rust/crates/ra_mbe/src/lib.rs

//! `mbe` (short for Macro By Example) crate contains code for handling
//! `macro_rules` macros. It uses `TokenTree` (from `ra_tt` package) as the
//! interface, although it contains some code to bridge `SyntaxNode`s and
//! `TokenTree`s as well!

mod parser;
mod mbe_expander;
mod syntax_bridge;
mod tt_iter;
mod subtree_source;

pub use tt::{Delimiter, Punct};

use crate::{
    parser::{parse_pattern, Op},
    tt_iter::TtIter,
};

#[derive(Debug, PartialEq, Eq)]
pub enum ParseError {
    Expected(String),
}

#[derive(Debug, PartialEq, Eq)]
pub enum ExpandError {
    NoMatchingRule,
    UnexpectedToken,
    BindingError(String),
    ConversionError,
    InvalidRepeat,
}

pub use crate::syntax_bridge::{
    ast_to_token_tree, syntax_node_to_token_tree, token_tree_to_expr, token_tree_to_items,
    token_tree_to_macro_stmts, token_tree_to_pat, token_tree_to_ty,
};

/// This struct contains AST for a single `macro_rules` definition. What might
/// be very confusing is that AST has almost exactly the same shape as
/// `tt::TokenTree`, but there's a crucial difference: in macro rules, `$ident`
/// and `$()*` have special meaning (see `Var` and `Repeat` data structures)
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct MacroRules {
    pub(crate) rules: Vec<Rule>,
    /// Highest id of the token we have in TokenMap
    pub(crate) shift: u32,
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) struct Rule {
    pub(crate) lhs: tt::Subtree,
    pub(crate) rhs: tt::Subtree,
}

/// Find the "shift" (the highest id of the TokenId) inside a subtree
fn find_subtree_shift(tt: &tt::Subtree, mut cur: u32) -> u32 {
    use std::cmp::max;

    for t in &tt.token_trees {
        cur = match t {
            tt::TokenTree::Leaf(leaf) => match leaf {
                tt::Leaf::Ident(ident) if ident.id != tt::TokenId::unspecified() => {
                    max(cur, ident.id.0)
                }
                _ => cur,
            },
            tt::TokenTree::Subtree(tt) => find_subtree_shift(tt, cur),
        }
    }

    cur
}

/// Shift given TokenTree token id
fn shift_subtree(tt: &mut tt::Subtree, shift: u32) {
    for t in tt.token_trees.iter_mut() {
        match t {
            tt::TokenTree::Leaf(leaf) => match leaf {
                tt::Leaf::Ident(ident) if ident.id != tt::TokenId::unspecified() => {
                    // Note that TokenId is started from zero,
                    // We have to add 1 to prevent duplication.
                    ident.id.0 += shift + 1;
                }
                _ => (),
            },
            tt::TokenTree::Subtree(tt) => shift_subtree(tt, shift),
        }
    }
}

impl MacroRules {
    pub fn parse(tt: &tt::Subtree) -> Result<MacroRules, ParseError> {
        // Note: this parsing can be implemented using mbe machinery itself, by
        // matching against `$($lhs:tt => $rhs:tt);*` pattern, but implementing
        // manually seems easier.
        let mut src = TtIter::new(tt);
        let mut rules = Vec::new();
        while src.len() > 0 {
            let rule = Rule::parse(&mut src)?;
            rules.push(rule);
            if let Err(()) = src.expect_char(';') {
                if src.len() > 0 {
                    return Err(ParseError::Expected("expected `:`".to_string()));
                }
                break;
            }
        }

        for rule in rules.iter() {
            validate(&rule.lhs)?;
        }

        Ok(MacroRules { rules, shift: find_subtree_shift(tt, 0) })
    }

    pub fn expand(&self, tt: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
        // apply shift
        let mut tt = tt.clone();
        shift_subtree(&mut tt, self.shift);
        mbe_expander::expand(self, &tt)
    }
}

impl Rule {
    fn parse(src: &mut TtIter) -> Result<Rule, ParseError> {
        let mut lhs = src
            .expect_subtree()
            .map_err(|()| ParseError::Expected("expected subtree".to_string()))?
            .clone();
        lhs.delimiter = tt::Delimiter::None;
        src.expect_char('=').map_err(|()| ParseError::Expected("expected `=`".to_string()))?;
        src.expect_char('>').map_err(|()| ParseError::Expected("expected `>`".to_string()))?;
        let mut rhs = src
            .expect_subtree()
            .map_err(|()| ParseError::Expected("expected subtree".to_string()))?
            .clone();
        rhs.delimiter = tt::Delimiter::None;
        Ok(crate::Rule { lhs, rhs })
    }
}

fn validate(pattern: &tt::Subtree) -> Result<(), ParseError> {
    for op in parse_pattern(pattern) {
        let op = match op {
            Ok(it) => it,
            Err(e) => {
                let msg = match e {
                    ExpandError::InvalidRepeat => "invalid repeat".to_string(),
                    _ => "invalid macro definition".to_string(),
                };
                return Err(ParseError::Expected(msg));
            }
        };
        match op {
            Op::TokenTree(tt::TokenTree::Subtree(subtree)) | Op::Repeat { subtree, .. } => {
                validate(subtree)?
            }
            _ => (),
        }
    }
    Ok(())
}

#[cfg(test)]
mod tests;