Frozen strings and character literal syntax

[viralpraxis]

I'm trying to figure out why

RuboCop::AST::ProcessedSource.new('"\n"', 3.3).ast.value.frozen?
=> false

but

RuboCop::AST::ProcessedSource.new('?\n', 3.3).ast.value.frozen?
=> true

Is this intentional? Both these expressions have the same AST (str "\n")

[marcandre]

Hmmm, I don't think that would be intentional and think it would be best frozen.

Is that using parser or prism?

[viralpraxis]

RuboCop::AST::ProcessedSource.new('?\n', 3.3, parser_engine: "parser_prism").ast.value.frozen?
=> false
RuboCop::AST::ProcessedSource.new('?\n', 3.3, parser_engine: "parser_whitequark").ast.value.frozen?
=> true

[marcandre]

AFAIK, rubocop-ast does not process the arguments of the nodes, so I'd open an issue with the parser (Prism only?) which should, imo, freeze these at parsing.

[kddnewton]

I'm not sure I understand what is intentional and what is not here.

irb(main):012> RuboCop::AST::ProcessedSource.new('?\n', 3.3, parser_engine: "parser_whitequark").ast.value.frozen?
=> true
irb(main):013> RuboCop::AST::ProcessedSource.new('"\n"', 3.3, parser_engine: "parser_whitequark").ast.value.frozen?
=> false

Is it just character literals? It looks like most string literals are unfrozen coming back from the parser gem:

irb(main):016> Parser::CurrentRuby.parse('?\n').children[0].frozen?
=> true
irb(main):017> Parser::CurrentRuby.parse('"\n"').children[0].frozen?
=> false

[kddnewton]

Funny enough, it looks like it's not even consistent within character literals:

irb(main):019> Parser::CurrentRuby.parse('?a').children[0].frozen?
=> false

[kddnewton]

Okay, further investigation reveals that it depends on if the parser gem determines something is string content or if something is a token. Tokens are frozen, string content isn't. It seems to be relatively arbitrary. I'm okay freezing strings in the prism AST in general, but matching this behavior feels a bit odd.