Sorbet runtime does not support limitless ranges properly

[alexevanczuk]

Input

→ View on sorbet.run

class Test
  extend T::Sig
  sig { returns(T::Range[T.nilable(Date)]) }
  def range
    Range.new(nil, nil)
  end

  sig { returns(T::Range[T.nilable(Date)]) }
  def range_1
    Range.new(nil, Date.today)
  end

  sig { returns(T::Range[T.nilable(Date)]) }
  def range_1
    Range.new(nil, nil)
  end
end

Observed output

Static Output

No errors! Great job.

Runtime output

development 25> Test.new.range
RangeError: cannot get the last element of endless range
from /Users/alex.evanczuk/workspace/app/vendor/bundle/ruby/2.6.0/gems/sorbet-runtime-0.5.5585/lib/types/types/typed_enumerable.rb:127:in `last'

Expected behavior

No error when validating runtime signatures.

[jez]

Probably just a matter of editing this:

sorbet/gems/sorbet-runtime/lib/types/types/typed_enumerable.rb

Lines 52 to 53 in ba767ec

	when Range
	@type.valid?(obj.first) && @type.valid?(obj.last)

to check if obj.begin / obj.end is nil before checking first / last

[alexevanczuk]

I created a PR for this: #3094

I'll wait until tests pass before assigning it out.

The main documentation doesn't say how to run tests -- how am I able to run these tests? I want to verify locally these tests fail with the old code and pass with the new.