use std::cell::Cell; use drop_bomb::DropBomb; use crate::{ SyntaxKind::{self, ERROR, EOF, TOMBSTONE}, parsing::{ TokenSource, ParseError, token_set::TokenSet, event::Event, }, }; /// `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> { token_source: &'t dyn TokenSource, token_pos: usize, events: Vec, steps: Cell, } impl<'t> Parser<'t> { pub(super) fn new(token_source: &'t dyn TokenSource) -> Parser<'t> { Parser { token_source, token_pos: 0, events: Vec::new(), steps: Cell::new(0) } } pub(crate) fn finish(self) -> Vec { self.events } /// 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) } /// Returns the kinds of the current two tokens, if they are not separated /// by trivia. /// /// Useful for parsing things like `>>`. pub(crate) fn current2(&self) -> Option<(SyntaxKind, SyntaxKind)> { let c1 = self.token_source.token_kind(self.token_pos); let c2 = self.token_source.token_kind(self.token_pos + 1); if self.token_source.is_token_joint_to_next(self.token_pos) { Some((c1, c2)) } else { None } } /// Returns the kinds of the current three tokens, if they are not separated /// by trivia. /// /// Useful for parsing things like `=>>`. pub(crate) fn current3(&self) -> Option<(SyntaxKind, SyntaxKind, SyntaxKind)> { let c1 = self.token_source.token_kind(self.token_pos); let c2 = self.token_source.token_kind(self.token_pos + 1); let c3 = self.token_source.token_kind(self.token_pos + 2); if self.token_source.is_token_joint_to_next(self.token_pos) && self.token_source.is_token_joint_to_next(self.token_pos + 1) { Some((c1, c2, c3)) } else { None } } /// Lookahead operation: returns the kind of the next nth /// token. pub(crate) fn nth(&self, n: usize) -> SyntaxKind { let steps = self.steps.get(); assert!(steps <= 10_000_000, "the parser seems stuck"); self.steps.set(steps + 1); self.token_source.token_kind(self.token_pos + 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 in `kinds`. pub(crate) fn at_ts(&self, kinds: TokenSet) -> bool { kinds.contains(self.current()) } /// Checks if the current token is contextual keyword with text `t`. pub(crate) fn at_contextual_kw(&self, kw: &str) -> bool { self.token_source.is_keyword(self.token_pos, kw) } /// 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 { let pos = self.events.len() as u32; self.push_event(Event::tombstone()); Marker::new(pos) } /// Advances the parser by one token unconditionally. pub(crate) fn bump(&mut self) { let kind = self.nth(0); if kind == EOF { return; } self.do_bump(kind, 1); } /// 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) { if self.nth(0) == EOF { // TODO: panic!? return; } self.do_bump(kind, 1); } /// 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.do_bump(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) { let msg = ParseError(message.into()); self.push_event(Event::Error { msg }) } /// Consume the next token if `kind` matches. 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); }; } fn do_bump(&mut self, kind: SyntaxKind, n_raw_tokens: u8) { self.token_pos += usize::from(n_raw_tokens); self.push_event(Event::Token { kind, n_raw_tokens }); } fn push_event(&mut self, event: Event) { self.events.push(event) } } /// 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, /// and mark the create a `CompletedMarker` for possible future /// operation like `.precede()` to deal with forward_parent. pub(crate) fn complete(mut self, p: &mut Parser, kind: SyntaxKind) -> CompletedMarker { self.bomb.defuse(); let idx = self.pos as usize; match p.events[idx] { Event::Start { kind: ref mut slot, .. } => { *slot = kind; } _ => unreachable!(), } p.push_event(Event::Finish); CompletedMarker::new(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(); let idx = self.pos as usize; if idx == p.events.len() - 1 { match p.events.pop() { Some(Event::Start { kind: TOMBSTONE, forward_parent: None }) => (), _ => unreachable!(), } } } } pub(crate) struct CompletedMarker(u32, SyntaxKind); impl CompletedMarker { fn new(pos: u32, kind: SyntaxKind) -> Self { CompletedMarker(pos, kind) } /// 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`. /// /// Given completed events `[START, FINISH]` and its corresponding /// `CompletedMarker(pos: 0, _)`. /// Append a new `START` events as `[START, FINISH, NEWSTART]`, /// then mark `NEWSTART` as `START`'s parent with saving its relative /// distance to `NEWSTART` into forward_parent(=2 in this case); pub(crate) fn precede(self, p: &mut Parser) -> Marker { let new_pos = p.start(); let idx = self.0 as usize; match p.events[idx] { Event::Start { ref mut forward_parent, .. } => { *forward_parent = Some(new_pos.pos - self.0); } _ => unreachable!(), } new_pos } pub(crate) fn kind(&self) -> SyntaxKind { self.1 } }