Fix validation of underscored names

lib/dry/initializer/dispatchers/build_nested_type.rb

@@ -13,7 +13,7 @@ module Dry::Initializer::Dispatchers::BuildNestedType
  # rubocop: disable Metrics/ParameterLists
  def call(parent:, source:, target:, type: nil, block: nil, **options)
  check_certainty!(source, type, block)
- check_name!(target)
+ check_name!(target, block)
  type ||= build_nested_type(parent, target, block)
  { parent: parent, source: source, target: target, type: type, **options }
  end
@@ -22,16 +22,17 @@ def call(parent:, source:, target:, type: nil, block: nil, **options)
  private
 
  def check_certainty!(source, type, block)
- return unless type
  return unless block
+ return unless type
 
  raise ArgumentError, <<~MESSAGE
  You should define coercer of values of argument '#{source}'
  either though the parameter/option, or via nested block, but not the both.
  MESSAGE
  end
 
- def check_name!(name)
+ def check_name!(name, block)
+ return unless block
  return unless name[/^_|__|_$/]
 
  raise ArgumentError, <<~MESSAGE

spec/type_constraint_spec.rb

@@ -5,14 +5,14 @@
  before do
  class Test::Foo
  extend Dry::Initializer
- param :foo, proc(&:to_s), optional: true
+ param :__foo__, proc(&:to_s), optional: true
  end
  end
 
  subject { Test::Foo.new :foo }
 
  it "coerces a value" do
- expect(subject.foo).to eq "foo"
+ expect(subject.__foo__).to eq "foo"
  end
  end