token enum rule

[davemackintosh]

So I've got a grammar, say something like this:

pointer_semantics = { "*" | "&" }
variable_access = { pointer_semantics* ~ IDENT }

I would like to be able to create an enum using pest_ast like this, but I've tried a few different ways and I can't seem to get it to work, I.E it won't select the case based on the token/rule applied.

#[derive(Debug, FromPest, PartialEq, Eq)]
pub enum PointerSemantics {
    Pointer,
    Reference,
}

I've also tried (with the literals replaced by lexer tokens)

#[derive(Debug, FromPest, PartialEq, Eq)]
pub enum PointerSemantics {
    #[pest_ast(rule(Rule::POINTER))]
    Pointer,
    #[pest_ast(rule(Rule::REFERENCE))]
    Reference,
}

fails my tests with

thread 'ast::variable_access::tests::variable_access_with_pointer_semantics' panicked at crates/parser/src/ast/variable_access.rs:88:77:
called `Result::unwrap()` on an `Err` value: Extraneous { current_node: "Reference" }

And I've also implemented my own FromPest method

impl<'pest> FromPest<'pest> for PointerSemantics {
    type Rule = crate::Rule;
    type FatalError = Void;

    fn from_pest(
        pest: &mut Pairs<'pest, Self::Rule>,
    ) -> Result<Self, ConversionError<Self::FatalError>> {
        let symbol = pest.next().unwrap();

        match symbol.as_str() {
            "*" => Ok(PointerSemantics::Pointer),
            "&" => Ok(PointerSemantics::Reference),
            _ => Err(ConversionError::NoMatch),
        }
    }
}

But I get a NoMatch error when I try to use it in conjunction with my variable_access rule when there are no explicit pointer semantics, which makes sense if it's trying to parse an IDENT as a pointer_semantics but it is a zero-or-more rule so I'm a little stumped.

How can I do this?

I've reduced my example to a failing case but here are my full implementations for reference.

• grammar: https://github.com/elp-lang/elp/blob/main/crates/parser/src/elp.pest
• ast: https://github.com/elp-lang/elp/blob/main/crates/parser/src/ast/variable_access.rs

[davemackintosh]

I don't really like the solution but I solved this by creating two new empty structs for the POINTER and REFERENCE rules to add to the enum. Which means I have to instantiate a new struct for each one but it'll do for now.

elp-lang/elp@5be8ea8