src/librustc_resolve/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::lifetimes::{ElisionFailureInfo, LifetimeContext};
   3 use crate::late::{LateResolutionVisitor, RibKind};
   4 use crate::path_names_to_string;
   5 use crate::{CrateLint, Module, ModuleKind, ModuleOrUniformRoot};
   6 use crate::{PathResult, PathSource, Segment};
   7
   8 use rustc_ast::ast::{self, Expr, ExprKind, Item, ItemKind, NodeId, Path, Ty, TyKind};
   9 use rustc_ast::util::lev_distance::find_best_match_for_name;
  10 use rustc_ast::visit::FnKind;
  11 use rustc_data_structures::fx::FxHashSet;
  12 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
  13 use rustc_hir as hir;
  14 use rustc_hir::def::Namespace::{self, *};
  15 use rustc_hir::def::{self, CtorKind, DefKind};
  16 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  17 use rustc_hir::PrimTy;
  18 use rustc_session::config::nightly_options;
  19 use rustc_span::hygiene::MacroKind;
  20 use rustc_span::symbol::{kw, sym, Ident};
  21 use rustc_span::{BytePos, Span};
  22
  23 use log::debug;
  24
  25 type Res = def::Res<ast::NodeId>;
  26
  27 /// A field or associated item from self type suggested in case of resolution failure.
  28 enum AssocSuggestion {
  29     Field,
  30     MethodWithSelf,
  31     AssocItem,
  32 }
  33
  34 crate enum MissingLifetimeSpot<'tcx> {
  35     Generics(&'tcx hir::Generics<'tcx>),
  36     HigherRanked { span: Span, span_type: ForLifetimeSpanType },
  37 }
  38
  39 crate enum ForLifetimeSpanType {
  40     BoundEmpty,
  41     BoundTail,
  42     TypeEmpty,
  43     TypeTail,
  44 }
  45
  46 impl ForLifetimeSpanType {
  47     crate fn descr(&self) -> &'static str {
  48         match self {
  49             Self::BoundEmpty | Self::BoundTail => "bound",
  50             Self::TypeEmpty | Self::TypeTail => "type",
  51         }
  52     }
  53
  54     crate fn suggestion(&self, sugg: &str) -> String {
  55         match self {
  56             Self::BoundEmpty | Self::TypeEmpty => format!("for<{}> ", sugg),
  57             Self::BoundTail | Self::TypeTail => format!(", {}", sugg),
  58         }
  59     }
  60 }
  61
  62 impl<'tcx> Into<MissingLifetimeSpot<'tcx>> for &'tcx hir::Generics<'tcx> {
  63     fn into(self) -> MissingLifetimeSpot<'tcx> {
  64         MissingLifetimeSpot::Generics(self)
  65     }
  66 }
  67
  68 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  69     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  70 }
  71
  72 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  73     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  74 }
  75
  76 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  77 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
  78     let variant_path = &suggestion.path;
  79     let variant_path_string = path_names_to_string(variant_path);
  80
  81     let path_len = suggestion.path.segments.len();
  82     let enum_path = ast::Path {
  83         span: suggestion.path.span,
  84         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
  85     };
  86     let enum_path_string = path_names_to_string(&enum_path);
  87
  88     (variant_path_string, enum_path_string)
  89 }
  90
  91 impl<'a> LateResolutionVisitor<'a, '_, '_> {
  92     fn def_span(&self, def_id: DefId) -> Option<Span> {
  93         match def_id.krate {
  94             LOCAL_CRATE => self.r.opt_span(def_id),
  95             _ => Some(
  96                 self.r
  97                     .session
  98                     .source_map()
  99                     .guess_head_span(self.r.cstore().get_span_untracked(def_id, self.r.session)),
 100             ),
 101         }
 102     }
 103
 104     /// Handles error reporting for `smart_resolve_path_fragment` function.
 105     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 106     pub(crate) fn smart_resolve_report_errors(
 107         &mut self,
 108         path: &[Segment],
 109         span: Span,
 110         source: PathSource<'_>,
 111         res: Option<Res>,
 112     ) -> (DiagnosticBuilder<'a>, Vec<ImportSuggestion>) {
 113         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 114         let ns = source.namespace();
 115         let is_expected = &|res| source.is_expected(res);
 116         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 117
 118         // Make the base error.
 119         let expected = source.descr_expected();
 120         let path_str = Segment::names_to_string(path);
 121         let item_str = path.last().unwrap().ident;
 122         let (base_msg, fallback_label, base_span, could_be_expr) = if let Some(res) = res {
 123             (
 124                 format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 125                 format!("not a {}", expected),
 126                 span,
 127                 match res {
 128                     Res::Def(DefKind::Fn, _) => {
 129                         // Verify whether this is a fn call or an Fn used as a type.
 130                         self.r
 131                             .session
 132                             .source_map()
 133                             .span_to_snippet(span)
 134                             .map(|snippet| snippet.ends_with(')'))
 135                             .unwrap_or(false)
 136                     }
 137                     Res::Def(
 138                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 139                         _,
 140                     )
 141                     | Res::SelfCtor(_)
 142                     | Res::PrimTy(_)
 143                     | Res::Local(_) => true,
 144                     _ => false,
 145                 },
 146             )
 147         } else {
 148             let item_span = path.last().unwrap().ident.span;
 149             let (mod_prefix, mod_str) = if path.len() == 1 {
 150                 (String::new(), "this scope".to_string())
 151             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 152                 (String::new(), "the crate root".to_string())
 153             } else {
 154                 let mod_path = &path[..path.len() - 1];
 155                 let mod_prefix =
 156                     match self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No) {
 157                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 158                         _ => None,
 159                     }
 160                     .map_or(String::new(), |res| format!("{} ", res.descr()));
 161                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)))
 162             };
 163             (
 164                 format!("cannot find {} `{}` in {}{}", expected, item_str, mod_prefix, mod_str),
 165                 if path_str == "async" && expected.starts_with("struct") {
 166                     "`async` blocks are only allowed in the 2018 edition".to_string()
 167                 } else {
 168                     format!("not found in {}", mod_str)
 169                 },
 170                 item_span,
 171                 false,
 172             )
 173         };
 174
 175         let code = source.error_code(res.is_some());
 176         let mut err = self.r.session.struct_span_err_with_code(base_span, &base_msg, code);
 177
 178         let is_assoc_fn = self.self_type_is_available(span);
 179         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 180         if ["this", "my"].contains(&&*item_str.as_str()) && is_assoc_fn {
 181             err.span_suggestion_short(
 182                 span,
 183                 "you might have meant to use `self` here instead",
 184                 "self".to_string(),
 185                 Applicability::MaybeIncorrect,
 186             );
 187             if !self.self_value_is_available(path[0].ident.span, span) {
 188                 if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
 189                     &self.diagnostic_metadata.current_function
 190                 {
 191                     let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
 192                         (param.span.shrink_to_lo(), "&self, ")
 193                     } else {
 194                         (
 195                             self.r
 196                                 .session
 197                                 .source_map()
 198                                 .span_through_char(*fn_span, '(')
 199                                 .shrink_to_hi(),
 200                             "&self",
 201                         )
 202                     };
 203                     err.span_suggestion_verbose(
 204                         span,
 205                         "you are also missing a `self` receiver argument",
 206                         sugg.to_string(),
 207                         Applicability::MaybeIncorrect,
 208                     );
 209                 }
 210             }
 211         }
 212
 213         // Emit special messages for unresolved `Self` and `self`.
 214         if is_self_type(path, ns) {
 215             err.code(rustc_errors::error_code!(E0411));
 216             err.span_label(
 217                 span,
 218                 "`Self` is only available in impls, traits, and type definitions".to_string(),
 219             );
 220             return (err, Vec::new());
 221         }
 222         if is_self_value(path, ns) {
 223             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 224
 225             err.code(rustc_errors::error_code!(E0424));
 226             err.span_label(span, match source {
 227                 PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed"
 228                                    .to_string(),
 229                 _ => "`self` value is a keyword only available in methods with a `self` parameter"
 230                      .to_string(),
 231             });
 232             if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 233                 // The current function has a `self' parameter, but we were unable to resolve
 234                 // a reference to `self`. This can only happen if the `self` identifier we
 235                 // are resolving came from a different hygiene context.
 236                 if fn_kind.decl().inputs.get(0).map(|p| p.is_self()).unwrap_or(false) {
 237                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 238                 } else {
 239                     let doesnt = if is_assoc_fn {
 240                         let (span, sugg) = fn_kind
 241                             .decl()
 242                             .inputs
 243                             .get(0)
 244                             .map(|p| (p.span.shrink_to_lo(), "&self, "))
 245                             .unwrap_or_else(|| {
 246                                 (
 247                                     self.r
 248                                         .session
 249                                         .source_map()
 250                                         .span_through_char(*span, '(')
 251                                         .shrink_to_hi(),
 252                                     "&self",
 253                                 )
 254                             });
 255                         err.span_suggestion_verbose(
 256                             span,
 257                             "add a `self` receiver parameter to make the associated `fn` a method",
 258                             sugg.to_string(),
 259                             Applicability::MaybeIncorrect,
 260                         );
 261                         "doesn't"
 262                     } else {
 263                         "can't"
 264                     };
 265                     if let Some(ident) = fn_kind.ident() {
 266                         err.span_label(
 267                             ident.span,
 268                             &format!("this function {} have a `self` parameter", doesnt),
 269                         );
 270                     }
 271                 }
 272             }
 273             return (err, Vec::new());
 274         }
 275
 276         // Try to lookup name in more relaxed fashion for better error reporting.
 277         let ident = path.last().unwrap().ident;
 278         let candidates = self
 279             .r
 280             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 281             .drain(..)
 282             .filter(|ImportSuggestion { did, .. }| {
 283                 match (did, res.and_then(|res| res.opt_def_id())) {
 284                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 285                     _ => true,
 286                 }
 287             })
 288             .collect::<Vec<_>>();
 289         let crate_def_id = DefId::local(CRATE_DEF_INDEX);
 290         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 291             let enum_candidates =
 292                 self.r.lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant);
 293
 294             if !enum_candidates.is_empty() {
 295                 if let (PathSource::Type, Some(span)) =
 296                     (source, self.diagnostic_metadata.current_type_ascription.last())
 297                 {
 298                     if self
 299                         .r
 300                         .session
 301                         .parse_sess
 302                         .type_ascription_path_suggestions
 303                         .borrow()
 304                         .contains(span)
 305                     {
 306                         // Already reported this issue on the lhs of the type ascription.
 307                         err.delay_as_bug();
 308                         return (err, candidates);
 309                     }
 310                 }
 311
 312                 let mut enum_candidates = enum_candidates
 313                     .iter()
 314                     .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 315                     .collect::<Vec<_>>();
 316                 enum_candidates.sort();
 317
 318                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 319                 // (that it's a variant) for E0573 "expected type, found variant".
 320                 let preamble = if res.is_none() {
 321                     let others = match enum_candidates.len() {
 322                         1 => String::new(),
 323                         2 => " and 1 other".to_owned(),
 324                         n => format!(" and {} others", n),
 325                     };
 326                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 327                 } else {
 328                     String::new()
 329                 };
 330                 let msg = format!("{}try using the variant's enum", preamble);
 331
 332                 err.span_suggestions(
 333                     span,
 334                     &msg,
 335                     enum_candidates
 336                         .into_iter()
 337                         .map(|(_variant_path, enum_ty_path)| enum_ty_path)
 338                         // Variants re-exported in prelude doesn't mean `prelude::v1` is the
 339                         // type name!
 340                         // FIXME: is there a more principled way to do this that
 341                         // would work for other re-exports?
 342                         .filter(|enum_ty_path| enum_ty_path != "std::prelude::v1")
 343                         // Also write `Option` rather than `std::prelude::v1::Option`.
 344                         .map(|enum_ty_path| {
 345                             // FIXME #56861: DRY-er prelude filtering.
 346                             enum_ty_path.trim_start_matches("std::prelude::v1::").to_owned()
 347                         }),
 348                     Applicability::MachineApplicable,
 349                 );
 350             }
 351         }
 352         if path.len() == 1 && self.self_type_is_available(span) {
 353             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 354                 let self_is_available = self.self_value_is_available(path[0].ident.span, span);
 355                 match candidate {
 356                     AssocSuggestion::Field => {
 357                         if self_is_available {
 358                             err.span_suggestion(
 359                                 span,
 360                                 "you might have meant to use the available field",
 361                                 format!("self.{}", path_str),
 362                                 Applicability::MachineApplicable,
 363                             );
 364                         } else {
 365                             err.span_label(span, "a field by this name exists in `Self`");
 366                         }
 367                     }
 368                     AssocSuggestion::MethodWithSelf if self_is_available => {
 369                         err.span_suggestion(
 370                             span,
 371                             "try",
 372                             format!("self.{}", path_str),
 373                             Applicability::MachineApplicable,
 374                         );
 375                     }
 376                     AssocSuggestion::MethodWithSelf | AssocSuggestion::AssocItem => {
 377                         err.span_suggestion(
 378                             span,
 379                             "try",
 380                             format!("Self::{}", path_str),
 381                             Applicability::MachineApplicable,
 382                         );
 383                     }
 384                 }
 385                 return (err, candidates);
 386             }
 387
 388             // If the first argument in call is `self` suggest calling a method.
 389             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 390                 let mut args_snippet = String::new();
 391                 if let Some(args_span) = args_span {
 392                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 393                         args_snippet = snippet;
 394                     }
 395                 }
 396
 397                 err.span_suggestion(
 398                     call_span,
 399                     &format!("try calling `{}` as a method", ident),
 400                     format!("self.{}({})", path_str, args_snippet),
 401                     Applicability::MachineApplicable,
 402                 );
 403                 return (err, candidates);
 404             }
 405         }
 406
 407         // Try Levenshtein algorithm.
 408         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected, span);
 409         // Try context-dependent help if relaxed lookup didn't work.
 410         if let Some(res) = res {
 411             if self.smart_resolve_context_dependent_help(
 412                 &mut err,
 413                 span,
 414                 source,
 415                 res,
 416                 &path_str,
 417                 &fallback_label,
 418             ) {
 419                 // We do this to avoid losing a secondary span when we override the main error span.
 420                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 421                 return (err, candidates);
 422             }
 423         }
 424
 425         if !self.type_ascription_suggestion(&mut err, base_span)
 426             && !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span)
 427         {
 428             // Fallback label.
 429             err.span_label(base_span, fallback_label);
 430
 431             match self.diagnostic_metadata.current_let_binding {
 432                 Some((pat_sp, Some(ty_sp), None)) if ty_sp.contains(base_span) && could_be_expr => {
 433                     err.span_suggestion_short(
 434                         pat_sp.between(ty_sp),
 435                         "use `=` if you meant to assign",
 436                         " = ".to_string(),
 437                         Applicability::MaybeIncorrect,
 438                     );
 439                 }
 440                 _ => {}
 441             }
 442         }
 443         (err, candidates)
 444     }
 445
 446     /// Check if the source is call expression and the first argument is `self`. If true,
 447     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 448     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 449         let mut has_self_arg = None;
 450         if let PathSource::Expr(Some(parent)) = source {
 451             match &parent.kind {
 452                 ExprKind::Call(_, args) if !args.is_empty() => {
 453                     let mut expr_kind = &args[0].kind;
 454                     loop {
 455                         match expr_kind {
 456                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 457                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 458                                     let call_span = parent.span;
 459                                     let tail_args_span = if args.len() > 1 {
 460                                         Some(Span::new(
 461                                             args[1].span.lo(),
 462                                             args.last().unwrap().span.hi(),
 463                                             call_span.ctxt(),
 464                                         ))
 465                                     } else {
 466                                         None
 467                                     };
 468                                     has_self_arg = Some((call_span, tail_args_span));
 469                                 }
 470                                 break;
 471                             }
 472                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 473                             _ => break,
 474                         }
 475                     }
 476                 }
 477                 _ => (),
 478             }
 479         };
 480         has_self_arg
 481     }
 482
 483     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 484         // HACK(estebank): find a better way to figure out that this was a
 485         // parser issue where a struct literal is being used on an expression
 486         // where a brace being opened means a block is being started. Look
 487         // ahead for the next text to see if `span` is followed by a `{`.
 488         let sm = self.r.session.source_map();
 489         let mut sp = span;
 490         loop {
 491             sp = sm.next_point(sp);
 492             match sm.span_to_snippet(sp) {
 493                 Ok(ref snippet) => {
 494                     if snippet.chars().any(|c| !c.is_whitespace()) {
 495                         break;
 496                     }
 497                 }
 498                 _ => break,
 499             }
 500         }
 501         let followed_by_brace = match sm.span_to_snippet(sp) {
 502             Ok(ref snippet) if snippet == "{" => true,
 503             _ => false,
 504         };
 505         // In case this could be a struct literal that needs to be surrounded
 506         // by parentheses, find the appropriate span.
 507         let mut i = 0;
 508         let mut closing_brace = None;
 509         loop {
 510             sp = sm.next_point(sp);
 511             match sm.span_to_snippet(sp) {
 512                 Ok(ref snippet) => {
 513                     if snippet == "}" {
 514                         closing_brace = Some(span.to(sp));
 515                         break;
 516                     }
 517                 }
 518                 _ => break,
 519             }
 520             i += 1;
 521             // The bigger the span, the more likely we're incorrect --
 522             // bound it to 100 chars long.
 523             if i > 100 {
 524                 break;
 525             }
 526         }
 527         (followed_by_brace, closing_brace)
 528     }
 529
 530     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 531     /// function.
 532     /// Returns `true` if able to provide context-dependent help.
 533     fn smart_resolve_context_dependent_help(
 534         &mut self,
 535         err: &mut DiagnosticBuilder<'a>,
 536         span: Span,
 537         source: PathSource<'_>,
 538         res: Res,
 539         path_str: &str,
 540         fallback_label: &str,
 541     ) -> bool {
 542         let ns = source.namespace();
 543         let is_expected = &|res| source.is_expected(res);
 544
 545         let path_sep = |err: &mut DiagnosticBuilder<'_>, expr: &Expr| match expr.kind {
 546             ExprKind::Field(_, ident) => {
 547                 err.span_suggestion(
 548                     expr.span,
 549                     "use the path separator to refer to an item",
 550                     format!("{}::{}", path_str, ident),
 551                     Applicability::MaybeIncorrect,
 552                 );
 553                 true
 554             }
 555             ExprKind::MethodCall(ref segment, ..) => {
 556                 let span = expr.span.with_hi(segment.ident.span.hi());
 557                 err.span_suggestion(
 558                     span,
 559                     "use the path separator to refer to an item",
 560                     format!("{}::{}", path_str, segment.ident),
 561                     Applicability::MaybeIncorrect,
 562                 );
 563                 true
 564             }
 565             _ => false,
 566         };
 567
 568         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 569             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 570
 571             match source {
 572                 PathSource::Expr(Some(
 573                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
 574                 )) if path_sep(err, &parent) => {}
 575                 PathSource::Expr(
 576                     None
 577                     | Some(Expr {
 578                         kind:
 579                             ExprKind::Path(..)
 580                             | ExprKind::Binary(..)
 581                             | ExprKind::Unary(..)
 582                             | ExprKind::If(..)
 583                             | ExprKind::While(..)
 584                             | ExprKind::ForLoop(..)
 585                             | ExprKind::Match(..),
 586                         ..
 587                     }),
 588                 ) if followed_by_brace => {
 589                     if let Some(sp) = closing_brace {
 590                         err.span_label(span, fallback_label);
 591                         err.multipart_suggestion(
 592                             "surround the struct literal with parentheses",
 593                             vec![
 594                                 (sp.shrink_to_lo(), "(".to_string()),
 595                                 (sp.shrink_to_hi(), ")".to_string()),
 596                             ],
 597                             Applicability::MaybeIncorrect,
 598                         );
 599                     } else {
 600                         err.span_label(
 601                             span, // Note the parentheses surrounding the suggestion below
 602                             format!(
 603                                 "you might want to surround a struct literal with parentheses: \
 604                                  `({} {{ /* fields */ }})`?",
 605                                 path_str
 606                             ),
 607                         );
 608                     }
 609                 }
 610                 PathSource::Expr(_) | PathSource::TupleStruct(_) | PathSource::Pat => {
 611                     let span = match &source {
 612                         PathSource::Expr(Some(Expr {
 613                             span, kind: ExprKind::Call(_, _), ..
 614                         }))
 615                         | PathSource::TupleStruct(span) => {
 616                             // We want the main underline to cover the suggested code as well for
 617                             // cleaner output.
 618                             err.set_span(*span);
 619                             *span
 620                         }
 621                         _ => span,
 622                     };
 623                     if let Some(span) = self.def_span(def_id) {
 624                         err.span_label(span, &format!("`{}` defined here", path_str));
 625                     }
 626                     let (tail, descr, applicability) = match source {
 627                         PathSource::Pat | PathSource::TupleStruct(_) => {
 628                             ("", "pattern", Applicability::MachineApplicable)
 629                         }
 630                         _ => (": val", "literal", Applicability::HasPlaceholders),
 631                     };
 632                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
 633                         Some(fields) => (
 634                             fields
 635                                 .iter()
 636                                 .map(|f| format!("{}{}", f.node, tail))
 637                                 .collect::<Vec<String>>()
 638                                 .join(", "),
 639                             applicability,
 640                         ),
 641                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
 642                     };
 643                     let pad = match self.r.field_names.get(&def_id) {
 644                         Some(fields) if fields.is_empty() => "",
 645                         _ => " ",
 646                     };
 647                     err.span_suggestion(
 648                         span,
 649                         &format!("use struct {} syntax instead", descr),
 650                         format!("{} {{{pad}{}{pad}}}", path_str, fields, pad = pad),
 651                         applicability,
 652                     );
 653                 }
 654                 _ => {
 655                     err.span_label(span, fallback_label);
 656                 }
 657             }
 658         };
 659
 660         match (res, source) {
 661             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
 662                 err.span_label(span, fallback_label);
 663                 err.span_suggestion_verbose(
 664                     span.shrink_to_hi(),
 665                     "use `!` to invoke the macro",
 666                     "!".to_string(),
 667                     Applicability::MaybeIncorrect,
 668                 );
 669                 if path_str == "try" && span.rust_2015() {
 670                     err.note("if you want the `try` keyword, you need to be in the 2018 edition");
 671                 }
 672             }
 673             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
 674                 err.span_label(span, "type aliases cannot be used as traits");
 675                 if nightly_options::is_nightly_build() {
 676                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
 677                                `type` alias";
 678                     if let Some(span) = self.def_span(def_id) {
 679                         err.span_help(span, msg);
 680                     } else {
 681                         err.help(msg);
 682                     }
 683                 }
 684             }
 685             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
 686                 if !path_sep(err, &parent) {
 687                     return false;
 688                 }
 689             }
 690             (
 691                 Res::Def(DefKind::Enum, def_id),
 692                 PathSource::TupleStruct(_) | PathSource::Expr(..),
 693             ) => {
 694                 if self
 695                     .diagnostic_metadata
 696                     .current_type_ascription
 697                     .last()
 698                     .map(|sp| {
 699                         self.r
 700                             .session
 701                             .parse_sess
 702                             .type_ascription_path_suggestions
 703                             .borrow()
 704                             .contains(&sp)
 705                     })
 706                     .unwrap_or(false)
 707                 {
 708                     err.delay_as_bug();
 709                     // We already suggested changing `:` into `::` during parsing.
 710                     return false;
 711                 }
 712                 if let Some(variants) = self.collect_enum_variants(def_id) {
 713                     if !variants.is_empty() {
 714                         let msg = if variants.len() == 1 {
 715                             "try using the enum's variant"
 716                         } else {
 717                             "try using one of the enum's variants"
 718                         };
 719
 720                         err.span_suggestions(
 721                             span,
 722                             msg,
 723                             variants.iter().map(path_names_to_string),
 724                             Applicability::MaybeIncorrect,
 725                         );
 726                     }
 727                 } else {
 728                     err.note("you might have meant to use one of the enum's variants");
 729                 }
 730             }
 731             (Res::Def(DefKind::Struct, def_id), _) if ns == ValueNS => {
 732                 if let Some((ctor_def, ctor_vis)) = self.r.struct_constructors.get(&def_id).cloned()
 733                 {
 734                     let accessible_ctor =
 735                         self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
 736                     if is_expected(ctor_def) && !accessible_ctor {
 737                         err.span_label(
 738                             span,
 739                             "constructor is not visible here due to private fields".to_string(),
 740                         );
 741                     }
 742                 } else {
 743                     bad_struct_syntax_suggestion(def_id);
 744                 }
 745             }
 746             (
 747                 Res::Def(
 748                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
 749                     def_id,
 750                 ),
 751                 _,
 752             ) if ns == ValueNS => {
 753                 bad_struct_syntax_suggestion(def_id);
 754             }
 755             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
 756                 if let Some(span) = self.def_span(def_id) {
 757                     err.span_label(span, &format!("`{}` defined here", path_str));
 758                 }
 759                 err.span_label(span, format!("did you mean `{}( /* fields */ )`?", path_str));
 760             }
 761             (Res::SelfTy(..), _) if ns == ValueNS => {
 762                 err.span_label(span, fallback_label);
 763                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
 764             }
 765             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
 766                 err.note("can't use a type alias as a constructor");
 767             }
 768             _ => return false,
 769         }
 770         true
 771     }
 772
 773     fn lookup_assoc_candidate<FilterFn>(
 774         &mut self,
 775         ident: Ident,
 776         ns: Namespace,
 777         filter_fn: FilterFn,
 778     ) -> Option<AssocSuggestion>
 779     where
 780         FilterFn: Fn(Res) -> bool,
 781     {
 782         fn extract_node_id(t: &Ty) -> Option<NodeId> {
 783             match t.kind {
 784                 TyKind::Path(None, _) => Some(t.id),
 785                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
 786                 // This doesn't handle the remaining `Ty` variants as they are not
 787                 // that commonly the self_type, it might be interesting to provide
 788                 // support for those in future.
 789                 _ => None,
 790             }
 791         }
 792
 793         // Fields are generally expected in the same contexts as locals.
 794         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
 795             if let Some(node_id) =
 796                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
 797             {
 798                 // Look for a field with the same name in the current self_type.
 799                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
 800                     match resolution.base_res() {
 801                         Res::Def(DefKind::Struct | DefKind::Union, did)
 802                             if resolution.unresolved_segments() == 0 =>
 803                         {
 804                             if let Some(field_names) = self.r.field_names.get(&did) {
 805                                 if field_names
 806                                     .iter()
 807                                     .any(|&field_name| ident.name == field_name.node)
 808                                 {
 809                                     return Some(AssocSuggestion::Field);
 810                                 }
 811                             }
 812                         }
 813                         _ => {}
 814                     }
 815                 }
 816             }
 817         }
 818
 819         for assoc_type_ident in &self.diagnostic_metadata.current_trait_assoc_types {
 820             if *assoc_type_ident == ident {
 821                 return Some(AssocSuggestion::AssocItem);
 822             }
 823         }
 824
 825         // Look for associated items in the current trait.
 826         if let Some((module, _)) = self.current_trait_ref {
 827             if let Ok(binding) = self.r.resolve_ident_in_module(
 828                 ModuleOrUniformRoot::Module(module),
 829                 ident,
 830                 ns,
 831                 &self.parent_scope,
 832                 false,
 833                 module.span,
 834             ) {
 835                 let res = binding.res();
 836                 if filter_fn(res) {
 837                     return Some(if self.r.has_self.contains(&res.def_id()) {
 838                         AssocSuggestion::MethodWithSelf
 839                     } else {
 840                         AssocSuggestion::AssocItem
 841                     });
 842                 }
 843             }
 844         }
 845
 846         None
 847     }
 848
 849     fn lookup_typo_candidate(
 850         &mut self,
 851         path: &[Segment],
 852         ns: Namespace,
 853         filter_fn: &impl Fn(Res) -> bool,
 854         span: Span,
 855     ) -> Option<TypoSuggestion> {
 856         let mut names = Vec::new();
 857         if path.len() == 1 {
 858             // Search in lexical scope.
 859             // Walk backwards up the ribs in scope and collect candidates.
 860             for rib in self.ribs[ns].iter().rev() {
 861                 // Locals and type parameters
 862                 for (ident, &res) in &rib.bindings {
 863                     if filter_fn(res) {
 864                         names.push(TypoSuggestion::from_res(ident.name, res));
 865                     }
 866                 }
 867                 // Items in scope
 868                 if let RibKind::ModuleRibKind(module) = rib.kind {
 869                     // Items from this module
 870                     self.r.add_module_candidates(module, &mut names, &filter_fn);
 871
 872                     if let ModuleKind::Block(..) = module.kind {
 873                         // We can see through blocks
 874                     } else {
 875                         // Items from the prelude
 876                         if !module.no_implicit_prelude {
 877                             let extern_prelude = self.r.extern_prelude.clone();
 878                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
 879                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
 880                                     |crate_id| {
 881                                         let crate_mod = Res::Def(
 882                                             DefKind::Mod,
 883                                             DefId { krate: crate_id, index: CRATE_DEF_INDEX },
 884                                         );
 885
 886                                         if filter_fn(crate_mod) {
 887                                             Some(TypoSuggestion::from_res(ident.name, crate_mod))
 888                                         } else {
 889                                             None
 890                                         }
 891                                     },
 892                                 )
 893                             }));
 894
 895                             if let Some(prelude) = self.r.prelude {
 896                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
 897                             }
 898                         }
 899                         break;
 900                     }
 901                 }
 902             }
 903             // Add primitive types to the mix
 904             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
 905                 names.extend(
 906                     self.r.primitive_type_table.primitive_types.iter().map(|(name, prim_ty)| {
 907                         TypoSuggestion::from_res(*name, Res::PrimTy(*prim_ty))
 908                     }),
 909                 )
 910             }
 911         } else {
 912             // Search in module.
 913             let mod_path = &path[..path.len() - 1];
 914             if let PathResult::Module(module) =
 915                 self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No)
 916             {
 917                 if let ModuleOrUniformRoot::Module(module) = module {
 918                     self.r.add_module_candidates(module, &mut names, &filter_fn);
 919                 }
 920             }
 921         }
 922
 923         let name = path[path.len() - 1].ident.name;
 924         // Make sure error reporting is deterministic.
 925         names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 926
 927         match find_best_match_for_name(
 928             names.iter().map(|suggestion| &suggestion.candidate),
 929             name,
 930             None,
 931         ) {
 932             Some(found) if found != name => {
 933                 names.into_iter().find(|suggestion| suggestion.candidate == found)
 934             }
 935             _ => None,
 936         }
 937     }
 938
 939     /// Only used in a specific case of type ascription suggestions
 940     fn get_colon_suggestion_span(&self, start: Span) -> Span {
 941         let sm = self.r.session.source_map();
 942         start.to(sm.next_point(start))
 943     }
 944
 945     fn type_ascription_suggestion(&self, err: &mut DiagnosticBuilder<'_>, base_span: Span) -> bool {
 946         let sm = self.r.session.source_map();
 947         let base_snippet = sm.span_to_snippet(base_span);
 948         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
 949             if let Ok(snippet) = sm.span_to_snippet(sp) {
 950                 let len = snippet.trim_end().len() as u32;
 951                 if snippet.trim() == ":" {
 952                     let colon_sp =
 953                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
 954                     let mut show_label = true;
 955                     if sm.is_multiline(sp) {
 956                         err.span_suggestion_short(
 957                             colon_sp,
 958                             "maybe you meant to write `;` here",
 959                             ";".to_string(),
 960                             Applicability::MaybeIncorrect,
 961                         );
 962                     } else {
 963                         let after_colon_sp =
 964                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
 965                         if snippet.len() == 1 {
 966                             // `foo:bar`
 967                             err.span_suggestion(
 968                                 colon_sp,
 969                                 "maybe you meant to write a path separator here",
 970                                 "::".to_string(),
 971                                 Applicability::MaybeIncorrect,
 972                             );
 973                             show_label = false;
 974                             if !self
 975                                 .r
 976                                 .session
 977                                 .parse_sess
 978                                 .type_ascription_path_suggestions
 979                                 .borrow_mut()
 980                                 .insert(colon_sp)
 981                             {
 982                                 err.delay_as_bug();
 983                             }
 984                         }
 985                         if let Ok(base_snippet) = base_snippet {
 986                             let mut sp = after_colon_sp;
 987                             for _ in 0..100 {
 988                                 // Try to find an assignment
 989                                 sp = sm.next_point(sp);
 990                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
 991                                 match snippet {
 992                                     Ok(ref x) if x.as_str() == "=" => {
 993                                         err.span_suggestion(
 994                                             base_span,
 995                                             "maybe you meant to write an assignment here",
 996                                             format!("let {}", base_snippet),
 997                                             Applicability::MaybeIncorrect,
 998                                         );
 999                                         show_label = false;
1000                                         break;
1001                                     }
1002                                     Ok(ref x) if x.as_str() == "\n" => break,
1003                                     Err(_) => break,
1004                                     Ok(_) => {}
1005                                 }
1006                             }
1007                         }
1008                     }
1009                     if show_label {
1010                         err.span_label(
1011                             base_span,
1012                             "expecting a type here because of type ascription",
1013                         );
1014                     }
1015                     return show_label;
1016                 }
1017             }
1018         }
1019         false
1020     }
1021
1022     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1023         let mut result = None;
1024         let mut seen_modules = FxHashSet::default();
1025         let mut worklist = vec![(self.r.graph_root, Vec::new())];
1026
1027         while let Some((in_module, path_segments)) = worklist.pop() {
1028             // abort if the module is already found
1029             if result.is_some() {
1030                 break;
1031             }
1032
1033             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1034                 // abort if the module is already found or if name_binding is private external
1035                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1036                     return;
1037                 }
1038                 if let Some(module) = name_binding.module() {
1039                     // form the path
1040                     let mut path_segments = path_segments.clone();
1041                     path_segments.push(ast::PathSegment::from_ident(ident));
1042                     let module_def_id = module.def_id().unwrap();
1043                     if module_def_id == def_id {
1044                         let path = Path { span: name_binding.span, segments: path_segments };
1045                         result = Some((
1046                             module,
1047                             ImportSuggestion {
1048                                 did: Some(def_id),
1049                                 descr: "module",
1050                                 path,
1051                                 accessible: true,
1052                             },
1053                         ));
1054                     } else {
1055                         // add the module to the lookup
1056                         if seen_modules.insert(module_def_id) {
1057                             worklist.push((module, path_segments));
1058                         }
1059                     }
1060                 }
1061             });
1062         }
1063
1064         result
1065     }
1066
1067     fn collect_enum_variants(&mut self, def_id: DefId) -> Option<Vec<Path>> {
1068         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1069             let mut variants = Vec::new();
1070             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1071                 if let Res::Def(DefKind::Variant, _) = name_binding.res() {
1072                     let mut segms = enum_import_suggestion.path.segments.clone();
1073                     segms.push(ast::PathSegment::from_ident(ident));
1074                     variants.push(Path { span: name_binding.span, segments: segms });
1075                 }
1076             });
1077             variants
1078         })
1079     }
1080
1081     crate fn report_missing_type_error(
1082         &self,
1083         path: &[Segment],
1084     ) -> Option<(Span, &'static str, String, Applicability)> {
1085         let (ident, span) = match path {
1086             [segment] if !segment.has_generic_args => {
1087                 (segment.ident.to_string(), segment.ident.span)
1088             }
1089             _ => return None,
1090         };
1091         let mut iter = ident.chars().map(|c| c.is_uppercase());
1092         let single_uppercase_char =
1093             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1094         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1095             return None;
1096         }
1097         match (self.diagnostic_metadata.current_item, single_uppercase_char) {
1098             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _) if ident.name == sym::main => {
1099                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1100             }
1101             (
1102                 Some(Item {
1103                     kind:
1104                         kind @ ItemKind::Fn(..)
1105                         | kind @ ItemKind::Enum(..)
1106                         | kind @ ItemKind::Struct(..)
1107                         | kind @ ItemKind::Union(..),
1108                     ..
1109                 }),
1110                 true,
1111             )
1112             | (Some(Item { kind, .. }), false) => {
1113                 // Likely missing type parameter.
1114                 if let Some(generics) = kind.generics() {
1115                     if span.overlaps(generics.span) {
1116                         // Avoid the following:
1117                         // error[E0405]: cannot find trait `A` in this scope
1118                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1119                         //   |
1120                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1121                         //   |           ^- help: you might be missing a type parameter: `, A`
1122                         //   |           |
1123                         //   |           not found in this scope
1124                         return None;
1125                     }
1126                     let msg = "you might be missing a type parameter";
1127                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1128                         let span = if let [.., bound] = &param.bounds[..] {
1129                             bound.span()
1130                         } else {
1131                             param.ident.span
1132                         };
1133                         (span, format!(", {}", ident))
1134                     } else {
1135                         (generics.span, format!("<{}>", ident))
1136                     };
1137                     // Do not suggest if this is coming from macro expansion.
1138                     if !span.from_expansion() {
1139                         return Some((
1140                             span.shrink_to_hi(),
1141                             msg,
1142                             sugg,
1143                             Applicability::MaybeIncorrect,
1144                         ));
1145                     }
1146                 }
1147             }
1148             _ => {}
1149         }
1150         None
1151     }
1152
1153     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1154     /// optionally returning the closest match and whether it is reachable.
1155     crate fn suggestion_for_label_in_rib(
1156         &self,
1157         rib_index: usize,
1158         label: Ident,
1159     ) -> Option<LabelSuggestion> {
1160         // Are ribs from this `rib_index` within scope?
1161         let within_scope = self.is_label_valid_from_rib(rib_index);
1162
1163         let rib = &self.label_ribs[rib_index];
1164         let names = rib
1165             .bindings
1166             .iter()
1167             .filter(|(id, _)| id.span.ctxt() == label.span.ctxt())
1168             .map(|(id, _)| &id.name);
1169
1170         find_best_match_for_name(names, label.name, None).map(|symbol| {
1171             // Upon finding a similar name, get the ident that it was from - the span
1172             // contained within helps make a useful diagnostic. In addition, determine
1173             // whether this candidate is within scope.
1174             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1175             (*ident, within_scope)
1176         })
1177     }
1178 }
1179
1180 impl<'tcx> LifetimeContext<'_, 'tcx> {
1181     crate fn report_missing_lifetime_specifiers(
1182         &self,
1183         span: Span,
1184         count: usize,
1185     ) -> DiagnosticBuilder<'tcx> {
1186         struct_span_err!(
1187             self.tcx.sess,
1188             span,
1189             E0106,
1190             "missing lifetime specifier{}",
1191             pluralize!(count)
1192         )
1193     }
1194
1195     crate fn emit_undeclared_lifetime_error(&self, lifetime_ref: &hir::Lifetime) {
1196         let mut err = struct_span_err!(
1197             self.tcx.sess,
1198             lifetime_ref.span,
1199             E0261,
1200             "use of undeclared lifetime name `{}`",
1201             lifetime_ref
1202         );
1203         err.span_label(lifetime_ref.span, "undeclared lifetime");
1204         let mut suggests_in_band = false;
1205         for missing in &self.missing_named_lifetime_spots {
1206             match missing {
1207                 MissingLifetimeSpot::Generics(generics) => {
1208                     let (span, sugg) = if let Some(param) =
1209                         generics.params.iter().find(|p| match p.kind {
1210                             hir::GenericParamKind::Type {
1211                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1212                                 ..
1213                             } => false,
1214                             _ => true,
1215                         }) {
1216                         (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref))
1217                     } else {
1218                         suggests_in_band = true;
1219                         (generics.span, format!("<{}>", lifetime_ref))
1220                     };
1221                     err.span_suggestion(
1222                         span,
1223                         &format!("consider introducing lifetime `{}` here", lifetime_ref),
1224                         sugg,
1225                         Applicability::MaybeIncorrect,
1226                     );
1227                 }
1228                 MissingLifetimeSpot::HigherRanked { span, span_type } => {
1229                     err.span_suggestion(
1230                         *span,
1231                         &format!(
1232                             "consider making the {} lifetime-generic with a new `{}` lifetime",
1233                             span_type.descr(),
1234                             lifetime_ref
1235                         ),
1236                         span_type.suggestion(&lifetime_ref.to_string()),
1237                         Applicability::MaybeIncorrect,
1238                     );
1239                     err.note(
1240                         "for more information on higher-ranked polymorphism, visit \
1241                             https://doc.rust-lang.org/nomicon/hrtb.html",
1242                     );
1243                 }
1244             }
1245         }
1246         if nightly_options::is_nightly_build()
1247             && !self.tcx.features().in_band_lifetimes
1248             && suggests_in_band
1249         {
1250             err.help(
1251                 "if you want to experiment with in-band lifetime bindings, \
1252                     add `#![feature(in_band_lifetimes)]` to the crate attributes",
1253             );
1254         }
1255         err.emit();
1256     }
1257
1258     // FIXME(const_generics): This patches over a ICE caused by non-'static lifetimes in const
1259     // generics. We are disallowing this until we can decide on how we want to handle non-'static
1260     // lifetimes in const generics. See issue #74052 for discussion.
1261     crate fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &hir::Lifetime) {
1262         let mut err = struct_span_err!(
1263             self.tcx.sess,
1264             lifetime_ref.span,
1265             E0771,
1266             "use of non-static lifetime `{}` in const generic",
1267             lifetime_ref
1268         );
1269         err.note(
1270             "for more information, see issue #74052 \
1271             <https://github.com/rust-lang/rust/issues/74052>",
1272         );
1273         err.emit();
1274     }
1275
1276     crate fn is_trait_ref_fn_scope(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) -> bool {
1277         if let def::Res::Def(_, did) = trait_ref.trait_ref.path.res {
1278             if [
1279                 self.tcx.lang_items().fn_once_trait(),
1280                 self.tcx.lang_items().fn_trait(),
1281                 self.tcx.lang_items().fn_mut_trait(),
1282             ]
1283             .contains(&Some(did))
1284             {
1285                 let (span, span_type) = match &trait_ref.bound_generic_params {
1286                     [] => (trait_ref.span.shrink_to_lo(), ForLifetimeSpanType::BoundEmpty),
1287                     [.., bound] => (bound.span.shrink_to_hi(), ForLifetimeSpanType::BoundTail),
1288                 };
1289                 self.missing_named_lifetime_spots
1290                     .push(MissingLifetimeSpot::HigherRanked { span, span_type });
1291                 return true;
1292             }
1293         };
1294         false
1295     }
1296
1297     crate fn add_missing_lifetime_specifiers_label(
1298         &self,
1299         err: &mut DiagnosticBuilder<'_>,
1300         span: Span,
1301         count: usize,
1302         lifetime_names: &FxHashSet<Ident>,
1303         params: &[ElisionFailureInfo],
1304     ) {
1305         let snippet = self.tcx.sess.source_map().span_to_snippet(span).ok();
1306
1307         err.span_label(
1308             span,
1309             &format!(
1310                 "expected {} lifetime parameter{}",
1311                 if count == 1 { "named".to_string() } else { count.to_string() },
1312                 pluralize!(count)
1313             ),
1314         );
1315
1316         let suggest_existing = |err: &mut DiagnosticBuilder<'_>, sugg| {
1317             err.span_suggestion_verbose(
1318                 span,
1319                 &format!("consider using the `{}` lifetime", lifetime_names.iter().next().unwrap()),
1320                 sugg,
1321                 Applicability::MaybeIncorrect,
1322             );
1323         };
1324         let suggest_new = |err: &mut DiagnosticBuilder<'_>, sugg: &str| {
1325             for missing in self.missing_named_lifetime_spots.iter().rev() {
1326                 let mut introduce_suggestion = vec![];
1327                 let msg;
1328                 let should_break;
1329                 introduce_suggestion.push(match missing {
1330                     MissingLifetimeSpot::Generics(generics) => {
1331                         msg = "consider introducing a named lifetime parameter".to_string();
1332                         should_break = true;
1333                         if let Some(param) = generics.params.iter().find(|p| match p.kind {
1334                             hir::GenericParamKind::Type {
1335                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1336                                 ..
1337                             } => false,
1338                             _ => true,
1339                         }) {
1340                             (param.span.shrink_to_lo(), "'a, ".to_string())
1341                         } else {
1342                             (generics.span, "<'a>".to_string())
1343                         }
1344                     }
1345                     MissingLifetimeSpot::HigherRanked { span, span_type } => {
1346                         msg = format!(
1347                             "consider making the {} lifetime-generic with a new `'a` lifetime",
1348                             span_type.descr(),
1349                         );
1350                         should_break = false;
1351                         err.note(
1352                             "for more information on higher-ranked polymorphism, visit \
1353                             https://doc.rust-lang.org/nomicon/hrtb.html",
1354                         );
1355                         (*span, span_type.suggestion("'a"))
1356                     }
1357                 });
1358                 for param in params {
1359                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
1360                         if snippet.starts_with('&') && !snippet.starts_with("&'") {
1361                             introduce_suggestion
1362                                 .push((param.span, format!("&'a {}", &snippet[1..])));
1363                         } else if snippet.starts_with("&'_ ") {
1364                             introduce_suggestion
1365                                 .push((param.span, format!("&'a {}", &snippet[4..])));
1366                         }
1367                     }
1368                 }
1369                 introduce_suggestion.push((span, sugg.to_string()));
1370                 err.multipart_suggestion(&msg, introduce_suggestion, Applicability::MaybeIncorrect);
1371                 if should_break {
1372                     break;
1373                 }
1374             }
1375         };
1376
1377         match (lifetime_names.len(), lifetime_names.iter().next(), snippet.as_deref()) {
1378             (1, Some(name), Some("&")) => {
1379                 suggest_existing(err, format!("&{} ", name));
1380             }
1381             (1, Some(name), Some("'_")) => {
1382                 suggest_existing(err, name.to_string());
1383             }
1384             (1, Some(name), Some("")) => {
1385                 suggest_existing(err, format!("{}, ", name).repeat(count));
1386             }
1387             (1, Some(name), Some(snippet)) if !snippet.ends_with('>') => {
1388                 suggest_existing(
1389                     err,
1390                     format!(
1391                         "{}<{}>",
1392                         snippet,
1393                         std::iter::repeat(name.to_string())
1394                             .take(count)
1395                             .collect::<Vec<_>>()
1396                             .join(", ")
1397                     ),
1398                 );
1399             }
1400             (0, _, Some("&")) if count == 1 => {
1401                 suggest_new(err, "&'a ");
1402             }
1403             (0, _, Some("'_")) if count == 1 => {
1404                 suggest_new(err, "'a");
1405             }
1406             (0, _, Some(snippet)) if !snippet.ends_with('>') && count == 1 => {
1407                 suggest_new(err, &format!("{}<'a>", snippet));
1408             }
1409             (n, ..) if n > 1 => {
1410                 let spans: Vec<Span> = lifetime_names.iter().map(|lt| lt.span).collect();
1411                 err.span_note(spans, "these named lifetimes are available to use");
1412                 if Some("") == snippet.as_deref() {
1413                     // This happens when we have `Foo<T>` where we point at the space before `T`,
1414                     // but this can be confusing so we give a suggestion with placeholders.
1415                     err.span_suggestion_verbose(
1416                         span,
1417                         "consider using one of the available lifetimes here",
1418                         "'lifetime, ".repeat(count),
1419                         Applicability::HasPlaceholders,
1420                     );
1421                 }
1422             }
1423             _ => {}
1424         }
1425     }
1426 }