Module: Audition::Rewriters::Memoization

Defined in:
lib/audition/rewriters.rb

Overview

Rewrites singleton-scope memoization, both idioms:

@x ||= expr
return @x if defined?(@x); @x = expr

Preferred strategy is freeze-on-memoize, the pattern Rails core applies to its own code: the memoization stays exactly as written and only the memoized value becomes shareable (.freeze appended; Ractor.make_shareable for containers). Non-main Ractors may then read the ivar once it has been computed; the first write must still happen on the main Ractor, which is a boot-warming concern the static check reports as an info note. Chosen when the value expression carries no block (a proxy for one-time side effects) and no writes exist outside the memo sites.

Otherwise falls back to Ractor-local storage:

@x ||= expr   ->  Ractor.store_if_absent(:"Klass/@x") { expr }
@x = expr     ->  Ractor.current[:"Klass/@x"] = expr
@x            ->  Ractor.current[:"Klass/@x"]

Only when every reference in singleton scope is visible in this file, none sit directly in the class body, and no compound writes exist. Caveat (why this is unsafe): freezing changes value mutability, and each Ractor computes its own copy under store_if_absent.

Defined Under Namespace

Classes: SingletonIvars

Class Method Summary collapse

Class Method Details

.accumulator?(value) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 322

def self.accumulator?(value)
  (value.is_a?(Prism::ArrayNode) ||
    value.is_a?(Prism::HashNode)) && value.elements.empty?
end

.blockless?(node) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 423

def self.blockless?(node)
  queue = [node]
  until queue.empty?
    current = queue.shift
    if current.is_a?(Prism::BlockNode) ||
        current.is_a?(Prism::LambdaNode)
      return false
    end
    queue.concat(current.child_nodes.compact)
  end
  true
end

.classifier(file) ⇒ Object 



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# File 'lib/audition/rewriters.rb', line 293

def self.classifier(file)
  Static::LiteralClassifier.new(
    frozen_string_literal: file.frozen_string_literal?
  )
end

.constructor?(value, classifier) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 299

def self.constructor?(value, classifier)
  value.is_a?(Prism::CallNode) &&
    %i[new dup clone].include?(value.name) &&
    classifier.classify(value) != :shareable
end

.deletion(source, node) ⇒ Object

Deletes the guard statement together with its line and any blank lines that follow, so the method body does not open with a hole. Falls back to the bare node span when other code shares the line.



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# File 'lib/audition/rewriters.rb', line 584

def self.deletion(source, node)
  raw = source.dup.force_encoding(Encoding::BINARY)
  from = node.location.start_offset
  upto = node.location.end_offset
  start = from.zero? ? 0 : (raw.rindex("\n", from - 1) || -1) + 1
  if raw[start...from].match?(/\A[ \t]*\z/n)
    newline = raw.index("\n", upto)
    stop = newline ? newline + 1 : raw.length
    loop do
      newline = raw.index("\n", stop)
      break unless newline
      break unless raw[stop...newline].match?(/\A[ \t]*\z/n)

      stop = newline + 1
    end
    Autofix.new(start_offset: start, end_offset: stop,
      replacement: "", safety: :unsafe)
  else
    Autofix.new(start_offset: from, end_offset: upto,
      replacement: "", safety: :unsafe)
  end
end

.freezable?(ops, memos) ⇒ Boolean

Freeze-on-memoize applies when every write is a memo site (a stray write means cache invalidation; frozen values cannot support that) and no value needs a block to build.

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 415

def self.freezable?(ops, memos)
  memo_ops = memos.map { |memo| memo[:op] }
  writes = ops.select { |op| op[:kind] == :write }
  return false unless (writes - memo_ops).empty?

  memos.all? { |memo| blockless?(memo[:op][:node].value) }
end

.freeze_edits(file, memos) ⇒ Object

One edit per memo site: make the memoized value shareable while leaving the memoization intact. Guards, sibling reads, and method shapes stay untouched.



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# File 'lib/audition/rewriters.rb', line 439

def self.freeze_edits(file, memos)
  kinds = classifier(file)
  memos.filter_map do |memo|
    value = memo[:op][:node].value
    freeze_value(value, kinds.classify(value))
  end
end

.freeze_value(value, kind) ⇒ Object

Plain .freeze only where the value is provably a string; everything unproven gets Ractor.make_shareable, which is a no-op for already-shareable values. This matters for memoized classes (multi_json memoizes adapter classes): .freeze on a Class freezes the class object and later ivar writes on it raise FrozenError.



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# File 'lib/audition/rewriters.rb', line 453

def self.freeze_value(value, kind)
  return nil if kind == :shareable
  # Freezing or wrapping a sync primitive raises; leave the
  # finding in place for a human.
  return nil if kind == :sync_primitive
  return nil if frozen_call?(value)

  slice = value.location.slice
  replacement =
    if kind == :mutable_string
      parens?(value) ? "(#{slice}).freeze" : "#{slice}.freeze"
    else
      "Ractor.make_shareable(#{slice})"
    end
  Autofix.new(
    start_offset: value.location.start_offset,
    end_offset: value.location.end_offset,
    replacement: replacement,
    safety: :unsafe
  )
end

.frozen_call?(value) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 475

def self.frozen_call?(value)
  value.is_a?(Prism::CallNode) &&
    value.name == :freeze &&
    value.receiver && value.arguments.nil?
end

.guarded_with_strays?(ops, memos) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 392

def self.guarded_with_strays?(ops, memos)
  return false if memos.none? { |memo| memo[:guard] }

  memo_ops = memos.map { |memo| memo[:op] }
  ops.any? do |op|
    op[:kind] == :write && !memo_ops.include?(op)
  end
end

.memo_sites(ops) ⇒ Object

A memo site is an ||= write, or a plain write paired with a defined? return guard inside the same method. A guarded method with more than one write is nobody's memoization; such groups are dropped by the orphan check below.



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# File 'lib/audition/rewriters.rb', line 309

def self.memo_sites(ops)
  guards = ops.select { |op| op[:kind] == :guard }
  ops.filter_map do |op|
    case op[:kind]
    when :or_write
      {op: op, guard: nil}
    when :write
      guard = guards.find { |g| g[:def_id] == op[:def_id] }
      {op: op, guard: guard} if guard
    end
  end
end

.mutator_receivers(file) ⇒ Object

Receivers of in-place mutator calls anywhere in the file, index writes included; mirrors SourceFile#mutated_constants.



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# File 'lib/audition/rewriters.rb', line 373

def self.mutator_receivers(file)
  receivers = []
  queue = [file.root]
  until queue.empty?
    node = queue.shift
    queue.concat(node.child_nodes.compact)
    mutator =
      (node.is_a?(Prism::CallNode) &&
        Static::SourceFile::CONST_MUTATORS
          .include?(node.name)) ||
      Static::SourceFile::INDEX_WRITES
        .any? { |type| node.is_a?(type) }
    next unless mutator && node.receiver

    receivers << node.receiver
  end
  receivers
end

.orphan_guards?(ops, memos) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 401

def self.orphan_guards?(ops, memos)
  used = memos.filter_map { |m| m[:guard] }
  guards = ops.select { |op| op[:kind] == :guard }
  return true if guards.size != used.size

  writes = ops.select { |op| op[:kind] == :write }
  guards.any? do |guard|
    writes.count { |w| w[:def_id] == guard[:def_id] } != 1
  end
end

.parens?(value) ⇒ Boolean

.freeze binds tighter than operators and ternaries, so compound expressions get wrapped; message sends and plain literals do not need it.

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 484

def self.parens?(value)
  case value
  when Prism::CallNode
    !value.name.to_s.match?(/\A[a-z_]/i)
  when Prism::StringNode, Prism::InterpolatedStringNode,
       Prism::ArrayNode, Prism::HashNode,
       Prism::ConstantReadNode, Prism::ConstantPathNode
    false
  else
    true
  end
end

.plan(file, findings) ⇒ Object 



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# File 'lib/audition/rewriters.rb', line 215

def self.plan(file, findings)
  return [] if findings.none? { |f| f.check == "class-level-state" }

  collector = SingletonIvars.new
  collector.visit(file.root)
  bundles = []
  collector.groups.each do |(namespace, name), ops|
    next if namespace.empty?

    kinds = ops.map { |op| op[:kind] }
    next if kinds.include?(:other)
    next if ops.any? { |op| op[:body] }

    memos = memo_sites(ops)
    if memos.empty?
      bundles << Rewriters.bundle(ops, setter_edits(file, ops))
      next
    end
    next if orphan_guards?(ops, memos)
    next if guarded_with_strays?(ops, memos)
    # `@x ||= {}` is a lazily-built accumulator, mutated
    # through the accessor after memoization (jwt's
    # algorithm registry). Freezing it breaks registration
    # and Ractor-local copies would leave other Ractors an
    # empty registry; the copy-on-write refactor is human
    # work, so no edit is offered. Constructor memos (`new`,
    # `Set.new`, `.dup`) are the same family: liquid's
    # filter set and money's bank singleton both broke under
    # freezing, and per-Ractor copies hide main-Ractor
    # registrations.
    next if memos.any? { |m| accumulator?(m[:op][:node].value) }
    next if memos.any? do |m|
      constructor?(m[:op][:node].value, classifier(file))
    end

    if freezable?(ops, memos)
      bundles << Rewriters.bundle(ops, freeze_edits(file, memos))
    else
      # Ractor-local slots are keyed by lexical owner; on a
      # class the ivar is per-subclass (faraday's
      # DEFAULT_OPTIONS), and one shared key would merge
      # every subclass's state. Modules cannot be
      # subclassed, so only module-owned state converts.
      next if ops.any? { |op| op[:class_owner] }
      # Deleting the defined? guard sends every call through
      # the statements after the write, so the warm path
      # only keeps returning the memo when the guarded write
      # ends its def body (or a bare read of the same ivar
      # does).
      next unless memos.all? do |m|
        m[:guard].nil? || tail_write?(m[:op])
      end

      key = %(:"#{namespace}/#{name}")
      bundles << Rewriters.bundle(
        ops, ractor_edits(file, ops, memos, key)
      )
    end
  end
  bundles.compact
end

.ractor_edits(file, ops, memos, key) ⇒ Object

Two Ractor-local flavors. With stray writes present (cache invalidation, @x = nil), memo sites become Ractor.current[key] ||= expr: it recomputes after a nil reset exactly like the original ||=, where store_if_absent would treat the stored nil as present and never recompute (this broke i18n's reserved_keys_pattern). Without strays, store_if_absent keeps its atomic lazy init. Guard-idiom groups with strays are skipped entirely in plan: the defined? guard caches nil deliberately and neither flavor reproduces that alongside invalidation.



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# File 'lib/audition/rewriters.rb', line 507

def self.ractor_edits(file, ops, memos, key)
  guarded = memos.filter_map { |m| m[:op] if m[:guard] }
  memo_ops = memos.map { |memo| memo[:op] }
  strays = ops.any? do |op|
    op[:kind] == :write && !memo_ops.include?(op)
  end
  edits = memos.filter_map do |memo|
    deletion(file.source, memo[:guard][:node]) if memo[:guard]
  end
  ops.each do |op|
    node = op[:node]
    edits <<
      if op[:kind] == :or_write || guarded.include?(op)
        replacement =
          if strays
            value = node.value.location.slice
            "Ractor.current[#{key}] ||= #{value}"
          else
            store_wrap(file.source, node, key)
          end
        Autofix.new(
          start_offset: node.location.start_offset,
          end_offset: node.location.end_offset,
          replacement: replacement,
          safety: :unsafe
        )
      elsif op[:kind] == :write
        Autofix.new(
          start_offset: node.name_loc.start_offset,
          end_offset: node.name_loc.end_offset,
          replacement: "Ractor.current[#{key}]",
          safety: :unsafe
        )
      else
        Autofix.new(
          start_offset: node.location.start_offset,
          end_offset: node.location.end_offset,
          replacement: "Ractor.current[#{key}]",
          safety: :unsafe
        )
      end
  end
  edits
end

.setter_edits(file, ops) ⇒ Object

Config setters (def self.backend=(value); @backend = value; end) get the Rails try_make_shareable recipe in plain Ruby: shareable values are deeply frozen so reads from any Ractor become legal, unshareable values keep today's behavior through the rescue. Only bare local reads are wrapped; computed values are left for a human.



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# File 'lib/audition/rewriters.rb', line 333

def self.setter_edits(file, ops)
  receivers = nil
  ops.filter_map do |op|
    next unless op[:kind] == :write
    # Only genuine setters: a plain method restoring a saved
    # local (sinatra's route conditions) and operator defs
    # ([]=) must stay untouched.
    setter = op[:def_name].to_s
    next unless setter.match?(/\A\w+=\z/)

    value = op[:node].value
    next unless value.is_a?(Prism::LocalVariableReadNode)

    # A value the file mutates in place through the reader
    # accessor (`def self.set(k, v); options[k] = v; end`)
    # or through a direct read of the ivar must never be
    # frozen: the mutation would raise FrozenError.
    receivers ||= mutator_receivers(file)
    reader = setter.delete_suffix("=").to_sym
    mutated = receivers.any? do |receiver|
      (receiver.is_a?(Prism::CallNode) &&
        receiver.name == reader) ||
        (receiver.is_a?(Prism::InstanceVariableReadNode) &&
          receiver.name == op[:node].name)
    end
    next if mutated

    local = value.name
    Autofix.new(
      start_offset: value.location.start_offset,
      end_offset: value.location.end_offset,
      replacement:
        "(Ractor.make_shareable(#{local}) rescue #{local})",
      safety: :unsafe
    )
  end
end

.store_wrap(source, node, key) ⇒ Object

A single-line value keeps the brace form; a multi-line value becomes a do..end block with the body shifted one level right, so the rewrite stays idiomatic. When the write shares its line with other code, layout cannot be inferred and the brace form is kept as-is.



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# File 'lib/audition/rewriters.rb', line 557

def self.store_wrap(source, node, key)
  value = node.value.location.slice
  call = "Ractor.store_if_absent(#{key})"
  return "#{call} { #{value} }" unless value.include?("\n")

  raw = source.dup.force_encoding(Encoding::BINARY)
  from = node.location.start_offset
  start = from.zero? ? 0 : (raw.rindex("\n", from - 1) || -1) + 1
  indent = raw[start...from].force_encoding(source.encoding)
  return "#{call} { #{value} }" unless indent.match?(/\A[ \t]*\z/)

  body = value.lines.map.with_index do |line, index|
    if index.zero?
      "#{indent}  #{line}"
    elsif line.match?(/\A\s*\z/)
      line
    else
      "  #{line}"
    end
  end.join
  "#{call} do\n#{body}\n#{indent}end"
end

.tail_write?(op) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/audition/rewriters.rb', line 277

def self.tail_write?(op)
  body = op[:def_node]&.body
  return false unless body.is_a?(Prism::StatementsNode)

  statements = body.body
  index = statements.index { |s| s.equal?(op[:node]) }
  return false unless index

  rest = statements[(index + 1)..]
  return true if rest.empty?

  rest.size == 1 &&
    rest[0].is_a?(Prism::InstanceVariableReadNode) &&
    rest[0].name == op[:node].name
end