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|
//! `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>,
}
#[derive(Clone, Debug, PartialEq, Eq)]
pub(crate) struct Rule {
pub(crate) lhs: tt::Subtree,
pub(crate) rhs: tt::Subtree,
}
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 })
}
pub fn expand(&self, tt: &tt::Subtree) -> Result<tt::Subtree, ExpandError> {
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;
|
