compiler/rustc_resolve/src/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::lifetimes::{ElisionFailureInfo, LifetimeContext};
   3 use crate::late::{AliasPossibility, 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::visit::FnKind;
   9 use rustc_ast::{self as ast, Expr, ExprKind, Item, ItemKind, NodeId, Path, Ty, TyKind};
  10 use rustc_ast_pretty::pprust::path_segment_to_string;
  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, CtorOf, DefKind};
  16 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  17 use rustc_hir::PrimTy;
  18 use rustc_session::parse::feature_err;
  19 use rustc_span::hygiene::MacroKind;
  20 use rustc_span::lev_distance::find_best_match_for_name;
  21 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  22 use rustc_span::{BytePos, MultiSpan, Span, DUMMY_SP};
  23
  24 use tracing::debug;
  25
  26 type Res = def::Res<ast::NodeId>;
  27
  28 /// A field or associated item from self type suggested in case of resolution failure.
  29 enum AssocSuggestion {
  30     Field,
  31     MethodWithSelf,
  32     AssocFn,
  33     AssocType,
  34     AssocConst,
  35 }
  36
  37 impl AssocSuggestion {
  38     fn action(&self) -> &'static str {
  39         match self {
  40             AssocSuggestion::Field => "use the available field",
  41             AssocSuggestion::MethodWithSelf => "call the method with the fully-qualified path",
  42             AssocSuggestion::AssocFn => "call the associated function",
  43             AssocSuggestion::AssocConst => "use the associated `const`",
  44             AssocSuggestion::AssocType => "use the associated type",
  45         }
  46     }
  47 }
  48
  49 crate enum MissingLifetimeSpot<'tcx> {
  50     Generics(&'tcx hir::Generics<'tcx>),
  51     HigherRanked { span: Span, span_type: ForLifetimeSpanType },
  52     Static,
  53 }
  54
  55 crate enum ForLifetimeSpanType {
  56     BoundEmpty,
  57     BoundTail,
  58     TypeEmpty,
  59     TypeTail,
  60 }
  61
  62 impl ForLifetimeSpanType {
  63     crate fn descr(&self) -> &'static str {
  64         match self {
  65             Self::BoundEmpty | Self::BoundTail => "bound",
  66             Self::TypeEmpty | Self::TypeTail => "type",
  67         }
  68     }
  69
  70     crate fn suggestion(&self, sugg: &str) -> String {
  71         match self {
  72             Self::BoundEmpty | Self::TypeEmpty => format!("for<{}> ", sugg),
  73             Self::BoundTail | Self::TypeTail => format!(", {}", sugg),
  74         }
  75     }
  76 }
  77
  78 impl<'tcx> Into<MissingLifetimeSpot<'tcx>> for &'tcx hir::Generics<'tcx> {
  79     fn into(self) -> MissingLifetimeSpot<'tcx> {
  80         MissingLifetimeSpot::Generics(self)
  81     }
  82 }
  83
  84 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  85     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  86 }
  87
  88 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  89     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  90 }
  91
  92 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  93 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
  94     let variant_path = &suggestion.path;
  95     let variant_path_string = path_names_to_string(variant_path);
  96
  97     let path_len = suggestion.path.segments.len();
  98     let enum_path = ast::Path {
  99         span: suggestion.path.span,
 100         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
 101         tokens: None,
 102     };
 103     let enum_path_string = path_names_to_string(&enum_path);
 104
 105     (variant_path_string, enum_path_string)
 106 }
 107
 108 impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 109     fn def_span(&self, def_id: DefId) -> Option<Span> {
 110         match def_id.krate {
 111             LOCAL_CRATE => self.r.opt_span(def_id),
 112             _ => Some(
 113                 self.r
 114                     .session
 115                     .source_map()
 116                     .guess_head_span(self.r.cstore().get_span_untracked(def_id, self.r.session)),
 117             ),
 118         }
 119     }
 120
 121     /// Handles error reporting for `smart_resolve_path_fragment` function.
 122     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 123     pub(crate) fn smart_resolve_report_errors(
 124         &mut self,
 125         path: &[Segment],
 126         span: Span,
 127         source: PathSource<'_>,
 128         res: Option<Res>,
 129     ) -> (DiagnosticBuilder<'a>, Vec<ImportSuggestion>) {
 130         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 131         let ns = source.namespace();
 132         let is_expected = &|res| source.is_expected(res);
 133         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 134
 135         // Make the base error.
 136         let expected = source.descr_expected();
 137         let path_str = Segment::names_to_string(path);
 138         let item_str = path.last().unwrap().ident;
 139         let (base_msg, fallback_label, base_span, could_be_expr) = if let Some(res) = res {
 140             (
 141                 format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 142                 format!("not a {}", expected),
 143                 span,
 144                 match res {
 145                     Res::Def(DefKind::Fn, _) => {
 146                         // Verify whether this is a fn call or an Fn used as a type.
 147                         self.r
 148                             .session
 149                             .source_map()
 150                             .span_to_snippet(span)
 151                             .map(|snippet| snippet.ends_with(')'))
 152                             .unwrap_or(false)
 153                     }
 154                     Res::Def(
 155                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 156                         _,
 157                     )
 158                     | Res::SelfCtor(_)
 159                     | Res::PrimTy(_)
 160                     | Res::Local(_) => true,
 161                     _ => false,
 162                 },
 163             )
 164         } else {
 165             let item_span = path.last().unwrap().ident.span;
 166             let (mod_prefix, mod_str) = if path.len() == 1 {
 167                 (String::new(), "this scope".to_string())
 168             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 169                 (String::new(), "the crate root".to_string())
 170             } else {
 171                 let mod_path = &path[..path.len() - 1];
 172                 let mod_prefix =
 173                     match self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No) {
 174                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 175                         _ => None,
 176                     }
 177                     .map_or(String::new(), |res| format!("{} ", res.descr()));
 178                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)))
 179             };
 180             (
 181                 format!("cannot find {} `{}` in {}{}", expected, item_str, mod_prefix, mod_str),
 182                 if path_str == "async" && expected.starts_with("struct") {
 183                     "`async` blocks are only allowed in the 2018 edition".to_string()
 184                 } else {
 185                     format!("not found in {}", mod_str)
 186                 },
 187                 item_span,
 188                 false,
 189             )
 190         };
 191
 192         let code = source.error_code(res.is_some());
 193         let mut err = self.r.session.struct_span_err_with_code(base_span, &base_msg, code);
 194
 195         match (source, self.diagnostic_metadata.in_if_condition) {
 196             (PathSource::Expr(_), Some(Expr { span, kind: ExprKind::Assign(..), .. })) => {
 197                 err.span_suggestion_verbose(
 198                     span.shrink_to_lo(),
 199                     "you might have meant to use pattern matching",
 200                     "let ".to_string(),
 201                     Applicability::MaybeIncorrect,
 202                 );
 203                 self.r.session.if_let_suggestions.borrow_mut().insert(*span);
 204             }
 205             _ => {}
 206         }
 207
 208         let is_assoc_fn = self.self_type_is_available(span);
 209         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 210         if ["this", "my"].contains(&&*item_str.as_str()) && is_assoc_fn {
 211             err.span_suggestion_short(
 212                 span,
 213                 "you might have meant to use `self` here instead",
 214                 "self".to_string(),
 215                 Applicability::MaybeIncorrect,
 216             );
 217             if !self.self_value_is_available(path[0].ident.span, span) {
 218                 if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
 219                     &self.diagnostic_metadata.current_function
 220                 {
 221                     let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
 222                         (param.span.shrink_to_lo(), "&self, ")
 223                     } else {
 224                         (
 225                             self.r
 226                                 .session
 227                                 .source_map()
 228                                 .span_through_char(*fn_span, '(')
 229                                 .shrink_to_hi(),
 230                             "&self",
 231                         )
 232                     };
 233                     err.span_suggestion_verbose(
 234                         span,
 235                         "if you meant to use `self`, you are also missing a `self` receiver \
 236                          argument",
 237                         sugg.to_string(),
 238                         Applicability::MaybeIncorrect,
 239                     );
 240                 }
 241             }
 242         }
 243
 244         // Emit special messages for unresolved `Self` and `self`.
 245         if is_self_type(path, ns) {
 246             err.code(rustc_errors::error_code!(E0411));
 247             err.span_label(
 248                 span,
 249                 "`Self` is only available in impls, traits, and type definitions".to_string(),
 250             );
 251             return (err, Vec::new());
 252         }
 253         if is_self_value(path, ns) {
 254             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 255
 256             err.code(rustc_errors::error_code!(E0424));
 257             err.span_label(span, match source {
 258                 PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed"
 259                                    .to_string(),
 260                 _ => "`self` value is a keyword only available in methods with a `self` parameter"
 261                      .to_string(),
 262             });
 263             if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 264                 // The current function has a `self' parameter, but we were unable to resolve
 265                 // a reference to `self`. This can only happen if the `self` identifier we
 266                 // are resolving came from a different hygiene context.
 267                 if fn_kind.decl().inputs.get(0).map(|p| p.is_self()).unwrap_or(false) {
 268                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 269                 } else {
 270                     let doesnt = if is_assoc_fn {
 271                         let (span, sugg) = fn_kind
 272                             .decl()
 273                             .inputs
 274                             .get(0)
 275                             .map(|p| (p.span.shrink_to_lo(), "&self, "))
 276                             .unwrap_or_else(|| {
 277                                 (
 278                                     self.r
 279                                         .session
 280                                         .source_map()
 281                                         .span_through_char(*span, '(')
 282                                         .shrink_to_hi(),
 283                                     "&self",
 284                                 )
 285                             });
 286                         err.span_suggestion_verbose(
 287                             span,
 288                             "add a `self` receiver parameter to make the associated `fn` a method",
 289                             sugg.to_string(),
 290                             Applicability::MaybeIncorrect,
 291                         );
 292                         "doesn't"
 293                     } else {
 294                         "can't"
 295                     };
 296                     if let Some(ident) = fn_kind.ident() {
 297                         err.span_label(
 298                             ident.span,
 299                             &format!("this function {} have a `self` parameter", doesnt),
 300                         );
 301                     }
 302                 }
 303             }
 304             return (err, Vec::new());
 305         }
 306
 307         // Try to lookup name in more relaxed fashion for better error reporting.
 308         let ident = path.last().unwrap().ident;
 309         let candidates = self
 310             .r
 311             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 312             .drain(..)
 313             .filter(|ImportSuggestion { did, .. }| {
 314                 match (did, res.and_then(|res| res.opt_def_id())) {
 315                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 316                     _ => true,
 317                 }
 318             })
 319             .collect::<Vec<_>>();
 320         let crate_def_id = DefId::local(CRATE_DEF_INDEX);
 321         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 322             let enum_candidates =
 323                 self.r.lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant);
 324
 325             if !enum_candidates.is_empty() {
 326                 if let (PathSource::Type, Some(span)) =
 327                     (source, self.diagnostic_metadata.current_type_ascription.last())
 328                 {
 329                     if self
 330                         .r
 331                         .session
 332                         .parse_sess
 333                         .type_ascription_path_suggestions
 334                         .borrow()
 335                         .contains(span)
 336                     {
 337                         // Already reported this issue on the lhs of the type ascription.
 338                         err.delay_as_bug();
 339                         return (err, candidates);
 340                     }
 341                 }
 342
 343                 let mut enum_candidates = enum_candidates
 344                     .iter()
 345                     .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 346                     .collect::<Vec<_>>();
 347                 enum_candidates.sort();
 348
 349                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 350                 // (that it's a variant) for E0573 "expected type, found variant".
 351                 let preamble = if res.is_none() {
 352                     let others = match enum_candidates.len() {
 353                         1 => String::new(),
 354                         2 => " and 1 other".to_owned(),
 355                         n => format!(" and {} others", n),
 356                     };
 357                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 358                 } else {
 359                     String::new()
 360                 };
 361                 let msg = format!("{}try using the variant's enum", preamble);
 362
 363                 err.span_suggestions(
 364                     span,
 365                     &msg,
 366                     enum_candidates
 367                         .into_iter()
 368                         .map(|(_variant_path, enum_ty_path)| enum_ty_path)
 369                         // Variants re-exported in prelude doesn't mean `prelude::v1` is the
 370                         // type name!
 371                         // FIXME: is there a more principled way to do this that
 372                         // would work for other re-exports?
 373                         .filter(|enum_ty_path| enum_ty_path != "std::prelude::v1")
 374                         // Also write `Option` rather than `std::prelude::v1::Option`.
 375                         .map(|enum_ty_path| {
 376                             // FIXME #56861: DRY-er prelude filtering.
 377                             enum_ty_path.trim_start_matches("std::prelude::v1::").to_owned()
 378                         }),
 379                     Applicability::MachineApplicable,
 380                 );
 381             }
 382         }
 383         if path.len() == 1 && self.self_type_is_available(span) {
 384             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 385                 let self_is_available = self.self_value_is_available(path[0].ident.span, span);
 386                 match candidate {
 387                     AssocSuggestion::Field => {
 388                         if self_is_available {
 389                             err.span_suggestion(
 390                                 span,
 391                                 "you might have meant to use the available field",
 392                                 format!("self.{}", path_str),
 393                                 Applicability::MachineApplicable,
 394                             );
 395                         } else {
 396                             err.span_label(span, "a field by this name exists in `Self`");
 397                         }
 398                     }
 399                     AssocSuggestion::MethodWithSelf if self_is_available => {
 400                         err.span_suggestion(
 401                             span,
 402                             "you might have meant to call the method",
 403                             format!("self.{}", path_str),
 404                             Applicability::MachineApplicable,
 405                         );
 406                     }
 407                     AssocSuggestion::MethodWithSelf
 408                     | AssocSuggestion::AssocFn
 409                     | AssocSuggestion::AssocConst
 410                     | AssocSuggestion::AssocType => {
 411                         err.span_suggestion(
 412                             span,
 413                             &format!("you might have meant to {}", candidate.action()),
 414                             format!("Self::{}", path_str),
 415                             Applicability::MachineApplicable,
 416                         );
 417                     }
 418                 }
 419                 return (err, candidates);
 420             }
 421
 422             // If the first argument in call is `self` suggest calling a method.
 423             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 424                 let mut args_snippet = String::new();
 425                 if let Some(args_span) = args_span {
 426                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 427                         args_snippet = snippet;
 428                     }
 429                 }
 430
 431                 err.span_suggestion(
 432                     call_span,
 433                     &format!("try calling `{}` as a method", ident),
 434                     format!("self.{}({})", path_str, args_snippet),
 435                     Applicability::MachineApplicable,
 436                 );
 437                 return (err, candidates);
 438             }
 439         }
 440
 441         // Try Levenshtein algorithm.
 442         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected, span);
 443         // Try context-dependent help if relaxed lookup didn't work.
 444         if let Some(res) = res {
 445             if self.smart_resolve_context_dependent_help(
 446                 &mut err,
 447                 span,
 448                 source,
 449                 res,
 450                 &path_str,
 451                 &fallback_label,
 452             ) {
 453                 // We do this to avoid losing a secondary span when we override the main error span.
 454                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 455                 return (err, candidates);
 456             }
 457         }
 458
 459         if !self.type_ascription_suggestion(&mut err, base_span) {
 460             let mut fallback = false;
 461             if let (
 462                 PathSource::Trait(AliasPossibility::Maybe),
 463                 Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
 464             ) = (source, res)
 465             {
 466                 if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
 467                     fallback = true;
 468                     let spans: Vec<Span> = bounds
 469                         .iter()
 470                         .map(|bound| bound.span())
 471                         .filter(|&sp| sp != base_span)
 472                         .collect();
 473
 474                     let start_span = bounds.iter().map(|bound| bound.span()).next().unwrap();
 475                     // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
 476                     let end_span = bounds.iter().map(|bound| bound.span()).last().unwrap();
 477                     // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
 478                     let last_bound_span = spans.last().cloned().unwrap();
 479                     let mut multi_span: MultiSpan = spans.clone().into();
 480                     for sp in spans {
 481                         let msg = if sp == last_bound_span {
 482                             format!(
 483                                 "...because of {} bound{}",
 484                                 if bounds.len() <= 2 { "this" } else { "these" },
 485                                 if bounds.len() <= 2 { "" } else { "s" },
 486                             )
 487                         } else {
 488                             String::new()
 489                         };
 490                         multi_span.push_span_label(sp, msg);
 491                     }
 492                     multi_span.push_span_label(
 493                         base_span,
 494                         "expected this type to be a trait...".to_string(),
 495                     );
 496                     err.span_help(
 497                         multi_span,
 498                         "`+` is used to constrain a \"trait object\" type with lifetimes or \
 499                          auto-traits; structs and enums can't be bound in that way",
 500                     );
 501                     if bounds.iter().all(|bound| match bound {
 502                         ast::GenericBound::Outlives(_) => true,
 503                         ast::GenericBound::Trait(tr, _) => tr.span == base_span,
 504                     }) {
 505                         let mut sugg = vec![];
 506                         if base_span != start_span {
 507                             sugg.push((start_span.until(base_span), String::new()));
 508                         }
 509                         if base_span != end_span {
 510                             sugg.push((base_span.shrink_to_hi().to(end_span), String::new()));
 511                         }
 512
 513                         err.multipart_suggestion(
 514                             "if you meant to use a type and not a trait here, remove the bounds",
 515                             sugg,
 516                             Applicability::MaybeIncorrect,
 517                         );
 518                     }
 519                 }
 520             }
 521
 522             fallback |= self.restrict_assoc_type_in_where_clause(span, &mut err);
 523
 524             if !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span) {
 525                 fallback = true;
 526                 match self.diagnostic_metadata.current_let_binding {
 527                     Some((pat_sp, Some(ty_sp), None))
 528                         if ty_sp.contains(base_span) && could_be_expr =>
 529                     {
 530                         err.span_suggestion_short(
 531                             pat_sp.between(ty_sp),
 532                             "use `=` if you meant to assign",
 533                             " = ".to_string(),
 534                             Applicability::MaybeIncorrect,
 535                         );
 536                     }
 537                     _ => {}
 538                 }
 539             }
 540             if fallback {
 541                 // Fallback label.
 542                 err.span_label(base_span, fallback_label);
 543             }
 544         }
 545         (err, candidates)
 546     }
 547
 548     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
 549     fn restrict_assoc_type_in_where_clause(
 550         &mut self,
 551         span: Span,
 552         err: &mut DiagnosticBuilder<'_>,
 553     ) -> bool {
 554         // Detect that we are actually in a `where` predicate.
 555         let (bounded_ty, bounds, where_span) =
 556             if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 557                 bounded_ty,
 558                 bound_generic_params,
 559                 bounds,
 560                 span,
 561             })) = self.diagnostic_metadata.current_where_predicate
 562             {
 563                 if !bound_generic_params.is_empty() {
 564                     return false;
 565                 }
 566                 (bounded_ty, bounds, span)
 567             } else {
 568                 return false;
 569             };
 570
 571         // Confirm that the target is an associated type.
 572         let (ty, position, path) = if let ast::TyKind::Path(
 573             Some(ast::QSelf { ty, position, .. }),
 574             path,
 575         ) = &bounded_ty.kind
 576         {
 577             // use this to verify that ident is a type param.
 578             let partial_res = if let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
 579                 bounded_ty.id,
 580                 None,
 581                 &Segment::from_path(path),
 582                 Namespace::TypeNS,
 583                 span,
 584                 true,
 585                 CrateLint::No,
 586             ) {
 587                 partial_res
 588             } else {
 589                 return false;
 590             };
 591             if !(matches!(
 592                 partial_res.base_res(),
 593                 hir::def::Res::Def(hir::def::DefKind::AssocTy, _)
 594             ) && partial_res.unresolved_segments() == 0)
 595             {
 596                 return false;
 597             }
 598             (ty, position, path)
 599         } else {
 600             return false;
 601         };
 602
 603         if let ast::TyKind::Path(None, type_param_path) = &ty.peel_refs().kind {
 604             // Confirm that the `SelfTy` is a type parameter.
 605             let partial_res = if let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
 606                 bounded_ty.id,
 607                 None,
 608                 &Segment::from_path(type_param_path),
 609                 Namespace::TypeNS,
 610                 span,
 611                 true,
 612                 CrateLint::No,
 613             ) {
 614                 partial_res
 615             } else {
 616                 return false;
 617             };
 618             if !(matches!(
 619                 partial_res.base_res(),
 620                 hir::def::Res::Def(hir::def::DefKind::TyParam, _)
 621             ) && partial_res.unresolved_segments() == 0)
 622             {
 623                 return false;
 624             }
 625             if let (
 626                 [ast::PathSegment { ident: constrain_ident, args: None, .. }],
 627                 [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
 628             ) = (&type_param_path.segments[..], &bounds[..])
 629             {
 630                 if let [ast::PathSegment { ident, args: None, .. }] =
 631                     &poly_trait_ref.trait_ref.path.segments[..]
 632                 {
 633                     if ident.span == span {
 634                         err.span_suggestion_verbose(
 635                             *where_span,
 636                             &format!("constrain the associated type to `{}`", ident),
 637                             format!(
 638                                 "{}: {}<{} = {}>",
 639                                 self.r
 640                                     .session
 641                                     .source_map()
 642                                     .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
 643                                     .unwrap_or_else(|_| constrain_ident.to_string()),
 644                                 path.segments[..*position]
 645                                     .iter()
 646                                     .map(|segment| path_segment_to_string(segment))
 647                                     .collect::<Vec<_>>()
 648                                     .join("::"),
 649                                 path.segments[*position..]
 650                                     .iter()
 651                                     .map(|segment| path_segment_to_string(segment))
 652                                     .collect::<Vec<_>>()
 653                                     .join("::"),
 654                                 ident,
 655                             ),
 656                             Applicability::MaybeIncorrect,
 657                         );
 658                     }
 659                     return true;
 660                 }
 661             }
 662         }
 663         false
 664     }
 665
 666     /// Check if the source is call expression and the first argument is `self`. If true,
 667     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 668     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 669         let mut has_self_arg = None;
 670         if let PathSource::Expr(Some(parent)) = source {
 671             match &parent.kind {
 672                 ExprKind::Call(_, args) if !args.is_empty() => {
 673                     let mut expr_kind = &args[0].kind;
 674                     loop {
 675                         match expr_kind {
 676                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 677                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 678                                     let call_span = parent.span;
 679                                     let tail_args_span = if args.len() > 1 {
 680                                         Some(Span::new(
 681                                             args[1].span.lo(),
 682                                             args.last().unwrap().span.hi(),
 683                                             call_span.ctxt(),
 684                                         ))
 685                                     } else {
 686                                         None
 687                                     };
 688                                     has_self_arg = Some((call_span, tail_args_span));
 689                                 }
 690                                 break;
 691                             }
 692                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 693                             _ => break,
 694                         }
 695                     }
 696                 }
 697                 _ => (),
 698             }
 699         };
 700         has_self_arg
 701     }
 702
 703     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 704         // HACK(estebank): find a better way to figure out that this was a
 705         // parser issue where a struct literal is being used on an expression
 706         // where a brace being opened means a block is being started. Look
 707         // ahead for the next text to see if `span` is followed by a `{`.
 708         let sm = self.r.session.source_map();
 709         let mut sp = span;
 710         loop {
 711             sp = sm.next_point(sp);
 712             match sm.span_to_snippet(sp) {
 713                 Ok(ref snippet) => {
 714                     if snippet.chars().any(|c| !c.is_whitespace()) {
 715                         break;
 716                     }
 717                 }
 718                 _ => break,
 719             }
 720         }
 721         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
 722         // In case this could be a struct literal that needs to be surrounded
 723         // by parentheses, find the appropriate span.
 724         let mut i = 0;
 725         let mut closing_brace = None;
 726         loop {
 727             sp = sm.next_point(sp);
 728             match sm.span_to_snippet(sp) {
 729                 Ok(ref snippet) => {
 730                     if snippet == "}" {
 731                         closing_brace = Some(span.to(sp));
 732                         break;
 733                     }
 734                 }
 735                 _ => break,
 736             }
 737             i += 1;
 738             // The bigger the span, the more likely we're incorrect --
 739             // bound it to 100 chars long.
 740             if i > 100 {
 741                 break;
 742             }
 743         }
 744         (followed_by_brace, closing_brace)
 745     }
 746
 747     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 748     /// function.
 749     /// Returns `true` if able to provide context-dependent help.
 750     fn smart_resolve_context_dependent_help(
 751         &mut self,
 752         err: &mut DiagnosticBuilder<'a>,
 753         span: Span,
 754         source: PathSource<'_>,
 755         res: Res,
 756         path_str: &str,
 757         fallback_label: &str,
 758     ) -> bool {
 759         let ns = source.namespace();
 760         let is_expected = &|res| source.is_expected(res);
 761
 762         let path_sep = |err: &mut DiagnosticBuilder<'_>, expr: &Expr| match expr.kind {
 763             ExprKind::Field(_, ident) => {
 764                 err.span_suggestion(
 765                     expr.span,
 766                     "use the path separator to refer to an item",
 767                     format!("{}::{}", path_str, ident),
 768                     Applicability::MaybeIncorrect,
 769                 );
 770                 true
 771             }
 772             ExprKind::MethodCall(ref segment, ..) => {
 773                 let span = expr.span.with_hi(segment.ident.span.hi());
 774                 err.span_suggestion(
 775                     span,
 776                     "use the path separator to refer to an item",
 777                     format!("{}::{}", path_str, segment.ident),
 778                     Applicability::MaybeIncorrect,
 779                 );
 780                 true
 781             }
 782             _ => false,
 783         };
 784
 785         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 786             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 787
 788             match source {
 789                 PathSource::Expr(Some(
 790                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
 791                 )) if path_sep(err, &parent) => {}
 792                 PathSource::Expr(
 793                     None
 794                     | Some(Expr {
 795                         kind:
 796                             ExprKind::Path(..)
 797                             | ExprKind::Binary(..)
 798                             | ExprKind::Unary(..)
 799                             | ExprKind::If(..)
 800                             | ExprKind::While(..)
 801                             | ExprKind::ForLoop(..)
 802                             | ExprKind::Match(..),
 803                         ..
 804                     }),
 805                 ) if followed_by_brace => {
 806                     if let Some(sp) = closing_brace {
 807                         err.span_label(span, fallback_label);
 808                         err.multipart_suggestion(
 809                             "surround the struct literal with parentheses",
 810                             vec![
 811                                 (sp.shrink_to_lo(), "(".to_string()),
 812                                 (sp.shrink_to_hi(), ")".to_string()),
 813                             ],
 814                             Applicability::MaybeIncorrect,
 815                         );
 816                     } else {
 817                         err.span_label(
 818                             span, // Note the parentheses surrounding the suggestion below
 819                             format!(
 820                                 "you might want to surround a struct literal with parentheses: \
 821                                  `({} {{ /* fields */ }})`?",
 822                                 path_str
 823                             ),
 824                         );
 825                     }
 826                 }
 827                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
 828                     let span = match &source {
 829                         PathSource::Expr(Some(Expr {
 830                             span, kind: ExprKind::Call(_, _), ..
 831                         }))
 832                         | PathSource::TupleStruct(span, _) => {
 833                             // We want the main underline to cover the suggested code as well for
 834                             // cleaner output.
 835                             err.set_span(*span);
 836                             *span
 837                         }
 838                         _ => span,
 839                     };
 840                     if let Some(span) = self.def_span(def_id) {
 841                         err.span_label(span, &format!("`{}` defined here", path_str));
 842                     }
 843                     let (tail, descr, applicability) = match source {
 844                         PathSource::Pat | PathSource::TupleStruct(..) => {
 845                             ("", "pattern", Applicability::MachineApplicable)
 846                         }
 847                         _ => (": val", "literal", Applicability::HasPlaceholders),
 848                     };
 849                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
 850                         Some(fields) => (
 851                             fields
 852                                 .iter()
 853                                 .map(|f| format!("{}{}", f.node, tail))
 854                                 .collect::<Vec<String>>()
 855                                 .join(", "),
 856                             applicability,
 857                         ),
 858                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
 859                     };
 860                     let pad = match self.r.field_names.get(&def_id) {
 861                         Some(fields) if fields.is_empty() => "",
 862                         _ => " ",
 863                     };
 864                     err.span_suggestion(
 865                         span,
 866                         &format!("use struct {} syntax instead", descr),
 867                         format!("{path_str} {{{pad}{fields}{pad}}}"),
 868                         applicability,
 869                     );
 870                 }
 871                 _ => {
 872                     err.span_label(span, fallback_label);
 873                 }
 874             }
 875         };
 876
 877         match (res, source) {
 878             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
 879                 err.span_label(span, fallback_label);
 880                 err.span_suggestion_verbose(
 881                     span.shrink_to_hi(),
 882                     "use `!` to invoke the macro",
 883                     "!".to_string(),
 884                     Applicability::MaybeIncorrect,
 885                 );
 886                 if path_str == "try" && span.rust_2015() {
 887                     err.note("if you want the `try` keyword, you need to be in the 2018 edition");
 888                 }
 889             }
 890             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
 891                 err.span_label(span, "type aliases cannot be used as traits");
 892                 if self.r.session.is_nightly_build() {
 893                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
 894                                `type` alias";
 895                     if let Some(span) = self.def_span(def_id) {
 896                         err.span_help(span, msg);
 897                     } else {
 898                         err.help(msg);
 899                     }
 900                 }
 901             }
 902             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
 903                 if !path_sep(err, &parent) {
 904                     return false;
 905                 }
 906             }
 907             (
 908                 Res::Def(DefKind::Enum, def_id),
 909                 PathSource::TupleStruct(..) | PathSource::Expr(..),
 910             ) => {
 911                 if self
 912                     .diagnostic_metadata
 913                     .current_type_ascription
 914                     .last()
 915                     .map(|sp| {
 916                         self.r
 917                             .session
 918                             .parse_sess
 919                             .type_ascription_path_suggestions
 920                             .borrow()
 921                             .contains(&sp)
 922                     })
 923                     .unwrap_or(false)
 924                 {
 925                     err.delay_as_bug();
 926                     // We already suggested changing `:` into `::` during parsing.
 927                     return false;
 928                 }
 929
 930                 self.suggest_using_enum_variant(err, source, def_id, span);
 931             }
 932             (Res::Def(DefKind::Struct, def_id), _) if ns == ValueNS => {
 933                 let (ctor_def, ctor_vis, fields) =
 934                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
 935                         struct_ctor
 936                     } else {
 937                         bad_struct_syntax_suggestion(def_id);
 938                         return true;
 939                     };
 940
 941                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
 942                 if !is_expected(ctor_def) || is_accessible {
 943                     return true;
 944                 }
 945
 946                 let field_spans = match source {
 947                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
 948                     PathSource::TupleStruct(_, pattern_spans) => {
 949                         err.set_primary_message(
 950                             "cannot match against a tuple struct which contains private fields",
 951                         );
 952
 953                         // Use spans of the tuple struct pattern.
 954                         Some(Vec::from(pattern_spans))
 955                     }
 956                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
 957                     _ if source.is_call() => {
 958                         err.set_primary_message(
 959                             "cannot initialize a tuple struct which contains private fields",
 960                         );
 961
 962                         // Use spans of the tuple struct definition.
 963                         self.r
 964                             .field_names
 965                             .get(&def_id)
 966                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
 967                     }
 968                     _ => None,
 969                 };
 970
 971                 if let Some(spans) =
 972                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
 973                 {
 974                     let non_visible_spans: Vec<Span> = fields
 975                         .iter()
 976                         .zip(spans.iter())
 977                         .filter(|(vis, _)| {
 978                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
 979                         })
 980                         .map(|(_, span)| *span)
 981                         .collect();
 982
 983                     if non_visible_spans.len() > 0 {
 984                         let mut m: rustc_span::MultiSpan = non_visible_spans.clone().into();
 985                         non_visible_spans
 986                             .into_iter()
 987                             .for_each(|s| m.push_span_label(s, "private field".to_string()));
 988                         err.span_note(m, "constructor is not visible here due to private fields");
 989                     }
 990
 991                     return true;
 992                 }
 993
 994                 err.span_label(
 995                     span,
 996                     "constructor is not visible here due to private fields".to_string(),
 997                 );
 998             }
 999             (
1000                 Res::Def(
1001                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
1002                     def_id,
1003                 ),
1004                 _,
1005             ) if ns == ValueNS => {
1006                 bad_struct_syntax_suggestion(def_id);
1007             }
1008             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
1009                 if let Some(span) = self.def_span(def_id) {
1010                     err.span_label(span, &format!("`{}` defined here", path_str));
1011                 }
1012                 let fields =
1013                     self.r.field_names.get(&def_id).map_or("/* fields */".to_string(), |fields| {
1014                         vec!["_"; fields.len()].join(", ")
1015                     });
1016                 err.span_suggestion(
1017                     span,
1018                     "use the tuple variant pattern syntax instead",
1019                     format!("{}({})", path_str, fields),
1020                     Applicability::HasPlaceholders,
1021                 );
1022             }
1023             (Res::SelfTy(..), _) if ns == ValueNS => {
1024                 err.span_label(span, fallback_label);
1025                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1026             }
1027             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1028                 err.note("can't use a type alias as a constructor");
1029             }
1030             _ => return false,
1031         }
1032         true
1033     }
1034
1035     fn lookup_assoc_candidate<FilterFn>(
1036         &mut self,
1037         ident: Ident,
1038         ns: Namespace,
1039         filter_fn: FilterFn,
1040     ) -> Option<AssocSuggestion>
1041     where
1042         FilterFn: Fn(Res) -> bool,
1043     {
1044         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1045             match t.kind {
1046                 TyKind::Path(None, _) => Some(t.id),
1047                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1048                 // This doesn't handle the remaining `Ty` variants as they are not
1049                 // that commonly the self_type, it might be interesting to provide
1050                 // support for those in future.
1051                 _ => None,
1052             }
1053         }
1054
1055         // Fields are generally expected in the same contexts as locals.
1056         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1057             if let Some(node_id) =
1058                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1059             {
1060                 // Look for a field with the same name in the current self_type.
1061                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1062                     match resolution.base_res() {
1063                         Res::Def(DefKind::Struct | DefKind::Union, did)
1064                             if resolution.unresolved_segments() == 0 =>
1065                         {
1066                             if let Some(field_names) = self.r.field_names.get(&did) {
1067                                 if field_names
1068                                     .iter()
1069                                     .any(|&field_name| ident.name == field_name.node)
1070                                 {
1071                                     return Some(AssocSuggestion::Field);
1072                                 }
1073                             }
1074                         }
1075                         _ => {}
1076                     }
1077                 }
1078             }
1079         }
1080
1081         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1082             for assoc_item in &items[..] {
1083                 if assoc_item.ident == ident {
1084                     return Some(match &assoc_item.kind {
1085                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1086                         ast::AssocItemKind::Fn(_, sig, ..) if sig.decl.has_self() => {
1087                             AssocSuggestion::MethodWithSelf
1088                         }
1089                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn,
1090                         ast::AssocItemKind::TyAlias(..) => AssocSuggestion::AssocType,
1091                         ast::AssocItemKind::MacCall(_) => continue,
1092                     });
1093                 }
1094             }
1095         }
1096
1097         // Look for associated items in the current trait.
1098         if let Some((module, _)) = self.current_trait_ref {
1099             if let Ok(binding) = self.r.resolve_ident_in_module(
1100                 ModuleOrUniformRoot::Module(module),
1101                 ident,
1102                 ns,
1103                 &self.parent_scope,
1104                 false,
1105                 module.span,
1106             ) {
1107                 let res = binding.res();
1108                 if filter_fn(res) {
1109                     if self.r.has_self.contains(&res.def_id()) {
1110                         return Some(AssocSuggestion::MethodWithSelf);
1111                     } else {
1112                         match res {
1113                             Res::Def(DefKind::AssocFn, _) => return Some(AssocSuggestion::AssocFn),
1114                             Res::Def(DefKind::AssocConst, _) => {
1115                                 return Some(AssocSuggestion::AssocConst);
1116                             }
1117                             Res::Def(DefKind::AssocTy, _) => {
1118                                 return Some(AssocSuggestion::AssocType);
1119                             }
1120                             _ => {}
1121                         }
1122                     }
1123                 }
1124             }
1125         }
1126
1127         None
1128     }
1129
1130     fn lookup_typo_candidate(
1131         &mut self,
1132         path: &[Segment],
1133         ns: Namespace,
1134         filter_fn: &impl Fn(Res) -> bool,
1135         span: Span,
1136     ) -> Option<TypoSuggestion> {
1137         let mut names = Vec::new();
1138         if path.len() == 1 {
1139             // Search in lexical scope.
1140             // Walk backwards up the ribs in scope and collect candidates.
1141             for rib in self.ribs[ns].iter().rev() {
1142                 // Locals and type parameters
1143                 for (ident, &res) in &rib.bindings {
1144                     if filter_fn(res) {
1145                         names.push(TypoSuggestion::from_res(ident.name, res));
1146                     }
1147                 }
1148                 // Items in scope
1149                 if let RibKind::ModuleRibKind(module) = rib.kind {
1150                     // Items from this module
1151                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1152
1153                     if let ModuleKind::Block(..) = module.kind {
1154                         // We can see through blocks
1155                     } else {
1156                         // Items from the prelude
1157                         if !module.no_implicit_prelude {
1158                             let extern_prelude = self.r.extern_prelude.clone();
1159                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1160                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
1161                                     |crate_id| {
1162                                         let crate_mod = Res::Def(
1163                                             DefKind::Mod,
1164                                             DefId { krate: crate_id, index: CRATE_DEF_INDEX },
1165                                         );
1166
1167                                         if filter_fn(crate_mod) {
1168                                             Some(TypoSuggestion::from_res(ident.name, crate_mod))
1169                                         } else {
1170                                             None
1171                                         }
1172                                     },
1173                                 )
1174                             }));
1175
1176                             if let Some(prelude) = self.r.prelude {
1177                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
1178                             }
1179                         }
1180                         break;
1181                     }
1182                 }
1183             }
1184             // Add primitive types to the mix
1185             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1186                 names.extend(
1187                     self.r.primitive_type_table.primitive_types.iter().map(|(name, prim_ty)| {
1188                         TypoSuggestion::from_res(*name, Res::PrimTy(*prim_ty))
1189                     }),
1190                 )
1191             }
1192         } else {
1193             // Search in module.
1194             let mod_path = &path[..path.len() - 1];
1195             if let PathResult::Module(module) =
1196                 self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No)
1197             {
1198                 if let ModuleOrUniformRoot::Module(module) = module {
1199                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1200                 }
1201             }
1202         }
1203
1204         let name = path[path.len() - 1].ident.name;
1205         // Make sure error reporting is deterministic.
1206         names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
1207
1208         match find_best_match_for_name(
1209             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1210             name,
1211             None,
1212         ) {
1213             Some(found) if found != name => {
1214                 names.into_iter().find(|suggestion| suggestion.candidate == found)
1215             }
1216             _ => None,
1217         }
1218     }
1219
1220     /// Only used in a specific case of type ascription suggestions
1221     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1222         let sm = self.r.session.source_map();
1223         start.to(sm.next_point(start))
1224     }
1225
1226     fn type_ascription_suggestion(&self, err: &mut DiagnosticBuilder<'_>, base_span: Span) -> bool {
1227         let sm = self.r.session.source_map();
1228         let base_snippet = sm.span_to_snippet(base_span);
1229         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1230             if let Ok(snippet) = sm.span_to_snippet(sp) {
1231                 let len = snippet.trim_end().len() as u32;
1232                 if snippet.trim() == ":" {
1233                     let colon_sp =
1234                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1235                     let mut show_label = true;
1236                     if sm.is_multiline(sp) {
1237                         err.span_suggestion_short(
1238                             colon_sp,
1239                             "maybe you meant to write `;` here",
1240                             ";".to_string(),
1241                             Applicability::MaybeIncorrect,
1242                         );
1243                     } else {
1244                         let after_colon_sp =
1245                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1246                         if snippet.len() == 1 {
1247                             // `foo:bar`
1248                             err.span_suggestion(
1249                                 colon_sp,
1250                                 "maybe you meant to write a path separator here",
1251                                 "::".to_string(),
1252                                 Applicability::MaybeIncorrect,
1253                             );
1254                             show_label = false;
1255                             if !self
1256                                 .r
1257                                 .session
1258                                 .parse_sess
1259                                 .type_ascription_path_suggestions
1260                                 .borrow_mut()
1261                                 .insert(colon_sp)
1262                             {
1263                                 err.delay_as_bug();
1264                             }
1265                         }
1266                         if let Ok(base_snippet) = base_snippet {
1267                             let mut sp = after_colon_sp;
1268                             for _ in 0..100 {
1269                                 // Try to find an assignment
1270                                 sp = sm.next_point(sp);
1271                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
1272                                 match snippet {
1273                                     Ok(ref x) if x.as_str() == "=" => {
1274                                         err.span_suggestion(
1275                                             base_span,
1276                                             "maybe you meant to write an assignment here",
1277                                             format!("let {}", base_snippet),
1278                                             Applicability::MaybeIncorrect,
1279                                         );
1280                                         show_label = false;
1281                                         break;
1282                                     }
1283                                     Ok(ref x) if x.as_str() == "\n" => break,
1284                                     Err(_) => break,
1285                                     Ok(_) => {}
1286                                 }
1287                             }
1288                         }
1289                     }
1290                     if show_label {
1291                         err.span_label(
1292                             base_span,
1293                             "expecting a type here because of type ascription",
1294                         );
1295                     }
1296                     return show_label;
1297                 }
1298             }
1299         }
1300         false
1301     }
1302
1303     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1304         let mut result = None;
1305         let mut seen_modules = FxHashSet::default();
1306         let mut worklist = vec![(self.r.graph_root, Vec::new())];
1307
1308         while let Some((in_module, path_segments)) = worklist.pop() {
1309             // abort if the module is already found
1310             if result.is_some() {
1311                 break;
1312             }
1313
1314             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1315                 // abort if the module is already found or if name_binding is private external
1316                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1317                     return;
1318                 }
1319                 if let Some(module) = name_binding.module() {
1320                     // form the path
1321                     let mut path_segments = path_segments.clone();
1322                     path_segments.push(ast::PathSegment::from_ident(ident));
1323                     let module_def_id = module.def_id().unwrap();
1324                     if module_def_id == def_id {
1325                         let path =
1326                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1327                         result = Some((
1328                             module,
1329                             ImportSuggestion {
1330                                 did: Some(def_id),
1331                                 descr: "module",
1332                                 path,
1333                                 accessible: true,
1334                             },
1335                         ));
1336                     } else {
1337                         // add the module to the lookup
1338                         if seen_modules.insert(module_def_id) {
1339                             worklist.push((module, path_segments));
1340                         }
1341                     }
1342                 }
1343             });
1344         }
1345
1346         result
1347     }
1348
1349     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1350         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1351             let mut variants = Vec::new();
1352             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1353                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1354                     let mut segms = enum_import_suggestion.path.segments.clone();
1355                     segms.push(ast::PathSegment::from_ident(ident));
1356                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1357                     variants.push((path, def_id, kind));
1358                 }
1359             });
1360             variants
1361         })
1362     }
1363
1364     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1365     fn suggest_using_enum_variant(
1366         &mut self,
1367         err: &mut DiagnosticBuilder<'a>,
1368         source: PathSource<'_>,
1369         def_id: DefId,
1370         span: Span,
1371     ) {
1372         let variants = match self.collect_enum_ctors(def_id) {
1373             Some(variants) => variants,
1374             None => {
1375                 err.note("you might have meant to use one of the enum's variants");
1376                 return;
1377             }
1378         };
1379
1380         let suggest_only_tuple_variants =
1381             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1382         if suggest_only_tuple_variants {
1383             // Suggest only tuple variants regardless of whether they have fields and do not
1384             // suggest path with added parenthesis.
1385             let mut suggestable_variants = variants
1386                 .iter()
1387                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1388                 .map(|(variant, ..)| path_names_to_string(variant))
1389                 .collect::<Vec<_>>();
1390
1391             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1392
1393             let source_msg = if source.is_call() {
1394                 "to construct"
1395             } else if matches!(source, PathSource::TupleStruct(..)) {
1396                 "to match against"
1397             } else {
1398                 unreachable!()
1399             };
1400
1401             if !suggestable_variants.is_empty() {
1402                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1403                     format!("try {} the enum's variant", source_msg)
1404                 } else {
1405                     format!("try {} one of the enum's variants", source_msg)
1406                 };
1407
1408                 err.span_suggestions(
1409                     span,
1410                     &msg,
1411                     suggestable_variants.drain(..),
1412                     Applicability::MaybeIncorrect,
1413                 );
1414             }
1415
1416             // If the enum has no tuple variants..
1417             if non_suggestable_variant_count == variants.len() {
1418                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1419             }
1420
1421             // If there are also non-tuple variants..
1422             if non_suggestable_variant_count == 1 {
1423                 err.help(&format!(
1424                     "you might have meant {} the enum's non-tuple variant",
1425                     source_msg
1426                 ));
1427             } else if non_suggestable_variant_count >= 1 {
1428                 err.help(&format!(
1429                     "you might have meant {} one of the enum's non-tuple variants",
1430                     source_msg
1431                 ));
1432             }
1433         } else {
1434             let needs_placeholder = |def_id: DefId, kind: CtorKind| {
1435                 let has_no_fields =
1436                     self.r.field_names.get(&def_id).map(|f| f.is_empty()).unwrap_or(false);
1437                 match kind {
1438                     CtorKind::Const => false,
1439                     CtorKind::Fn | CtorKind::Fictive if has_no_fields => false,
1440                     _ => true,
1441                 }
1442             };
1443
1444             let mut suggestable_variants = variants
1445                 .iter()
1446                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1447                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1448                 .map(|(variant, kind)| match kind {
1449                     CtorKind::Const => variant,
1450                     CtorKind::Fn => format!("({}())", variant),
1451                     CtorKind::Fictive => format!("({} {{}})", variant),
1452                 })
1453                 .collect::<Vec<_>>();
1454
1455             if !suggestable_variants.is_empty() {
1456                 let msg = if suggestable_variants.len() == 1 {
1457                     "you might have meant to use the following enum variant"
1458                 } else {
1459                     "you might have meant to use one of the following enum variants"
1460                 };
1461
1462                 err.span_suggestions(
1463                     span,
1464                     msg,
1465                     suggestable_variants.drain(..),
1466                     Applicability::MaybeIncorrect,
1467                 );
1468             }
1469
1470             let mut suggestable_variants_with_placeholders = variants
1471                 .iter()
1472                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
1473                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1474                 .filter_map(|(variant, kind)| match kind {
1475                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
1476                     CtorKind::Fictive => Some(format!("({} {{ /* fields */ }})", variant)),
1477                     _ => None,
1478                 })
1479                 .collect::<Vec<_>>();
1480
1481             if !suggestable_variants_with_placeholders.is_empty() {
1482                 let msg = match (
1483                     suggestable_variants.is_empty(),
1484                     suggestable_variants_with_placeholders.len(),
1485                 ) {
1486                     (true, 1) => "the following enum variant is available",
1487                     (true, _) => "the following enum variants are available",
1488                     (false, 1) => "alternatively, the following enum variant is available",
1489                     (false, _) => "alternatively, the following enum variants are also available",
1490                 };
1491
1492                 err.span_suggestions(
1493                     span,
1494                     msg,
1495                     suggestable_variants_with_placeholders.drain(..),
1496                     Applicability::HasPlaceholders,
1497                 );
1498             }
1499         };
1500
1501         if def_id.is_local() {
1502             if let Some(span) = self.def_span(def_id) {
1503                 err.span_note(span, "the enum is defined here");
1504             }
1505         }
1506     }
1507
1508     crate fn report_missing_type_error(
1509         &self,
1510         path: &[Segment],
1511     ) -> Option<(Span, &'static str, String, Applicability)> {
1512         let (ident, span) = match path {
1513             [segment] if !segment.has_generic_args => {
1514                 (segment.ident.to_string(), segment.ident.span)
1515             }
1516             _ => return None,
1517         };
1518         let mut iter = ident.chars().map(|c| c.is_uppercase());
1519         let single_uppercase_char =
1520             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1521         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1522             return None;
1523         }
1524         match (self.diagnostic_metadata.current_item, single_uppercase_char) {
1525             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _) if ident.name == sym::main => {
1526                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1527             }
1528             (
1529                 Some(Item {
1530                     kind:
1531                         kind @ ItemKind::Fn(..)
1532                         | kind @ ItemKind::Enum(..)
1533                         | kind @ ItemKind::Struct(..)
1534                         | kind @ ItemKind::Union(..),
1535                     ..
1536                 }),
1537                 true,
1538             )
1539             | (Some(Item { kind, .. }), false) => {
1540                 // Likely missing type parameter.
1541                 if let Some(generics) = kind.generics() {
1542                     if span.overlaps(generics.span) {
1543                         // Avoid the following:
1544                         // error[E0405]: cannot find trait `A` in this scope
1545                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1546                         //   |
1547                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1548                         //   |           ^- help: you might be missing a type parameter: `, A`
1549                         //   |           |
1550                         //   |           not found in this scope
1551                         return None;
1552                     }
1553                     let msg = "you might be missing a type parameter";
1554                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1555                         let span = if let [.., bound] = &param.bounds[..] {
1556                             bound.span()
1557                         } else {
1558                             param.ident.span
1559                         };
1560                         (span, format!(", {}", ident))
1561                     } else {
1562                         (generics.span, format!("<{}>", ident))
1563                     };
1564                     // Do not suggest if this is coming from macro expansion.
1565                     if !span.from_expansion() {
1566                         return Some((
1567                             span.shrink_to_hi(),
1568                             msg,
1569                             sugg,
1570                             Applicability::MaybeIncorrect,
1571                         ));
1572                     }
1573                 }
1574             }
1575             _ => {}
1576         }
1577         None
1578     }
1579
1580     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1581     /// optionally returning the closest match and whether it is reachable.
1582     crate fn suggestion_for_label_in_rib(
1583         &self,
1584         rib_index: usize,
1585         label: Ident,
1586     ) -> Option<LabelSuggestion> {
1587         // Are ribs from this `rib_index` within scope?
1588         let within_scope = self.is_label_valid_from_rib(rib_index);
1589
1590         let rib = &self.label_ribs[rib_index];
1591         let names = rib
1592             .bindings
1593             .iter()
1594             .filter(|(id, _)| id.span.ctxt() == label.span.ctxt())
1595             .map(|(id, _)| id.name)
1596             .collect::<Vec<Symbol>>();
1597
1598         find_best_match_for_name(&names, label.name, None).map(|symbol| {
1599             // Upon finding a similar name, get the ident that it was from - the span
1600             // contained within helps make a useful diagnostic. In addition, determine
1601             // whether this candidate is within scope.
1602             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1603             (*ident, within_scope)
1604         })
1605     }
1606 }
1607
1608 impl<'tcx> LifetimeContext<'_, 'tcx> {
1609     crate fn report_missing_lifetime_specifiers(
1610         &self,
1611         span: Span,
1612         count: usize,
1613     ) -> DiagnosticBuilder<'tcx> {
1614         struct_span_err!(
1615             self.tcx.sess,
1616             span,
1617             E0106,
1618             "missing lifetime specifier{}",
1619             pluralize!(count)
1620         )
1621     }
1622
1623     crate fn emit_undeclared_lifetime_error(&self, lifetime_ref: &hir::Lifetime) {
1624         let mut err = struct_span_err!(
1625             self.tcx.sess,
1626             lifetime_ref.span,
1627             E0261,
1628             "use of undeclared lifetime name `{}`",
1629             lifetime_ref
1630         );
1631         err.span_label(lifetime_ref.span, "undeclared lifetime");
1632         let mut suggests_in_band = false;
1633         for missing in &self.missing_named_lifetime_spots {
1634             match missing {
1635                 MissingLifetimeSpot::Generics(generics) => {
1636                     let (span, sugg) = if let Some(param) =
1637                         generics.params.iter().find(|p| match p.kind {
1638                             hir::GenericParamKind::Type {
1639                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1640                                 ..
1641                             } => false,
1642                             hir::GenericParamKind::Lifetime {
1643                                 kind: hir::LifetimeParamKind::Elided,
1644                             } => false,
1645                             _ => true,
1646                         }) {
1647                         (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref))
1648                     } else {
1649                         suggests_in_band = true;
1650                         (generics.span, format!("<{}>", lifetime_ref))
1651                     };
1652                     err.span_suggestion(
1653                         span,
1654                         &format!("consider introducing lifetime `{}` here", lifetime_ref),
1655                         sugg,
1656                         Applicability::MaybeIncorrect,
1657                     );
1658                 }
1659                 MissingLifetimeSpot::HigherRanked { span, span_type } => {
1660                     err.span_suggestion(
1661                         *span,
1662                         &format!(
1663                             "consider making the {} lifetime-generic with a new `{}` lifetime",
1664                             span_type.descr(),
1665                             lifetime_ref
1666                         ),
1667                         span_type.suggestion(&lifetime_ref.to_string()),
1668                         Applicability::MaybeIncorrect,
1669                     );
1670                     err.note(
1671                         "for more information on higher-ranked polymorphism, visit \
1672                             https://doc.rust-lang.org/nomicon/hrtb.html",
1673                     );
1674                 }
1675                 _ => {}
1676             }
1677         }
1678         if self.tcx.sess.is_nightly_build()
1679             && !self.tcx.features().in_band_lifetimes
1680             && suggests_in_band
1681         {
1682             err.help(
1683                 "if you want to experiment with in-band lifetime bindings, \
1684                     add `#![feature(in_band_lifetimes)]` to the crate attributes",
1685             );
1686         }
1687         err.emit();
1688     }
1689
1690     // FIXME(const_generics): This patches over a ICE caused by non-'static lifetimes in const
1691     // generics. We are disallowing this until we can decide on how we want to handle non-'static
1692     // lifetimes in const generics. See issue #74052 for discussion.
1693     crate fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &hir::Lifetime) {
1694         let mut err = struct_span_err!(
1695             self.tcx.sess,
1696             lifetime_ref.span,
1697             E0771,
1698             "use of non-static lifetime `{}` in const generic",
1699             lifetime_ref
1700         );
1701         err.note(
1702             "for more information, see issue #74052 \
1703             <https://github.com/rust-lang/rust/issues/74052>",
1704         );
1705         err.emit();
1706     }
1707
1708     crate fn is_trait_ref_fn_scope(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) -> bool {
1709         if let def::Res::Def(_, did) = trait_ref.trait_ref.path.res {
1710             if [
1711                 self.tcx.lang_items().fn_once_trait(),
1712                 self.tcx.lang_items().fn_trait(),
1713                 self.tcx.lang_items().fn_mut_trait(),
1714             ]
1715             .contains(&Some(did))
1716             {
1717                 let (span, span_type) = match &trait_ref.bound_generic_params {
1718                     [] => (trait_ref.span.shrink_to_lo(), ForLifetimeSpanType::BoundEmpty),
1719                     [.., bound] => (bound.span.shrink_to_hi(), ForLifetimeSpanType::BoundTail),
1720                 };
1721                 self.missing_named_lifetime_spots
1722                     .push(MissingLifetimeSpot::HigherRanked { span, span_type });
1723                 return true;
1724             }
1725         };
1726         false
1727     }
1728
1729     crate fn add_missing_lifetime_specifiers_label(
1730         &self,
1731         err: &mut DiagnosticBuilder<'_>,
1732         span: Span,
1733         count: usize,
1734         lifetime_names: &FxHashSet<Symbol>,
1735         lifetime_spans: Vec<Span>,
1736         params: &[ElisionFailureInfo],
1737     ) {
1738         let snippet = self.tcx.sess.source_map().span_to_snippet(span).ok();
1739
1740         err.span_label(
1741             span,
1742             &format!(
1743                 "expected {} lifetime parameter{}",
1744                 if count == 1 { "named".to_string() } else { count.to_string() },
1745                 pluralize!(count)
1746             ),
1747         );
1748
1749         let suggest_existing = |err: &mut DiagnosticBuilder<'_>,
1750                                 name: &str,
1751                                 formatter: &dyn Fn(&str) -> String| {
1752             if let Some(MissingLifetimeSpot::HigherRanked { span: for_span, span_type }) =
1753                 self.missing_named_lifetime_spots.iter().rev().next()
1754             {
1755                 // When we have `struct S<'a>(&'a dyn Fn(&X) -> &X);` we want to not only suggest
1756                 // using `'a`, but also introduce the concept of HRLTs by suggesting
1757                 // `struct S<'a>(&'a dyn for<'b> Fn(&X) -> &'b X);`. (#72404)
1758                 let mut introduce_suggestion = vec![];
1759
1760                 let a_to_z_repeat_n = |n| {
1761                     (b'a'..=b'z').map(move |c| {
1762                         let mut s = '\''.to_string();
1763                         s.extend(std::iter::repeat(char::from(c)).take(n));
1764                         s
1765                     })
1766                 };
1767
1768                 // If all single char lifetime names are present, we wrap around and double the chars.
1769                 let lt_name = (1..)
1770                     .flat_map(a_to_z_repeat_n)
1771                     .find(|lt| !lifetime_names.contains(&Symbol::intern(&lt)))
1772                     .unwrap();
1773                 let msg = format!(
1774                     "consider making the {} lifetime-generic with a new `{}` lifetime",
1775                     span_type.descr(),
1776                     lt_name,
1777                 );
1778                 err.note(
1779                     "for more information on higher-ranked polymorphism, visit \
1780                     https://doc.rust-lang.org/nomicon/hrtb.html",
1781                 );
1782                 let for_sugg = span_type.suggestion(&lt_name);
1783                 for param in params {
1784                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
1785                         if snippet.starts_with('&') && !snippet.starts_with("&'") {
1786                             introduce_suggestion
1787                                 .push((param.span, format!("&{} {}", lt_name, &snippet[1..])));
1788                         } else if let Some(stripped) = snippet.strip_prefix("&'_ ") {
1789                             introduce_suggestion
1790                                 .push((param.span, format!("&{} {}", lt_name, stripped)));
1791                         }
1792                     }
1793                 }
1794                 introduce_suggestion.push((*for_span, for_sugg));
1795                 introduce_suggestion.push((span, formatter(&lt_name)));
1796                 err.multipart_suggestion(&msg, introduce_suggestion, Applicability::MaybeIncorrect);
1797             }
1798
1799             err.span_suggestion_verbose(
1800                 span,
1801                 &format!("consider using the `{}` lifetime", lifetime_names.iter().next().unwrap()),
1802                 formatter(name),
1803                 Applicability::MaybeIncorrect,
1804             );
1805         };
1806         let suggest_new = |err: &mut DiagnosticBuilder<'_>, sugg: &str| {
1807             for missing in self.missing_named_lifetime_spots.iter().rev() {
1808                 let mut introduce_suggestion = vec![];
1809                 let msg;
1810                 let should_break;
1811                 introduce_suggestion.push(match missing {
1812                     MissingLifetimeSpot::Generics(generics) => {
1813                         if generics.span == DUMMY_SP {
1814                             // Account for malformed generics in the HIR. This shouldn't happen,
1815                             // but if we make a mistake elsewhere, mainly by keeping something in
1816                             // `missing_named_lifetime_spots` that we shouldn't, like associated
1817                             // `const`s or making a mistake in the AST lowering we would provide
1818                             // non-sensical suggestions. Guard against that by skipping these.
1819                             // (#74264)
1820                             continue;
1821                         }
1822                         msg = "consider introducing a named lifetime parameter".to_string();
1823                         should_break = true;
1824                         if let Some(param) = generics.params.iter().find(|p| {
1825                             !matches!(p.kind, hir::GenericParamKind::Type {
1826                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1827                                 ..
1828                             })
1829                         }) {
1830                             (param.span.shrink_to_lo(), "'a, ".to_string())
1831                         } else {
1832                             (generics.span, "<'a>".to_string())
1833                         }
1834                     }
1835                     MissingLifetimeSpot::HigherRanked { span, span_type } => {
1836                         msg = format!(
1837                             "consider making the {} lifetime-generic with a new `'a` lifetime",
1838                             span_type.descr(),
1839                         );
1840                         should_break = false;
1841                         err.note(
1842                             "for more information on higher-ranked polymorphism, visit \
1843                             https://doc.rust-lang.org/nomicon/hrtb.html",
1844                         );
1845                         (*span, span_type.suggestion("'a"))
1846                     }
1847                     MissingLifetimeSpot::Static => {
1848                         let (span, sugg) = match snippet.as_deref() {
1849                             Some("&") => (span.shrink_to_hi(), "'static ".to_owned()),
1850                             Some("'_") => (span, "'static".to_owned()),
1851                             Some(snippet) if !snippet.ends_with('>') => {
1852                                 if snippet == "" {
1853                                     (
1854                                         span,
1855                                         std::iter::repeat("'static")
1856                                             .take(count)
1857                                             .collect::<Vec<_>>()
1858                                             .join(", "),
1859                                     )
1860                                 } else {
1861                                     (
1862                                         span.shrink_to_hi(),
1863                                         format!(
1864                                             "<{}>",
1865                                             std::iter::repeat("'static")
1866                                                 .take(count)
1867                                                 .collect::<Vec<_>>()
1868                                                 .join(", ")
1869                                         ),
1870                                     )
1871                                 }
1872                             }
1873                             _ => continue,
1874                         };
1875                         err.span_suggestion_verbose(
1876                             span,
1877                             "consider using the `'static` lifetime",
1878                             sugg.to_string(),
1879                             Applicability::MaybeIncorrect,
1880                         );
1881                         continue;
1882                     }
1883                 });
1884                 for param in params {
1885                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
1886                         if snippet.starts_with('&') && !snippet.starts_with("&'") {
1887                             introduce_suggestion
1888                                 .push((param.span, format!("&'a {}", &snippet[1..])));
1889                         } else if let Some(stripped) = snippet.strip_prefix("&'_ ") {
1890                             introduce_suggestion.push((param.span, format!("&'a {}", &stripped)));
1891                         }
1892                     }
1893                 }
1894                 introduce_suggestion.push((span, sugg.to_string()));
1895                 err.multipart_suggestion(&msg, introduce_suggestion, Applicability::MaybeIncorrect);
1896                 if should_break {
1897                     break;
1898                 }
1899             }
1900         };
1901
1902         let lifetime_names: Vec<_> = lifetime_names.iter().collect();
1903         match (&lifetime_names[..], snippet.as_deref()) {
1904             ([name], Some("&")) => {
1905                 suggest_existing(err, &name.as_str()[..], &|name| format!("&{} ", name));
1906             }
1907             ([name], Some("'_")) => {
1908                 suggest_existing(err, &name.as_str()[..], &|n| n.to_string());
1909             }
1910             ([name], Some("")) => {
1911                 suggest_existing(err, &name.as_str()[..], &|n| format!("{}, ", n).repeat(count));
1912             }
1913             ([name], Some(snippet)) if !snippet.ends_with('>') => {
1914                 let f = |name: &str| {
1915                     format!(
1916                         "{}<{}>",
1917                         snippet,
1918                         std::iter::repeat(name.to_string())
1919                             .take(count)
1920                             .collect::<Vec<_>>()
1921                             .join(", ")
1922                     )
1923                 };
1924                 suggest_existing(err, &name.as_str()[..], &f);
1925             }
1926             ([], Some("&")) if count == 1 => {
1927                 suggest_new(err, "&'a ");
1928             }
1929             ([], Some("'_")) if count == 1 => {
1930                 suggest_new(err, "'a");
1931             }
1932             ([], Some(snippet)) if !snippet.ends_with('>') => {
1933                 if snippet == "" {
1934                     // This happens when we have `type Bar<'a> = Foo<T>` where we point at the space
1935                     // before `T`. We will suggest `type Bar<'a> = Foo<'a, T>`.
1936                     suggest_new(
1937                         err,
1938                         &std::iter::repeat("'a, ").take(count).collect::<Vec<_>>().join(""),
1939                     );
1940                 } else {
1941                     suggest_new(
1942                         err,
1943                         &format!(
1944                             "{}<{}>",
1945                             snippet,
1946                             std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", ")
1947                         ),
1948                     );
1949                 }
1950             }
1951             (lts, ..) if lts.len() > 1 => {
1952                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
1953                 if Some("") == snippet.as_deref() {
1954                     // This happens when we have `Foo<T>` where we point at the space before `T`,
1955                     // but this can be confusing so we give a suggestion with placeholders.
1956                     err.span_suggestion_verbose(
1957                         span,
1958                         "consider using one of the available lifetimes here",
1959                         "'lifetime, ".repeat(count),
1960                         Applicability::HasPlaceholders,
1961                     );
1962                 }
1963             }
1964             _ => {}
1965         }
1966     }
1967
1968     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics` so
1969     /// this function will emit an error if `min_const_generics` is enabled, the body identified by
1970     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
1971     crate fn maybe_emit_forbidden_non_static_lifetime_error(
1972         &self,
1973         body_id: hir::BodyId,
1974         lifetime_ref: &'tcx hir::Lifetime,
1975     ) {
1976         let is_anon_const = matches!(
1977             self.tcx.def_kind(self.tcx.hir().body_owner_def_id(body_id)),
1978             hir::def::DefKind::AnonConst
1979         );
1980         let is_allowed_lifetime = matches!(
1981             lifetime_ref.name,
1982             hir::LifetimeName::Implicit | hir::LifetimeName::Static | hir::LifetimeName::Underscore
1983         );
1984
1985         if self.tcx.features().min_const_generics && is_anon_const && !is_allowed_lifetime {
1986             feature_err(
1987                 &self.tcx.sess.parse_sess,
1988                 sym::const_generics,
1989                 lifetime_ref.span,
1990                 "a non-static lifetime is not allowed in a `const`",
1991             )
1992             .emit();
1993         }
1994     }
1995 }