compiler/rustc_parse/src/parser/item.rs

   1 use super::diagnostics::{dummy_arg, ConsumeClosingDelim, Error};
   2 use super::ty::{AllowPlus, RecoverQPath, RecoverReturnSign};
   3 use super::{AttrWrapper, FollowedByType, ForceCollect, Parser, PathStyle, TrailingToken};
   4
   5 use rustc_ast::ast::*;
   6 use rustc_ast::ptr::P;
   7 use rustc_ast::token::{self, TokenKind};
   8 use rustc_ast::tokenstream::{DelimSpan, TokenStream, TokenTree};
   9 use rustc_ast::{self as ast, AttrVec, Attribute, DUMMY_NODE_ID};
  10 use rustc_ast::{Async, Const, Defaultness, IsAuto, Mutability, Unsafe, UseTree, UseTreeKind};
  11 use rustc_ast::{BindingMode, Block, FnDecl, FnSig, Param, SelfKind};
  12 use rustc_ast::{EnumDef, FieldDef, Generics, TraitRef, Ty, TyKind, Variant, VariantData};
  13 use rustc_ast::{FnHeader, ForeignItem, Path, PathSegment, Visibility, VisibilityKind};
  14 use rustc_ast::{MacArgs, MacCall, MacDelimiter};
  15 use rustc_ast_pretty::pprust;
  16 use rustc_errors::{struct_span_err, Applicability, PResult, StashKey};
  17 use rustc_span::edition::{Edition, LATEST_STABLE_EDITION};
  18 use rustc_span::source_map::{self, Span};
  19 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  20
  21 use std::convert::TryFrom;
  22 use std::mem;
  23 use tracing::debug;
  24
  25 impl<'a> Parser<'a> {
  26     /// Parses a source module as a crate. This is the main entry point for the parser.
  27     pub fn parse_crate_mod(&mut self) -> PResult<'a, ast::Crate> {
  28         let (attrs, items, span) = self.parse_mod(&token::Eof)?;
  29         Ok(ast::Crate { attrs, items, span })
  30     }
  31
  32     /// Parses a `mod <foo> { ... }` or `mod <foo>;` item.
  33     fn parse_item_mod(&mut self, attrs: &mut Vec<Attribute>) -> PResult<'a, ItemInfo> {
  34         let unsafety = self.parse_unsafety();
  35         self.expect_keyword(kw::Mod)?;
  36         let id = self.parse_ident()?;
  37         let mod_kind = if self.eat(&token::Semi) {
  38             ModKind::Unloaded
  39         } else {
  40             self.expect(&token::OpenDelim(token::Brace))?;
  41             let (mut inner_attrs, items, inner_span) =
  42                 self.parse_mod(&token::CloseDelim(token::Brace))?;
  43             attrs.append(&mut inner_attrs);
  44             ModKind::Loaded(items, Inline::Yes, inner_span)
  45         };
  46         Ok((id, ItemKind::Mod(unsafety, mod_kind)))
  47     }
  48
  49     /// Parses the contents of a module (inner attributes followed by module items).
  50     pub fn parse_mod(
  51         &mut self,
  52         term: &TokenKind,
  53     ) -> PResult<'a, (Vec<Attribute>, Vec<P<Item>>, Span)> {
  54         let lo = self.token.span;
  55         let attrs = self.parse_inner_attributes()?;
  56
  57         let mut items = vec![];
  58         while let Some(item) = self.parse_item(ForceCollect::No)? {
  59             items.push(item);
  60             self.maybe_consume_incorrect_semicolon(&items);
  61         }
  62
  63         if !self.eat(term) {
  64             let token_str = super::token_descr(&self.token);
  65             if !self.maybe_consume_incorrect_semicolon(&items) {
  66                 let msg = &format!("expected item, found {}", token_str);
  67                 let mut err = self.struct_span_err(self.token.span, msg);
  68                 err.span_label(self.token.span, "expected item");
  69                 return Err(err);
  70             }
  71         }
  72
  73         Ok((attrs, items, lo.to(self.prev_token.span)))
  74     }
  75 }
  76
  77 pub(super) type ItemInfo = (Ident, ItemKind);
  78
  79 impl<'a> Parser<'a> {
  80     pub fn parse_item(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<P<Item>>> {
  81         self.parse_item_(|_| true, force_collect).map(|i| i.map(P))
  82     }
  83
  84     fn parse_item_(
  85         &mut self,
  86         req_name: ReqName,
  87         force_collect: ForceCollect,
  88     ) -> PResult<'a, Option<Item>> {
  89         let attrs = self.parse_outer_attributes()?;
  90         self.parse_item_common(attrs, true, false, req_name, force_collect)
  91     }
  92
  93     pub(super) fn parse_item_common(
  94         &mut self,
  95         attrs: AttrWrapper,
  96         mac_allowed: bool,
  97         attrs_allowed: bool,
  98         req_name: ReqName,
  99         force_collect: ForceCollect,
 100     ) -> PResult<'a, Option<Item>> {
 101         // Don't use `maybe_whole` so that we have precise control
 102         // over when we bump the parser
 103         if let token::Interpolated(nt) = &self.token.kind {
 104             if let token::NtItem(item) = &**nt {
 105                 let mut item = item.clone();
 106                 self.bump();
 107
 108                 attrs.prepend_to_nt_inner(&mut item.attrs);
 109                 return Ok(Some(item.into_inner()));
 110             }
 111         };
 112
 113         let mut unclosed_delims = vec![];
 114         let item =
 115             self.collect_tokens_trailing_token(attrs, force_collect, |this: &mut Self, attrs| {
 116                 let item = this.parse_item_common_(attrs, mac_allowed, attrs_allowed, req_name);
 117                 unclosed_delims.append(&mut this.unclosed_delims);
 118                 Ok((item?, TrailingToken::None))
 119             })?;
 120
 121         self.unclosed_delims.append(&mut unclosed_delims);
 122         Ok(item)
 123     }
 124
 125     fn parse_item_common_(
 126         &mut self,
 127         mut attrs: Vec<Attribute>,
 128         mac_allowed: bool,
 129         attrs_allowed: bool,
 130         req_name: ReqName,
 131     ) -> PResult<'a, Option<Item>> {
 132         let lo = self.token.span;
 133         let vis = self.parse_visibility(FollowedByType::No)?;
 134         let mut def = self.parse_defaultness();
 135         let kind = self.parse_item_kind(&mut attrs, mac_allowed, lo, &vis, &mut def, req_name)?;
 136         if let Some((ident, kind)) = kind {
 137             self.error_on_unconsumed_default(def, &kind);
 138             let span = lo.to(self.prev_token.span);
 139             let id = DUMMY_NODE_ID;
 140             let item = Item { ident, attrs, id, kind, vis, span, tokens: None };
 141             return Ok(Some(item));
 142         }
 143
 144         // At this point, we have failed to parse an item.
 145         self.error_on_unmatched_vis(&vis);
 146         self.error_on_unmatched_defaultness(def);
 147         if !attrs_allowed {
 148             self.recover_attrs_no_item(&attrs)?;
 149         }
 150         Ok(None)
 151     }
 152
 153     /// Error in-case a non-inherited visibility was parsed but no item followed.
 154     fn error_on_unmatched_vis(&self, vis: &Visibility) {
 155         if let VisibilityKind::Inherited = vis.kind {
 156             return;
 157         }
 158         let vs = pprust::vis_to_string(&vis);
 159         let vs = vs.trim_end();
 160         self.struct_span_err(vis.span, &format!("visibility `{}` is not followed by an item", vs))
 161             .span_label(vis.span, "the visibility")
 162             .help(&format!("you likely meant to define an item, e.g., `{} fn foo() {{}}`", vs))
 163             .emit();
 164     }
 165
 166     /// Error in-case a `default` was parsed but no item followed.
 167     fn error_on_unmatched_defaultness(&self, def: Defaultness) {
 168         if let Defaultness::Default(sp) = def {
 169             self.struct_span_err(sp, "`default` is not followed by an item")
 170                 .span_label(sp, "the `default` qualifier")
 171                 .note("only `fn`, `const`, `type`, or `impl` items may be prefixed by `default`")
 172                 .emit();
 173         }
 174     }
 175
 176     /// Error in-case `default` was parsed in an in-appropriate context.
 177     fn error_on_unconsumed_default(&self, def: Defaultness, kind: &ItemKind) {
 178         if let Defaultness::Default(span) = def {
 179             let msg = format!("{} {} cannot be `default`", kind.article(), kind.descr());
 180             self.struct_span_err(span, &msg)
 181                 .span_label(span, "`default` because of this")
 182                 .note("only associated `fn`, `const`, and `type` items can be `default`")
 183                 .emit();
 184         }
 185     }
 186
 187     /// Parses one of the items allowed by the flags.
 188     fn parse_item_kind(
 189         &mut self,
 190         attrs: &mut Vec<Attribute>,
 191         macros_allowed: bool,
 192         lo: Span,
 193         vis: &Visibility,
 194         def: &mut Defaultness,
 195         req_name: ReqName,
 196     ) -> PResult<'a, Option<ItemInfo>> {
 197         let def_final = def == &Defaultness::Final;
 198         let mut def = || mem::replace(def, Defaultness::Final);
 199
 200         let info = if self.eat_keyword(kw::Use) {
 201             // USE ITEM
 202             let tree = self.parse_use_tree()?;
 203
 204             // If wildcard or glob-like brace syntax doesn't have `;`,
 205             // the user may not know `*` or `{}` should be the last.
 206             if let Err(mut e) = self.expect_semi() {
 207                 match tree.kind {
 208                     UseTreeKind::Glob => {
 209                         e.note("the wildcard token must be last on the path").emit();
 210                     }
 211                     UseTreeKind::Nested(..) => {
 212                         e.note("glob-like brace syntax must be last on the path").emit();
 213                     }
 214                     _ => (),
 215                 }
 216                 return Err(e);
 217             }
 218
 219             (Ident::empty(), ItemKind::Use(tree))
 220         } else if self.check_fn_front_matter(def_final) {
 221             // FUNCTION ITEM
 222             let (ident, sig, generics, body) = self.parse_fn(attrs, req_name, lo)?;
 223             (ident, ItemKind::Fn(Box::new(FnKind(def(), sig, generics, body))))
 224         } else if self.eat_keyword(kw::Extern) {
 225             if self.eat_keyword(kw::Crate) {
 226                 // EXTERN CRATE
 227                 self.parse_item_extern_crate()?
 228             } else {
 229                 // EXTERN BLOCK
 230                 self.parse_item_foreign_mod(attrs, Unsafe::No)?
 231             }
 232         } else if self.is_unsafe_foreign_mod() {
 233             // EXTERN BLOCK
 234             let unsafety = self.parse_unsafety();
 235             self.expect_keyword(kw::Extern)?;
 236             self.parse_item_foreign_mod(attrs, unsafety)?
 237         } else if self.is_static_global() {
 238             // STATIC ITEM
 239             self.bump(); // `static`
 240             let m = self.parse_mutability();
 241             let (ident, ty, expr) = self.parse_item_global(Some(m))?;
 242             (ident, ItemKind::Static(ty, m, expr))
 243         } else if let Const::Yes(const_span) = self.parse_constness() {
 244             // CONST ITEM
 245             if self.token.is_keyword(kw::Impl) {
 246                 // recover from `const impl`, suggest `impl const`
 247                 self.recover_const_impl(const_span, attrs, def())?
 248             } else {
 249                 self.recover_const_mut(const_span);
 250                 let (ident, ty, expr) = self.parse_item_global(None)?;
 251                 (ident, ItemKind::Const(def(), ty, expr))
 252             }
 253         } else if self.check_keyword(kw::Trait) || self.check_auto_or_unsafe_trait_item() {
 254             // TRAIT ITEM
 255             self.parse_item_trait(attrs, lo)?
 256         } else if self.check_keyword(kw::Impl)
 257             || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Impl])
 258         {
 259             // IMPL ITEM
 260             self.parse_item_impl(attrs, def())?
 261         } else if self.check_keyword(kw::Mod)
 262             || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Mod])
 263         {
 264             // MODULE ITEM
 265             self.parse_item_mod(attrs)?
 266         } else if self.eat_keyword(kw::Type) {
 267             // TYPE ITEM
 268             self.parse_type_alias(def())?
 269         } else if self.eat_keyword(kw::Enum) {
 270             // ENUM ITEM
 271             self.parse_item_enum()?
 272         } else if self.eat_keyword(kw::Struct) {
 273             // STRUCT ITEM
 274             self.parse_item_struct()?
 275         } else if self.is_kw_followed_by_ident(kw::Union) {
 276             // UNION ITEM
 277             self.bump(); // `union`
 278             self.parse_item_union()?
 279         } else if self.eat_keyword(kw::Macro) {
 280             // MACROS 2.0 ITEM
 281             self.parse_item_decl_macro(lo)?
 282         } else if self.is_macro_rules_item() {
 283             // MACRO_RULES ITEM
 284             self.parse_item_macro_rules(vis)?
 285         } else if vis.kind.is_pub() && self.isnt_macro_invocation() {
 286             self.recover_missing_kw_before_item()?;
 287             return Ok(None);
 288         } else if macros_allowed && self.check_path() {
 289             // MACRO INVOCATION ITEM
 290             (Ident::empty(), ItemKind::MacCall(self.parse_item_macro(vis)?))
 291         } else {
 292             return Ok(None);
 293         };
 294         Ok(Some(info))
 295     }
 296
 297     /// When parsing a statement, would the start of a path be an item?
 298     pub(super) fn is_path_start_item(&mut self) -> bool {
 299         self.is_crate_vis() // no: `crate::b`, yes: `crate $item`
 300         || self.is_kw_followed_by_ident(kw::Union) // no: `union::b`, yes: `union U { .. }`
 301         || self.check_auto_or_unsafe_trait_item() // no: `auto::b`, yes: `auto trait X { .. }`
 302         || self.is_async_fn() // no(2015): `async::b`, yes: `async fn`
 303         || self.is_macro_rules_item() // no: `macro_rules::b`, yes: `macro_rules! mac`
 304     }
 305
 306     /// Are we sure this could not possibly be a macro invocation?
 307     fn isnt_macro_invocation(&mut self) -> bool {
 308         self.check_ident() && self.look_ahead(1, |t| *t != token::Not && *t != token::ModSep)
 309     }
 310
 311     /// Recover on encountering a struct or method definition where the user
 312     /// forgot to add the `struct` or `fn` keyword after writing `pub`: `pub S {}`.
 313     fn recover_missing_kw_before_item(&mut self) -> PResult<'a, ()> {
 314         // Space between `pub` keyword and the identifier
 315         //
 316         //     pub   S {}
 317         //        ^^^ `sp` points here
 318         let sp = self.prev_token.span.between(self.token.span);
 319         let full_sp = self.prev_token.span.to(self.token.span);
 320         let ident_sp = self.token.span;
 321         if self.look_ahead(1, |t| *t == token::OpenDelim(token::Brace)) {
 322             // possible public struct definition where `struct` was forgotten
 323             let ident = self.parse_ident().unwrap();
 324             let msg = format!("add `struct` here to parse `{}` as a public struct", ident);
 325             let mut err = self.struct_span_err(sp, "missing `struct` for struct definition");
 326             err.span_suggestion_short(
 327                 sp,
 328                 &msg,
 329                 " struct ".into(),
 330                 Applicability::MaybeIncorrect, // speculative
 331             );
 332             Err(err)
 333         } else if self.look_ahead(1, |t| *t == token::OpenDelim(token::Paren)) {
 334             let ident = self.parse_ident().unwrap();
 335             self.bump(); // `(`
 336             let kw_name = self.recover_first_param();
 337             self.consume_block(token::Paren, ConsumeClosingDelim::Yes);
 338             let (kw, kw_name, ambiguous) = if self.check(&token::RArrow) {
 339                 self.eat_to_tokens(&[&token::OpenDelim(token::Brace)]);
 340                 self.bump(); // `{`
 341                 ("fn", kw_name, false)
 342             } else if self.check(&token::OpenDelim(token::Brace)) {
 343                 self.bump(); // `{`
 344                 ("fn", kw_name, false)
 345             } else if self.check(&token::Colon) {
 346                 let kw = "struct";
 347                 (kw, kw, false)
 348             } else {
 349                 ("fn` or `struct", "function or struct", true)
 350             };
 351
 352             let msg = format!("missing `{}` for {} definition", kw, kw_name);
 353             let mut err = self.struct_span_err(sp, &msg);
 354             if !ambiguous {
 355                 self.consume_block(token::Brace, ConsumeClosingDelim::Yes);
 356                 let suggestion =
 357                     format!("add `{}` here to parse `{}` as a public {}", kw, ident, kw_name);
 358                 err.span_suggestion_short(
 359                     sp,
 360                     &suggestion,
 361                     format!(" {} ", kw),
 362                     Applicability::MachineApplicable,
 363                 );
 364             } else if let Ok(snippet) = self.span_to_snippet(ident_sp) {
 365                 err.span_suggestion(
 366                     full_sp,
 367                     "if you meant to call a macro, try",
 368                     format!("{}!", snippet),
 369                     // this is the `ambiguous` conditional branch
 370                     Applicability::MaybeIncorrect,
 371                 );
 372             } else {
 373                 err.help(
 374                     "if you meant to call a macro, remove the `pub` \
 375                               and add a trailing `!` after the identifier",
 376                 );
 377             }
 378             Err(err)
 379         } else if self.look_ahead(1, |t| *t == token::Lt) {
 380             let ident = self.parse_ident().unwrap();
 381             self.eat_to_tokens(&[&token::Gt]);
 382             self.bump(); // `>`
 383             let (kw, kw_name, ambiguous) = if self.eat(&token::OpenDelim(token::Paren)) {
 384                 ("fn", self.recover_first_param(), false)
 385             } else if self.check(&token::OpenDelim(token::Brace)) {
 386                 ("struct", "struct", false)
 387             } else {
 388                 ("fn` or `struct", "function or struct", true)
 389             };
 390             let msg = format!("missing `{}` for {} definition", kw, kw_name);
 391             let mut err = self.struct_span_err(sp, &msg);
 392             if !ambiguous {
 393                 err.span_suggestion_short(
 394                     sp,
 395                     &format!("add `{}` here to parse `{}` as a public {}", kw, ident, kw_name),
 396                     format!(" {} ", kw),
 397                     Applicability::MachineApplicable,
 398                 );
 399             }
 400             Err(err)
 401         } else {
 402             Ok(())
 403         }
 404     }
 405
 406     /// Parses an item macro, e.g., `item!();`.
 407     fn parse_item_macro(&mut self, vis: &Visibility) -> PResult<'a, MacCall> {
 408         let path = self.parse_path(PathStyle::Mod)?; // `foo::bar`
 409         self.expect(&token::Not)?; // `!`
 410         let args = self.parse_mac_args()?; // `( .. )` or `[ .. ]` (followed by `;`), or `{ .. }`.
 411         self.eat_semi_for_macro_if_needed(&args);
 412         self.complain_if_pub_macro(vis, false);
 413         Ok(MacCall { path, args, prior_type_ascription: self.last_type_ascription })
 414     }
 415
 416     /// Recover if we parsed attributes and expected an item but there was none.
 417     fn recover_attrs_no_item(&mut self, attrs: &[Attribute]) -> PResult<'a, ()> {
 418         let (start, end) = match attrs {
 419             [] => return Ok(()),
 420             [x0 @ xn] | [x0, .., xn] => (x0, xn),
 421         };
 422         let msg = if end.is_doc_comment() {
 423             "expected item after doc comment"
 424         } else {
 425             "expected item after attributes"
 426         };
 427         let mut err = self.struct_span_err(end.span, msg);
 428         if end.is_doc_comment() {
 429             err.span_label(end.span, "this doc comment doesn't document anything");
 430         }
 431         if let [.., penultimate, _] = attrs {
 432             err.span_label(start.span.to(penultimate.span), "other attributes here");
 433         }
 434         Err(err)
 435     }
 436
 437     fn is_async_fn(&self) -> bool {
 438         self.token.is_keyword(kw::Async) && self.is_keyword_ahead(1, &[kw::Fn])
 439     }
 440
 441     fn parse_polarity(&mut self) -> ast::ImplPolarity {
 442         // Disambiguate `impl !Trait for Type { ... }` and `impl ! { ... }` for the never type.
 443         if self.check(&token::Not) && self.look_ahead(1, |t| t.can_begin_type()) {
 444             self.bump(); // `!`
 445             ast::ImplPolarity::Negative(self.prev_token.span)
 446         } else {
 447             ast::ImplPolarity::Positive
 448         }
 449     }
 450
 451     /// Parses an implementation item.
 452     ///
 453     /// ```
 454     /// impl<'a, T> TYPE { /* impl items */ }
 455     /// impl<'a, T> TRAIT for TYPE { /* impl items */ }
 456     /// impl<'a, T> !TRAIT for TYPE { /* impl items */ }
 457     /// impl<'a, T> const TRAIT for TYPE { /* impl items */ }
 458     /// ```
 459     ///
 460     /// We actually parse slightly more relaxed grammar for better error reporting and recovery.
 461     /// ```
 462     /// "impl" GENERICS "const"? "!"? TYPE "for"? (TYPE | "..") ("where" PREDICATES)? "{" BODY "}"
 463     /// "impl" GENERICS "const"? "!"? TYPE ("where" PREDICATES)? "{" BODY "}"
 464     /// ```
 465     fn parse_item_impl(
 466         &mut self,
 467         attrs: &mut Vec<Attribute>,
 468         defaultness: Defaultness,
 469     ) -> PResult<'a, ItemInfo> {
 470         let unsafety = self.parse_unsafety();
 471         self.expect_keyword(kw::Impl)?;
 472
 473         // First, parse generic parameters if necessary.
 474         let mut generics = if self.choose_generics_over_qpath(0) {
 475             self.parse_generics()?
 476         } else {
 477             let mut generics = Generics::default();
 478             // impl A for B {}
 479             //    /\ this is where `generics.span` should point when there are no type params.
 480             generics.span = self.prev_token.span.shrink_to_hi();
 481             generics
 482         };
 483
 484         let constness = self.parse_constness();
 485         if let Const::Yes(span) = constness {
 486             self.sess.gated_spans.gate(sym::const_trait_impl, span);
 487         }
 488
 489         let polarity = self.parse_polarity();
 490
 491         // Parse both types and traits as a type, then reinterpret if necessary.
 492         let err_path = |span| ast::Path::from_ident(Ident::new(kw::Empty, span));
 493         let ty_first = if self.token.is_keyword(kw::For) && self.look_ahead(1, |t| t != &token::Lt)
 494         {
 495             let span = self.prev_token.span.between(self.token.span);
 496             self.struct_span_err(span, "missing trait in a trait impl")
 497                 .span_suggestion(
 498                     span,
 499                     "add a trait here",
 500                     " Trait ".into(),
 501                     Applicability::HasPlaceholders,
 502                 )
 503                 .span_suggestion(
 504                     span.to(self.token.span),
 505                     "for an inherent impl, drop this `for`",
 506                     "".into(),
 507                     Applicability::MaybeIncorrect,
 508                 )
 509                 .emit();
 510             P(Ty {
 511                 kind: TyKind::Path(None, err_path(span)),
 512                 span,
 513                 id: DUMMY_NODE_ID,
 514                 tokens: None,
 515             })
 516         } else {
 517             self.parse_ty()?
 518         };
 519
 520         // If `for` is missing we try to recover.
 521         let has_for = self.eat_keyword(kw::For);
 522         let missing_for_span = self.prev_token.span.between(self.token.span);
 523
 524         let ty_second = if self.token == token::DotDot {
 525             // We need to report this error after `cfg` expansion for compatibility reasons
 526             self.bump(); // `..`, do not add it to expected tokens
 527             Some(self.mk_ty(self.prev_token.span, TyKind::Err))
 528         } else if has_for || self.token.can_begin_type() {
 529             Some(self.parse_ty()?)
 530         } else {
 531             None
 532         };
 533
 534         generics.where_clause = self.parse_where_clause()?;
 535
 536         let impl_items = self.parse_item_list(attrs, |p| p.parse_impl_item(ForceCollect::No))?;
 537
 538         let item_kind = match ty_second {
 539             Some(ty_second) => {
 540                 // impl Trait for Type
 541                 if !has_for {
 542                     self.struct_span_err(missing_for_span, "missing `for` in a trait impl")
 543                         .span_suggestion_short(
 544                             missing_for_span,
 545                             "add `for` here",
 546                             " for ".to_string(),
 547                             Applicability::MachineApplicable,
 548                         )
 549                         .emit();
 550                 }
 551
 552                 let ty_first = ty_first.into_inner();
 553                 let path = match ty_first.kind {
 554                     // This notably includes paths passed through `ty` macro fragments (#46438).
 555                     TyKind::Path(None, path) => path,
 556                     _ => {
 557                         self.struct_span_err(ty_first.span, "expected a trait, found type").emit();
 558                         err_path(ty_first.span)
 559                     }
 560                 };
 561                 let trait_ref = TraitRef { path, ref_id: ty_first.id };
 562
 563                 ItemKind::Impl(Box::new(ImplKind {
 564                     unsafety,
 565                     polarity,
 566                     defaultness,
 567                     constness,
 568                     generics,
 569                     of_trait: Some(trait_ref),
 570                     self_ty: ty_second,
 571                     items: impl_items,
 572                 }))
 573             }
 574             None => {
 575                 // impl Type
 576                 ItemKind::Impl(Box::new(ImplKind {
 577                     unsafety,
 578                     polarity,
 579                     defaultness,
 580                     constness,
 581                     generics,
 582                     of_trait: None,
 583                     self_ty: ty_first,
 584                     items: impl_items,
 585                 }))
 586             }
 587         };
 588
 589         Ok((Ident::empty(), item_kind))
 590     }
 591
 592     fn parse_item_list<T>(
 593         &mut self,
 594         attrs: &mut Vec<Attribute>,
 595         mut parse_item: impl FnMut(&mut Parser<'a>) -> PResult<'a, Option<Option<T>>>,
 596     ) -> PResult<'a, Vec<T>> {
 597         let open_brace_span = self.token.span;
 598         self.expect(&token::OpenDelim(token::Brace))?;
 599         attrs.append(&mut self.parse_inner_attributes()?);
 600
 601         let mut items = Vec::new();
 602         while !self.eat(&token::CloseDelim(token::Brace)) {
 603             if self.recover_doc_comment_before_brace() {
 604                 continue;
 605             }
 606             match parse_item(self) {
 607                 Ok(None) => {
 608                     // We have to bail or we'll potentially never make progress.
 609                     let non_item_span = self.token.span;
 610                     self.consume_block(token::Brace, ConsumeClosingDelim::Yes);
 611                     self.struct_span_err(non_item_span, "non-item in item list")
 612                         .span_label(open_brace_span, "item list starts here")
 613                         .span_label(non_item_span, "non-item starts here")
 614                         .span_label(self.prev_token.span, "item list ends here")
 615                         .emit();
 616                     break;
 617                 }
 618                 Ok(Some(item)) => items.extend(item),
 619                 Err(mut err) => {
 620                     self.consume_block(token::Brace, ConsumeClosingDelim::Yes);
 621                     err.span_label(open_brace_span, "while parsing this item list starting here")
 622                         .span_label(self.prev_token.span, "the item list ends here")
 623                         .emit();
 624                     break;
 625                 }
 626             }
 627         }
 628         Ok(items)
 629     }
 630
 631     /// Recover on a doc comment before `}`.
 632     fn recover_doc_comment_before_brace(&mut self) -> bool {
 633         if let token::DocComment(..) = self.token.kind {
 634             if self.look_ahead(1, |tok| tok == &token::CloseDelim(token::Brace)) {
 635                 struct_span_err!(
 636                     self.diagnostic(),
 637                     self.token.span,
 638                     E0584,
 639                     "found a documentation comment that doesn't document anything",
 640                 )
 641                 .span_label(self.token.span, "this doc comment doesn't document anything")
 642                 .help(
 643                     "doc comments must come before what they document, maybe a \
 644                     comment was intended with `//`?",
 645                 )
 646                 .emit();
 647                 self.bump();
 648                 return true;
 649             }
 650         }
 651         false
 652     }
 653
 654     /// Parses defaultness (i.e., `default` or nothing).
 655     fn parse_defaultness(&mut self) -> Defaultness {
 656         // We are interested in `default` followed by another identifier.
 657         // However, we must avoid keywords that occur as binary operators.
 658         // Currently, the only applicable keyword is `as` (`default as Ty`).
 659         if self.check_keyword(kw::Default)
 660             && self.look_ahead(1, |t| t.is_non_raw_ident_where(|i| i.name != kw::As))
 661         {
 662             self.bump(); // `default`
 663             Defaultness::Default(self.prev_token.uninterpolated_span())
 664         } else {
 665             Defaultness::Final
 666         }
 667     }
 668
 669     /// Is this an `(unsafe auto? | auto) trait` item?
 670     fn check_auto_or_unsafe_trait_item(&mut self) -> bool {
 671         // auto trait
 672         self.check_keyword(kw::Auto) && self.is_keyword_ahead(1, &[kw::Trait])
 673             // unsafe auto trait
 674             || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
 675     }
 676
 677     /// Parses `unsafe? auto? trait Foo { ... }` or `trait Foo = Bar;`.
 678     fn parse_item_trait(&mut self, attrs: &mut Vec<Attribute>, lo: Span) -> PResult<'a, ItemInfo> {
 679         let unsafety = self.parse_unsafety();
 680         // Parse optional `auto` prefix.
 681         let is_auto = if self.eat_keyword(kw::Auto) { IsAuto::Yes } else { IsAuto::No };
 682
 683         self.expect_keyword(kw::Trait)?;
 684         let ident = self.parse_ident()?;
 685         let mut tps = self.parse_generics()?;
 686
 687         // Parse optional colon and supertrait bounds.
 688         let had_colon = self.eat(&token::Colon);
 689         let span_at_colon = self.prev_token.span;
 690         let bounds = if had_colon {
 691             self.parse_generic_bounds(Some(self.prev_token.span))?
 692         } else {
 693             Vec::new()
 694         };
 695
 696         let span_before_eq = self.prev_token.span;
 697         if self.eat(&token::Eq) {
 698             // It's a trait alias.
 699             if had_colon {
 700                 let span = span_at_colon.to(span_before_eq);
 701                 self.struct_span_err(span, "bounds are not allowed on trait aliases").emit();
 702             }
 703
 704             let bounds = self.parse_generic_bounds(None)?;
 705             tps.where_clause = self.parse_where_clause()?;
 706             self.expect_semi()?;
 707
 708             let whole_span = lo.to(self.prev_token.span);
 709             if is_auto == IsAuto::Yes {
 710                 let msg = "trait aliases cannot be `auto`";
 711                 self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
 712             }
 713             if let Unsafe::Yes(_) = unsafety {
 714                 let msg = "trait aliases cannot be `unsafe`";
 715                 self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
 716             }
 717
 718             self.sess.gated_spans.gate(sym::trait_alias, whole_span);
 719
 720             Ok((ident, ItemKind::TraitAlias(tps, bounds)))
 721         } else {
 722             // It's a normal trait.
 723             tps.where_clause = self.parse_where_clause()?;
 724             let items = self.parse_item_list(attrs, |p| p.parse_trait_item(ForceCollect::No))?;
 725             Ok((ident, ItemKind::Trait(Box::new(TraitKind(is_auto, unsafety, tps, bounds, items)))))
 726         }
 727     }
 728
 729     pub fn parse_impl_item(
 730         &mut self,
 731         force_collect: ForceCollect,
 732     ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
 733         self.parse_assoc_item(|_| true, force_collect)
 734     }
 735
 736     pub fn parse_trait_item(
 737         &mut self,
 738         force_collect: ForceCollect,
 739     ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
 740         self.parse_assoc_item(|edition| edition >= Edition::Edition2018, force_collect)
 741     }
 742
 743     /// Parses associated items.
 744     fn parse_assoc_item(
 745         &mut self,
 746         req_name: ReqName,
 747         force_collect: ForceCollect,
 748     ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
 749         Ok(self.parse_item_(req_name, force_collect)?.map(
 750             |Item { attrs, id, span, vis, ident, kind, tokens }| {
 751                 let kind = match AssocItemKind::try_from(kind) {
 752                     Ok(kind) => kind,
 753                     Err(kind) => match kind {
 754                         ItemKind::Static(a, _, b) => {
 755                             self.struct_span_err(span, "associated `static` items are not allowed")
 756                                 .emit();
 757                             AssocItemKind::Const(Defaultness::Final, a, b)
 758                         }
 759                         _ => return self.error_bad_item_kind(span, &kind, "`trait`s or `impl`s"),
 760                     },
 761                 };
 762                 Some(P(Item { attrs, id, span, vis, ident, kind, tokens }))
 763             },
 764         ))
 765     }
 766
 767     /// Parses a `type` alias with the following grammar:
 768     /// ```
 769     /// TypeAlias = "type" Ident Generics {":" GenericBounds}? {"=" Ty}? ";" ;
 770     /// ```
 771     /// The `"type"` has already been eaten.
 772     fn parse_type_alias(&mut self, def: Defaultness) -> PResult<'a, ItemInfo> {
 773         let ident = self.parse_ident()?;
 774         let mut generics = self.parse_generics()?;
 775
 776         // Parse optional colon and param bounds.
 777         let bounds =
 778             if self.eat(&token::Colon) { self.parse_generic_bounds(None)? } else { Vec::new() };
 779         generics.where_clause = self.parse_where_clause()?;
 780
 781         let default = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
 782         self.expect_semi()?;
 783
 784         Ok((ident, ItemKind::TyAlias(Box::new(TyAliasKind(def, generics, bounds, default)))))
 785     }
 786
 787     /// Parses a `UseTree`.
 788     ///
 789     /// ```text
 790     /// USE_TREE = [`::`] `*` |
 791     ///            [`::`] `{` USE_TREE_LIST `}` |
 792     ///            PATH `::` `*` |
 793     ///            PATH `::` `{` USE_TREE_LIST `}` |
 794     ///            PATH [`as` IDENT]
 795     /// ```
 796     fn parse_use_tree(&mut self) -> PResult<'a, UseTree> {
 797         let lo = self.token.span;
 798
 799         let mut prefix = ast::Path { segments: Vec::new(), span: lo.shrink_to_lo(), tokens: None };
 800         let kind = if self.check(&token::OpenDelim(token::Brace))
 801             || self.check(&token::BinOp(token::Star))
 802             || self.is_import_coupler()
 803         {
 804             // `use *;` or `use ::*;` or `use {...};` or `use ::{...};`
 805             let mod_sep_ctxt = self.token.span.ctxt();
 806             if self.eat(&token::ModSep) {
 807                 prefix
 808                     .segments
 809                     .push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
 810             }
 811
 812             self.parse_use_tree_glob_or_nested()?
 813         } else {
 814             // `use path::*;` or `use path::{...};` or `use path;` or `use path as bar;`
 815             prefix = self.parse_path(PathStyle::Mod)?;
 816
 817             if self.eat(&token::ModSep) {
 818                 self.parse_use_tree_glob_or_nested()?
 819             } else {
 820                 UseTreeKind::Simple(self.parse_rename()?, DUMMY_NODE_ID, DUMMY_NODE_ID)
 821             }
 822         };
 823
 824         Ok(UseTree { prefix, kind, span: lo.to(self.prev_token.span) })
 825     }
 826
 827     /// Parses `*` or `{...}`.
 828     fn parse_use_tree_glob_or_nested(&mut self) -> PResult<'a, UseTreeKind> {
 829         Ok(if self.eat(&token::BinOp(token::Star)) {
 830             UseTreeKind::Glob
 831         } else {
 832             UseTreeKind::Nested(self.parse_use_tree_list()?)
 833         })
 834     }
 835
 836     /// Parses a `UseTreeKind::Nested(list)`.
 837     ///
 838     /// ```text
 839     /// USE_TREE_LIST = Ø | (USE_TREE `,`)* USE_TREE [`,`]
 840     /// ```
 841     fn parse_use_tree_list(&mut self) -> PResult<'a, Vec<(UseTree, ast::NodeId)>> {
 842         self.parse_delim_comma_seq(token::Brace, |p| Ok((p.parse_use_tree()?, DUMMY_NODE_ID)))
 843             .map(|(r, _)| r)
 844     }
 845
 846     fn parse_rename(&mut self) -> PResult<'a, Option<Ident>> {
 847         if self.eat_keyword(kw::As) { self.parse_ident_or_underscore().map(Some) } else { Ok(None) }
 848     }
 849
 850     fn parse_ident_or_underscore(&mut self) -> PResult<'a, Ident> {
 851         match self.token.ident() {
 852             Some((ident @ Ident { name: kw::Underscore, .. }, false)) => {
 853                 self.bump();
 854                 Ok(ident)
 855             }
 856             _ => self.parse_ident(),
 857         }
 858     }
 859
 860     /// Parses `extern crate` links.
 861     ///
 862     /// # Examples
 863     ///
 864     /// ```
 865     /// extern crate foo;
 866     /// extern crate bar as foo;
 867     /// ```
 868     fn parse_item_extern_crate(&mut self) -> PResult<'a, ItemInfo> {
 869         // Accept `extern crate name-like-this` for better diagnostics
 870         let orig_name = self.parse_crate_name_with_dashes()?;
 871         let (item_name, orig_name) = if let Some(rename) = self.parse_rename()? {
 872             (rename, Some(orig_name.name))
 873         } else {
 874             (orig_name, None)
 875         };
 876         self.expect_semi()?;
 877         Ok((item_name, ItemKind::ExternCrate(orig_name)))
 878     }
 879
 880     fn parse_crate_name_with_dashes(&mut self) -> PResult<'a, Ident> {
 881         let error_msg = "crate name using dashes are not valid in `extern crate` statements";
 882         let suggestion_msg = "if the original crate name uses dashes you need to use underscores \
 883                               in the code";
 884         let mut ident = if self.token.is_keyword(kw::SelfLower) {
 885             self.parse_path_segment_ident()
 886         } else {
 887             self.parse_ident()
 888         }?;
 889         let mut idents = vec![];
 890         let mut replacement = vec![];
 891         let mut fixed_crate_name = false;
 892         // Accept `extern crate name-like-this` for better diagnostics.
 893         let dash = token::BinOp(token::BinOpToken::Minus);
 894         if self.token == dash {
 895             // Do not include `-` as part of the expected tokens list.
 896             while self.eat(&dash) {
 897                 fixed_crate_name = true;
 898                 replacement.push((self.prev_token.span, "_".to_string()));
 899                 idents.push(self.parse_ident()?);
 900             }
 901         }
 902         if fixed_crate_name {
 903             let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
 904             let mut fixed_name = format!("{}", ident.name);
 905             for part in idents {
 906                 fixed_name.push_str(&format!("_{}", part.name));
 907             }
 908             ident = Ident::from_str_and_span(&fixed_name, fixed_name_sp);
 909
 910             self.struct_span_err(fixed_name_sp, error_msg)
 911                 .span_label(fixed_name_sp, "dash-separated idents are not valid")
 912                 .multipart_suggestion(suggestion_msg, replacement, Applicability::MachineApplicable)
 913                 .emit();
 914         }
 915         Ok(ident)
 916     }
 917
 918     /// Parses `extern` for foreign ABIs modules.
 919     ///
 920     /// `extern` is expected to have been consumed before calling this method.
 921     ///
 922     /// # Examples
 923     ///
 924     /// ```ignore (only-for-syntax-highlight)
 925     /// extern "C" {}
 926     /// extern {}
 927     /// ```
 928     fn parse_item_foreign_mod(
 929         &mut self,
 930         attrs: &mut Vec<Attribute>,
 931         unsafety: Unsafe,
 932     ) -> PResult<'a, ItemInfo> {
 933         let abi = self.parse_abi(); // ABI?
 934         let items = self.parse_item_list(attrs, |p| p.parse_foreign_item(ForceCollect::No))?;
 935         let module = ast::ForeignMod { unsafety, abi, items };
 936         Ok((Ident::empty(), ItemKind::ForeignMod(module)))
 937     }
 938
 939     /// Parses a foreign item (one in an `extern { ... }` block).
 940     pub fn parse_foreign_item(
 941         &mut self,
 942         force_collect: ForceCollect,
 943     ) -> PResult<'a, Option<Option<P<ForeignItem>>>> {
 944         Ok(self.parse_item_(|_| true, force_collect)?.map(
 945             |Item { attrs, id, span, vis, ident, kind, tokens }| {
 946                 let kind = match ForeignItemKind::try_from(kind) {
 947                     Ok(kind) => kind,
 948                     Err(kind) => match kind {
 949                         ItemKind::Const(_, a, b) => {
 950                             self.error_on_foreign_const(span, ident);
 951                             ForeignItemKind::Static(a, Mutability::Not, b)
 952                         }
 953                         _ => return self.error_bad_item_kind(span, &kind, "`extern` blocks"),
 954                     },
 955                 };
 956                 Some(P(Item { attrs, id, span, vis, ident, kind, tokens }))
 957             },
 958         ))
 959     }
 960
 961     fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &str) -> Option<T> {
 962         let span = self.sess.source_map().guess_head_span(span);
 963         let descr = kind.descr();
 964         self.struct_span_err(span, &format!("{} is not supported in {}", descr, ctx))
 965             .help(&format!("consider moving the {} out to a nearby module scope", descr))
 966             .emit();
 967         None
 968     }
 969
 970     fn error_on_foreign_const(&self, span: Span, ident: Ident) {
 971         self.struct_span_err(ident.span, "extern items cannot be `const`")
 972             .span_suggestion(
 973                 span.with_hi(ident.span.lo()),
 974                 "try using a static value",
 975                 "static ".to_string(),
 976                 Applicability::MachineApplicable,
 977             )
 978             .note("for more information, visit https://doc.rust-lang.org/std/keyword.extern.html")
 979             .emit();
 980     }
 981
 982     fn is_unsafe_foreign_mod(&self) -> bool {
 983         self.token.is_keyword(kw::Unsafe)
 984             && self.is_keyword_ahead(1, &[kw::Extern])
 985             && self.look_ahead(
 986                 2 + self.look_ahead(2, |t| t.can_begin_literal_maybe_minus() as usize),
 987                 |t| t.kind == token::OpenDelim(token::Brace),
 988             )
 989     }
 990
 991     fn is_static_global(&mut self) -> bool {
 992         if self.check_keyword(kw::Static) {
 993             // Check if this could be a closure.
 994             !self.look_ahead(1, |token| {
 995                 if token.is_keyword(kw::Move) {
 996                     return true;
 997                 }
 998                 matches!(token.kind, token::BinOp(token::Or) | token::OrOr)
 999             })
1000         } else {
1001             false
1002         }
1003     }
1004
1005     /// Recover on `const mut` with `const` already eaten.
1006     fn recover_const_mut(&mut self, const_span: Span) {
1007         if self.eat_keyword(kw::Mut) {
1008             let span = self.prev_token.span;
1009             self.struct_span_err(span, "const globals cannot be mutable")
1010                 .span_label(span, "cannot be mutable")
1011                 .span_suggestion(
1012                     const_span,
1013                     "you might want to declare a static instead",
1014                     "static".to_owned(),
1015                     Applicability::MaybeIncorrect,
1016                 )
1017                 .emit();
1018         }
1019     }
1020
1021     /// Recover on `const impl` with `const` already eaten.
1022     fn recover_const_impl(
1023         &mut self,
1024         const_span: Span,
1025         attrs: &mut Vec<Attribute>,
1026         defaultness: Defaultness,
1027     ) -> PResult<'a, ItemInfo> {
1028         let impl_span = self.token.span;
1029         let mut err = self.expected_ident_found();
1030
1031         // Only try to recover if this is implementing a trait for a type
1032         let mut impl_info = match self.parse_item_impl(attrs, defaultness) {
1033             Ok(impl_info) => impl_info,
1034             Err(mut recovery_error) => {
1035                 // Recovery failed, raise the "expected identifier" error
1036                 recovery_error.cancel();
1037                 return Err(err);
1038             }
1039         };
1040
1041         match impl_info.1 {
1042             ItemKind::Impl(box ImplKind {
1043                 of_trait: Some(ref trai), ref mut constness, ..
1044             }) => {
1045                 *constness = Const::Yes(const_span);
1046
1047                 let before_trait = trai.path.span.shrink_to_lo();
1048                 let const_up_to_impl = const_span.with_hi(impl_span.lo());
1049                 err.multipart_suggestion(
1050                     "you might have meant to write a const trait impl",
1051                     vec![(const_up_to_impl, "".to_owned()), (before_trait, "const ".to_owned())],
1052                     Applicability::MaybeIncorrect,
1053                 )
1054                 .emit();
1055             }
1056             ItemKind::Impl { .. } => return Err(err),
1057             _ => unreachable!(),
1058         }
1059
1060         Ok(impl_info)
1061     }
1062
1063     /// Parse `["const" | ("static" "mut"?)] $ident ":" $ty (= $expr)?` with
1064     /// `["const" | ("static" "mut"?)]` already parsed and stored in `m`.
1065     ///
1066     /// When `m` is `"const"`, `$ident` may also be `"_"`.
1067     fn parse_item_global(
1068         &mut self,
1069         m: Option<Mutability>,
1070     ) -> PResult<'a, (Ident, P<Ty>, Option<P<ast::Expr>>)> {
1071         let id = if m.is_none() { self.parse_ident_or_underscore() } else { self.parse_ident() }?;
1072
1073         // Parse the type of a `const` or `static mut?` item.
1074         // That is, the `":" $ty` fragment.
1075         let ty = if self.eat(&token::Colon) {
1076             self.parse_ty()?
1077         } else {
1078             self.recover_missing_const_type(id, m)
1079         };
1080
1081         let expr = if self.eat(&token::Eq) { Some(self.parse_expr()?) } else { None };
1082         self.expect_semi()?;
1083         Ok((id, ty, expr))
1084     }
1085
1086     /// We were supposed to parse `:` but the `:` was missing.
1087     /// This means that the type is missing.
1088     fn recover_missing_const_type(&mut self, id: Ident, m: Option<Mutability>) -> P<Ty> {
1089         // Construct the error and stash it away with the hope
1090         // that typeck will later enrich the error with a type.
1091         let kind = match m {
1092             Some(Mutability::Mut) => "static mut",
1093             Some(Mutability::Not) => "static",
1094             None => "const",
1095         };
1096         let mut err = self.struct_span_err(id.span, &format!("missing type for `{}` item", kind));
1097         err.span_suggestion(
1098             id.span,
1099             "provide a type for the item",
1100             format!("{}: <type>", id),
1101             Applicability::HasPlaceholders,
1102         );
1103         err.stash(id.span, StashKey::ItemNoType);
1104
1105         // The user intended that the type be inferred,
1106         // so treat this as if the user wrote e.g. `const A: _ = expr;`.
1107         P(Ty { kind: TyKind::Infer, span: id.span, id: ast::DUMMY_NODE_ID, tokens: None })
1108     }
1109
1110     /// Parses an enum declaration.
1111     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
1112         let id = self.parse_ident()?;
1113         let mut generics = self.parse_generics()?;
1114         generics.where_clause = self.parse_where_clause()?;
1115
1116         let (variants, _) =
1117             self.parse_delim_comma_seq(token::Brace, |p| p.parse_enum_variant()).map_err(|e| {
1118                 self.recover_stmt();
1119                 e
1120             })?;
1121
1122         let enum_definition = EnumDef { variants: variants.into_iter().flatten().collect() };
1123         Ok((id, ItemKind::Enum(enum_definition, generics)))
1124     }
1125
1126     fn parse_enum_variant(&mut self) -> PResult<'a, Option<Variant>> {
1127         let variant_attrs = self.parse_outer_attributes()?;
1128         self.collect_tokens_trailing_token(
1129             variant_attrs,
1130             ForceCollect::No,
1131             |this, variant_attrs| {
1132                 let vlo = this.token.span;
1133
1134                 let vis = this.parse_visibility(FollowedByType::No)?;
1135                 if !this.recover_nested_adt_item(kw::Enum)? {
1136                     return Ok((None, TrailingToken::None));
1137                 }
1138                 let ident = this.parse_field_ident("enum", vlo)?;
1139
1140                 let struct_def = if this.check(&token::OpenDelim(token::Brace)) {
1141                     // Parse a struct variant.
1142                     let (fields, recovered) = this.parse_record_struct_body("struct")?;
1143                     VariantData::Struct(fields, recovered)
1144                 } else if this.check(&token::OpenDelim(token::Paren)) {
1145                     VariantData::Tuple(this.parse_tuple_struct_body()?, DUMMY_NODE_ID)
1146                 } else {
1147                     VariantData::Unit(DUMMY_NODE_ID)
1148                 };
1149
1150                 let disr_expr =
1151                     if this.eat(&token::Eq) { Some(this.parse_anon_const_expr()?) } else { None };
1152
1153                 let vr = ast::Variant {
1154                     ident,
1155                     vis,
1156                     id: DUMMY_NODE_ID,
1157                     attrs: variant_attrs.into(),
1158                     data: struct_def,
1159                     disr_expr,
1160                     span: vlo.to(this.prev_token.span),
1161                     is_placeholder: false,
1162                 };
1163
1164                 Ok((Some(vr), TrailingToken::MaybeComma))
1165             },
1166         )
1167     }
1168
1169     /// Parses `struct Foo { ... }`.
1170     fn parse_item_struct(&mut self) -> PResult<'a, ItemInfo> {
1171         let class_name = self.parse_ident()?;
1172
1173         let mut generics = self.parse_generics()?;
1174
1175         // There is a special case worth noting here, as reported in issue #17904.
1176         // If we are parsing a tuple struct it is the case that the where clause
1177         // should follow the field list. Like so:
1178         //
1179         // struct Foo<T>(T) where T: Copy;
1180         //
1181         // If we are parsing a normal record-style struct it is the case
1182         // that the where clause comes before the body, and after the generics.
1183         // So if we look ahead and see a brace or a where-clause we begin
1184         // parsing a record style struct.
1185         //
1186         // Otherwise if we look ahead and see a paren we parse a tuple-style
1187         // struct.
1188
1189         let vdata = if self.token.is_keyword(kw::Where) {
1190             generics.where_clause = self.parse_where_clause()?;
1191             if self.eat(&token::Semi) {
1192                 // If we see a: `struct Foo<T> where T: Copy;` style decl.
1193                 VariantData::Unit(DUMMY_NODE_ID)
1194             } else {
1195                 // If we see: `struct Foo<T> where T: Copy { ... }`
1196                 let (fields, recovered) = self.parse_record_struct_body("struct")?;
1197                 VariantData::Struct(fields, recovered)
1198             }
1199         // No `where` so: `struct Foo<T>;`
1200         } else if self.eat(&token::Semi) {
1201             VariantData::Unit(DUMMY_NODE_ID)
1202         // Record-style struct definition
1203         } else if self.token == token::OpenDelim(token::Brace) {
1204             let (fields, recovered) = self.parse_record_struct_body("struct")?;
1205             VariantData::Struct(fields, recovered)
1206         // Tuple-style struct definition with optional where-clause.
1207         } else if self.token == token::OpenDelim(token::Paren) {
1208             let body = VariantData::Tuple(self.parse_tuple_struct_body()?, DUMMY_NODE_ID);
1209             generics.where_clause = self.parse_where_clause()?;
1210             self.expect_semi()?;
1211             body
1212         } else {
1213             let token_str = super::token_descr(&self.token);
1214             let msg = &format!(
1215                 "expected `where`, `{{`, `(`, or `;` after struct name, found {}",
1216                 token_str
1217             );
1218             let mut err = self.struct_span_err(self.token.span, msg);
1219             err.span_label(self.token.span, "expected `where`, `{`, `(`, or `;` after struct name");
1220             return Err(err);
1221         };
1222
1223         Ok((class_name, ItemKind::Struct(vdata, generics)))
1224     }
1225
1226     /// Parses `union Foo { ... }`.
1227     fn parse_item_union(&mut self) -> PResult<'a, ItemInfo> {
1228         let class_name = self.parse_ident()?;
1229
1230         let mut generics = self.parse_generics()?;
1231
1232         let vdata = if self.token.is_keyword(kw::Where) {
1233             generics.where_clause = self.parse_where_clause()?;
1234             let (fields, recovered) = self.parse_record_struct_body("union")?;
1235             VariantData::Struct(fields, recovered)
1236         } else if self.token == token::OpenDelim(token::Brace) {
1237             let (fields, recovered) = self.parse_record_struct_body("union")?;
1238             VariantData::Struct(fields, recovered)
1239         } else {
1240             let token_str = super::token_descr(&self.token);
1241             let msg = &format!("expected `where` or `{{` after union name, found {}", token_str);
1242             let mut err = self.struct_span_err(self.token.span, msg);
1243             err.span_label(self.token.span, "expected `where` or `{` after union name");
1244             return Err(err);
1245         };
1246
1247         Ok((class_name, ItemKind::Union(vdata, generics)))
1248     }
1249
1250     fn parse_record_struct_body(
1251         &mut self,
1252         adt_ty: &str,
1253     ) -> PResult<'a, (Vec<FieldDef>, /* recovered */ bool)> {
1254         let mut fields = Vec::new();
1255         let mut recovered = false;
1256         if self.eat(&token::OpenDelim(token::Brace)) {
1257             while self.token != token::CloseDelim(token::Brace) {
1258                 let field = self.parse_field_def(adt_ty).map_err(|e| {
1259                     self.consume_block(token::Brace, ConsumeClosingDelim::No);
1260                     recovered = true;
1261                     e
1262                 });
1263                 match field {
1264                     Ok(field) => fields.push(field),
1265                     Err(mut err) => {
1266                         err.emit();
1267                         break;
1268                     }
1269                 }
1270             }
1271             self.eat(&token::CloseDelim(token::Brace));
1272         } else {
1273             let token_str = super::token_descr(&self.token);
1274             let msg = &format!("expected `where`, or `{{` after struct name, found {}", token_str);
1275             let mut err = self.struct_span_err(self.token.span, msg);
1276             err.span_label(self.token.span, "expected `where`, or `{` after struct name");
1277             return Err(err);
1278         }
1279
1280         Ok((fields, recovered))
1281     }
1282
1283     fn parse_tuple_struct_body(&mut self) -> PResult<'a, Vec<FieldDef>> {
1284         // This is the case where we find `struct Foo<T>(T) where T: Copy;`
1285         // Unit like structs are handled in parse_item_struct function
1286         self.parse_paren_comma_seq(|p| {
1287             let attrs = p.parse_outer_attributes()?;
1288             p.collect_tokens_trailing_token(attrs, ForceCollect::No, |p, attrs| {
1289                 let lo = p.token.span;
1290                 let vis = p.parse_visibility(FollowedByType::Yes)?;
1291                 let ty = p.parse_ty()?;
1292
1293                 Ok((
1294                     FieldDef {
1295                         span: lo.to(ty.span),
1296                         vis,
1297                         ident: None,
1298                         id: DUMMY_NODE_ID,
1299                         ty,
1300                         attrs: attrs.into(),
1301                         is_placeholder: false,
1302                     },
1303                     TrailingToken::MaybeComma,
1304                 ))
1305             })
1306         })
1307         .map(|(r, _)| r)
1308     }
1309
1310     /// Parses an element of a struct declaration.
1311     fn parse_field_def(&mut self, adt_ty: &str) -> PResult<'a, FieldDef> {
1312         let attrs = self.parse_outer_attributes()?;
1313         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
1314             let lo = this.token.span;
1315             let vis = this.parse_visibility(FollowedByType::No)?;
1316             Ok((this.parse_single_struct_field(adt_ty, lo, vis, attrs)?, TrailingToken::None))
1317         })
1318     }
1319
1320     /// Parses a structure field declaration.
1321     fn parse_single_struct_field(
1322         &mut self,
1323         adt_ty: &str,
1324         lo: Span,
1325         vis: Visibility,
1326         attrs: Vec<Attribute>,
1327     ) -> PResult<'a, FieldDef> {
1328         let mut seen_comma: bool = false;
1329         let a_var = self.parse_name_and_ty(adt_ty, lo, vis, attrs)?;
1330         if self.token == token::Comma {
1331             seen_comma = true;
1332         }
1333         match self.token.kind {
1334             token::Comma => {
1335                 self.bump();
1336             }
1337             token::CloseDelim(token::Brace) => {}
1338             token::DocComment(..) => {
1339                 let previous_span = self.prev_token.span;
1340                 let mut err = self.span_err(self.token.span, Error::UselessDocComment);
1341                 self.bump(); // consume the doc comment
1342                 let comma_after_doc_seen = self.eat(&token::Comma);
1343                 // `seen_comma` is always false, because we are inside doc block
1344                 // condition is here to make code more readable
1345                 if !seen_comma && comma_after_doc_seen {
1346                     seen_comma = true;
1347                 }
1348                 if comma_after_doc_seen || self.token == token::CloseDelim(token::Brace) {
1349                     err.emit();
1350                 } else {
1351                     if !seen_comma {
1352                         let sp = self.sess.source_map().next_point(previous_span);
1353                         err.span_suggestion(
1354                             sp,
1355                             "missing comma here",
1356                             ",".into(),
1357                             Applicability::MachineApplicable,
1358                         );
1359                     }
1360                     return Err(err);
1361                 }
1362             }
1363             _ => {
1364                 let sp = self.prev_token.span.shrink_to_hi();
1365                 let mut err = self.struct_span_err(
1366                     sp,
1367                     &format!("expected `,`, or `}}`, found {}", super::token_descr(&self.token)),
1368                 );
1369
1370                 // Try to recover extra trailing angle brackets
1371                 let mut recovered = false;
1372                 if let TyKind::Path(_, Path { segments, .. }) = &a_var.ty.kind {
1373                     if let Some(last_segment) = segments.last() {
1374                         recovered = self.check_trailing_angle_brackets(
1375                             last_segment,
1376                             &[&token::Comma, &token::CloseDelim(token::Brace)],
1377                         );
1378                         if recovered {
1379                             // Handle a case like `Vec<u8>>,` where we can continue parsing fields
1380                             // after the comma
1381                             self.eat(&token::Comma);
1382                             // `check_trailing_angle_brackets` already emitted a nicer error
1383                             err.cancel();
1384                         }
1385                     }
1386                 }
1387
1388                 if self.token.is_ident() {
1389                     // This is likely another field; emit the diagnostic and keep going
1390                     err.span_suggestion(
1391                         sp,
1392                         "try adding a comma",
1393                         ",".into(),
1394                         Applicability::MachineApplicable,
1395                     );
1396                     err.emit();
1397                     recovered = true;
1398                 }
1399
1400                 if recovered {
1401                     // Make sure an error was emitted (either by recovering an angle bracket,
1402                     // or by finding an identifier as the next token), since we're
1403                     // going to continue parsing
1404                     assert!(self.sess.span_diagnostic.has_errors());
1405                 } else {
1406                     return Err(err);
1407                 }
1408             }
1409         }
1410         Ok(a_var)
1411     }
1412
1413     fn expect_field_ty_separator(&mut self) -> PResult<'a, ()> {
1414         if let Err(mut err) = self.expect(&token::Colon) {
1415             let sm = self.sess.source_map();
1416             let eq_typo = self.token.kind == token::Eq && self.look_ahead(1, |t| t.is_path_start());
1417             let semi_typo = self.token.kind == token::Semi
1418                 && self.look_ahead(1, |t| {
1419                     t.is_path_start()
1420                     // We check that we are in a situation like `foo; bar` to avoid bad suggestions
1421                     // when there's no type and `;` was used instead of a comma.
1422                     && match (sm.lookup_line(self.token.span.hi()), sm.lookup_line(t.span.lo())) {
1423                         (Ok(l), Ok(r)) => l.line == r.line,
1424                         _ => true,
1425                     }
1426                 });
1427             if eq_typo || semi_typo {
1428                 self.bump();
1429                 // Gracefully handle small typos.
1430                 err.span_suggestion_short(
1431                     self.prev_token.span,
1432                     "field names and their types are separated with `:`",
1433                     ":".to_string(),
1434                     Applicability::MachineApplicable,
1435                 );
1436                 err.emit();
1437             } else {
1438                 return Err(err);
1439             }
1440         }
1441         Ok(())
1442     }
1443
1444     /// Parses a structure field.
1445     fn parse_name_and_ty(
1446         &mut self,
1447         adt_ty: &str,
1448         lo: Span,
1449         vis: Visibility,
1450         attrs: Vec<Attribute>,
1451     ) -> PResult<'a, FieldDef> {
1452         let name = self.parse_field_ident(adt_ty, lo)?;
1453         self.expect_field_ty_separator()?;
1454         let ty = self.parse_ty()?;
1455         if self.token.kind == token::Eq {
1456             self.bump();
1457             let const_expr = self.parse_anon_const_expr()?;
1458             let sp = ty.span.shrink_to_hi().to(const_expr.value.span);
1459             self.struct_span_err(sp, "default values on `struct` fields aren't supported")
1460                 .span_suggestion(
1461                     sp,
1462                     "remove this unsupported default value",
1463                     String::new(),
1464                     Applicability::MachineApplicable,
1465                 )
1466                 .emit();
1467         }
1468         Ok(FieldDef {
1469             span: lo.to(self.prev_token.span),
1470             ident: Some(name),
1471             vis,
1472             id: DUMMY_NODE_ID,
1473             ty,
1474             attrs: attrs.into(),
1475             is_placeholder: false,
1476         })
1477     }
1478
1479     /// Parses a field identifier. Specialized version of `parse_ident_common`
1480     /// for better diagnostics and suggestions.
1481     fn parse_field_ident(&mut self, adt_ty: &str, lo: Span) -> PResult<'a, Ident> {
1482         let (ident, is_raw) = self.ident_or_err()?;
1483         if !is_raw && ident.is_reserved() {
1484             let err = if self.check_fn_front_matter(false) {
1485                 // We use `parse_fn` to get a span for the function
1486                 if let Err(mut db) = self.parse_fn(&mut Vec::new(), |_| true, lo) {
1487                     db.delay_as_bug();
1488                 }
1489                 let mut err = self.struct_span_err(
1490                     lo.to(self.prev_token.span),
1491                     &format!("functions are not allowed in {} definitions", adt_ty),
1492                 );
1493                 err.help("unlike in C++, Java, and C#, functions are declared in `impl` blocks");
1494                 err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
1495                 err
1496             } else {
1497                 self.expected_ident_found()
1498             };
1499             return Err(err);
1500         }
1501         self.bump();
1502         Ok(ident)
1503     }
1504
1505     /// Parses a declarative macro 2.0 definition.
1506     /// The `macro` keyword has already been parsed.
1507     /// ```
1508     /// MacBody = "{" TOKEN_STREAM "}" ;
1509     /// MacParams = "(" TOKEN_STREAM ")" ;
1510     /// DeclMac = "macro" Ident MacParams? MacBody ;
1511     /// ```
1512     fn parse_item_decl_macro(&mut self, lo: Span) -> PResult<'a, ItemInfo> {
1513         let ident = self.parse_ident()?;
1514         let body = if self.check(&token::OpenDelim(token::Brace)) {
1515             self.parse_mac_args()? // `MacBody`
1516         } else if self.check(&token::OpenDelim(token::Paren)) {
1517             let params = self.parse_token_tree(); // `MacParams`
1518             let pspan = params.span();
1519             if !self.check(&token::OpenDelim(token::Brace)) {
1520                 return self.unexpected();
1521             }
1522             let body = self.parse_token_tree(); // `MacBody`
1523             // Convert `MacParams MacBody` into `{ MacParams => MacBody }`.
1524             let bspan = body.span();
1525             let arrow = TokenTree::token(token::FatArrow, pspan.between(bspan)); // `=>`
1526             let tokens = TokenStream::new(vec![params.into(), arrow.into(), body.into()]);
1527             let dspan = DelimSpan::from_pair(pspan.shrink_to_lo(), bspan.shrink_to_hi());
1528             P(MacArgs::Delimited(dspan, MacDelimiter::Brace, tokens))
1529         } else {
1530             return self.unexpected();
1531         };
1532
1533         self.sess.gated_spans.gate(sym::decl_macro, lo.to(self.prev_token.span));
1534         Ok((ident, ItemKind::MacroDef(ast::MacroDef { body, macro_rules: false })))
1535     }
1536
1537     /// Is this unambiguously the start of a `macro_rules! foo` item definition?
1538     fn is_macro_rules_item(&mut self) -> bool {
1539         self.check_keyword(kw::MacroRules)
1540             && self.look_ahead(1, |t| *t == token::Not)
1541             && self.look_ahead(2, |t| t.is_ident())
1542     }
1543
1544     /// Parses a `macro_rules! foo { ... }` declarative macro.
1545     fn parse_item_macro_rules(&mut self, vis: &Visibility) -> PResult<'a, ItemInfo> {
1546         self.expect_keyword(kw::MacroRules)?; // `macro_rules`
1547         self.expect(&token::Not)?; // `!`
1548
1549         let ident = self.parse_ident()?;
1550
1551         if self.eat(&token::Not) {
1552             // Handle macro_rules! foo!
1553             let span = self.prev_token.span;
1554             self.struct_span_err(span, "macro names aren't followed by a `!`")
1555                 .span_suggestion(
1556                     span,
1557                     "remove the `!`",
1558                     "".to_owned(),
1559                     Applicability::MachineApplicable,
1560                 )
1561                 .emit();
1562         }
1563
1564         let body = self.parse_mac_args()?;
1565         self.eat_semi_for_macro_if_needed(&body);
1566         self.complain_if_pub_macro(vis, true);
1567
1568         Ok((ident, ItemKind::MacroDef(ast::MacroDef { body, macro_rules: true })))
1569     }
1570
1571     /// Item macro invocations or `macro_rules!` definitions need inherited visibility.
1572     /// If that's not the case, emit an error.
1573     fn complain_if_pub_macro(&self, vis: &Visibility, macro_rules: bool) {
1574         if let VisibilityKind::Inherited = vis.kind {
1575             return;
1576         }
1577
1578         let vstr = pprust::vis_to_string(vis);
1579         let vstr = vstr.trim_end();
1580         if macro_rules {
1581             let msg = format!("can't qualify macro_rules invocation with `{}`", vstr);
1582             self.struct_span_err(vis.span, &msg)
1583                 .span_suggestion(
1584                     vis.span,
1585                     "try exporting the macro",
1586                     "#[macro_export]".to_owned(),
1587                     Applicability::MaybeIncorrect, // speculative
1588                 )
1589                 .emit();
1590         } else {
1591             self.struct_span_err(vis.span, "can't qualify macro invocation with `pub`")
1592                 .span_suggestion(
1593                     vis.span,
1594                     "remove the visibility",
1595                     String::new(),
1596                     Applicability::MachineApplicable,
1597                 )
1598                 .help(&format!("try adjusting the macro to put `{}` inside the invocation", vstr))
1599                 .emit();
1600         }
1601     }
1602
1603     fn eat_semi_for_macro_if_needed(&mut self, args: &MacArgs) {
1604         if args.need_semicolon() && !self.eat(&token::Semi) {
1605             self.report_invalid_macro_expansion_item(args);
1606         }
1607     }
1608
1609     fn report_invalid_macro_expansion_item(&self, args: &MacArgs) {
1610         let span = args.span().expect("undelimited macro call");
1611         let mut err = self.struct_span_err(
1612             span,
1613             "macros that expand to items must be delimited with braces or followed by a semicolon",
1614         );
1615         if self.unclosed_delims.is_empty() {
1616             let DelimSpan { open, close } = match args {
1617                 MacArgs::Empty | MacArgs::Eq(..) => unreachable!(),
1618                 MacArgs::Delimited(dspan, ..) => *dspan,
1619             };
1620             err.multipart_suggestion(
1621                 "change the delimiters to curly braces",
1622                 vec![(open, "{".to_string()), (close, '}'.to_string())],
1623                 Applicability::MaybeIncorrect,
1624             );
1625         } else {
1626             err.span_suggestion(
1627                 span,
1628                 "change the delimiters to curly braces",
1629                 " { /* items */ }".to_string(),
1630                 Applicability::HasPlaceholders,
1631             );
1632         }
1633         err.span_suggestion(
1634             span.shrink_to_hi(),
1635             "add a semicolon",
1636             ';'.to_string(),
1637             Applicability::MaybeIncorrect,
1638         );
1639         err.emit();
1640     }
1641
1642     /// Checks if current token is one of tokens which cannot be nested like `kw::Enum`. In case
1643     /// it is, we try to parse the item and report error about nested types.
1644     fn recover_nested_adt_item(&mut self, keyword: Symbol) -> PResult<'a, bool> {
1645         if (self.token.is_keyword(kw::Enum)
1646             || self.token.is_keyword(kw::Struct)
1647             || self.token.is_keyword(kw::Union))
1648             && self.look_ahead(1, |t| t.is_ident())
1649         {
1650             let kw_token = self.token.clone();
1651             let kw_str = pprust::token_to_string(&kw_token);
1652             let item = self.parse_item(ForceCollect::No)?;
1653
1654             self.struct_span_err(
1655                 kw_token.span,
1656                 &format!("`{}` definition cannot be nested inside `{}`", kw_str, keyword),
1657             )
1658             .span_suggestion(
1659                 item.unwrap().span,
1660                 &format!("consider creating a new `{}` definition instead of nesting", kw_str),
1661                 String::new(),
1662                 Applicability::MaybeIncorrect,
1663             )
1664             .emit();
1665             // We successfully parsed the item but we must inform the caller about nested problem.
1666             return Ok(false);
1667         }
1668         Ok(true)
1669     }
1670 }
1671
1672 /// The parsing configuration used to parse a parameter list (see `parse_fn_params`).
1673 ///
1674 /// The function decides if, per-parameter `p`, `p` must have a pattern or just a type.
1675 type ReqName = fn(Edition) -> bool;
1676
1677 /// Parsing of functions and methods.
1678 impl<'a> Parser<'a> {
1679     /// Parse a function starting from the front matter (`const ...`) to the body `{ ... }` or `;`.
1680     fn parse_fn(
1681         &mut self,
1682         attrs: &mut Vec<Attribute>,
1683         req_name: ReqName,
1684         sig_lo: Span,
1685     ) -> PResult<'a, (Ident, FnSig, Generics, Option<P<Block>>)> {
1686         let header = self.parse_fn_front_matter()?; // `const ... fn`
1687         let ident = self.parse_ident()?; // `foo`
1688         let mut generics = self.parse_generics()?; // `<'a, T, ...>`
1689         let decl = self.parse_fn_decl(req_name, AllowPlus::Yes, RecoverReturnSign::Yes)?; // `(p: u8, ...)`
1690         generics.where_clause = self.parse_where_clause()?; // `where T: Ord`
1691
1692         let mut sig_hi = self.prev_token.span;
1693         let body = self.parse_fn_body(attrs, &ident, &mut sig_hi)?; // `;` or `{ ... }`.
1694         let fn_sig_span = sig_lo.to(sig_hi);
1695         Ok((ident, FnSig { header, decl, span: fn_sig_span }, generics, body))
1696     }
1697
1698     /// Parse the "body" of a function.
1699     /// This can either be `;` when there's no body,
1700     /// or e.g. a block when the function is a provided one.
1701     fn parse_fn_body(
1702         &mut self,
1703         attrs: &mut Vec<Attribute>,
1704         ident: &Ident,
1705         sig_hi: &mut Span,
1706     ) -> PResult<'a, Option<P<Block>>> {
1707         let (inner_attrs, body) = if self.eat(&token::Semi) {
1708             // Include the trailing semicolon in the span of the signature
1709             *sig_hi = self.prev_token.span;
1710             (Vec::new(), None)
1711         } else if self.check(&token::OpenDelim(token::Brace)) || self.token.is_whole_block() {
1712             self.parse_inner_attrs_and_block().map(|(attrs, body)| (attrs, Some(body)))?
1713         } else if self.token.kind == token::Eq {
1714             // Recover `fn foo() = $expr;`.
1715             self.bump(); // `=`
1716             let eq_sp = self.prev_token.span;
1717             let _ = self.parse_expr()?;
1718             self.expect_semi()?; // `;`
1719             let span = eq_sp.to(self.prev_token.span);
1720             self.struct_span_err(span, "function body cannot be `= expression;`")
1721                 .multipart_suggestion(
1722                     "surround the expression with `{` and `}` instead of `=` and `;`",
1723                     vec![(eq_sp, "{".to_string()), (self.prev_token.span, " }".to_string())],
1724                     Applicability::MachineApplicable,
1725                 )
1726                 .emit();
1727             (Vec::new(), Some(self.mk_block_err(span)))
1728         } else {
1729             if let Err(mut err) =
1730                 self.expected_one_of_not_found(&[], &[token::Semi, token::OpenDelim(token::Brace)])
1731             {
1732                 if self.token.kind == token::CloseDelim(token::Brace) {
1733                     // The enclosing `mod`, `trait` or `impl` is being closed, so keep the `fn` in
1734                     // the AST for typechecking.
1735                     err.span_label(ident.span, "while parsing this `fn`");
1736                     err.emit();
1737                 } else {
1738                     return Err(err);
1739                 }
1740             }
1741             (Vec::new(), None)
1742         };
1743         attrs.extend(inner_attrs);
1744         Ok(body)
1745     }
1746
1747     /// Is the current token the start of an `FnHeader` / not a valid parse?
1748     ///
1749     /// `check_pub` adds additional `pub` to the checks in case users place it
1750     /// wrongly, can be used to ensure `pub` never comes after `default`.
1751     pub(super) fn check_fn_front_matter(&mut self, check_pub: bool) -> bool {
1752         // We use an over-approximation here.
1753         // `const const`, `fn const` won't parse, but we're not stepping over other syntax either.
1754         // `pub` is added in case users got confused with the ordering like `async pub fn`,
1755         // only if it wasn't preceeded by `default` as `default pub` is invalid.
1756         let quals: &[Symbol] = if check_pub {
1757             &[kw::Pub, kw::Const, kw::Async, kw::Unsafe, kw::Extern]
1758         } else {
1759             &[kw::Const, kw::Async, kw::Unsafe, kw::Extern]
1760         };
1761         self.check_keyword(kw::Fn) // Definitely an `fn`.
1762             // `$qual fn` or `$qual $qual`:
1763             || quals.iter().any(|&kw| self.check_keyword(kw))
1764                 && self.look_ahead(1, |t| {
1765                     // `$qual fn`, e.g. `const fn` or `async fn`.
1766                     t.is_keyword(kw::Fn)
1767                     // Two qualifiers `$qual $qual` is enough, e.g. `async unsafe`.
1768                     || t.is_non_raw_ident_where(|i| quals.contains(&i.name)
1769                         // Rule out 2015 `const async: T = val`.
1770                         && i.is_reserved()
1771                         // Rule out unsafe extern block.
1772                         && !self.is_unsafe_foreign_mod())
1773                 })
1774             // `extern ABI fn`
1775             || self.check_keyword(kw::Extern)
1776                 && self.look_ahead(1, |t| t.can_begin_literal_maybe_minus())
1777                 && self.look_ahead(2, |t| t.is_keyword(kw::Fn))
1778     }
1779
1780     /// Parses all the "front matter" (or "qualifiers") for a `fn` declaration,
1781     /// up to and including the `fn` keyword. The formal grammar is:
1782     ///
1783     /// ```
1784     /// Extern = "extern" StringLit? ;
1785     /// FnQual = "const"? "async"? "unsafe"? Extern? ;
1786     /// FnFrontMatter = FnQual "fn" ;
1787     /// ```
1788     pub(super) fn parse_fn_front_matter(&mut self) -> PResult<'a, FnHeader> {
1789         let sp_start = self.token.span;
1790         let constness = self.parse_constness();
1791
1792         let async_start_sp = self.token.span;
1793         let asyncness = self.parse_asyncness();
1794
1795         let unsafe_start_sp = self.token.span;
1796         let unsafety = self.parse_unsafety();
1797
1798         let ext_start_sp = self.token.span;
1799         let ext = self.parse_extern();
1800
1801         if let Async::Yes { span, .. } = asyncness {
1802             self.ban_async_in_2015(span);
1803         }
1804
1805         if !self.eat_keyword(kw::Fn) {
1806             // It is possible for `expect_one_of` to recover given the contents of
1807             // `self.expected_tokens`, therefore, do not use `self.unexpected()` which doesn't
1808             // account for this.
1809             match self.expect_one_of(&[], &[]) {
1810                 Ok(true) => {}
1811                 Ok(false) => unreachable!(),
1812                 Err(mut err) => {
1813                     // Qualifier keywords ordering check
1814
1815                     // This will allow the machine fix to directly place the keyword in the correct place
1816                     let current_qual_sp = if self.check_keyword(kw::Const) {
1817                         Some(async_start_sp)
1818                     } else if self.check_keyword(kw::Async) {
1819                         Some(unsafe_start_sp)
1820                     } else if self.check_keyword(kw::Unsafe) {
1821                         Some(ext_start_sp)
1822                     } else {
1823                         None
1824                     };
1825
1826                     if let Some(current_qual_sp) = current_qual_sp {
1827                         let current_qual_sp = current_qual_sp.to(self.prev_token.span);
1828                         if let Ok(current_qual) = self.span_to_snippet(current_qual_sp) {
1829                             let invalid_qual_sp = self.token.uninterpolated_span();
1830                             let invalid_qual = self.span_to_snippet(invalid_qual_sp).unwrap();
1831
1832                             err.span_suggestion(
1833                                 current_qual_sp.to(invalid_qual_sp),
1834                                 &format!("`{}` must come before `{}`", invalid_qual, current_qual),
1835                                 format!("{} {}", invalid_qual, current_qual),
1836                                 Applicability::MachineApplicable,
1837                             ).note("keyword order for functions declaration is `default`, `pub`, `const`, `async`, `unsafe`, `extern`");
1838                         }
1839                     }
1840                     // Recover incorrect visibility order such as `async pub`.
1841                     else if self.check_keyword(kw::Pub) {
1842                         let sp = sp_start.to(self.prev_token.span);
1843                         if let Ok(snippet) = self.span_to_snippet(sp) {
1844                             let vis = match self.parse_visibility(FollowedByType::No) {
1845                                 Ok(v) => v,
1846                                 Err(mut d) => {
1847                                     d.cancel();
1848                                     return Err(err);
1849                                 }
1850                             };
1851                             let vs = pprust::vis_to_string(&vis);
1852                             let vs = vs.trim_end();
1853                             err.span_suggestion(
1854                                 sp_start.to(self.prev_token.span),
1855                                 &format!("visibility `{}` must come before `{}`", vs, snippet),
1856                                 format!("{} {}", vs, snippet),
1857                                 Applicability::MachineApplicable,
1858                             );
1859                         }
1860                     }
1861                     return Err(err);
1862                 }
1863             }
1864         }
1865
1866         Ok(FnHeader { constness, unsafety, asyncness, ext })
1867     }
1868
1869     /// We are parsing `async fn`. If we are on Rust 2015, emit an error.
1870     fn ban_async_in_2015(&self, span: Span) {
1871         if span.rust_2015() {
1872             let diag = self.diagnostic();
1873             struct_span_err!(diag, span, E0670, "`async fn` is not permitted in Rust 2015")
1874                 .span_label(span, "to use `async fn`, switch to Rust 2018 or later")
1875                 .help(&format!("set `edition = \"{}\"` in `Cargo.toml`", LATEST_STABLE_EDITION))
1876                 .note("for more on editions, read https://doc.rust-lang.org/edition-guide")
1877                 .emit();
1878         }
1879     }
1880
1881     /// Parses the parameter list and result type of a function declaration.
1882     pub(super) fn parse_fn_decl(
1883         &mut self,
1884         req_name: ReqName,
1885         ret_allow_plus: AllowPlus,
1886         recover_return_sign: RecoverReturnSign,
1887     ) -> PResult<'a, P<FnDecl>> {
1888         Ok(P(FnDecl {
1889             inputs: self.parse_fn_params(req_name)?,
1890             output: self.parse_ret_ty(ret_allow_plus, RecoverQPath::Yes, recover_return_sign)?,
1891         }))
1892     }
1893
1894     /// Parses the parameter list of a function, including the `(` and `)` delimiters.
1895     fn parse_fn_params(&mut self, req_name: ReqName) -> PResult<'a, Vec<Param>> {
1896         let mut first_param = true;
1897         // Parse the arguments, starting out with `self` being allowed...
1898         let (mut params, _) = self.parse_paren_comma_seq(|p| {
1899             let param = p.parse_param_general(req_name, first_param).or_else(|mut e| {
1900                 e.emit();
1901                 let lo = p.prev_token.span;
1902                 // Skip every token until next possible arg or end.
1903                 p.eat_to_tokens(&[&token::Comma, &token::CloseDelim(token::Paren)]);
1904                 // Create a placeholder argument for proper arg count (issue #34264).
1905                 Ok(dummy_arg(Ident::new(kw::Empty, lo.to(p.prev_token.span))))
1906             });
1907             // ...now that we've parsed the first argument, `self` is no longer allowed.
1908             first_param = false;
1909             param
1910         })?;
1911         // Replace duplicated recovered params with `_` pattern to avoid unnecessary errors.
1912         self.deduplicate_recovered_params_names(&mut params);
1913         Ok(params)
1914     }
1915
1916     /// Parses a single function parameter.
1917     ///
1918     /// - `self` is syntactically allowed when `first_param` holds.
1919     fn parse_param_general(&mut self, req_name: ReqName, first_param: bool) -> PResult<'a, Param> {
1920         let lo = self.token.span;
1921         let attrs = self.parse_outer_attributes()?;
1922         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
1923             // Possibly parse `self`. Recover if we parsed it and it wasn't allowed here.
1924             if let Some(mut param) = this.parse_self_param()? {
1925                 param.attrs = attrs.into();
1926                 let res = if first_param { Ok(param) } else { this.recover_bad_self_param(param) };
1927                 return Ok((res?, TrailingToken::None));
1928             }
1929
1930             let is_name_required = match this.token.kind {
1931                 token::DotDotDot => false,
1932                 _ => req_name(this.token.span.edition()),
1933             };
1934             let (pat, ty) = if is_name_required || this.is_named_param() {
1935                 debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);
1936
1937                 let (pat, colon) = this.parse_fn_param_pat_colon()?;
1938                 if !colon {
1939                     let mut err = this.unexpected::<()>().unwrap_err();
1940                     return if let Some(ident) =
1941                         this.parameter_without_type(&mut err, pat, is_name_required, first_param)
1942                     {
1943                         err.emit();
1944                         Ok((dummy_arg(ident), TrailingToken::None))
1945                     } else {
1946                         Err(err)
1947                     };
1948                 }
1949
1950                 this.eat_incorrect_doc_comment_for_param_type();
1951                 (pat, this.parse_ty_for_param()?)
1952             } else {
1953                 debug!("parse_param_general ident_to_pat");
1954                 let parser_snapshot_before_ty = this.clone();
1955                 this.eat_incorrect_doc_comment_for_param_type();
1956                 let mut ty = this.parse_ty_for_param();
1957                 if ty.is_ok()
1958                     && this.token != token::Comma
1959                     && this.token != token::CloseDelim(token::Paren)
1960                 {
1961                     // This wasn't actually a type, but a pattern looking like a type,
1962                     // so we are going to rollback and re-parse for recovery.
1963                     ty = this.unexpected();
1964                 }
1965                 match ty {
1966                     Ok(ty) => {
1967                         let ident = Ident::new(kw::Empty, this.prev_token.span);
1968                         let bm = BindingMode::ByValue(Mutability::Not);
1969                         let pat = this.mk_pat_ident(ty.span, bm, ident);
1970                         (pat, ty)
1971                     }
1972                     // If this is a C-variadic argument and we hit an error, return the error.
1973                     Err(err) if this.token == token::DotDotDot => return Err(err),
1974                     // Recover from attempting to parse the argument as a type without pattern.
1975                     Err(mut err) => {
1976                         err.cancel();
1977                         *this = parser_snapshot_before_ty;
1978                         this.recover_arg_parse()?
1979                     }
1980                 }
1981             };
1982
1983             let span = lo.until(this.token.span);
1984
1985             Ok((
1986                 Param {
1987                     attrs: attrs.into(),
1988                     id: ast::DUMMY_NODE_ID,
1989                     is_placeholder: false,
1990                     pat,
1991                     span,
1992                     ty,
1993                 },
1994                 TrailingToken::None,
1995             ))
1996         })
1997     }
1998
1999     /// Returns the parsed optional self parameter and whether a self shortcut was used.
2000     fn parse_self_param(&mut self) -> PResult<'a, Option<Param>> {
2001         // Extract an identifier *after* having confirmed that the token is one.
2002         let expect_self_ident = |this: &mut Self| match this.token.ident() {
2003             Some((ident, false)) => {
2004                 this.bump();
2005                 ident
2006             }
2007             _ => unreachable!(),
2008         };
2009         // Is `self` `n` tokens ahead?
2010         let is_isolated_self = |this: &Self, n| {
2011             this.is_keyword_ahead(n, &[kw::SelfLower])
2012                 && this.look_ahead(n + 1, |t| t != &token::ModSep)
2013         };
2014         // Is `mut self` `n` tokens ahead?
2015         let is_isolated_mut_self =
2016             |this: &Self, n| this.is_keyword_ahead(n, &[kw::Mut]) && is_isolated_self(this, n + 1);
2017         // Parse `self` or `self: TYPE`. We already know the current token is `self`.
2018         let parse_self_possibly_typed = |this: &mut Self, m| {
2019             let eself_ident = expect_self_ident(this);
2020             let eself_hi = this.prev_token.span;
2021             let eself = if this.eat(&token::Colon) {
2022                 SelfKind::Explicit(this.parse_ty()?, m)
2023             } else {
2024                 SelfKind::Value(m)
2025             };
2026             Ok((eself, eself_ident, eself_hi))
2027         };
2028         // Recover for the grammar `*self`, `*const self`, and `*mut self`.
2029         let recover_self_ptr = |this: &mut Self| {
2030             let msg = "cannot pass `self` by raw pointer";
2031             let span = this.token.span;
2032             this.struct_span_err(span, msg).span_label(span, msg).emit();
2033
2034             Ok((SelfKind::Value(Mutability::Not), expect_self_ident(this), this.prev_token.span))
2035         };
2036
2037         // Parse optional `self` parameter of a method.
2038         // Only a limited set of initial token sequences is considered `self` parameters; anything
2039         // else is parsed as a normal function parameter list, so some lookahead is required.
2040         let eself_lo = self.token.span;
2041         let (eself, eself_ident, eself_hi) = match self.token.uninterpolate().kind {
2042             token::BinOp(token::And) => {
2043                 let eself = if is_isolated_self(self, 1) {
2044                     // `&self`
2045                     self.bump();
2046                     SelfKind::Region(None, Mutability::Not)
2047                 } else if is_isolated_mut_self(self, 1) {
2048                     // `&mut self`
2049                     self.bump();
2050                     self.bump();
2051                     SelfKind::Region(None, Mutability::Mut)
2052                 } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_self(self, 2) {
2053                     // `&'lt self`
2054                     self.bump();
2055                     let lt = self.expect_lifetime();
2056                     SelfKind::Region(Some(lt), Mutability::Not)
2057                 } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_mut_self(self, 2) {
2058                     // `&'lt mut self`
2059                     self.bump();
2060                     let lt = self.expect_lifetime();
2061                     self.bump();
2062                     SelfKind::Region(Some(lt), Mutability::Mut)
2063                 } else {
2064                     // `&not_self`
2065                     return Ok(None);
2066                 };
2067                 (eself, expect_self_ident(self), self.prev_token.span)
2068             }
2069             // `*self`
2070             token::BinOp(token::Star) if is_isolated_self(self, 1) => {
2071                 self.bump();
2072                 recover_self_ptr(self)?
2073             }
2074             // `*mut self` and `*const self`
2075             token::BinOp(token::Star)
2076                 if self.look_ahead(1, |t| t.is_mutability()) && is_isolated_self(self, 2) =>
2077             {
2078                 self.bump();
2079                 self.bump();
2080                 recover_self_ptr(self)?
2081             }
2082             // `self` and `self: TYPE`
2083             token::Ident(..) if is_isolated_self(self, 0) => {
2084                 parse_self_possibly_typed(self, Mutability::Not)?
2085             }
2086             // `mut self` and `mut self: TYPE`
2087             token::Ident(..) if is_isolated_mut_self(self, 0) => {
2088                 self.bump();
2089                 parse_self_possibly_typed(self, Mutability::Mut)?
2090             }
2091             _ => return Ok(None),
2092         };
2093
2094         let eself = source_map::respan(eself_lo.to(eself_hi), eself);
2095         Ok(Some(Param::from_self(AttrVec::default(), eself, eself_ident)))
2096     }
2097
2098     fn is_named_param(&self) -> bool {
2099         let offset = match self.token.kind {
2100             token::Interpolated(ref nt) => match **nt {
2101                 token::NtPat(..) => return self.look_ahead(1, |t| t == &token::Colon),
2102                 _ => 0,
2103             },
2104             token::BinOp(token::And) | token::AndAnd => 1,
2105             _ if self.token.is_keyword(kw::Mut) => 1,
2106             _ => 0,
2107         };
2108
2109         self.look_ahead(offset, |t| t.is_ident())
2110             && self.look_ahead(offset + 1, |t| t == &token::Colon)
2111     }
2112
2113     fn recover_first_param(&mut self) -> &'static str {
2114         match self
2115             .parse_outer_attributes()
2116             .and_then(|_| self.parse_self_param())
2117             .map_err(|mut e| e.cancel())
2118         {
2119             Ok(Some(_)) => "method",
2120             _ => "function",
2121         }
2122     }
2123 }