rust/src/libsyntax/parse/attr.rs

use crate::attr;
use crate::ast;
use crate::source_map::respan;
use crate::parse::{SeqSep, PResult};
use crate::parse::token::{self, Nonterminal, DelimToken};
use crate::parse::parser::{Parser, TokenType, PathStyle};
use crate::tokenstream::{TokenStream, TokenTree};

use log::debug;

#[derive(Debug)]
enum InnerAttributeParsePolicy<'a> {
    Permitted,
    NotPermitted { reason: &'a str },
}

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

impl<'a> Parser<'a> {
    /// Parse attributes that appear before an item
    crate 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);
            match self.token {
                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 =
                        InnerAttributeParsePolicy::NotPermitted { reason: inner_error_reason };
                    attrs.push(self.parse_attribute_with_inner_parse_policy(inner_parse_policy)?);
                    just_parsed_doc_comment = false;
                }
                token::DocComment(s) => {
                    let attr = attr::mk_sugared_doc_attr(attr::mk_attr_id(), s, self.span);
                    if attr.style != ast::AttrStyle::Outer {
                        let mut err = self.fatal("expected outer doc comment");
                        err.note("inner doc comments like this (starting with \
                                  `//!` or `/*!`) can only appear before items");
                        return Err(err);
                    }
                    attrs.push(attr);
                    self.bump();
                    just_parsed_doc_comment = true;
                }
                _ => 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 {
            InnerAttributeParsePolicy::Permitted
        } else {
            InnerAttributeParsePolicy::NotPermitted
                { reason: DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG }
        };
        self.parse_attribute_with_inner_parse_policy(inner_parse_policy)
    }

    /// The same as `parse_attribute`, except it takes in an `InnerAttributeParsePolicy`
    /// that prescribes how to handle inner attributes.
    fn parse_attribute_with_inner_parse_policy(&mut self,
                                               inner_parse_policy: InnerAttributeParsePolicy<'_>)
                                               -> PResult<'a, ast::Attribute> {
        debug!("parse_attribute_with_inner_parse_policy: inner_parse_policy={:?} self.token={:?}",
               inner_parse_policy,
               self.token);
        let (span, path, tokens, style) = match self.token {
            token::Pound => {
                let lo = self.span;
                self.bump();

                if let InnerAttributeParsePolicy::Permitted = inner_parse_policy {
                    self.expected_tokens.push(TokenType::Token(token::Not));
                }
                let style = if self.token == token::Not {
                    self.bump();
                    if let InnerAttributeParsePolicy::NotPermitted { reason } = inner_parse_policy
                    {
                        let span = self.span;
                        self.diagnostic()
                            .struct_span_err(span, reason)
                            .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()
                    }
                    ast::AttrStyle::Inner
                } else {
                    ast::AttrStyle::Outer
                };

                self.expect(&token::OpenDelim(token::Bracket))?;
                let (path, tokens) = self.parse_meta_item_unrestricted()?;
                self.expect(&token::CloseDelim(token::Bracket))?;
                let hi = self.prev_span;

                (lo.to(hi), path, tokens, style)
            }
            _ => {
                let token_str = self.this_token_to_string();
                return Err(self.fatal(&format!("expected `#`, found `{}`", token_str)));
            }
        };

        Ok(ast::Attribute {
            id: attr::mk_attr_id(),
            style,
            path,
            tokens,
            is_sugared_doc: false,
            span,
        })
    }

    /// Parse an inner part of attribute - 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 `=` TOKEN_TREE
    /// The delimiters or `=` are still put into the resulting token stream.
    crate fn parse_meta_item_unrestricted(&mut self) -> PResult<'a, (ast::Path, TokenStream)> {
        let meta = match self.token {
            token::Interpolated(ref nt) => match **nt {
                Nonterminal::NtMeta(ref meta) => Some(meta.clone()),
                _ => None,
            },
            _ => None,
        };
        Ok(if let Some(meta) = meta {
            self.bump();
            (meta.ident, meta.node.tokens(meta.span))
        } else {
            let path = self.parse_path(PathStyle::Mod)?;
            let tokens = if self.check(&token::OpenDelim(DelimToken::Paren)) ||
               self.check(&token::OpenDelim(DelimToken::Bracket)) ||
               self.check(&token::OpenDelim(DelimToken::Brace)) {
                   self.parse_token_tree().into()
            } else if self.eat(&token::Eq) {
                let eq = TokenTree::Token(self.prev_span, token::Eq);
                let mut is_interpolated_expr = false;
                if let token::Interpolated(nt) = &self.token {
                    if let token::NtExpr(..) = **nt {
                        is_interpolated_expr = true;
                    }
                }
                let tokens = if is_interpolated_expr {
                    // We need to accept arbitrary interpolated expressions to continue
                    // supporting things like `doc = $expr` that work on stable.
                    // Non-literal interpolated expressions are rejected after expansion.
                    self.parse_token_tree().into()
                } else {
                    self.parse_unsuffixed_lit()?.tokens()
                };
                TokenStream::from_streams(vec![eq.into(), tokens])
            } else {
                TokenStream::empty()
            };
            (path, tokens)
        })
    }

    /// Parse 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 {
            match self.token {
                token::Pound => {
                    // Don't even try to parse if it's not an inner attribute.
                    if !self.look_ahead(1, |t| t == &token::Not) {
                        break;
                    }

                    let attr = self.parse_attribute(true)?;
                    assert_eq!(attr.style, ast::AttrStyle::Inner);
                    attrs.push(attr);
                }
                token::DocComment(s) => {
                    // we need to get the position of this token before we bump.
                    let attr = attr::mk_sugared_doc_attr(attr::mk_attr_id(), s, self.span);
                    if attr.style == ast::AttrStyle::Inner {
                        attrs.push(attr);
                        self.bump();
                    } else {
                        break;
                    }
                }
                _ => break,
            }
        }
        Ok(attrs)
    }

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

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

        Ok(lit)
    }

    /// Per RFC#1559, matches the following grammar:
    ///
    /// meta_item : IDENT ( '=' 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 {
            token::Interpolated(ref nt) => match **nt {
                token::NtMeta(ref e) => Some(e.clone()),
                _ => None,
            },
            _ => None,
        };

        if let Some(meta) = nt_meta {
            self.bump();
            return Ok(meta);
        }

        let lo = self.span;
        let ident = self.parse_path(PathStyle::Mod)?;
        let node = self.parse_meta_item_kind()?;
        let span = lo.to(self.prev_span);
        Ok(ast::MetaItem { ident, node, 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.eat(&token::OpenDelim(token::Paren)) {
            ast::MetaItemKind::List(self.parse_meta_seq()?)
        } else {
            ast::MetaItemKind::Word
        })
    }

    /// matches meta_item_inner : (meta_item | UNSUFFIXED_LIT) ;
    fn parse_meta_item_inner(&mut self) -> PResult<'a, ast::NestedMetaItem> {
        let lo = self.span;

        match self.parse_unsuffixed_lit() {
            Ok(lit) => {
                return Ok(respan(lo.to(self.prev_span), ast::NestedMetaItemKind::Literal(lit)))
            }
            Err(ref mut err) => self.diagnostic().cancel(err)
        }

        match self.parse_meta_item() {
            Ok(mi) => {
                return Ok(respan(lo.to(self.prev_span), ast::NestedMetaItemKind::MetaItem(mi)))
            }
            Err(ref mut err) => self.diagnostic().cancel(err)
        }

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

    /// matches meta_seq = ( COMMASEP(meta_item_inner) )
    fn parse_meta_seq(&mut self) -> PResult<'a, Vec<ast::NestedMetaItem>> {
        self.parse_seq_to_end(&token::CloseDelim(token::Paren),
                              SeqSep::trailing_allowed(token::Comma),
                              |p: &mut Parser<'a>| p.parse_meta_item_inner())
    }
}