//! The parser: turns a series of tokens into an AST

use std::{collections::VecDeque, fmt};

use rowan::{Checkpoint, GreenNode, GreenNodeBuilder, Language, TextRange, TextSize};

use crate::{
    tokenizer::Token,
    NixLanguage,
    SyntaxKind::{self, *},
    TokenSet,
};

/// An error that occurred during parsing
#[derive(Clone, Debug, PartialEq)]
#[non_exhaustive]
pub enum ParseError {
    /// Unexpected is used when the cause cannot be specified further
    Unexpected(TextRange),
    /// UnexpectedExtra is used when there are additional tokens to the root in the tree
    UnexpectedExtra(TextRange),
    /// UnexpectedWanted is used when specific tokens are expected, but different one is found
    UnexpectedWanted(SyntaxKind, TextRange, Box<[SyntaxKind]>),
    /// UnexpectedDoubleBind is used when a pattern is bound twice
    UnexpectedDoubleBind(TextRange),
    /// UnexpectedEOF is used when the end of file is reached, while tokens are still expected
    UnexpectedEOF,
    /// UnexpectedEOFWanted is used when specific tokens are expected, but the end of file is reached
    UnexpectedEOFWanted(Box<[SyntaxKind]>),
    /// DuplicatedArgs is used when formal arguments are duplicated, e.g. `{ a, a }`
    DuplicatedArgs(TextRange, String),
    /// RecursionLimitExceeded is used when we're unable to parse further due to likely being close to
    /// a stack overflow.
    RecursionLimitExceeded,
}

impl fmt::Display for ParseError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            ParseError::Unexpected(range) => {
                write!(
                    f,
                    "error node at {}..{}",
                    usize::from(range.start()),
                    usize::from(range.end())
                )
            }
            ParseError::UnexpectedExtra(range) => {
                write!(
                    f,
                    "unexpected token at {}..{}",
                    usize::from(range.start()),
                    usize::from(range.end())
                )
            }
            ParseError::UnexpectedWanted(got, range, kinds) => write!(
                f,
                "unexpected {:?} at {}..{}, wanted any of {:?}",
                got,
                usize::from(range.start()),
                usize::from(range.end()),
                kinds
            ),
            ParseError::UnexpectedDoubleBind(range) => {
                write!(
                    f,
                    "unexpected double bind at {}..{}",
                    usize::from(range.start()),
                    usize::from(range.end())
                )
            }
            ParseError::UnexpectedEOF => write!(f, "unexpected end of file"),
            ParseError::UnexpectedEOFWanted(kinds) => {
                write!(f, "unexpected end of file, wanted any of {:?}", kinds)
            }
            ParseError::DuplicatedArgs(range, ident) => {
                write!(
                    f,
                    "argument `{}` is duplicated in {}..{}",
                    ident,
                    usize::from(range.start()),
                    usize::from(range.end())
                )
            }
            ParseError::RecursionLimitExceeded => write!(f, "recursion limit exceeded"),
        }
    }
}

impl std::error::Error for ParseError {}

struct Parser<'a, I>
where
    I: Iterator<Item = Token<'a>>,
{
    builder: GreenNodeBuilder<'static>,
    errors: Vec<ParseError>,

    trivia_buffer: Vec<Token<'a>>,
    buffer: VecDeque<Token<'a>>,
    iter: I,
    consumed: TextSize,

    // Recursion depth, used for avoiding stack overflows. This may be incremented
    // by any method as long as it is decremented when that method returns.
    depth: u32,
}
impl<'a, I> Parser<'a, I>
where
    I: Iterator<Item = Token<'a>>,
{
    fn new(iter: I) -> Self {
        Self {
            builder: GreenNodeBuilder::new(),
            errors: Vec::new(),

            trivia_buffer: Vec::with_capacity(1),
            buffer: VecDeque::with_capacity(1),
            iter,
            consumed: TextSize::from(0),

            depth: 0,
        }
    }

    fn get_text_position(&self) -> TextSize {
        self.consumed
    }

    fn peek_raw(&mut self) -> Option<&Token<'a>> {
        if self.buffer.is_empty() {
            if let Some(token) = self.iter.next() {
                self.buffer.push_back(token);
            }
        }
        self.buffer.front()
    }
    fn drain_trivia_buffer(&mut self) {
        for (t, s) in self.trivia_buffer.drain(..) {
            self.consumed += TextSize::of(s);
            self.builder.token(NixLanguage::kind_to_raw(t), s);
        }
    }
    fn eat_trivia(&mut self) {
        self.peek();
        self.drain_trivia_buffer();
    }
    fn start_node(&mut self, kind: SyntaxKind) {
        self.eat_trivia();
        self.builder.start_node(NixLanguage::kind_to_raw(kind));
    }
    fn checkpoint(&mut self) -> Checkpoint {
        self.eat_trivia();
        self.builder.checkpoint()
    }
    fn start_node_at(&mut self, checkpoint: Checkpoint, kind: SyntaxKind) {
        self.builder.start_node_at(checkpoint, NixLanguage::kind_to_raw(kind));
    }
    fn finish_node(&mut self) {
        self.builder.finish_node();
    }
    fn start_error_node(&mut self) -> TextSize {
        self.start_node(NODE_ERROR);
        self.get_text_position()
    }
    fn finish_error_node(&mut self) -> TextSize {
        self.finish_node();
        self.get_text_position()
    }
    fn bump(&mut self) {
        match self.try_next() {
            Some((token, s)) => {
                if token.is_trivia() {
                    self.trivia_buffer.push((token, s))
                } else {
                    self.drain_trivia_buffer();
                    self.manual_bump(s, token);
                }
            }
            None => self.errors.push(ParseError::UnexpectedEOF),
        }
    }
    fn try_next(&mut self) -> Option<Token<'a>> {
        self.buffer.pop_front().or_else(|| self.iter.next())
    }
    fn manual_bump(&mut self, s: &str, token: SyntaxKind) {
        self.consumed += TextSize::of(s);
        self.builder.token(NixLanguage::kind_to_raw(token), s)
    }
    fn peek(&mut self) -> Option<SyntaxKind> {
        while self.peek_raw().map(|&(t, _)| t.is_trivia()).unwrap_or(false) {
            self.bump();
        }
        self.peek_ahead(0)
    }
    fn peek_ahead(&mut self, n: usize) -> Option<SyntaxKind> {
        let mut non_trivia_seen = 0;
        let mut cursor = 0;
        loop {
            if self.buffer.len() <= cursor {
                self.buffer.push_back(self.iter.next()?);
            }
            let kind = self.buffer[cursor].0;
            cursor += 1;
            if !kind.is_trivia() {
                if non_trivia_seen == n {
                    return Some(kind);
                }
                non_trivia_seen += 1;
            }
        }
    }
    fn expect_peek_any(&mut self, allowed_slice: &[SyntaxKind]) -> Option<SyntaxKind> {
        let allowed = TokenSet::from_slice(allowed_slice);

        let next = match self.peek() {
            None => None,
            Some(kind) if allowed.contains(kind) => Some(kind),
            Some(kind) => {
                let start = self.start_error_node();
                loop {
                    self.bump();
                    if self.peek().map(|kind| allowed.contains(kind)).unwrap_or(true) {
                        break;
                    }
                }
                let end = self.finish_error_node();
                self.errors.push(ParseError::UnexpectedWanted(
                    kind,
                    TextRange::new(start, end),
                    allowed_slice.to_vec().into_boxed_slice(),
                ));

                self.peek()
            }
        };
        if next.is_none() {
            self.errors
                .push(ParseError::UnexpectedEOFWanted(allowed_slice.to_vec().into_boxed_slice()));
        }
        next
    }
    fn expect(&mut self, expected: SyntaxKind) {
        if self.expect_peek_any(&[expected]).is_some() {
            self.bump();
        }
    }

    fn expect_ident(&mut self) {
        if self.expect_peek_any(&[TOKEN_IDENT]).is_some() {
            self.start_node(NODE_IDENT);
            self.bump();
            self.finish_node()
        }
    }

    fn parse_dynamic(&mut self) {
        self.start_node(NODE_DYNAMIC);
        self.bump();
        while self.peek().map(|t| t != TOKEN_INTERPOL_END).unwrap_or(false) {
            self.parse_expr();
        }
        self.bump();
        self.finish_node();
    }

    fn parse_string(&mut self) {
        self.start_node(NODE_STRING);
        self.expect(TOKEN_STRING_START);

        loop {
            match self.expect_peek_any(&[
                TOKEN_STRING_END,
                TOKEN_STRING_CONTENT,
                TOKEN_INTERPOL_START,
            ]) {
                Some(TOKEN_STRING_CONTENT) => self.bump(),
                Some(TOKEN_INTERPOL_START) => {
                    self.start_node(NODE_INTERPOL);
                    self.bump();
                    self.parse_expr();
                    self.expect(TOKEN_INTERPOL_END);
                    self.finish_node();
                }
                // handled by expect_peek_any
                _ => break,
            }
        }
        self.expect(TOKEN_STRING_END);

        self.finish_node();
    }
    fn parse_attr(&mut self) {
        match self.peek() {
            Some(TOKEN_INTERPOL_START) => self.parse_dynamic(),
            Some(TOKEN_STRING_START) => self.parse_string(),
            _ => {
                // NB: the tokenizer always emits TOKEN_IDENT for __curPos;
                // TOKEN_CUR_POS is included for completeness but cannot
                // currently be produced by the tokenizer.
                if self.expect_peek_any(&[TOKEN_IDENT, TOKEN_OR, TOKEN_CUR_POS]).is_some() {
                    self.start_node(NODE_IDENT);
                    let (_, s) = self.try_next().unwrap();
                    self.manual_bump(s, TOKEN_IDENT);
                    self.finish_node()
                }
            }
        }
    }
    fn parse_attrpath(&mut self) {
        self.start_node(NODE_ATTRPATH);
        loop {
            self.parse_attr();

            if self.peek() == Some(T![.]) {
                self.bump();
            } else {
                break;
            }
        }
        self.finish_node();
    }
    fn parse_pattern(&mut self, bound: bool) {
        if self.peek().map(|t| t == T!['}']).unwrap_or(true) {
            self.bump();
        } else {
            loop {
                match self.expect_peek_any(&[T!['}'], T![...], TOKEN_IDENT]) {
                    Some(T!['}']) => {
                        self.bump();
                        break;
                    }
                    Some(T![...]) => {
                        self.bump();
                        self.expect(T!['}']);
                        break;
                    }
                    Some(TOKEN_IDENT) => {
                        self.start_node(NODE_PAT_ENTRY);
                        self.expect_ident();
                        if let Some(T![?]) = self.peek() {
                            self.bump();
                            self.parse_expr();
                        }
                        self.finish_node();
                        match self.peek() {
                            Some(T![,]) => self.bump(),
                            _ => {
                                self.expect(T!['}']);
                                break;
                            }
                        }
                    }
                    // handled by expect_peek_any
                    _ => break,
                }
            }
        }

        if self.peek() == Some(T![@]) {
            let kind = if bound { NODE_ERROR } else { NODE_PAT_BIND };
            self.start_node(kind);
            let start = self.get_text_position();
            self.bump();
            self.expect_ident();
            let end = self.finish_error_node();
            if bound {
                self.errors.push(ParseError::UnexpectedDoubleBind(TextRange::new(start, end)));
            }
        }
    }
    fn parse_set(&mut self, until: SyntaxKind) {
        loop {
            match self.peek() {
                None => break,
                token if token == Some(until) => break,
                Some(T![inherit]) => {
                    self.start_node(NODE_INHERIT);
                    self.bump();

                    if self.peek() == Some(T!['(']) {
                        self.start_node(NODE_INHERIT_FROM);
                        self.bump();
                        self.parse_expr();
                        self.expect(T![')']);
                        self.finish_node();
                    }

                    loop {
                        match self.peek() {
                            Some(t) if t != T![;] => {
                                self.parse_attr();
                            }
                            Some(_) => {
                                break;
                            }
                            None => {
                                self.errors.push(ParseError::UnexpectedEOF);
                                break;
                            }
                        }
                    }

                    self.expect(T![;]);
                    self.finish_node();
                }
                Some(_) => {
                    self.start_node(NODE_ATTRPATH_VALUE);
                    self.parse_attrpath();
                    self.expect(T![=]);
                    self.parse_expr();
                    self.expect(T![;]);
                    self.finish_node();
                }
            }
        }
        self.bump(); // the final close, like '}'
    }

    fn parse_simple(&mut self) -> Checkpoint {
        let peek = match self.peek() {
            Some(it) => it,
            None => {
                self.errors.push(ParseError::UnexpectedEOF);
                // NB: we don't use `self.checkpoint()` here in order to avoid
                // eating the whitespace. The actual checkpoint doesn't matter
                // in this case and, ideally, should be returning `None`, but
                // that makes code slightly more complex for little real
                // benefit.
                return self.builder.checkpoint();
            }
        };
        let checkpoint = self.checkpoint();
        match peek {
            T!['('] => {
                self.start_node(NODE_PAREN);
                self.bump();
                self.parse_expr();
                self.bump();
                self.finish_node();
            }
            T![rec] => {
                self.start_node(NODE_ATTR_SET);
                self.bump();
                self.expect(T!['{']);
                self.parse_set(T!['}']);
                self.finish_node();
            }
            T!['{'] => {
                // Do a lookahead:
                let mut peek = [None, None];
                for i in &mut peek {
                    let mut token;
                    *i = loop {
                        token = self.iter.next();
                        let kind = token.as_ref().map(|&(t, _)| t);
                        if let Some(token) = token {
                            self.buffer.push_back(token);
                        }
                        if kind.map(|t| !t.is_trivia()).unwrap_or(true) {
                            break kind;
                        }
                    };
                }

                match peek {
                    [Some(TOKEN_IDENT), Some(T![,])]
                    | [Some(TOKEN_IDENT), Some(T![?])]
                    | [Some(TOKEN_IDENT), Some(T!['}'])]
                    | [Some(T![...]), Some(T!['}'])]
                    | [Some(T!['}']), Some(T![:])]
                    | [Some(T!['}']), Some(T![@])] => {
                        // This looks like a pattern
                        self.start_node(NODE_LAMBDA);

                        self.start_node(NODE_PATTERN);
                        self.bump();
                        self.parse_pattern(false);
                        self.finish_node();

                        self.expect(T![:]);
                        self.parse_expr();

                        self.finish_node();
                    }
                    _ => {
                        // This looks like a set
                        self.start_node(NODE_ATTR_SET);
                        self.bump();
                        self.parse_set(T!['}']);
                        self.finish_node();
                    }
                }
            }
            T!['['] => {
                self.start_node(NODE_LIST);
                self.bump();
                while self.peek().map(|t| t != T![']']).unwrap_or(false) {
                    self.parse_simple();
                }
                self.bump();
                self.finish_node();
            }
            TOKEN_STRING_START => self.parse_string(),
            TOKEN_PATH_ABS | TOKEN_PATH_REL | TOKEN_PATH_HOME | TOKEN_PATH_SEARCH => {
                let node_kind = match self.peek().unwrap() {
                    TOKEN_PATH_ABS => NODE_PATH_ABS,
                    TOKEN_PATH_REL => NODE_PATH_REL,
                    TOKEN_PATH_HOME => NODE_PATH_HOME,
                    TOKEN_PATH_SEARCH => NODE_PATH_SEARCH,
                    _ => unreachable!(),
                };
                self.start_node(node_kind);
                self.bump();

                // Search paths (<nixpkgs>) don't support interpolation
                let is_search_path = node_kind == NODE_PATH_SEARCH;
                let is_complex_path = !is_search_path && self.peek() == Some(TOKEN_INTERPOL_START);

                if is_complex_path {
                    loop {
                        match self.peek_raw().map(|(t, _)| t) {
                            Some(TOKEN_PATH_ABS) | Some(TOKEN_PATH_REL) | Some(TOKEN_PATH_HOME) => {
                                self.bump()
                            }
                            Some(TOKEN_INTERPOL_START) => {
                                self.start_node(NODE_INTERPOL);
                                self.bump();
                                self.parse_expr();
                                self.expect(TOKEN_INTERPOL_END);
                                self.finish_node();
                            }
                            _ => break,
                        }
                    }
                }
                self.finish_node();
            }
            t if t.is_literal() => {
                self.start_node(NODE_LITERAL);
                self.bump();
                self.finish_node();
            }
            TOKEN_IDENT => {
                let ident = self.peek_raw().map(|&(_, s)| s);

                match self.peek_ahead(1) {
                    Some(T![:]) => {
                        self.expect_ident();

                        self.start_node_at(checkpoint, NODE_LAMBDA);
                        self.start_node_at(checkpoint, NODE_IDENT_PARAM);
                        self.finish_node();
                        self.expect(T![:]);
                        self.parse_expr();
                        self.finish_node();
                    }
                    Some(T![@]) => {
                        self.expect_ident();

                        self.start_node_at(checkpoint, NODE_LAMBDA);
                        self.start_node_at(checkpoint, NODE_PATTERN);
                        self.start_node_at(checkpoint, NODE_PAT_BIND);
                        self.expect(T![@]);
                        self.finish_node(); // PatBind

                        self.expect(T!['{']);
                        self.parse_pattern(true);
                        self.finish_node(); // Pattern

                        self.expect(T![:]);
                        self.parse_expr();
                        self.finish_node(); // Lambda
                    }
                    _ if ident == Some("__curPos") => {
                        self.start_node(NODE_CUR_POS);
                        let (_, s) = self.try_next().unwrap();
                        self.manual_bump(s, TOKEN_CUR_POS);
                        self.finish_node();
                    }
                    _ => self.expect_ident(),
                }
            }
            kind => {
                let start = self.start_error_node();
                self.bump();
                let end = self.finish_error_node();
                self.errors.push(ParseError::UnexpectedWanted(
                    kind,
                    TextRange::new(start, end),
                    [T!['('], T![rec], T!['{'], T!['['], TOKEN_STRING_START, TOKEN_IDENT]
                        .to_vec()
                        .into_boxed_slice(),
                ));
            }
        };

        if self.peek() == Some(T![.]) {
            self.start_node_at(checkpoint, NODE_SELECT);
            self.bump();
            self.parse_attrpath();
            if self.peek() == Some(T![or]) {
                self.bump();
                self.parse_simple();
            }
            self.finish_node();

        // This seems weird, but it matches Nix's behavior.
        // If there is no "." but a "or" immediately followed a primary expression,
        // we construct a application node, with "or" parsed as an identifier,
        // ignoring the associativity of ancestor applications.
        // Eg.
        // "a b or c" => "((a (b or)) c)"
        // "or a" => fail
        } else if self.peek() == Some(T![or]) {
            self.start_node_at(checkpoint, NODE_APPLY);
            self.start_node(NODE_IDENT);
            let (_, s) = self.try_next().unwrap();
            self.manual_bump(s, TOKEN_IDENT);
            self.finish_node();
            self.finish_node();
        }

        checkpoint
    }
    fn parse_fn(&mut self) -> Checkpoint {
        let checkpoint = self.parse_simple();

        while self.peek().map(|t| t.is_fn_arg()).unwrap_or(false) {
            self.start_node_at(checkpoint, NODE_APPLY);
            self.parse_simple();
            self.finish_node();
        }
        checkpoint
    }
    fn parse_negate(&mut self) -> Checkpoint {
        if self.peek() == Some(T![-]) {
            let checkpoint = self.checkpoint();
            self.start_node(NODE_UNARY_OP);
            self.bump();
            self.parse_negate();
            self.finish_node();
            checkpoint
        } else {
            self.parse_fn()
        }
    }
    fn parse_non_assoc(&mut self, next: fn(&mut Self) -> Checkpoint, ops: TokenSet) -> Checkpoint {
        let checkpoint = next(self);
        if self.peek().map(|t| ops.contains(t)).unwrap_or(false) {
            self.start_node_at(checkpoint, NODE_BIN_OP);
            self.bump();
            next(self);
            self.finish_node();
        }
        checkpoint
    }
    fn parse_left_assoc(&mut self, next: fn(&mut Self) -> Checkpoint, ops: TokenSet) -> Checkpoint {
        let checkpoint = next(self);
        while self.peek().map(|t| ops.contains(t)).unwrap_or(false) {
            self.start_node_at(checkpoint, NODE_BIN_OP);
            self.bump();
            next(self);
            self.finish_node();
        }
        checkpoint
    }
    fn parse_right_assoc(
        &mut self,
        next: fn(&mut Self) -> Checkpoint,
        ops: TokenSet,
    ) -> Checkpoint {
        let checkpoint = next(self);
        if self.peek().map(|t| ops.contains(t)).unwrap_or(false) {
            self.start_node_at(checkpoint, NODE_BIN_OP);
            self.bump();
            self.parse_right_assoc(next, ops);
            self.finish_node();
        }
        checkpoint
    }
    fn parse_hasattr(&mut self) -> Checkpoint {
        let checkpoint = self.parse_negate();
        while self.peek().map(|t| t == T![?]).unwrap_or(false) {
            self.start_node_at(checkpoint, NODE_HAS_ATTR);
            self.bump();
            self.parse_attrpath();
            self.finish_node();
        }
        checkpoint
    }
    fn parse_concat(&mut self) -> Checkpoint {
        self.parse_right_assoc(Self::parse_hasattr, T![++] | ())
    }
    fn parse_mul(&mut self) -> Checkpoint {
        self.parse_left_assoc(Self::parse_concat, T![*] | T![/])
    }
    fn parse_add(&mut self) -> Checkpoint {
        self.parse_left_assoc(Self::parse_mul, T![+] | T![-])
    }
    fn parse_invert(&mut self) -> Checkpoint {
        if self.peek() == Some(TOKEN_INVERT) {
            let checkpoint = self.checkpoint();
            self.start_node(NODE_UNARY_OP);
            self.bump();
            self.parse_invert();
            self.finish_node();
            checkpoint
        } else {
            self.parse_add()
        }
    }
    fn parse_merge(&mut self) -> Checkpoint {
        self.parse_right_assoc(Self::parse_invert, T!["//"] | ())
    }
    fn parse_compare(&mut self) -> Checkpoint {
        self.parse_non_assoc(Self::parse_merge, T![<] | T![<=] | T![>] | T![>=])
    }
    fn parse_equal(&mut self) -> Checkpoint {
        self.parse_non_assoc(Self::parse_compare, T![==] | T![!=])
    }
    fn parse_and(&mut self) -> Checkpoint {
        self.parse_left_assoc(Self::parse_equal, T![&&] | ())
    }
    fn parse_or(&mut self) -> Checkpoint {
        self.parse_left_assoc(Self::parse_and, T![||] | ())
    }
    fn parse_implication(&mut self) -> Checkpoint {
        self.parse_right_assoc(Self::parse_or, T![->] | ())
    }
    #[inline(always)]
    fn parse_math(&mut self) -> Checkpoint {
        // Always point this to the lowest-level math function there is
        self.parse_implication()
    }
    fn parse_pipe_right(&mut self) -> Checkpoint {
        self.parse_left_assoc(Self::parse_math, T!["|>"] | ())
    }
    fn parse_pipe_left(&mut self) -> Checkpoint {
        self.parse_right_assoc(Self::parse_pipe_right, T!["<|"] | ())
    }
    /// Parse Nix code into an AST
    pub fn parse_expr(&mut self) -> Checkpoint {
        // Limit chosen somewhat arbitrarily
        if self.depth >= 512 {
            self.errors.push(ParseError::RecursionLimitExceeded);
            // Consume tokens to the end of the file. Erroring without bumping might cause
            // infinite looping elsewhere.
            self.start_error_node();
            while self.peek().is_some() {
                self.bump()
            }
            self.finish_error_node();
            return self.checkpoint();
        }
        self.depth += 1;
        let out = match self.peek() {
            Some(T![let]) => {
                let checkpoint = self.checkpoint();
                self.bump();

                if self.peek() == Some(T!['{']) {
                    self.start_node_at(checkpoint, NODE_LEGACY_LET);
                    self.bump();
                    self.parse_set(T!['}']);
                    self.finish_node();
                } else {
                    self.start_node_at(checkpoint, NODE_LET_IN);
                    self.parse_set(T![in]);
                    self.parse_expr();
                    self.finish_node();
                }
                checkpoint
            }
            Some(T![with]) => {
                let checkpoint = self.checkpoint();
                self.start_node(NODE_WITH);
                self.bump();
                self.parse_expr();
                self.expect(T![;]);
                self.parse_expr();
                self.finish_node();
                checkpoint
            }
            Some(T![if]) => {
                let checkpoint = self.checkpoint();
                self.start_node(NODE_IF_ELSE);
                self.bump();
                self.parse_expr();
                self.expect(T![then]);
                self.parse_expr();
                self.expect(TOKEN_ELSE);
                self.parse_expr();
                self.finish_node();
                checkpoint
            }
            Some(T![assert]) => {
                let checkpoint = self.checkpoint();
                self.start_node(NODE_ASSERT);
                self.bump();
                self.parse_expr();
                self.expect(T![;]);
                self.parse_expr();
                self.finish_node();
                checkpoint
            }
            _ => self.parse_pipe_left(),
        };
        self.depth -= 1;
        out
    }
}

/// Parse tokens into an AST
pub fn parse<'s, I>(iter: I) -> (GreenNode, Vec<ParseError>)
where
    I: Iterator<Item = Token<'s>>,
{
    let mut parser = Parser::new(iter);
    parser.builder.start_node(NixLanguage::kind_to_raw(NODE_ROOT));
    parser.parse_expr();
    parser.eat_trivia();
    if parser.peek().is_some() {
        let start = parser.start_error_node();
        while parser.peek().is_some() {
            parser.bump();
        }
        let end = parser.finish_error_node();
        parser.errors.push(ParseError::UnexpectedExtra(TextRange::new(start, end)));
        parser.eat_trivia();
    }
    parser.builder.finish_node();
    (parser.builder.finish(), parser.errors)
}