[Writer] Escape method names that are invalid with def syntax

[pocke]

This pull request fixes the escaping strategy of RBS::Writer to escape invalid method names for def syntax correctly.

Problem

Currently RBS::Writer doesn't escape invalid method names for def syntax. For example

require 'rbs'
require 'stringio'

rbs = RBS::Parser.parse_signature(<<~RBS)
  class C
    def `foo!=`: () -> untyped
  end
RBS

io = StringIO.new

RBS::Writer.new(out: io).write(rbs)

puts io.string
# => class C
#      def foo!=: () -> untyped
#    end

RBS::Parser.parse_signature(io.string)
# => RBS::Parser::SyntaxError

I expect def `foo!=`: () -> untyped as the output, but it displays without backtick escaping. So it generates invalid RBS.

By the way, we can't define foo!= method with def syntax even in Ruby. But we can use define_method for this method name.

class C
  define_method(:'foo!=') {}
end

p C.instance_methods(false) # => [:"foo!="]

Solution

Escape method names correctly.

[pocke]

RBS::Writer escapes keywords, for example: ``def def: () -> untyped`. But this escaping is not necessary because it is allowed.

I keep this escaping because of compatibility, and I'm not sure why this escaping needs to keep.

rbs/test/rbs/writer_test.rb

Line 114 in a1e6261

def `def`: () -> Symbol

If this escaping is not necessary, I can remove the escaping easily by removing && !/\A#{Parser::KEYWORDS_RE}\z/.match?(s) condition.

What do you think? @soutaro

[soutaro]

It makes sense. I don't think we need to keep the quoting behavior.

Let's make it:

1. Unquoted even if it is a keyword (I'm proposing this change)
2. Unquoted if it is safe /\A[a-zA-Z_]\w*[?!=]?\z/
3. Quoted otherwise

[pocke]

Thanks for your comment. I applied this charge with 2b03212.

But I noticed we still need to quote self and self? as a method name because it causes syntax error without quote.
So I replace Parser::KEYWORDS_RE with /\Aself\??\z/.

[soutaro]

💯