compiler/rustc_resolve/src/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::{AliasPossibility, LateResolutionVisitor, RibKind};
   3 use crate::late::{LifetimeBinderKind, LifetimeRes, LifetimeRibKind, LifetimeUseSet};
   4 use crate::path_names_to_string;
   5 use crate::{Module, ModuleKind, ModuleOrUniformRoot};
   6 use crate::{PathResult, PathSource, Segment};
   7
   8 use rustc_ast::visit::{FnCtxt, FnKind, LifetimeCtxt};
   9 use rustc_ast::{
  10     self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
  11     MethodCall, NodeId, Path, Ty, TyKind, DUMMY_NODE_ID,
  12 };
  13 use rustc_ast_pretty::pprust::path_segment_to_string;
  14 use rustc_data_structures::fx::FxHashSet;
  15 use rustc_errors::{
  16     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
  17     MultiSpan,
  18 };
  19 use rustc_hir as hir;
  20 use rustc_hir::def::Namespace::{self, *};
  21 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
  22 use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
  23 use rustc_hir::PrimTy;
  24 use rustc_middle::ty::DefIdTree;
  25 use rustc_session::lint;
  26 use rustc_session::parse::feature_err;
  27 use rustc_session::Session;
  28 use rustc_span::edition::Edition;
  29 use rustc_span::hygiene::MacroKind;
  30 use rustc_span::lev_distance::find_best_match_for_name;
  31 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  32 use rustc_span::{BytePos, Span};
  33
  34 use std::iter;
  35 use std::ops::Deref;
  36
  37 use thin_vec::ThinVec;
  38
  39 type Res = def::Res<ast::NodeId>;
  40
  41 /// A field or associated item from self type suggested in case of resolution failure.
  42 enum AssocSuggestion {
  43     Field,
  44     MethodWithSelf { called: bool },
  45     AssocFn { called: bool },
  46     AssocType,
  47     AssocConst,
  48 }
  49
  50 impl AssocSuggestion {
  51     fn action(&self) -> &'static str {
  52         match self {
  53             AssocSuggestion::Field => "use the available field",
  54             AssocSuggestion::MethodWithSelf { called: true } => {
  55                 "call the method with the fully-qualified path"
  56             }
  57             AssocSuggestion::MethodWithSelf { called: false } => {
  58                 "refer to the method with the fully-qualified path"
  59             }
  60             AssocSuggestion::AssocFn { called: true } => "call the associated function",
  61             AssocSuggestion::AssocFn { called: false } => "refer to the associated function",
  62             AssocSuggestion::AssocConst => "use the associated `const`",
  63             AssocSuggestion::AssocType => "use the associated type",
  64         }
  65     }
  66 }
  67
  68 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  69     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  70 }
  71
  72 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  73     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  74 }
  75
  76 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  77 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
  78     let variant_path = &suggestion.path;
  79     let variant_path_string = path_names_to_string(variant_path);
  80
  81     let path_len = suggestion.path.segments.len();
  82     let enum_path = ast::Path {
  83         span: suggestion.path.span,
  84         segments: suggestion.path.segments[0..path_len - 1].iter().cloned().collect(),
  85         tokens: None,
  86     };
  87     let enum_path_string = path_names_to_string(&enum_path);
  88
  89     (variant_path_string, enum_path_string)
  90 }
  91
  92 /// Description of an elided lifetime.
  93 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
  94 pub(super) struct MissingLifetime {
  95     /// Used to overwrite the resolution with the suggestion, to avoid cascasing errors.
  96     pub id: NodeId,
  97     /// Where to suggest adding the lifetime.
  98     pub span: Span,
  99     /// How the lifetime was introduced, to have the correct space and comma.
 100     pub kind: MissingLifetimeKind,
 101     /// Number of elided lifetimes, used for elision in path.
 102     pub count: usize,
 103 }
 104
 105 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
 106 pub(super) enum MissingLifetimeKind {
 107     /// An explicit `'_`.
 108     Underscore,
 109     /// An elided lifetime `&' ty`.
 110     Ampersand,
 111     /// An elided lifetime in brackets with written brackets.
 112     Comma,
 113     /// An elided lifetime with elided brackets.
 114     Brackets,
 115 }
 116
 117 /// Description of the lifetimes appearing in a function parameter.
 118 /// This is used to provide a literal explanation to the elision failure.
 119 #[derive(Clone, Debug)]
 120 pub(super) struct ElisionFnParameter {
 121     /// The index of the argument in the original definition.
 122     pub index: usize,
 123     /// The name of the argument if it's a simple ident.
 124     pub ident: Option<Ident>,
 125     /// The number of lifetimes in the parameter.
 126     pub lifetime_count: usize,
 127     /// The span of the parameter.
 128     pub span: Span,
 129 }
 130
 131 /// Description of lifetimes that appear as candidates for elision.
 132 /// This is used to suggest introducing an explicit lifetime.
 133 #[derive(Debug)]
 134 pub(super) enum LifetimeElisionCandidate {
 135     /// This is not a real lifetime.
 136     Ignore,
 137     /// There is a named lifetime, we won't suggest anything.
 138     Named,
 139     Missing(MissingLifetime),
 140 }
 141
 142 /// Only used for diagnostics.
 143 #[derive(Debug)]
 144 struct BaseError {
 145     msg: String,
 146     fallback_label: String,
 147     span: Span,
 148     span_label: Option<(Span, &'static str)>,
 149     could_be_expr: bool,
 150     suggestion: Option<(Span, &'static str, String)>,
 151 }
 152
 153 #[derive(Debug)]
 154 enum TypoCandidate {
 155     Typo(TypoSuggestion),
 156     Shadowed(Res, Option<Span>),
 157     None,
 158 }
 159
 160 impl TypoCandidate {
 161     fn to_opt_suggestion(self) -> Option<TypoSuggestion> {
 162         match self {
 163             TypoCandidate::Typo(sugg) => Some(sugg),
 164             TypoCandidate::Shadowed(_, _) | TypoCandidate::None => None,
 165         }
 166     }
 167 }
 168
 169 impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 170     fn def_span(&self, def_id: DefId) -> Option<Span> {
 171         match def_id.krate {
 172             LOCAL_CRATE => self.r.opt_span(def_id),
 173             _ => Some(self.r.cstore().get_span_untracked(def_id, self.r.session)),
 174         }
 175     }
 176
 177     fn make_base_error(
 178         &mut self,
 179         path: &[Segment],
 180         span: Span,
 181         source: PathSource<'_>,
 182         res: Option<Res>,
 183     ) -> BaseError {
 184         // Make the base error.
 185         let mut expected = source.descr_expected();
 186         let path_str = Segment::names_to_string(path);
 187         let item_str = path.last().unwrap().ident;
 188         if let Some(res) = res {
 189             BaseError {
 190                 msg: format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 191                 fallback_label: format!("not a {expected}"),
 192                 span,
 193                 span_label: match res {
 194                     Res::Def(kind, def_id) if kind == DefKind::TyParam => {
 195                         self.def_span(def_id).map(|span| (span, "found this type parameter"))
 196                     }
 197                     _ => None,
 198                 },
 199                 could_be_expr: match res {
 200                     Res::Def(DefKind::Fn, _) => {
 201                         // Verify whether this is a fn call or an Fn used as a type.
 202                         self.r
 203                             .session
 204                             .source_map()
 205                             .span_to_snippet(span)
 206                             .map(|snippet| snippet.ends_with(')'))
 207                             .unwrap_or(false)
 208                     }
 209                     Res::Def(
 210                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 211                         _,
 212                     )
 213                     | Res::SelfCtor(_)
 214                     | Res::PrimTy(_)
 215                     | Res::Local(_) => true,
 216                     _ => false,
 217                 },
 218                 suggestion: None,
 219             }
 220         } else {
 221             let item_span = path.last().unwrap().ident.span;
 222             let (mod_prefix, mod_str, suggestion) = if path.len() == 1 {
 223                 debug!(?self.diagnostic_metadata.current_impl_items);
 224                 debug!(?self.diagnostic_metadata.current_function);
 225                 let suggestion = if self.current_trait_ref.is_none()
 226                     && let Some((fn_kind, _)) = self.diagnostic_metadata.current_function
 227                     && let Some(FnCtxt::Assoc(_)) = fn_kind.ctxt()
 228                     && let Some(items) = self.diagnostic_metadata.current_impl_items
 229                     && let Some(item) = items.iter().find(|i| {
 230                         if let AssocItemKind::Fn(_) = &i.kind && i.ident.name == item_str.name
 231                         {
 232                             debug!(?item_str.name);
 233                             return true
 234                         }
 235                         false
 236                     })
 237                     && let AssocItemKind::Fn(fn_) = &item.kind
 238                 {
 239                     debug!(?fn_);
 240                     let self_sugg = if fn_.sig.decl.has_self() { "self." } else { "Self::" };
 241                     Some((
 242                         item_span.shrink_to_lo(),
 243                         "consider using the associated function",
 244                         self_sugg.to_string()
 245                     ))
 246                 } else {
 247                     None
 248                 };
 249                 (String::new(), "this scope".to_string(), suggestion)
 250             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 251                 if self.r.session.edition() > Edition::Edition2015 {
 252                     // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
 253                     // which overrides all other expectations of item type
 254                     expected = "crate";
 255                     (String::new(), "the list of imported crates".to_string(), None)
 256                 } else {
 257                     (String::new(), "the crate root".to_string(), None)
 258                 }
 259             } else if path.len() == 2 && path[0].ident.name == kw::Crate {
 260                 (String::new(), "the crate root".to_string(), None)
 261             } else {
 262                 let mod_path = &path[..path.len() - 1];
 263                 let mod_prefix = match self.resolve_path(mod_path, Some(TypeNS), None) {
 264                     PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 265                     _ => None,
 266                 }
 267                 .map_or_else(String::new, |res| format!("{} ", res.descr()));
 268                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)), None)
 269             };
 270
 271             let (fallback_label, suggestion) = if path_str == "async"
 272                 && expected.starts_with("struct")
 273             {
 274                 ("`async` blocks are only allowed in Rust 2018 or later".to_string(), suggestion)
 275             } else {
 276                 // check if we are in situation of typo like `True` instead of `true`.
 277                 let override_suggestion =
 278                     if ["true", "false"].contains(&item_str.to_string().to_lowercase().as_str()) {
 279                         let item_typo = item_str.to_string().to_lowercase();
 280                         Some((
 281                             item_span,
 282                             "you may want to use a bool value instead",
 283                             format!("{}", item_typo),
 284                         ))
 285                     // FIXME(vincenzopalazzo): make the check smarter,
 286                     // and maybe expand with levenshtein distance checks
 287                     } else if item_str.as_str() == "printf" {
 288                         Some((
 289                             item_span,
 290                             "you may have meant to use the `print` macro",
 291                             "print!".to_owned(),
 292                         ))
 293                     } else {
 294                         suggestion
 295                     };
 296                 (format!("not found in {mod_str}"), override_suggestion)
 297             };
 298
 299             BaseError {
 300                 msg: format!("cannot find {expected} `{item_str}` in {mod_prefix}{mod_str}"),
 301                 fallback_label,
 302                 span: item_span,
 303                 span_label: None,
 304                 could_be_expr: false,
 305                 suggestion,
 306             }
 307         }
 308     }
 309
 310     /// Handles error reporting for `smart_resolve_path_fragment` function.
 311     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 312     pub(crate) fn smart_resolve_report_errors(
 313         &mut self,
 314         path: &[Segment],
 315         span: Span,
 316         source: PathSource<'_>,
 317         res: Option<Res>,
 318     ) -> (DiagnosticBuilder<'a, ErrorGuaranteed>, Vec<ImportSuggestion>) {
 319         debug!(?res, ?source);
 320         let base_error = self.make_base_error(path, span, source, res);
 321         let code = source.error_code(res.is_some());
 322         let mut err =
 323             self.r.session.struct_span_err_with_code(base_error.span, &base_error.msg, code);
 324
 325         self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
 326
 327         if let Some((span, label)) = base_error.span_label {
 328             err.span_label(span, label);
 329         }
 330
 331         if let Some(ref sugg) = base_error.suggestion {
 332             err.span_suggestion_verbose(sugg.0, sugg.1, &sugg.2, Applicability::MaybeIncorrect);
 333         }
 334
 335         self.suggest_bare_struct_literal(&mut err);
 336
 337         if self.suggest_pattern_match_with_let(&mut err, source, span) {
 338             // Fallback label.
 339             err.span_label(base_error.span, &base_error.fallback_label);
 340             return (err, Vec::new());
 341         }
 342
 343         self.suggest_self_or_self_ref(&mut err, path, span);
 344         self.detect_assoct_type_constraint_meant_as_path(&mut err, &base_error);
 345         if self.suggest_self_ty(&mut err, source, path, span)
 346             || self.suggest_self_value(&mut err, source, path, span)
 347         {
 348             return (err, Vec::new());
 349         }
 350
 351         let (found, candidates) =
 352             self.try_lookup_name_relaxed(&mut err, source, path, span, res, &base_error);
 353         if found {
 354             return (err, candidates);
 355         }
 356
 357         if !self.type_ascription_suggestion(&mut err, base_error.span) {
 358             let mut fallback =
 359                 self.suggest_trait_and_bounds(&mut err, source, res, span, &base_error);
 360
 361             // if we have suggested using pattern matching, then don't add needless suggestions
 362             // for typos.
 363             fallback |= self.suggest_typo(&mut err, source, path, span, &base_error);
 364
 365             if fallback {
 366                 // Fallback label.
 367                 err.span_label(base_error.span, &base_error.fallback_label);
 368             }
 369         }
 370         self.err_code_special_cases(&mut err, source, path, span);
 371
 372         (err, candidates)
 373     }
 374
 375     fn detect_assoct_type_constraint_meant_as_path(
 376         &self,
 377         err: &mut Diagnostic,
 378         base_error: &BaseError,
 379     ) {
 380         let Some(ty) = self.diagnostic_metadata.current_type_path else { return; };
 381         let TyKind::Path(_, path) = &ty.kind else { return; };
 382         for segment in &path.segments {
 383             let Some(params) = &segment.args else { continue; };
 384             let ast::GenericArgs::AngleBracketed(ref params) = params.deref() else { continue; };
 385             for param in &params.args {
 386                 let ast::AngleBracketedArg::Constraint(constraint) = param else { continue; };
 387                 let ast::AssocConstraintKind::Bound { bounds } = &constraint.kind else {
 388                     continue;
 389                 };
 390                 for bound in bounds {
 391                     let ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifier::None)
 392                         = bound else
 393                     {
 394                         continue;
 395                     };
 396                     if base_error.span == trait_ref.span {
 397                         err.span_suggestion_verbose(
 398                             constraint.ident.span.between(trait_ref.span),
 399                             "you might have meant to write a path instead of an associated type bound",
 400                             "::",
 401                             Applicability::MachineApplicable,
 402                         );
 403                     }
 404                 }
 405             }
 406         }
 407     }
 408
 409     fn suggest_self_or_self_ref(&mut self, err: &mut Diagnostic, path: &[Segment], span: Span) {
 410         if !self.self_type_is_available() {
 411             return;
 412         }
 413         let Some(path_last_segment) = path.last() else { return };
 414         let item_str = path_last_segment.ident;
 415         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 416         if ["this", "my"].contains(&item_str.as_str()) {
 417             err.span_suggestion_short(
 418                 span,
 419                 "you might have meant to use `self` here instead",
 420                 "self",
 421                 Applicability::MaybeIncorrect,
 422             );
 423             if !self.self_value_is_available(path[0].ident.span) {
 424                 if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
 425                     &self.diagnostic_metadata.current_function
 426                 {
 427                     let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
 428                         (param.span.shrink_to_lo(), "&self, ")
 429                     } else {
 430                         (
 431                             self.r
 432                                 .session
 433                                 .source_map()
 434                                 .span_through_char(*fn_span, '(')
 435                                 .shrink_to_hi(),
 436                             "&self",
 437                         )
 438                     };
 439                     err.span_suggestion_verbose(
 440                         span,
 441                         "if you meant to use `self`, you are also missing a `self` receiver \
 442                          argument",
 443                         sugg,
 444                         Applicability::MaybeIncorrect,
 445                     );
 446                 }
 447             }
 448         }
 449     }
 450
 451     fn try_lookup_name_relaxed(
 452         &mut self,
 453         err: &mut Diagnostic,
 454         source: PathSource<'_>,
 455         path: &[Segment],
 456         span: Span,
 457         res: Option<Res>,
 458         base_error: &BaseError,
 459     ) -> (bool, Vec<ImportSuggestion>) {
 460         // Try to lookup name in more relaxed fashion for better error reporting.
 461         let ident = path.last().unwrap().ident;
 462         let is_expected = &|res| source.is_expected(res);
 463         let ns = source.namespace();
 464         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 465         let path_str = Segment::names_to_string(path);
 466         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 467         let mut candidates = self
 468             .r
 469             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 470             .into_iter()
 471             .filter(|ImportSuggestion { did, .. }| {
 472                 match (did, res.and_then(|res| res.opt_def_id())) {
 473                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 474                     _ => true,
 475                 }
 476             })
 477             .collect::<Vec<_>>();
 478         let crate_def_id = CRATE_DEF_ID.to_def_id();
 479         // Try to filter out intrinsics candidates, as long as we have
 480         // some other candidates to suggest.
 481         let intrinsic_candidates: Vec<_> = candidates
 482             .drain_filter(|sugg| {
 483                 let path = path_names_to_string(&sugg.path);
 484                 path.starts_with("core::intrinsics::") || path.starts_with("std::intrinsics::")
 485             })
 486             .collect();
 487         if candidates.is_empty() {
 488             // Put them back if we have no more candidates to suggest...
 489             candidates.extend(intrinsic_candidates);
 490         }
 491         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 492             let mut enum_candidates: Vec<_> = self
 493                 .r
 494                 .lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant)
 495                 .into_iter()
 496                 .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 497                 .filter(|(_, enum_ty_path)| !enum_ty_path.starts_with("std::prelude::"))
 498                 .collect();
 499             if !enum_candidates.is_empty() {
 500                 if let (PathSource::Type, Some(span)) =
 501                     (source, self.diagnostic_metadata.current_type_ascription.last())
 502                 {
 503                     if self
 504                         .r
 505                         .session
 506                         .parse_sess
 507                         .type_ascription_path_suggestions
 508                         .borrow()
 509                         .contains(span)
 510                     {
 511                         // Already reported this issue on the lhs of the type ascription.
 512                         err.downgrade_to_delayed_bug();
 513                         return (true, candidates);
 514                     }
 515                 }
 516
 517                 enum_candidates.sort();
 518
 519                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 520                 // (that it's a variant) for E0573 "expected type, found variant".
 521                 let preamble = if res.is_none() {
 522                     let others = match enum_candidates.len() {
 523                         1 => String::new(),
 524                         2 => " and 1 other".to_owned(),
 525                         n => format!(" and {} others", n),
 526                     };
 527                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 528                 } else {
 529                     String::new()
 530                 };
 531                 let msg = format!("{}try using the variant's enum", preamble);
 532
 533                 err.span_suggestions(
 534                     span,
 535                     &msg,
 536                     enum_candidates.into_iter().map(|(_variant_path, enum_ty_path)| enum_ty_path),
 537                     Applicability::MachineApplicable,
 538                 );
 539             }
 540         }
 541
 542         // Try Levenshtein algorithm.
 543         let typo_sugg =
 544             self.lookup_typo_candidate(path, source.namespace(), is_expected).to_opt_suggestion();
 545         if path.len() == 1 && self.self_type_is_available() {
 546             if let Some(candidate) =
 547                 self.lookup_assoc_candidate(ident, ns, is_expected, source.is_call())
 548             {
 549                 let self_is_available = self.self_value_is_available(path[0].ident.span);
 550                 match candidate {
 551                     AssocSuggestion::Field => {
 552                         if self_is_available {
 553                             err.span_suggestion(
 554                                 span,
 555                                 "you might have meant to use the available field",
 556                                 format!("self.{path_str}"),
 557                                 Applicability::MachineApplicable,
 558                             );
 559                         } else {
 560                             err.span_label(span, "a field by this name exists in `Self`");
 561                         }
 562                     }
 563                     AssocSuggestion::MethodWithSelf { called } if self_is_available => {
 564                         let msg = if called {
 565                             "you might have meant to call the method"
 566                         } else {
 567                             "you might have meant to refer to the method"
 568                         };
 569                         err.span_suggestion(
 570                             span,
 571                             msg,
 572                             format!("self.{path_str}"),
 573                             Applicability::MachineApplicable,
 574                         );
 575                     }
 576                     AssocSuggestion::MethodWithSelf { .. }
 577                     | AssocSuggestion::AssocFn { .. }
 578                     | AssocSuggestion::AssocConst
 579                     | AssocSuggestion::AssocType => {
 580                         err.span_suggestion(
 581                             span,
 582                             &format!("you might have meant to {}", candidate.action()),
 583                             format!("Self::{path_str}"),
 584                             Applicability::MachineApplicable,
 585                         );
 586                     }
 587                 }
 588                 self.r.add_typo_suggestion(err, typo_sugg, ident_span);
 589                 return (true, candidates);
 590             }
 591
 592             // If the first argument in call is `self` suggest calling a method.
 593             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 594                 let mut args_snippet = String::new();
 595                 if let Some(args_span) = args_span {
 596                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 597                         args_snippet = snippet;
 598                     }
 599                 }
 600
 601                 err.span_suggestion(
 602                     call_span,
 603                     &format!("try calling `{ident}` as a method"),
 604                     format!("self.{path_str}({args_snippet})"),
 605                     Applicability::MachineApplicable,
 606                 );
 607                 return (true, candidates);
 608             }
 609         }
 610
 611         // Try context-dependent help if relaxed lookup didn't work.
 612         if let Some(res) = res {
 613             if self.smart_resolve_context_dependent_help(
 614                 err,
 615                 span,
 616                 source,
 617                 res,
 618                 &path_str,
 619                 &base_error.fallback_label,
 620             ) {
 621                 // We do this to avoid losing a secondary span when we override the main error span.
 622                 self.r.add_typo_suggestion(err, typo_sugg, ident_span);
 623                 return (true, candidates);
 624             }
 625         }
 626         return (false, candidates);
 627     }
 628
 629     fn suggest_trait_and_bounds(
 630         &mut self,
 631         err: &mut Diagnostic,
 632         source: PathSource<'_>,
 633         res: Option<Res>,
 634         span: Span,
 635         base_error: &BaseError,
 636     ) -> bool {
 637         let is_macro =
 638             base_error.span.from_expansion() && base_error.span.desugaring_kind().is_none();
 639         let mut fallback = false;
 640
 641         if let (
 642             PathSource::Trait(AliasPossibility::Maybe),
 643             Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
 644             false,
 645         ) = (source, res, is_macro)
 646         {
 647             if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
 648                 fallback = true;
 649                 let spans: Vec<Span> = bounds
 650                     .iter()
 651                     .map(|bound| bound.span())
 652                     .filter(|&sp| sp != base_error.span)
 653                     .collect();
 654
 655                 let start_span = bounds[0].span();
 656                 // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
 657                 let end_span = bounds.last().unwrap().span();
 658                 // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
 659                 let last_bound_span = spans.last().cloned().unwrap();
 660                 let mut multi_span: MultiSpan = spans.clone().into();
 661                 for sp in spans {
 662                     let msg = if sp == last_bound_span {
 663                         format!(
 664                             "...because of {these} bound{s}",
 665                             these = pluralize!("this", bounds.len() - 1),
 666                             s = pluralize!(bounds.len() - 1),
 667                         )
 668                     } else {
 669                         String::new()
 670                     };
 671                     multi_span.push_span_label(sp, msg);
 672                 }
 673                 multi_span.push_span_label(base_error.span, "expected this type to be a trait...");
 674                 err.span_help(
 675                     multi_span,
 676                     "`+` is used to constrain a \"trait object\" type with lifetimes or \
 677                         auto-traits; structs and enums can't be bound in that way",
 678                 );
 679                 if bounds.iter().all(|bound| match bound {
 680                     ast::GenericBound::Outlives(_) => true,
 681                     ast::GenericBound::Trait(tr, _) => tr.span == base_error.span,
 682                 }) {
 683                     let mut sugg = vec![];
 684                     if base_error.span != start_span {
 685                         sugg.push((start_span.until(base_error.span), String::new()));
 686                     }
 687                     if base_error.span != end_span {
 688                         sugg.push((base_error.span.shrink_to_hi().to(end_span), String::new()));
 689                     }
 690
 691                     err.multipart_suggestion(
 692                         "if you meant to use a type and not a trait here, remove the bounds",
 693                         sugg,
 694                         Applicability::MaybeIncorrect,
 695                     );
 696                 }
 697             }
 698         }
 699
 700         fallback |= self.restrict_assoc_type_in_where_clause(span, err);
 701         fallback
 702     }
 703
 704     fn suggest_typo(
 705         &mut self,
 706         err: &mut Diagnostic,
 707         source: PathSource<'_>,
 708         path: &[Segment],
 709         span: Span,
 710         base_error: &BaseError,
 711     ) -> bool {
 712         let is_expected = &|res| source.is_expected(res);
 713         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 714         let typo_sugg = self.lookup_typo_candidate(path, source.namespace(), is_expected);
 715         let is_in_same_file = &|sp1, sp2| {
 716             let source_map = self.r.session.source_map();
 717             let file1 = source_map.span_to_filename(sp1);
 718             let file2 = source_map.span_to_filename(sp2);
 719             file1 == file2
 720         };
 721         // print 'you might have meant' if the candidate is (1) is a shadowed name with
 722         // accessible definition and (2) either defined in the same crate as the typo
 723         // (could be in a different file) or introduced in the same file as the typo
 724         // (could belong to a different crate)
 725         if let TypoCandidate::Shadowed(res, Some(sugg_span)) = typo_sugg
 726             && res
 727                 .opt_def_id()
 728                 .map_or(false, |id| id.is_local() || is_in_same_file(span, sugg_span))
 729         {
 730             err.span_label(
 731                 sugg_span,
 732                 format!("you might have meant to refer to this {}", res.descr()),
 733             );
 734             return true;
 735         }
 736         let mut fallback = false;
 737         let typo_sugg = typo_sugg.to_opt_suggestion();
 738         if !self.r.add_typo_suggestion(err, typo_sugg, ident_span) {
 739             fallback = true;
 740             match self.diagnostic_metadata.current_let_binding {
 741                 Some((pat_sp, Some(ty_sp), None))
 742                     if ty_sp.contains(base_error.span) && base_error.could_be_expr =>
 743                 {
 744                     err.span_suggestion_short(
 745                         pat_sp.between(ty_sp),
 746                         "use `=` if you meant to assign",
 747                         " = ",
 748                         Applicability::MaybeIncorrect,
 749                     );
 750                 }
 751                 _ => {}
 752             }
 753
 754             // If the trait has a single item (which wasn't matched by Levenshtein), suggest it
 755             let suggestion = self.get_single_associated_item(&path, &source, is_expected);
 756             if !self.r.add_typo_suggestion(err, suggestion, ident_span) {
 757                 fallback = !self.let_binding_suggestion(err, ident_span);
 758             }
 759         }
 760         fallback
 761     }
 762
 763     fn err_code_special_cases(
 764         &mut self,
 765         err: &mut Diagnostic,
 766         source: PathSource<'_>,
 767         path: &[Segment],
 768         span: Span,
 769     ) {
 770         if let Some(err_code) = &err.code {
 771             if err_code == &rustc_errors::error_code!(E0425) {
 772                 for label_rib in &self.label_ribs {
 773                     for (label_ident, node_id) in &label_rib.bindings {
 774                         let ident = path.last().unwrap().ident;
 775                         if format!("'{}", ident) == label_ident.to_string() {
 776                             err.span_label(label_ident.span, "a label with a similar name exists");
 777                             if let PathSource::Expr(Some(Expr {
 778                                 kind: ExprKind::Break(None, Some(_)),
 779                                 ..
 780                             })) = source
 781                             {
 782                                 err.span_suggestion(
 783                                     span,
 784                                     "use the similarly named label",
 785                                     label_ident.name,
 786                                     Applicability::MaybeIncorrect,
 787                                 );
 788                                 // Do not lint against unused label when we suggest them.
 789                                 self.diagnostic_metadata.unused_labels.remove(node_id);
 790                             }
 791                         }
 792                     }
 793                 }
 794             } else if err_code == &rustc_errors::error_code!(E0412) {
 795                 if let Some(correct) = Self::likely_rust_type(path) {
 796                     err.span_suggestion(
 797                         span,
 798                         "perhaps you intended to use this type",
 799                         correct,
 800                         Applicability::MaybeIncorrect,
 801                     );
 802                 }
 803             }
 804         }
 805     }
 806
 807     /// Emit special messages for unresolved `Self` and `self`.
 808     fn suggest_self_ty(
 809         &mut self,
 810         err: &mut Diagnostic,
 811         source: PathSource<'_>,
 812         path: &[Segment],
 813         span: Span,
 814     ) -> bool {
 815         if !is_self_type(path, source.namespace()) {
 816             return false;
 817         }
 818         err.code(rustc_errors::error_code!(E0411));
 819         err.span_label(span, "`Self` is only available in impls, traits, and type definitions");
 820         if let Some(item_kind) = self.diagnostic_metadata.current_item {
 821             if !item_kind.ident.span.is_dummy() {
 822                 err.span_label(
 823                     item_kind.ident.span,
 824                     format!(
 825                         "`Self` not allowed in {} {}",
 826                         item_kind.kind.article(),
 827                         item_kind.kind.descr()
 828                     ),
 829                 );
 830             }
 831         }
 832         true
 833     }
 834
 835     fn suggest_self_value(
 836         &mut self,
 837         err: &mut Diagnostic,
 838         source: PathSource<'_>,
 839         path: &[Segment],
 840         span: Span,
 841     ) -> bool {
 842         if !is_self_value(path, source.namespace()) {
 843             return false;
 844         }
 845
 846         debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 847         err.code(rustc_errors::error_code!(E0424));
 848         err.span_label(
 849             span,
 850             match source {
 851                 PathSource::Pat => {
 852                     "`self` value is a keyword and may not be bound to variables or shadowed"
 853                 }
 854                 _ => "`self` value is a keyword only available in methods with a `self` parameter",
 855             },
 856         );
 857         let is_assoc_fn = self.self_type_is_available();
 858         if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 859             // The current function has a `self' parameter, but we were unable to resolve
 860             // a reference to `self`. This can only happen if the `self` identifier we
 861             // are resolving came from a different hygiene context.
 862             if fn_kind.decl().inputs.get(0).map_or(false, |p| p.is_self()) {
 863                 err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 864             } else {
 865                 let doesnt = if is_assoc_fn {
 866                     let (span, sugg) = fn_kind
 867                         .decl()
 868                         .inputs
 869                         .get(0)
 870                         .map(|p| (p.span.shrink_to_lo(), "&self, "))
 871                         .unwrap_or_else(|| {
 872                             // Try to look for the "(" after the function name, if possible.
 873                             // This avoids placing the suggestion into the visibility specifier.
 874                             let span = fn_kind
 875                                 .ident()
 876                                 .map_or(*span, |ident| span.with_lo(ident.span.hi()));
 877                             (
 878                                 self.r
 879                                     .session
 880                                     .source_map()
 881                                     .span_through_char(span, '(')
 882                                     .shrink_to_hi(),
 883                                 "&self",
 884                             )
 885                         });
 886                     err.span_suggestion_verbose(
 887                         span,
 888                         "add a `self` receiver parameter to make the associated `fn` a method",
 889                         sugg,
 890                         Applicability::MaybeIncorrect,
 891                     );
 892                     "doesn't"
 893                 } else {
 894                     "can't"
 895                 };
 896                 if let Some(ident) = fn_kind.ident() {
 897                     err.span_label(
 898                         ident.span,
 899                         &format!("this function {} have a `self` parameter", doesnt),
 900                     );
 901                 }
 902             }
 903         } else if let Some(item_kind) = self.diagnostic_metadata.current_item {
 904             err.span_label(
 905                 item_kind.ident.span,
 906                 format!(
 907                     "`self` not allowed in {} {}",
 908                     item_kind.kind.article(),
 909                     item_kind.kind.descr()
 910                 ),
 911             );
 912         }
 913         true
 914     }
 915
 916     fn suggest_swapping_misplaced_self_ty_and_trait(
 917         &mut self,
 918         err: &mut Diagnostic,
 919         source: PathSource<'_>,
 920         res: Option<Res>,
 921         span: Span,
 922     ) {
 923         if let Some((trait_ref, self_ty)) =
 924             self.diagnostic_metadata.currently_processing_impl_trait.clone()
 925             && let TyKind::Path(_, self_ty_path) = &self_ty.kind
 926             && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 927                 self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
 928             && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
 929             && trait_ref.path.span == span
 930             && let PathSource::Trait(_) = source
 931             && let Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)) = res
 932             && let Ok(self_ty_str) =
 933                 self.r.session.source_map().span_to_snippet(self_ty.span)
 934             && let Ok(trait_ref_str) =
 935                 self.r.session.source_map().span_to_snippet(trait_ref.path.span)
 936         {
 937                 err.multipart_suggestion(
 938                     "`impl` items mention the trait being implemented first and the type it is being implemented for second",
 939                     vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
 940                     Applicability::MaybeIncorrect,
 941                 );
 942         }
 943     }
 944
 945     fn suggest_bare_struct_literal(&mut self, err: &mut Diagnostic) {
 946         if let Some(span) = self.diagnostic_metadata.current_block_could_be_bare_struct_literal {
 947             err.multipart_suggestion(
 948                 "you might have meant to write a `struct` literal",
 949                 vec![
 950                     (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
 951                     (span.shrink_to_hi(), "}".to_string()),
 952                 ],
 953                 Applicability::HasPlaceholders,
 954             );
 955         }
 956     }
 957
 958     fn suggest_pattern_match_with_let(
 959         &mut self,
 960         err: &mut Diagnostic,
 961         source: PathSource<'_>,
 962         span: Span,
 963     ) -> bool {
 964         if let PathSource::Expr(_) = source &&
 965         let Some(Expr {
 966                     span: expr_span,
 967                     kind: ExprKind::Assign(lhs, _, _),
 968                     ..
 969                 })  = self.diagnostic_metadata.in_if_condition {
 970             // Icky heuristic so we don't suggest:
 971             // `if (i + 2) = 2` => `if let (i + 2) = 2` (approximately pattern)
 972             // `if 2 = i` => `if let 2 = i` (lhs needs to contain error span)
 973             if lhs.is_approximately_pattern() && lhs.span.contains(span) {
 974                 err.span_suggestion_verbose(
 975                     expr_span.shrink_to_lo(),
 976                     "you might have meant to use pattern matching",
 977                     "let ",
 978                     Applicability::MaybeIncorrect,
 979                 );
 980                 return true;
 981             }
 982         }
 983         false
 984     }
 985
 986     fn get_single_associated_item(
 987         &mut self,
 988         path: &[Segment],
 989         source: &PathSource<'_>,
 990         filter_fn: &impl Fn(Res) -> bool,
 991     ) -> Option<TypoSuggestion> {
 992         if let crate::PathSource::TraitItem(_) = source {
 993             let mod_path = &path[..path.len() - 1];
 994             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 995                 self.resolve_path(mod_path, None, None)
 996             {
 997                 let resolutions = self.r.resolutions(module).borrow();
 998                 let targets: Vec<_> =
 999                     resolutions
1000                         .iter()
1001                         .filter_map(|(key, resolution)| {
1002                             resolution.borrow().binding.map(|binding| binding.res()).and_then(
1003                                 |res| if filter_fn(res) { Some((key, res)) } else { None },
1004                             )
1005                         })
1006                         .collect();
1007                 if targets.len() == 1 {
1008                     let target = targets[0];
1009                     return Some(TypoSuggestion::single_item_from_ident(target.0.ident, target.1));
1010                 }
1011             }
1012         }
1013         None
1014     }
1015
1016     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
1017     fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diagnostic) -> bool {
1018         // Detect that we are actually in a `where` predicate.
1019         let (bounded_ty, bounds, where_span) =
1020             if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
1021                 bounded_ty,
1022                 bound_generic_params,
1023                 bounds,
1024                 span,
1025             })) = self.diagnostic_metadata.current_where_predicate
1026             {
1027                 if !bound_generic_params.is_empty() {
1028                     return false;
1029                 }
1030                 (bounded_ty, bounds, span)
1031             } else {
1032                 return false;
1033             };
1034
1035         // Confirm that the target is an associated type.
1036         let (ty, position, path) = if let ast::TyKind::Path(Some(qself), path) = &bounded_ty.kind {
1037             // use this to verify that ident is a type param.
1038             let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
1039                 return false;
1040             };
1041             if !matches!(
1042                 partial_res.full_res(),
1043                 Some(hir::def::Res::Def(hir::def::DefKind::AssocTy, _))
1044             ) {
1045                 return false;
1046             }
1047             (&qself.ty, qself.position, path)
1048         } else {
1049             return false;
1050         };
1051
1052         let peeled_ty = ty.peel_refs();
1053         if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
1054             // Confirm that the `SelfTy` is a type parameter.
1055             let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
1056                 return false;
1057             };
1058             if !matches!(
1059                 partial_res.full_res(),
1060                 Some(hir::def::Res::Def(hir::def::DefKind::TyParam, _))
1061             ) {
1062                 return false;
1063             }
1064             if let (
1065                 [ast::PathSegment { ident: constrain_ident, args: None, .. }],
1066                 [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
1067             ) = (&type_param_path.segments[..], &bounds[..])
1068             {
1069                 if let [ast::PathSegment { ident, args: None, .. }] =
1070                     &poly_trait_ref.trait_ref.path.segments[..]
1071                 {
1072                     if ident.span == span {
1073                         err.span_suggestion_verbose(
1074                             *where_span,
1075                             &format!("constrain the associated type to `{}`", ident),
1076                             format!(
1077                                 "{}: {}<{} = {}>",
1078                                 self.r
1079                                     .session
1080                                     .source_map()
1081                                     .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
1082                                     .unwrap_or_else(|_| constrain_ident.to_string()),
1083                                 path.segments[..position]
1084                                     .iter()
1085                                     .map(|segment| path_segment_to_string(segment))
1086                                     .collect::<Vec<_>>()
1087                                     .join("::"),
1088                                 path.segments[position..]
1089                                     .iter()
1090                                     .map(|segment| path_segment_to_string(segment))
1091                                     .collect::<Vec<_>>()
1092                                     .join("::"),
1093                                 ident,
1094                             ),
1095                             Applicability::MaybeIncorrect,
1096                         );
1097                     }
1098                     return true;
1099                 }
1100             }
1101         }
1102         false
1103     }
1104
1105     /// Check if the source is call expression and the first argument is `self`. If true,
1106     /// return the span of whole call and the span for all arguments expect the first one (`self`).
1107     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
1108         let mut has_self_arg = None;
1109         if let PathSource::Expr(Some(parent)) = source {
1110             match &parent.kind {
1111                 ExprKind::Call(_, args) if !args.is_empty() => {
1112                     let mut expr_kind = &args[0].kind;
1113                     loop {
1114                         match expr_kind {
1115                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
1116                                 if arg_name.segments[0].ident.name == kw::SelfLower {
1117                                     let call_span = parent.span;
1118                                     let tail_args_span = if args.len() > 1 {
1119                                         Some(Span::new(
1120                                             args[1].span.lo(),
1121                                             args.last().unwrap().span.hi(),
1122                                             call_span.ctxt(),
1123                                             None,
1124                                         ))
1125                                     } else {
1126                                         None
1127                                     };
1128                                     has_self_arg = Some((call_span, tail_args_span));
1129                                 }
1130                                 break;
1131                             }
1132                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
1133                             _ => break,
1134                         }
1135                     }
1136                 }
1137                 _ => (),
1138             }
1139         };
1140         has_self_arg
1141     }
1142
1143     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
1144         // HACK(estebank): find a better way to figure out that this was a
1145         // parser issue where a struct literal is being used on an expression
1146         // where a brace being opened means a block is being started. Look
1147         // ahead for the next text to see if `span` is followed by a `{`.
1148         let sm = self.r.session.source_map();
1149         let sp = sm.span_look_ahead(span, None, Some(50));
1150         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
1151         // In case this could be a struct literal that needs to be surrounded
1152         // by parentheses, find the appropriate span.
1153         let closing_span = sm.span_look_ahead(span, Some("}"), Some(50));
1154         let closing_brace: Option<Span> = sm
1155             .span_to_snippet(closing_span)
1156             .map_or(None, |s| if s == "}" { Some(span.to(closing_span)) } else { None });
1157         (followed_by_brace, closing_brace)
1158     }
1159
1160     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
1161     /// function.
1162     /// Returns `true` if able to provide context-dependent help.
1163     fn smart_resolve_context_dependent_help(
1164         &mut self,
1165         err: &mut Diagnostic,
1166         span: Span,
1167         source: PathSource<'_>,
1168         res: Res,
1169         path_str: &str,
1170         fallback_label: &str,
1171     ) -> bool {
1172         let ns = source.namespace();
1173         let is_expected = &|res| source.is_expected(res);
1174
1175         let path_sep = |err: &mut Diagnostic, expr: &Expr, kind: DefKind| {
1176             const MESSAGE: &str = "use the path separator to refer to an item";
1177
1178             let (lhs_span, rhs_span) = match &expr.kind {
1179                 ExprKind::Field(base, ident) => (base.span, ident.span),
1180                 ExprKind::MethodCall(box MethodCall { receiver, span, .. }) => {
1181                     (receiver.span, *span)
1182                 }
1183                 _ => return false,
1184             };
1185
1186             if lhs_span.eq_ctxt(rhs_span) {
1187                 err.span_suggestion(
1188                     lhs_span.between(rhs_span),
1189                     MESSAGE,
1190                     "::",
1191                     Applicability::MaybeIncorrect,
1192                 );
1193                 true
1194             } else if kind == DefKind::Struct
1195             && let Some(lhs_source_span) = lhs_span.find_ancestor_inside(expr.span)
1196             && let Ok(snippet) = self.r.session.source_map().span_to_snippet(lhs_source_span)
1197             {
1198                 // The LHS is a type that originates from a macro call.
1199                 // We have to add angle brackets around it.
1200
1201                 err.span_suggestion_verbose(
1202                     lhs_source_span.until(rhs_span),
1203                     MESSAGE,
1204                     format!("<{snippet}>::"),
1205                     Applicability::MaybeIncorrect,
1206                 );
1207                 true
1208             } else {
1209                 // Either we were unable to obtain the source span / the snippet or
1210                 // the LHS originates from a macro call and it is not a type and thus
1211                 // there is no way to replace `.` with `::` and still somehow suggest
1212                 // valid Rust code.
1213
1214                 false
1215             }
1216         };
1217
1218         let find_span = |source: &PathSource<'_>, err: &mut Diagnostic| {
1219             match source {
1220                 PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
1221                 | PathSource::TupleStruct(span, _) => {
1222                     // We want the main underline to cover the suggested code as well for
1223                     // cleaner output.
1224                     err.set_span(*span);
1225                     *span
1226                 }
1227                 _ => span,
1228             }
1229         };
1230
1231         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
1232             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
1233
1234             match source {
1235                 PathSource::Expr(Some(
1236                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
1237                 )) if path_sep(err, &parent, DefKind::Struct) => {}
1238                 PathSource::Expr(
1239                     None
1240                     | Some(Expr {
1241                         kind:
1242                             ExprKind::Path(..)
1243                             | ExprKind::Binary(..)
1244                             | ExprKind::Unary(..)
1245                             | ExprKind::If(..)
1246                             | ExprKind::While(..)
1247                             | ExprKind::ForLoop(..)
1248                             | ExprKind::Match(..),
1249                         ..
1250                     }),
1251                 ) if followed_by_brace => {
1252                     if let Some(sp) = closing_brace {
1253                         err.span_label(span, fallback_label);
1254                         err.multipart_suggestion(
1255                             "surround the struct literal with parentheses",
1256                             vec![
1257                                 (sp.shrink_to_lo(), "(".to_string()),
1258                                 (sp.shrink_to_hi(), ")".to_string()),
1259                             ],
1260                             Applicability::MaybeIncorrect,
1261                         );
1262                     } else {
1263                         err.span_label(
1264                             span, // Note the parentheses surrounding the suggestion below
1265                             format!(
1266                                 "you might want to surround a struct literal with parentheses: \
1267                                  `({} {{ /* fields */ }})`?",
1268                                 path_str
1269                             ),
1270                         );
1271                     }
1272                 }
1273                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1274                     let span = find_span(&source, err);
1275                     if let Some(span) = self.def_span(def_id) {
1276                         err.span_label(span, &format!("`{}` defined here", path_str));
1277                     }
1278                     let (tail, descr, applicability) = match source {
1279                         PathSource::Pat | PathSource::TupleStruct(..) => {
1280                             ("", "pattern", Applicability::MachineApplicable)
1281                         }
1282                         _ => (": val", "literal", Applicability::HasPlaceholders),
1283                     };
1284                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
1285                         Some(fields) => (
1286                             fields
1287                                 .iter()
1288                                 .map(|f| format!("{}{}", f.node, tail))
1289                                 .collect::<Vec<String>>()
1290                                 .join(", "),
1291                             applicability,
1292                         ),
1293                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
1294                     };
1295                     let pad = match self.r.field_names.get(&def_id) {
1296                         Some(fields) if fields.is_empty() => "",
1297                         _ => " ",
1298                     };
1299                     err.span_suggestion(
1300                         span,
1301                         &format!("use struct {} syntax instead", descr),
1302                         format!("{path_str} {{{pad}{fields}{pad}}}"),
1303                         applicability,
1304                     );
1305                 }
1306                 _ => {
1307                     err.span_label(span, fallback_label);
1308                 }
1309             }
1310         };
1311
1312         match (res, source) {
1313             (
1314                 Res::Def(DefKind::Macro(MacroKind::Bang), _),
1315                 PathSource::Expr(Some(Expr {
1316                     kind: ExprKind::Index(..) | ExprKind::Call(..), ..
1317                 }))
1318                 | PathSource::Struct,
1319             ) => {
1320                 err.span_label(span, fallback_label);
1321                 err.span_suggestion_verbose(
1322                     span.shrink_to_hi(),
1323                     "use `!` to invoke the macro",
1324                     "!",
1325                     Applicability::MaybeIncorrect,
1326                 );
1327                 if path_str == "try" && span.rust_2015() {
1328                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
1329                 }
1330             }
1331             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
1332                 err.span_label(span, fallback_label);
1333             }
1334             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
1335                 err.span_label(span, "type aliases cannot be used as traits");
1336                 if self.r.session.is_nightly_build() {
1337                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
1338                                `type` alias";
1339                     if let Some(span) = self.def_span(def_id) {
1340                         if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
1341                             // The span contains a type alias so we should be able to
1342                             // replace `type` with `trait`.
1343                             let snip = snip.replacen("type", "trait", 1);
1344                             err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
1345                         } else {
1346                             err.span_help(span, msg);
1347                         }
1348                     } else {
1349                         err.help(msg);
1350                     }
1351                 }
1352             }
1353             (
1354                 Res::Def(kind @ (DefKind::Mod | DefKind::Trait), _),
1355                 PathSource::Expr(Some(parent)),
1356             ) => {
1357                 if !path_sep(err, &parent, kind) {
1358                     return false;
1359                 }
1360             }
1361             (
1362                 Res::Def(DefKind::Enum, def_id),
1363                 PathSource::TupleStruct(..) | PathSource::Expr(..),
1364             ) => {
1365                 if self
1366                     .diagnostic_metadata
1367                     .current_type_ascription
1368                     .last()
1369                     .map(|sp| {
1370                         self.r
1371                             .session
1372                             .parse_sess
1373                             .type_ascription_path_suggestions
1374                             .borrow()
1375                             .contains(&sp)
1376                     })
1377                     .unwrap_or(false)
1378                 {
1379                     err.downgrade_to_delayed_bug();
1380                     // We already suggested changing `:` into `::` during parsing.
1381                     return false;
1382                 }
1383
1384                 self.suggest_using_enum_variant(err, source, def_id, span);
1385             }
1386             (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
1387                 let (ctor_def, ctor_vis, fields) =
1388                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
1389                         if let PathSource::Expr(Some(parent)) = source {
1390                             if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
1391                                 bad_struct_syntax_suggestion(def_id);
1392                                 return true;
1393                             }
1394                         }
1395                         struct_ctor
1396                     } else {
1397                         bad_struct_syntax_suggestion(def_id);
1398                         return true;
1399                     };
1400
1401                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
1402                 if !is_expected(ctor_def) || is_accessible {
1403                     return true;
1404                 }
1405
1406                 let field_spans = match source {
1407                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
1408                     PathSource::TupleStruct(_, pattern_spans) => {
1409                         err.set_primary_message(
1410                             "cannot match against a tuple struct which contains private fields",
1411                         );
1412
1413                         // Use spans of the tuple struct pattern.
1414                         Some(Vec::from(pattern_spans))
1415                     }
1416                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
1417                     _ if source.is_call() => {
1418                         err.set_primary_message(
1419                             "cannot initialize a tuple struct which contains private fields",
1420                         );
1421
1422                         // Use spans of the tuple struct definition.
1423                         self.r
1424                             .field_names
1425                             .get(&def_id)
1426                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
1427                     }
1428                     _ => None,
1429                 };
1430
1431                 if let Some(spans) =
1432                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
1433                 {
1434                     let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
1435                         .filter(|(vis, _)| {
1436                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
1437                         })
1438                         .map(|(_, span)| *span)
1439                         .collect();
1440
1441                     if non_visible_spans.len() > 0 {
1442                         let mut m: MultiSpan = non_visible_spans.clone().into();
1443                         non_visible_spans
1444                             .into_iter()
1445                             .for_each(|s| m.push_span_label(s, "private field"));
1446                         err.span_note(m, "constructor is not visible here due to private fields");
1447                     }
1448
1449                     return true;
1450                 }
1451
1452                 err.span_label(span, "constructor is not visible here due to private fields");
1453             }
1454             (Res::Def(DefKind::Union | DefKind::Variant, def_id), _) if ns == ValueNS => {
1455                 bad_struct_syntax_suggestion(def_id);
1456             }
1457             (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
1458                 match source {
1459                     PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1460                         let span = find_span(&source, err);
1461                         if let Some(span) = self.def_span(def_id) {
1462                             err.span_label(span, &format!("`{}` defined here", path_str));
1463                         }
1464                         err.span_suggestion(
1465                             span,
1466                             "use this syntax instead",
1467                             path_str,
1468                             Applicability::MaybeIncorrect,
1469                         );
1470                     }
1471                     _ => return false,
1472                 }
1473             }
1474             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), ctor_def_id), _) if ns == ValueNS => {
1475                 let def_id = self.r.parent(ctor_def_id);
1476                 if let Some(span) = self.def_span(def_id) {
1477                     err.span_label(span, &format!("`{}` defined here", path_str));
1478                 }
1479                 let fields = self.r.field_names.get(&def_id).map_or_else(
1480                     || "/* fields */".to_string(),
1481                     |fields| vec!["_"; fields.len()].join(", "),
1482                 );
1483                 err.span_suggestion(
1484                     span,
1485                     "use the tuple variant pattern syntax instead",
1486                     format!("{}({})", path_str, fields),
1487                     Applicability::HasPlaceholders,
1488                 );
1489             }
1490             (Res::SelfTyParam { .. } | Res::SelfTyAlias { .. }, _) if ns == ValueNS => {
1491                 err.span_label(span, fallback_label);
1492                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1493             }
1494             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1495                 err.note("can't use a type alias as a constructor");
1496             }
1497             _ => return false,
1498         }
1499         true
1500     }
1501
1502     /// Given the target `ident` and `kind`, search for the similarly named associated item
1503     /// in `self.current_trait_ref`.
1504     pub(crate) fn find_similarly_named_assoc_item(
1505         &mut self,
1506         ident: Symbol,
1507         kind: &AssocItemKind,
1508     ) -> Option<Symbol> {
1509         let (module, _) = self.current_trait_ref.as_ref()?;
1510         if ident == kw::Underscore {
1511             // We do nothing for `_`.
1512             return None;
1513         }
1514
1515         let resolutions = self.r.resolutions(module);
1516         let targets = resolutions
1517             .borrow()
1518             .iter()
1519             .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
1520             .filter(|(_, res)| match (kind, res) {
1521                 (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
1522                 (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
1523                 (AssocItemKind::Type(..), Res::Def(DefKind::AssocTy, _)) => true,
1524                 _ => false,
1525             })
1526             .map(|(key, _)| key.ident.name)
1527             .collect::<Vec<_>>();
1528
1529         find_best_match_for_name(&targets, ident, None)
1530     }
1531
1532     fn lookup_assoc_candidate<FilterFn>(
1533         &mut self,
1534         ident: Ident,
1535         ns: Namespace,
1536         filter_fn: FilterFn,
1537         called: bool,
1538     ) -> Option<AssocSuggestion>
1539     where
1540         FilterFn: Fn(Res) -> bool,
1541     {
1542         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1543             match t.kind {
1544                 TyKind::Path(None, _) => Some(t.id),
1545                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1546                 // This doesn't handle the remaining `Ty` variants as they are not
1547                 // that commonly the self_type, it might be interesting to provide
1548                 // support for those in future.
1549                 _ => None,
1550             }
1551         }
1552         // Fields are generally expected in the same contexts as locals.
1553         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1554             if let Some(node_id) =
1555                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1556             {
1557                 // Look for a field with the same name in the current self_type.
1558                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1559                     if let Some(Res::Def(DefKind::Struct | DefKind::Union, did)) =
1560                         resolution.full_res()
1561                     {
1562                         if let Some(field_names) = self.r.field_names.get(&did) {
1563                             if field_names.iter().any(|&field_name| ident.name == field_name.node) {
1564                                 return Some(AssocSuggestion::Field);
1565                             }
1566                         }
1567                     }
1568                 }
1569             }
1570         }
1571
1572         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1573             for assoc_item in items {
1574                 if assoc_item.ident == ident {
1575                     return Some(match &assoc_item.kind {
1576                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1577                         ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
1578                             AssocSuggestion::MethodWithSelf { called }
1579                         }
1580                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn { called },
1581                         ast::AssocItemKind::Type(..) => AssocSuggestion::AssocType,
1582                         ast::AssocItemKind::MacCall(_) => continue,
1583                     });
1584                 }
1585             }
1586         }
1587
1588         // Look for associated items in the current trait.
1589         if let Some((module, _)) = self.current_trait_ref {
1590             if let Ok(binding) = self.r.maybe_resolve_ident_in_module(
1591                 ModuleOrUniformRoot::Module(module),
1592                 ident,
1593                 ns,
1594                 &self.parent_scope,
1595             ) {
1596                 let res = binding.res();
1597                 if filter_fn(res) {
1598                     if self.r.has_self.contains(&res.def_id()) {
1599                         return Some(AssocSuggestion::MethodWithSelf { called });
1600                     } else {
1601                         match res {
1602                             Res::Def(DefKind::AssocFn, _) => {
1603                                 return Some(AssocSuggestion::AssocFn { called });
1604                             }
1605                             Res::Def(DefKind::AssocConst, _) => {
1606                                 return Some(AssocSuggestion::AssocConst);
1607                             }
1608                             Res::Def(DefKind::AssocTy, _) => {
1609                                 return Some(AssocSuggestion::AssocType);
1610                             }
1611                             _ => {}
1612                         }
1613                     }
1614                 }
1615             }
1616         }
1617
1618         None
1619     }
1620
1621     fn lookup_typo_candidate(
1622         &mut self,
1623         path: &[Segment],
1624         ns: Namespace,
1625         filter_fn: &impl Fn(Res) -> bool,
1626     ) -> TypoCandidate {
1627         let mut names = Vec::new();
1628         if path.len() == 1 {
1629             let mut ctxt = path.last().unwrap().ident.span.ctxt();
1630
1631             // Search in lexical scope.
1632             // Walk backwards up the ribs in scope and collect candidates.
1633             for rib in self.ribs[ns].iter().rev() {
1634                 let rib_ctxt = if rib.kind.contains_params() {
1635                     ctxt.normalize_to_macros_2_0()
1636                 } else {
1637                     ctxt.normalize_to_macro_rules()
1638                 };
1639
1640                 // Locals and type parameters
1641                 for (ident, &res) in &rib.bindings {
1642                     if filter_fn(res) && ident.span.ctxt() == rib_ctxt {
1643                         names.push(TypoSuggestion::typo_from_ident(*ident, res));
1644                     }
1645                 }
1646
1647                 if let RibKind::MacroDefinition(def) = rib.kind && def == self.r.macro_def(ctxt) {
1648                     // If an invocation of this macro created `ident`, give up on `ident`
1649                     // and switch to `ident`'s source from the macro definition.
1650                     ctxt.remove_mark();
1651                     continue;
1652                 }
1653
1654                 // Items in scope
1655                 if let RibKind::ModuleRibKind(module) = rib.kind {
1656                     // Items from this module
1657                     self.r.add_module_candidates(module, &mut names, &filter_fn, Some(ctxt));
1658
1659                     if let ModuleKind::Block = module.kind {
1660                         // We can see through blocks
1661                     } else {
1662                         // Items from the prelude
1663                         if !module.no_implicit_prelude {
1664                             let extern_prelude = self.r.extern_prelude.clone();
1665                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1666                                 self.r
1667                                     .crate_loader()
1668                                     .maybe_process_path_extern(ident.name)
1669                                     .and_then(|crate_id| {
1670                                         let crate_mod =
1671                                             Res::Def(DefKind::Mod, crate_id.as_def_id());
1672
1673                                         if filter_fn(crate_mod) {
1674                                             Some(TypoSuggestion::typo_from_ident(*ident, crate_mod))
1675                                         } else {
1676                                             None
1677                                         }
1678                                     })
1679                             }));
1680
1681                             if let Some(prelude) = self.r.prelude {
1682                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn, None);
1683                             }
1684                         }
1685                         break;
1686                     }
1687                 }
1688             }
1689             // Add primitive types to the mix
1690             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1691                 names.extend(PrimTy::ALL.iter().map(|prim_ty| {
1692                     TypoSuggestion::typo_from_name(prim_ty.name(), Res::PrimTy(*prim_ty))
1693                 }))
1694             }
1695         } else {
1696             // Search in module.
1697             let mod_path = &path[..path.len() - 1];
1698             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1699                 self.resolve_path(mod_path, Some(TypeNS), None)
1700             {
1701                 self.r.add_module_candidates(module, &mut names, &filter_fn, None);
1702             }
1703         }
1704
1705         let name = path[path.len() - 1].ident.name;
1706         // Make sure error reporting is deterministic.
1707         names.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
1708
1709         match find_best_match_for_name(
1710             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1711             name,
1712             None,
1713         ) {
1714             Some(found) => {
1715                 let Some(sugg) = names.into_iter().find(|suggestion| suggestion.candidate == found) else {
1716                     return TypoCandidate::None;
1717                 };
1718                 if found == name {
1719                     TypoCandidate::Shadowed(sugg.res, sugg.span)
1720                 } else {
1721                     TypoCandidate::Typo(sugg)
1722                 }
1723             }
1724             _ => TypoCandidate::None,
1725         }
1726     }
1727
1728     // Returns the name of the Rust type approximately corresponding to
1729     // a type name in another programming language.
1730     fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
1731         let name = path[path.len() - 1].ident.as_str();
1732         // Common Java types
1733         Some(match name {
1734             "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
1735             "short" => sym::i16,
1736             "Bool" => sym::bool,
1737             "Boolean" => sym::bool,
1738             "boolean" => sym::bool,
1739             "int" => sym::i32,
1740             "long" => sym::i64,
1741             "float" => sym::f32,
1742             "double" => sym::f64,
1743             _ => return None,
1744         })
1745     }
1746
1747     /// Only used in a specific case of type ascription suggestions
1748     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1749         let sm = self.r.session.source_map();
1750         start.to(sm.next_point(start))
1751     }
1752
1753     fn type_ascription_suggestion(&self, err: &mut Diagnostic, base_span: Span) -> bool {
1754         let sm = self.r.session.source_map();
1755         let base_snippet = sm.span_to_snippet(base_span);
1756         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1757             if let Ok(snippet) = sm.span_to_snippet(sp) {
1758                 let len = snippet.trim_end().len() as u32;
1759                 if snippet.trim() == ":" {
1760                     let colon_sp =
1761                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1762                     let mut show_label = true;
1763                     if sm.is_multiline(sp) {
1764                         err.span_suggestion_short(
1765                             colon_sp,
1766                             "maybe you meant to write `;` here",
1767                             ";",
1768                             Applicability::MaybeIncorrect,
1769                         );
1770                     } else {
1771                         let after_colon_sp =
1772                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1773                         if snippet.len() == 1 {
1774                             // `foo:bar`
1775                             err.span_suggestion(
1776                                 colon_sp,
1777                                 "maybe you meant to write a path separator here",
1778                                 "::",
1779                                 Applicability::MaybeIncorrect,
1780                             );
1781                             show_label = false;
1782                             if !self
1783                                 .r
1784                                 .session
1785                                 .parse_sess
1786                                 .type_ascription_path_suggestions
1787                                 .borrow_mut()
1788                                 .insert(colon_sp)
1789                             {
1790                                 err.downgrade_to_delayed_bug();
1791                             }
1792                         }
1793                         if let Ok(base_snippet) = base_snippet {
1794                             // Try to find an assignment
1795                             let eq_span = sm.span_look_ahead(after_colon_sp, Some("="), Some(50));
1796                             if let Ok(ref snippet) = sm.span_to_snippet(eq_span) && snippet == "=" {
1797                                 err.span_suggestion(
1798                                     base_span,
1799                                     "maybe you meant to write an assignment here",
1800                                     format!("let {}", base_snippet),
1801                                     Applicability::MaybeIncorrect,
1802                                 );
1803                                 show_label = false;
1804                             }
1805                         }
1806                     }
1807                     if show_label {
1808                         err.span_label(
1809                             base_span,
1810                             "expecting a type here because of type ascription",
1811                         );
1812                     }
1813                     return show_label;
1814                 }
1815             }
1816         }
1817         false
1818     }
1819
1820     // try to give a suggestion for this pattern: `name = blah`, which is common in other languages
1821     // suggest `let name = blah` to introduce a new binding
1822     fn let_binding_suggestion(&mut self, err: &mut Diagnostic, ident_span: Span) -> bool {
1823         if let Some(Expr { kind: ExprKind::Assign(lhs, .. ), .. }) = self.diagnostic_metadata.in_assignment &&
1824             let ast::ExprKind::Path(None, _) = lhs.kind {
1825                 if !ident_span.from_expansion() {
1826                     err.span_suggestion_verbose(
1827                         ident_span.shrink_to_lo(),
1828                         "you might have meant to introduce a new binding",
1829                         "let ".to_string(),
1830                         Applicability::MaybeIncorrect,
1831                     );
1832                     return true;
1833                 }
1834             }
1835         false
1836     }
1837
1838     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1839         let mut result = None;
1840         let mut seen_modules = FxHashSet::default();
1841         let mut worklist = vec![(self.r.graph_root, ThinVec::new())];
1842
1843         while let Some((in_module, path_segments)) = worklist.pop() {
1844             // abort if the module is already found
1845             if result.is_some() {
1846                 break;
1847             }
1848
1849             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1850                 // abort if the module is already found or if name_binding is private external
1851                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1852                     return;
1853                 }
1854                 if let Some(module) = name_binding.module() {
1855                     // form the path
1856                     let mut path_segments = path_segments.clone();
1857                     path_segments.push(ast::PathSegment::from_ident(ident));
1858                     let module_def_id = module.def_id();
1859                     if module_def_id == def_id {
1860                         let path =
1861                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1862                         result = Some((
1863                             module,
1864                             ImportSuggestion {
1865                                 did: Some(def_id),
1866                                 descr: "module",
1867                                 path,
1868                                 accessible: true,
1869                                 note: None,
1870                             },
1871                         ));
1872                     } else {
1873                         // add the module to the lookup
1874                         if seen_modules.insert(module_def_id) {
1875                             worklist.push((module, path_segments));
1876                         }
1877                     }
1878                 }
1879             });
1880         }
1881
1882         result
1883     }
1884
1885     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1886         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1887             let mut variants = Vec::new();
1888             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1889                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1890                     let mut segms = enum_import_suggestion.path.segments.clone();
1891                     segms.push(ast::PathSegment::from_ident(ident));
1892                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1893                     variants.push((path, def_id, kind));
1894                 }
1895             });
1896             variants
1897         })
1898     }
1899
1900     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1901     fn suggest_using_enum_variant(
1902         &mut self,
1903         err: &mut Diagnostic,
1904         source: PathSource<'_>,
1905         def_id: DefId,
1906         span: Span,
1907     ) {
1908         let Some(variants) = self.collect_enum_ctors(def_id) else {
1909             err.note("you might have meant to use one of the enum's variants");
1910             return;
1911         };
1912
1913         let suggest_only_tuple_variants =
1914             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1915         if suggest_only_tuple_variants {
1916             // Suggest only tuple variants regardless of whether they have fields and do not
1917             // suggest path with added parentheses.
1918             let suggestable_variants = variants
1919                 .iter()
1920                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1921                 .map(|(variant, ..)| path_names_to_string(variant))
1922                 .collect::<Vec<_>>();
1923
1924             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1925
1926             let source_msg = if source.is_call() {
1927                 "to construct"
1928             } else if matches!(source, PathSource::TupleStruct(..)) {
1929                 "to match against"
1930             } else {
1931                 unreachable!()
1932             };
1933
1934             if !suggestable_variants.is_empty() {
1935                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1936                     format!("try {} the enum's variant", source_msg)
1937                 } else {
1938                     format!("try {} one of the enum's variants", source_msg)
1939                 };
1940
1941                 err.span_suggestions(
1942                     span,
1943                     &msg,
1944                     suggestable_variants,
1945                     Applicability::MaybeIncorrect,
1946                 );
1947             }
1948
1949             // If the enum has no tuple variants..
1950             if non_suggestable_variant_count == variants.len() {
1951                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1952             }
1953
1954             // If there are also non-tuple variants..
1955             if non_suggestable_variant_count == 1 {
1956                 err.help(&format!(
1957                     "you might have meant {} the enum's non-tuple variant",
1958                     source_msg
1959                 ));
1960             } else if non_suggestable_variant_count >= 1 {
1961                 err.help(&format!(
1962                     "you might have meant {} one of the enum's non-tuple variants",
1963                     source_msg
1964                 ));
1965             }
1966         } else {
1967             let needs_placeholder = |ctor_def_id: DefId, kind: CtorKind| {
1968                 let def_id = self.r.parent(ctor_def_id);
1969                 let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
1970                 match kind {
1971                     CtorKind::Const => false,
1972                     CtorKind::Fn if has_no_fields => false,
1973                     _ => true,
1974                 }
1975             };
1976
1977             let suggestable_variants = variants
1978                 .iter()
1979                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1980                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1981                 .map(|(variant, kind)| match kind {
1982                     CtorKind::Const => variant,
1983                     CtorKind::Fn => format!("({}())", variant),
1984                 })
1985                 .collect::<Vec<_>>();
1986             let no_suggestable_variant = suggestable_variants.is_empty();
1987
1988             if !no_suggestable_variant {
1989                 let msg = if suggestable_variants.len() == 1 {
1990                     "you might have meant to use the following enum variant"
1991                 } else {
1992                     "you might have meant to use one of the following enum variants"
1993                 };
1994
1995                 err.span_suggestions(
1996                     span,
1997                     msg,
1998                     suggestable_variants,
1999                     Applicability::MaybeIncorrect,
2000                 );
2001             }
2002
2003             let suggestable_variants_with_placeholders = variants
2004                 .iter()
2005                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
2006                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
2007                 .filter_map(|(variant, kind)| match kind {
2008                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
2009                     _ => None,
2010                 })
2011                 .collect::<Vec<_>>();
2012
2013             if !suggestable_variants_with_placeholders.is_empty() {
2014                 let msg =
2015                     match (no_suggestable_variant, suggestable_variants_with_placeholders.len()) {
2016                         (true, 1) => "the following enum variant is available",
2017                         (true, _) => "the following enum variants are available",
2018                         (false, 1) => "alternatively, the following enum variant is available",
2019                         (false, _) => {
2020                             "alternatively, the following enum variants are also available"
2021                         }
2022                     };
2023
2024                 err.span_suggestions(
2025                     span,
2026                     msg,
2027                     suggestable_variants_with_placeholders,
2028                     Applicability::HasPlaceholders,
2029                 );
2030             }
2031         };
2032
2033         if def_id.is_local() {
2034             if let Some(span) = self.def_span(def_id) {
2035                 err.span_note(span, "the enum is defined here");
2036             }
2037         }
2038     }
2039
2040     pub(crate) fn report_missing_type_error(
2041         &self,
2042         path: &[Segment],
2043     ) -> Option<(Span, &'static str, String, Applicability)> {
2044         let (ident, span) = match path {
2045             [segment] if !segment.has_generic_args && segment.ident.name != kw::SelfUpper => {
2046                 (segment.ident.to_string(), segment.ident.span)
2047             }
2048             _ => return None,
2049         };
2050         let mut iter = ident.chars().map(|c| c.is_uppercase());
2051         let single_uppercase_char =
2052             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
2053         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
2054             return None;
2055         }
2056         match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
2057             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
2058                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
2059             }
2060             (
2061                 Some(Item {
2062                     kind:
2063                         kind @ ItemKind::Fn(..)
2064                         | kind @ ItemKind::Enum(..)
2065                         | kind @ ItemKind::Struct(..)
2066                         | kind @ ItemKind::Union(..),
2067                     ..
2068                 }),
2069                 true, _
2070             )
2071             // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
2072             | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
2073             | (Some(Item { kind, .. }), false, _) => {
2074                 // Likely missing type parameter.
2075                 if let Some(generics) = kind.generics() {
2076                     if span.overlaps(generics.span) {
2077                         // Avoid the following:
2078                         // error[E0405]: cannot find trait `A` in this scope
2079                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
2080                         //   |
2081                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
2082                         //   |           ^- help: you might be missing a type parameter: `, A`
2083                         //   |           |
2084                         //   |           not found in this scope
2085                         return None;
2086                     }
2087                     let msg = "you might be missing a type parameter";
2088                     let (span, sugg) = if let [.., param] = &generics.params[..] {
2089                         let span = if let [.., bound] = &param.bounds[..] {
2090                             bound.span()
2091                         } else if let GenericParam {
2092                             kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
2093                         } = param {
2094                             default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
2095                         } else {
2096                             param.ident.span
2097                         };
2098                         (span, format!(", {}", ident))
2099                     } else {
2100                         (generics.span, format!("<{}>", ident))
2101                     };
2102                     // Do not suggest if this is coming from macro expansion.
2103                     if span.can_be_used_for_suggestions() {
2104                         return Some((
2105                             span.shrink_to_hi(),
2106                             msg,
2107                             sugg,
2108                             Applicability::MaybeIncorrect,
2109                         ));
2110                     }
2111                 }
2112             }
2113             _ => {}
2114         }
2115         None
2116     }
2117
2118     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
2119     /// optionally returning the closest match and whether it is reachable.
2120     pub(crate) fn suggestion_for_label_in_rib(
2121         &self,
2122         rib_index: usize,
2123         label: Ident,
2124     ) -> Option<LabelSuggestion> {
2125         // Are ribs from this `rib_index` within scope?
2126         let within_scope = self.is_label_valid_from_rib(rib_index);
2127
2128         let rib = &self.label_ribs[rib_index];
2129         let names = rib
2130             .bindings
2131             .iter()
2132             .filter(|(id, _)| id.span.eq_ctxt(label.span))
2133             .map(|(id, _)| id.name)
2134             .collect::<Vec<Symbol>>();
2135
2136         find_best_match_for_name(&names, label.name, None).map(|symbol| {
2137             // Upon finding a similar name, get the ident that it was from - the span
2138             // contained within helps make a useful diagnostic. In addition, determine
2139             // whether this candidate is within scope.
2140             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
2141             (*ident, within_scope)
2142         })
2143     }
2144
2145     pub(crate) fn maybe_report_lifetime_uses(
2146         &mut self,
2147         generics_span: Span,
2148         params: &[ast::GenericParam],
2149     ) {
2150         for (param_index, param) in params.iter().enumerate() {
2151             let GenericParamKind::Lifetime = param.kind else { continue };
2152
2153             let def_id = self.r.local_def_id(param.id);
2154
2155             let use_set = self.lifetime_uses.remove(&def_id);
2156             debug!(
2157                 "Use set for {:?}({:?} at {:?}) is {:?}",
2158                 def_id, param.ident, param.ident.span, use_set
2159             );
2160
2161             let deletion_span = || {
2162                 if params.len() == 1 {
2163                     // if sole lifetime, remove the entire `<>` brackets
2164                     generics_span
2165                 } else if param_index == 0 {
2166                     // if removing within `<>` brackets, we also want to
2167                     // delete a leading or trailing comma as appropriate
2168                     param.span().to(params[param_index + 1].span().shrink_to_lo())
2169                 } else {
2170                     // if removing within `<>` brackets, we also want to
2171                     // delete a leading or trailing comma as appropriate
2172                     params[param_index - 1].span().shrink_to_hi().to(param.span())
2173                 }
2174             };
2175             match use_set {
2176                 Some(LifetimeUseSet::Many) => {}
2177                 Some(LifetimeUseSet::One { use_span, use_ctxt }) => {
2178                     debug!(?param.ident, ?param.ident.span, ?use_span);
2179
2180                     let elidable = matches!(use_ctxt, LifetimeCtxt::Rptr);
2181
2182                     let deletion_span = deletion_span();
2183                     self.r.lint_buffer.buffer_lint_with_diagnostic(
2184                         lint::builtin::SINGLE_USE_LIFETIMES,
2185                         param.id,
2186                         param.ident.span,
2187                         &format!("lifetime parameter `{}` only used once", param.ident),
2188                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
2189                             param_span: param.ident.span,
2190                             use_span: Some((use_span, elidable)),
2191                             deletion_span,
2192                         },
2193                     );
2194                 }
2195                 None => {
2196                     debug!(?param.ident, ?param.ident.span);
2197
2198                     let deletion_span = deletion_span();
2199                     self.r.lint_buffer.buffer_lint_with_diagnostic(
2200                         lint::builtin::UNUSED_LIFETIMES,
2201                         param.id,
2202                         param.ident.span,
2203                         &format!("lifetime parameter `{}` never used", param.ident),
2204                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
2205                             param_span: param.ident.span,
2206                             use_span: None,
2207                             deletion_span,
2208                         },
2209                     );
2210                 }
2211             }
2212         }
2213     }
2214
2215     pub(crate) fn emit_undeclared_lifetime_error(
2216         &self,
2217         lifetime_ref: &ast::Lifetime,
2218         outer_lifetime_ref: Option<Ident>,
2219     ) {
2220         debug_assert_ne!(lifetime_ref.ident.name, kw::UnderscoreLifetime);
2221         let mut err = if let Some(outer) = outer_lifetime_ref {
2222             let mut err = struct_span_err!(
2223                 self.r.session,
2224                 lifetime_ref.ident.span,
2225                 E0401,
2226                 "can't use generic parameters from outer item",
2227             );
2228             err.span_label(lifetime_ref.ident.span, "use of generic parameter from outer item");
2229             err.span_label(outer.span, "lifetime parameter from outer item");
2230             err
2231         } else {
2232             let mut err = struct_span_err!(
2233                 self.r.session,
2234                 lifetime_ref.ident.span,
2235                 E0261,
2236                 "use of undeclared lifetime name `{}`",
2237                 lifetime_ref.ident
2238             );
2239             err.span_label(lifetime_ref.ident.span, "undeclared lifetime");
2240             err
2241         };
2242         self.suggest_introducing_lifetime(
2243             &mut err,
2244             Some(lifetime_ref.ident.name.as_str()),
2245             |err, _, span, message, suggestion| {
2246                 err.span_suggestion(span, message, suggestion, Applicability::MaybeIncorrect);
2247                 true
2248             },
2249         );
2250         err.emit();
2251     }
2252
2253     fn suggest_introducing_lifetime(
2254         &self,
2255         err: &mut Diagnostic,
2256         name: Option<&str>,
2257         suggest: impl Fn(&mut Diagnostic, bool, Span, &str, String) -> bool,
2258     ) {
2259         let mut suggest_note = true;
2260         for rib in self.lifetime_ribs.iter().rev() {
2261             let mut should_continue = true;
2262             match rib.kind {
2263                 LifetimeRibKind::Generics { binder: _, span, kind } => {
2264                     if !span.can_be_used_for_suggestions() && suggest_note && let Some(name) = name {
2265                         suggest_note = false; // Avoid displaying the same help multiple times.
2266                         err.span_label(
2267                             span,
2268                             &format!(
2269                                 "lifetime `{}` is missing in item created through this procedural macro",
2270                                 name,
2271                             ),
2272                         );
2273                         continue;
2274                     }
2275
2276                     let higher_ranked = matches!(
2277                         kind,
2278                         LifetimeBinderKind::BareFnType
2279                             | LifetimeBinderKind::PolyTrait
2280                             | LifetimeBinderKind::WhereBound
2281                     );
2282                     let (span, sugg) = if span.is_empty() {
2283                         let sugg = format!(
2284                             "{}<{}>{}",
2285                             if higher_ranked { "for" } else { "" },
2286                             name.unwrap_or("'a"),
2287                             if higher_ranked { " " } else { "" },
2288                         );
2289                         (span, sugg)
2290                     } else {
2291                         let span =
2292                             self.r.session.source_map().span_through_char(span, '<').shrink_to_hi();
2293                         let sugg = format!("{}, ", name.unwrap_or("'a"));
2294                         (span, sugg)
2295                     };
2296                     if higher_ranked {
2297                         let message = format!(
2298                             "consider making the {} lifetime-generic with a new `{}` lifetime",
2299                             kind.descr(),
2300                             name.unwrap_or("'a"),
2301                         );
2302                         should_continue = suggest(err, true, span, &message, sugg);
2303                         err.note_once(
2304                             "for more information on higher-ranked polymorphism, visit \
2305                              https://doc.rust-lang.org/nomicon/hrtb.html",
2306                         );
2307                     } else if let Some(name) = name {
2308                         let message = format!("consider introducing lifetime `{}` here", name);
2309                         should_continue = suggest(err, false, span, &message, sugg);
2310                     } else {
2311                         let message = format!("consider introducing a named lifetime parameter");
2312                         should_continue = suggest(err, false, span, &message, sugg);
2313                     }
2314                 }
2315                 LifetimeRibKind::Item => break,
2316                 _ => {}
2317             }
2318             if !should_continue {
2319                 break;
2320             }
2321         }
2322     }
2323
2324     pub(crate) fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &ast::Lifetime) {
2325         struct_span_err!(
2326             self.r.session,
2327             lifetime_ref.ident.span,
2328             E0771,
2329             "use of non-static lifetime `{}` in const generic",
2330             lifetime_ref.ident
2331         )
2332         .note(
2333             "for more information, see issue #74052 \
2334             <https://github.com/rust-lang/rust/issues/74052>",
2335         )
2336         .emit();
2337     }
2338
2339     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
2340     /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
2341     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
2342     pub(crate) fn maybe_emit_forbidden_non_static_lifetime_error(
2343         &self,
2344         lifetime_ref: &ast::Lifetime,
2345     ) {
2346         let feature_active = self.r.session.features_untracked().generic_const_exprs;
2347         if !feature_active {
2348             feature_err(
2349                 &self.r.session.parse_sess,
2350                 sym::generic_const_exprs,
2351                 lifetime_ref.ident.span,
2352                 "a non-static lifetime is not allowed in a `const`",
2353             )
2354             .emit();
2355         }
2356     }
2357
2358     pub(crate) fn report_missing_lifetime_specifiers(
2359         &mut self,
2360         lifetime_refs: Vec<MissingLifetime>,
2361         function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
2362     ) -> ErrorGuaranteed {
2363         let num_lifetimes: usize = lifetime_refs.iter().map(|lt| lt.count).sum();
2364         let spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();
2365
2366         let mut err = struct_span_err!(
2367             self.r.session,
2368             spans,
2369             E0106,
2370             "missing lifetime specifier{}",
2371             pluralize!(num_lifetimes)
2372         );
2373         self.add_missing_lifetime_specifiers_label(
2374             &mut err,
2375             lifetime_refs,
2376             function_param_lifetimes,
2377         );
2378         err.emit()
2379     }
2380
2381     fn add_missing_lifetime_specifiers_label(
2382         &mut self,
2383         err: &mut Diagnostic,
2384         lifetime_refs: Vec<MissingLifetime>,
2385         function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
2386     ) {
2387         for &lt in &lifetime_refs {
2388             err.span_label(
2389                 lt.span,
2390                 format!(
2391                     "expected {} lifetime parameter{}",
2392                     if lt.count == 1 { "named".to_string() } else { lt.count.to_string() },
2393                     pluralize!(lt.count),
2394                 ),
2395             );
2396         }
2397
2398         let mut in_scope_lifetimes: Vec<_> = self
2399             .lifetime_ribs
2400             .iter()
2401             .rev()
2402             .take_while(|rib| !matches!(rib.kind, LifetimeRibKind::Item))
2403             .flat_map(|rib| rib.bindings.iter())
2404             .map(|(&ident, &res)| (ident, res))
2405             .filter(|(ident, _)| ident.name != kw::UnderscoreLifetime)
2406             .collect();
2407         debug!(?in_scope_lifetimes);
2408
2409         debug!(?function_param_lifetimes);
2410         if let Some((param_lifetimes, params)) = &function_param_lifetimes {
2411             let elided_len = param_lifetimes.len();
2412             let num_params = params.len();
2413
2414             let mut m = String::new();
2415
2416             for (i, info) in params.iter().enumerate() {
2417                 let ElisionFnParameter { ident, index, lifetime_count, span } = *info;
2418                 debug_assert_ne!(lifetime_count, 0);
2419
2420                 err.span_label(span, "");
2421
2422                 if i != 0 {
2423                     if i + 1 < num_params {
2424                         m.push_str(", ");
2425                     } else if num_params == 2 {
2426                         m.push_str(" or ");
2427                     } else {
2428                         m.push_str(", or ");
2429                     }
2430                 }
2431
2432                 let help_name = if let Some(ident) = ident {
2433                     format!("`{}`", ident)
2434                 } else {
2435                     format!("argument {}", index + 1)
2436                 };
2437
2438                 if lifetime_count == 1 {
2439                     m.push_str(&help_name[..])
2440                 } else {
2441                     m.push_str(&format!("one of {}'s {} lifetimes", help_name, lifetime_count)[..])
2442                 }
2443             }
2444
2445             if num_params == 0 {
2446                 err.help(
2447                     "this function's return type contains a borrowed value, \
2448                  but there is no value for it to be borrowed from",
2449                 );
2450                 if in_scope_lifetimes.is_empty() {
2451                     in_scope_lifetimes = vec![(
2452                         Ident::with_dummy_span(kw::StaticLifetime),
2453                         (DUMMY_NODE_ID, LifetimeRes::Static),
2454                     )];
2455                 }
2456             } else if elided_len == 0 {
2457                 err.help(
2458                     "this function's return type contains a borrowed value with \
2459                  an elided lifetime, but the lifetime cannot be derived from \
2460                  the arguments",
2461                 );
2462                 if in_scope_lifetimes.is_empty() {
2463                     in_scope_lifetimes = vec![(
2464                         Ident::with_dummy_span(kw::StaticLifetime),
2465                         (DUMMY_NODE_ID, LifetimeRes::Static),
2466                     )];
2467                 }
2468             } else if num_params == 1 {
2469                 err.help(&format!(
2470                     "this function's return type contains a borrowed value, \
2471                  but the signature does not say which {} it is borrowed from",
2472                     m
2473                 ));
2474             } else {
2475                 err.help(&format!(
2476                     "this function's return type contains a borrowed value, \
2477                  but the signature does not say whether it is borrowed from {}",
2478                     m
2479                 ));
2480             }
2481         }
2482
2483         let existing_name = match &in_scope_lifetimes[..] {
2484             [] => Symbol::intern("'a"),
2485             [(existing, _)] => existing.name,
2486             _ => Symbol::intern("'lifetime"),
2487         };
2488
2489         let mut spans_suggs: Vec<_> = Vec::new();
2490         let build_sugg = |lt: MissingLifetime| match lt.kind {
2491             MissingLifetimeKind::Underscore => {
2492                 debug_assert_eq!(lt.count, 1);
2493                 (lt.span, existing_name.to_string())
2494             }
2495             MissingLifetimeKind::Ampersand => {
2496                 debug_assert_eq!(lt.count, 1);
2497                 (lt.span.shrink_to_hi(), format!("{} ", existing_name))
2498             }
2499             MissingLifetimeKind::Comma => {
2500                 let sugg: String = std::iter::repeat([existing_name.as_str(), ", "])
2501                     .take(lt.count)
2502                     .flatten()
2503                     .collect();
2504                 (lt.span.shrink_to_hi(), sugg)
2505             }
2506             MissingLifetimeKind::Brackets => {
2507                 let sugg: String = std::iter::once("<")
2508                     .chain(
2509                         std::iter::repeat(existing_name.as_str()).take(lt.count).intersperse(", "),
2510                     )
2511                     .chain([">"])
2512                     .collect();
2513                 (lt.span.shrink_to_hi(), sugg)
2514             }
2515         };
2516         for &lt in &lifetime_refs {
2517             spans_suggs.push(build_sugg(lt));
2518         }
2519         debug!(?spans_suggs);
2520         match in_scope_lifetimes.len() {
2521             0 => {
2522                 if let Some((param_lifetimes, _)) = function_param_lifetimes {
2523                     for lt in param_lifetimes {
2524                         spans_suggs.push(build_sugg(lt))
2525                     }
2526                 }
2527                 self.suggest_introducing_lifetime(
2528                     err,
2529                     None,
2530                     |err, higher_ranked, span, message, intro_sugg| {
2531                         err.multipart_suggestion_verbose(
2532                             message,
2533                             std::iter::once((span, intro_sugg))
2534                                 .chain(spans_suggs.iter().cloned())
2535                                 .collect(),
2536                             Applicability::MaybeIncorrect,
2537                         );
2538                         higher_ranked
2539                     },
2540                 );
2541             }
2542             1 => {
2543                 err.multipart_suggestion_verbose(
2544                     &format!("consider using the `{}` lifetime", existing_name),
2545                     spans_suggs,
2546                     Applicability::MaybeIncorrect,
2547                 );
2548
2549                 // Record as using the suggested resolution.
2550                 let (_, (_, res)) = in_scope_lifetimes[0];
2551                 for &lt in &lifetime_refs {
2552                     self.r.lifetimes_res_map.insert(lt.id, res);
2553                 }
2554             }
2555             _ => {
2556                 let lifetime_spans: Vec<_> =
2557                     in_scope_lifetimes.iter().map(|(ident, _)| ident.span).collect();
2558                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
2559
2560                 if spans_suggs.len() > 0 {
2561                     // This happens when we have `Foo<T>` where we point at the space before `T`,
2562                     // but this can be confusing so we give a suggestion with placeholders.
2563                     err.multipart_suggestion_verbose(
2564                         "consider using one of the available lifetimes here",
2565                         spans_suggs,
2566                         Applicability::HasPlaceholders,
2567                     );
2568                 }
2569             }
2570         }
2571     }
2572 }
2573
2574 /// Report lifetime/lifetime shadowing as an error.
2575 pub fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: Ident) {
2576     let mut err = struct_span_err!(
2577         sess,
2578         shadower.span,
2579         E0496,
2580         "lifetime name `{}` shadows a lifetime name that is already in scope",
2581         orig.name,
2582     );
2583     err.span_label(orig.span, "first declared here");
2584     err.span_label(shadower.span, format!("lifetime `{}` already in scope", orig.name));
2585     err.emit();
2586 }
2587
2588 /// Shadowing involving a label is only a warning for historical reasons.
2589 //FIXME: make this a proper lint.
2590 pub fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {
2591     let name = shadower.name;
2592     let shadower = shadower.span;
2593     let mut err = sess.struct_span_warn(
2594         shadower,
2595         &format!("label name `{}` shadows a label name that is already in scope", name),
2596     );
2597     err.span_label(orig, "first declared here");
2598     err.span_label(shadower, format!("label `{}` already in scope", name));
2599     err.emit();
2600 }