reshuffle

crates/ra_macros/src/mbe_parser.rs

@@ -0,0 +1,184 @@
+use crate::{tt, mbe};
+
+/// 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.
+
+struct RulesParser<'a> {
+    subtree: &'a tt::Subtree,
+    pos: usize,
+}
+
+impl<'a> RulesParser<'a> {
+    fn new(subtree: &'a tt::Subtree) -> RulesParser<'a> {
+        RulesParser { subtree, pos: 0 }
+    }
+
+    fn is_eof(&self) -> bool {
+        self.pos == self.subtree.token_trees.len()
+    }
+
+    fn current(&self) -> Option<&'a tt::TokenTree> {
+        self.subtree.token_trees.get(self.pos)
+    }
+
+    fn at_punct(&self) -> Option<&'a tt::Punct> {
+        match self.current() {
+            Some(tt::TokenTree::Leaf(tt::Leaf::Punct(it))) => Some(it),
+            _ => None,
+        }
+    }
+
+    fn at_char(&self, char: char) -> bool {
+        match self.at_punct() {
+            Some(tt::Punct { char: c }) if *c == char => true,
+            _ => false,
+        }
+    }
+
+    fn at_ident(&mut self) -> Option<&'a tt::Ident> {
+        match self.current() {
+            Some(tt::TokenTree::Leaf(tt::Leaf::Ident(i))) => Some(i),
+            _ => None,
+        }
+    }
+
+    fn bump(&mut self) {
+        self.pos += 1;
+    }
+
+    fn eat(&mut self) -> Option<&'a tt::TokenTree> {
+        match self.current() {
+            Some(it) => {
+                self.bump();
+                Some(it)
+            }
+            None => None,
+        }
+    }
+
+    fn eat_subtree(&mut self) -> Option<&'a tt::Subtree> {
+        match self.current()? {
+            tt::TokenTree::Subtree(sub) => {
+                self.bump();
+                Some(sub)
+            }
+            _ => return None,
+        }
+    }
+
+    fn eat_punct(&mut self) -> Option<&'a tt::Punct> {
+        if let Some(it) = self.at_punct() {
+            self.bump();
+            return Some(it);
+        }
+        None
+    }
+
+    fn eat_ident(&mut self) -> Option<&'a tt::Ident> {
+        if let Some(i) = self.at_ident() {
+            self.bump();
+            return Some(i);
+        }
+        None
+    }
+
+    fn expect_char(&mut self, char: char) -> Option<()> {
+        if self.at_char(char) {
+            self.bump();
+            return Some(());
+        }
+        None
+    }
+}
+
+pub fn parse(tt: &tt::Subtree) -> Option<mbe::MacroRules> {
+    let mut parser = RulesParser::new(tt);
+    let mut rules = Vec::new();
+    while !parser.is_eof() {
+        rules.push(parse_rule(&mut parser)?)
+    }
+    Some(mbe::MacroRules { rules })
+}
+
+fn parse_rule(p: &mut RulesParser) -> Option<mbe::Rule> {
+    let lhs = parse_subtree(p.eat_subtree()?)?;
+    p.expect_char('=')?;
+    p.expect_char('>')?;
+    let rhs = parse_subtree(p.eat_subtree()?)?;
+    Some(mbe::Rule { lhs, rhs })
+}
+
+fn parse_subtree(tt: &tt::Subtree) -> Option<mbe::Subtree> {
+    let mut token_trees = Vec::new();
+    let mut p = RulesParser::new(tt);
+    while let Some(tt) = p.eat() {
+        let child: mbe::TokenTree = match tt {
+            tt::TokenTree::Leaf(leaf) => match leaf {
+                tt::Leaf::Punct(tt::Punct { char: '$' }) => {
+                    if p.at_ident().is_some() {
+                        mbe::Leaf::from(parse_var(&mut p)?).into()
+                    } else {
+                        parse_repeat(&mut p)?.into()
+                    }
+                }
+                tt::Leaf::Punct(tt::Punct { char }) => {
+                    mbe::Leaf::from(mbe::Punct { char: *char }).into()
+                }
+                tt::Leaf::Ident(tt::Ident { text }) => {
+                    mbe::Leaf::from(mbe::Ident { text: text.clone() }).into()
+                }
+                tt::Leaf::Literal(tt::Literal { text }) => {
+                    mbe::Leaf::from(mbe::Literal { text: text.clone() }).into()
+                }
+            },
+            tt::TokenTree::Subtree(subtree) => parse_subtree(subtree)?.into(),
+        };
+        token_trees.push(child);
+    }
+    Some(mbe::Subtree {
+        token_trees,
+        delimiter: tt.delimiter,
+    })
+}
+
+fn parse_var(p: &mut RulesParser) -> Option<mbe::Var> {
+    let ident = p.eat_ident().unwrap();
+    let text = ident.text.clone();
+    let kind = if p.at_char(':') {
+        p.bump();
+        if let Some(ident) = p.eat_ident() {
+            Some(ident.text.clone())
+        } else {
+            // ugly as hell :(
+            p.pos -= 1;
+            None
+        }
+    } else {
+        None
+    };
+    Some(mbe::Var { text, kind })
+}
+
+fn parse_repeat(p: &mut RulesParser) -> Option<mbe::Repeat> {
+    let subtree = p.eat_subtree().unwrap();
+    let subtree = parse_subtree(subtree)?;
+    let sep = p.eat_punct()?;
+    let (separator, rep) = match sep.char {
+        '*' | '+' | '?' => (None, sep.char),
+        char => (Some(mbe::Punct { char }), p.eat_punct()?.char),
+    };
+
+    let kind = match rep {
+        '*' => mbe::RepeatKind::ZeroOrMore,
+        '+' => mbe::RepeatKind::OneOrMore,
+        '?' => mbe::RepeatKind::ZeroOrMore,
+        _ => return None,
+    };
+    p.bump();
+    Some(mbe::Repeat {
+        subtree,
+        kind,
+        separator,
+    })
+}