compiler/rustc_parse/src/parser/attr.rs

   1 use super::{Parser, PathStyle};
   2 use rustc_ast as ast;
   3 use rustc_ast::attr;
   4 use rustc_ast::token::{self, Nonterminal};
   5 use rustc_ast_pretty::pprust;
   6 use rustc_errors::{error_code, PResult};
   7 use rustc_span::{sym, Span};
   8
   9 use tracing::debug;
  10
  11 // Public for rustfmt usage
  12 #[derive(Debug)]
  13 pub enum InnerAttrPolicy<'a> {
  14     Permitted,
  15     Forbidden { reason: &'a str, saw_doc_comment: bool, prev_attr_sp: Option<Span> },
  16 }
  17
  18 const DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG: &str = "an inner attribute is not \
  19                                                      permitted in this context";
  20
  21 pub(super) const DEFAULT_INNER_ATTR_FORBIDDEN: InnerAttrPolicy<'_> = InnerAttrPolicy::Forbidden {
  22     reason: DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG,
  23     saw_doc_comment: false,
  24     prev_attr_sp: None,
  25 };
  26
  27 impl<'a> Parser<'a> {
  28     /// Parses attributes that appear before an item.
  29     pub(super) fn parse_outer_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
  30         let mut attrs: Vec<ast::Attribute> = Vec::new();
  31         let mut just_parsed_doc_comment = false;
  32         loop {
  33             debug!("parse_outer_attributes: self.token={:?}", self.token);
  34             let attr = if self.check(&token::Pound) {
  35                 let inner_error_reason = if just_parsed_doc_comment {
  36                     "an inner attribute is not permitted following an outer doc comment"
  37                 } else if !attrs.is_empty() {
  38                     "an inner attribute is not permitted following an outer attribute"
  39                 } else {
  40                     DEFAULT_UNEXPECTED_INNER_ATTR_ERR_MSG
  41                 };
  42                 let inner_parse_policy = InnerAttrPolicy::Forbidden {
  43                     reason: inner_error_reason,
  44                     saw_doc_comment: just_parsed_doc_comment,
  45                     prev_attr_sp: attrs.last().map(|a| a.span),
  46                 };
  47                 just_parsed_doc_comment = false;
  48                 Some(self.parse_attribute(inner_parse_policy)?)
  49             } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
  50                 if attr_style != ast::AttrStyle::Outer {
  51                     self.sess
  52                         .span_diagnostic
  53                         .struct_span_err_with_code(
  54                             self.token.span,
  55                             "expected outer doc comment",
  56                             error_code!(E0753),
  57                         )
  58                         .note(
  59                             "inner doc comments like this (starting with \
  60                          `//!` or `/*!`) can only appear before items",
  61                         )
  62                         .emit();
  63                 }
  64                 self.bump();
  65                 just_parsed_doc_comment = true;
  66                 Some(attr::mk_doc_comment(comment_kind, attr_style, data, self.prev_token.span))
  67             } else {
  68                 None
  69             };
  70
  71             if let Some(attr) = attr {
  72                 attrs.push(attr);
  73             } else {
  74                 break;
  75             }
  76         }
  77         Ok(attrs)
  78     }
  79
  80     /// Matches `attribute = # ! [ meta_item ]`.
  81     /// `inner_parse_policy` prescribes how to handle inner attributes.
  82     // Public for rustfmt usage.
  83     pub fn parse_attribute(
  84         &mut self,
  85         inner_parse_policy: InnerAttrPolicy<'_>,
  86     ) -> PResult<'a, ast::Attribute> {
  87         debug!(
  88             "parse_attribute: inner_parse_policy={:?} self.token={:?}",
  89             inner_parse_policy, self.token
  90         );
  91         let lo = self.token.span;
  92         let ((item, style, span), tokens) = self.collect_tokens(|this| {
  93             if this.eat(&token::Pound) {
  94                 let style = if this.eat(&token::Not) {
  95                     ast::AttrStyle::Inner
  96                 } else {
  97                     ast::AttrStyle::Outer
  98                 };
  99
 100                 this.expect(&token::OpenDelim(token::Bracket))?;
 101                 let item = this.parse_attr_item(false)?;
 102                 this.expect(&token::CloseDelim(token::Bracket))?;
 103                 let attr_sp = lo.to(this.prev_token.span);
 104
 105                 // Emit error if inner attribute is encountered and forbidden.
 106                 if style == ast::AttrStyle::Inner {
 107                     this.error_on_forbidden_inner_attr(attr_sp, inner_parse_policy);
 108                 }
 109
 110                 Ok((item, style, attr_sp))
 111             } else {
 112                 let token_str = pprust::token_to_string(&this.token);
 113                 let msg = &format!("expected `#`, found `{}`", token_str);
 114                 Err(this.struct_span_err(this.token.span, msg))
 115             }
 116         })?;
 117
 118         Ok(attr::mk_attr_from_item(item, tokens, style, span))
 119     }
 120
 121     pub(super) fn error_on_forbidden_inner_attr(&self, attr_sp: Span, policy: InnerAttrPolicy<'_>) {
 122         if let InnerAttrPolicy::Forbidden { reason, saw_doc_comment, prev_attr_sp } = policy {
 123             let prev_attr_note =
 124                 if saw_doc_comment { "previous doc comment" } else { "previous outer attribute" };
 125
 126             let mut diag = self.struct_span_err(attr_sp, reason);
 127
 128             if let Some(prev_attr_sp) = prev_attr_sp {
 129                 diag.span_label(attr_sp, "not permitted following an outer attribute")
 130                     .span_label(prev_attr_sp, prev_attr_note);
 131             }
 132
 133             diag.note(
 134                 "inner attributes, like `#![no_std]`, annotate the item enclosing them, \
 135                 and are usually found at the beginning of source files. \
 136                 Outer attributes, like `#[test]`, annotate the item following them.",
 137             )
 138             .emit();
 139         }
 140     }
 141
 142     /// Parses an inner part of an attribute (the path and following tokens).
 143     /// The tokens must be either a delimited token stream, or empty token stream,
 144     /// or the "legacy" key-value form.
 145     ///     PATH `(` TOKEN_STREAM `)`
 146     ///     PATH `[` TOKEN_STREAM `]`
 147     ///     PATH `{` TOKEN_STREAM `}`
 148     ///     PATH
 149     ///     PATH `=` UNSUFFIXED_LIT
 150     /// The delimiters or `=` are still put into the resulting token stream.
 151     pub fn parse_attr_item(&mut self, capture_tokens: bool) -> PResult<'a, ast::AttrItem> {
 152         let item = match self.token.kind {
 153             token::Interpolated(ref nt) => match **nt {
 154                 Nonterminal::NtMeta(ref item) => Some(item.clone().into_inner()),
 155                 _ => None,
 156             },
 157             _ => None,
 158         };
 159         Ok(if let Some(item) = item {
 160             self.bump();
 161             item
 162         } else {
 163             let do_parse = |this: &mut Self| {
 164                 let path = this.parse_path(PathStyle::Mod)?;
 165                 let args = this.parse_attr_args()?;
 166                 Ok(ast::AttrItem { path, args, tokens: None })
 167             };
 168             if capture_tokens {
 169                 let (mut item, tokens) = self.collect_tokens(do_parse)?;
 170                 item.tokens = tokens;
 171                 item
 172             } else {
 173                 do_parse(self)?
 174             }
 175         })
 176     }
 177
 178     /// Parses attributes that appear after the opening of an item. These should
 179     /// be preceded by an exclamation mark, but we accept and warn about one
 180     /// terminated by a semicolon.
 181     ///
 182     /// Matches `inner_attrs*`.
 183     crate fn parse_inner_attributes(&mut self) -> PResult<'a, Vec<ast::Attribute>> {
 184         let mut attrs: Vec<ast::Attribute> = vec![];
 185         loop {
 186             // Only try to parse if it is an inner attribute (has `!`).
 187             let attr = if self.check(&token::Pound) && self.look_ahead(1, |t| t == &token::Not) {
 188                 Some(self.parse_attribute(InnerAttrPolicy::Permitted)?)
 189             } else if let token::DocComment(comment_kind, attr_style, data) = self.token.kind {
 190                 if attr_style == ast::AttrStyle::Inner {
 191                     self.bump();
 192                     Some(attr::mk_doc_comment(comment_kind, attr_style, data, self.prev_token.span))
 193                 } else {
 194                     None
 195                 }
 196             } else {
 197                 None
 198             };
 199             if let Some(attr) = attr {
 200                 attrs.push(attr);
 201             } else {
 202                 break;
 203             }
 204         }
 205         Ok(attrs)
 206     }
 207
 208     crate fn parse_unsuffixed_lit(&mut self) -> PResult<'a, ast::Lit> {
 209         let lit = self.parse_lit()?;
 210         debug!("checking if {:?} is unusuffixed", lit);
 211
 212         if !lit.kind.is_unsuffixed() {
 213             self.struct_span_err(lit.span, "suffixed literals are not allowed in attributes")
 214                 .help(
 215                     "instead of using a suffixed literal (`1u8`, `1.0f32`, etc.), \
 216                     use an unsuffixed version (`1`, `1.0`, etc.)",
 217                 )
 218                 .emit();
 219         }
 220
 221         Ok(lit)
 222     }
 223
 224     /// Parses `cfg_attr(pred, attr_item_list)` where `attr_item_list` is comma-delimited.
 225     pub fn parse_cfg_attr(&mut self) -> PResult<'a, (ast::MetaItem, Vec<(ast::AttrItem, Span)>)> {
 226         let cfg_predicate = self.parse_meta_item()?;
 227         self.expect(&token::Comma)?;
 228
 229         // Presumably, the majority of the time there will only be one attr.
 230         let mut expanded_attrs = Vec::with_capacity(1);
 231         while self.token.kind != token::Eof {
 232             let lo = self.token.span;
 233             let item = self.parse_attr_item(true)?;
 234             expanded_attrs.push((item, lo.to(self.prev_token.span)));
 235             if !self.eat(&token::Comma) {
 236                 break;
 237             }
 238         }
 239
 240         Ok((cfg_predicate, expanded_attrs))
 241     }
 242
 243     /// Matches `COMMASEP(meta_item_inner)`.
 244     crate fn parse_meta_seq_top(&mut self) -> PResult<'a, Vec<ast::NestedMetaItem>> {
 245         // Presumably, the majority of the time there will only be one attr.
 246         let mut nmis = Vec::with_capacity(1);
 247         while self.token.kind != token::Eof {
 248             nmis.push(self.parse_meta_item_inner()?);
 249             if !self.eat(&token::Comma) {
 250                 break;
 251             }
 252         }
 253         Ok(nmis)
 254     }
 255
 256     /// Matches the following grammar (per RFC 1559).
 257     ///
 258     ///     meta_item : PATH ( '=' UNSUFFIXED_LIT | '(' meta_item_inner? ')' )? ;
 259     ///     meta_item_inner : (meta_item | UNSUFFIXED_LIT) (',' meta_item_inner)? ;
 260     pub fn parse_meta_item(&mut self) -> PResult<'a, ast::MetaItem> {
 261         let nt_meta = match self.token.kind {
 262             token::Interpolated(ref nt) => match **nt {
 263                 token::NtMeta(ref e) => Some(e.clone()),
 264                 _ => None,
 265             },
 266             _ => None,
 267         };
 268
 269         if let Some(item) = nt_meta {
 270             return match item.meta(item.path.span) {
 271                 Some(meta) => {
 272                     self.bump();
 273                     Ok(meta)
 274                 }
 275                 None => self.unexpected(),
 276             };
 277         }
 278
 279         let lo = self.token.span;
 280         let path = self.parse_path(PathStyle::Mod)?;
 281         let kind = self.parse_meta_item_kind()?;
 282         let span = lo.to(self.prev_token.span);
 283         Ok(ast::MetaItem { path, kind, span })
 284     }
 285
 286     crate fn parse_meta_item_kind(&mut self) -> PResult<'a, ast::MetaItemKind> {
 287         Ok(if self.eat(&token::Eq) {
 288             ast::MetaItemKind::NameValue(self.parse_unsuffixed_lit()?)
 289         } else if self.check(&token::OpenDelim(token::Paren)) {
 290             // Matches `meta_seq = ( COMMASEP(meta_item_inner) )`.
 291             let (list, _) = self.parse_paren_comma_seq(|p| p.parse_meta_item_inner())?;
 292             ast::MetaItemKind::List(list)
 293         } else {
 294             ast::MetaItemKind::Word
 295         })
 296     }
 297
 298     /// Matches `meta_item_inner : (meta_item | UNSUFFIXED_LIT) ;`.
 299     fn parse_meta_item_inner(&mut self) -> PResult<'a, ast::NestedMetaItem> {
 300         match self.parse_unsuffixed_lit() {
 301             Ok(lit) => return Ok(ast::NestedMetaItem::Literal(lit)),
 302             Err(ref mut err) => err.cancel(),
 303         }
 304
 305         match self.parse_meta_item() {
 306             Ok(mi) => return Ok(ast::NestedMetaItem::MetaItem(mi)),
 307             Err(ref mut err) => err.cancel(),
 308         }
 309
 310         let found = pprust::token_to_string(&self.token);
 311         let msg = format!("expected unsuffixed literal or identifier, found `{}`", found);
 312         Err(self.struct_span_err(self.token.span, &msg))
 313     }
 314 }
 315
 316 pub fn maybe_needs_tokens(attrs: &[ast::Attribute]) -> bool {
 317     // One of the attributes may either itself be a macro, or apply derive macros (`derive`),
 318     // or expand to macro attributes (`cfg_attr`).
 319     attrs.iter().any(|attr| {
 320         attr.ident().map_or(true, |ident| {
 321             ident.name == sym::derive
 322                 || ident.name == sym::cfg_attr
 323                 || !rustc_feature::is_builtin_attr_name(ident.name)
 324         })
 325     })
 326 }