Module: Audition::Rewriters::WriteOnce

Defined in:

lib/audition/rewriters.rb

Overview

A variable written exactly once, at a scope where constant assignment is legal, with every other reference a plain read in the same file, converts mechanically to a frozen constant. Unsafe because cross-file readers are invisible.

Defined Under Namespace

Classes: Variables

Class Method Summary

• .class_variables(file) ⇒ Object
• .convert(collector, file) ⇒ Object
• .globals(file) ⇒ Object
• .plan(file, findings) ⇒ Object

Class Method Details

.class_variables(file) ⇒ Object

# File 'lib/audition/rewriters.rb', line 825

def self.class_variables(file)
  collector = Variables.new(:cvar)
  collector.visit(file.root)
  convert(collector, file) do |name|
    name.delete_prefix("@@").upcase
  end
end

.convert(collector, file) ⇒ Object

# File 'lib/audition/rewriters.rb', line 833

def self.convert(collector, file)
  classifier = Static::LiteralClassifier.new(
    frozen_string_literal: file.frozen_string_literal?
  )
  # The same bare @@name under two namespaces of one file is
  # usually same-file inheritance sharing one runtime
  # variable; converting either copy strands the other's
  # readers with a NameError.
  bare = collector.groups.keys
    .map { |key| key.split("/").last }
    .tally
  planned = []
  bundles = []
  collector.groups.each do |name, ops|
    next if bare[name.split("/").last] > 1

    writes = ops.select { |op| op[:kind] == :write }
    next unless writes.size == 1 && writes[0][:assignable]
    next unless (ops - writes).all? { |op| op[:kind] == :read }

    write = writes[0][:node]
    kind = classifier.classify(write.value)
    next if kind == :sync_primitive
    # A constructed object may gain singleton methods or be
    # mutated later (sinatra's @@eats_errors); wrapping it
    # in make_shareable freezes it and those break.
    next if Memoization.constructor?(write.value, classifier)

    shareable = kind == :shareable
    # A mutable value that would get deep-frozen must never be
    # the receiver of a call afterwards: `X[k] = v`, `X << v`
    # and friends would raise FrozenError at runtime. The same
    # goes for reads that escape into a local (`list = $x;
    # list << h`) or a call argument, where an alias can be
    # mutated out of sight. Reads of immutable values are
    # safe anywhere.
    unless shareable
      escapes = (ops - writes).any? do |op|
        id = op[:node].object_id
        collector.receiver_reads.include?(id) ||
          collector.escaping_reads.include?(id)
      end
      next if escapes
    end

    constant = yield(name.split("/").last)
    next unless constant.match?(/\A[A-Z][A-Z0-9_]*\z/)
    next if collector.taken_constants.include?(constant)

    # `$max` and `$MAX` both map to MAX; only the first may
    # take the name, the second stays a variable.
    target = [name.rpartition("/").first, constant]
    next if planned.include?(target)

    planned << target
    edits = [Autofix.new(
      start_offset: write.name_loc.start_offset,
      end_offset: write.name_loc.end_offset,
      replacement: constant,
      safety: :unsafe
    )]
    unless shareable
      value = write.value
      source = value.location.slice
      if value.is_a?(Prism::ArrayNode) &&
          value.opening_loc.nil?
        source = "[#{source}]"
      end
      edits << Autofix.new(
        start_offset: value.location.start_offset,
        end_offset: value.location.end_offset,
        replacement: "Ractor.make_shareable(#{source})",
        safety: :unsafe
      )
    end
    (ops - writes).each do |op|
      node = op[:node]
      edits << Autofix.new(
        start_offset: node.location.start_offset,
        end_offset: node.location.end_offset,
        replacement: constant,
        safety: :unsafe
      )
    end
    bundles << Rewriters.bundle(ops, edits)
  end
  bundles.compact
end

.globals(file) ⇒ Object

# File 'lib/audition/rewriters.rb', line 817

def self.globals(file)
  collector = Variables.new(:gvar)
  collector.visit(file.root)
  convert(collector, file) do |name|
    name.delete_prefix("$").upcase
  end
end

.plan(file, findings) ⇒ Object

# File 'lib/audition/rewriters.rb', line 806

def self.plan(file, findings)
  bundles = []
  if findings.any? { |f| f.check == "global-variables" }
    bundles += globals(file)
  end
  if findings.any? { |f| f.check == "class-variables" }
    bundles += class_variables(file)
  end
  bundles
end