Prism::RipperCompat differences with Ripper

[schneems]

I found that Ripper and Prism::RipperCompat produced different results on this invalid ruby code %Q* lol. This is using %Q to define a string and then declaring it will use the * character to end the string. It's invalid because it is missing a second * like %Q* lol*.

Reproduction

Define subclasses:

require 'prism'
require 'ripper'

class RipperErrors < Ripper
  attr_reader :errors

  # Comes from ripper, called
  # on every parse error, msg
  # is a string
  def on_parse_error(msg)
    @errors ||= []
    @errors << msg
  end

  alias_method :on_alias_error, :on_parse_error
  alias_method :on_assign_error, :on_parse_error
  alias_method :on_class_name_error, :on_parse_error
  alias_method :on_param_error, :on_parse_error
  alias_method :compile_error, :on_parse_error

  def call
    @run_once ||= begin
      @errors = []
      parse
      true
    end
    self
  end
end

class PrismErrors < Prism::RipperCompat
  attr_reader :errors

  # Comes from ripper, called
  # on every parse error, msg
  # is a string
  def on_parse_error(msg)
    @errors ||= []
    @errors << msg
  end

  alias_method :on_alias_error, :on_parse_error
  alias_method :on_assign_error, :on_parse_error
  alias_method :on_class_name_error, :on_parse_error
  alias_method :on_param_error, :on_parse_error
  alias_method :compile_error, :on_parse_error

  def call
    @run_once ||= begin
      @errors = []
      parse
      true
    end
    self
  end
end

Expected

I would expect that the output of these two are the same

Actual

Ripper reports an error but prism does not:

puts RipperErrors.new('%Q* lol').call.errors.inspect
# => ["unterminated string meets end of file"]
puts PrismErrors.new('%Q* lol').call.errors.inspect
# => []

It's also worth noting that Ripper can parse the valid code but prism cannot:

puts RipperErrors.new('%Q* lol*').call.errors.inspect
# => []

puts PrismErrors.new('%Q* lol*').call.errors.inspect
/Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/node.rb:15270:in `accept': undefined method `visit_string_node' for #<PrismErrors:0x00000001065e67d8 @source="%Q* lol*", @result=#<Prism::ParseResult:0x00000001065e62d8 @value=@ ProgramNode (location: (1,0)-(1,8)) (NoMethodError)
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,8))
    └── body: (length: 1)
        └── @ StringNode (location: (1,0)-(1,8))
            ├── flags: ∅
            ├── opening_loc: (1,0)-(1,3) = "%Q*"
            ├── content_loc: (1,3)-(1,7) = " lol"
            ├── closing_loc: (1,7)-(1,8) = "*"
            └── unescaped: " lol"
, @comments=[], @magic_comments=[], @errors=[], @warnings=[], @source=#<Prism::Source:0x00000001065e6710 @source="%Q* lol*", @start_line=1, @offsets=[0]>>, @lineno=1, @column=0, @errors=[]>

      visitor.visit_string_node(self)
             ^^^^^^^^^^^^^^^^^^
Did you mean?  visit_integer_node
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:95:in `visit'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:123:in `block in visit_statements_node'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:122:in `each'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:122:in `inject'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:122:in `visit_statements_node'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/node.rb:15161:in `accept'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:95:in `visit'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:144:in `visit_program_node'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/node.rb:13305:in `accept'
	from /Users/rschneeman/.gem/ruby/3.1.4/gems/prism-0.18.0/lib/prism/ripper_compat.rb:85:in `parse'
	from (irb):104:in `call'
	from (irb):123:in `<main>'
	from /Users/rschneeman/.rubies/ruby-3.1.4/lib/ruby/gems/3.1.0/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
	from /Users/rschneeman/.rubies/ruby-3.1.4/bin/irb:25:in `load'
	from /Users/rschneeman/.rubies/ruby-3.1.4/bin/irb:25:in `<main>'

This is with prism 0.18.0 and Ruby 3.1.4 (also tested with 3.2.2, same result).

[schneems]

FWIW Prism.parse('%Q* lol').errors.map(&:message) gives me what I need so this isn't blocking:

Prism.parse('%Q* lol').errors.map(&:message)
# => ["Expected a closing delimiter for the interpolated string"]

The message is different, but that's fine. I just need a message.

[kddnewton]

I just pushed an update to main that should help this.

Unfortunately ripper compat is not done, but the documentation didn't say that. So it says that now. On the otherhand, I made it so that it reports errors in the same way as ripper, so that itself is done now. It also won't error on missing node implementations now, it will just skip them. Not great, but much better. I'm going to close this for now since the actual bug you reported has been fixed.