compiler/rustc_parse/src/lexer/tokentrees.rs

use super::{StringReader, UnmatchedBrace};

use rustc_ast::token::{self, DelimToken, Token};
use rustc_ast::tokenstream::{
    DelimSpan,
    Spacing::{self, *},
    TokenStream, TokenTree, TreeAndSpacing,
};
use rustc_ast_pretty::pprust::token_to_string;
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::PResult;
use rustc_span::Span;

impl<'a> StringReader<'a> {
    pub(super) fn into_token_trees(self) -> (PResult<'a, TokenStream>, Vec<UnmatchedBrace>) {
        let mut tt_reader = TokenTreesReader {
            string_reader: self,
            token: Token::dummy(),
            open_braces: Vec::new(),
            unmatched_braces: Vec::new(),
            matching_delim_spans: Vec::new(),
            last_unclosed_found_span: None,
            last_delim_empty_block_spans: FxHashMap::default(),
            matching_block_spans: Vec::new(),
        };
        let res = tt_reader.parse_all_token_trees();
        (res, tt_reader.unmatched_braces)
    }
}

struct TokenTreesReader<'a> {
    string_reader: StringReader<'a>,
    token: Token,
    /// Stack of open delimiters and their spans. Used for error message.
    open_braces: Vec<(token::DelimToken, Span)>,
    unmatched_braces: Vec<UnmatchedBrace>,
    /// The type and spans for all braces
    ///
    /// Used only for error recovery when arriving to EOF with mismatched braces.
    matching_delim_spans: Vec<(token::DelimToken, Span, Span)>,
    last_unclosed_found_span: Option<Span>,
    /// Collect empty block spans that might have been auto-inserted by editors.
    last_delim_empty_block_spans: FxHashMap<token::DelimToken, Span>,
    /// Collect the spans of braces (Open, Close). Used only
    /// for detecting if blocks are empty and only braces.
    matching_block_spans: Vec<(Span, Span)>,
}

impl<'a> TokenTreesReader<'a> {
    // Parse a stream of tokens into a list of `TokenTree`s, up to an `Eof`.
    fn parse_all_token_trees(&mut self) -> PResult<'a, TokenStream> {
        let mut buf = TokenStreamBuilder::default();

        self.bump();
        while self.token != token::Eof {
            buf.push(self.parse_token_tree()?);
        }

        Ok(buf.into_token_stream())
    }

    // Parse a stream of tokens into a list of `TokenTree`s, up to a `CloseDelim`.
    fn parse_token_trees_until_close_delim(&mut self) -> TokenStream {
        let mut buf = TokenStreamBuilder::default();
        loop {
            if let token::CloseDelim(..) = self.token.kind {
                return buf.into_token_stream();
            }

            match self.parse_token_tree() {
                Ok(tree) => buf.push(tree),
                Err(mut e) => {
                    e.emit();
                    return buf.into_token_stream();
                }
            }
        }
    }

    fn parse_token_tree(&mut self) -> PResult<'a, TreeAndSpacing> {
        let sm = self.string_reader.sess.source_map();

        match self.token.kind {
            token::Eof => {
                let msg = "this file contains an unclosed delimiter";
                let mut err =
                    self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, msg);
                for &(_, sp) in &self.open_braces {
                    err.span_label(sp, "unclosed delimiter");
                    self.unmatched_braces.push(UnmatchedBrace {
                        expected_delim: token::DelimToken::Brace,
                        found_delim: None,
                        found_span: self.token.span,
                        unclosed_span: Some(sp),
                        candidate_span: None,
                    });
                }

                if let Some((delim, _)) = self.open_braces.last() {
                    if let Some((_, open_sp, close_sp)) =
                        self.matching_delim_spans.iter().find(|(d, open_sp, close_sp)| {
                            if let Some(close_padding) = sm.span_to_margin(*close_sp) {
                                if let Some(open_padding) = sm.span_to_margin(*open_sp) {
                                    return delim == d && close_padding != open_padding;
                                }
                            }
                            false
                        })
                    // these are in reverse order as they get inserted on close, but
                    {
                        // we want the last open/first close
                        err.span_label(*open_sp, "this delimiter might not be properly closed...");
                        err.span_label(
                            *close_sp,
                            "...as it matches this but it has different indentation",
                        );
                    }
                }
                Err(err)
            }
            token::OpenDelim(delim) => {
                // The span for beginning of the delimited section
                let pre_span = self.token.span;

                // Parse the open delimiter.
                self.open_braces.push((delim, self.token.span));
                self.bump();

                // Parse the token trees within the delimiters.
                // We stop at any delimiter so we can try to recover if the user
                // uses an incorrect delimiter.
                let tts = self.parse_token_trees_until_close_delim();

                // Expand to cover the entire delimited token tree
                let delim_span = DelimSpan::from_pair(pre_span, self.token.span);

                match self.token.kind {
                    // Correct delimiter.
                    token::CloseDelim(d) if d == delim => {
                        let (open_brace, open_brace_span) = self.open_braces.pop().unwrap();
                        let close_brace_span = self.token.span;

                        if tts.is_empty() {
                            let empty_block_span = open_brace_span.to(close_brace_span);
                            if !sm.is_multiline(empty_block_span) {
                                // Only track if the block is in the form of `{}`, otherwise it is
                                // likely that it was written on purpose.
                                self.last_delim_empty_block_spans.insert(delim, empty_block_span);
                            }
                        }

                        //only add braces
                        if let (DelimToken::Brace, DelimToken::Brace) = (open_brace, delim) {
                            self.matching_block_spans.push((open_brace_span, close_brace_span));
                        }

                        if self.open_braces.is_empty() {
                            // Clear up these spans to avoid suggesting them as we've found
                            // properly matched delimiters so far for an entire block.
                            self.matching_delim_spans.clear();
                        } else {
                            self.matching_delim_spans.push((
                                open_brace,
                                open_brace_span,
                                close_brace_span,
                            ));
                        }
                        // Parse the closing delimiter.
                        self.bump();
                    }
                    // Incorrect delimiter.
                    token::CloseDelim(other) => {
                        let mut unclosed_delimiter = None;
                        let mut candidate = None;

                        if self.last_unclosed_found_span != Some(self.token.span) {
                            // do not complain about the same unclosed delimiter multiple times
                            self.last_unclosed_found_span = Some(self.token.span);
                            // This is a conservative error: only report the last unclosed
                            // delimiter. The previous unclosed delimiters could actually be
                            // closed! The parser just hasn't gotten to them yet.
                            if let Some(&(_, sp)) = self.open_braces.last() {
                                unclosed_delimiter = Some(sp);
                            };
                            if let Some(current_padding) = sm.span_to_margin(self.token.span) {
                                for (brace, brace_span) in &self.open_braces {
                                    if let Some(padding) = sm.span_to_margin(*brace_span) {
                                        // high likelihood of these two corresponding
                                        if current_padding == padding && brace == &other {
                                            candidate = Some(*brace_span);
                                        }
                                    }
                                }
                            }
                            let (tok, _) = self.open_braces.pop().unwrap();
                            self.unmatched_braces.push(UnmatchedBrace {
                                expected_delim: tok,
                                found_delim: Some(other),
                                found_span: self.token.span,
                                unclosed_span: unclosed_delimiter,
                                candidate_span: candidate,
                            });
                        } else {
                            self.open_braces.pop();
                        }

                        // If the incorrect delimiter matches an earlier opening
                        // delimiter, then don't consume it (it can be used to
                        // close the earlier one). Otherwise, consume it.
                        // E.g., we try to recover from:
                        // fn foo() {
                        //     bar(baz(
                        // }  // Incorrect delimiter but matches the earlier `{`
                        if !self.open_braces.iter().any(|&(b, _)| b == other) {
                            self.bump();
                        }
                    }
                    token::Eof => {
                        // Silently recover, the EOF token will be seen again
                        // and an error emitted then. Thus we don't pop from
                        // self.open_braces here.
                    }
                    _ => {}
                }

                Ok(TokenTree::Delimited(delim_span, delim, tts).into())
            }
            token::CloseDelim(delim) => {
                // An unexpected closing delimiter (i.e., there is no
                // matching opening delimiter).
                let token_str = token_to_string(&self.token);
                let msg = format!("unexpected closing delimiter: `{}`", token_str);
                let mut err =
                    self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, &msg);

                // Braces are added at the end, so the last element is the biggest block
                if let Some(parent) = self.matching_block_spans.last() {
                    if let Some(span) = self.last_delim_empty_block_spans.remove(&delim) {
                        // Check if the (empty block) is in the last properly closed block
                        if (parent.0.to(parent.1)).contains(span) {
                            err.span_label(
                                span,
                                "block is empty, you might have not meant to close it",
                            );
                        } else {
                            err.span_label(parent.0, "this opening brace...");

                            err.span_label(parent.1, "...matches this closing brace");
                        }
                    } else {
                        err.span_label(parent.0, "this opening brace...");

                        err.span_label(parent.1, "...matches this closing brace");
                    }
                }

                err.span_label(self.token.span, "unexpected closing delimiter");
                Err(err)
            }
            _ => {
                let tt = TokenTree::Token(self.token.take());
                let mut spacing = self.bump();
                if !self.token.is_op() {
                    spacing = Alone;
                }
                Ok((tt, spacing))
            }
        }
    }

    fn bump(&mut self) -> Spacing {
        let (spacing, token) = self.string_reader.next_token();
        self.token = token;
        spacing
    }
}

#[derive(Default)]
struct TokenStreamBuilder {
    buf: Vec<TreeAndSpacing>,
}

impl TokenStreamBuilder {
    fn push(&mut self, (tree, joint): TreeAndSpacing) {
        if let Some((TokenTree::Token(prev_token), Joint)) = self.buf.last() {
            if let TokenTree::Token(token) = &tree {
                if let Some(glued) = prev_token.glue(token) {
                    self.buf.pop();
                    self.buf.push((TokenTree::Token(glued), joint));
                    return;
                }
            }
        }
        self.buf.push((tree, joint))
    }

    fn into_token_stream(self) -> TokenStream {
        TokenStream::new(self.buf)
    }
}