rust-analyzer/crates/ra_mbe/src/mbe_parser.rs

use crate::tt_cursor::TtCursor;
/// This module parses a raw `tt::TokenStream` into macro-by-example token
/// stream. This is a *mostly* identify function, expect for handling of
/// `$var:tt_kind` and `$(repeat),*` constructs.
use crate::ParseError;

pub(crate) fn parse(tt: &tt::Subtree) -> Result<crate::MacroRules, ParseError> {
    let mut parser = TtCursor::new(tt);
    let mut rules = Vec::new();
    while !parser.is_eof() {
        rules.push(parse_rule(&mut parser)?);
        if let Err(e) = parser.expect_char(';') {
            if !parser.is_eof() {
                return Err(e);
            }
            break;
        }
    }
    Ok(crate::MacroRules { rules })
}

fn parse_rule(p: &mut TtCursor) -> Result<crate::Rule, ParseError> {
    let lhs = parse_subtree(p.eat_subtree()?, false)?;
    p.expect_char('=')?;
    p.expect_char('>')?;
    let mut rhs = parse_subtree(p.eat_subtree()?, true)?;
    rhs.delimiter = crate::Delimiter::None;
    Ok(crate::Rule { lhs, rhs })
}

fn is_boolean_literal(lit: Option<&tt::TokenTree>) -> bool {
    if let Some(tt::TokenTree::Leaf(tt::Leaf::Literal(lit))) = lit {
        if lit.text == "true" || lit.text == "false" {
            return true;
        }
    }

    false
}

fn parse_subtree(tt: &tt::Subtree, transcriber: bool) -> Result<crate::Subtree, ParseError> {
    let mut token_trees = Vec::new();
    let mut p = TtCursor::new(tt);
    while let Some(tt) = p.eat() {
        let child: crate::TokenTree = match tt {
            tt::TokenTree::Leaf(leaf) => match leaf {
                tt::Leaf::Punct(tt::Punct { char: '$', spacing }) => {
                    // mbe var can be an ident or keyword, including `true` and `false`
                    if p.at_ident().is_some() || is_boolean_literal(p.current()) {
                        crate::Leaf::from(parse_var(&mut p, transcriber)?).into()
                    } else if let Some(tt::TokenTree::Subtree(_)) = p.current() {
                        parse_repeat(&mut p, transcriber)?.into()
                    } else {
                        // Treat it as normal punct
                        crate::Leaf::from(tt::Punct { char: '$', spacing: *spacing }).into()
                    }
                }
                tt::Leaf::Punct(punct) => crate::Leaf::from(*punct).into(),
                tt::Leaf::Ident(tt::Ident { text, .. }) => {
                    crate::Leaf::from(crate::Ident { text: text.clone() }).into()
                }
                tt::Leaf::Literal(tt::Literal { text }) => {
                    crate::Leaf::from(crate::Literal { text: text.clone() }).into()
                }
            },
            tt::TokenTree::Subtree(subtree) => parse_subtree(&subtree, transcriber)?.into(),
        };
        token_trees.push(child);
    }
    Ok(crate::Subtree { token_trees, delimiter: tt.delimiter })
}

fn parse_var(p: &mut TtCursor, transcriber: bool) -> Result<crate::Var, ParseError> {
    let text = {
        if is_boolean_literal(p.current()) {
            let lit = p.eat_literal().unwrap();
            lit.text.clone()
        } else {
            let ident = p.eat_ident().unwrap();
            ident.text.clone()
        }
    };

    let kind = if !transcriber && p.at_char(':') {
        p.bump();
        if let Some(ident) = p.eat_ident() {
            Some(ident.text.clone())
        } else {
            p.rev_bump();
            None
        }
    } else {
        None
    };

    Ok(crate::Var { text, kind })
}

fn mk_repeat(
    rep: char,
    subtree: crate::Subtree,
    separator: Option<crate::Separator>,
) -> Result<crate::Repeat, ParseError> {
    let kind = match rep {
        '*' => crate::RepeatKind::ZeroOrMore,
        '+' => crate::RepeatKind::OneOrMore,
        '?' => crate::RepeatKind::ZeroOrOne,
        _ => return Err(ParseError::Expected(String::from("repeat"))),
    };
    Ok(crate::Repeat { subtree, kind, separator })
}

fn parse_repeat(p: &mut TtCursor, transcriber: bool) -> Result<crate::Repeat, ParseError> {
    let subtree = p.eat_subtree()?;
    let mut subtree = parse_subtree(subtree, transcriber)?;
    subtree.delimiter = crate::Delimiter::None;

    if let Some(rep) = p.at_punct() {
        match rep.char {
            '*' | '+' | '?' => {
                p.bump();
                return mk_repeat(rep.char, subtree, None);
            }
            _ => {}
        }
    }

    let sep = p.eat_seperator().ok_or_else(|| ParseError::Expected(String::from("separator")))?;
    let rep = p.eat_punct().ok_or_else(|| ParseError::Expected(String::from("repeat")))?;

    mk_repeat(rep.char, subtree, Some(sep))
}

#[cfg(test)]
mod tests {
    use ra_syntax::{ast, AstNode};

    use super::*;
    use crate::ast_to_token_tree;

    #[test]
    fn test_invalid_parse() {
        expect_err("invalid", "subtree");

        is_valid("($i:ident) => ()");
        is_valid("($($i:ident)*) => ($_)");
        is_valid("($($true:ident)*) => ($true)");
        is_valid("($($false:ident)*) => ($false)");

        expect_err("$i:ident => ()", "subtree");
        expect_err("($i:ident) ()", "`=`");
        expect_err("($($i:ident)_) => ()", "repeat");
    }

    fn expect_err(macro_body: &str, expected: &str) {
        assert_eq!(
            create_rules(&format_macro(macro_body)),
            Err(ParseError::Expected(String::from(expected)))
        );
    }

    fn is_valid(macro_body: &str) {
        assert!(create_rules(&format_macro(macro_body)).is_ok());
    }

    fn format_macro(macro_body: &str) -> String {
        format!(
            "
        macro_rules! foo {{
            {}
        }}
",
            macro_body
        )
    }

    fn create_rules(macro_definition: &str) -> Result<crate::MacroRules, ParseError> {
        let source_file = ast::SourceFile::parse(macro_definition).ok().unwrap();
        let macro_definition =
            source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();

        let (definition_tt, _) =
            ast_to_token_tree(&macro_definition.token_tree().unwrap()).unwrap();
        parse(&definition_tt)
    }

}