Type Alias can start with a capital letter accidentally

[pocke]

Problem

Type Alias should start with a small letter.
But it can start with a capital letter accidentally in the syntax.

# test.rbs

type T = String

class C
  def m: () -> T
end

$ rbs parse test.rbs
$ echo $?
0

$ rbs -I . validate --silent
/path/to/rbs-1.0.0/lib/rbs/errors.rb:96:in `check!': test.rbs:4:15...4:16: Could not find ::T (RBS::NoTypeFoundError)
	from /path/to/rbs-1.0.0/lib/rbs/variance_calculator.rb:114:in `type'
	from /path/to/rbs-1.0.0/lib/rbs/variance_calculator.rb:83:in `in_method_type'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:523:in `block (2 levels) in validate_type_params'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:522:in `each'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:522:in `block in validate_type_params'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder/method_builder.rb:48:in `block in each'
	from /home/pocke/.rbenv/versions/trunk/lib/ruby/3.1.0/tsort.rb:350:in `block (2 levels) in each_strongly_connected_component'
	from /home/pocke/.rbenv/versions/trunk/lib/ruby/3.1.0/tsort.rb:431:in `each_strongly_connected_component_from'
	from /home/pocke/.rbenv/versions/trunk/lib/ruby/3.1.0/tsort.rb:349:in `block in each_strongly_connected_component'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder/method_builder.rb:65:in `each_value'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder/method_builder.rb:65:in `tsort_each_node'
	from /home/pocke/.rbenv/versions/trunk/lib/ruby/3.1.0/tsort.rb:347:in `call'
	from /home/pocke/.rbenv/versions/trunk/lib/ruby/3.1.0/tsort.rb:347:in `each_strongly_connected_component'
	from /home/pocke/.rbenv/versions/trunk/lib/ruby/3.1.0/tsort.rb:316:in `each_strongly_connected_component'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder/method_builder.rb:43:in `each'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:485:in `validate_type_params'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:150:in `block (2 levels) in build_instance'
	from <internal:kernel>:90:in `tap'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:146:in `block in build_instance'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:765:in `try_cache'
	from /path/to/rbs-1.0.0/lib/rbs/definition_builder.rb:135:in `build_instance'
	from /path/to/rbs-1.0.0/lib/rbs/cli.rb:423:in `block in run_validate'
	from /path/to/rbs-1.0.0/lib/rbs/cli.rb:421:in `each_key'
	from /path/to/rbs-1.0.0/lib/rbs/cli.rb:421:in `run_validate'
	from /path/to/rbs-1.0.0/lib/rbs/cli.rb:113:in `run'
	from /path/to/rbs-1.0.0/exe/rbs:7:in `<top (required)>'
	from /home/pocke/.rbenv/versions/trunk/bin/rbs:23:in `load'
	from /home/pocke/.rbenv/versions/trunk/bin/rbs:23:in `<main>'

Expected Behavior

I think it should cause a syntax error.
The type alias T can't be referred because a name that starts with a capital letter is a class or module. So it is confusing if it doesn't cause a syntax error.