq_head) click to toggle source
# File lib/rubocop/node_pattern.rb, line 272
def union_terms(tokens, temp_node, seq_head)
  # we need to ensure that each branch of the {} contains the same
  # number of captures (since only one branch of the {} can actually
  # match, the same variables are used to hold the captures for each
  # branch)
  compile_expr_with_captures(tokens,
                             temp_node, seq_head) do |term, before, after|
    terms = [term]
    until tokens.first == '}'
      terms << compile_expr_with_capture_check(tokens, temp_node,
                                               seq_head, before, after)
    end
    tokens.shift

    terms
  end
end
with_temp_node(cur_node) { |"#{temp_var} = #{cur_node}; #{temp_var} = #{temp_var}", temp_var| ... } click to toggle source
# File lib/rubocop/node_pattern.rb, line 462
def with_temp_node(cur_node)
  with_temp_variable do |temp_var|
    # double assign to temp#{n} to avoid "assigned but unused variable"
    yield "#{temp_var} = #{cur_node}; #{temp_var} = #{temp_var}", temp_var
  end
end
with_temp_variable() { |"temp#{next_temp_value}"| ... } click to toggle source
# File lib/rubocop/node_pattern.rb, line 469
def with_temp_variable
  yield "temp#{next_temp_value}"
end