Class: Parser::Source::Rewriter

Inherits:
Object
  • Object
show all
Defined in:
lib/parser/source/rewriter.rb

Overview

Rewriter performs the heavy lifting in the source rewriting process. It schedules code updates to be performed in the correct order and verifies that no two updates clobber each other, that is, attempt to modify the same part of code.

If it is detected that one update clobbers another one, an :error and a :note diagnostics describing both updates are generated and passed to the diagnostic engine. After that, an exception is raised.

The default diagnostic engine consumer simply prints the diagnostics to stderr.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(source_buffer) ⇒ Rewriter

Returns a new instance of Rewriter.

Parameters:



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# File 'lib/parser/source/rewriter.rb', line 31

def initialize(source_buffer)
  @diagnostics = Diagnostic::Engine.new
  @diagnostics.consumer = lambda do |diag|
    $stderr.puts diag.render
  end

  @source_buffer = source_buffer
  @queue         = []
  @clobber       = 0
end

Instance Attribute Details

#diagnostics ⇒ Diagnostic::Engine (readonly)

Returns:



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# File 'lib/parser/source/rewriter.rb', line 24

class Rewriter
  attr_reader :source_buffer
  attr_reader :diagnostics

  ##
  # @param [Source::Buffer] source_buffer
  #
  def initialize(source_buffer)
    @diagnostics = Diagnostic::Engine.new
    @diagnostics.consumer = lambda do |diag|
      $stderr.puts diag.render
    end

    @source_buffer = source_buffer
    @queue         = []
    @clobber       = 0
  end

  ##
  # Removes the source range.
  #
  # @param [Range] range
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def remove(range)
    append Rewriter::Action.new(range, '')
  end

  ##
  # Inserts new code before the given source range.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def insert_before(range, content)
    append Rewriter::Action.new(range.begin, content)
  end

  ##
  # Inserts new code after the given source range.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def insert_after(range, content)
    append Rewriter::Action.new(range.end, content)
  end

  ##
  # Replaces the code of the source range `range` with `content`.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def replace(range, content)
    append Rewriter::Action.new(range, content)
  end

  ##
  # Applies all scheduled changes to the `source_buffer` and returns
  # modified source as a new string.
  #
  # @return [String]
  #
  def process
    if in_transaction?
      raise "Do not call #{self.class}##{__method__} inside a transaction"
    end

    adjustment = 0
    source     = @source_buffer.source.dup

    sorted_queue = @queue.sort_by.with_index do |action, index|
      [action.range.begin_pos, index]
    end

    sorted_queue.each do |action|
      begin_pos = action.range.begin_pos + adjustment
      end_pos   = begin_pos + action.range.length

      source[begin_pos...end_pos] = action.replacement

      adjustment += (action.replacement.length - action.range.length)
    end

    source
  end

  ##
  # Provides a protected block where a sequence of multiple rewrite actions
  # are handled atomic. If any of the action failed by clobbering,
  # all the actions are rolled back.
  #
  # @example
  #  begin
  #    rewriter.transaction do
  #      rewriter.insert_before(range_of_something, '(')
  #      rewriter.insert_after(range_of_something, ')')
  #    end
  #  rescue Parser::ClobberingError
  #  end
  #
  # @raise [RuntimeError] when no block is passed
  # @raise [RuntimeError] when already in a transaction
  #
  def transaction
    unless block_given?
      raise "#{self.class}##{__method__} requires block"
    end

    if in_transaction?
      raise 'Nested transaction is not supported'
    end

    @pending_queue = @queue.dup
    @pending_clobber = @clobber

    yield

    @queue = @pending_queue
    @clobber = @pending_clobber

    self
  ensure
    @pending_queue = nil
    @pending_clobber = nil
  end

  private

  def append(action)
    if (clobber_actions = clobbered?(action.range))
      handle_clobber(action, clobber_actions)
    else
      clobber(action.range)
      active_queue << action
    end

    self
  end

  def clobber(range)
    self.active_clobber = active_clobber | (2 ** range.size - 1) << range.begin_pos
  end

  def clobbered?(range)
    if active_clobber & ((2 ** range.size - 1) << range.begin_pos) != 0
      active_queue.select do |action|
        action.range.end_pos > range.begin_pos &&
          range.end_pos > action.range.begin_pos
      end
    end
  end

  def handle_clobber(action, existing)
    if can_merge?(action, existing)
      merge_actions!(action, existing)
    else
      # cannot replace 3 characters with "foobar"
      diagnostic = Diagnostic.new(:error,
                                  :invalid_action,
                                  { :action => action },
                                  action.range)
      @diagnostics.process(diagnostic)

      # clobbered by: remove 3 characters
      diagnostic = Diagnostic.new(:note,
                                  :clobbered,
                                  { :action => existing[0] },
                                  existing[0].range)
      @diagnostics.process(diagnostic)

      raise ClobberingError, "Parser::Source::Rewriter detected clobbering"
    end
  end

  def can_merge?(action, existing)
    existing.all? do |other|
      overlap       = action.range.intersect(other.range)
      action_offset = overlap.begin_pos - action.range.begin_pos
      other_offset  = overlap.begin_pos - other.range.begin_pos

      replacement1 = action.replacement[action_offset, overlap.size] || ''
      replacement2 = other.replacement[other_offset, overlap.size] || ''
      replacement1 == replacement2
    end
  end

  def merge_actions!(action, existing)
    actions      = existing.push(action).sort_by { |a| a.range.begin_pos }
    merged_begin = actions.map { |act| act.range.begin_pos }.min
    merged_end   = actions.map { |act| act.range.end_pos }.max
    range        = Source::Range.new(@source_buffer,
                                     merged_begin,
                                     merged_end)
    clobber(range)

    replacement = merge_replacements(actions)
    replace_actions(actions, Rewriter::Action.new(range, replacement))
  end

  def replace_actions(old, updated)
    old.each { |act| active_queue.delete(act) }
    active_queue << updated
  end

  def merge_replacements(actions)
    # `actions` must be sorted by beginning position
    begin_pos = actions.first.range.begin_pos
    result    = ''

    actions.each do |act|
      offset = result.size - act.range.begin_pos + begin_pos
      next if offset < 0 || offset >= act.replacement.size
      result << act.replacement[offset..-1]
    end

    result
  end

  def in_transaction?
    !@pending_queue.nil?
  end

  def active_queue
    @pending_queue || @queue
  end

  def active_clobber
    @pending_clobber || @clobber
  end

  def active_clobber=(value)
    if @pending_clobber
      @pending_clobber = value
    else
      @clobber = value
    end
  end
end

#source_buffer ⇒ Source::Buffer (readonly)

Returns:



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# File 'lib/parser/source/rewriter.rb', line 24

class Rewriter
  attr_reader :source_buffer
  attr_reader :diagnostics

  ##
  # @param [Source::Buffer] source_buffer
  #
  def initialize(source_buffer)
    @diagnostics = Diagnostic::Engine.new
    @diagnostics.consumer = lambda do |diag|
      $stderr.puts diag.render
    end

    @source_buffer = source_buffer
    @queue         = []
    @clobber       = 0
  end

  ##
  # Removes the source range.
  #
  # @param [Range] range
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def remove(range)
    append Rewriter::Action.new(range, '')
  end

  ##
  # Inserts new code before the given source range.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def insert_before(range, content)
    append Rewriter::Action.new(range.begin, content)
  end

  ##
  # Inserts new code after the given source range.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def insert_after(range, content)
    append Rewriter::Action.new(range.end, content)
  end

  ##
  # Replaces the code of the source range `range` with `content`.
  #
  # @param [Range] range
  # @param [String] content
  # @return [Rewriter] self
  # @raise [ClobberingError] when clobbering is detected
  #
  def replace(range, content)
    append Rewriter::Action.new(range, content)
  end

  ##
  # Applies all scheduled changes to the `source_buffer` and returns
  # modified source as a new string.
  #
  # @return [String]
  #
  def process
    if in_transaction?
      raise "Do not call #{self.class}##{__method__} inside a transaction"
    end

    adjustment = 0
    source     = @source_buffer.source.dup

    sorted_queue = @queue.sort_by.with_index do |action, index|
      [action.range.begin_pos, index]
    end

    sorted_queue.each do |action|
      begin_pos = action.range.begin_pos + adjustment
      end_pos   = begin_pos + action.range.length

      source[begin_pos...end_pos] = action.replacement

      adjustment += (action.replacement.length - action.range.length)
    end

    source
  end

  ##
  # Provides a protected block where a sequence of multiple rewrite actions
  # are handled atomic. If any of the action failed by clobbering,
  # all the actions are rolled back.
  #
  # @example
  #  begin
  #    rewriter.transaction do
  #      rewriter.insert_before(range_of_something, '(')
  #      rewriter.insert_after(range_of_something, ')')
  #    end
  #  rescue Parser::ClobberingError
  #  end
  #
  # @raise [RuntimeError] when no block is passed
  # @raise [RuntimeError] when already in a transaction
  #
  def transaction
    unless block_given?
      raise "#{self.class}##{__method__} requires block"
    end

    if in_transaction?
      raise 'Nested transaction is not supported'
    end

    @pending_queue = @queue.dup
    @pending_clobber = @clobber

    yield

    @queue = @pending_queue
    @clobber = @pending_clobber

    self
  ensure
    @pending_queue = nil
    @pending_clobber = nil
  end

  private

  def append(action)
    if (clobber_actions = clobbered?(action.range))
      handle_clobber(action, clobber_actions)
    else
      clobber(action.range)
      active_queue << action
    end

    self
  end

  def clobber(range)
    self.active_clobber = active_clobber | (2 ** range.size - 1) << range.begin_pos
  end

  def clobbered?(range)
    if active_clobber & ((2 ** range.size - 1) << range.begin_pos) != 0
      active_queue.select do |action|
        action.range.end_pos > range.begin_pos &&
          range.end_pos > action.range.begin_pos
      end
    end
  end

  def handle_clobber(action, existing)
    if can_merge?(action, existing)
      merge_actions!(action, existing)
    else
      # cannot replace 3 characters with "foobar"
      diagnostic = Diagnostic.new(:error,
                                  :invalid_action,
                                  { :action => action },
                                  action.range)
      @diagnostics.process(diagnostic)

      # clobbered by: remove 3 characters
      diagnostic = Diagnostic.new(:note,
                                  :clobbered,
                                  { :action => existing[0] },
                                  existing[0].range)
      @diagnostics.process(diagnostic)

      raise ClobberingError, "Parser::Source::Rewriter detected clobbering"
    end
  end

  def can_merge?(action, existing)
    existing.all? do |other|
      overlap       = action.range.intersect(other.range)
      action_offset = overlap.begin_pos - action.range.begin_pos
      other_offset  = overlap.begin_pos - other.range.begin_pos

      replacement1 = action.replacement[action_offset, overlap.size] || ''
      replacement2 = other.replacement[other_offset, overlap.size] || ''
      replacement1 == replacement2
    end
  end

  def merge_actions!(action, existing)
    actions      = existing.push(action).sort_by { |a| a.range.begin_pos }
    merged_begin = actions.map { |act| act.range.begin_pos }.min
    merged_end   = actions.map { |act| act.range.end_pos }.max
    range        = Source::Range.new(@source_buffer,
                                     merged_begin,
                                     merged_end)
    clobber(range)

    replacement = merge_replacements(actions)
    replace_actions(actions, Rewriter::Action.new(range, replacement))
  end

  def replace_actions(old, updated)
    old.each { |act| active_queue.delete(act) }
    active_queue << updated
  end

  def merge_replacements(actions)
    # `actions` must be sorted by beginning position
    begin_pos = actions.first.range.begin_pos
    result    = ''

    actions.each do |act|
      offset = result.size - act.range.begin_pos + begin_pos
      next if offset < 0 || offset >= act.replacement.size
      result << act.replacement[offset..-1]
    end

    result
  end

  def in_transaction?
    !@pending_queue.nil?
  end

  def active_queue
    @pending_queue || @queue
  end

  def active_clobber
    @pending_clobber || @clobber
  end

  def active_clobber=(value)
    if @pending_clobber
      @pending_clobber = value
    else
      @clobber = value
    end
  end
end

Instance Method Details

#insert_after(range, content) ⇒ Rewriter

Inserts new code after the given source range.

Parameters:

Returns:

Raises:



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# File 'lib/parser/source/rewriter.rb', line 73

def insert_after(range, content)
  append Rewriter::Action.new(range.end, content)
end

#insert_before(range, content) ⇒ Rewriter

Inserts new code before the given source range.

Parameters:

Returns:

Raises:



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# File 'lib/parser/source/rewriter.rb', line 61

def insert_before(range, content)
  append Rewriter::Action.new(range.begin, content)
end

#process ⇒ String

Applies all scheduled changes to the source_buffer and returns modified source as a new string.

Returns:



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# File 'lib/parser/source/rewriter.rb', line 95

def process
  if in_transaction?
    raise "Do not call #{self.class}##{__method__} inside a transaction"
  end

  adjustment = 0
  source     = @source_buffer.source.dup

  sorted_queue = @queue.sort_by.with_index do |action, index|
    [action.range.begin_pos, index]
  end

  sorted_queue.each do |action|
    begin_pos = action.range.begin_pos + adjustment
    end_pos   = begin_pos + action.range.length

    source[begin_pos...end_pos] = action.replacement

    adjustment += (action.replacement.length - action.range.length)
  end

  source
end

#remove(range) ⇒ Rewriter

Removes the source range.

Parameters:

Returns:

Raises:



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# File 'lib/parser/source/rewriter.rb', line 49

def remove(range)
  append Rewriter::Action.new(range, '')
end

#replace(range, content) ⇒ Rewriter

Replaces the code of the source range range with content.

Parameters:

Returns:

Raises:



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# File 'lib/parser/source/rewriter.rb', line 85

def replace(range, content)
  append Rewriter::Action.new(range, content)
end

#transaction ⇒ Object

Provides a protected block where a sequence of multiple rewrite actions are handled atomic. If any of the action failed by clobbering, all the actions are rolled back.

Examples:

begin
  rewriter.transaction do
    rewriter.insert_before(range_of_something, '(')
    rewriter.insert_after(range_of_something, ')')
  end
rescue Parser::ClobberingError
end

Raises:

  • (RuntimeError) —

    when no block is passed

  • (RuntimeError) —

    when already in a transaction



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# File 'lib/parser/source/rewriter.rb', line 136

def transaction
  unless block_given?
    raise "#{self.class}##{__method__} requires block"
  end

  if in_transaction?
    raise 'Nested transaction is not supported'
  end

  @pending_queue = @queue.dup
  @pending_clobber = @clobber

  yield

  @queue = @pending_queue
  @clobber = @pending_clobber

  self
ensure
  @pending_queue = nil
  @pending_clobber = nil
end