Map Forwardable delegations to method pins

[apiology]

Problem

def_delegators and def_delegator define real methods, but Solargraph maps neither, so every call to a delegated method is unresolved and any method returning one cannot infer its return type:

require 'forwardable'

class Records
  # @return [Integer]
  def size = 3
end

class Holder
  extend Forwardable

  def_delegators :@records, :size

  # @return [void]
  def initialize
    # @type [Records]
    @records = Records.new
  end

  # @return [Integer]
  def total = size
end

test.rb:20: Holder#total return type could not be inferred
test.rb:20: Unresolved call to size

Separately, alias_method in a class body reports a false positive at strong level today:

class Widget
  # @return [String]
  def name = 'x'

  alias_method :title, :name
end

test.rb:5: Unresolved call to alias_method

Solution

SendNode maps both Forwardable forms into Pin::DelegatedMethod — the pin class added in #602, until now constructed only by external plugins — which resolves the receiver and the forwarded method lazily, so a delegated method reports the forwarded method's parameters, return type and signatures, and passes arguments and blocks through. Instance-variable, class-variable and method receivers are supported, as is def_delegator's optional alias argument. Expansion fires only in a namespace that extends Forwardable; SingleForwardable's class-scope delegation is not covered.

The alias_method false positive shares one cause with what would otherwise have been a def_delegators false positive: method pins synthesized from a class-body statement cover that statement's range but have no body of their own, so _locate_pin treating them as closures makes the declaring statement resolve in instance scope, where alias_method and def_delegators are not available. _locate_pin already skipped attribute pins for this reason, with a @todo noting the hack; aliases and delegations now answer the same Pin::Method#body_less? predicate.

Test plan

Six strong-level specs — ivar receiver, method receiver, aliased delegation, argument and block passthrough, no expansion without extend Forwardable, and no false positive on the declaring statement. Five fail without this change. Full suite: 1541 examples, 0 failures, 59 pending.

Opened as a draft. This PR was written by Claude (Anthropic's Claude Code) on behalf of @apiology.

🤖 Generated with Claude Code

https://claude.ai/code/session_01H1FEjW6nMpZrWPmeWX9miT