Support inverting boolish value

refs: soutaro#939

lib/steep/interface/builder.rb

@@ -166,7 +166,16 @@ def shape(type, public_only:, config:)
  if expanded = factory.deep_expand_alias(type)
  shape(expanded, public_only: public_only, config: config)&.update(type: type)
  end
- when AST::Types::Any, AST::Types::Bot, AST::Types::Void, AST::Types::Top
+ when AST::Types::Top
+ if definition_builder.env.interface_decls.key?(TypeName('::_Top'))
+ # rbs-3.3 or newer
+ type_ = AST::Types::Name::Interface.new(name: TypeName('::_Top'), args: [])
+ else
+ type_ = AST::Types::Name::Instance.new(name: TypeName('::BasicObject'), args: [])
+ end
+
+ shape(type_, public_only: public_only, config: config)&.update(type: type)
+ when AST::Types::Any, AST::Types::Bot, AST::Types::Void
  nil
  when AST::Types::Var
  if bound = config.variable_bounds[type.name]

test/type_construction_test.rb

@@ -6596,6 +6596,47 @@ def test_send_top_void
  end
  end
 
+ def test_send_boolish1
+ with_checker(<<RBS) do |checker|
+type boolish = top
+
+interface _Top
+ def !: () -> bool
+end
+RBS
+ source = parse_ruby(<<-RUBY)
+# @type var a: boolish
+a = _ = nil
+puts 'Hello' if !a
+ RUBY
+
+ with_standard_construction(checker, source) do |construction, typing|
+ _, constr = construction.synthesize(source.node)
+
+ assert_equal 0, typing.errors.size
+ end
+ end
+ end
+
+ def test_send_boolish2
+ # for old RBS package (no _Top interface definition)
+ with_checker(<<RBS) do |checker|
+type boolish = top
+RBS
+ source = parse_ruby(<<-RUBY)
+# @type var a: boolish
+a = _ = nil
+puts 'Hello' if !a
+ RUBY
+
+ with_standard_construction(checker, source) do |construction, typing|
+ _, constr = construction.synthesize(source.node)
+
+ assert_equal 0, typing.errors.size
+ end
+ end
+ end
+
  def test_send_concrete_receiver
  with_checker(<<RBS) do |checker|
 class SendTest