use crate::{ token_set::TokenSet, parser_impl::ParserImpl, SyntaxKind::{self, ERROR}, drop_bomb::DropBomb, }; /// `Parser` struct provides the low-level API for /// navigating through the stream of tokens and /// constructing the parse tree. The actual parsing /// happens in the `grammar` module. /// /// However, the result of this `Parser` is not a real /// tree, but rather a flat stream of events of the form /// "start expression, consume number literal, /// finish expression". See `Event` docs for more. pub(crate) struct Parser<'t>(pub(super) ParserImpl<'t>); impl<'t> Parser<'t> { /// Returns the kind of the current token. /// If parser has already reached the end of input, /// the special `EOF` kind is returned. pub(crate) fn current(&self) -> SyntaxKind { self.nth(0) } /// Lookahead operation: returns the kind of the next nth /// token. pub(crate) fn nth(&self, n: u32) -> SyntaxKind { self.0.nth(n) } /// Checks if the current token is `kind`. pub(crate) fn at(&self, kind: SyntaxKind) -> bool { self.current() == kind } /// Checks if the current token is `kind`. pub(crate) fn at_ts(&self, kinds: TokenSet) -> bool { kinds.contains(self.current()) } pub(crate) fn next2(&self) -> Option<(SyntaxKind, SyntaxKind)> { self.0.next2() } pub(crate) fn next3(&self) -> Option<(SyntaxKind, SyntaxKind, SyntaxKind)> { self.0.next3() } /// Checks if the current token is contextual keyword with text `t`. pub(crate) fn at_contextual_kw(&self, t: &str) -> bool { self.0.at_kw(t) } /// Starts a new node in the syntax tree. All nodes and tokens /// consumed between the `start` and the corresponding `Marker::complete` /// belong to the same node. pub(crate) fn start(&mut self) -> Marker { Marker::new(self.0.start()) } /// Advances the parser by one token. pub(crate) fn bump(&mut self) { self.0.bump(); } /// Advances the parser by one token, remapping its kind. /// This is useful to create contextual keywords from /// identifiers. For example, the lexer creates an `union` /// *identifier* token, but the parser remaps it to the /// `union` keyword, and keyword is what ends up in the /// final tree. pub(crate) fn bump_remap(&mut self, kind: SyntaxKind) { self.0.bump_remap(kind); } /// Advances the parser by `n` tokens, remapping its kind. /// This is useful to create compound tokens from parts. For /// example, an `<<` token is two consecutive remapped `<` tokens pub(crate) fn bump_compound(&mut self, kind: SyntaxKind, n: u8) { self.0.bump_compound(kind, n); } /// Emit error with the `message` /// TODO: this should be much more fancy and support /// structured errors with spans and notes, like rustc /// does. pub(crate) fn error>(&mut self, message: T) { self.0.error(message.into()) } /// Consume the next token if it is `kind`. pub(crate) fn eat(&mut self, kind: SyntaxKind) -> bool { if !self.at(kind) { return false; } self.bump(); true } /// Consume the next token if it is `kind` or emit an error /// otherwise. pub(crate) fn expect(&mut self, kind: SyntaxKind) -> bool { if self.eat(kind) { return true; } self.error(format!("expected {:?}", kind)); false } /// Create an error node and consume the next token. pub(crate) fn err_and_bump(&mut self, message: &str) { self.err_recover(message, TokenSet::EMPTY); } /// Create an error node and consume the next token. pub(crate) fn err_recover(&mut self, message: &str, recovery: TokenSet) { if self.at(SyntaxKind::L_CURLY) || self.at(SyntaxKind::R_CURLY) || self.at_ts(recovery) { self.error(message); } else { let m = self.start(); self.error(message); self.bump(); m.complete(self, ERROR); }; } } /// See `Parser::start`. pub(crate) struct Marker { pos: u32, bomb: DropBomb, } impl Marker { fn new(pos: u32) -> Marker { Marker { pos, bomb: DropBomb::new("Marker must be either completed or abandoned"), } } /// Finishes the syntax tree node and assigns `kind` to it. pub(crate) fn complete(mut self, p: &mut Parser, kind: SyntaxKind) -> CompletedMarker { self.bomb.defuse(); p.0.complete(self.pos, kind); CompletedMarker(self.pos, kind) } /// Abandons the syntax tree node. All its children /// are attached to its parent instead. pub(crate) fn abandon(mut self, p: &mut Parser) { self.bomb.defuse(); p.0.abandon(self.pos); } } pub(crate) struct CompletedMarker(u32, SyntaxKind); impl CompletedMarker { /// This one is tricky :-) /// This method allows to create a new node which starts /// *before* the current one. That is, parser could start /// node `A`, then complete it, and then after parsing the /// whole `A`, decide that it should have started some node /// `B` before starting `A`. `precede` allows to do exactly /// that. See also docs about `forward_parent` in `Event::Start`. pub(crate) fn precede(self, p: &mut Parser) -> Marker { Marker::new(p.0.precede(self.0)) } pub(crate) fn kind(&self) -> SyntaxKind { self.1 } }