rust/compiler/rustc_parse/src/parser/attr.rs

use super::{Parser, PathStyle};
use rustc_ast as ast;
use rustc_ast::attr;
use rustc_ast::token::{self, Nonterminal};
use rustc_ast_pretty::pprust;
use rustc_errors::{error_code, PResult};
use rustc_span::Span;

use tracing::debug;

#[derive(Debug)]
pub(super) enum InnerAttrPolicy<'a> {
    Permitted,
    Forbidden { reason: &'a str, saw_doc_comment: bool, prev_attr_sp: Option<Span> },
}

const DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG: &str = "an inner attribute is not \
                                                     permitted in this context";

pub(super) const DEFAULT_INNER_ATTR_FORBIDDEN: InnerAttrPolicy<'_> = InnerAttrPolicy::Forbidden {
    reason: DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG,
    saw_doc_comment: false,
    prev_attr_sp: None,
};

impl<'a> Parser<'a> {
    /// Parses attributes that appear before an item.
    pub(super) fn parse_outer_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
        let mut attrs: Vec<ast::Attribute> = Vec::new();
        let mut just_parsed_doc_comment = false;
        loop {
            debug!("parse_outer_attributes: self.token={:?}", self.token);
            if self.check(&token::Pound) {
                let inner_error_reason = if just_parsed_doc_comment {
                    "an inner attribute is not permitted following an outer doc comment"
                } else if !attrs.is_empty() {
                    "an inner attribute is not permitted following an outer attribute"
                } else {
                    DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG
                };
                let inner_parse_policy = InnerAttrPolicy::Forbidden {
                    reason: inner_error_reason,
                    saw_doc_comment: just_parsed_doc_comment,
                    prev_attr_sp: attrs.last().map(|a| a.span),
                };
                let attr = self.parse_attribute_with_inner_parse_policy(inner_parse_policy)?;
                attrs.push(attr);
                just_parsed_doc_comment = false;
            } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
                let attr = attr::mk_doc_comment(comment_kind, attr_style, data, self.token.span);
                if attr.style != ast::AttrStyle::Outer {
                    self.sess
                        .span_diagnostic
                        .struct_span_err_with_code(
                            self.token.span,
                            "expected outer doc comment",
                            error_code!(E0753),
                        )
                        .note(
                            "inner doc comments like this (starting with \
                             `//!` or `/*!`) can only appear before items",
                        )
                        .emit();
                }
                attrs.push(attr);
                self.bump();
                just_parsed_doc_comment = true;
            } else {
                break;
            }
        }
        Ok(attrs)
    }

    /// Matches `attribute = # ! [ meta_item ]`.
    ///
    /// If `permit_inner` is `true`, then a leading `!` indicates an inner
    /// attribute.
    pub fn parse_attribute(&mut self, permit_inner: bool) -> PResult<'a, ast::Attribute> {
        debug!("parse_attribute: permit_inner={:?} self.token={:?}", permit_inner, self.token);
        let inner_parse_policy =
            if permit_inner { InnerAttrPolicy::Permitted } else { DEFAULT_INNER_ATTR_FORBIDDEN };
        self.parse_attribute_with_inner_parse_policy(inner_parse_policy)
    }

    /// The same as `parse_attribute`, except it takes in an `InnerAttrPolicy`
    /// that prescribes how to handle inner attributes.
    fn parse_attribute_with_inner_parse_policy(
        &mut self,
        inner_parse_policy: InnerAttrPolicy<'_>,
    ) -> PResult<'a, ast::Attribute> {
        debug!(
            "parse_attribute_with_inner_parse_policy: inner_parse_policy={:?} self.token={:?}",
            inner_parse_policy, self.token
        );
        let lo = self.token.span;
        let (span, item, style) = if self.eat(&token::Pound) {
            let style =
                if self.eat(&token::Not) { ast::AttrStyle::Inner } else { ast::AttrStyle::Outer };

            self.expect(&token::OpenDelim(token::Bracket))?;
            let item = self.parse_attr_item()?;
            self.expect(&token::CloseDelim(token::Bracket))?;
            let attr_sp = lo.to(self.prev_token.span);

            // Emit error if inner attribute is encountered and forbidden.
            if style == ast::AttrStyle::Inner {
                self.error_on_forbidden_inner_attr(attr_sp, inner_parse_policy);
            }

            (attr_sp, item, style)
        } else {
            let token_str = pprust::token_to_string(&self.token);
            let msg = &format!("expected `#`, found `{}`", token_str);
            return Err(self.struct_span_err(self.token.span, msg));
        };

        Ok(attr::mk_attr_from_item(style, item, span))
    }

    pub(super) fn error_on_forbidden_inner_attr(&self, attr_sp: Span, policy: InnerAttrPolicy<'_>) {
        if let InnerAttrPolicy::Forbidden { reason, saw_doc_comment, prev_attr_sp } = policy {
            let prev_attr_note =
                if saw_doc_comment { "previous doc comment" } else { "previous outer attribute" };

            let mut diag = self.struct_span_err(attr_sp, reason);

            if let Some(prev_attr_sp) = prev_attr_sp {
                diag.span_label(attr_sp, "not permitted following an outer attribute")
                    .span_label(prev_attr_sp, prev_attr_note);
            }

            diag.note(
                "inner attributes, like `#![no_std]`, annotate the item enclosing them, \
                and are usually found at the beginning of source files. \
                Outer attributes, like `#[test]`, annotate the item following them.",
            )
            .emit();
        }
    }

    /// Parses an inner part of an attribute (the path and following tokens).
    /// The tokens must be either a delimited token stream, or empty token stream,
    /// or the "legacy" key-value form.
    ///     PATH `(` TOKEN_STREAM `)`
    ///     PATH `[` TOKEN_STREAM `]`
    ///     PATH `{` TOKEN_STREAM `}`
    ///     PATH
    ///     PATH `=` UNSUFFIXED_LIT
    /// The delimiters or `=` are still put into the resulting token stream.
    pub fn parse_attr_item(&mut self) -> PResult<'a, ast::AttrItem> {
        let item = match self.token.kind {
            token::Interpolated(ref nt) => match **nt {
                Nonterminal::NtMeta(ref item) => Some(item.clone().into_inner()),
                _ => None,
            },
            _ => None,
        };
        Ok(if let Some(item) = item {
            self.bump();
            item
        } else {
            let path = self.parse_path(PathStyle::Mod)?;
            let args = self.parse_attr_args()?;
            ast::AttrItem { path, args }
        })
    }

    /// Parses attributes that appear after the opening of an item. These should
    /// be preceded by an exclamation mark, but we accept and warn about one
    /// terminated by a semicolon.
    ///
    /// Matches `inner_attrs*`.
    crate fn parse_inner_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
        let mut attrs: Vec<ast::Attribute> = vec![];
        loop {
            // Only try to parse if it is an inner attribute (has `!`).
            if self.check(&token::Pound) && self.look_ahead(1, |t| t == &token::Not) {
                let attr = self.parse_attribute(true)?;
                assert_eq!(attr.style, ast::AttrStyle::Inner);
                attrs.push(attr);
            } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
                // We need to get the position of this token before we bump.
                let attr = attr::mk_doc_comment(comment_kind, attr_style, data, self.token.span);
                if attr.style == ast::AttrStyle::Inner {
                    attrs.push(attr);
                    self.bump();
                } else {
                    break;
                }
            } else {
                break;
            }
        }
        Ok(attrs)
    }

    crate fn parse_unsuffixed_lit(&mut self) -> PResult<'a, ast::Lit> {
        let lit = self.parse_lit()?;
        debug!("checking if {:?} is unusuffixed", lit);

        if !lit.kind.is_unsuffixed() {
            self.struct_span_err(lit.span, "suffixed literals are not allowed in attributes")
                .help(
                    "instead of using a suffixed literal (`1u8`, `1.0f32`, etc.), \
                    use an unsuffixed version (`1`, `1.0`, etc.)",
                )
                .emit();
        }

        Ok(lit)
    }

    /// Parses `cfg_attr(pred, attr_item_list)` where `attr_item_list` is comma-delimited.
    pub fn parse_cfg_attr(&mut self) -> PResult<'a, (ast::MetaItem, Vec<(ast::AttrItem, Span)>)> {
        let cfg_predicate = self.parse_meta_item()?;
        self.expect(&token::Comma)?;

        // Presumably, the majority of the time there will only be one attr.
        let mut expanded_attrs = Vec::with_capacity(1);
        while self.token.kind != token::Eof {
            let lo = self.token.span;
            let item = self.parse_attr_item()?;
            expanded_attrs.push((item, lo.to(self.prev_token.span)));
            if !self.eat(&token::Comma) {
                break;
            }
        }

        Ok((cfg_predicate, expanded_attrs))
    }

    /// Matches `COMMASEP(meta_item_inner)`.
    crate fn parse_meta_seq_top(&mut self) -> PResult<'a, Vec<ast::NestedMetaItem>> {
        // Presumably, the majority of the time there will only be one attr.
        let mut nmis = Vec::with_capacity(1);
        while self.token.kind != token::Eof {
            nmis.push(self.parse_meta_item_inner()?);
            if !self.eat(&token::Comma) {
                break;
            }
        }
        Ok(nmis)
    }

    /// Matches the following grammar (per RFC 1559).
    ///
    ///     meta_item : PATH ( '=' UNSUFFIXED_LIT | '(' meta_item_inner? ')' )? ;
    ///     meta_item_inner : (meta_item | UNSUFFIXED_LIT) (',' meta_item_inner)? ;
    pub fn parse_meta_item(&mut self) -> PResult<'a, ast::MetaItem> {
        let nt_meta = match self.token.kind {
            token::Interpolated(ref nt) => match **nt {
                token::NtMeta(ref e) => Some(e.clone()),
                _ => None,
            },
            _ => None,
        };

        if let Some(item) = nt_meta {
            return match item.meta(item.path.span) {
                Some(meta) => {
                    self.bump();
                    Ok(meta)
                }
                None => self.unexpected(),
            };
        }

        let lo = self.token.span;
        let path = self.parse_path(PathStyle::Mod)?;
        let kind = self.parse_meta_item_kind()?;
        let span = lo.to(self.prev_token.span);
        Ok(ast::MetaItem { path, kind, span })
    }

    crate fn parse_meta_item_kind(&mut self) -> PResult<'a, ast::MetaItemKind> {
        Ok(if self.eat(&token::Eq) {
            ast::MetaItemKind::NameValue(self.parse_unsuffixed_lit()?)
        } else if self.check(&token::OpenDelim(token::Paren)) {
            // Matches `meta_seq = ( COMMASEP(meta_item_inner) )`.
            let (list, _) = self.parse_paren_comma_seq(|p| p.parse_meta_item_inner())?;
            ast::MetaItemKind::List(list)
        } else {
            ast::MetaItemKind::Word
        })
    }

    /// Matches `meta_item_inner : (meta_item | UNSUFFIXED_LIT) ;`.
    fn parse_meta_item_inner(&mut self) -> PResult<'a, ast::NestedMetaItem> {
        match self.parse_unsuffixed_lit() {
            Ok(lit) => return Ok(ast::NestedMetaItem::Literal(lit)),
            Err(ref mut err) => err.cancel(),
        }

        match self.parse_meta_item() {
            Ok(mi) => return Ok(ast::NestedMetaItem::MetaItem(mi)),
            Err(ref mut err) => err.cancel(),
        }

        let found = pprust::token_to_string(&self.token);
        let msg = format!("expected unsuffixed literal or identifier, found `{}`", found);
        Err(self.struct_span_err(self.token.span, &msg))
    }
}