attr.rs

use super::{SeqSep, Parser, TokenType, PathStyle};
use syntax::attr;
use syntax::ast;
use syntax::util::comments;
use syntax::token::{self, Nonterminal, DelimToken};
use syntax::tokenstream::{TokenStream, TokenTree};
use syntax_pos::{Span, Symbol};
use errors::PResult;

use log::debug;

#[derive(Debug)]
enum InnerAttributeParsePolicy<'a> {
    Permitted,
    NotPermitted { 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";

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);
            match self.token.kind {
                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,
                            saw_doc_comment: just_parsed_doc_comment,
                            prev_attr_sp: attrs.last().and_then(|a| Some(a.span))
                        };
                    let attr = self.parse_attribute_with_inner_parse_policy(inner_parse_policy)?;
                    attrs.push(attr);
                    just_parsed_doc_comment = false;
                }
                token::DocComment(s) => {
                    let attr = self.mk_doc_comment(s);
                    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)
    }

    fn mk_doc_comment(&self, s: Symbol) -> ast::Attribute {
        let style = comments::doc_comment_style(&s.as_str());
        attr::mk_doc_comment(style, s, self.token.span)
    }

    /// 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,
                saw_doc_comment: false,
                prev_attr_sp: None
            }
        };
        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, item, style) = match self.token.kind {
            token::Pound => {
                let lo = self.token.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();
                    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 hi = self.prev_span;

                let attr_sp = lo.to(hi);

                // Emit error if inner attribute is encountered and not permitted
                if style == ast::AttrStyle::Inner {
                    if let InnerAttributeParsePolicy::NotPermitted { reason,
                        saw_doc_comment, prev_attr_sp } = inner_parse_policy {
                        let prev_attr_note = if saw_doc_comment {
                            "previous doc comment"
                        } else {
                            "previous outer attribute"
                        };

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

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

                        diagnostic
                            .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()
                    }
                }

                (attr_sp, item, style)
            }
            _ => {
                let token_str = self.this_token_to_string();
                return Err(self.fatal(&format!("expected `#`, found `{}`", token_str)));
            }
        };

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

    /// 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()),
                _ => None,
            },
            _ => None,
        };
        Ok(if let Some(item) = item {
            self.bump();
            item
        } 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(token::Eq, self.prev_span);
                let mut is_interpolated_expr = false;
                if let token::Interpolated(nt) = &self.token.kind {
                    if let token::NtExpr(..) = **nt {
                        is_interpolated_expr = true;
                    }
                }
                let token_tree = 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()
                } else {
                    self.parse_unsuffixed_lit()?.token_tree()
                };
                TokenStream::new(vec![eq.into(), token_tree.into()])
            } else {
                TokenStream::default()
            };
            ast::AttrItem { path, tokens }
        })
    }

    /// 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 {
            match self.token.kind {
                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 = self.mk_doc_comment(s);
                    if attr.style == ast::AttrStyle::Inner {
                        attrs.push(attr);
                        self.bump();
                    } else {
                        break;
                    }
                }
                _ => break,
            }
        }
        Ok(attrs)
    }

    pub(super) 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() {
            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)
    }

    /// 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)>)> {
        self.expect(&token::OpenDelim(token::Paren))?;

        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.check(&token::CloseDelim(token::Paren)) {
            let lo = self.token.span.lo();
            let item = self.parse_attr_item()?;
            expanded_attrs.push((item, self.prev_span.with_lo(lo)));
            self.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Paren)])?;
        }

        self.expect(&token::CloseDelim(token::Paren))?;
        Ok((cfg_predicate, expanded_attrs))
    }

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