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
 627         // Try to find in last block rib
 628         if let Some(rib) = &self.last_block_rib && let RibKind::NormalRibKind = rib.kind {
 629             for (ident, &res) in &rib.bindings {
 630                 if let Res::Local(_) = res && path.len() == 1 &&
 631                     ident.span.eq_ctxt(path[0].ident.span) &&
 632                     ident.name == path[0].ident.name {
 633                     err.span_help(
 634                         ident.span,
 635                         &format!("the binding `{}` is available in a different scope in the same function", path_str),
 636                     );
 637                     return (true, candidates);
 638                 }
 639             }
 640         }
 641
 642         return (false, candidates);
 643     }
 644
 645     fn suggest_trait_and_bounds(
 646         &mut self,
 647         err: &mut Diagnostic,
 648         source: PathSource<'_>,
 649         res: Option<Res>,
 650         span: Span,
 651         base_error: &BaseError,
 652     ) -> bool {
 653         let is_macro =
 654             base_error.span.from_expansion() && base_error.span.desugaring_kind().is_none();
 655         let mut fallback = false;
 656
 657         if let (
 658             PathSource::Trait(AliasPossibility::Maybe),
 659             Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
 660             false,
 661         ) = (source, res, is_macro)
 662         {
 663             if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
 664                 fallback = true;
 665                 let spans: Vec<Span> = bounds
 666                     .iter()
 667                     .map(|bound| bound.span())
 668                     .filter(|&sp| sp != base_error.span)
 669                     .collect();
 670
 671                 let start_span = bounds[0].span();
 672                 // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
 673                 let end_span = bounds.last().unwrap().span();
 674                 // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
 675                 let last_bound_span = spans.last().cloned().unwrap();
 676                 let mut multi_span: MultiSpan = spans.clone().into();
 677                 for sp in spans {
 678                     let msg = if sp == last_bound_span {
 679                         format!(
 680                             "...because of {these} bound{s}",
 681                             these = pluralize!("this", bounds.len() - 1),
 682                             s = pluralize!(bounds.len() - 1),
 683                         )
 684                     } else {
 685                         String::new()
 686                     };
 687                     multi_span.push_span_label(sp, msg);
 688                 }
 689                 multi_span.push_span_label(base_error.span, "expected this type to be a trait...");
 690                 err.span_help(
 691                     multi_span,
 692                     "`+` is used to constrain a \"trait object\" type with lifetimes or \
 693                         auto-traits; structs and enums can't be bound in that way",
 694                 );
 695                 if bounds.iter().all(|bound| match bound {
 696                     ast::GenericBound::Outlives(_) => true,
 697                     ast::GenericBound::Trait(tr, _) => tr.span == base_error.span,
 698                 }) {
 699                     let mut sugg = vec![];
 700                     if base_error.span != start_span {
 701                         sugg.push((start_span.until(base_error.span), String::new()));
 702                     }
 703                     if base_error.span != end_span {
 704                         sugg.push((base_error.span.shrink_to_hi().to(end_span), String::new()));
 705                     }
 706
 707                     err.multipart_suggestion(
 708                         "if you meant to use a type and not a trait here, remove the bounds",
 709                         sugg,
 710                         Applicability::MaybeIncorrect,
 711                     );
 712                 }
 713             }
 714         }
 715
 716         fallback |= self.restrict_assoc_type_in_where_clause(span, err);
 717         fallback
 718     }
 719
 720     fn suggest_typo(
 721         &mut self,
 722         err: &mut Diagnostic,
 723         source: PathSource<'_>,
 724         path: &[Segment],
 725         span: Span,
 726         base_error: &BaseError,
 727     ) -> bool {
 728         let is_expected = &|res| source.is_expected(res);
 729         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 730         let typo_sugg = self.lookup_typo_candidate(path, source.namespace(), is_expected);
 731         let is_in_same_file = &|sp1, sp2| {
 732             let source_map = self.r.session.source_map();
 733             let file1 = source_map.span_to_filename(sp1);
 734             let file2 = source_map.span_to_filename(sp2);
 735             file1 == file2
 736         };
 737         // print 'you might have meant' if the candidate is (1) is a shadowed name with
 738         // accessible definition and (2) either defined in the same crate as the typo
 739         // (could be in a different file) or introduced in the same file as the typo
 740         // (could belong to a different crate)
 741         if let TypoCandidate::Shadowed(res, Some(sugg_span)) = typo_sugg
 742             && res
 743                 .opt_def_id()
 744                 .map_or(false, |id| id.is_local() || is_in_same_file(span, sugg_span))
 745         {
 746             err.span_label(
 747                 sugg_span,
 748                 format!("you might have meant to refer to this {}", res.descr()),
 749             );
 750             return true;
 751         }
 752         let mut fallback = false;
 753         let typo_sugg = typo_sugg.to_opt_suggestion();
 754         if !self.r.add_typo_suggestion(err, typo_sugg, ident_span) {
 755             fallback = true;
 756             match self.diagnostic_metadata.current_let_binding {
 757                 Some((pat_sp, Some(ty_sp), None))
 758                     if ty_sp.contains(base_error.span) && base_error.could_be_expr =>
 759                 {
 760                     err.span_suggestion_short(
 761                         pat_sp.between(ty_sp),
 762                         "use `=` if you meant to assign",
 763                         " = ",
 764                         Applicability::MaybeIncorrect,
 765                     );
 766                 }
 767                 _ => {}
 768             }
 769
 770             // If the trait has a single item (which wasn't matched by Levenshtein), suggest it
 771             let suggestion = self.get_single_associated_item(&path, &source, is_expected);
 772             if !self.r.add_typo_suggestion(err, suggestion, ident_span) {
 773                 fallback = !self.let_binding_suggestion(err, ident_span);
 774             }
 775         }
 776         fallback
 777     }
 778
 779     fn err_code_special_cases(
 780         &mut self,
 781         err: &mut Diagnostic,
 782         source: PathSource<'_>,
 783         path: &[Segment],
 784         span: Span,
 785     ) {
 786         if let Some(err_code) = &err.code {
 787             if err_code == &rustc_errors::error_code!(E0425) {
 788                 for label_rib in &self.label_ribs {
 789                     for (label_ident, node_id) in &label_rib.bindings {
 790                         let ident = path.last().unwrap().ident;
 791                         if format!("'{}", ident) == label_ident.to_string() {
 792                             err.span_label(label_ident.span, "a label with a similar name exists");
 793                             if let PathSource::Expr(Some(Expr {
 794                                 kind: ExprKind::Break(None, Some(_)),
 795                                 ..
 796                             })) = source
 797                             {
 798                                 err.span_suggestion(
 799                                     span,
 800                                     "use the similarly named label",
 801                                     label_ident.name,
 802                                     Applicability::MaybeIncorrect,
 803                                 );
 804                                 // Do not lint against unused label when we suggest them.
 805                                 self.diagnostic_metadata.unused_labels.remove(node_id);
 806                             }
 807                         }
 808                     }
 809                 }
 810             } else if err_code == &rustc_errors::error_code!(E0412) {
 811                 if let Some(correct) = Self::likely_rust_type(path) {
 812                     err.span_suggestion(
 813                         span,
 814                         "perhaps you intended to use this type",
 815                         correct,
 816                         Applicability::MaybeIncorrect,
 817                     );
 818                 }
 819             }
 820         }
 821     }
 822
 823     /// Emit special messages for unresolved `Self` and `self`.
 824     fn suggest_self_ty(
 825         &mut self,
 826         err: &mut Diagnostic,
 827         source: PathSource<'_>,
 828         path: &[Segment],
 829         span: Span,
 830     ) -> bool {
 831         if !is_self_type(path, source.namespace()) {
 832             return false;
 833         }
 834         err.code(rustc_errors::error_code!(E0411));
 835         err.span_label(span, "`Self` is only available in impls, traits, and type definitions");
 836         if let Some(item_kind) = self.diagnostic_metadata.current_item {
 837             if !item_kind.ident.span.is_dummy() {
 838                 err.span_label(
 839                     item_kind.ident.span,
 840                     format!(
 841                         "`Self` not allowed in {} {}",
 842                         item_kind.kind.article(),
 843                         item_kind.kind.descr()
 844                     ),
 845                 );
 846             }
 847         }
 848         true
 849     }
 850
 851     fn suggest_self_value(
 852         &mut self,
 853         err: &mut Diagnostic,
 854         source: PathSource<'_>,
 855         path: &[Segment],
 856         span: Span,
 857     ) -> bool {
 858         if !is_self_value(path, source.namespace()) {
 859             return false;
 860         }
 861
 862         debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 863         err.code(rustc_errors::error_code!(E0424));
 864         err.span_label(
 865             span,
 866             match source {
 867                 PathSource::Pat => {
 868                     "`self` value is a keyword and may not be bound to variables or shadowed"
 869                 }
 870                 _ => "`self` value is a keyword only available in methods with a `self` parameter",
 871             },
 872         );
 873         let is_assoc_fn = self.self_type_is_available();
 874         if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 875             // The current function has a `self' parameter, but we were unable to resolve
 876             // a reference to `self`. This can only happen if the `self` identifier we
 877             // are resolving came from a different hygiene context.
 878             if fn_kind.decl().inputs.get(0).map_or(false, |p| p.is_self()) {
 879                 err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 880             } else {
 881                 let doesnt = if is_assoc_fn {
 882                     let (span, sugg) = fn_kind
 883                         .decl()
 884                         .inputs
 885                         .get(0)
 886                         .map(|p| (p.span.shrink_to_lo(), "&self, "))
 887                         .unwrap_or_else(|| {
 888                             // Try to look for the "(" after the function name, if possible.
 889                             // This avoids placing the suggestion into the visibility specifier.
 890                             let span = fn_kind
 891                                 .ident()
 892                                 .map_or(*span, |ident| span.with_lo(ident.span.hi()));
 893                             (
 894                                 self.r
 895                                     .session
 896                                     .source_map()
 897                                     .span_through_char(span, '(')
 898                                     .shrink_to_hi(),
 899                                 "&self",
 900                             )
 901                         });
 902                     err.span_suggestion_verbose(
 903                         span,
 904                         "add a `self` receiver parameter to make the associated `fn` a method",
 905                         sugg,
 906                         Applicability::MaybeIncorrect,
 907                     );
 908                     "doesn't"
 909                 } else {
 910                     "can't"
 911                 };
 912                 if let Some(ident) = fn_kind.ident() {
 913                     err.span_label(
 914                         ident.span,
 915                         &format!("this function {} have a `self` parameter", doesnt),
 916                     );
 917                 }
 918             }
 919         } else if let Some(item_kind) = self.diagnostic_metadata.current_item {
 920             err.span_label(
 921                 item_kind.ident.span,
 922                 format!(
 923                     "`self` not allowed in {} {}",
 924                     item_kind.kind.article(),
 925                     item_kind.kind.descr()
 926                 ),
 927             );
 928         }
 929         true
 930     }
 931
 932     fn suggest_swapping_misplaced_self_ty_and_trait(
 933         &mut self,
 934         err: &mut Diagnostic,
 935         source: PathSource<'_>,
 936         res: Option<Res>,
 937         span: Span,
 938     ) {
 939         if let Some((trait_ref, self_ty)) =
 940             self.diagnostic_metadata.currently_processing_impl_trait.clone()
 941             && let TyKind::Path(_, self_ty_path) = &self_ty.kind
 942             && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 943                 self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
 944             && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
 945             && trait_ref.path.span == span
 946             && let PathSource::Trait(_) = source
 947             && let Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)) = res
 948             && let Ok(self_ty_str) =
 949                 self.r.session.source_map().span_to_snippet(self_ty.span)
 950             && let Ok(trait_ref_str) =
 951                 self.r.session.source_map().span_to_snippet(trait_ref.path.span)
 952         {
 953                 err.multipart_suggestion(
 954                     "`impl` items mention the trait being implemented first and the type it is being implemented for second",
 955                     vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
 956                     Applicability::MaybeIncorrect,
 957                 );
 958         }
 959     }
 960
 961     fn suggest_bare_struct_literal(&mut self, err: &mut Diagnostic) {
 962         if let Some(span) = self.diagnostic_metadata.current_block_could_be_bare_struct_literal {
 963             err.multipart_suggestion(
 964                 "you might have meant to write a `struct` literal",
 965                 vec![
 966                     (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
 967                     (span.shrink_to_hi(), "}".to_string()),
 968                 ],
 969                 Applicability::HasPlaceholders,
 970             );
 971         }
 972     }
 973
 974     fn suggest_pattern_match_with_let(
 975         &mut self,
 976         err: &mut Diagnostic,
 977         source: PathSource<'_>,
 978         span: Span,
 979     ) -> bool {
 980         if let PathSource::Expr(_) = source &&
 981         let Some(Expr {
 982                     span: expr_span,
 983                     kind: ExprKind::Assign(lhs, _, _),
 984                     ..
 985                 })  = self.diagnostic_metadata.in_if_condition {
 986             // Icky heuristic so we don't suggest:
 987             // `if (i + 2) = 2` => `if let (i + 2) = 2` (approximately pattern)
 988             // `if 2 = i` => `if let 2 = i` (lhs needs to contain error span)
 989             if lhs.is_approximately_pattern() && lhs.span.contains(span) {
 990                 err.span_suggestion_verbose(
 991                     expr_span.shrink_to_lo(),
 992                     "you might have meant to use pattern matching",
 993                     "let ",
 994                     Applicability::MaybeIncorrect,
 995                 );
 996                 return true;
 997             }
 998         }
 999         false
1000     }
1001
1002     fn get_single_associated_item(
1003         &mut self,
1004         path: &[Segment],
1005         source: &PathSource<'_>,
1006         filter_fn: &impl Fn(Res) -> bool,
1007     ) -> Option<TypoSuggestion> {
1008         if let crate::PathSource::TraitItem(_) = source {
1009             let mod_path = &path[..path.len() - 1];
1010             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1011                 self.resolve_path(mod_path, None, None)
1012             {
1013                 let resolutions = self.r.resolutions(module).borrow();
1014                 let targets: Vec<_> =
1015                     resolutions
1016                         .iter()
1017                         .filter_map(|(key, resolution)| {
1018                             resolution.borrow().binding.map(|binding| binding.res()).and_then(
1019                                 |res| if filter_fn(res) { Some((key, res)) } else { None },
1020                             )
1021                         })
1022                         .collect();
1023                 if targets.len() == 1 {
1024                     let target = targets[0];
1025                     return Some(TypoSuggestion::single_item_from_ident(target.0.ident, target.1));
1026                 }
1027             }
1028         }
1029         None
1030     }
1031
1032     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
1033     fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diagnostic) -> bool {
1034         // Detect that we are actually in a `where` predicate.
1035         let (bounded_ty, bounds, where_span) =
1036             if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
1037                 bounded_ty,
1038                 bound_generic_params,
1039                 bounds,
1040                 span,
1041             })) = self.diagnostic_metadata.current_where_predicate
1042             {
1043                 if !bound_generic_params.is_empty() {
1044                     return false;
1045                 }
1046                 (bounded_ty, bounds, span)
1047             } else {
1048                 return false;
1049             };
1050
1051         // Confirm that the target is an associated type.
1052         let (ty, position, path) = if let ast::TyKind::Path(Some(qself), path) = &bounded_ty.kind {
1053             // use this to verify that ident is a type param.
1054             let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
1055                 return false;
1056             };
1057             if !matches!(
1058                 partial_res.full_res(),
1059                 Some(hir::def::Res::Def(hir::def::DefKind::AssocTy, _))
1060             ) {
1061                 return false;
1062             }
1063             (&qself.ty, qself.position, path)
1064         } else {
1065             return false;
1066         };
1067
1068         let peeled_ty = ty.peel_refs();
1069         if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
1070             // Confirm that the `SelfTy` is a type parameter.
1071             let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
1072                 return false;
1073             };
1074             if !matches!(
1075                 partial_res.full_res(),
1076                 Some(hir::def::Res::Def(hir::def::DefKind::TyParam, _))
1077             ) {
1078                 return false;
1079             }
1080             if let (
1081                 [ast::PathSegment { ident: constrain_ident, args: None, .. }],
1082                 [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
1083             ) = (&type_param_path.segments[..], &bounds[..])
1084             {
1085                 if let [ast::PathSegment { ident, args: None, .. }] =
1086                     &poly_trait_ref.trait_ref.path.segments[..]
1087                 {
1088                     if ident.span == span {
1089                         err.span_suggestion_verbose(
1090                             *where_span,
1091                             &format!("constrain the associated type to `{}`", ident),
1092                             format!(
1093                                 "{}: {}<{} = {}>",
1094                                 self.r
1095                                     .session
1096                                     .source_map()
1097                                     .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
1098                                     .unwrap_or_else(|_| constrain_ident.to_string()),
1099                                 path.segments[..position]
1100                                     .iter()
1101                                     .map(|segment| path_segment_to_string(segment))
1102                                     .collect::<Vec<_>>()
1103                                     .join("::"),
1104                                 path.segments[position..]
1105                                     .iter()
1106                                     .map(|segment| path_segment_to_string(segment))
1107                                     .collect::<Vec<_>>()
1108                                     .join("::"),
1109                                 ident,
1110                             ),
1111                             Applicability::MaybeIncorrect,
1112                         );
1113                     }
1114                     return true;
1115                 }
1116             }
1117         }
1118         false
1119     }
1120
1121     /// Check if the source is call expression and the first argument is `self`. If true,
1122     /// return the span of whole call and the span for all arguments expect the first one (`self`).
1123     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
1124         let mut has_self_arg = None;
1125         if let PathSource::Expr(Some(parent)) = source {
1126             match &parent.kind {
1127                 ExprKind::Call(_, args) if !args.is_empty() => {
1128                     let mut expr_kind = &args[0].kind;
1129                     loop {
1130                         match expr_kind {
1131                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
1132                                 if arg_name.segments[0].ident.name == kw::SelfLower {
1133                                     let call_span = parent.span;
1134                                     let tail_args_span = if args.len() > 1 {
1135                                         Some(Span::new(
1136                                             args[1].span.lo(),
1137                                             args.last().unwrap().span.hi(),
1138                                             call_span.ctxt(),
1139                                             None,
1140                                         ))
1141                                     } else {
1142                                         None
1143                                     };
1144                                     has_self_arg = Some((call_span, tail_args_span));
1145                                 }
1146                                 break;
1147                             }
1148                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
1149                             _ => break,
1150                         }
1151                     }
1152                 }
1153                 _ => (),
1154             }
1155         };
1156         has_self_arg
1157     }
1158
1159     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
1160         // HACK(estebank): find a better way to figure out that this was a
1161         // parser issue where a struct literal is being used on an expression
1162         // where a brace being opened means a block is being started. Look
1163         // ahead for the next text to see if `span` is followed by a `{`.
1164         let sm = self.r.session.source_map();
1165         let sp = sm.span_look_ahead(span, None, Some(50));
1166         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
1167         // In case this could be a struct literal that needs to be surrounded
1168         // by parentheses, find the appropriate span.
1169         let closing_span = sm.span_look_ahead(span, Some("}"), Some(50));
1170         let closing_brace: Option<Span> = sm
1171             .span_to_snippet(closing_span)
1172             .map_or(None, |s| if s == "}" { Some(span.to(closing_span)) } else { None });
1173         (followed_by_brace, closing_brace)
1174     }
1175
1176     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
1177     /// function.
1178     /// Returns `true` if able to provide context-dependent help.
1179     fn smart_resolve_context_dependent_help(
1180         &mut self,
1181         err: &mut Diagnostic,
1182         span: Span,
1183         source: PathSource<'_>,
1184         res: Res,
1185         path_str: &str,
1186         fallback_label: &str,
1187     ) -> bool {
1188         let ns = source.namespace();
1189         let is_expected = &|res| source.is_expected(res);
1190
1191         let path_sep = |err: &mut Diagnostic, expr: &Expr, kind: DefKind| {
1192             const MESSAGE: &str = "use the path separator to refer to an item";
1193
1194             let (lhs_span, rhs_span) = match &expr.kind {
1195                 ExprKind::Field(base, ident) => (base.span, ident.span),
1196                 ExprKind::MethodCall(box MethodCall { receiver, span, .. }) => {
1197                     (receiver.span, *span)
1198                 }
1199                 _ => return false,
1200             };
1201
1202             if lhs_span.eq_ctxt(rhs_span) {
1203                 err.span_suggestion(
1204                     lhs_span.between(rhs_span),
1205                     MESSAGE,
1206                     "::",
1207                     Applicability::MaybeIncorrect,
1208                 );
1209                 true
1210             } else if kind == DefKind::Struct
1211             && let Some(lhs_source_span) = lhs_span.find_ancestor_inside(expr.span)
1212             && let Ok(snippet) = self.r.session.source_map().span_to_snippet(lhs_source_span)
1213             {
1214                 // The LHS is a type that originates from a macro call.
1215                 // We have to add angle brackets around it.
1216
1217                 err.span_suggestion_verbose(
1218                     lhs_source_span.until(rhs_span),
1219                     MESSAGE,
1220                     format!("<{snippet}>::"),
1221                     Applicability::MaybeIncorrect,
1222                 );
1223                 true
1224             } else {
1225                 // Either we were unable to obtain the source span / the snippet or
1226                 // the LHS originates from a macro call and it is not a type and thus
1227                 // there is no way to replace `.` with `::` and still somehow suggest
1228                 // valid Rust code.
1229
1230                 false
1231             }
1232         };
1233
1234         let find_span = |source: &PathSource<'_>, err: &mut Diagnostic| {
1235             match source {
1236                 PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
1237                 | PathSource::TupleStruct(span, _) => {
1238                     // We want the main underline to cover the suggested code as well for
1239                     // cleaner output.
1240                     err.set_span(*span);
1241                     *span
1242                 }
1243                 _ => span,
1244             }
1245         };
1246
1247         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
1248             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
1249
1250             match source {
1251                 PathSource::Expr(Some(
1252                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
1253                 )) if path_sep(err, &parent, DefKind::Struct) => {}
1254                 PathSource::Expr(
1255                     None
1256                     | Some(Expr {
1257                         kind:
1258                             ExprKind::Path(..)
1259                             | ExprKind::Binary(..)
1260                             | ExprKind::Unary(..)
1261                             | ExprKind::If(..)
1262                             | ExprKind::While(..)
1263                             | ExprKind::ForLoop(..)
1264                             | ExprKind::Match(..),
1265                         ..
1266                     }),
1267                 ) if followed_by_brace => {
1268                     if let Some(sp) = closing_brace {
1269                         err.span_label(span, fallback_label);
1270                         err.multipart_suggestion(
1271                             "surround the struct literal with parentheses",
1272                             vec![
1273                                 (sp.shrink_to_lo(), "(".to_string()),
1274                                 (sp.shrink_to_hi(), ")".to_string()),
1275                             ],
1276                             Applicability::MaybeIncorrect,
1277                         );
1278                     } else {
1279                         err.span_label(
1280                             span, // Note the parentheses surrounding the suggestion below
1281                             format!(
1282                                 "you might want to surround a struct literal with parentheses: \
1283                                  `({} {{ /* fields */ }})`?",
1284                                 path_str
1285                             ),
1286                         );
1287                     }
1288                 }
1289                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1290                     let span = find_span(&source, err);
1291                     if let Some(span) = self.def_span(def_id) {
1292                         err.span_label(span, &format!("`{}` defined here", path_str));
1293                     }
1294                     let (tail, descr, applicability) = match source {
1295                         PathSource::Pat | PathSource::TupleStruct(..) => {
1296                             ("", "pattern", Applicability::MachineApplicable)
1297                         }
1298                         _ => (": val", "literal", Applicability::HasPlaceholders),
1299                     };
1300                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
1301                         Some(fields) => (
1302                             fields
1303                                 .iter()
1304                                 .map(|f| format!("{}{}", f.node, tail))
1305                                 .collect::<Vec<String>>()
1306                                 .join(", "),
1307                             applicability,
1308                         ),
1309                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
1310                     };
1311                     let pad = match self.r.field_names.get(&def_id) {
1312                         Some(fields) if fields.is_empty() => "",
1313                         _ => " ",
1314                     };
1315                     err.span_suggestion(
1316                         span,
1317                         &format!("use struct {} syntax instead", descr),
1318                         format!("{path_str} {{{pad}{fields}{pad}}}"),
1319                         applicability,
1320                     );
1321                 }
1322                 _ => {
1323                     err.span_label(span, fallback_label);
1324                 }
1325             }
1326         };
1327
1328         match (res, source) {
1329             (
1330                 Res::Def(DefKind::Macro(MacroKind::Bang), _),
1331                 PathSource::Expr(Some(Expr {
1332                     kind: ExprKind::Index(..) | ExprKind::Call(..), ..
1333                 }))
1334                 | PathSource::Struct,
1335             ) => {
1336                 err.span_label(span, fallback_label);
1337                 err.span_suggestion_verbose(
1338                     span.shrink_to_hi(),
1339                     "use `!` to invoke the macro",
1340                     "!",
1341                     Applicability::MaybeIncorrect,
1342                 );
1343                 if path_str == "try" && span.rust_2015() {
1344                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
1345                 }
1346             }
1347             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
1348                 err.span_label(span, fallback_label);
1349             }
1350             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
1351                 err.span_label(span, "type aliases cannot be used as traits");
1352                 if self.r.session.is_nightly_build() {
1353                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
1354                                `type` alias";
1355                     if let Some(span) = self.def_span(def_id) {
1356                         if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
1357                             // The span contains a type alias so we should be able to
1358                             // replace `type` with `trait`.
1359                             let snip = snip.replacen("type", "trait", 1);
1360                             err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
1361                         } else {
1362                             err.span_help(span, msg);
1363                         }
1364                     } else {
1365                         err.help(msg);
1366                     }
1367                 }
1368             }
1369             (
1370                 Res::Def(kind @ (DefKind::Mod | DefKind::Trait), _),
1371                 PathSource::Expr(Some(parent)),
1372             ) => {
1373                 if !path_sep(err, &parent, kind) {
1374                     return false;
1375                 }
1376             }
1377             (
1378                 Res::Def(DefKind::Enum, def_id),
1379                 PathSource::TupleStruct(..) | PathSource::Expr(..),
1380             ) => {
1381                 if self
1382                     .diagnostic_metadata
1383                     .current_type_ascription
1384                     .last()
1385                     .map(|sp| {
1386                         self.r
1387                             .session
1388                             .parse_sess
1389                             .type_ascription_path_suggestions
1390                             .borrow()
1391                             .contains(&sp)
1392                     })
1393                     .unwrap_or(false)
1394                 {
1395                     err.downgrade_to_delayed_bug();
1396                     // We already suggested changing `:` into `::` during parsing.
1397                     return false;
1398                 }
1399
1400                 self.suggest_using_enum_variant(err, source, def_id, span);
1401             }
1402             (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
1403                 let (ctor_def, ctor_vis, fields) =
1404                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
1405                         if let PathSource::Expr(Some(parent)) = source {
1406                             if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
1407                                 bad_struct_syntax_suggestion(def_id);
1408                                 return true;
1409                             }
1410                         }
1411                         struct_ctor
1412                     } else {
1413                         bad_struct_syntax_suggestion(def_id);
1414                         return true;
1415                     };
1416
1417                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
1418                 if !is_expected(ctor_def) || is_accessible {
1419                     return true;
1420                 }
1421
1422                 let field_spans = match source {
1423                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
1424                     PathSource::TupleStruct(_, pattern_spans) => {
1425                         err.set_primary_message(
1426                             "cannot match against a tuple struct which contains private fields",
1427                         );
1428
1429                         // Use spans of the tuple struct pattern.
1430                         Some(Vec::from(pattern_spans))
1431                     }
1432                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
1433                     _ if source.is_call() => {
1434                         err.set_primary_message(
1435                             "cannot initialize a tuple struct which contains private fields",
1436                         );
1437
1438                         // Use spans of the tuple struct definition.
1439                         self.r
1440                             .field_names
1441                             .get(&def_id)
1442                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
1443                     }
1444                     _ => None,
1445                 };
1446
1447                 if let Some(spans) =
1448                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
1449                 {
1450                     let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
1451                         .filter(|(vis, _)| {
1452                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
1453                         })
1454                         .map(|(_, span)| *span)
1455                         .collect();
1456
1457                     if non_visible_spans.len() > 0 {
1458                         let mut m: MultiSpan = non_visible_spans.clone().into();
1459                         non_visible_spans
1460                             .into_iter()
1461                             .for_each(|s| m.push_span_label(s, "private field"));
1462                         err.span_note(m, "constructor is not visible here due to private fields");
1463                     }
1464
1465                     return true;
1466                 }
1467
1468                 err.span_label(span, "constructor is not visible here due to private fields");
1469             }
1470             (Res::Def(DefKind::Union | DefKind::Variant, def_id), _) if ns == ValueNS => {
1471                 bad_struct_syntax_suggestion(def_id);
1472             }
1473             (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
1474                 match source {
1475                     PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1476                         let span = find_span(&source, err);
1477                         if let Some(span) = self.def_span(def_id) {
1478                             err.span_label(span, &format!("`{}` defined here", path_str));
1479                         }
1480                         err.span_suggestion(
1481                             span,
1482                             "use this syntax instead",
1483                             path_str,
1484                             Applicability::MaybeIncorrect,
1485                         );
1486                     }
1487                     _ => return false,
1488                 }
1489             }
1490             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), ctor_def_id), _) if ns == ValueNS => {
1491                 let def_id = self.r.parent(ctor_def_id);
1492                 if let Some(span) = self.def_span(def_id) {
1493                     err.span_label(span, &format!("`{}` defined here", path_str));
1494                 }
1495                 let fields = self.r.field_names.get(&def_id).map_or_else(
1496                     || "/* fields */".to_string(),
1497                     |fields| vec!["_"; fields.len()].join(", "),
1498                 );
1499                 err.span_suggestion(
1500                     span,
1501                     "use the tuple variant pattern syntax instead",
1502                     format!("{}({})", path_str, fields),
1503                     Applicability::HasPlaceholders,
1504                 );
1505             }
1506             (Res::SelfTyParam { .. } | Res::SelfTyAlias { .. }, _) if ns == ValueNS => {
1507                 err.span_label(span, fallback_label);
1508                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1509             }
1510             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1511                 err.note("can't use a type alias as a constructor");
1512             }
1513             _ => return false,
1514         }
1515         true
1516     }
1517
1518     /// Given the target `ident` and `kind`, search for the similarly named associated item
1519     /// in `self.current_trait_ref`.
1520     pub(crate) fn find_similarly_named_assoc_item(
1521         &mut self,
1522         ident: Symbol,
1523         kind: &AssocItemKind,
1524     ) -> Option<Symbol> {
1525         let (module, _) = self.current_trait_ref.as_ref()?;
1526         if ident == kw::Underscore {
1527             // We do nothing for `_`.
1528             return None;
1529         }
1530
1531         let resolutions = self.r.resolutions(module);
1532         let targets = resolutions
1533             .borrow()
1534             .iter()
1535             .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
1536             .filter(|(_, res)| match (kind, res) {
1537                 (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
1538                 (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
1539                 (AssocItemKind::Type(..), Res::Def(DefKind::AssocTy, _)) => true,
1540                 _ => false,
1541             })
1542             .map(|(key, _)| key.ident.name)
1543             .collect::<Vec<_>>();
1544
1545         find_best_match_for_name(&targets, ident, None)
1546     }
1547
1548     fn lookup_assoc_candidate<FilterFn>(
1549         &mut self,
1550         ident: Ident,
1551         ns: Namespace,
1552         filter_fn: FilterFn,
1553         called: bool,
1554     ) -> Option<AssocSuggestion>
1555     where
1556         FilterFn: Fn(Res) -> bool,
1557     {
1558         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1559             match t.kind {
1560                 TyKind::Path(None, _) => Some(t.id),
1561                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1562                 // This doesn't handle the remaining `Ty` variants as they are not
1563                 // that commonly the self_type, it might be interesting to provide
1564                 // support for those in future.
1565                 _ => None,
1566             }
1567         }
1568         // Fields are generally expected in the same contexts as locals.
1569         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1570             if let Some(node_id) =
1571                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1572             {
1573                 // Look for a field with the same name in the current self_type.
1574                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1575                     if let Some(Res::Def(DefKind::Struct | DefKind::Union, did)) =
1576                         resolution.full_res()
1577                     {
1578                         if let Some(field_names) = self.r.field_names.get(&did) {
1579                             if field_names.iter().any(|&field_name| ident.name == field_name.node) {
1580                                 return Some(AssocSuggestion::Field);
1581                             }
1582                         }
1583                     }
1584                 }
1585             }
1586         }
1587
1588         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1589             for assoc_item in items {
1590                 if assoc_item.ident == ident {
1591                     return Some(match &assoc_item.kind {
1592                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1593                         ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
1594                             AssocSuggestion::MethodWithSelf { called }
1595                         }
1596                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn { called },
1597                         ast::AssocItemKind::Type(..) => AssocSuggestion::AssocType,
1598                         ast::AssocItemKind::MacCall(_) => continue,
1599                     });
1600                 }
1601             }
1602         }
1603
1604         // Look for associated items in the current trait.
1605         if let Some((module, _)) = self.current_trait_ref {
1606             if let Ok(binding) = self.r.maybe_resolve_ident_in_module(
1607                 ModuleOrUniformRoot::Module(module),
1608                 ident,
1609                 ns,
1610                 &self.parent_scope,
1611             ) {
1612                 let res = binding.res();
1613                 if filter_fn(res) {
1614                     if self.r.has_self.contains(&res.def_id()) {
1615                         return Some(AssocSuggestion::MethodWithSelf { called });
1616                     } else {
1617                         match res {
1618                             Res::Def(DefKind::AssocFn, _) => {
1619                                 return Some(AssocSuggestion::AssocFn { called });
1620                             }
1621                             Res::Def(DefKind::AssocConst, _) => {
1622                                 return Some(AssocSuggestion::AssocConst);
1623                             }
1624                             Res::Def(DefKind::AssocTy, _) => {
1625                                 return Some(AssocSuggestion::AssocType);
1626                             }
1627                             _ => {}
1628                         }
1629                     }
1630                 }
1631             }
1632         }
1633
1634         None
1635     }
1636
1637     fn lookup_typo_candidate(
1638         &mut self,
1639         path: &[Segment],
1640         ns: Namespace,
1641         filter_fn: &impl Fn(Res) -> bool,
1642     ) -> TypoCandidate {
1643         let mut names = Vec::new();
1644         if path.len() == 1 {
1645             let mut ctxt = path.last().unwrap().ident.span.ctxt();
1646
1647             // Search in lexical scope.
1648             // Walk backwards up the ribs in scope and collect candidates.
1649             for rib in self.ribs[ns].iter().rev() {
1650                 let rib_ctxt = if rib.kind.contains_params() {
1651                     ctxt.normalize_to_macros_2_0()
1652                 } else {
1653                     ctxt.normalize_to_macro_rules()
1654                 };
1655
1656                 // Locals and type parameters
1657                 for (ident, &res) in &rib.bindings {
1658                     if filter_fn(res) && ident.span.ctxt() == rib_ctxt {
1659                         names.push(TypoSuggestion::typo_from_ident(*ident, res));
1660                     }
1661                 }
1662
1663                 if let RibKind::MacroDefinition(def) = rib.kind && def == self.r.macro_def(ctxt) {
1664                     // If an invocation of this macro created `ident`, give up on `ident`
1665                     // and switch to `ident`'s source from the macro definition.
1666                     ctxt.remove_mark();
1667                     continue;
1668                 }
1669
1670                 // Items in scope
1671                 if let RibKind::ModuleRibKind(module) = rib.kind {
1672                     // Items from this module
1673                     self.r.add_module_candidates(module, &mut names, &filter_fn, Some(ctxt));
1674
1675                     if let ModuleKind::Block = module.kind {
1676                         // We can see through blocks
1677                     } else {
1678                         // Items from the prelude
1679                         if !module.no_implicit_prelude {
1680                             let extern_prelude = self.r.extern_prelude.clone();
1681                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1682                                 self.r
1683                                     .crate_loader()
1684                                     .maybe_process_path_extern(ident.name)
1685                                     .and_then(|crate_id| {
1686                                         let crate_mod =
1687                                             Res::Def(DefKind::Mod, crate_id.as_def_id());
1688
1689                                         if filter_fn(crate_mod) {
1690                                             Some(TypoSuggestion::typo_from_ident(*ident, crate_mod))
1691                                         } else {
1692                                             None
1693                                         }
1694                                     })
1695                             }));
1696
1697                             if let Some(prelude) = self.r.prelude {
1698                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn, None);
1699                             }
1700                         }
1701                         break;
1702                     }
1703                 }
1704             }
1705             // Add primitive types to the mix
1706             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1707                 names.extend(PrimTy::ALL.iter().map(|prim_ty| {
1708                     TypoSuggestion::typo_from_name(prim_ty.name(), Res::PrimTy(*prim_ty))
1709                 }))
1710             }
1711         } else {
1712             // Search in module.
1713             let mod_path = &path[..path.len() - 1];
1714             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1715                 self.resolve_path(mod_path, Some(TypeNS), None)
1716             {
1717                 self.r.add_module_candidates(module, &mut names, &filter_fn, None);
1718             }
1719         }
1720
1721         let name = path[path.len() - 1].ident.name;
1722         // Make sure error reporting is deterministic.
1723         names.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
1724
1725         match find_best_match_for_name(
1726             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1727             name,
1728             None,
1729         ) {
1730             Some(found) => {
1731                 let Some(sugg) = names.into_iter().find(|suggestion| suggestion.candidate == found) else {
1732                     return TypoCandidate::None;
1733                 };
1734                 if found == name {
1735                     TypoCandidate::Shadowed(sugg.res, sugg.span)
1736                 } else {
1737                     TypoCandidate::Typo(sugg)
1738                 }
1739             }
1740             _ => TypoCandidate::None,
1741         }
1742     }
1743
1744     // Returns the name of the Rust type approximately corresponding to
1745     // a type name in another programming language.
1746     fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
1747         let name = path[path.len() - 1].ident.as_str();
1748         // Common Java types
1749         Some(match name {
1750             "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
1751             "short" => sym::i16,
1752             "Bool" => sym::bool,
1753             "Boolean" => sym::bool,
1754             "boolean" => sym::bool,
1755             "int" => sym::i32,
1756             "long" => sym::i64,
1757             "float" => sym::f32,
1758             "double" => sym::f64,
1759             _ => return None,
1760         })
1761     }
1762
1763     /// Only used in a specific case of type ascription suggestions
1764     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1765         let sm = self.r.session.source_map();
1766         start.to(sm.next_point(start))
1767     }
1768
1769     fn type_ascription_suggestion(&self, err: &mut Diagnostic, base_span: Span) -> bool {
1770         let sm = self.r.session.source_map();
1771         let base_snippet = sm.span_to_snippet(base_span);
1772         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1773             if let Ok(snippet) = sm.span_to_snippet(sp) {
1774                 let len = snippet.trim_end().len() as u32;
1775                 if snippet.trim() == ":" {
1776                     let colon_sp =
1777                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1778                     let mut show_label = true;
1779                     if sm.is_multiline(sp) {
1780                         err.span_suggestion_short(
1781                             colon_sp,
1782                             "maybe you meant to write `;` here",
1783                             ";",
1784                             Applicability::MaybeIncorrect,
1785                         );
1786                     } else {
1787                         let after_colon_sp =
1788                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1789                         if snippet.len() == 1 {
1790                             // `foo:bar`
1791                             err.span_suggestion(
1792                                 colon_sp,
1793                                 "maybe you meant to write a path separator here",
1794                                 "::",
1795                                 Applicability::MaybeIncorrect,
1796                             );
1797                             show_label = false;
1798                             if !self
1799                                 .r
1800                                 .session
1801                                 .parse_sess
1802                                 .type_ascription_path_suggestions
1803                                 .borrow_mut()
1804                                 .insert(colon_sp)
1805                             {
1806                                 err.downgrade_to_delayed_bug();
1807                             }
1808                         }
1809                         if let Ok(base_snippet) = base_snippet {
1810                             // Try to find an assignment
1811                             let eq_span = sm.span_look_ahead(after_colon_sp, Some("="), Some(50));
1812                             if let Ok(ref snippet) = sm.span_to_snippet(eq_span) && snippet == "=" {
1813                                 err.span_suggestion(
1814                                     base_span,
1815                                     "maybe you meant to write an assignment here",
1816                                     format!("let {}", base_snippet),
1817                                     Applicability::MaybeIncorrect,
1818                                 );
1819                                 show_label = false;
1820                             }
1821                         }
1822                     }
1823                     if show_label {
1824                         err.span_label(
1825                             base_span,
1826                             "expecting a type here because of type ascription",
1827                         );
1828                     }
1829                     return show_label;
1830                 }
1831             }
1832         }
1833         false
1834     }
1835
1836     // try to give a suggestion for this pattern: `name = blah`, which is common in other languages
1837     // suggest `let name = blah` to introduce a new binding
1838     fn let_binding_suggestion(&mut self, err: &mut Diagnostic, ident_span: Span) -> bool {
1839         if let Some(Expr { kind: ExprKind::Assign(lhs, .. ), .. }) = self.diagnostic_metadata.in_assignment &&
1840             let ast::ExprKind::Path(None, _) = lhs.kind {
1841                 if !ident_span.from_expansion() {
1842                     err.span_suggestion_verbose(
1843                         ident_span.shrink_to_lo(),
1844                         "you might have meant to introduce a new binding",
1845                         "let ".to_string(),
1846                         Applicability::MaybeIncorrect,
1847                     );
1848                     return true;
1849                 }
1850             }
1851         false
1852     }
1853
1854     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1855         let mut result = None;
1856         let mut seen_modules = FxHashSet::default();
1857         let mut worklist = vec![(self.r.graph_root, ThinVec::new())];
1858
1859         while let Some((in_module, path_segments)) = worklist.pop() {
1860             // abort if the module is already found
1861             if result.is_some() {
1862                 break;
1863             }
1864
1865             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1866                 // abort if the module is already found or if name_binding is private external
1867                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1868                     return;
1869                 }
1870                 if let Some(module) = name_binding.module() {
1871                     // form the path
1872                     let mut path_segments = path_segments.clone();
1873                     path_segments.push(ast::PathSegment::from_ident(ident));
1874                     let module_def_id = module.def_id();
1875                     if module_def_id == def_id {
1876                         let path =
1877                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1878                         result = Some((
1879                             module,
1880                             ImportSuggestion {
1881                                 did: Some(def_id),
1882                                 descr: "module",
1883                                 path,
1884                                 accessible: true,
1885                                 note: None,
1886                             },
1887                         ));
1888                     } else {
1889                         // add the module to the lookup
1890                         if seen_modules.insert(module_def_id) {
1891                             worklist.push((module, path_segments));
1892                         }
1893                     }
1894                 }
1895             });
1896         }
1897
1898         result
1899     }
1900
1901     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1902         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1903             let mut variants = Vec::new();
1904             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1905                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1906                     let mut segms = enum_import_suggestion.path.segments.clone();
1907                     segms.push(ast::PathSegment::from_ident(ident));
1908                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1909                     variants.push((path, def_id, kind));
1910                 }
1911             });
1912             variants
1913         })
1914     }
1915
1916     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1917     fn suggest_using_enum_variant(
1918         &mut self,
1919         err: &mut Diagnostic,
1920         source: PathSource<'_>,
1921         def_id: DefId,
1922         span: Span,
1923     ) {
1924         let Some(variants) = self.collect_enum_ctors(def_id) else {
1925             err.note("you might have meant to use one of the enum's variants");
1926             return;
1927         };
1928
1929         let suggest_only_tuple_variants =
1930             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1931         if suggest_only_tuple_variants {
1932             // Suggest only tuple variants regardless of whether they have fields and do not
1933             // suggest path with added parentheses.
1934             let suggestable_variants = variants
1935                 .iter()
1936                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1937                 .map(|(variant, ..)| path_names_to_string(variant))
1938                 .collect::<Vec<_>>();
1939
1940             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1941
1942             let source_msg = if source.is_call() {
1943                 "to construct"
1944             } else if matches!(source, PathSource::TupleStruct(..)) {
1945                 "to match against"
1946             } else {
1947                 unreachable!()
1948             };
1949
1950             if !suggestable_variants.is_empty() {
1951                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1952                     format!("try {} the enum's variant", source_msg)
1953                 } else {
1954                     format!("try {} one of the enum's variants", source_msg)
1955                 };
1956
1957                 err.span_suggestions(
1958                     span,
1959                     &msg,
1960                     suggestable_variants,
1961                     Applicability::MaybeIncorrect,
1962                 );
1963             }
1964
1965             // If the enum has no tuple variants..
1966             if non_suggestable_variant_count == variants.len() {
1967                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1968             }
1969
1970             // If there are also non-tuple variants..
1971             if non_suggestable_variant_count == 1 {
1972                 err.help(&format!(
1973                     "you might have meant {} the enum's non-tuple variant",
1974                     source_msg
1975                 ));
1976             } else if non_suggestable_variant_count >= 1 {
1977                 err.help(&format!(
1978                     "you might have meant {} one of the enum's non-tuple variants",
1979                     source_msg
1980                 ));
1981             }
1982         } else {
1983             let needs_placeholder = |ctor_def_id: DefId, kind: CtorKind| {
1984                 let def_id = self.r.parent(ctor_def_id);
1985                 let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
1986                 match kind {
1987                     CtorKind::Const => false,
1988                     CtorKind::Fn if has_no_fields => false,
1989                     _ => true,
1990                 }
1991             };
1992
1993             let suggestable_variants = variants
1994                 .iter()
1995                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1996                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1997                 .map(|(variant, kind)| match kind {
1998                     CtorKind::Const => variant,
1999                     CtorKind::Fn => format!("({}())", variant),
2000                 })
2001                 .collect::<Vec<_>>();
2002             let no_suggestable_variant = suggestable_variants.is_empty();
2003
2004             if !no_suggestable_variant {
2005                 let msg = if suggestable_variants.len() == 1 {
2006                     "you might have meant to use the following enum variant"
2007                 } else {
2008                     "you might have meant to use one of the following enum variants"
2009                 };
2010
2011                 err.span_suggestions(
2012                     span,
2013                     msg,
2014                     suggestable_variants,
2015                     Applicability::MaybeIncorrect,
2016                 );
2017             }
2018
2019             let suggestable_variants_with_placeholders = variants
2020                 .iter()
2021                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
2022                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
2023                 .filter_map(|(variant, kind)| match kind {
2024                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
2025                     _ => None,
2026                 })
2027                 .collect::<Vec<_>>();
2028
2029             if !suggestable_variants_with_placeholders.is_empty() {
2030                 let msg =
2031                     match (no_suggestable_variant, suggestable_variants_with_placeholders.len()) {
2032                         (true, 1) => "the following enum variant is available",
2033                         (true, _) => "the following enum variants are available",
2034                         (false, 1) => "alternatively, the following enum variant is available",
2035                         (false, _) => {
2036                             "alternatively, the following enum variants are also available"
2037                         }
2038                     };
2039
2040                 err.span_suggestions(
2041                     span,
2042                     msg,
2043                     suggestable_variants_with_placeholders,
2044                     Applicability::HasPlaceholders,
2045                 );
2046             }
2047         };
2048
2049         if def_id.is_local() {
2050             if let Some(span) = self.def_span(def_id) {
2051                 err.span_note(span, "the enum is defined here");
2052             }
2053         }
2054     }
2055
2056     pub(crate) fn report_missing_type_error(
2057         &self,
2058         path: &[Segment],
2059     ) -> Option<(Span, &'static str, String, Applicability)> {
2060         let (ident, span) = match path {
2061             [segment] if !segment.has_generic_args && segment.ident.name != kw::SelfUpper => {
2062                 (segment.ident.to_string(), segment.ident.span)
2063             }
2064             _ => return None,
2065         };
2066         let mut iter = ident.chars().map(|c| c.is_uppercase());
2067         let single_uppercase_char =
2068             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
2069         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
2070             return None;
2071         }
2072         match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
2073             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
2074                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
2075             }
2076             (
2077                 Some(Item {
2078                     kind:
2079                         kind @ ItemKind::Fn(..)
2080                         | kind @ ItemKind::Enum(..)
2081                         | kind @ ItemKind::Struct(..)
2082                         | kind @ ItemKind::Union(..),
2083                     ..
2084                 }),
2085                 true, _
2086             )
2087             // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
2088             | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
2089             | (Some(Item { kind, .. }), false, _) => {
2090                 // Likely missing type parameter.
2091                 if let Some(generics) = kind.generics() {
2092                     if span.overlaps(generics.span) {
2093                         // Avoid the following:
2094                         // error[E0405]: cannot find trait `A` in this scope
2095                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
2096                         //   |
2097                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
2098                         //   |           ^- help: you might be missing a type parameter: `, A`
2099                         //   |           |
2100                         //   |           not found in this scope
2101                         return None;
2102                     }
2103                     let msg = "you might be missing a type parameter";
2104                     let (span, sugg) = if let [.., param] = &generics.params[..] {
2105                         let span = if let [.., bound] = &param.bounds[..] {
2106                             bound.span()
2107                         } else if let GenericParam {
2108                             kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
2109                         } = param {
2110                             default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
2111                         } else {
2112                             param.ident.span
2113                         };
2114                         (span, format!(", {}", ident))
2115                     } else {
2116                         (generics.span, format!("<{}>", ident))
2117                     };
2118                     // Do not suggest if this is coming from macro expansion.
2119                     if span.can_be_used_for_suggestions() {
2120                         return Some((
2121                             span.shrink_to_hi(),
2122                             msg,
2123                             sugg,
2124                             Applicability::MaybeIncorrect,
2125                         ));
2126                     }
2127                 }
2128             }
2129             _ => {}
2130         }
2131         None
2132     }
2133
2134     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
2135     /// optionally returning the closest match and whether it is reachable.
2136     pub(crate) fn suggestion_for_label_in_rib(
2137         &self,
2138         rib_index: usize,
2139         label: Ident,
2140     ) -> Option<LabelSuggestion> {
2141         // Are ribs from this `rib_index` within scope?
2142         let within_scope = self.is_label_valid_from_rib(rib_index);
2143
2144         let rib = &self.label_ribs[rib_index];
2145         let names = rib
2146             .bindings
2147             .iter()
2148             .filter(|(id, _)| id.span.eq_ctxt(label.span))
2149             .map(|(id, _)| id.name)
2150             .collect::<Vec<Symbol>>();
2151
2152         find_best_match_for_name(&names, label.name, None).map(|symbol| {
2153             // Upon finding a similar name, get the ident that it was from - the span
2154             // contained within helps make a useful diagnostic. In addition, determine
2155             // whether this candidate is within scope.
2156             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
2157             (*ident, within_scope)
2158         })
2159     }
2160
2161     pub(crate) fn maybe_report_lifetime_uses(
2162         &mut self,
2163         generics_span: Span,
2164         params: &[ast::GenericParam],
2165     ) {
2166         for (param_index, param) in params.iter().enumerate() {
2167             let GenericParamKind::Lifetime = param.kind else { continue };
2168
2169             let def_id = self.r.local_def_id(param.id);
2170
2171             let use_set = self.lifetime_uses.remove(&def_id);
2172             debug!(
2173                 "Use set for {:?}({:?} at {:?}) is {:?}",
2174                 def_id, param.ident, param.ident.span, use_set
2175             );
2176
2177             let deletion_span = || {
2178                 if params.len() == 1 {
2179                     // if sole lifetime, remove the entire `<>` brackets
2180                     generics_span
2181                 } else if param_index == 0 {
2182                     // if removing within `<>` brackets, we also want to
2183                     // delete a leading or trailing comma as appropriate
2184                     param.span().to(params[param_index + 1].span().shrink_to_lo())
2185                 } else {
2186                     // if removing within `<>` brackets, we also want to
2187                     // delete a leading or trailing comma as appropriate
2188                     params[param_index - 1].span().shrink_to_hi().to(param.span())
2189                 }
2190             };
2191             match use_set {
2192                 Some(LifetimeUseSet::Many) => {}
2193                 Some(LifetimeUseSet::One { use_span, use_ctxt }) => {
2194                     debug!(?param.ident, ?param.ident.span, ?use_span);
2195
2196                     let elidable = matches!(use_ctxt, LifetimeCtxt::Rptr);
2197
2198                     let deletion_span = deletion_span();
2199                     self.r.lint_buffer.buffer_lint_with_diagnostic(
2200                         lint::builtin::SINGLE_USE_LIFETIMES,
2201                         param.id,
2202                         param.ident.span,
2203                         &format!("lifetime parameter `{}` only used once", param.ident),
2204                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
2205                             param_span: param.ident.span,
2206                             use_span: Some((use_span, elidable)),
2207                             deletion_span,
2208                         },
2209                     );
2210                 }
2211                 None => {
2212                     debug!(?param.ident, ?param.ident.span);
2213
2214                     let deletion_span = deletion_span();
2215                     self.r.lint_buffer.buffer_lint_with_diagnostic(
2216                         lint::builtin::UNUSED_LIFETIMES,
2217                         param.id,
2218                         param.ident.span,
2219                         &format!("lifetime parameter `{}` never used", param.ident),
2220                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
2221                             param_span: param.ident.span,
2222                             use_span: None,
2223                             deletion_span,
2224                         },
2225                     );
2226                 }
2227             }
2228         }
2229     }
2230
2231     pub(crate) fn emit_undeclared_lifetime_error(
2232         &self,
2233         lifetime_ref: &ast::Lifetime,
2234         outer_lifetime_ref: Option<Ident>,
2235     ) {
2236         debug_assert_ne!(lifetime_ref.ident.name, kw::UnderscoreLifetime);
2237         let mut err = if let Some(outer) = outer_lifetime_ref {
2238             let mut err = struct_span_err!(
2239                 self.r.session,
2240                 lifetime_ref.ident.span,
2241                 E0401,
2242                 "can't use generic parameters from outer item",
2243             );
2244             err.span_label(lifetime_ref.ident.span, "use of generic parameter from outer item");
2245             err.span_label(outer.span, "lifetime parameter from outer item");
2246             err
2247         } else {
2248             let mut err = struct_span_err!(
2249                 self.r.session,
2250                 lifetime_ref.ident.span,
2251                 E0261,
2252                 "use of undeclared lifetime name `{}`",
2253                 lifetime_ref.ident
2254             );
2255             err.span_label(lifetime_ref.ident.span, "undeclared lifetime");
2256             err
2257         };
2258         self.suggest_introducing_lifetime(
2259             &mut err,
2260             Some(lifetime_ref.ident.name.as_str()),
2261             |err, _, span, message, suggestion| {
2262                 err.span_suggestion(span, message, suggestion, Applicability::MaybeIncorrect);
2263                 true
2264             },
2265         );
2266         err.emit();
2267     }
2268
2269     fn suggest_introducing_lifetime(
2270         &self,
2271         err: &mut Diagnostic,
2272         name: Option<&str>,
2273         suggest: impl Fn(&mut Diagnostic, bool, Span, &str, String) -> bool,
2274     ) {
2275         let mut suggest_note = true;
2276         for rib in self.lifetime_ribs.iter().rev() {
2277             let mut should_continue = true;
2278             match rib.kind {
2279                 LifetimeRibKind::Generics { binder: _, span, kind } => {
2280                     if !span.can_be_used_for_suggestions() && suggest_note && let Some(name) = name {
2281                         suggest_note = false; // Avoid displaying the same help multiple times.
2282                         err.span_label(
2283                             span,
2284                             &format!(
2285                                 "lifetime `{}` is missing in item created through this procedural macro",
2286                                 name,
2287                             ),
2288                         );
2289                         continue;
2290                     }
2291
2292                     let higher_ranked = matches!(
2293                         kind,
2294                         LifetimeBinderKind::BareFnType
2295                             | LifetimeBinderKind::PolyTrait
2296                             | LifetimeBinderKind::WhereBound
2297                     );
2298                     let (span, sugg) = if span.is_empty() {
2299                         let sugg = format!(
2300                             "{}<{}>{}",
2301                             if higher_ranked { "for" } else { "" },
2302                             name.unwrap_or("'a"),
2303                             if higher_ranked { " " } else { "" },
2304                         );
2305                         (span, sugg)
2306                     } else {
2307                         let span =
2308                             self.r.session.source_map().span_through_char(span, '<').shrink_to_hi();
2309                         let sugg = format!("{}, ", name.unwrap_or("'a"));
2310                         (span, sugg)
2311                     };
2312                     if higher_ranked {
2313                         let message = format!(
2314                             "consider making the {} lifetime-generic with a new `{}` lifetime",
2315                             kind.descr(),
2316                             name.unwrap_or("'a"),
2317                         );
2318                         should_continue = suggest(err, true, span, &message, sugg);
2319                         err.note_once(
2320                             "for more information on higher-ranked polymorphism, visit \
2321                              https://doc.rust-lang.org/nomicon/hrtb.html",
2322                         );
2323                     } else if let Some(name) = name {
2324                         let message = format!("consider introducing lifetime `{}` here", name);
2325                         should_continue = suggest(err, false, span, &message, sugg);
2326                     } else {
2327                         let message = format!("consider introducing a named lifetime parameter");
2328                         should_continue = suggest(err, false, span, &message, sugg);
2329                     }
2330                 }
2331                 LifetimeRibKind::Item => break,
2332                 _ => {}
2333             }
2334             if !should_continue {
2335                 break;
2336             }
2337         }
2338     }
2339
2340     pub(crate) fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &ast::Lifetime) {
2341         struct_span_err!(
2342             self.r.session,
2343             lifetime_ref.ident.span,
2344             E0771,
2345             "use of non-static lifetime `{}` in const generic",
2346             lifetime_ref.ident
2347         )
2348         .note(
2349             "for more information, see issue #74052 \
2350             <https://github.com/rust-lang/rust/issues/74052>",
2351         )
2352         .emit();
2353     }
2354
2355     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
2356     /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
2357     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
2358     pub(crate) fn maybe_emit_forbidden_non_static_lifetime_error(
2359         &self,
2360         lifetime_ref: &ast::Lifetime,
2361     ) {
2362         let feature_active = self.r.session.features_untracked().generic_const_exprs;
2363         if !feature_active {
2364             feature_err(
2365                 &self.r.session.parse_sess,
2366                 sym::generic_const_exprs,
2367                 lifetime_ref.ident.span,
2368                 "a non-static lifetime is not allowed in a `const`",
2369             )
2370             .emit();
2371         }
2372     }
2373
2374     pub(crate) fn report_missing_lifetime_specifiers(
2375         &mut self,
2376         lifetime_refs: Vec<MissingLifetime>,
2377         function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
2378     ) -> ErrorGuaranteed {
2379         let num_lifetimes: usize = lifetime_refs.iter().map(|lt| lt.count).sum();
2380         let spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();
2381
2382         let mut err = struct_span_err!(
2383             self.r.session,
2384             spans,
2385             E0106,
2386             "missing lifetime specifier{}",
2387             pluralize!(num_lifetimes)
2388         );
2389         self.add_missing_lifetime_specifiers_label(
2390             &mut err,
2391             lifetime_refs,
2392             function_param_lifetimes,
2393         );
2394         err.emit()
2395     }
2396
2397     fn add_missing_lifetime_specifiers_label(
2398         &mut self,
2399         err: &mut Diagnostic,
2400         lifetime_refs: Vec<MissingLifetime>,
2401         function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
2402     ) {
2403         for &lt in &lifetime_refs {
2404             err.span_label(
2405                 lt.span,
2406                 format!(
2407                     "expected {} lifetime parameter{}",
2408                     if lt.count == 1 { "named".to_string() } else { lt.count.to_string() },
2409                     pluralize!(lt.count),
2410                 ),
2411             );
2412         }
2413
2414         let mut in_scope_lifetimes: Vec<_> = self
2415             .lifetime_ribs
2416             .iter()
2417             .rev()
2418             .take_while(|rib| !matches!(rib.kind, LifetimeRibKind::Item))
2419             .flat_map(|rib| rib.bindings.iter())
2420             .map(|(&ident, &res)| (ident, res))
2421             .filter(|(ident, _)| ident.name != kw::UnderscoreLifetime)
2422             .collect();
2423         debug!(?in_scope_lifetimes);
2424
2425         debug!(?function_param_lifetimes);
2426         if let Some((param_lifetimes, params)) = &function_param_lifetimes {
2427             let elided_len = param_lifetimes.len();
2428             let num_params = params.len();
2429
2430             let mut m = String::new();
2431
2432             for (i, info) in params.iter().enumerate() {
2433                 let ElisionFnParameter { ident, index, lifetime_count, span } = *info;
2434                 debug_assert_ne!(lifetime_count, 0);
2435
2436                 err.span_label(span, "");
2437
2438                 if i != 0 {
2439                     if i + 1 < num_params {
2440                         m.push_str(", ");
2441                     } else if num_params == 2 {
2442                         m.push_str(" or ");
2443                     } else {
2444                         m.push_str(", or ");
2445                     }
2446                 }
2447
2448                 let help_name = if let Some(ident) = ident {
2449                     format!("`{}`", ident)
2450                 } else {
2451                     format!("argument {}", index + 1)
2452                 };
2453
2454                 if lifetime_count == 1 {
2455                     m.push_str(&help_name[..])
2456                 } else {
2457                     m.push_str(&format!("one of {}'s {} lifetimes", help_name, lifetime_count)[..])
2458                 }
2459             }
2460
2461             if num_params == 0 {
2462                 err.help(
2463                     "this function's return type contains a borrowed value, \
2464                  but there is no value for it to be borrowed from",
2465                 );
2466                 if in_scope_lifetimes.is_empty() {
2467                     in_scope_lifetimes = vec![(
2468                         Ident::with_dummy_span(kw::StaticLifetime),
2469                         (DUMMY_NODE_ID, LifetimeRes::Static),
2470                     )];
2471                 }
2472             } else if elided_len == 0 {
2473                 err.help(
2474                     "this function's return type contains a borrowed value with \
2475                  an elided lifetime, but the lifetime cannot be derived from \
2476                  the arguments",
2477                 );
2478                 if in_scope_lifetimes.is_empty() {
2479                     in_scope_lifetimes = vec![(
2480                         Ident::with_dummy_span(kw::StaticLifetime),
2481                         (DUMMY_NODE_ID, LifetimeRes::Static),
2482                     )];
2483                 }
2484             } else if num_params == 1 {
2485                 err.help(&format!(
2486                     "this function's return type contains a borrowed value, \
2487                  but the signature does not say which {} it is borrowed from",
2488                     m
2489                 ));
2490             } else {
2491                 err.help(&format!(
2492                     "this function's return type contains a borrowed value, \
2493                  but the signature does not say whether it is borrowed from {}",
2494                     m
2495                 ));
2496             }
2497         }
2498
2499         let existing_name = match &in_scope_lifetimes[..] {
2500             [] => Symbol::intern("'a"),
2501             [(existing, _)] => existing.name,
2502             _ => Symbol::intern("'lifetime"),
2503         };
2504
2505         let mut spans_suggs: Vec<_> = Vec::new();
2506         let build_sugg = |lt: MissingLifetime| match lt.kind {
2507             MissingLifetimeKind::Underscore => {
2508                 debug_assert_eq!(lt.count, 1);
2509                 (lt.span, existing_name.to_string())
2510             }
2511             MissingLifetimeKind::Ampersand => {
2512                 debug_assert_eq!(lt.count, 1);
2513                 (lt.span.shrink_to_hi(), format!("{} ", existing_name))
2514             }
2515             MissingLifetimeKind::Comma => {
2516                 let sugg: String = std::iter::repeat([existing_name.as_str(), ", "])
2517                     .take(lt.count)
2518                     .flatten()
2519                     .collect();
2520                 (lt.span.shrink_to_hi(), sugg)
2521             }
2522             MissingLifetimeKind::Brackets => {
2523                 let sugg: String = std::iter::once("<")
2524                     .chain(
2525                         std::iter::repeat(existing_name.as_str()).take(lt.count).intersperse(", "),
2526                     )
2527                     .chain([">"])
2528                     .collect();
2529                 (lt.span.shrink_to_hi(), sugg)
2530             }
2531         };
2532         for &lt in &lifetime_refs {
2533             spans_suggs.push(build_sugg(lt));
2534         }
2535         debug!(?spans_suggs);
2536         match in_scope_lifetimes.len() {
2537             0 => {
2538                 if let Some((param_lifetimes, _)) = function_param_lifetimes {
2539                     for lt in param_lifetimes {
2540                         spans_suggs.push(build_sugg(lt))
2541                     }
2542                 }
2543                 self.suggest_introducing_lifetime(
2544                     err,
2545                     None,
2546                     |err, higher_ranked, span, message, intro_sugg| {
2547                         err.multipart_suggestion_verbose(
2548                             message,
2549                             std::iter::once((span, intro_sugg))
2550                                 .chain(spans_suggs.iter().cloned())
2551                                 .collect(),
2552                             Applicability::MaybeIncorrect,
2553                         );
2554                         higher_ranked
2555                     },
2556                 );
2557             }
2558             1 => {
2559                 err.multipart_suggestion_verbose(
2560                     &format!("consider using the `{}` lifetime", existing_name),
2561                     spans_suggs,
2562                     Applicability::MaybeIncorrect,
2563                 );
2564
2565                 // Record as using the suggested resolution.
2566                 let (_, (_, res)) = in_scope_lifetimes[0];
2567                 for &lt in &lifetime_refs {
2568                     self.r.lifetimes_res_map.insert(lt.id, res);
2569                 }
2570             }
2571             _ => {
2572                 let lifetime_spans: Vec<_> =
2573                     in_scope_lifetimes.iter().map(|(ident, _)| ident.span).collect();
2574                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
2575
2576                 if spans_suggs.len() > 0 {
2577                     // This happens when we have `Foo<T>` where we point at the space before `T`,
2578                     // but this can be confusing so we give a suggestion with placeholders.
2579                     err.multipart_suggestion_verbose(
2580                         "consider using one of the available lifetimes here",
2581                         spans_suggs,
2582                         Applicability::HasPlaceholders,
2583                     );
2584                 }
2585             }
2586         }
2587     }
2588 }
2589
2590 /// Report lifetime/lifetime shadowing as an error.
2591 pub fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: Ident) {
2592     let mut err = struct_span_err!(
2593         sess,
2594         shadower.span,
2595         E0496,
2596         "lifetime name `{}` shadows a lifetime name that is already in scope",
2597         orig.name,
2598     );
2599     err.span_label(orig.span, "first declared here");
2600     err.span_label(shadower.span, format!("lifetime `{}` already in scope", orig.name));
2601     err.emit();
2602 }
2603
2604 /// Shadowing involving a label is only a warning for historical reasons.
2605 //FIXME: make this a proper lint.
2606 pub fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {
2607     let name = shadower.name;
2608     let shadower = shadower.span;
2609     let mut err = sess.struct_span_warn(
2610         shadower,
2611         &format!("label name `{}` shadows a label name that is already in scope", name),
2612     );
2613     err.span_label(orig, "first declared here");
2614     err.span_label(shadower, format!("label `{}` already in scope", name));
2615     err.emit();
2616 }