Stripping leading whitespace in ruby heredocs

whitespace.rb

# <<foo doesn't trim leading whitespace.  No problem.  :cake:
<<EOS
  hi
EOS
=> "  hi\n"

# I thought the difference between << and <<- was the leading whitespace trimming.
<<-EOS
  hi
EOS
=> "  hi\n"

# Am I missing something?  Almost all of homebrew monkey patches string to "unindent" heredocs.

# Some people use gsub.  Some people monkey patch string.  That's fine I guess.
# I think I would use the activesupport gem in a bigger project.
# In a smaller project, just use unindent from homebrew.
require 'active_support/core_ext'
test = <<EOS
  hi
EOS
=> "  hi\n"
test.strip_heredoc
=> "hi\n"