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, Delimiter, 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;
  18 use rustc_span::lev_distance::lev_distance;
  19 use rustc_span::source_map::{self, Span};
  20 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  21 use rustc_span::DUMMY_SP;
  22
  23 use std::convert::TryFrom;
  24 use std::mem;
  25 use tracing::debug;
  26
  27 impl<'a> Parser<'a> {
  28     /// Parses a source module as a crate. This is the main entry point for the parser.
  29     pub fn parse_crate_mod(&mut self) -> PResult<'a, ast::Crate> {
  30         let (attrs, items, spans) = self.parse_mod(&token::Eof)?;
  31         Ok(ast::Crate { attrs, items, spans, id: DUMMY_NODE_ID, is_placeholder: false })
  32     }
  33
  34     /// Parses a `mod <foo> { ... }` or `mod <foo>;` item.
  35     fn parse_item_mod(&mut self, attrs: &mut Vec<Attribute>) -> PResult<'a, ItemInfo> {
  36         let unsafety = self.parse_unsafety();
  37         self.expect_keyword(kw::Mod)?;
  38         let id = self.parse_ident()?;
  39         let mod_kind = if self.eat(&token::Semi) {
  40             ModKind::Unloaded
  41         } else {
  42             self.expect(&token::OpenDelim(Delimiter::Brace))?;
  43             let (mut inner_attrs, items, inner_span) =
  44                 self.parse_mod(&token::CloseDelim(Delimiter::Brace))?;
  45             attrs.append(&mut inner_attrs);
  46             ModKind::Loaded(items, Inline::Yes, inner_span)
  47         };
  48         Ok((id, ItemKind::Mod(unsafety, mod_kind)))
  49     }
  50
  51     /// Parses the contents of a module (inner attributes followed by module items).
  52     pub fn parse_mod(
  53         &mut self,
  54         term: &TokenKind,
  55     ) -> PResult<'a, (Vec<Attribute>, Vec<P<Item>>, ModSpans)> {
  56         let lo = self.token.span;
  57         let attrs = self.parse_inner_attributes()?;
  58
  59         let post_attr_lo = self.token.span;
  60         let mut items = vec![];
  61         while let Some(item) = self.parse_item(ForceCollect::No)? {
  62             items.push(item);
  63             self.maybe_consume_incorrect_semicolon(&items);
  64         }
  65
  66         if !self.eat(term) {
  67             let token_str = super::token_descr(&self.token);
  68             if !self.maybe_consume_incorrect_semicolon(&items) {
  69                 let msg = &format!("expected item, found {token_str}");
  70                 let mut err = self.struct_span_err(self.token.span, msg);
  71                 err.span_label(self.token.span, "expected item");
  72                 return Err(err);
  73             }
  74         }
  75
  76         let inject_use_span = post_attr_lo.data().with_hi(post_attr_lo.lo());
  77         let mod_spans = ModSpans { inner_span: lo.to(self.prev_token.span), inject_use_span };
  78         Ok((attrs, items, mod_spans))
  79     }
  80 }
  81
  82 pub(super) type ItemInfo = (Ident, ItemKind);
  83
  84 impl<'a> Parser<'a> {
  85     pub fn parse_item(&mut self, force_collect: ForceCollect) -> PResult<'a, Option<P<Item>>> {
  86         let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
  87         self.parse_item_(fn_parse_mode, force_collect).map(|i| i.map(P))
  88     }
  89
  90     fn parse_item_(
  91         &mut self,
  92         fn_parse_mode: FnParseMode,
  93         force_collect: ForceCollect,
  94     ) -> PResult<'a, Option<Item>> {
  95         let attrs = self.parse_outer_attributes()?;
  96         self.parse_item_common(attrs, true, false, fn_parse_mode, force_collect)
  97     }
  98
  99     pub(super) fn parse_item_common(
 100         &mut self,
 101         attrs: AttrWrapper,
 102         mac_allowed: bool,
 103         attrs_allowed: bool,
 104         fn_parse_mode: FnParseMode,
 105         force_collect: ForceCollect,
 106     ) -> PResult<'a, Option<Item>> {
 107         // Don't use `maybe_whole` so that we have precise control
 108         // over when we bump the parser
 109         if let token::Interpolated(nt) = &self.token.kind && let token::NtItem(item) = &**nt {
 110             let mut item = item.clone();
 111             self.bump();
 112
 113             attrs.prepend_to_nt_inner(&mut item.attrs);
 114             return Ok(Some(item.into_inner()));
 115         };
 116
 117         let mut unclosed_delims = vec![];
 118         let item =
 119             self.collect_tokens_trailing_token(attrs, force_collect, |this: &mut Self, attrs| {
 120                 let item =
 121                     this.parse_item_common_(attrs, mac_allowed, attrs_allowed, fn_parse_mode);
 122                 unclosed_delims.append(&mut this.unclosed_delims);
 123                 Ok((item?, TrailingToken::None))
 124             })?;
 125
 126         self.unclosed_delims.append(&mut unclosed_delims);
 127         Ok(item)
 128     }
 129
 130     fn parse_item_common_(
 131         &mut self,
 132         mut attrs: Vec<Attribute>,
 133         mac_allowed: bool,
 134         attrs_allowed: bool,
 135         fn_parse_mode: FnParseMode,
 136     ) -> PResult<'a, Option<Item>> {
 137         let lo = self.token.span;
 138         let vis = self.parse_visibility(FollowedByType::No)?;
 139         let mut def = self.parse_defaultness();
 140         let kind =
 141             self.parse_item_kind(&mut attrs, mac_allowed, lo, &vis, &mut def, fn_parse_mode)?;
 142         if let Some((ident, kind)) = kind {
 143             self.error_on_unconsumed_default(def, &kind);
 144             let span = lo.to(self.prev_token.span);
 145             let id = DUMMY_NODE_ID;
 146             let item = Item { ident, attrs, id, kind, vis, span, tokens: None };
 147             return Ok(Some(item));
 148         }
 149
 150         // At this point, we have failed to parse an item.
 151         self.error_on_unmatched_vis(&vis);
 152         self.error_on_unmatched_defaultness(def);
 153         if !attrs_allowed {
 154             self.recover_attrs_no_item(&attrs)?;
 155         }
 156         Ok(None)
 157     }
 158
 159     /// Error in-case a non-inherited visibility was parsed but no item followed.
 160     fn error_on_unmatched_vis(&self, vis: &Visibility) {
 161         if let VisibilityKind::Inherited = vis.kind {
 162             return;
 163         }
 164         let vs = pprust::vis_to_string(&vis);
 165         let vs = vs.trim_end();
 166         self.struct_span_err(vis.span, &format!("visibility `{vs}` is not followed by an item"))
 167             .span_label(vis.span, "the visibility")
 168             .help(&format!("you likely meant to define an item, e.g., `{vs} fn foo() {{}}`"))
 169             .emit();
 170     }
 171
 172     /// Error in-case a `default` was parsed but no item followed.
 173     fn error_on_unmatched_defaultness(&self, def: Defaultness) {
 174         if let Defaultness::Default(sp) = def {
 175             self.struct_span_err(sp, "`default` is not followed by an item")
 176                 .span_label(sp, "the `default` qualifier")
 177                 .note("only `fn`, `const`, `type`, or `impl` items may be prefixed by `default`")
 178                 .emit();
 179         }
 180     }
 181
 182     /// Error in-case `default` was parsed in an in-appropriate context.
 183     fn error_on_unconsumed_default(&self, def: Defaultness, kind: &ItemKind) {
 184         if let Defaultness::Default(span) = def {
 185             let msg = format!("{} {} cannot be `default`", kind.article(), kind.descr());
 186             self.struct_span_err(span, &msg)
 187                 .span_label(span, "`default` because of this")
 188                 .note("only associated `fn`, `const`, and `type` items can be `default`")
 189                 .emit();
 190         }
 191     }
 192
 193     /// Parses one of the items allowed by the flags.
 194     fn parse_item_kind(
 195         &mut self,
 196         attrs: &mut Vec<Attribute>,
 197         macros_allowed: bool,
 198         lo: Span,
 199         vis: &Visibility,
 200         def: &mut Defaultness,
 201         fn_parse_mode: FnParseMode,
 202     ) -> PResult<'a, Option<ItemInfo>> {
 203         let def_final = def == &Defaultness::Final;
 204         let mut def = || mem::replace(def, Defaultness::Final);
 205
 206         let info = if self.eat_keyword(kw::Use) {
 207             // USE ITEM
 208             let tree = self.parse_use_tree()?;
 209
 210             // If wildcard or glob-like brace syntax doesn't have `;`,
 211             // the user may not know `*` or `{}` should be the last.
 212             if let Err(mut e) = self.expect_semi() {
 213                 match tree.kind {
 214                     UseTreeKind::Glob => {
 215                         e.note("the wildcard token must be last on the path");
 216                     }
 217                     UseTreeKind::Nested(..) => {
 218                         e.note("glob-like brace syntax must be last on the path");
 219                     }
 220                     _ => (),
 221                 }
 222                 return Err(e);
 223             }
 224
 225             (Ident::empty(), ItemKind::Use(tree))
 226         } else if self.check_fn_front_matter(def_final) {
 227             // FUNCTION ITEM
 228             let (ident, sig, generics, body) = self.parse_fn(attrs, fn_parse_mode, lo, vis)?;
 229             (ident, ItemKind::Fn(Box::new(Fn { defaultness: def(), sig, generics, body })))
 230         } else if self.eat_keyword(kw::Extern) {
 231             if self.eat_keyword(kw::Crate) {
 232                 // EXTERN CRATE
 233                 self.parse_item_extern_crate()?
 234             } else {
 235                 // EXTERN BLOCK
 236                 self.parse_item_foreign_mod(attrs, Unsafe::No)?
 237             }
 238         } else if self.is_unsafe_foreign_mod() {
 239             // EXTERN BLOCK
 240             let unsafety = self.parse_unsafety();
 241             self.expect_keyword(kw::Extern)?;
 242             self.parse_item_foreign_mod(attrs, unsafety)?
 243         } else if self.is_static_global() {
 244             // STATIC ITEM
 245             self.bump(); // `static`
 246             let m = self.parse_mutability();
 247             let (ident, ty, expr) = self.parse_item_global(Some(m))?;
 248             (ident, ItemKind::Static(ty, m, expr))
 249         } else if let Const::Yes(const_span) = self.parse_constness() {
 250             // CONST ITEM
 251             if self.token.is_keyword(kw::Impl) {
 252                 // recover from `const impl`, suggest `impl const`
 253                 self.recover_const_impl(const_span, attrs, def())?
 254             } else {
 255                 self.recover_const_mut(const_span);
 256                 let (ident, ty, expr) = self.parse_item_global(None)?;
 257                 (ident, ItemKind::Const(def(), ty, expr))
 258             }
 259         } else if self.check_keyword(kw::Trait) || self.check_auto_or_unsafe_trait_item() {
 260             // TRAIT ITEM
 261             self.parse_item_trait(attrs, lo)?
 262         } else if self.check_keyword(kw::Impl)
 263             || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Impl])
 264         {
 265             // IMPL ITEM
 266             self.parse_item_impl(attrs, def())?
 267         } else if self.check_keyword(kw::Mod)
 268             || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Mod])
 269         {
 270             // MODULE ITEM
 271             self.parse_item_mod(attrs)?
 272         } else if self.eat_keyword(kw::Type) {
 273             // TYPE ITEM
 274             self.parse_type_alias(def())?
 275         } else if self.eat_keyword(kw::Enum) {
 276             // ENUM ITEM
 277             self.parse_item_enum()?
 278         } else if self.eat_keyword(kw::Struct) {
 279             // STRUCT ITEM
 280             self.parse_item_struct()?
 281         } else if self.is_kw_followed_by_ident(kw::Union) {
 282             // UNION ITEM
 283             self.bump(); // `union`
 284             self.parse_item_union()?
 285         } else if self.eat_keyword(kw::Macro) {
 286             // MACROS 2.0 ITEM
 287             self.parse_item_decl_macro(lo)?
 288         } else if let IsMacroRulesItem::Yes { has_bang } = self.is_macro_rules_item() {
 289             // MACRO_RULES ITEM
 290             self.parse_item_macro_rules(vis, has_bang)?
 291         } else if vis.kind.is_pub() && self.isnt_macro_invocation() {
 292             self.recover_missing_kw_before_item()?;
 293             return Ok(None);
 294         } else if macros_allowed && self.check_path() {
 295             // MACRO INVOCATION ITEM
 296             (Ident::empty(), ItemKind::MacCall(self.parse_item_macro(vis)?))
 297         } else {
 298             return Ok(None);
 299         };
 300         Ok(Some(info))
 301     }
 302
 303     /// When parsing a statement, would the start of a path be an item?
 304     pub(super) fn is_path_start_item(&mut self) -> bool {
 305         self.is_crate_vis() // no: `crate::b`, yes: `crate $item`
 306         || self.is_kw_followed_by_ident(kw::Union) // no: `union::b`, yes: `union U { .. }`
 307         || self.check_auto_or_unsafe_trait_item() // no: `auto::b`, yes: `auto trait X { .. }`
 308         || self.is_async_fn() // no(2015): `async::b`, yes: `async fn`
 309         || matches!(self.is_macro_rules_item(), IsMacroRulesItem::Yes{..}) // no: `macro_rules::b`, yes: `macro_rules! mac`
 310     }
 311
 312     /// Are we sure this could not possibly be a macro invocation?
 313     fn isnt_macro_invocation(&mut self) -> bool {
 314         self.check_ident() && self.look_ahead(1, |t| *t != token::Not && *t != token::ModSep)
 315     }
 316
 317     /// Recover on encountering a struct or method definition where the user
 318     /// forgot to add the `struct` or `fn` keyword after writing `pub`: `pub S {}`.
 319     fn recover_missing_kw_before_item(&mut self) -> PResult<'a, ()> {
 320         // Space between `pub` keyword and the identifier
 321         //
 322         //     pub   S {}
 323         //        ^^^ `sp` points here
 324         let sp = self.prev_token.span.between(self.token.span);
 325         let full_sp = self.prev_token.span.to(self.token.span);
 326         let ident_sp = self.token.span;
 327         if self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace)) {
 328             // possible public struct definition where `struct` was forgotten
 329             let ident = self.parse_ident().unwrap();
 330             let msg = format!("add `struct` here to parse `{ident}` as a public struct");
 331             let mut err = self.struct_span_err(sp, "missing `struct` for struct definition");
 332             err.span_suggestion_short(
 333                 sp,
 334                 &msg,
 335                 " struct ",
 336                 Applicability::MaybeIncorrect, // speculative
 337             );
 338             Err(err)
 339         } else if self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Parenthesis)) {
 340             let ident = self.parse_ident().unwrap();
 341             self.bump(); // `(`
 342             let kw_name = self.recover_first_param();
 343             self.consume_block(Delimiter::Parenthesis, ConsumeClosingDelim::Yes);
 344             let (kw, kw_name, ambiguous) = if self.check(&token::RArrow) {
 345                 self.eat_to_tokens(&[&token::OpenDelim(Delimiter::Brace)]);
 346                 self.bump(); // `{`
 347                 ("fn", kw_name, false)
 348             } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
 349                 self.bump(); // `{`
 350                 ("fn", kw_name, false)
 351             } else if self.check(&token::Colon) {
 352                 let kw = "struct";
 353                 (kw, kw, false)
 354             } else {
 355                 ("fn` or `struct", "function or struct", true)
 356             };
 357
 358             let msg = format!("missing `{kw}` for {kw_name} definition");
 359             let mut err = self.struct_span_err(sp, &msg);
 360             if !ambiguous {
 361                 self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
 362                 let suggestion =
 363                     format!("add `{kw}` here to parse `{ident}` as a public {kw_name}");
 364                 err.span_suggestion_short(
 365                     sp,
 366                     &suggestion,
 367                     format!(" {kw} "),
 368                     Applicability::MachineApplicable,
 369                 );
 370             } else if let Ok(snippet) = self.span_to_snippet(ident_sp) {
 371                 err.span_suggestion(
 372                     full_sp,
 373                     "if you meant to call a macro, try",
 374                     format!("{}!", snippet),
 375                     // this is the `ambiguous` conditional branch
 376                     Applicability::MaybeIncorrect,
 377                 );
 378             } else {
 379                 err.help(
 380                     "if you meant to call a macro, remove the `pub` \
 381                               and add a trailing `!` after the identifier",
 382                 );
 383             }
 384             Err(err)
 385         } else if self.look_ahead(1, |t| *t == token::Lt) {
 386             let ident = self.parse_ident().unwrap();
 387             self.eat_to_tokens(&[&token::Gt]);
 388             self.bump(); // `>`
 389             let (kw, kw_name, ambiguous) = if self.eat(&token::OpenDelim(Delimiter::Parenthesis)) {
 390                 ("fn", self.recover_first_param(), false)
 391             } else if self.check(&token::OpenDelim(Delimiter::Brace)) {
 392                 ("struct", "struct", false)
 393             } else {
 394                 ("fn` or `struct", "function or struct", true)
 395             };
 396             let msg = format!("missing `{kw}` for {kw_name} definition");
 397             let mut err = self.struct_span_err(sp, &msg);
 398             if !ambiguous {
 399                 err.span_suggestion_short(
 400                     sp,
 401                     &format!("add `{kw}` here to parse `{ident}` as a public {kw_name}"),
 402                     format!(" {} ", kw),
 403                     Applicability::MachineApplicable,
 404                 );
 405             }
 406             Err(err)
 407         } else {
 408             Ok(())
 409         }
 410     }
 411
 412     /// Parses an item macro, e.g., `item!();`.
 413     fn parse_item_macro(&mut self, vis: &Visibility) -> PResult<'a, MacCall> {
 414         let path = self.parse_path(PathStyle::Mod)?; // `foo::bar`
 415         self.expect(&token::Not)?; // `!`
 416         match self.parse_mac_args() {
 417             // `( .. )` or `[ .. ]` (followed by `;`), or `{ .. }`.
 418             Ok(args) => {
 419                 self.eat_semi_for_macro_if_needed(&args);
 420                 self.complain_if_pub_macro(vis, false);
 421                 Ok(MacCall { path, args, prior_type_ascription: self.last_type_ascription })
 422             }
 423
 424             Err(mut err) => {
 425                 // Maybe the user misspelled `macro_rules` (issue #91227)
 426                 if self.token.is_ident()
 427                     && path.segments.len() == 1
 428                     && lev_distance("macro_rules", &path.segments[0].ident.to_string(), 3).is_some()
 429                 {
 430                     err.span_suggestion(
 431                         path.span,
 432                         "perhaps you meant to define a macro",
 433                         "macro_rules".to_string(),
 434                         Applicability::MachineApplicable,
 435                     );
 436                 }
 437                 Err(err)
 438             }
 439         }
 440     }
 441
 442     /// Recover if we parsed attributes and expected an item but there was none.
 443     fn recover_attrs_no_item(&mut self, attrs: &[Attribute]) -> PResult<'a, ()> {
 444         let ([start @ end] | [start, .., end]) = attrs else {
 445             return Ok(());
 446         };
 447         let msg = if end.is_doc_comment() {
 448             "expected item after doc comment"
 449         } else {
 450             "expected item after attributes"
 451         };
 452         let mut err = self.struct_span_err(end.span, msg);
 453         if end.is_doc_comment() {
 454             err.span_label(end.span, "this doc comment doesn't document anything");
 455         }
 456         if end.meta_kind().is_some() {
 457             if self.token.kind == TokenKind::Semi {
 458                 err.span_suggestion_verbose(
 459                     self.token.span,
 460                     "consider removing this semicolon",
 461                     String::new(),
 462                     Applicability::MaybeIncorrect,
 463                 );
 464             }
 465         }
 466         if let [.., penultimate, _] = attrs {
 467             err.span_label(start.span.to(penultimate.span), "other attributes here");
 468         }
 469         Err(err)
 470     }
 471
 472     fn is_async_fn(&self) -> bool {
 473         self.token.is_keyword(kw::Async) && self.is_keyword_ahead(1, &[kw::Fn])
 474     }
 475
 476     fn parse_polarity(&mut self) -> ast::ImplPolarity {
 477         // Disambiguate `impl !Trait for Type { ... }` and `impl ! { ... }` for the never type.
 478         if self.check(&token::Not) && self.look_ahead(1, |t| t.can_begin_type()) {
 479             self.bump(); // `!`
 480             ast::ImplPolarity::Negative(self.prev_token.span)
 481         } else {
 482             ast::ImplPolarity::Positive
 483         }
 484     }
 485
 486     /// Parses an implementation item.
 487     ///
 488     /// ```ignore (illustrative)
 489     /// impl<'a, T> TYPE { /* impl items */ }
 490     /// impl<'a, T> TRAIT for TYPE { /* impl items */ }
 491     /// impl<'a, T> !TRAIT for TYPE { /* impl items */ }
 492     /// impl<'a, T> const TRAIT for TYPE { /* impl items */ }
 493     /// ```
 494     ///
 495     /// We actually parse slightly more relaxed grammar for better error reporting and recovery.
 496     /// ```ebnf
 497     /// "impl" GENERICS "const"? "!"? TYPE "for"? (TYPE | "..") ("where" PREDICATES)? "{" BODY "}"
 498     /// "impl" GENERICS "const"? "!"? TYPE ("where" PREDICATES)? "{" BODY "}"
 499     /// ```
 500     fn parse_item_impl(
 501         &mut self,
 502         attrs: &mut Vec<Attribute>,
 503         defaultness: Defaultness,
 504     ) -> PResult<'a, ItemInfo> {
 505         let unsafety = self.parse_unsafety();
 506         self.expect_keyword(kw::Impl)?;
 507
 508         // First, parse generic parameters if necessary.
 509         let mut generics = if self.choose_generics_over_qpath(0) {
 510             self.parse_generics()?
 511         } else {
 512             let mut generics = Generics::default();
 513             // impl A for B {}
 514             //    /\ this is where `generics.span` should point when there are no type params.
 515             generics.span = self.prev_token.span.shrink_to_hi();
 516             generics
 517         };
 518
 519         let constness = self.parse_constness();
 520         if let Const::Yes(span) = constness {
 521             self.sess.gated_spans.gate(sym::const_trait_impl, span);
 522         }
 523
 524         let polarity = self.parse_polarity();
 525
 526         // Parse both types and traits as a type, then reinterpret if necessary.
 527         let err_path = |span| ast::Path::from_ident(Ident::new(kw::Empty, span));
 528         let ty_first = if self.token.is_keyword(kw::For) && self.look_ahead(1, |t| t != &token::Lt)
 529         {
 530             let span = self.prev_token.span.between(self.token.span);
 531             self.struct_span_err(span, "missing trait in a trait impl")
 532                 .span_suggestion(
 533                     span,
 534                     "add a trait here",
 535                     " Trait ",
 536                     Applicability::HasPlaceholders,
 537                 )
 538                 .span_suggestion(
 539                     span.to(self.token.span),
 540                     "for an inherent impl, drop this `for`",
 541                     "",
 542                     Applicability::MaybeIncorrect,
 543                 )
 544                 .emit();
 545             P(Ty {
 546                 kind: TyKind::Path(None, err_path(span)),
 547                 span,
 548                 id: DUMMY_NODE_ID,
 549                 tokens: None,
 550             })
 551         } else {
 552             self.parse_ty_with_generics_recovery(&generics)?
 553         };
 554
 555         // If `for` is missing we try to recover.
 556         let has_for = self.eat_keyword(kw::For);
 557         let missing_for_span = self.prev_token.span.between(self.token.span);
 558
 559         let ty_second = if self.token == token::DotDot {
 560             // We need to report this error after `cfg` expansion for compatibility reasons
 561             self.bump(); // `..`, do not add it to expected tokens
 562             Some(self.mk_ty(self.prev_token.span, TyKind::Err))
 563         } else if has_for || self.token.can_begin_type() {
 564             Some(self.parse_ty()?)
 565         } else {
 566             None
 567         };
 568
 569         generics.where_clause = self.parse_where_clause()?;
 570
 571         let impl_items = self.parse_item_list(attrs, |p| p.parse_impl_item(ForceCollect::No))?;
 572
 573         let item_kind = match ty_second {
 574             Some(ty_second) => {
 575                 // impl Trait for Type
 576                 if !has_for {
 577                     self.struct_span_err(missing_for_span, "missing `for` in a trait impl")
 578                         .span_suggestion_short(
 579                             missing_for_span,
 580                             "add `for` here",
 581                             " for ".to_string(),
 582                             Applicability::MachineApplicable,
 583                         )
 584                         .emit();
 585                 }
 586
 587                 let ty_first = ty_first.into_inner();
 588                 let path = match ty_first.kind {
 589                     // This notably includes paths passed through `ty` macro fragments (#46438).
 590                     TyKind::Path(None, path) => path,
 591                     _ => {
 592                         self.struct_span_err(ty_first.span, "expected a trait, found type").emit();
 593                         err_path(ty_first.span)
 594                     }
 595                 };
 596                 let trait_ref = TraitRef { path, ref_id: ty_first.id };
 597
 598                 ItemKind::Impl(Box::new(Impl {
 599                     unsafety,
 600                     polarity,
 601                     defaultness,
 602                     constness,
 603                     generics,
 604                     of_trait: Some(trait_ref),
 605                     self_ty: ty_second,
 606                     items: impl_items,
 607                 }))
 608             }
 609             None => {
 610                 // impl Type
 611                 ItemKind::Impl(Box::new(Impl {
 612                     unsafety,
 613                     polarity,
 614                     defaultness,
 615                     constness,
 616                     generics,
 617                     of_trait: None,
 618                     self_ty: ty_first,
 619                     items: impl_items,
 620                 }))
 621             }
 622         };
 623
 624         Ok((Ident::empty(), item_kind))
 625     }
 626
 627     fn parse_item_list<T>(
 628         &mut self,
 629         attrs: &mut Vec<Attribute>,
 630         mut parse_item: impl FnMut(&mut Parser<'a>) -> PResult<'a, Option<Option<T>>>,
 631     ) -> PResult<'a, Vec<T>> {
 632         let open_brace_span = self.token.span;
 633         self.expect(&token::OpenDelim(Delimiter::Brace))?;
 634         attrs.append(&mut self.parse_inner_attributes()?);
 635
 636         let mut items = Vec::new();
 637         while !self.eat(&token::CloseDelim(Delimiter::Brace)) {
 638             if self.recover_doc_comment_before_brace() {
 639                 continue;
 640             }
 641             match parse_item(self) {
 642                 Ok(None) => {
 643                     // We have to bail or we'll potentially never make progress.
 644                     let non_item_span = self.token.span;
 645                     self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
 646                     self.struct_span_err(non_item_span, "non-item in item list")
 647                         .span_label(open_brace_span, "item list starts here")
 648                         .span_label(non_item_span, "non-item starts here")
 649                         .span_label(self.prev_token.span, "item list ends here")
 650                         .emit();
 651                     break;
 652                 }
 653                 Ok(Some(item)) => items.extend(item),
 654                 Err(mut err) => {
 655                     self.consume_block(Delimiter::Brace, ConsumeClosingDelim::Yes);
 656                     err.span_label(open_brace_span, "while parsing this item list starting here")
 657                         .span_label(self.prev_token.span, "the item list ends here")
 658                         .emit();
 659                     break;
 660                 }
 661             }
 662         }
 663         Ok(items)
 664     }
 665
 666     /// Recover on a doc comment before `}`.
 667     fn recover_doc_comment_before_brace(&mut self) -> bool {
 668         if let token::DocComment(..) = self.token.kind {
 669             if self.look_ahead(1, |tok| tok == &token::CloseDelim(Delimiter::Brace)) {
 670                 struct_span_err!(
 671                     self.diagnostic(),
 672                     self.token.span,
 673                     E0584,
 674                     "found a documentation comment that doesn't document anything",
 675                 )
 676                 .span_label(self.token.span, "this doc comment doesn't document anything")
 677                 .help(
 678                     "doc comments must come before what they document, maybe a \
 679                     comment was intended with `//`?",
 680                 )
 681                 .emit();
 682                 self.bump();
 683                 return true;
 684             }
 685         }
 686         false
 687     }
 688
 689     /// Parses defaultness (i.e., `default` or nothing).
 690     fn parse_defaultness(&mut self) -> Defaultness {
 691         // We are interested in `default` followed by another identifier.
 692         // However, we must avoid keywords that occur as binary operators.
 693         // Currently, the only applicable keyword is `as` (`default as Ty`).
 694         if self.check_keyword(kw::Default)
 695             && self.look_ahead(1, |t| t.is_non_raw_ident_where(|i| i.name != kw::As))
 696         {
 697             self.bump(); // `default`
 698             Defaultness::Default(self.prev_token.uninterpolated_span())
 699         } else {
 700             Defaultness::Final
 701         }
 702     }
 703
 704     /// Is this an `(unsafe auto? | auto) trait` item?
 705     fn check_auto_or_unsafe_trait_item(&mut self) -> bool {
 706         // auto trait
 707         self.check_keyword(kw::Auto) && self.is_keyword_ahead(1, &[kw::Trait])
 708             // unsafe auto trait
 709             || self.check_keyword(kw::Unsafe) && self.is_keyword_ahead(1, &[kw::Trait, kw::Auto])
 710     }
 711
 712     /// Parses `unsafe? auto? trait Foo { ... }` or `trait Foo = Bar;`.
 713     fn parse_item_trait(&mut self, attrs: &mut Vec<Attribute>, lo: Span) -> PResult<'a, ItemInfo> {
 714         let unsafety = self.parse_unsafety();
 715         // Parse optional `auto` prefix.
 716         let is_auto = if self.eat_keyword(kw::Auto) { IsAuto::Yes } else { IsAuto::No };
 717
 718         self.expect_keyword(kw::Trait)?;
 719         let ident = self.parse_ident()?;
 720         let mut generics = self.parse_generics()?;
 721
 722         // Parse optional colon and supertrait bounds.
 723         let had_colon = self.eat(&token::Colon);
 724         let span_at_colon = self.prev_token.span;
 725         let bounds = if had_colon {
 726             self.parse_generic_bounds(Some(self.prev_token.span))?
 727         } else {
 728             Vec::new()
 729         };
 730
 731         let span_before_eq = self.prev_token.span;
 732         if self.eat(&token::Eq) {
 733             // It's a trait alias.
 734             if had_colon {
 735                 let span = span_at_colon.to(span_before_eq);
 736                 self.struct_span_err(span, "bounds are not allowed on trait aliases").emit();
 737             }
 738
 739             let bounds = self.parse_generic_bounds(None)?;
 740             generics.where_clause = self.parse_where_clause()?;
 741             self.expect_semi()?;
 742
 743             let whole_span = lo.to(self.prev_token.span);
 744             if is_auto == IsAuto::Yes {
 745                 let msg = "trait aliases cannot be `auto`";
 746                 self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
 747             }
 748             if let Unsafe::Yes(_) = unsafety {
 749                 let msg = "trait aliases cannot be `unsafe`";
 750                 self.struct_span_err(whole_span, msg).span_label(whole_span, msg).emit();
 751             }
 752
 753             self.sess.gated_spans.gate(sym::trait_alias, whole_span);
 754
 755             Ok((ident, ItemKind::TraitAlias(generics, bounds)))
 756         } else {
 757             // It's a normal trait.
 758             generics.where_clause = self.parse_where_clause()?;
 759             let items = self.parse_item_list(attrs, |p| p.parse_trait_item(ForceCollect::No))?;
 760             Ok((
 761                 ident,
 762                 ItemKind::Trait(Box::new(Trait { is_auto, unsafety, generics, bounds, items })),
 763             ))
 764         }
 765     }
 766
 767     pub fn parse_impl_item(
 768         &mut self,
 769         force_collect: ForceCollect,
 770     ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
 771         let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
 772         self.parse_assoc_item(fn_parse_mode, force_collect)
 773     }
 774
 775     pub fn parse_trait_item(
 776         &mut self,
 777         force_collect: ForceCollect,
 778     ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
 779         let fn_parse_mode =
 780             FnParseMode { req_name: |edition| edition >= Edition::Edition2018, req_body: false };
 781         self.parse_assoc_item(fn_parse_mode, force_collect)
 782     }
 783
 784     /// Parses associated items.
 785     fn parse_assoc_item(
 786         &mut self,
 787         fn_parse_mode: FnParseMode,
 788         force_collect: ForceCollect,
 789     ) -> PResult<'a, Option<Option<P<AssocItem>>>> {
 790         Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
 791             |Item { attrs, id, span, vis, ident, kind, tokens }| {
 792                 let kind = match AssocItemKind::try_from(kind) {
 793                     Ok(kind) => kind,
 794                     Err(kind) => match kind {
 795                         ItemKind::Static(a, _, b) => {
 796                             self.struct_span_err(span, "associated `static` items are not allowed")
 797                                 .emit();
 798                             AssocItemKind::Const(Defaultness::Final, a, b)
 799                         }
 800                         _ => return self.error_bad_item_kind(span, &kind, "`trait`s or `impl`s"),
 801                     },
 802                 };
 803                 Some(P(Item { attrs, id, span, vis, ident, kind, tokens }))
 804             },
 805         ))
 806     }
 807
 808     /// Parses a `type` alias with the following grammar:
 809     /// ```ebnf
 810     /// TypeAlias = "type" Ident Generics {":" GenericBounds}? {"=" Ty}? ";" ;
 811     /// ```
 812     /// The `"type"` has already been eaten.
 813     fn parse_type_alias(&mut self, defaultness: Defaultness) -> PResult<'a, ItemInfo> {
 814         let ident = self.parse_ident()?;
 815         let mut generics = self.parse_generics()?;
 816
 817         // Parse optional colon and param bounds.
 818         let bounds =
 819             if self.eat(&token::Colon) { self.parse_generic_bounds(None)? } else { Vec::new() };
 820         let before_where_clause = self.parse_where_clause()?;
 821
 822         let ty = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
 823
 824         let after_where_clause = self.parse_where_clause()?;
 825
 826         let where_clauses = (
 827             TyAliasWhereClause(before_where_clause.has_where_token, before_where_clause.span),
 828             TyAliasWhereClause(after_where_clause.has_where_token, after_where_clause.span),
 829         );
 830         let where_predicates_split = before_where_clause.predicates.len();
 831         let mut predicates = before_where_clause.predicates;
 832         predicates.extend(after_where_clause.predicates.into_iter());
 833         let where_clause = WhereClause {
 834             has_where_token: before_where_clause.has_where_token
 835                 || after_where_clause.has_where_token,
 836             predicates,
 837             span: DUMMY_SP,
 838         };
 839         generics.where_clause = where_clause;
 840
 841         self.expect_semi()?;
 842
 843         Ok((
 844             ident,
 845             ItemKind::TyAlias(Box::new(TyAlias {
 846                 defaultness,
 847                 generics,
 848                 where_clauses,
 849                 where_predicates_split,
 850                 bounds,
 851                 ty,
 852             })),
 853         ))
 854     }
 855
 856     /// Parses a `UseTree`.
 857     ///
 858     /// ```text
 859     /// USE_TREE = [`::`] `*` |
 860     ///            [`::`] `{` USE_TREE_LIST `}` |
 861     ///            PATH `::` `*` |
 862     ///            PATH `::` `{` USE_TREE_LIST `}` |
 863     ///            PATH [`as` IDENT]
 864     /// ```
 865     fn parse_use_tree(&mut self) -> PResult<'a, UseTree> {
 866         let lo = self.token.span;
 867
 868         let mut prefix = ast::Path { segments: Vec::new(), span: lo.shrink_to_lo(), tokens: None };
 869         let kind = if self.check(&token::OpenDelim(Delimiter::Brace))
 870             || self.check(&token::BinOp(token::Star))
 871             || self.is_import_coupler()
 872         {
 873             // `use *;` or `use ::*;` or `use {...};` or `use ::{...};`
 874             let mod_sep_ctxt = self.token.span.ctxt();
 875             if self.eat(&token::ModSep) {
 876                 prefix
 877                     .segments
 878                     .push(PathSegment::path_root(lo.shrink_to_lo().with_ctxt(mod_sep_ctxt)));
 879             }
 880
 881             self.parse_use_tree_glob_or_nested()?
 882         } else {
 883             // `use path::*;` or `use path::{...};` or `use path;` or `use path as bar;`
 884             prefix = self.parse_path(PathStyle::Mod)?;
 885
 886             if self.eat(&token::ModSep) {
 887                 self.parse_use_tree_glob_or_nested()?
 888             } else {
 889                 UseTreeKind::Simple(self.parse_rename()?, DUMMY_NODE_ID, DUMMY_NODE_ID)
 890             }
 891         };
 892
 893         Ok(UseTree { prefix, kind, span: lo.to(self.prev_token.span) })
 894     }
 895
 896     /// Parses `*` or `{...}`.
 897     fn parse_use_tree_glob_or_nested(&mut self) -> PResult<'a, UseTreeKind> {
 898         Ok(if self.eat(&token::BinOp(token::Star)) {
 899             UseTreeKind::Glob
 900         } else {
 901             UseTreeKind::Nested(self.parse_use_tree_list()?)
 902         })
 903     }
 904
 905     /// Parses a `UseTreeKind::Nested(list)`.
 906     ///
 907     /// ```text
 908     /// USE_TREE_LIST = Ø | (USE_TREE `,`)* USE_TREE [`,`]
 909     /// ```
 910     fn parse_use_tree_list(&mut self) -> PResult<'a, Vec<(UseTree, ast::NodeId)>> {
 911         self.parse_delim_comma_seq(Delimiter::Brace, |p| Ok((p.parse_use_tree()?, DUMMY_NODE_ID)))
 912             .map(|(r, _)| r)
 913     }
 914
 915     fn parse_rename(&mut self) -> PResult<'a, Option<Ident>> {
 916         if self.eat_keyword(kw::As) { self.parse_ident_or_underscore().map(Some) } else { Ok(None) }
 917     }
 918
 919     fn parse_ident_or_underscore(&mut self) -> PResult<'a, Ident> {
 920         match self.token.ident() {
 921             Some((ident @ Ident { name: kw::Underscore, .. }, false)) => {
 922                 self.bump();
 923                 Ok(ident)
 924             }
 925             _ => self.parse_ident(),
 926         }
 927     }
 928
 929     /// Parses `extern crate` links.
 930     ///
 931     /// # Examples
 932     ///
 933     /// ```ignore (illustrative)
 934     /// extern crate foo;
 935     /// extern crate bar as foo;
 936     /// ```
 937     fn parse_item_extern_crate(&mut self) -> PResult<'a, ItemInfo> {
 938         // Accept `extern crate name-like-this` for better diagnostics
 939         let orig_name = self.parse_crate_name_with_dashes()?;
 940         let (item_name, orig_name) = if let Some(rename) = self.parse_rename()? {
 941             (rename, Some(orig_name.name))
 942         } else {
 943             (orig_name, None)
 944         };
 945         self.expect_semi()?;
 946         Ok((item_name, ItemKind::ExternCrate(orig_name)))
 947     }
 948
 949     fn parse_crate_name_with_dashes(&mut self) -> PResult<'a, Ident> {
 950         let error_msg = "crate name using dashes are not valid in `extern crate` statements";
 951         let suggestion_msg = "if the original crate name uses dashes you need to use underscores \
 952                               in the code";
 953         let mut ident = if self.token.is_keyword(kw::SelfLower) {
 954             self.parse_path_segment_ident()
 955         } else {
 956             self.parse_ident()
 957         }?;
 958         let mut idents = vec![];
 959         let mut replacement = vec![];
 960         let mut fixed_crate_name = false;
 961         // Accept `extern crate name-like-this` for better diagnostics.
 962         let dash = token::BinOp(token::BinOpToken::Minus);
 963         if self.token == dash {
 964             // Do not include `-` as part of the expected tokens list.
 965             while self.eat(&dash) {
 966                 fixed_crate_name = true;
 967                 replacement.push((self.prev_token.span, "_".to_string()));
 968                 idents.push(self.parse_ident()?);
 969             }
 970         }
 971         if fixed_crate_name {
 972             let fixed_name_sp = ident.span.to(idents.last().unwrap().span);
 973             let mut fixed_name = ident.name.to_string();
 974             for part in idents {
 975                 fixed_name.push_str(&format!("_{}", part.name));
 976             }
 977             ident = Ident::from_str_and_span(&fixed_name, fixed_name_sp);
 978
 979             self.struct_span_err(fixed_name_sp, error_msg)
 980                 .span_label(fixed_name_sp, "dash-separated idents are not valid")
 981                 .multipart_suggestion(suggestion_msg, replacement, Applicability::MachineApplicable)
 982                 .emit();
 983         }
 984         Ok(ident)
 985     }
 986
 987     /// Parses `extern` for foreign ABIs modules.
 988     ///
 989     /// `extern` is expected to have been consumed before calling this method.
 990     ///
 991     /// # Examples
 992     ///
 993     /// ```ignore (only-for-syntax-highlight)
 994     /// extern "C" {}
 995     /// extern {}
 996     /// ```
 997     fn parse_item_foreign_mod(
 998         &mut self,
 999         attrs: &mut Vec<Attribute>,
1000         unsafety: Unsafe,
1001     ) -> PResult<'a, ItemInfo> {
1002         let sp_start = self.prev_token.span;
1003         let abi = self.parse_abi(); // ABI?
1004         match self.parse_item_list(attrs, |p| p.parse_foreign_item(ForceCollect::No)) {
1005             Ok(items) => {
1006                 let module = ast::ForeignMod { unsafety, abi, items };
1007                 Ok((Ident::empty(), ItemKind::ForeignMod(module)))
1008             }
1009             Err(mut err) => {
1010                 let current_qual_sp = self.prev_token.span;
1011                 let current_qual_sp = current_qual_sp.to(sp_start);
1012                 if let Ok(current_qual) = self.span_to_snippet(current_qual_sp) {
1013                     // FIXME(davidtwco): avoid depending on the error message text
1014                     if err.message[0].0.expect_str() == "expected `{`, found keyword `unsafe`" {
1015                         let invalid_qual_sp = self.token.uninterpolated_span();
1016                         let invalid_qual = self.span_to_snippet(invalid_qual_sp).unwrap();
1017
1018                         err.span_suggestion(
1019                                 current_qual_sp.to(invalid_qual_sp),
1020                                 &format!("`{}` must come before `{}`", invalid_qual, current_qual),
1021                                 format!("{} {}", invalid_qual, current_qual),
1022                                 Applicability::MachineApplicable,
1023                             ).note("keyword order for functions declaration is `default`, `pub`, `const`, `async`, `unsafe`, `extern`");
1024                     }
1025                 }
1026                 Err(err)
1027             }
1028         }
1029     }
1030
1031     /// Parses a foreign item (one in an `extern { ... }` block).
1032     pub fn parse_foreign_item(
1033         &mut self,
1034         force_collect: ForceCollect,
1035     ) -> PResult<'a, Option<Option<P<ForeignItem>>>> {
1036         let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: false };
1037         Ok(self.parse_item_(fn_parse_mode, force_collect)?.map(
1038             |Item { attrs, id, span, vis, ident, kind, tokens }| {
1039                 let kind = match ForeignItemKind::try_from(kind) {
1040                     Ok(kind) => kind,
1041                     Err(kind) => match kind {
1042                         ItemKind::Const(_, a, b) => {
1043                             self.error_on_foreign_const(span, ident);
1044                             ForeignItemKind::Static(a, Mutability::Not, b)
1045                         }
1046                         _ => return self.error_bad_item_kind(span, &kind, "`extern` blocks"),
1047                     },
1048                 };
1049                 Some(P(Item { attrs, id, span, vis, ident, kind, tokens }))
1050             },
1051         ))
1052     }
1053
1054     fn error_bad_item_kind<T>(&self, span: Span, kind: &ItemKind, ctx: &str) -> Option<T> {
1055         let span = self.sess.source_map().guess_head_span(span);
1056         let descr = kind.descr();
1057         self.struct_span_err(span, &format!("{descr} is not supported in {ctx}"))
1058             .help(&format!("consider moving the {descr} out to a nearby module scope"))
1059             .emit();
1060         None
1061     }
1062
1063     fn error_on_foreign_const(&self, span: Span, ident: Ident) {
1064         self.struct_span_err(ident.span, "extern items cannot be `const`")
1065             .span_suggestion(
1066                 span.with_hi(ident.span.lo()),
1067                 "try using a static value",
1068                 "static ".to_string(),
1069                 Applicability::MachineApplicable,
1070             )
1071             .note("for more information, visit https://doc.rust-lang.org/std/keyword.extern.html")
1072             .emit();
1073     }
1074
1075     fn is_unsafe_foreign_mod(&self) -> bool {
1076         self.token.is_keyword(kw::Unsafe)
1077             && self.is_keyword_ahead(1, &[kw::Extern])
1078             && self.look_ahead(
1079                 2 + self.look_ahead(2, |t| t.can_begin_literal_maybe_minus() as usize),
1080                 |t| t.kind == token::OpenDelim(Delimiter::Brace),
1081             )
1082     }
1083
1084     fn is_static_global(&mut self) -> bool {
1085         if self.check_keyword(kw::Static) {
1086             // Check if this could be a closure.
1087             !self.look_ahead(1, |token| {
1088                 if token.is_keyword(kw::Move) {
1089                     return true;
1090                 }
1091                 matches!(token.kind, token::BinOp(token::Or) | token::OrOr)
1092             })
1093         } else {
1094             false
1095         }
1096     }
1097
1098     /// Recover on `const mut` with `const` already eaten.
1099     fn recover_const_mut(&mut self, const_span: Span) {
1100         if self.eat_keyword(kw::Mut) {
1101             let span = self.prev_token.span;
1102             self.struct_span_err(span, "const globals cannot be mutable")
1103                 .span_label(span, "cannot be mutable")
1104                 .span_suggestion(
1105                     const_span,
1106                     "you might want to declare a static instead",
1107                     "static".to_owned(),
1108                     Applicability::MaybeIncorrect,
1109                 )
1110                 .emit();
1111         }
1112     }
1113
1114     /// Recover on `const impl` with `const` already eaten.
1115     fn recover_const_impl(
1116         &mut self,
1117         const_span: Span,
1118         attrs: &mut Vec<Attribute>,
1119         defaultness: Defaultness,
1120     ) -> PResult<'a, ItemInfo> {
1121         let impl_span = self.token.span;
1122         let mut err = self.expected_ident_found();
1123
1124         // Only try to recover if this is implementing a trait for a type
1125         let mut impl_info = match self.parse_item_impl(attrs, defaultness) {
1126             Ok(impl_info) => impl_info,
1127             Err(recovery_error) => {
1128                 // Recovery failed, raise the "expected identifier" error
1129                 recovery_error.cancel();
1130                 return Err(err);
1131             }
1132         };
1133
1134         match impl_info.1 {
1135             ItemKind::Impl(box Impl { of_trait: Some(ref trai), ref mut constness, .. }) => {
1136                 *constness = Const::Yes(const_span);
1137
1138                 let before_trait = trai.path.span.shrink_to_lo();
1139                 let const_up_to_impl = const_span.with_hi(impl_span.lo());
1140                 err.multipart_suggestion(
1141                     "you might have meant to write a const trait impl",
1142                     vec![(const_up_to_impl, "".to_owned()), (before_trait, "const ".to_owned())],
1143                     Applicability::MaybeIncorrect,
1144                 )
1145                 .emit();
1146             }
1147             ItemKind::Impl { .. } => return Err(err),
1148             _ => unreachable!(),
1149         }
1150
1151         Ok(impl_info)
1152     }
1153
1154     /// Parse `["const" | ("static" "mut"?)] $ident ":" $ty (= $expr)?` with
1155     /// `["const" | ("static" "mut"?)]` already parsed and stored in `m`.
1156     ///
1157     /// When `m` is `"const"`, `$ident` may also be `"_"`.
1158     fn parse_item_global(
1159         &mut self,
1160         m: Option<Mutability>,
1161     ) -> PResult<'a, (Ident, P<Ty>, Option<P<ast::Expr>>)> {
1162         let id = if m.is_none() { self.parse_ident_or_underscore() } else { self.parse_ident() }?;
1163
1164         // Parse the type of a `const` or `static mut?` item.
1165         // That is, the `":" $ty` fragment.
1166         let ty = if self.eat(&token::Colon) {
1167             self.parse_ty()?
1168         } else {
1169             self.recover_missing_const_type(id, m)
1170         };
1171
1172         let expr = if self.eat(&token::Eq) { Some(self.parse_expr()?) } else { None };
1173         self.expect_semi()?;
1174         Ok((id, ty, expr))
1175     }
1176
1177     /// We were supposed to parse `:` but the `:` was missing.
1178     /// This means that the type is missing.
1179     fn recover_missing_const_type(&mut self, id: Ident, m: Option<Mutability>) -> P<Ty> {
1180         // Construct the error and stash it away with the hope
1181         // that typeck will later enrich the error with a type.
1182         let kind = match m {
1183             Some(Mutability::Mut) => "static mut",
1184             Some(Mutability::Not) => "static",
1185             None => "const",
1186         };
1187         let mut err = self.struct_span_err(id.span, &format!("missing type for `{kind}` item"));
1188         err.span_suggestion(
1189             id.span,
1190             "provide a type for the item",
1191             format!("{id}: <type>"),
1192             Applicability::HasPlaceholders,
1193         );
1194         err.stash(id.span, StashKey::ItemNoType);
1195
1196         // The user intended that the type be inferred,
1197         // so treat this as if the user wrote e.g. `const A: _ = expr;`.
1198         P(Ty { kind: TyKind::Infer, span: id.span, id: ast::DUMMY_NODE_ID, tokens: None })
1199     }
1200
1201     /// Parses an enum declaration.
1202     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
1203         let id = self.parse_ident()?;
1204         let mut generics = self.parse_generics()?;
1205         generics.where_clause = self.parse_where_clause()?;
1206
1207         let (variants, _) = self
1208             .parse_delim_comma_seq(Delimiter::Brace, |p| p.parse_enum_variant())
1209             .map_err(|e| {
1210                 self.recover_stmt();
1211                 e
1212             })?;
1213
1214         let enum_definition = EnumDef { variants: variants.into_iter().flatten().collect() };
1215         Ok((id, ItemKind::Enum(enum_definition, generics)))
1216     }
1217
1218     fn parse_enum_variant(&mut self) -> PResult<'a, Option<Variant>> {
1219         let variant_attrs = self.parse_outer_attributes()?;
1220         self.collect_tokens_trailing_token(
1221             variant_attrs,
1222             ForceCollect::No,
1223             |this, variant_attrs| {
1224                 let vlo = this.token.span;
1225
1226                 let vis = this.parse_visibility(FollowedByType::No)?;
1227                 if !this.recover_nested_adt_item(kw::Enum)? {
1228                     return Ok((None, TrailingToken::None));
1229                 }
1230                 let ident = this.parse_field_ident("enum", vlo)?;
1231
1232                 let struct_def = if this.check(&token::OpenDelim(Delimiter::Brace)) {
1233                     // Parse a struct variant.
1234                     let (fields, recovered) = this.parse_record_struct_body("struct", false)?;
1235                     VariantData::Struct(fields, recovered)
1236                 } else if this.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1237                     VariantData::Tuple(this.parse_tuple_struct_body()?, DUMMY_NODE_ID)
1238                 } else {
1239                     VariantData::Unit(DUMMY_NODE_ID)
1240                 };
1241
1242                 let disr_expr =
1243                     if this.eat(&token::Eq) { Some(this.parse_anon_const_expr()?) } else { None };
1244
1245                 let vr = ast::Variant {
1246                     ident,
1247                     vis,
1248                     id: DUMMY_NODE_ID,
1249                     attrs: variant_attrs.into(),
1250                     data: struct_def,
1251                     disr_expr,
1252                     span: vlo.to(this.prev_token.span),
1253                     is_placeholder: false,
1254                 };
1255
1256                 Ok((Some(vr), TrailingToken::MaybeComma))
1257             },
1258         )
1259     }
1260
1261     /// Parses `struct Foo { ... }`.
1262     fn parse_item_struct(&mut self) -> PResult<'a, ItemInfo> {
1263         let class_name = self.parse_ident()?;
1264
1265         let mut generics = self.parse_generics()?;
1266
1267         // There is a special case worth noting here, as reported in issue #17904.
1268         // If we are parsing a tuple struct it is the case that the where clause
1269         // should follow the field list. Like so:
1270         //
1271         // struct Foo<T>(T) where T: Copy;
1272         //
1273         // If we are parsing a normal record-style struct it is the case
1274         // that the where clause comes before the body, and after the generics.
1275         // So if we look ahead and see a brace or a where-clause we begin
1276         // parsing a record style struct.
1277         //
1278         // Otherwise if we look ahead and see a paren we parse a tuple-style
1279         // struct.
1280
1281         let vdata = if self.token.is_keyword(kw::Where) {
1282             generics.where_clause = self.parse_where_clause()?;
1283             if self.eat(&token::Semi) {
1284                 // If we see a: `struct Foo<T> where T: Copy;` style decl.
1285                 VariantData::Unit(DUMMY_NODE_ID)
1286             } else {
1287                 // If we see: `struct Foo<T> where T: Copy { ... }`
1288                 let (fields, recovered) =
1289                     self.parse_record_struct_body("struct", generics.where_clause.has_where_token)?;
1290                 VariantData::Struct(fields, recovered)
1291             }
1292         // No `where` so: `struct Foo<T>;`
1293         } else if self.eat(&token::Semi) {
1294             VariantData::Unit(DUMMY_NODE_ID)
1295         // Record-style struct definition
1296         } else if self.token == token::OpenDelim(Delimiter::Brace) {
1297             let (fields, recovered) =
1298                 self.parse_record_struct_body("struct", generics.where_clause.has_where_token)?;
1299             VariantData::Struct(fields, recovered)
1300         // Tuple-style struct definition with optional where-clause.
1301         } else if self.token == token::OpenDelim(Delimiter::Parenthesis) {
1302             let body = VariantData::Tuple(self.parse_tuple_struct_body()?, DUMMY_NODE_ID);
1303             generics.where_clause = self.parse_where_clause()?;
1304             self.expect_semi()?;
1305             body
1306         } else {
1307             let token_str = super::token_descr(&self.token);
1308             let msg = &format!(
1309                 "expected `where`, `{{`, `(`, or `;` after struct name, found {token_str}"
1310             );
1311             let mut err = self.struct_span_err(self.token.span, msg);
1312             err.span_label(self.token.span, "expected `where`, `{`, `(`, or `;` after struct name");
1313             return Err(err);
1314         };
1315
1316         Ok((class_name, ItemKind::Struct(vdata, generics)))
1317     }
1318
1319     /// Parses `union Foo { ... }`.
1320     fn parse_item_union(&mut self) -> PResult<'a, ItemInfo> {
1321         let class_name = self.parse_ident()?;
1322
1323         let mut generics = self.parse_generics()?;
1324
1325         let vdata = if self.token.is_keyword(kw::Where) {
1326             generics.where_clause = self.parse_where_clause()?;
1327             let (fields, recovered) =
1328                 self.parse_record_struct_body("union", generics.where_clause.has_where_token)?;
1329             VariantData::Struct(fields, recovered)
1330         } else if self.token == token::OpenDelim(Delimiter::Brace) {
1331             let (fields, recovered) =
1332                 self.parse_record_struct_body("union", generics.where_clause.has_where_token)?;
1333             VariantData::Struct(fields, recovered)
1334         } else {
1335             let token_str = super::token_descr(&self.token);
1336             let msg = &format!("expected `where` or `{{` after union name, found {token_str}");
1337             let mut err = self.struct_span_err(self.token.span, msg);
1338             err.span_label(self.token.span, "expected `where` or `{` after union name");
1339             return Err(err);
1340         };
1341
1342         Ok((class_name, ItemKind::Union(vdata, generics)))
1343     }
1344
1345     fn parse_record_struct_body(
1346         &mut self,
1347         adt_ty: &str,
1348         parsed_where: bool,
1349     ) -> PResult<'a, (Vec<FieldDef>, /* recovered */ bool)> {
1350         let mut fields = Vec::new();
1351         let mut recovered = false;
1352         if self.eat(&token::OpenDelim(Delimiter::Brace)) {
1353             while self.token != token::CloseDelim(Delimiter::Brace) {
1354                 let field = self.parse_field_def(adt_ty).map_err(|e| {
1355                     self.consume_block(Delimiter::Brace, ConsumeClosingDelim::No);
1356                     recovered = true;
1357                     e
1358                 });
1359                 match field {
1360                     Ok(field) => fields.push(field),
1361                     Err(mut err) => {
1362                         err.emit();
1363                         break;
1364                     }
1365                 }
1366             }
1367             self.eat(&token::CloseDelim(Delimiter::Brace));
1368         } else {
1369             let token_str = super::token_descr(&self.token);
1370             let msg = &format!(
1371                 "expected {}`{{` after struct name, found {}",
1372                 if parsed_where { "" } else { "`where`, or " },
1373                 token_str
1374             );
1375             let mut err = self.struct_span_err(self.token.span, msg);
1376             err.span_label(
1377                 self.token.span,
1378                 format!(
1379                     "expected {}`{{` after struct name",
1380                     if parsed_where { "" } else { "`where`, or " }
1381                 ),
1382             );
1383             return Err(err);
1384         }
1385
1386         Ok((fields, recovered))
1387     }
1388
1389     fn parse_tuple_struct_body(&mut self) -> PResult<'a, Vec<FieldDef>> {
1390         // This is the case where we find `struct Foo<T>(T) where T: Copy;`
1391         // Unit like structs are handled in parse_item_struct function
1392         self.parse_paren_comma_seq(|p| {
1393             let attrs = p.parse_outer_attributes()?;
1394             p.collect_tokens_trailing_token(attrs, ForceCollect::No, |p, attrs| {
1395                 let lo = p.token.span;
1396                 let vis = p.parse_visibility(FollowedByType::Yes)?;
1397                 let ty = p.parse_ty()?;
1398
1399                 Ok((
1400                     FieldDef {
1401                         span: lo.to(ty.span),
1402                         vis,
1403                         ident: None,
1404                         id: DUMMY_NODE_ID,
1405                         ty,
1406                         attrs: attrs.into(),
1407                         is_placeholder: false,
1408                     },
1409                     TrailingToken::MaybeComma,
1410                 ))
1411             })
1412         })
1413         .map(|(r, _)| r)
1414     }
1415
1416     /// Parses an element of a struct declaration.
1417     fn parse_field_def(&mut self, adt_ty: &str) -> PResult<'a, FieldDef> {
1418         let attrs = self.parse_outer_attributes()?;
1419         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
1420             let lo = this.token.span;
1421             let vis = this.parse_visibility(FollowedByType::No)?;
1422             Ok((this.parse_single_struct_field(adt_ty, lo, vis, attrs)?, TrailingToken::None))
1423         })
1424     }
1425
1426     /// Parses a structure field declaration.
1427     fn parse_single_struct_field(
1428         &mut self,
1429         adt_ty: &str,
1430         lo: Span,
1431         vis: Visibility,
1432         attrs: Vec<Attribute>,
1433     ) -> PResult<'a, FieldDef> {
1434         let mut seen_comma: bool = false;
1435         let a_var = self.parse_name_and_ty(adt_ty, lo, vis, attrs)?;
1436         if self.token == token::Comma {
1437             seen_comma = true;
1438         }
1439         match self.token.kind {
1440             token::Comma => {
1441                 self.bump();
1442             }
1443             token::CloseDelim(Delimiter::Brace) => {}
1444             token::DocComment(..) => {
1445                 let previous_span = self.prev_token.span;
1446                 let mut err = self.span_err(self.token.span, Error::UselessDocComment);
1447                 self.bump(); // consume the doc comment
1448                 let comma_after_doc_seen = self.eat(&token::Comma);
1449                 // `seen_comma` is always false, because we are inside doc block
1450                 // condition is here to make code more readable
1451                 if !seen_comma && comma_after_doc_seen {
1452                     seen_comma = true;
1453                 }
1454                 if comma_after_doc_seen || self.token == token::CloseDelim(Delimiter::Brace) {
1455                     err.emit();
1456                 } else {
1457                     if !seen_comma {
1458                         let sp = self.sess.source_map().next_point(previous_span);
1459                         err.span_suggestion(
1460                             sp,
1461                             "missing comma here",
1462                             ",",
1463                             Applicability::MachineApplicable,
1464                         );
1465                     }
1466                     return Err(err);
1467                 }
1468             }
1469             _ => {
1470                 let sp = self.prev_token.span.shrink_to_hi();
1471                 let mut err = self.struct_span_err(
1472                     sp,
1473                     &format!("expected `,`, or `}}`, found {}", super::token_descr(&self.token)),
1474                 );
1475
1476                 // Try to recover extra trailing angle brackets
1477                 let mut recovered = false;
1478                 if let TyKind::Path(_, Path { segments, .. }) = &a_var.ty.kind {
1479                     if let Some(last_segment) = segments.last() {
1480                         recovered = self.check_trailing_angle_brackets(
1481                             last_segment,
1482                             &[&token::Comma, &token::CloseDelim(Delimiter::Brace)],
1483                         );
1484                         if recovered {
1485                             // Handle a case like `Vec<u8>>,` where we can continue parsing fields
1486                             // after the comma
1487                             self.eat(&token::Comma);
1488                             // `check_trailing_angle_brackets` already emitted a nicer error
1489                             // NOTE(eddyb) this was `.cancel()`, but `err`
1490                             // gets returned, so we can't fully defuse it.
1491                             err.delay_as_bug();
1492                         }
1493                     }
1494                 }
1495
1496                 if self.token.is_ident() {
1497                     // This is likely another field; emit the diagnostic and keep going
1498                     err.span_suggestion(
1499                         sp,
1500                         "try adding a comma",
1501                         ",",
1502                         Applicability::MachineApplicable,
1503                     );
1504                     err.emit();
1505                     recovered = true;
1506                 }
1507
1508                 if recovered {
1509                     // Make sure an error was emitted (either by recovering an angle bracket,
1510                     // or by finding an identifier as the next token), since we're
1511                     // going to continue parsing
1512                     assert!(self.sess.span_diagnostic.has_errors().is_some());
1513                 } else {
1514                     return Err(err);
1515                 }
1516             }
1517         }
1518         Ok(a_var)
1519     }
1520
1521     fn expect_field_ty_separator(&mut self) -> PResult<'a, ()> {
1522         if let Err(mut err) = self.expect(&token::Colon) {
1523             let sm = self.sess.source_map();
1524             let eq_typo = self.token.kind == token::Eq && self.look_ahead(1, |t| t.is_path_start());
1525             let semi_typo = self.token.kind == token::Semi
1526                 && self.look_ahead(1, |t| {
1527                     t.is_path_start()
1528                     // We check that we are in a situation like `foo; bar` to avoid bad suggestions
1529                     // when there's no type and `;` was used instead of a comma.
1530                     && match (sm.lookup_line(self.token.span.hi()), sm.lookup_line(t.span.lo())) {
1531                         (Ok(l), Ok(r)) => l.line == r.line,
1532                         _ => true,
1533                     }
1534                 });
1535             if eq_typo || semi_typo {
1536                 self.bump();
1537                 // Gracefully handle small typos.
1538                 err.span_suggestion_short(
1539                     self.prev_token.span,
1540                     "field names and their types are separated with `:`",
1541                     ":".to_string(),
1542                     Applicability::MachineApplicable,
1543                 );
1544                 err.emit();
1545             } else {
1546                 return Err(err);
1547             }
1548         }
1549         Ok(())
1550     }
1551
1552     /// Parses a structure field.
1553     fn parse_name_and_ty(
1554         &mut self,
1555         adt_ty: &str,
1556         lo: Span,
1557         vis: Visibility,
1558         attrs: Vec<Attribute>,
1559     ) -> PResult<'a, FieldDef> {
1560         let name = self.parse_field_ident(adt_ty, lo)?;
1561         self.expect_field_ty_separator()?;
1562         let ty = self.parse_ty()?;
1563         if self.token.kind == token::Colon && self.look_ahead(1, |tok| tok.kind != token::Colon) {
1564             self.struct_span_err(self.token.span, "found single colon in a struct field type path")
1565                 .span_suggestion_verbose(
1566                     self.token.span,
1567                     "write a path separator here",
1568                     "::".to_string(),
1569                     Applicability::MaybeIncorrect,
1570                 )
1571                 .emit();
1572         }
1573         if self.token.kind == token::Eq {
1574             self.bump();
1575             let const_expr = self.parse_anon_const_expr()?;
1576             let sp = ty.span.shrink_to_hi().to(const_expr.value.span);
1577             self.struct_span_err(sp, "default values on `struct` fields aren't supported")
1578                 .span_suggestion(
1579                     sp,
1580                     "remove this unsupported default value",
1581                     String::new(),
1582                     Applicability::MachineApplicable,
1583                 )
1584                 .emit();
1585         }
1586         Ok(FieldDef {
1587             span: lo.to(self.prev_token.span),
1588             ident: Some(name),
1589             vis,
1590             id: DUMMY_NODE_ID,
1591             ty,
1592             attrs: attrs.into(),
1593             is_placeholder: false,
1594         })
1595     }
1596
1597     /// Parses a field identifier. Specialized version of `parse_ident_common`
1598     /// for better diagnostics and suggestions.
1599     fn parse_field_ident(&mut self, adt_ty: &str, lo: Span) -> PResult<'a, Ident> {
1600         let (ident, is_raw) = self.ident_or_err()?;
1601         if !is_raw && ident.is_reserved() {
1602             let err = if self.check_fn_front_matter(false) {
1603                 let inherited_vis = Visibility {
1604                     span: rustc_span::DUMMY_SP,
1605                     kind: VisibilityKind::Inherited,
1606                     tokens: None,
1607                 };
1608                 // We use `parse_fn` to get a span for the function
1609                 let fn_parse_mode = FnParseMode { req_name: |_| true, req_body: true };
1610                 if let Err(mut db) =
1611                     self.parse_fn(&mut Vec::new(), fn_parse_mode, lo, &inherited_vis)
1612                 {
1613                     db.delay_as_bug();
1614                 }
1615                 let mut err = self.struct_span_err(
1616                     lo.to(self.prev_token.span),
1617                     &format!("functions are not allowed in {adt_ty} definitions"),
1618                 );
1619                 err.help("unlike in C++, Java, and C#, functions are declared in `impl` blocks");
1620                 err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
1621                 err
1622             } else {
1623                 self.expected_ident_found()
1624             };
1625             return Err(err);
1626         }
1627         self.bump();
1628         Ok(ident)
1629     }
1630
1631     /// Parses a declarative macro 2.0 definition.
1632     /// The `macro` keyword has already been parsed.
1633     /// ```ebnf
1634     /// MacBody = "{" TOKEN_STREAM "}" ;
1635     /// MacParams = "(" TOKEN_STREAM ")" ;
1636     /// DeclMac = "macro" Ident MacParams? MacBody ;
1637     /// ```
1638     fn parse_item_decl_macro(&mut self, lo: Span) -> PResult<'a, ItemInfo> {
1639         let ident = self.parse_ident()?;
1640         let body = if self.check(&token::OpenDelim(Delimiter::Brace)) {
1641             self.parse_mac_args()? // `MacBody`
1642         } else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
1643             let params = self.parse_token_tree(); // `MacParams`
1644             let pspan = params.span();
1645             if !self.check(&token::OpenDelim(Delimiter::Brace)) {
1646                 return self.unexpected();
1647             }
1648             let body = self.parse_token_tree(); // `MacBody`
1649             // Convert `MacParams MacBody` into `{ MacParams => MacBody }`.
1650             let bspan = body.span();
1651             let arrow = TokenTree::token(token::FatArrow, pspan.between(bspan)); // `=>`
1652             let tokens = TokenStream::new(vec![params.into(), arrow.into(), body.into()]);
1653             let dspan = DelimSpan::from_pair(pspan.shrink_to_lo(), bspan.shrink_to_hi());
1654             P(MacArgs::Delimited(dspan, MacDelimiter::Brace, tokens))
1655         } else {
1656             return self.unexpected();
1657         };
1658
1659         self.sess.gated_spans.gate(sym::decl_macro, lo.to(self.prev_token.span));
1660         Ok((ident, ItemKind::MacroDef(ast::MacroDef { body, macro_rules: false })))
1661     }
1662
1663     /// Is this a possibly malformed start of a `macro_rules! foo` item definition?
1664
1665     fn is_macro_rules_item(&mut self) -> IsMacroRulesItem {
1666         if self.check_keyword(kw::MacroRules) {
1667             let macro_rules_span = self.token.span;
1668
1669             if self.look_ahead(1, |t| *t == token::Not) && self.look_ahead(2, |t| t.is_ident()) {
1670                 return IsMacroRulesItem::Yes { has_bang: true };
1671             } else if self.look_ahead(1, |t| (t.is_ident())) {
1672                 // macro_rules foo
1673                 self.struct_span_err(macro_rules_span, "expected `!` after `macro_rules`")
1674                     .span_suggestion(
1675                         macro_rules_span,
1676                         "add a `!`",
1677                         "macro_rules!".to_owned(),
1678                         Applicability::MachineApplicable,
1679                     )
1680                     .emit();
1681
1682                 return IsMacroRulesItem::Yes { has_bang: false };
1683             }
1684         }
1685
1686         IsMacroRulesItem::No
1687     }
1688
1689     /// Parses a `macro_rules! foo { ... }` declarative macro.
1690     fn parse_item_macro_rules(
1691         &mut self,
1692         vis: &Visibility,
1693         has_bang: bool,
1694     ) -> PResult<'a, ItemInfo> {
1695         self.expect_keyword(kw::MacroRules)?; // `macro_rules`
1696
1697         if has_bang {
1698             self.expect(&token::Not)?; // `!`
1699         }
1700         let ident = self.parse_ident()?;
1701
1702         if self.eat(&token::Not) {
1703             // Handle macro_rules! foo!
1704             let span = self.prev_token.span;
1705             self.struct_span_err(span, "macro names aren't followed by a `!`")
1706                 .span_suggestion(
1707                     span,
1708                     "remove the `!`",
1709                     "".to_owned(),
1710                     Applicability::MachineApplicable,
1711                 )
1712                 .emit();
1713         }
1714
1715         let body = self.parse_mac_args()?;
1716         self.eat_semi_for_macro_if_needed(&body);
1717         self.complain_if_pub_macro(vis, true);
1718
1719         Ok((ident, ItemKind::MacroDef(ast::MacroDef { body, macro_rules: true })))
1720     }
1721
1722     /// Item macro invocations or `macro_rules!` definitions need inherited visibility.
1723     /// If that's not the case, emit an error.
1724     fn complain_if_pub_macro(&self, vis: &Visibility, macro_rules: bool) {
1725         if let VisibilityKind::Inherited = vis.kind {
1726             return;
1727         }
1728
1729         let vstr = pprust::vis_to_string(vis);
1730         let vstr = vstr.trim_end();
1731         if macro_rules {
1732             let msg = format!("can't qualify macro_rules invocation with `{vstr}`");
1733             self.struct_span_err(vis.span, &msg)
1734                 .span_suggestion(
1735                     vis.span,
1736                     "try exporting the macro",
1737                     "#[macro_export]".to_owned(),
1738                     Applicability::MaybeIncorrect, // speculative
1739                 )
1740                 .emit();
1741         } else {
1742             self.struct_span_err(vis.span, "can't qualify macro invocation with `pub`")
1743                 .span_suggestion(
1744                     vis.span,
1745                     "remove the visibility",
1746                     String::new(),
1747                     Applicability::MachineApplicable,
1748                 )
1749                 .help(&format!("try adjusting the macro to put `{vstr}` inside the invocation"))
1750                 .emit();
1751         }
1752     }
1753
1754     fn eat_semi_for_macro_if_needed(&mut self, args: &MacArgs) {
1755         if args.need_semicolon() && !self.eat(&token::Semi) {
1756             self.report_invalid_macro_expansion_item(args);
1757         }
1758     }
1759
1760     fn report_invalid_macro_expansion_item(&self, args: &MacArgs) {
1761         let span = args.span().expect("undelimited macro call");
1762         let mut err = self.struct_span_err(
1763             span,
1764             "macros that expand to items must be delimited with braces or followed by a semicolon",
1765         );
1766         if self.unclosed_delims.is_empty() {
1767             let DelimSpan { open, close } = match args {
1768                 MacArgs::Empty | MacArgs::Eq(..) => unreachable!(),
1769                 MacArgs::Delimited(dspan, ..) => *dspan,
1770             };
1771             err.multipart_suggestion(
1772                 "change the delimiters to curly braces",
1773                 vec![(open, "{".to_string()), (close, '}'.to_string())],
1774                 Applicability::MaybeIncorrect,
1775             );
1776         } else {
1777             err.span_suggestion(
1778                 span,
1779                 "change the delimiters to curly braces",
1780                 " { /* items */ }".to_string(),
1781                 Applicability::HasPlaceholders,
1782             );
1783         }
1784         err.span_suggestion(
1785             span.shrink_to_hi(),
1786             "add a semicolon",
1787             ';'.to_string(),
1788             Applicability::MaybeIncorrect,
1789         );
1790         err.emit();
1791     }
1792
1793     /// Checks if current token is one of tokens which cannot be nested like `kw::Enum`. In case
1794     /// it is, we try to parse the item and report error about nested types.
1795     fn recover_nested_adt_item(&mut self, keyword: Symbol) -> PResult<'a, bool> {
1796         if (self.token.is_keyword(kw::Enum)
1797             || self.token.is_keyword(kw::Struct)
1798             || self.token.is_keyword(kw::Union))
1799             && self.look_ahead(1, |t| t.is_ident())
1800         {
1801             let kw_token = self.token.clone();
1802             let kw_str = pprust::token_to_string(&kw_token);
1803             let item = self.parse_item(ForceCollect::No)?;
1804
1805             self.struct_span_err(
1806                 kw_token.span,
1807                 &format!("`{kw_str}` definition cannot be nested inside `{keyword}`"),
1808             )
1809             .span_suggestion(
1810                 item.unwrap().span,
1811                 &format!("consider creating a new `{kw_str}` definition instead of nesting"),
1812                 String::new(),
1813                 Applicability::MaybeIncorrect,
1814             )
1815             .emit();
1816             // We successfully parsed the item but we must inform the caller about nested problem.
1817             return Ok(false);
1818         }
1819         Ok(true)
1820     }
1821 }
1822
1823 /// The parsing configuration used to parse a parameter list (see `parse_fn_params`).
1824 ///
1825 /// The function decides if, per-parameter `p`, `p` must have a pattern or just a type.
1826 ///
1827 /// This function pointer accepts an edition, because in edition 2015, trait declarations
1828 /// were allowed to omit parameter names. In 2018, they became required.
1829 type ReqName = fn(Edition) -> bool;
1830
1831 /// Parsing configuration for functions.
1832 ///
1833 /// The syntax of function items is slightly different within trait definitions,
1834 /// impl blocks, and modules. It is still parsed using the same code, just with
1835 /// different flags set, so that even when the input is wrong and produces a parse
1836 /// error, it still gets into the AST and the rest of the parser and
1837 /// type checker can run.
1838 #[derive(Clone, Copy)]
1839 pub(crate) struct FnParseMode {
1840     /// A function pointer that decides if, per-parameter `p`, `p` must have a
1841     /// pattern or just a type. This field affects parsing of the parameters list.
1842     ///
1843     /// ```text
1844     /// fn foo(alef: A) -> X { X::new() }
1845     ///        -----^^ affects parsing this part of the function signature
1846     ///        |
1847     ///        if req_name returns false, then this name is optional
1848     ///
1849     /// fn bar(A) -> X;
1850     ///        ^
1851     ///        |
1852     ///        if req_name returns true, this is an error
1853     /// ```
1854     ///
1855     /// Calling this function pointer should only return false if:
1856     ///
1857     ///   * The item is being parsed inside of a trait definition.
1858     ///     Within an impl block or a module, it should always evaluate
1859     ///     to true.
1860     ///   * The span is from Edition 2015. In particular, you can get a
1861     ///     2015 span inside a 2021 crate using macros.
1862     pub req_name: ReqName,
1863     /// If this flag is set to `true`, then plain, semicolon-terminated function
1864     /// prototypes are not allowed here.
1865     ///
1866     /// ```text
1867     /// fn foo(alef: A) -> X { X::new() }
1868     ///                      ^^^^^^^^^^^^
1869     ///                      |
1870     ///                      this is always allowed
1871     ///
1872     /// fn bar(alef: A, bet: B) -> X;
1873     ///                             ^
1874     ///                             |
1875     ///                             if req_body is set to true, this is an error
1876     /// ```
1877     ///
1878     /// This field should only be set to false if the item is inside of a trait
1879     /// definition or extern block. Within an impl block or a module, it should
1880     /// always be set to true.
1881     pub req_body: bool,
1882 }
1883
1884 /// Parsing of functions and methods.
1885 impl<'a> Parser<'a> {
1886     /// Parse a function starting from the front matter (`const ...`) to the body `{ ... }` or `;`.
1887     fn parse_fn(
1888         &mut self,
1889         attrs: &mut Vec<Attribute>,
1890         fn_parse_mode: FnParseMode,
1891         sig_lo: Span,
1892         vis: &Visibility,
1893     ) -> PResult<'a, (Ident, FnSig, Generics, Option<P<Block>>)> {
1894         let header = self.parse_fn_front_matter(vis)?; // `const ... fn`
1895         let ident = self.parse_ident()?; // `foo`
1896         let mut generics = self.parse_generics()?; // `<'a, T, ...>`
1897         let decl =
1898             self.parse_fn_decl(fn_parse_mode.req_name, AllowPlus::Yes, RecoverReturnSign::Yes)?; // `(p: u8, ...)`
1899         generics.where_clause = self.parse_where_clause()?; // `where T: Ord`
1900
1901         let mut sig_hi = self.prev_token.span;
1902         let body = self.parse_fn_body(attrs, &ident, &mut sig_hi, fn_parse_mode.req_body)?; // `;` or `{ ... }`.
1903         let fn_sig_span = sig_lo.to(sig_hi);
1904         Ok((ident, FnSig { header, decl, span: fn_sig_span }, generics, body))
1905     }
1906
1907     /// Parse the "body" of a function.
1908     /// This can either be `;` when there's no body,
1909     /// or e.g. a block when the function is a provided one.
1910     fn parse_fn_body(
1911         &mut self,
1912         attrs: &mut Vec<Attribute>,
1913         ident: &Ident,
1914         sig_hi: &mut Span,
1915         req_body: bool,
1916     ) -> PResult<'a, Option<P<Block>>> {
1917         let has_semi = if req_body {
1918             self.token.kind == TokenKind::Semi
1919         } else {
1920             // Only include `;` in list of expected tokens if body is not required
1921             self.check(&TokenKind::Semi)
1922         };
1923         let (inner_attrs, body) = if has_semi {
1924             // Include the trailing semicolon in the span of the signature
1925             self.expect_semi()?;
1926             *sig_hi = self.prev_token.span;
1927             (Vec::new(), None)
1928         } else if self.check(&token::OpenDelim(Delimiter::Brace)) || self.token.is_whole_block() {
1929             self.parse_inner_attrs_and_block().map(|(attrs, body)| (attrs, Some(body)))?
1930         } else if self.token.kind == token::Eq {
1931             // Recover `fn foo() = $expr;`.
1932             self.bump(); // `=`
1933             let eq_sp = self.prev_token.span;
1934             let _ = self.parse_expr()?;
1935             self.expect_semi()?; // `;`
1936             let span = eq_sp.to(self.prev_token.span);
1937             self.struct_span_err(span, "function body cannot be `= expression;`")
1938                 .multipart_suggestion(
1939                     "surround the expression with `{` and `}` instead of `=` and `;`",
1940                     vec![(eq_sp, "{".to_string()), (self.prev_token.span, " }".to_string())],
1941                     Applicability::MachineApplicable,
1942                 )
1943                 .emit();
1944             (Vec::new(), Some(self.mk_block_err(span)))
1945         } else {
1946             let expected = if req_body {
1947                 &[token::OpenDelim(Delimiter::Brace)][..]
1948             } else {
1949                 &[token::Semi, token::OpenDelim(Delimiter::Brace)]
1950             };
1951             if let Err(mut err) = self.expected_one_of_not_found(&[], &expected) {
1952                 if self.token.kind == token::CloseDelim(Delimiter::Brace) {
1953                     // The enclosing `mod`, `trait` or `impl` is being closed, so keep the `fn` in
1954                     // the AST for typechecking.
1955                     err.span_label(ident.span, "while parsing this `fn`");
1956                     err.emit();
1957                 } else {
1958                     return Err(err);
1959                 }
1960             }
1961             (Vec::new(), None)
1962         };
1963         attrs.extend(inner_attrs);
1964         Ok(body)
1965     }
1966
1967     /// Is the current token the start of an `FnHeader` / not a valid parse?
1968     ///
1969     /// `check_pub` adds additional `pub` to the checks in case users place it
1970     /// wrongly, can be used to ensure `pub` never comes after `default`.
1971     pub(super) fn check_fn_front_matter(&mut self, check_pub: bool) -> bool {
1972         // We use an over-approximation here.
1973         // `const const`, `fn const` won't parse, but we're not stepping over other syntax either.
1974         // `pub` is added in case users got confused with the ordering like `async pub fn`,
1975         // only if it wasn't preceded by `default` as `default pub` is invalid.
1976         let quals: &[Symbol] = if check_pub {
1977             &[kw::Pub, kw::Const, kw::Async, kw::Unsafe, kw::Extern]
1978         } else {
1979             &[kw::Const, kw::Async, kw::Unsafe, kw::Extern]
1980         };
1981         self.check_keyword(kw::Fn) // Definitely an `fn`.
1982             // `$qual fn` or `$qual $qual`:
1983             || quals.iter().any(|&kw| self.check_keyword(kw))
1984                 && self.look_ahead(1, |t| {
1985                     // `$qual fn`, e.g. `const fn` or `async fn`.
1986                     t.is_keyword(kw::Fn)
1987                     // Two qualifiers `$qual $qual` is enough, e.g. `async unsafe`.
1988                     || t.is_non_raw_ident_where(|i| quals.contains(&i.name)
1989                         // Rule out 2015 `const async: T = val`.
1990                         && i.is_reserved()
1991                         // Rule out unsafe extern block.
1992                         && !self.is_unsafe_foreign_mod())
1993                 })
1994             // `extern ABI fn`
1995             || self.check_keyword(kw::Extern)
1996                 && self.look_ahead(1, |t| t.can_begin_literal_maybe_minus())
1997                 && self.look_ahead(2, |t| t.is_keyword(kw::Fn))
1998     }
1999
2000     /// Parses all the "front matter" (or "qualifiers") for a `fn` declaration,
2001     /// up to and including the `fn` keyword. The formal grammar is:
2002     ///
2003     /// ```text
2004     /// Extern = "extern" StringLit? ;
2005     /// FnQual = "const"? "async"? "unsafe"? Extern? ;
2006     /// FnFrontMatter = FnQual "fn" ;
2007     /// ```
2008     ///
2009     /// `vis` represents the visibility that was already parsed, if any. Use
2010     /// `Visibility::Inherited` when no visibility is known.
2011     pub(super) fn parse_fn_front_matter(&mut self, orig_vis: &Visibility) -> PResult<'a, FnHeader> {
2012         let sp_start = self.token.span;
2013         let constness = self.parse_constness();
2014
2015         let async_start_sp = self.token.span;
2016         let asyncness = self.parse_asyncness();
2017
2018         let unsafe_start_sp = self.token.span;
2019         let unsafety = self.parse_unsafety();
2020
2021         let ext_start_sp = self.token.span;
2022         let ext = self.parse_extern();
2023
2024         if let Async::Yes { span, .. } = asyncness {
2025             self.ban_async_in_2015(span);
2026         }
2027
2028         if !self.eat_keyword(kw::Fn) {
2029             // It is possible for `expect_one_of` to recover given the contents of
2030             // `self.expected_tokens`, therefore, do not use `self.unexpected()` which doesn't
2031             // account for this.
2032             match self.expect_one_of(&[], &[]) {
2033                 Ok(true) => {}
2034                 Ok(false) => unreachable!(),
2035                 Err(mut err) => {
2036                     // Qualifier keywords ordering check
2037                     enum WrongKw {
2038                         Duplicated(Span),
2039                         Misplaced(Span),
2040                     }
2041
2042                     // This will allow the machine fix to directly place the keyword in the correct place or to indicate
2043                     // that the keyword is already present and the second instance should be removed.
2044                     let wrong_kw = if self.check_keyword(kw::Const) {
2045                         match constness {
2046                             Const::Yes(sp) => Some(WrongKw::Duplicated(sp)),
2047                             Const::No => Some(WrongKw::Misplaced(async_start_sp)),
2048                         }
2049                     } else if self.check_keyword(kw::Async) {
2050                         match asyncness {
2051                             Async::Yes { span, .. } => Some(WrongKw::Duplicated(span)),
2052                             Async::No => Some(WrongKw::Misplaced(unsafe_start_sp)),
2053                         }
2054                     } else if self.check_keyword(kw::Unsafe) {
2055                         match unsafety {
2056                             Unsafe::Yes(sp) => Some(WrongKw::Duplicated(sp)),
2057                             Unsafe::No => Some(WrongKw::Misplaced(ext_start_sp)),
2058                         }
2059                     } else {
2060                         None
2061                     };
2062
2063                     // The keyword is already present, suggest removal of the second instance
2064                     if let Some(WrongKw::Duplicated(original_sp)) = wrong_kw {
2065                         let original_kw = self
2066                             .span_to_snippet(original_sp)
2067                             .expect("Span extracted directly from keyword should always work");
2068
2069                         err.span_suggestion(
2070                             self.token.uninterpolated_span(),
2071                             &format!("`{original_kw}` already used earlier, remove this one"),
2072                             "".to_string(),
2073                             Applicability::MachineApplicable,
2074                         )
2075                         .span_note(original_sp, &format!("`{original_kw}` first seen here"));
2076                     }
2077                     // The keyword has not been seen yet, suggest correct placement in the function front matter
2078                     else if let Some(WrongKw::Misplaced(correct_pos_sp)) = wrong_kw {
2079                         let correct_pos_sp = correct_pos_sp.to(self.prev_token.span);
2080                         if let Ok(current_qual) = self.span_to_snippet(correct_pos_sp) {
2081                             let misplaced_qual_sp = self.token.uninterpolated_span();
2082                             let misplaced_qual = self.span_to_snippet(misplaced_qual_sp).unwrap();
2083
2084                             err.span_suggestion(
2085                                     correct_pos_sp.to(misplaced_qual_sp),
2086                                     &format!("`{misplaced_qual}` must come before `{current_qual}`"),
2087                                     format!("{misplaced_qual} {current_qual}"),
2088                                     Applicability::MachineApplicable,
2089                                 ).note("keyword order for functions declaration is `default`, `pub`, `const`, `async`, `unsafe`, `extern`");
2090                         }
2091                     }
2092                     // Recover incorrect visibility order such as `async pub`
2093                     else if self.check_keyword(kw::Pub) {
2094                         let sp = sp_start.to(self.prev_token.span);
2095                         if let Ok(snippet) = self.span_to_snippet(sp) {
2096                             let current_vis = match self.parse_visibility(FollowedByType::No) {
2097                                 Ok(v) => v,
2098                                 Err(d) => {
2099                                     d.cancel();
2100                                     return Err(err);
2101                                 }
2102                             };
2103                             let vs = pprust::vis_to_string(&current_vis);
2104                             let vs = vs.trim_end();
2105
2106                             // There was no explicit visibility
2107                             if matches!(orig_vis.kind, VisibilityKind::Inherited) {
2108                                 err.span_suggestion(
2109                                     sp_start.to(self.prev_token.span),
2110                                     &format!("visibility `{vs}` must come before `{snippet}`"),
2111                                     format!("{vs} {snippet}"),
2112                                     Applicability::MachineApplicable,
2113                                 );
2114                             }
2115                             // There was an explicit visibility
2116                             else {
2117                                 err.span_suggestion(
2118                                     current_vis.span,
2119                                     "there is already a visibility modifier, remove one",
2120                                     "".to_string(),
2121                                     Applicability::MachineApplicable,
2122                                 )
2123                                 .span_note(orig_vis.span, "explicit visibility first seen here");
2124                             }
2125                         }
2126                     }
2127                     return Err(err);
2128                 }
2129             }
2130         }
2131
2132         Ok(FnHeader { constness, unsafety, asyncness, ext })
2133     }
2134
2135     /// We are parsing `async fn`. If we are on Rust 2015, emit an error.
2136     fn ban_async_in_2015(&self, span: Span) {
2137         if span.rust_2015() {
2138             let diag = self.diagnostic();
2139             struct_span_err!(diag, span, E0670, "`async fn` is not permitted in Rust 2015")
2140                 .span_label(span, "to use `async fn`, switch to Rust 2018 or later")
2141                 .help_use_latest_edition()
2142                 .emit();
2143         }
2144     }
2145
2146     /// Parses the parameter list and result type of a function declaration.
2147     pub(super) fn parse_fn_decl(
2148         &mut self,
2149         req_name: ReqName,
2150         ret_allow_plus: AllowPlus,
2151         recover_return_sign: RecoverReturnSign,
2152     ) -> PResult<'a, P<FnDecl>> {
2153         Ok(P(FnDecl {
2154             inputs: self.parse_fn_params(req_name)?,
2155             output: self.parse_ret_ty(ret_allow_plus, RecoverQPath::Yes, recover_return_sign)?,
2156         }))
2157     }
2158
2159     /// Parses the parameter list of a function, including the `(` and `)` delimiters.
2160     fn parse_fn_params(&mut self, req_name: ReqName) -> PResult<'a, Vec<Param>> {
2161         let mut first_param = true;
2162         // Parse the arguments, starting out with `self` being allowed...
2163         let (mut params, _) = self.parse_paren_comma_seq(|p| {
2164             let param = p.parse_param_general(req_name, first_param).or_else(|mut e| {
2165                 e.emit();
2166                 let lo = p.prev_token.span;
2167                 // Skip every token until next possible arg or end.
2168                 p.eat_to_tokens(&[&token::Comma, &token::CloseDelim(Delimiter::Parenthesis)]);
2169                 // Create a placeholder argument for proper arg count (issue #34264).
2170                 Ok(dummy_arg(Ident::new(kw::Empty, lo.to(p.prev_token.span))))
2171             });
2172             // ...now that we've parsed the first argument, `self` is no longer allowed.
2173             first_param = false;
2174             param
2175         })?;
2176         // Replace duplicated recovered params with `_` pattern to avoid unnecessary errors.
2177         self.deduplicate_recovered_params_names(&mut params);
2178         Ok(params)
2179     }
2180
2181     /// Parses a single function parameter.
2182     ///
2183     /// - `self` is syntactically allowed when `first_param` holds.
2184     fn parse_param_general(&mut self, req_name: ReqName, first_param: bool) -> PResult<'a, Param> {
2185         let lo = self.token.span;
2186         let attrs = self.parse_outer_attributes()?;
2187         self.collect_tokens_trailing_token(attrs, ForceCollect::No, |this, attrs| {
2188             // Possibly parse `self`. Recover if we parsed it and it wasn't allowed here.
2189             if let Some(mut param) = this.parse_self_param()? {
2190                 param.attrs = attrs.into();
2191                 let res = if first_param { Ok(param) } else { this.recover_bad_self_param(param) };
2192                 return Ok((res?, TrailingToken::None));
2193             }
2194
2195             let is_name_required = match this.token.kind {
2196                 token::DotDotDot => false,
2197                 _ => req_name(this.token.span.edition()),
2198             };
2199             let (pat, ty) = if is_name_required || this.is_named_param() {
2200                 debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);
2201
2202                 let (pat, colon) = this.parse_fn_param_pat_colon()?;
2203                 if !colon {
2204                     let mut err = this.unexpected::<()>().unwrap_err();
2205                     return if let Some(ident) =
2206                         this.parameter_without_type(&mut err, pat, is_name_required, first_param)
2207                     {
2208                         err.emit();
2209                         Ok((dummy_arg(ident), TrailingToken::None))
2210                     } else {
2211                         Err(err)
2212                     };
2213                 }
2214
2215                 this.eat_incorrect_doc_comment_for_param_type();
2216                 (pat, this.parse_ty_for_param()?)
2217             } else {
2218                 debug!("parse_param_general ident_to_pat");
2219                 let parser_snapshot_before_ty = this.clone();
2220                 this.eat_incorrect_doc_comment_for_param_type();
2221                 let mut ty = this.parse_ty_for_param();
2222                 if ty.is_ok()
2223                     && this.token != token::Comma
2224                     && this.token != token::CloseDelim(Delimiter::Parenthesis)
2225                 {
2226                     // This wasn't actually a type, but a pattern looking like a type,
2227                     // so we are going to rollback and re-parse for recovery.
2228                     ty = this.unexpected();
2229                 }
2230                 match ty {
2231                     Ok(ty) => {
2232                         let ident = Ident::new(kw::Empty, this.prev_token.span);
2233                         let bm = BindingMode::ByValue(Mutability::Not);
2234                         let pat = this.mk_pat_ident(ty.span, bm, ident);
2235                         (pat, ty)
2236                     }
2237                     // If this is a C-variadic argument and we hit an error, return the error.
2238                     Err(err) if this.token == token::DotDotDot => return Err(err),
2239                     // Recover from attempting to parse the argument as a type without pattern.
2240                     Err(err) => {
2241                         err.cancel();
2242                         *this = parser_snapshot_before_ty;
2243                         this.recover_arg_parse()?
2244                     }
2245                 }
2246             };
2247
2248             let span = lo.until(this.token.span);
2249
2250             Ok((
2251                 Param {
2252                     attrs: attrs.into(),
2253                     id: ast::DUMMY_NODE_ID,
2254                     is_placeholder: false,
2255                     pat,
2256                     span,
2257                     ty,
2258                 },
2259                 TrailingToken::None,
2260             ))
2261         })
2262     }
2263
2264     /// Returns the parsed optional self parameter and whether a self shortcut was used.
2265     fn parse_self_param(&mut self) -> PResult<'a, Option<Param>> {
2266         // Extract an identifier *after* having confirmed that the token is one.
2267         let expect_self_ident = |this: &mut Self| match this.token.ident() {
2268             Some((ident, false)) => {
2269                 this.bump();
2270                 ident
2271             }
2272             _ => unreachable!(),
2273         };
2274         // Is `self` `n` tokens ahead?
2275         let is_isolated_self = |this: &Self, n| {
2276             this.is_keyword_ahead(n, &[kw::SelfLower])
2277                 && this.look_ahead(n + 1, |t| t != &token::ModSep)
2278         };
2279         // Is `mut self` `n` tokens ahead?
2280         let is_isolated_mut_self =
2281             |this: &Self, n| this.is_keyword_ahead(n, &[kw::Mut]) && is_isolated_self(this, n + 1);
2282         // Parse `self` or `self: TYPE`. We already know the current token is `self`.
2283         let parse_self_possibly_typed = |this: &mut Self, m| {
2284             let eself_ident = expect_self_ident(this);
2285             let eself_hi = this.prev_token.span;
2286             let eself = if this.eat(&token::Colon) {
2287                 SelfKind::Explicit(this.parse_ty()?, m)
2288             } else {
2289                 SelfKind::Value(m)
2290             };
2291             Ok((eself, eself_ident, eself_hi))
2292         };
2293         // Recover for the grammar `*self`, `*const self`, and `*mut self`.
2294         let recover_self_ptr = |this: &mut Self| {
2295             let msg = "cannot pass `self` by raw pointer";
2296             let span = this.token.span;
2297             this.struct_span_err(span, msg).span_label(span, msg).emit();
2298
2299             Ok((SelfKind::Value(Mutability::Not), expect_self_ident(this), this.prev_token.span))
2300         };
2301
2302         // Parse optional `self` parameter of a method.
2303         // Only a limited set of initial token sequences is considered `self` parameters; anything
2304         // else is parsed as a normal function parameter list, so some lookahead is required.
2305         let eself_lo = self.token.span;
2306         let (eself, eself_ident, eself_hi) = match self.token.uninterpolate().kind {
2307             token::BinOp(token::And) => {
2308                 let eself = if is_isolated_self(self, 1) {
2309                     // `&self`
2310                     self.bump();
2311                     SelfKind::Region(None, Mutability::Not)
2312                 } else if is_isolated_mut_self(self, 1) {
2313                     // `&mut self`
2314                     self.bump();
2315                     self.bump();
2316                     SelfKind::Region(None, Mutability::Mut)
2317                 } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_self(self, 2) {
2318                     // `&'lt self`
2319                     self.bump();
2320                     let lt = self.expect_lifetime();
2321                     SelfKind::Region(Some(lt), Mutability::Not)
2322                 } else if self.look_ahead(1, |t| t.is_lifetime()) && is_isolated_mut_self(self, 2) {
2323                     // `&'lt mut self`
2324                     self.bump();
2325                     let lt = self.expect_lifetime();
2326                     self.bump();
2327                     SelfKind::Region(Some(lt), Mutability::Mut)
2328                 } else {
2329                     // `&not_self`
2330                     return Ok(None);
2331                 };
2332                 (eself, expect_self_ident(self), self.prev_token.span)
2333             }
2334             // `*self`
2335             token::BinOp(token::Star) if is_isolated_self(self, 1) => {
2336                 self.bump();
2337                 recover_self_ptr(self)?
2338             }
2339             // `*mut self` and `*const self`
2340             token::BinOp(token::Star)
2341                 if self.look_ahead(1, |t| t.is_mutability()) && is_isolated_self(self, 2) =>
2342             {
2343                 self.bump();
2344                 self.bump();
2345                 recover_self_ptr(self)?
2346             }
2347             // `self` and `self: TYPE`
2348             token::Ident(..) if is_isolated_self(self, 0) => {
2349                 parse_self_possibly_typed(self, Mutability::Not)?
2350             }
2351             // `mut self` and `mut self: TYPE`
2352             token::Ident(..) if is_isolated_mut_self(self, 0) => {
2353                 self.bump();
2354                 parse_self_possibly_typed(self, Mutability::Mut)?
2355             }
2356             _ => return Ok(None),
2357         };
2358
2359         let eself = source_map::respan(eself_lo.to(eself_hi), eself);
2360         Ok(Some(Param::from_self(AttrVec::default(), eself, eself_ident)))
2361     }
2362
2363     fn is_named_param(&self) -> bool {
2364         let offset = match self.token.kind {
2365             token::Interpolated(ref nt) => match **nt {
2366                 token::NtPat(..) => return self.look_ahead(1, |t| t == &token::Colon),
2367                 _ => 0,
2368             },
2369             token::BinOp(token::And) | token::AndAnd => 1,
2370             _ if self.token.is_keyword(kw::Mut) => 1,
2371             _ => 0,
2372         };
2373
2374         self.look_ahead(offset, |t| t.is_ident())
2375             && self.look_ahead(offset + 1, |t| t == &token::Colon)
2376     }
2377
2378     fn recover_first_param(&mut self) -> &'static str {
2379         match self
2380             .parse_outer_attributes()
2381             .and_then(|_| self.parse_self_param())
2382             .map_err(|e| e.cancel())
2383         {
2384             Ok(Some(_)) => "method",
2385             _ => "function",
2386         }
2387     }
2388 }
2389
2390 enum IsMacroRulesItem {
2391     Yes { has_bang: bool },
2392     No,
2393 }