compiler/rustc_resolve/src/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::lifetimes::{ElisionFailureInfo, LifetimeContext};
   3 use crate::late::{AliasPossibility, LateResolutionVisitor, RibKind};
   4 use crate::late::{LifetimeBinderKind, LifetimeRibKind, LifetimeUseSet};
   5 use crate::path_names_to_string;
   6 use crate::{Module, ModuleKind, ModuleOrUniformRoot};
   7 use crate::{PathResult, PathSource, Segment};
   8
   9 use rustc_ast::visit::{FnCtxt, FnKind, LifetimeCtxt};
  10 use rustc_ast::{
  11     self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
  12     NodeId, Path, Ty, TyKind,
  13 };
  14 use rustc_ast_lowering::ResolverAstLowering;
  15 use rustc_ast_pretty::pprust::path_segment_to_string;
  16 use rustc_data_structures::fx::FxHashSet;
  17 use rustc_errors::{
  18     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
  19     MultiSpan,
  20 };
  21 use rustc_hir as hir;
  22 use rustc_hir::def::Namespace::{self, *};
  23 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
  24 use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
  25 use rustc_hir::PrimTy;
  26 use rustc_session::lint;
  27 use rustc_session::parse::feature_err;
  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, DUMMY_SP};
  33
  34 use std::iter;
  35 use std::ops::Deref;
  36
  37 use tracing::debug;
  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,
  45     AssocFn,
  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 => "call the method with the fully-qualified path",
  55             AssocSuggestion::AssocFn => "call the associated function",
  56             AssocSuggestion::AssocConst => "use the associated `const`",
  57             AssocSuggestion::AssocType => "use the associated type",
  58         }
  59     }
  60 }
  61
  62 pub(crate) enum MissingLifetimeSpot<'tcx> {
  63     Generics(&'tcx hir::Generics<'tcx>),
  64     HigherRanked { span: Span, span_type: ForLifetimeSpanType },
  65     Static,
  66 }
  67
  68 pub(crate) enum ForLifetimeSpanType {
  69     BoundEmpty,
  70     BoundTail,
  71     TypeEmpty,
  72     TypeTail,
  73 }
  74
  75 impl ForLifetimeSpanType {
  76     pub(crate) fn descr(&self) -> &'static str {
  77         match self {
  78             Self::BoundEmpty | Self::BoundTail => "bound",
  79             Self::TypeEmpty | Self::TypeTail => "type",
  80         }
  81     }
  82
  83     pub(crate) fn suggestion(&self, sugg: &str) -> String {
  84         match self {
  85             Self::BoundEmpty | Self::TypeEmpty => format!("for<{}> ", sugg),
  86             Self::BoundTail | Self::TypeTail => format!(", {}", sugg),
  87         }
  88     }
  89 }
  90
  91 impl<'tcx> Into<MissingLifetimeSpot<'tcx>> for &&'tcx hir::Generics<'tcx> {
  92     fn into(self) -> MissingLifetimeSpot<'tcx> {
  93         MissingLifetimeSpot::Generics(self)
  94     }
  95 }
  96
  97 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  98     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  99 }
 100
 101 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
 102     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
 103 }
 104
 105 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
 106 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
 107     let variant_path = &suggestion.path;
 108     let variant_path_string = path_names_to_string(variant_path);
 109
 110     let path_len = suggestion.path.segments.len();
 111     let enum_path = ast::Path {
 112         span: suggestion.path.span,
 113         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
 114         tokens: None,
 115     };
 116     let enum_path_string = path_names_to_string(&enum_path);
 117
 118     (variant_path_string, enum_path_string)
 119 }
 120
 121 impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 122     fn def_span(&self, def_id: DefId) -> Option<Span> {
 123         match def_id.krate {
 124             LOCAL_CRATE => self.r.opt_span(def_id),
 125             _ => Some(
 126                 self.r
 127                     .session
 128                     .source_map()
 129                     .guess_head_span(self.r.cstore().get_span_untracked(def_id, self.r.session)),
 130             ),
 131         }
 132     }
 133
 134     /// Handles error reporting for `smart_resolve_path_fragment` function.
 135     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 136     pub(crate) fn smart_resolve_report_errors(
 137         &mut self,
 138         path: &[Segment],
 139         span: Span,
 140         source: PathSource<'_>,
 141         res: Option<Res>,
 142     ) -> (DiagnosticBuilder<'a, ErrorGuaranteed>, Vec<ImportSuggestion>) {
 143         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 144         let ns = source.namespace();
 145         let is_expected = &|res| source.is_expected(res);
 146         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 147
 148         // Make the base error.
 149         struct BaseError<'a> {
 150             msg: String,
 151             fallback_label: String,
 152             span: Span,
 153             could_be_expr: bool,
 154             suggestion: Option<(Span, &'a str, String)>,
 155         }
 156         let mut expected = source.descr_expected();
 157         let path_str = Segment::names_to_string(path);
 158         let item_str = path.last().unwrap().ident;
 159         let base_error = if let Some(res) = res {
 160             BaseError {
 161                 msg: format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 162                 fallback_label: format!("not a {expected}"),
 163                 span,
 164                 could_be_expr: match res {
 165                     Res::Def(DefKind::Fn, _) => {
 166                         // Verify whether this is a fn call or an Fn used as a type.
 167                         self.r
 168                             .session
 169                             .source_map()
 170                             .span_to_snippet(span)
 171                             .map(|snippet| snippet.ends_with(')'))
 172                             .unwrap_or(false)
 173                     }
 174                     Res::Def(
 175                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 176                         _,
 177                     )
 178                     | Res::SelfCtor(_)
 179                     | Res::PrimTy(_)
 180                     | Res::Local(_) => true,
 181                     _ => false,
 182                 },
 183                 suggestion: None,
 184             }
 185         } else {
 186             let item_span = path.last().unwrap().ident.span;
 187             let (mod_prefix, mod_str, suggestion) = if path.len() == 1 {
 188                 debug!(?self.diagnostic_metadata.current_impl_items);
 189                 debug!(?self.diagnostic_metadata.current_function);
 190                 let suggestion = if let Some(items) = self.diagnostic_metadata.current_impl_items
 191                     && let Some((fn_kind, _)) = self.diagnostic_metadata.current_function
 192                     && self.current_trait_ref.is_none()
 193                     && let Some(FnCtxt::Assoc(_)) = fn_kind.ctxt()
 194                     && let Some(item) = items.iter().find(|i| {
 195                         if let AssocItemKind::Fn(fn_) = &i.kind
 196                             && !fn_.sig.decl.has_self()
 197                             && i.ident.name == item_str.name
 198                         {
 199                             debug!(?item_str.name);
 200                             debug!(?fn_.sig.decl.inputs);
 201                             return true
 202                         }
 203                         false
 204                     })
 205                 {
 206                     Some((
 207                         item_span,
 208                         "consider using the associated function",
 209                         format!("Self::{}", item.ident)
 210                     ))
 211                 } else {
 212                     None
 213                 };
 214                 (String::new(), "this scope".to_string(), suggestion)
 215             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 216                 if self.r.session.edition() > Edition::Edition2015 {
 217                     // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
 218                     // which overrides all other expectations of item type
 219                     expected = "crate";
 220                     (String::new(), "the list of imported crates".to_string(), None)
 221                 } else {
 222                     (String::new(), "the crate root".to_string(), None)
 223                 }
 224             } else if path.len() == 2 && path[0].ident.name == kw::Crate {
 225                 (String::new(), "the crate root".to_string(), None)
 226             } else {
 227                 let mod_path = &path[..path.len() - 1];
 228                 let mod_prefix = match self.resolve_path(mod_path, Some(TypeNS), None) {
 229                     PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 230                     _ => None,
 231                 }
 232                 .map_or_else(String::new, |res| format!("{} ", res.descr()));
 233                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)), None)
 234             };
 235             BaseError {
 236                 msg: format!("cannot find {expected} `{item_str}` in {mod_prefix}{mod_str}"),
 237                 fallback_label: if path_str == "async" && expected.starts_with("struct") {
 238                     "`async` blocks are only allowed in Rust 2018 or later".to_string()
 239                 } else {
 240                     format!("not found in {mod_str}")
 241                 },
 242                 span: item_span,
 243                 could_be_expr: false,
 244                 suggestion,
 245             }
 246         };
 247
 248         let code = source.error_code(res.is_some());
 249         let mut err =
 250             self.r.session.struct_span_err_with_code(base_error.span, &base_error.msg, code);
 251
 252         if let Some(sugg) = base_error.suggestion {
 253             err.span_suggestion_verbose(sugg.0, sugg.1, sugg.2, Applicability::MaybeIncorrect);
 254         }
 255
 256         if let Some(span) = self.diagnostic_metadata.current_block_could_be_bare_struct_literal {
 257             err.multipart_suggestion(
 258                 "you might have meant to write a `struct` literal",
 259                 vec![
 260                     (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
 261                     (span.shrink_to_hi(), "}".to_string()),
 262                 ],
 263                 Applicability::HasPlaceholders,
 264             );
 265         }
 266         match (source, self.diagnostic_metadata.in_if_condition) {
 267             (PathSource::Expr(_), Some(Expr { span, kind: ExprKind::Assign(..), .. })) => {
 268                 err.span_suggestion_verbose(
 269                     span.shrink_to_lo(),
 270                     "you might have meant to use pattern matching",
 271                     "let ".to_string(),
 272                     Applicability::MaybeIncorrect,
 273                 );
 274             }
 275             _ => {}
 276         }
 277
 278         let is_assoc_fn = self.self_type_is_available();
 279         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 280         if ["this", "my"].contains(&item_str.as_str()) && is_assoc_fn {
 281             err.span_suggestion_short(
 282                 span,
 283                 "you might have meant to use `self` here instead",
 284                 "self".to_string(),
 285                 Applicability::MaybeIncorrect,
 286             );
 287             if !self.self_value_is_available(path[0].ident.span) {
 288                 if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
 289                     &self.diagnostic_metadata.current_function
 290                 {
 291                     let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
 292                         (param.span.shrink_to_lo(), "&self, ")
 293                     } else {
 294                         (
 295                             self.r
 296                                 .session
 297                                 .source_map()
 298                                 .span_through_char(*fn_span, '(')
 299                                 .shrink_to_hi(),
 300                             "&self",
 301                         )
 302                     };
 303                     err.span_suggestion_verbose(
 304                         span,
 305                         "if you meant to use `self`, you are also missing a `self` receiver \
 306                          argument",
 307                         sugg.to_string(),
 308                         Applicability::MaybeIncorrect,
 309                     );
 310                 }
 311             }
 312         }
 313
 314         self.detect_assoct_type_constraint_meant_as_path(base_error.span, &mut err);
 315
 316         // Emit special messages for unresolved `Self` and `self`.
 317         if is_self_type(path, ns) {
 318             err.code(rustc_errors::error_code!(E0411));
 319             err.span_label(
 320                 span,
 321                 "`Self` is only available in impls, traits, and type definitions".to_string(),
 322             );
 323             return (err, Vec::new());
 324         }
 325         if is_self_value(path, ns) {
 326             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 327
 328             err.code(rustc_errors::error_code!(E0424));
 329             err.span_label(span, match source {
 330                 PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed"
 331                                    .to_string(),
 332                 _ => "`self` value is a keyword only available in methods with a `self` parameter"
 333                      .to_string(),
 334             });
 335             if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 336                 // The current function has a `self' parameter, but we were unable to resolve
 337                 // a reference to `self`. This can only happen if the `self` identifier we
 338                 // are resolving came from a different hygiene context.
 339                 if fn_kind.decl().inputs.get(0).map_or(false, |p| p.is_self()) {
 340                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 341                 } else {
 342                     let doesnt = if is_assoc_fn {
 343                         let (span, sugg) = fn_kind
 344                             .decl()
 345                             .inputs
 346                             .get(0)
 347                             .map(|p| (p.span.shrink_to_lo(), "&self, "))
 348                             .unwrap_or_else(|| {
 349                                 // Try to look for the "(" after the function name, if possible.
 350                                 // This avoids placing the suggestion into the visibility specifier.
 351                                 let span = fn_kind
 352                                     .ident()
 353                                     .map_or(*span, |ident| span.with_lo(ident.span.hi()));
 354                                 (
 355                                     self.r
 356                                         .session
 357                                         .source_map()
 358                                         .span_through_char(span, '(')
 359                                         .shrink_to_hi(),
 360                                     "&self",
 361                                 )
 362                             });
 363                         err.span_suggestion_verbose(
 364                             span,
 365                             "add a `self` receiver parameter to make the associated `fn` a method",
 366                             sugg.to_string(),
 367                             Applicability::MaybeIncorrect,
 368                         );
 369                         "doesn't"
 370                     } else {
 371                         "can't"
 372                     };
 373                     if let Some(ident) = fn_kind.ident() {
 374                         err.span_label(
 375                             ident.span,
 376                             &format!("this function {} have a `self` parameter", doesnt),
 377                         );
 378                     }
 379                 }
 380             }
 381             return (err, Vec::new());
 382         }
 383
 384         // Try to lookup name in more relaxed fashion for better error reporting.
 385         let ident = path.last().unwrap().ident;
 386         let candidates = self
 387             .r
 388             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 389             .into_iter()
 390             .filter(|ImportSuggestion { did, .. }| {
 391                 match (did, res.and_then(|res| res.opt_def_id())) {
 392                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 393                     _ => true,
 394                 }
 395             })
 396             .collect::<Vec<_>>();
 397         let crate_def_id = CRATE_DEF_ID.to_def_id();
 398         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 399             let mut enum_candidates: Vec<_> = self
 400                 .r
 401                 .lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant)
 402                 .into_iter()
 403                 .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 404                 .filter(|(_, enum_ty_path)| !enum_ty_path.starts_with("std::prelude::"))
 405                 .collect();
 406             if !enum_candidates.is_empty() {
 407                 if let (PathSource::Type, Some(span)) =
 408                     (source, self.diagnostic_metadata.current_type_ascription.last())
 409                 {
 410                     if self
 411                         .r
 412                         .session
 413                         .parse_sess
 414                         .type_ascription_path_suggestions
 415                         .borrow()
 416                         .contains(span)
 417                     {
 418                         // Already reported this issue on the lhs of the type ascription.
 419                         err.delay_as_bug();
 420                         return (err, candidates);
 421                     }
 422                 }
 423
 424                 enum_candidates.sort();
 425
 426                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 427                 // (that it's a variant) for E0573 "expected type, found variant".
 428                 let preamble = if res.is_none() {
 429                     let others = match enum_candidates.len() {
 430                         1 => String::new(),
 431                         2 => " and 1 other".to_owned(),
 432                         n => format!(" and {} others", n),
 433                     };
 434                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 435                 } else {
 436                     String::new()
 437                 };
 438                 let msg = format!("{}try using the variant's enum", preamble);
 439
 440                 err.span_suggestions(
 441                     span,
 442                     &msg,
 443                     enum_candidates.into_iter().map(|(_variant_path, enum_ty_path)| enum_ty_path),
 444                     Applicability::MachineApplicable,
 445                 );
 446             }
 447         }
 448         // Try Levenshtein algorithm.
 449         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected);
 450         if path.len() == 1 && self.self_type_is_available() {
 451             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 452                 let self_is_available = self.self_value_is_available(path[0].ident.span);
 453                 match candidate {
 454                     AssocSuggestion::Field => {
 455                         if self_is_available {
 456                             err.span_suggestion(
 457                                 span,
 458                                 "you might have meant to use the available field",
 459                                 format!("self.{path_str}"),
 460                                 Applicability::MachineApplicable,
 461                             );
 462                         } else {
 463                             err.span_label(span, "a field by this name exists in `Self`");
 464                         }
 465                     }
 466                     AssocSuggestion::MethodWithSelf if self_is_available => {
 467                         err.span_suggestion(
 468                             span,
 469                             "you might have meant to call the method",
 470                             format!("self.{path_str}"),
 471                             Applicability::MachineApplicable,
 472                         );
 473                     }
 474                     AssocSuggestion::MethodWithSelf
 475                     | AssocSuggestion::AssocFn
 476                     | AssocSuggestion::AssocConst
 477                     | AssocSuggestion::AssocType => {
 478                         err.span_suggestion(
 479                             span,
 480                             &format!("you might have meant to {}", candidate.action()),
 481                             format!("Self::{path_str}"),
 482                             Applicability::MachineApplicable,
 483                         );
 484                     }
 485                 }
 486                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 487                 return (err, candidates);
 488             }
 489
 490             // If the first argument in call is `self` suggest calling a method.
 491             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 492                 let mut args_snippet = String::new();
 493                 if let Some(args_span) = args_span {
 494                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 495                         args_snippet = snippet;
 496                     }
 497                 }
 498
 499                 err.span_suggestion(
 500                     call_span,
 501                     &format!("try calling `{ident}` as a method"),
 502                     format!("self.{path_str}({args_snippet})"),
 503                     Applicability::MachineApplicable,
 504                 );
 505                 return (err, candidates);
 506             }
 507         }
 508
 509         // Try context-dependent help if relaxed lookup didn't work.
 510         if let Some(res) = res {
 511             if self.smart_resolve_context_dependent_help(
 512                 &mut err,
 513                 span,
 514                 source,
 515                 res,
 516                 &path_str,
 517                 &base_error.fallback_label,
 518             ) {
 519                 // We do this to avoid losing a secondary span when we override the main error span.
 520                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 521                 return (err, candidates);
 522             }
 523         }
 524
 525         let is_macro =
 526             base_error.span.from_expansion() && base_error.span.desugaring_kind().is_none();
 527         if !self.type_ascription_suggestion(&mut err, base_error.span) {
 528             let mut fallback = false;
 529             if let (
 530                 PathSource::Trait(AliasPossibility::Maybe),
 531                 Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
 532                 false,
 533             ) = (source, res, is_macro)
 534             {
 535                 if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
 536                     fallback = true;
 537                     let spans: Vec<Span> = bounds
 538                         .iter()
 539                         .map(|bound| bound.span())
 540                         .filter(|&sp| sp != base_error.span)
 541                         .collect();
 542
 543                     let start_span = bounds.iter().map(|bound| bound.span()).next().unwrap();
 544                     // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
 545                     let end_span = bounds.iter().map(|bound| bound.span()).last().unwrap();
 546                     // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
 547                     let last_bound_span = spans.last().cloned().unwrap();
 548                     let mut multi_span: MultiSpan = spans.clone().into();
 549                     for sp in spans {
 550                         let msg = if sp == last_bound_span {
 551                             format!(
 552                                 "...because of {these} bound{s}",
 553                                 these = pluralize!("this", bounds.len() - 1),
 554                                 s = pluralize!(bounds.len() - 1),
 555                             )
 556                         } else {
 557                             String::new()
 558                         };
 559                         multi_span.push_span_label(sp, msg);
 560                     }
 561                     multi_span.push_span_label(
 562                         base_error.span,
 563                         "expected this type to be a trait...".to_string(),
 564                     );
 565                     err.span_help(
 566                         multi_span,
 567                         "`+` is used to constrain a \"trait object\" type with lifetimes or \
 568                          auto-traits; structs and enums can't be bound in that way",
 569                     );
 570                     if bounds.iter().all(|bound| match bound {
 571                         ast::GenericBound::Outlives(_) => true,
 572                         ast::GenericBound::Trait(tr, _) => tr.span == base_error.span,
 573                     }) {
 574                         let mut sugg = vec![];
 575                         if base_error.span != start_span {
 576                             sugg.push((start_span.until(base_error.span), String::new()));
 577                         }
 578                         if base_error.span != end_span {
 579                             sugg.push((base_error.span.shrink_to_hi().to(end_span), String::new()));
 580                         }
 581
 582                         err.multipart_suggestion(
 583                             "if you meant to use a type and not a trait here, remove the bounds",
 584                             sugg,
 585                             Applicability::MaybeIncorrect,
 586                         );
 587                     }
 588                 }
 589             }
 590
 591             fallback |= self.restrict_assoc_type_in_where_clause(span, &mut err);
 592
 593             if !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span) {
 594                 fallback = true;
 595                 match self.diagnostic_metadata.current_let_binding {
 596                     Some((pat_sp, Some(ty_sp), None))
 597                         if ty_sp.contains(base_error.span) && base_error.could_be_expr =>
 598                     {
 599                         err.span_suggestion_short(
 600                             pat_sp.between(ty_sp),
 601                             "use `=` if you meant to assign",
 602                             " = ".to_string(),
 603                             Applicability::MaybeIncorrect,
 604                         );
 605                     }
 606                     _ => {}
 607                 }
 608
 609                 // If the trait has a single item (which wasn't matched by Levenshtein), suggest it
 610                 let suggestion = self.get_single_associated_item(&path, &source, is_expected);
 611                 self.r.add_typo_suggestion(&mut err, suggestion, ident_span);
 612             }
 613             if fallback {
 614                 // Fallback label.
 615                 err.span_label(base_error.span, base_error.fallback_label);
 616             }
 617         }
 618         if let Some(err_code) = &err.code {
 619             if err_code == &rustc_errors::error_code!(E0425) {
 620                 for label_rib in &self.label_ribs {
 621                     for (label_ident, node_id) in &label_rib.bindings {
 622                         if format!("'{}", ident) == label_ident.to_string() {
 623                             err.span_label(label_ident.span, "a label with a similar name exists");
 624                             if let PathSource::Expr(Some(Expr {
 625                                 kind: ExprKind::Break(None, Some(_)),
 626                                 ..
 627                             })) = source
 628                             {
 629                                 err.span_suggestion(
 630                                     span,
 631                                     "use the similarly named label",
 632                                     label_ident.name.to_string(),
 633                                     Applicability::MaybeIncorrect,
 634                                 );
 635                                 // Do not lint against unused label when we suggest them.
 636                                 self.diagnostic_metadata.unused_labels.remove(node_id);
 637                             }
 638                         }
 639                     }
 640                 }
 641             } else if err_code == &rustc_errors::error_code!(E0412) {
 642                 if let Some(correct) = Self::likely_rust_type(path) {
 643                     err.span_suggestion(
 644                         span,
 645                         "perhaps you intended to use this type",
 646                         correct.to_string(),
 647                         Applicability::MaybeIncorrect,
 648                     );
 649                 }
 650             }
 651         }
 652
 653         (err, candidates)
 654     }
 655
 656     fn detect_assoct_type_constraint_meant_as_path(&self, base_span: Span, err: &mut Diagnostic) {
 657         let Some(ty) = self.diagnostic_metadata.current_type_path else { return; };
 658         let TyKind::Path(_, path) = &ty.kind else { return; };
 659         for segment in &path.segments {
 660             let Some(params) = &segment.args else { continue; };
 661             let ast::GenericArgs::AngleBracketed(ref params) = params.deref() else { continue; };
 662             for param in &params.args {
 663                 let ast::AngleBracketedArg::Constraint(constraint) = param else { continue; };
 664                 let ast::AssocConstraintKind::Bound { bounds } = &constraint.kind else {
 665                     continue;
 666                 };
 667                 for bound in bounds {
 668                     let ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifier::None)
 669                         = bound else
 670                     {
 671                         continue;
 672                     };
 673                     if base_span == trait_ref.span {
 674                         err.span_suggestion_verbose(
 675                             constraint.ident.span.between(trait_ref.span),
 676                             "you might have meant to write a path instead of an associated type bound",
 677                             "::".to_string(),
 678                             Applicability::MachineApplicable,
 679                         );
 680                     }
 681                 }
 682             }
 683         }
 684     }
 685
 686     fn get_single_associated_item(
 687         &mut self,
 688         path: &[Segment],
 689         source: &PathSource<'_>,
 690         filter_fn: &impl Fn(Res) -> bool,
 691     ) -> Option<TypoSuggestion> {
 692         if let crate::PathSource::TraitItem(_) = source {
 693             let mod_path = &path[..path.len() - 1];
 694             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 695                 self.resolve_path(mod_path, None, None)
 696             {
 697                 let resolutions = self.r.resolutions(module).borrow();
 698                 let targets: Vec<_> =
 699                     resolutions
 700                         .iter()
 701                         .filter_map(|(key, resolution)| {
 702                             resolution.borrow().binding.map(|binding| binding.res()).and_then(
 703                                 |res| if filter_fn(res) { Some((key, res)) } else { None },
 704                             )
 705                         })
 706                         .collect();
 707                 if targets.len() == 1 {
 708                     let target = targets[0];
 709                     return Some(TypoSuggestion::single_item_from_res(
 710                         target.0.ident.name,
 711                         target.1,
 712                     ));
 713                 }
 714             }
 715         }
 716         None
 717     }
 718
 719     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
 720     fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diagnostic) -> bool {
 721         // Detect that we are actually in a `where` predicate.
 722         let (bounded_ty, bounds, where_span) =
 723             if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 724                 bounded_ty,
 725                 bound_generic_params,
 726                 bounds,
 727                 span,
 728             })) = self.diagnostic_metadata.current_where_predicate
 729             {
 730                 if !bound_generic_params.is_empty() {
 731                     return false;
 732                 }
 733                 (bounded_ty, bounds, span)
 734             } else {
 735                 return false;
 736             };
 737
 738         // Confirm that the target is an associated type.
 739         let (ty, position, path) = if let ast::TyKind::Path(
 740             Some(ast::QSelf { ty, position, .. }),
 741             path,
 742         ) = &bounded_ty.kind
 743         {
 744             // use this to verify that ident is a type param.
 745             let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
 746                 return false;
 747             };
 748             if !(matches!(
 749                 partial_res.base_res(),
 750                 hir::def::Res::Def(hir::def::DefKind::AssocTy, _)
 751             ) && partial_res.unresolved_segments() == 0)
 752             {
 753                 return false;
 754             }
 755             (ty, position, path)
 756         } else {
 757             return false;
 758         };
 759
 760         let peeled_ty = ty.peel_refs();
 761         if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
 762             // Confirm that the `SelfTy` is a type parameter.
 763             let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
 764                 return false;
 765             };
 766             if !(matches!(
 767                 partial_res.base_res(),
 768                 hir::def::Res::Def(hir::def::DefKind::TyParam, _)
 769             ) && partial_res.unresolved_segments() == 0)
 770             {
 771                 return false;
 772             }
 773             if let (
 774                 [ast::PathSegment { ident: constrain_ident, args: None, .. }],
 775                 [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
 776             ) = (&type_param_path.segments[..], &bounds[..])
 777             {
 778                 if let [ast::PathSegment { ident, args: None, .. }] =
 779                     &poly_trait_ref.trait_ref.path.segments[..]
 780                 {
 781                     if ident.span == span {
 782                         err.span_suggestion_verbose(
 783                             *where_span,
 784                             &format!("constrain the associated type to `{}`", ident),
 785                             format!(
 786                                 "{}: {}<{} = {}>",
 787                                 self.r
 788                                     .session
 789                                     .source_map()
 790                                     .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
 791                                     .unwrap_or_else(|_| constrain_ident.to_string()),
 792                                 path.segments[..*position]
 793                                     .iter()
 794                                     .map(|segment| path_segment_to_string(segment))
 795                                     .collect::<Vec<_>>()
 796                                     .join("::"),
 797                                 path.segments[*position..]
 798                                     .iter()
 799                                     .map(|segment| path_segment_to_string(segment))
 800                                     .collect::<Vec<_>>()
 801                                     .join("::"),
 802                                 ident,
 803                             ),
 804                             Applicability::MaybeIncorrect,
 805                         );
 806                     }
 807                     return true;
 808                 }
 809             }
 810         }
 811         false
 812     }
 813
 814     /// Check if the source is call expression and the first argument is `self`. If true,
 815     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 816     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 817         let mut has_self_arg = None;
 818         if let PathSource::Expr(Some(parent)) = source {
 819             match &parent.kind {
 820                 ExprKind::Call(_, args) if !args.is_empty() => {
 821                     let mut expr_kind = &args[0].kind;
 822                     loop {
 823                         match expr_kind {
 824                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 825                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 826                                     let call_span = parent.span;
 827                                     let tail_args_span = if args.len() > 1 {
 828                                         Some(Span::new(
 829                                             args[1].span.lo(),
 830                                             args.last().unwrap().span.hi(),
 831                                             call_span.ctxt(),
 832                                             None,
 833                                         ))
 834                                     } else {
 835                                         None
 836                                     };
 837                                     has_self_arg = Some((call_span, tail_args_span));
 838                                 }
 839                                 break;
 840                             }
 841                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 842                             _ => break,
 843                         }
 844                     }
 845                 }
 846                 _ => (),
 847             }
 848         };
 849         has_self_arg
 850     }
 851
 852     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 853         // HACK(estebank): find a better way to figure out that this was a
 854         // parser issue where a struct literal is being used on an expression
 855         // where a brace being opened means a block is being started. Look
 856         // ahead for the next text to see if `span` is followed by a `{`.
 857         let sm = self.r.session.source_map();
 858         let mut sp = span;
 859         loop {
 860             sp = sm.next_point(sp);
 861             match sm.span_to_snippet(sp) {
 862                 Ok(ref snippet) => {
 863                     if snippet.chars().any(|c| !c.is_whitespace()) {
 864                         break;
 865                     }
 866                 }
 867                 _ => break,
 868             }
 869         }
 870         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
 871         // In case this could be a struct literal that needs to be surrounded
 872         // by parentheses, find the appropriate span.
 873         let mut i = 0;
 874         let mut closing_brace = None;
 875         loop {
 876             sp = sm.next_point(sp);
 877             match sm.span_to_snippet(sp) {
 878                 Ok(ref snippet) => {
 879                     if snippet == "}" {
 880                         closing_brace = Some(span.to(sp));
 881                         break;
 882                     }
 883                 }
 884                 _ => break,
 885             }
 886             i += 1;
 887             // The bigger the span, the more likely we're incorrect --
 888             // bound it to 100 chars long.
 889             if i > 100 {
 890                 break;
 891             }
 892         }
 893         (followed_by_brace, closing_brace)
 894     }
 895
 896     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 897     /// function.
 898     /// Returns `true` if able to provide context-dependent help.
 899     fn smart_resolve_context_dependent_help(
 900         &mut self,
 901         err: &mut Diagnostic,
 902         span: Span,
 903         source: PathSource<'_>,
 904         res: Res,
 905         path_str: &str,
 906         fallback_label: &str,
 907     ) -> bool {
 908         let ns = source.namespace();
 909         let is_expected = &|res| source.is_expected(res);
 910
 911         let path_sep = |err: &mut Diagnostic, expr: &Expr| match expr.kind {
 912             ExprKind::Field(_, ident) => {
 913                 err.span_suggestion(
 914                     expr.span,
 915                     "use the path separator to refer to an item",
 916                     format!("{}::{}", path_str, ident),
 917                     Applicability::MaybeIncorrect,
 918                 );
 919                 true
 920             }
 921             ExprKind::MethodCall(ref segment, ..) => {
 922                 let span = expr.span.with_hi(segment.ident.span.hi());
 923                 err.span_suggestion(
 924                     span,
 925                     "use the path separator to refer to an item",
 926                     format!("{}::{}", path_str, segment.ident),
 927                     Applicability::MaybeIncorrect,
 928                 );
 929                 true
 930             }
 931             _ => false,
 932         };
 933
 934         let find_span = |source: &PathSource<'_>, err: &mut Diagnostic| {
 935             match source {
 936                 PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
 937                 | PathSource::TupleStruct(span, _) => {
 938                     // We want the main underline to cover the suggested code as well for
 939                     // cleaner output.
 940                     err.set_span(*span);
 941                     *span
 942                 }
 943                 _ => span,
 944             }
 945         };
 946
 947         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 948             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 949
 950             match source {
 951                 PathSource::Expr(Some(
 952                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
 953                 )) if path_sep(err, &parent) => {}
 954                 PathSource::Expr(
 955                     None
 956                     | Some(Expr {
 957                         kind:
 958                             ExprKind::Path(..)
 959                             | ExprKind::Binary(..)
 960                             | ExprKind::Unary(..)
 961                             | ExprKind::If(..)
 962                             | ExprKind::While(..)
 963                             | ExprKind::ForLoop(..)
 964                             | ExprKind::Match(..),
 965                         ..
 966                     }),
 967                 ) if followed_by_brace => {
 968                     if let Some(sp) = closing_brace {
 969                         err.span_label(span, fallback_label);
 970                         err.multipart_suggestion(
 971                             "surround the struct literal with parentheses",
 972                             vec![
 973                                 (sp.shrink_to_lo(), "(".to_string()),
 974                                 (sp.shrink_to_hi(), ")".to_string()),
 975                             ],
 976                             Applicability::MaybeIncorrect,
 977                         );
 978                     } else {
 979                         err.span_label(
 980                             span, // Note the parentheses surrounding the suggestion below
 981                             format!(
 982                                 "you might want to surround a struct literal with parentheses: \
 983                                  `({} {{ /* fields */ }})`?",
 984                                 path_str
 985                             ),
 986                         );
 987                     }
 988                 }
 989                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
 990                     let span = find_span(&source, err);
 991                     if let Some(span) = self.def_span(def_id) {
 992                         err.span_label(span, &format!("`{}` defined here", path_str));
 993                     }
 994                     let (tail, descr, applicability) = match source {
 995                         PathSource::Pat | PathSource::TupleStruct(..) => {
 996                             ("", "pattern", Applicability::MachineApplicable)
 997                         }
 998                         _ => (": val", "literal", Applicability::HasPlaceholders),
 999                     };
1000                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
1001                         Some(fields) => (
1002                             fields
1003                                 .iter()
1004                                 .map(|f| format!("{}{}", f.node, tail))
1005                                 .collect::<Vec<String>>()
1006                                 .join(", "),
1007                             applicability,
1008                         ),
1009                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
1010                     };
1011                     let pad = match self.r.field_names.get(&def_id) {
1012                         Some(fields) if fields.is_empty() => "",
1013                         _ => " ",
1014                     };
1015                     err.span_suggestion(
1016                         span,
1017                         &format!("use struct {} syntax instead", descr),
1018                         format!("{path_str} {{{pad}{fields}{pad}}}"),
1019                         applicability,
1020                     );
1021                 }
1022                 _ => {
1023                     err.span_label(span, fallback_label);
1024                 }
1025             }
1026         };
1027
1028         match (res, source) {
1029             (
1030                 Res::Def(DefKind::Macro(MacroKind::Bang), _),
1031                 PathSource::Expr(Some(Expr {
1032                     kind: ExprKind::Index(..) | ExprKind::Call(..), ..
1033                 }))
1034                 | PathSource::Struct,
1035             ) => {
1036                 err.span_label(span, fallback_label);
1037                 err.span_suggestion_verbose(
1038                     span.shrink_to_hi(),
1039                     "use `!` to invoke the macro",
1040                     "!".to_string(),
1041                     Applicability::MaybeIncorrect,
1042                 );
1043                 if path_str == "try" && span.rust_2015() {
1044                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
1045                 }
1046             }
1047             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
1048                 err.span_label(span, fallback_label);
1049             }
1050             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
1051                 err.span_label(span, "type aliases cannot be used as traits");
1052                 if self.r.session.is_nightly_build() {
1053                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
1054                                `type` alias";
1055                     if let Some(span) = self.def_span(def_id) {
1056                         if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
1057                             // The span contains a type alias so we should be able to
1058                             // replace `type` with `trait`.
1059                             let snip = snip.replacen("type", "trait", 1);
1060                             err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
1061                         } else {
1062                             err.span_help(span, msg);
1063                         }
1064                     } else {
1065                         err.help(msg);
1066                     }
1067                 }
1068             }
1069             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
1070                 if !path_sep(err, &parent) {
1071                     return false;
1072                 }
1073             }
1074             (
1075                 Res::Def(DefKind::Enum, def_id),
1076                 PathSource::TupleStruct(..) | PathSource::Expr(..),
1077             ) => {
1078                 if self
1079                     .diagnostic_metadata
1080                     .current_type_ascription
1081                     .last()
1082                     .map(|sp| {
1083                         self.r
1084                             .session
1085                             .parse_sess
1086                             .type_ascription_path_suggestions
1087                             .borrow()
1088                             .contains(&sp)
1089                     })
1090                     .unwrap_or(false)
1091                 {
1092                     err.downgrade_to_delayed_bug();
1093                     // We already suggested changing `:` into `::` during parsing.
1094                     return false;
1095                 }
1096
1097                 self.suggest_using_enum_variant(err, source, def_id, span);
1098             }
1099             (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
1100                 let (ctor_def, ctor_vis, fields) =
1101                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
1102                         if let PathSource::Expr(Some(parent)) = source {
1103                             if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
1104                                 bad_struct_syntax_suggestion(def_id);
1105                                 return true;
1106                             }
1107                         }
1108                         struct_ctor
1109                     } else {
1110                         bad_struct_syntax_suggestion(def_id);
1111                         return true;
1112                     };
1113
1114                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
1115                 if !is_expected(ctor_def) || is_accessible {
1116                     return true;
1117                 }
1118
1119                 let field_spans = match source {
1120                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
1121                     PathSource::TupleStruct(_, pattern_spans) => {
1122                         err.set_primary_message(
1123                             "cannot match against a tuple struct which contains private fields",
1124                         );
1125
1126                         // Use spans of the tuple struct pattern.
1127                         Some(Vec::from(pattern_spans))
1128                     }
1129                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
1130                     _ if source.is_call() => {
1131                         err.set_primary_message(
1132                             "cannot initialize a tuple struct which contains private fields",
1133                         );
1134
1135                         // Use spans of the tuple struct definition.
1136                         self.r
1137                             .field_names
1138                             .get(&def_id)
1139                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
1140                     }
1141                     _ => None,
1142                 };
1143
1144                 if let Some(spans) =
1145                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
1146                 {
1147                     let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
1148                         .filter(|(vis, _)| {
1149                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
1150                         })
1151                         .map(|(_, span)| *span)
1152                         .collect();
1153
1154                     if non_visible_spans.len() > 0 {
1155                         let mut m: MultiSpan = non_visible_spans.clone().into();
1156                         non_visible_spans
1157                             .into_iter()
1158                             .for_each(|s| m.push_span_label(s, "private field".to_string()));
1159                         err.span_note(m, "constructor is not visible here due to private fields");
1160                     }
1161
1162                     return true;
1163                 }
1164
1165                 err.span_label(
1166                     span,
1167                     "constructor is not visible here due to private fields".to_string(),
1168                 );
1169             }
1170             (
1171                 Res::Def(
1172                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
1173                     def_id,
1174                 ),
1175                 _,
1176             ) if ns == ValueNS => {
1177                 bad_struct_syntax_suggestion(def_id);
1178             }
1179             (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
1180                 match source {
1181                     PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1182                         let span = find_span(&source, err);
1183                         if let Some(span) = self.def_span(def_id) {
1184                             err.span_label(span, &format!("`{}` defined here", path_str));
1185                         }
1186                         err.span_suggestion(
1187                             span,
1188                             "use this syntax instead",
1189                             path_str.to_string(),
1190                             Applicability::MaybeIncorrect,
1191                         );
1192                     }
1193                     _ => return false,
1194                 }
1195             }
1196             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
1197                 if let Some(span) = self.def_span(def_id) {
1198                     err.span_label(span, &format!("`{}` defined here", path_str));
1199                 }
1200                 let fields = self.r.field_names.get(&def_id).map_or_else(
1201                     || "/* fields */".to_string(),
1202                     |fields| vec!["_"; fields.len()].join(", "),
1203                 );
1204                 err.span_suggestion(
1205                     span,
1206                     "use the tuple variant pattern syntax instead",
1207                     format!("{}({})", path_str, fields),
1208                     Applicability::HasPlaceholders,
1209                 );
1210             }
1211             (Res::SelfTy { .. }, _) if ns == ValueNS => {
1212                 err.span_label(span, fallback_label);
1213                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1214             }
1215             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1216                 err.note("can't use a type alias as a constructor");
1217             }
1218             _ => return false,
1219         }
1220         true
1221     }
1222
1223     /// Given the target `ident` and `kind`, search for the similarly named associated item
1224     /// in `self.current_trait_ref`.
1225     pub(crate) fn find_similarly_named_assoc_item(
1226         &mut self,
1227         ident: Symbol,
1228         kind: &AssocItemKind,
1229     ) -> Option<Symbol> {
1230         let (module, _) = self.current_trait_ref.as_ref()?;
1231         if ident == kw::Underscore {
1232             // We do nothing for `_`.
1233             return None;
1234         }
1235
1236         let resolutions = self.r.resolutions(module);
1237         let targets = resolutions
1238             .borrow()
1239             .iter()
1240             .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
1241             .filter(|(_, res)| match (kind, res) {
1242                 (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
1243                 (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
1244                 (AssocItemKind::TyAlias(..), Res::Def(DefKind::AssocTy, _)) => true,
1245                 _ => false,
1246             })
1247             .map(|(key, _)| key.ident.name)
1248             .collect::<Vec<_>>();
1249
1250         find_best_match_for_name(&targets, ident, None)
1251     }
1252
1253     fn lookup_assoc_candidate<FilterFn>(
1254         &mut self,
1255         ident: Ident,
1256         ns: Namespace,
1257         filter_fn: FilterFn,
1258     ) -> Option<AssocSuggestion>
1259     where
1260         FilterFn: Fn(Res) -> bool,
1261     {
1262         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1263             match t.kind {
1264                 TyKind::Path(None, _) => Some(t.id),
1265                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1266                 // This doesn't handle the remaining `Ty` variants as they are not
1267                 // that commonly the self_type, it might be interesting to provide
1268                 // support for those in future.
1269                 _ => None,
1270             }
1271         }
1272
1273         // Fields are generally expected in the same contexts as locals.
1274         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1275             if let Some(node_id) =
1276                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1277             {
1278                 // Look for a field with the same name in the current self_type.
1279                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1280                     match resolution.base_res() {
1281                         Res::Def(DefKind::Struct | DefKind::Union, did)
1282                             if resolution.unresolved_segments() == 0 =>
1283                         {
1284                             if let Some(field_names) = self.r.field_names.get(&did) {
1285                                 if field_names
1286                                     .iter()
1287                                     .any(|&field_name| ident.name == field_name.node)
1288                                 {
1289                                     return Some(AssocSuggestion::Field);
1290                                 }
1291                             }
1292                         }
1293                         _ => {}
1294                     }
1295                 }
1296             }
1297         }
1298
1299         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1300             for assoc_item in items {
1301                 if assoc_item.ident == ident {
1302                     return Some(match &assoc_item.kind {
1303                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1304                         ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
1305                             AssocSuggestion::MethodWithSelf
1306                         }
1307                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn,
1308                         ast::AssocItemKind::TyAlias(..) => AssocSuggestion::AssocType,
1309                         ast::AssocItemKind::MacCall(_) => continue,
1310                     });
1311                 }
1312             }
1313         }
1314
1315         // Look for associated items in the current trait.
1316         if let Some((module, _)) = self.current_trait_ref {
1317             if let Ok(binding) = self.r.maybe_resolve_ident_in_module(
1318                 ModuleOrUniformRoot::Module(module),
1319                 ident,
1320                 ns,
1321                 &self.parent_scope,
1322             ) {
1323                 let res = binding.res();
1324                 if filter_fn(res) {
1325                     if self.r.has_self.contains(&res.def_id()) {
1326                         return Some(AssocSuggestion::MethodWithSelf);
1327                     } else {
1328                         match res {
1329                             Res::Def(DefKind::AssocFn, _) => return Some(AssocSuggestion::AssocFn),
1330                             Res::Def(DefKind::AssocConst, _) => {
1331                                 return Some(AssocSuggestion::AssocConst);
1332                             }
1333                             Res::Def(DefKind::AssocTy, _) => {
1334                                 return Some(AssocSuggestion::AssocType);
1335                             }
1336                             _ => {}
1337                         }
1338                     }
1339                 }
1340             }
1341         }
1342
1343         None
1344     }
1345
1346     fn lookup_typo_candidate(
1347         &mut self,
1348         path: &[Segment],
1349         ns: Namespace,
1350         filter_fn: &impl Fn(Res) -> bool,
1351     ) -> Option<TypoSuggestion> {
1352         let mut names = Vec::new();
1353         if path.len() == 1 {
1354             // Search in lexical scope.
1355             // Walk backwards up the ribs in scope and collect candidates.
1356             for rib in self.ribs[ns].iter().rev() {
1357                 // Locals and type parameters
1358                 for (ident, &res) in &rib.bindings {
1359                     if filter_fn(res) {
1360                         names.push(TypoSuggestion::typo_from_res(ident.name, res));
1361                     }
1362                 }
1363                 // Items in scope
1364                 if let RibKind::ModuleRibKind(module) = rib.kind {
1365                     // Items from this module
1366                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1367
1368                     if let ModuleKind::Block(..) = module.kind {
1369                         // We can see through blocks
1370                     } else {
1371                         // Items from the prelude
1372                         if !module.no_implicit_prelude {
1373                             let extern_prelude = self.r.extern_prelude.clone();
1374                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1375                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
1376                                     |crate_id| {
1377                                         let crate_mod =
1378                                             Res::Def(DefKind::Mod, crate_id.as_def_id());
1379
1380                                         if filter_fn(crate_mod) {
1381                                             Some(TypoSuggestion::typo_from_res(
1382                                                 ident.name, crate_mod,
1383                                             ))
1384                                         } else {
1385                                             None
1386                                         }
1387                                     },
1388                                 )
1389                             }));
1390
1391                             if let Some(prelude) = self.r.prelude {
1392                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
1393                             }
1394                         }
1395                         break;
1396                     }
1397                 }
1398             }
1399             // Add primitive types to the mix
1400             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1401                 names.extend(PrimTy::ALL.iter().map(|prim_ty| {
1402                     TypoSuggestion::typo_from_res(prim_ty.name(), Res::PrimTy(*prim_ty))
1403                 }))
1404             }
1405         } else {
1406             // Search in module.
1407             let mod_path = &path[..path.len() - 1];
1408             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1409                 self.resolve_path(mod_path, Some(TypeNS), None)
1410             {
1411                 self.r.add_module_candidates(module, &mut names, &filter_fn);
1412             }
1413         }
1414
1415         let name = path[path.len() - 1].ident.name;
1416         // Make sure error reporting is deterministic.
1417         names.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
1418
1419         match find_best_match_for_name(
1420             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1421             name,
1422             None,
1423         ) {
1424             Some(found) if found != name => {
1425                 names.into_iter().find(|suggestion| suggestion.candidate == found)
1426             }
1427             _ => None,
1428         }
1429     }
1430
1431     // Returns the name of the Rust type approximately corresponding to
1432     // a type name in another programming language.
1433     fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
1434         let name = path[path.len() - 1].ident.as_str();
1435         // Common Java types
1436         Some(match name {
1437             "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
1438             "short" => sym::i16,
1439             "boolean" => sym::bool,
1440             "int" => sym::i32,
1441             "long" => sym::i64,
1442             "float" => sym::f32,
1443             "double" => sym::f64,
1444             _ => return None,
1445         })
1446     }
1447
1448     /// Only used in a specific case of type ascription suggestions
1449     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1450         let sm = self.r.session.source_map();
1451         start.to(sm.next_point(start))
1452     }
1453
1454     fn type_ascription_suggestion(&self, err: &mut Diagnostic, base_span: Span) -> bool {
1455         let sm = self.r.session.source_map();
1456         let base_snippet = sm.span_to_snippet(base_span);
1457         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1458             if let Ok(snippet) = sm.span_to_snippet(sp) {
1459                 let len = snippet.trim_end().len() as u32;
1460                 if snippet.trim() == ":" {
1461                     let colon_sp =
1462                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1463                     let mut show_label = true;
1464                     if sm.is_multiline(sp) {
1465                         err.span_suggestion_short(
1466                             colon_sp,
1467                             "maybe you meant to write `;` here",
1468                             ";".to_string(),
1469                             Applicability::MaybeIncorrect,
1470                         );
1471                     } else {
1472                         let after_colon_sp =
1473                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1474                         if snippet.len() == 1 {
1475                             // `foo:bar`
1476                             err.span_suggestion(
1477                                 colon_sp,
1478                                 "maybe you meant to write a path separator here",
1479                                 "::".to_string(),
1480                                 Applicability::MaybeIncorrect,
1481                             );
1482                             show_label = false;
1483                             if !self
1484                                 .r
1485                                 .session
1486                                 .parse_sess
1487                                 .type_ascription_path_suggestions
1488                                 .borrow_mut()
1489                                 .insert(colon_sp)
1490                             {
1491                                 err.downgrade_to_delayed_bug();
1492                             }
1493                         }
1494                         if let Ok(base_snippet) = base_snippet {
1495                             let mut sp = after_colon_sp;
1496                             for _ in 0..100 {
1497                                 // Try to find an assignment
1498                                 sp = sm.next_point(sp);
1499                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
1500                                 match snippet {
1501                                     Ok(ref x) if x.as_str() == "=" => {
1502                                         err.span_suggestion(
1503                                             base_span,
1504                                             "maybe you meant to write an assignment here",
1505                                             format!("let {}", base_snippet),
1506                                             Applicability::MaybeIncorrect,
1507                                         );
1508                                         show_label = false;
1509                                         break;
1510                                     }
1511                                     Ok(ref x) if x.as_str() == "\n" => break,
1512                                     Err(_) => break,
1513                                     Ok(_) => {}
1514                                 }
1515                             }
1516                         }
1517                     }
1518                     if show_label {
1519                         err.span_label(
1520                             base_span,
1521                             "expecting a type here because of type ascription",
1522                         );
1523                     }
1524                     return show_label;
1525                 }
1526             }
1527         }
1528         false
1529     }
1530
1531     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1532         let mut result = None;
1533         let mut seen_modules = FxHashSet::default();
1534         let mut worklist = vec![(self.r.graph_root, Vec::new())];
1535
1536         while let Some((in_module, path_segments)) = worklist.pop() {
1537             // abort if the module is already found
1538             if result.is_some() {
1539                 break;
1540             }
1541
1542             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1543                 // abort if the module is already found or if name_binding is private external
1544                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1545                     return;
1546                 }
1547                 if let Some(module) = name_binding.module() {
1548                     // form the path
1549                     let mut path_segments = path_segments.clone();
1550                     path_segments.push(ast::PathSegment::from_ident(ident));
1551                     let module_def_id = module.def_id();
1552                     if module_def_id == def_id {
1553                         let path =
1554                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1555                         result = Some((
1556                             module,
1557                             ImportSuggestion {
1558                                 did: Some(def_id),
1559                                 descr: "module",
1560                                 path,
1561                                 accessible: true,
1562                                 note: None,
1563                             },
1564                         ));
1565                     } else {
1566                         // add the module to the lookup
1567                         if seen_modules.insert(module_def_id) {
1568                             worklist.push((module, path_segments));
1569                         }
1570                     }
1571                 }
1572             });
1573         }
1574
1575         result
1576     }
1577
1578     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1579         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1580             let mut variants = Vec::new();
1581             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1582                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1583                     let mut segms = enum_import_suggestion.path.segments.clone();
1584                     segms.push(ast::PathSegment::from_ident(ident));
1585                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1586                     variants.push((path, def_id, kind));
1587                 }
1588             });
1589             variants
1590         })
1591     }
1592
1593     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1594     fn suggest_using_enum_variant(
1595         &mut self,
1596         err: &mut Diagnostic,
1597         source: PathSource<'_>,
1598         def_id: DefId,
1599         span: Span,
1600     ) {
1601         let Some(variants) = self.collect_enum_ctors(def_id) else {
1602             err.note("you might have meant to use one of the enum's variants");
1603             return;
1604         };
1605
1606         let suggest_only_tuple_variants =
1607             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1608         if suggest_only_tuple_variants {
1609             // Suggest only tuple variants regardless of whether they have fields and do not
1610             // suggest path with added parentheses.
1611             let suggestable_variants = variants
1612                 .iter()
1613                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1614                 .map(|(variant, ..)| path_names_to_string(variant))
1615                 .collect::<Vec<_>>();
1616
1617             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1618
1619             let source_msg = if source.is_call() {
1620                 "to construct"
1621             } else if matches!(source, PathSource::TupleStruct(..)) {
1622                 "to match against"
1623             } else {
1624                 unreachable!()
1625             };
1626
1627             if !suggestable_variants.is_empty() {
1628                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1629                     format!("try {} the enum's variant", source_msg)
1630                 } else {
1631                     format!("try {} one of the enum's variants", source_msg)
1632                 };
1633
1634                 err.span_suggestions(
1635                     span,
1636                     &msg,
1637                     suggestable_variants.into_iter(),
1638                     Applicability::MaybeIncorrect,
1639                 );
1640             }
1641
1642             // If the enum has no tuple variants..
1643             if non_suggestable_variant_count == variants.len() {
1644                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1645             }
1646
1647             // If there are also non-tuple variants..
1648             if non_suggestable_variant_count == 1 {
1649                 err.help(&format!(
1650                     "you might have meant {} the enum's non-tuple variant",
1651                     source_msg
1652                 ));
1653             } else if non_suggestable_variant_count >= 1 {
1654                 err.help(&format!(
1655                     "you might have meant {} one of the enum's non-tuple variants",
1656                     source_msg
1657                 ));
1658             }
1659         } else {
1660             let needs_placeholder = |def_id: DefId, kind: CtorKind| {
1661                 let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
1662                 match kind {
1663                     CtorKind::Const => false,
1664                     CtorKind::Fn | CtorKind::Fictive if has_no_fields => false,
1665                     _ => true,
1666                 }
1667             };
1668
1669             let mut suggestable_variants = variants
1670                 .iter()
1671                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1672                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1673                 .map(|(variant, kind)| match kind {
1674                     CtorKind::Const => variant,
1675                     CtorKind::Fn => format!("({}())", variant),
1676                     CtorKind::Fictive => format!("({} {{}})", variant),
1677                 })
1678                 .collect::<Vec<_>>();
1679
1680             if !suggestable_variants.is_empty() {
1681                 let msg = if suggestable_variants.len() == 1 {
1682                     "you might have meant to use the following enum variant"
1683                 } else {
1684                     "you might have meant to use one of the following enum variants"
1685                 };
1686
1687                 err.span_suggestions(
1688                     span,
1689                     msg,
1690                     suggestable_variants.drain(..),
1691                     Applicability::MaybeIncorrect,
1692                 );
1693             }
1694
1695             let suggestable_variants_with_placeholders = variants
1696                 .iter()
1697                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
1698                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1699                 .filter_map(|(variant, kind)| match kind {
1700                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
1701                     CtorKind::Fictive => Some(format!("({} {{ /* fields */ }})", variant)),
1702                     _ => None,
1703                 })
1704                 .collect::<Vec<_>>();
1705
1706             if !suggestable_variants_with_placeholders.is_empty() {
1707                 let msg = match (
1708                     suggestable_variants.is_empty(),
1709                     suggestable_variants_with_placeholders.len(),
1710                 ) {
1711                     (true, 1) => "the following enum variant is available",
1712                     (true, _) => "the following enum variants are available",
1713                     (false, 1) => "alternatively, the following enum variant is available",
1714                     (false, _) => "alternatively, the following enum variants are also available",
1715                 };
1716
1717                 err.span_suggestions(
1718                     span,
1719                     msg,
1720                     suggestable_variants_with_placeholders.into_iter(),
1721                     Applicability::HasPlaceholders,
1722                 );
1723             }
1724         };
1725
1726         if def_id.is_local() {
1727             if let Some(span) = self.def_span(def_id) {
1728                 err.span_note(span, "the enum is defined here");
1729             }
1730         }
1731     }
1732
1733     pub(crate) fn report_missing_type_error(
1734         &self,
1735         path: &[Segment],
1736     ) -> Option<(Span, &'static str, String, Applicability)> {
1737         let (ident, span) = match path {
1738             [segment] if !segment.has_generic_args => {
1739                 (segment.ident.to_string(), segment.ident.span)
1740             }
1741             _ => return None,
1742         };
1743         let mut iter = ident.chars().map(|c| c.is_uppercase());
1744         let single_uppercase_char =
1745             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1746         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1747             return None;
1748         }
1749         match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
1750             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
1751                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1752             }
1753             (
1754                 Some(Item {
1755                     kind:
1756                         kind @ ItemKind::Fn(..)
1757                         | kind @ ItemKind::Enum(..)
1758                         | kind @ ItemKind::Struct(..)
1759                         | kind @ ItemKind::Union(..),
1760                     ..
1761                 }),
1762                 true, _
1763             )
1764             // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
1765             | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
1766             | (Some(Item { kind, .. }), false, _) => {
1767                 // Likely missing type parameter.
1768                 if let Some(generics) = kind.generics() {
1769                     if span.overlaps(generics.span) {
1770                         // Avoid the following:
1771                         // error[E0405]: cannot find trait `A` in this scope
1772                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1773                         //   |
1774                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1775                         //   |           ^- help: you might be missing a type parameter: `, A`
1776                         //   |           |
1777                         //   |           not found in this scope
1778                         return None;
1779                     }
1780                     let msg = "you might be missing a type parameter";
1781                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1782                         let span = if let [.., bound] = &param.bounds[..] {
1783                             bound.span()
1784                         } else if let GenericParam {
1785                             kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
1786                         } = param {
1787                             default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
1788                         } else {
1789                             param.ident.span
1790                         };
1791                         (span, format!(", {}", ident))
1792                     } else {
1793                         (generics.span, format!("<{}>", ident))
1794                     };
1795                     // Do not suggest if this is coming from macro expansion.
1796                     if span.can_be_used_for_suggestions() {
1797                         return Some((
1798                             span.shrink_to_hi(),
1799                             msg,
1800                             sugg,
1801                             Applicability::MaybeIncorrect,
1802                         ));
1803                     }
1804                 }
1805             }
1806             _ => {}
1807         }
1808         None
1809     }
1810
1811     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1812     /// optionally returning the closest match and whether it is reachable.
1813     pub(crate) fn suggestion_for_label_in_rib(
1814         &self,
1815         rib_index: usize,
1816         label: Ident,
1817     ) -> Option<LabelSuggestion> {
1818         // Are ribs from this `rib_index` within scope?
1819         let within_scope = self.is_label_valid_from_rib(rib_index);
1820
1821         let rib = &self.label_ribs[rib_index];
1822         let names = rib
1823             .bindings
1824             .iter()
1825             .filter(|(id, _)| id.span.ctxt() == label.span.ctxt())
1826             .map(|(id, _)| id.name)
1827             .collect::<Vec<Symbol>>();
1828
1829         find_best_match_for_name(&names, label.name, None).map(|symbol| {
1830             // Upon finding a similar name, get the ident that it was from - the span
1831             // contained within helps make a useful diagnostic. In addition, determine
1832             // whether this candidate is within scope.
1833             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1834             (*ident, within_scope)
1835         })
1836     }
1837
1838     pub(crate) fn maybe_report_lifetime_uses(
1839         &mut self,
1840         generics_span: Span,
1841         params: &[ast::GenericParam],
1842     ) {
1843         for (param_index, param) in params.iter().enumerate() {
1844             let GenericParamKind::Lifetime = param.kind else { continue };
1845
1846             let def_id = self.r.local_def_id(param.id);
1847
1848             let use_set = self.lifetime_uses.remove(&def_id);
1849             debug!(
1850                 "Use set for {:?}({:?} at {:?}) is {:?}",
1851                 def_id, param.ident, param.ident.span, use_set
1852             );
1853
1854             let deletion_span = || {
1855                 if params.len() == 1 {
1856                     // if sole lifetime, remove the entire `<>` brackets
1857                     generics_span
1858                 } else if param_index == 0 {
1859                     // if removing within `<>` brackets, we also want to
1860                     // delete a leading or trailing comma as appropriate
1861                     param.span().to(params[param_index + 1].span().shrink_to_lo())
1862                 } else {
1863                     // if removing within `<>` brackets, we also want to
1864                     // delete a leading or trailing comma as appropriate
1865                     params[param_index - 1].span().shrink_to_hi().to(param.span())
1866                 }
1867             };
1868             match use_set {
1869                 Some(LifetimeUseSet::Many) => {}
1870                 Some(LifetimeUseSet::One { use_span, use_ctxt }) => {
1871                     debug!(?param.ident, ?param.ident.span, ?use_span);
1872
1873                     let elidable = matches!(use_ctxt, LifetimeCtxt::Rptr);
1874
1875                     let deletion_span = deletion_span();
1876                     self.r.lint_buffer.buffer_lint_with_diagnostic(
1877                         lint::builtin::SINGLE_USE_LIFETIMES,
1878                         param.id,
1879                         param.ident.span,
1880                         &format!("lifetime parameter `{}` only used once", param.ident),
1881                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
1882                             param_span: param.ident.span,
1883                             use_span: Some((use_span, elidable)),
1884                             deletion_span,
1885                         },
1886                     );
1887                 }
1888                 None => {
1889                     debug!(?param.ident, ?param.ident.span);
1890
1891                     let deletion_span = deletion_span();
1892                     self.r.lint_buffer.buffer_lint_with_diagnostic(
1893                         lint::builtin::UNUSED_LIFETIMES,
1894                         param.id,
1895                         param.ident.span,
1896                         &format!("lifetime parameter `{}` never used", param.ident),
1897                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
1898                             param_span: param.ident.span,
1899                             use_span: None,
1900                             deletion_span,
1901                         },
1902                     );
1903                 }
1904             }
1905         }
1906     }
1907
1908     pub(crate) fn emit_undeclared_lifetime_error(
1909         &self,
1910         lifetime_ref: &ast::Lifetime,
1911         outer_lifetime_ref: Option<Ident>,
1912     ) {
1913         debug_assert_ne!(lifetime_ref.ident.name, kw::UnderscoreLifetime);
1914         let mut err = if let Some(outer) = outer_lifetime_ref {
1915             let mut err = struct_span_err!(
1916                 self.r.session,
1917                 lifetime_ref.ident.span,
1918                 E0401,
1919                 "can't use generic parameters from outer item",
1920             );
1921             err.span_label(lifetime_ref.ident.span, "use of generic parameter from outer item");
1922             err.span_label(outer.span, "lifetime parameter from outer item");
1923             err
1924         } else {
1925             let mut err = struct_span_err!(
1926                 self.r.session,
1927                 lifetime_ref.ident.span,
1928                 E0261,
1929                 "use of undeclared lifetime name `{}`",
1930                 lifetime_ref.ident
1931             );
1932             err.span_label(lifetime_ref.ident.span, "undeclared lifetime");
1933             err
1934         };
1935         let mut suggest_note = true;
1936
1937         for rib in self.lifetime_ribs.iter().rev() {
1938             match rib.kind {
1939                 LifetimeRibKind::Generics { binder: _, span, kind } => {
1940                     if !span.can_be_used_for_suggestions() && suggest_note {
1941                         suggest_note = false; // Avoid displaying the same help multiple times.
1942                         err.span_label(
1943                             span,
1944                             &format!(
1945                                 "lifetime `{}` is missing in item created through this procedural macro",
1946                                 lifetime_ref.ident,
1947                             ),
1948                         );
1949                         continue;
1950                     }
1951
1952                     let higher_ranked = matches!(
1953                         kind,
1954                         LifetimeBinderKind::BareFnType
1955                             | LifetimeBinderKind::PolyTrait
1956                             | LifetimeBinderKind::WhereBound
1957                     );
1958                     let (span, sugg) = if span.is_empty() {
1959                         let sugg = format!(
1960                             "{}<{}>{}",
1961                             if higher_ranked { "for" } else { "" },
1962                             lifetime_ref.ident,
1963                             if higher_ranked { " " } else { "" },
1964                         );
1965                         (span, sugg)
1966                     } else {
1967                         let span =
1968                             self.r.session.source_map().span_through_char(span, '<').shrink_to_hi();
1969                         let sugg = format!("{}, ", lifetime_ref.ident);
1970                         (span, sugg)
1971                     };
1972                     if higher_ranked {
1973                         err.span_suggestion(
1974                             span,
1975                             &format!(
1976                                 "consider making the {} lifetime-generic with a new `{}` lifetime",
1977                                 kind.descr(),
1978                                 lifetime_ref
1979                             ),
1980                             sugg,
1981                             Applicability::MaybeIncorrect,
1982                         );
1983                         err.note_once(
1984                             "for more information on higher-ranked polymorphism, visit \
1985                              https://doc.rust-lang.org/nomicon/hrtb.html",
1986                         );
1987                     } else {
1988                         err.span_suggestion(
1989                             span,
1990                             &format!("consider introducing lifetime `{}` here", lifetime_ref.ident),
1991                             sugg,
1992                             Applicability::MaybeIncorrect,
1993                         );
1994                     }
1995                 }
1996                 LifetimeRibKind::Item => break,
1997                 _ => {}
1998             }
1999         }
2000
2001         err.emit();
2002     }
2003
2004     pub(crate) fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &ast::Lifetime) {
2005         struct_span_err!(
2006             self.r.session,
2007             lifetime_ref.ident.span,
2008             E0771,
2009             "use of non-static lifetime `{}` in const generic",
2010             lifetime_ref.ident
2011         )
2012         .note(
2013             "for more information, see issue #74052 \
2014             <https://github.com/rust-lang/rust/issues/74052>",
2015         )
2016         .emit();
2017     }
2018
2019     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
2020     /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
2021     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
2022     pub(crate) fn maybe_emit_forbidden_non_static_lifetime_error(
2023         &self,
2024         lifetime_ref: &ast::Lifetime,
2025     ) {
2026         let feature_active = self.r.session.features_untracked().generic_const_exprs;
2027         if !feature_active {
2028             feature_err(
2029                 &self.r.session.parse_sess,
2030                 sym::generic_const_exprs,
2031                 lifetime_ref.ident.span,
2032                 "a non-static lifetime is not allowed in a `const`",
2033             )
2034             .emit();
2035         }
2036     }
2037 }
2038
2039 impl<'tcx> LifetimeContext<'_, 'tcx> {
2040     pub(crate) fn report_missing_lifetime_specifiers(
2041         &self,
2042         spans: Vec<Span>,
2043         count: usize,
2044     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
2045         struct_span_err!(
2046             self.tcx.sess,
2047             spans,
2048             E0106,
2049             "missing lifetime specifier{}",
2050             pluralize!(count)
2051         )
2052     }
2053
2054     /// Returns whether to add `'static` lifetime to the suggested lifetime list.
2055     pub(crate) fn report_elision_failure(
2056         &mut self,
2057         diag: &mut Diagnostic,
2058         params: &[ElisionFailureInfo],
2059     ) -> bool {
2060         let mut m = String::new();
2061         let len = params.len();
2062
2063         let elided_params: Vec<_> =
2064             params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2065
2066         let elided_len = elided_params.len();
2067
2068         for (i, info) in elided_params.into_iter().enumerate() {
2069             let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions, span } =
2070                 info;
2071
2072             diag.span_label(span, "");
2073             let help_name = if let Some(ident) =
2074                 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2075             {
2076                 format!("`{}`", ident)
2077             } else {
2078                 format!("argument {}", index + 1)
2079             };
2080
2081             m.push_str(
2082                 &(if n == 1 {
2083                     help_name
2084                 } else {
2085                     format!(
2086                         "one of {}'s {} {}lifetimes",
2087                         help_name,
2088                         n,
2089                         if have_bound_regions { "free " } else { "" }
2090                     )
2091                 })[..],
2092             );
2093
2094             if elided_len == 2 && i == 0 {
2095                 m.push_str(" or ");
2096             } else if i + 2 == elided_len {
2097                 m.push_str(", or ");
2098             } else if i != elided_len - 1 {
2099                 m.push_str(", ");
2100             }
2101         }
2102
2103         if len == 0 {
2104             diag.help(
2105                 "this function's return type contains a borrowed value, \
2106                  but there is no value for it to be borrowed from",
2107             );
2108             true
2109         } else if elided_len == 0 {
2110             diag.help(
2111                 "this function's return type contains a borrowed value with \
2112                  an elided lifetime, but the lifetime cannot be derived from \
2113                  the arguments",
2114             );
2115             true
2116         } else if elided_len == 1 {
2117             diag.help(&format!(
2118                 "this function's return type contains a borrowed value, \
2119                  but the signature does not say which {} it is borrowed from",
2120                 m
2121             ));
2122             false
2123         } else {
2124             diag.help(&format!(
2125                 "this function's return type contains a borrowed value, \
2126                  but the signature does not say whether it is borrowed from {}",
2127                 m
2128             ));
2129             false
2130         }
2131     }
2132
2133     pub(crate) fn is_trait_ref_fn_scope(
2134         &mut self,
2135         trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
2136     ) -> bool {
2137         if let def::Res::Def(_, did) = trait_ref.trait_ref.path.res {
2138             if [
2139                 self.tcx.lang_items().fn_once_trait(),
2140                 self.tcx.lang_items().fn_trait(),
2141                 self.tcx.lang_items().fn_mut_trait(),
2142             ]
2143             .contains(&Some(did))
2144             {
2145                 let (span, span_type) = match &trait_ref.bound_generic_params {
2146                     [] => (trait_ref.span.shrink_to_lo(), ForLifetimeSpanType::BoundEmpty),
2147                     [.., bound] => (bound.span.shrink_to_hi(), ForLifetimeSpanType::BoundTail),
2148                 };
2149                 self.missing_named_lifetime_spots
2150                     .push(MissingLifetimeSpot::HigherRanked { span, span_type });
2151                 return true;
2152             }
2153         };
2154         false
2155     }
2156
2157     pub(crate) fn add_missing_lifetime_specifiers_label(
2158         &self,
2159         err: &mut Diagnostic,
2160         mut spans_with_counts: Vec<(Span, usize)>,
2161         lifetime_names: &FxHashSet<Symbol>,
2162         lifetime_spans: Vec<Span>,
2163         params: &[ElisionFailureInfo],
2164     ) {
2165         let snippets: Vec<Option<String>> = spans_with_counts
2166             .iter()
2167             .map(|(span, _)| self.tcx.sess.source_map().span_to_snippet(*span).ok())
2168             .collect();
2169
2170         // Empty generics are marked with a span of "<", but since from now on
2171         // that information is in the snippets it can be removed from the spans.
2172         for ((span, _), snippet) in spans_with_counts.iter_mut().zip(&snippets) {
2173             if snippet.as_deref() == Some("<") {
2174                 *span = span.shrink_to_hi();
2175             }
2176         }
2177
2178         for &(span, count) in &spans_with_counts {
2179             err.span_label(
2180                 span,
2181                 format!(
2182                     "expected {} lifetime parameter{}",
2183                     if count == 1 { "named".to_string() } else { count.to_string() },
2184                     pluralize!(count),
2185                 ),
2186             );
2187         }
2188
2189         let suggest_existing =
2190             |err: &mut Diagnostic,
2191              name: &str,
2192              formatters: Vec<Option<Box<dyn Fn(&str) -> String>>>| {
2193                 if let Some(MissingLifetimeSpot::HigherRanked { span: for_span, span_type }) =
2194                     self.missing_named_lifetime_spots.iter().rev().next()
2195                 {
2196                     // When we have `struct S<'a>(&'a dyn Fn(&X) -> &X);` we want to not only suggest
2197                     // using `'a`, but also introduce the concept of HRLTs by suggesting
2198                     // `struct S<'a>(&'a dyn for<'b> Fn(&X) -> &'b X);`. (#72404)
2199                     let mut introduce_suggestion = vec![];
2200
2201                     let a_to_z_repeat_n = |n| {
2202                         (b'a'..=b'z').map(move |c| {
2203                             let mut s = '\''.to_string();
2204                             s.extend(std::iter::repeat(char::from(c)).take(n));
2205                             s
2206                         })
2207                     };
2208
2209                     // If all single char lifetime names are present, we wrap around and double the chars.
2210                     let lt_name = (1..)
2211                         .flat_map(a_to_z_repeat_n)
2212                         .find(|lt| !lifetime_names.contains(&Symbol::intern(&lt)))
2213                         .unwrap();
2214                     let msg = format!(
2215                         "consider making the {} lifetime-generic with a new `{}` lifetime",
2216                         span_type.descr(),
2217                         lt_name,
2218                     );
2219                     err.note(
2220                         "for more information on higher-ranked polymorphism, visit \
2221                     https://doc.rust-lang.org/nomicon/hrtb.html",
2222                     );
2223                     let for_sugg = span_type.suggestion(&lt_name);
2224                     for param in params {
2225                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span)
2226                         {
2227                             if snippet.starts_with('&') && !snippet.starts_with("&'") {
2228                                 introduce_suggestion
2229                                     .push((param.span, format!("&{} {}", lt_name, &snippet[1..])));
2230                             } else if let Some(stripped) = snippet.strip_prefix("&'_ ") {
2231                                 introduce_suggestion
2232                                     .push((param.span, format!("&{} {}", lt_name, stripped)));
2233                             }
2234                         }
2235                     }
2236                     introduce_suggestion.push((*for_span, for_sugg));
2237                     for ((span, _), formatter) in spans_with_counts.iter().zip(formatters.iter()) {
2238                         if let Some(formatter) = formatter {
2239                             introduce_suggestion.push((*span, formatter(&lt_name)));
2240                         }
2241                     }
2242                     err.multipart_suggestion_verbose(
2243                         &msg,
2244                         introduce_suggestion,
2245                         Applicability::MaybeIncorrect,
2246                     );
2247                 }
2248
2249                 let spans_suggs: Vec<_> = formatters
2250                     .into_iter()
2251                     .zip(spans_with_counts.iter())
2252                     .filter_map(|(formatter, (span, _))| {
2253                         if let Some(formatter) = formatter {
2254                             Some((*span, formatter(name)))
2255                         } else {
2256                             None
2257                         }
2258                     })
2259                     .collect();
2260                 if spans_suggs.is_empty() {
2261                     // If all the spans come from macros, we cannot extract snippets and then
2262                     // `formatters` only contains None and `spans_suggs` is empty.
2263                     return;
2264                 }
2265                 err.multipart_suggestion_verbose(
2266                     &format!(
2267                         "consider using the `{}` lifetime",
2268                         lifetime_names.iter().next().unwrap()
2269                     ),
2270                     spans_suggs,
2271                     Applicability::MaybeIncorrect,
2272                 );
2273             };
2274         let suggest_new = |err: &mut Diagnostic, suggs: Vec<Option<String>>| {
2275             for missing in self.missing_named_lifetime_spots.iter().rev() {
2276                 let mut introduce_suggestion = vec![];
2277                 let msg;
2278                 let should_break;
2279                 introduce_suggestion.push(match missing {
2280                     MissingLifetimeSpot::Generics(generics) => {
2281                         if generics.span == DUMMY_SP {
2282                             // Account for malformed generics in the HIR. This shouldn't happen,
2283                             // but if we make a mistake elsewhere, mainly by keeping something in
2284                             // `missing_named_lifetime_spots` that we shouldn't, like associated
2285                             // `const`s or making a mistake in the AST lowering we would provide
2286                             // nonsensical suggestions. Guard against that by skipping these.
2287                             // (#74264)
2288                             continue;
2289                         }
2290                         msg = "consider introducing a named lifetime parameter".to_string();
2291                         should_break = true;
2292                         if let Some(param) = generics.params.iter().find(|p| {
2293                             !matches!(
2294                                 p.kind,
2295                                 hir::GenericParamKind::Type { synthetic: true, .. }
2296                                     | hir::GenericParamKind::Lifetime {
2297                                         kind: hir::LifetimeParamKind::Elided
2298                                     }
2299                             )
2300                         }) {
2301                             (param.span.shrink_to_lo(), "'a, ".to_string())
2302                         } else {
2303                             (generics.span, "<'a>".to_string())
2304                         }
2305                     }
2306                     MissingLifetimeSpot::HigherRanked { span, span_type } => {
2307                         msg = format!(
2308                             "consider making the {} lifetime-generic with a new `'a` lifetime",
2309                             span_type.descr(),
2310                         );
2311                         should_break = false;
2312                         err.note(
2313                             "for more information on higher-ranked polymorphism, visit \
2314                             https://doc.rust-lang.org/nomicon/hrtb.html",
2315                         );
2316                         (*span, span_type.suggestion("'a"))
2317                     }
2318                     MissingLifetimeSpot::Static => {
2319                         let mut spans_suggs = Vec::new();
2320                         for ((span, count), snippet) in
2321                             spans_with_counts.iter().copied().zip(snippets.iter())
2322                         {
2323                             let (span, sugg) = match snippet.as_deref() {
2324                                 Some("&") => (span.shrink_to_hi(), "'static ".to_owned()),
2325                                 Some("'_") => (span, "'static".to_owned()),
2326                                 Some(snippet) if !snippet.ends_with('>') => {
2327                                     if snippet == "" {
2328                                         (
2329                                             span,
2330                                             std::iter::repeat("'static")
2331                                                 .take(count)
2332                                                 .collect::<Vec<_>>()
2333                                                 .join(", "),
2334                                         )
2335                                     } else if snippet == "<" || snippet == "(" {
2336                                         (
2337                                             span.shrink_to_hi(),
2338                                             std::iter::repeat("'static")
2339                                                 .take(count)
2340                                                 .collect::<Vec<_>>()
2341                                                 .join(", "),
2342                                         )
2343                                     } else {
2344                                         (
2345                                             span.shrink_to_hi(),
2346                                             format!(
2347                                                 "<{}>",
2348                                                 std::iter::repeat("'static")
2349                                                     .take(count)
2350                                                     .collect::<Vec<_>>()
2351                                                     .join(", "),
2352                                             ),
2353                                         )
2354                                     }
2355                                 }
2356                                 _ => continue,
2357                             };
2358                             spans_suggs.push((span, sugg.to_string()));
2359                         }
2360                         err.multipart_suggestion_verbose(
2361                             "consider using the `'static` lifetime",
2362                             spans_suggs,
2363                             Applicability::MaybeIncorrect,
2364                         );
2365                         continue;
2366                     }
2367                 });
2368
2369                 struct Lifetime(Span, String);
2370                 impl Lifetime {
2371                     fn is_unnamed(&self) -> bool {
2372                         self.1.starts_with('&') && !self.1.starts_with("&'")
2373                     }
2374                     fn is_underscore(&self) -> bool {
2375                         self.1.starts_with("&'_ ")
2376                     }
2377                     fn is_named(&self) -> bool {
2378                         self.1.starts_with("&'")
2379                     }
2380                     fn suggestion(&self, sugg: String) -> Option<(Span, String)> {
2381                         Some(
2382                             match (
2383                                 self.is_unnamed(),
2384                                 self.is_underscore(),
2385                                 self.is_named(),
2386                                 sugg.starts_with('&'),
2387                             ) {
2388                                 (true, _, _, false) => (self.span_unnamed_borrow(), sugg),
2389                                 (true, _, _, true) => {
2390                                     (self.span_unnamed_borrow(), sugg[1..].to_string())
2391                                 }
2392                                 (_, true, _, false) => {
2393                                     (self.span_underscore_borrow(), sugg.trim().to_string())
2394                                 }
2395                                 (_, true, _, true) => {
2396                                     (self.span_underscore_borrow(), sugg[1..].trim().to_string())
2397                                 }
2398                                 (_, _, true, false) => {
2399                                     (self.span_named_borrow(), sugg.trim().to_string())
2400                                 }
2401                                 (_, _, true, true) => {
2402                                     (self.span_named_borrow(), sugg[1..].trim().to_string())
2403                                 }
2404                                 _ => return None,
2405                             },
2406                         )
2407                     }
2408                     fn span_unnamed_borrow(&self) -> Span {
2409                         let lo = self.0.lo() + BytePos(1);
2410                         self.0.with_lo(lo).with_hi(lo)
2411                     }
2412                     fn span_named_borrow(&self) -> Span {
2413                         let lo = self.0.lo() + BytePos(1);
2414                         self.0.with_lo(lo)
2415                     }
2416                     fn span_underscore_borrow(&self) -> Span {
2417                         let lo = self.0.lo() + BytePos(1);
2418                         let hi = lo + BytePos(2);
2419                         self.0.with_lo(lo).with_hi(hi)
2420                     }
2421                 }
2422
2423                 for param in params {
2424                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
2425                         if let Some((span, sugg)) =
2426                             Lifetime(param.span, snippet).suggestion("'a ".to_string())
2427                         {
2428                             introduce_suggestion.push((span, sugg));
2429                         }
2430                     }
2431                 }
2432                 for (span, sugg) in spans_with_counts.iter().copied().zip(suggs.iter()).filter_map(
2433                     |((span, _), sugg)| match &sugg {
2434                         Some(sugg) => Some((span, sugg.to_string())),
2435                         _ => None,
2436                     },
2437                 ) {
2438                     let (span, sugg) = self
2439                         .tcx
2440                         .sess
2441                         .source_map()
2442                         .span_to_snippet(span)
2443                         .ok()
2444                         .and_then(|snippet| Lifetime(span, snippet).suggestion(sugg.clone()))
2445                         .unwrap_or((span, sugg));
2446                     introduce_suggestion.push((span, sugg.to_string()));
2447                 }
2448                 err.multipart_suggestion_verbose(
2449                     &msg,
2450                     introduce_suggestion,
2451                     Applicability::MaybeIncorrect,
2452                 );
2453                 if should_break {
2454                     break;
2455                 }
2456             }
2457         };
2458
2459         let lifetime_names: Vec<_> = lifetime_names.iter().collect();
2460         match &lifetime_names[..] {
2461             [name] => {
2462                 let mut suggs: Vec<Option<Box<dyn Fn(&str) -> String>>> = Vec::new();
2463                 for (snippet, (_, count)) in snippets.iter().zip(spans_with_counts.iter().copied())
2464                 {
2465                     suggs.push(match snippet.as_deref() {
2466                         Some("&") => Some(Box::new(|name| format!("&{} ", name))),
2467                         Some("'_") => Some(Box::new(|n| n.to_string())),
2468                         Some("") => Some(Box::new(move |n| format!("{}, ", n).repeat(count))),
2469                         Some("<") => Some(Box::new(move |n| {
2470                             std::iter::repeat(n).take(count).collect::<Vec<_>>().join(", ")
2471                         })),
2472                         Some(snippet) if !snippet.ends_with('>') => Some(Box::new(move |name| {
2473                             format!(
2474                                 "{}<{}>",
2475                                 snippet,
2476                                 std::iter::repeat(name.to_string())
2477                                     .take(count)
2478                                     .collect::<Vec<_>>()
2479                                     .join(", ")
2480                             )
2481                         })),
2482                         _ => None,
2483                     });
2484                 }
2485                 suggest_existing(err, name.as_str(), suggs);
2486             }
2487             [] => {
2488                 let mut suggs = Vec::new();
2489                 for (snippet, (_, count)) in
2490                     snippets.iter().cloned().zip(spans_with_counts.iter().copied())
2491                 {
2492                     suggs.push(match snippet.as_deref() {
2493                         Some("&") => Some("&'a ".to_string()),
2494                         Some("'_") => Some("'a".to_string()),
2495                         Some("") => {
2496                             Some(std::iter::repeat("'a, ").take(count).collect::<Vec<_>>().join(""))
2497                         }
2498                         Some("<") => {
2499                             Some(std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", "))
2500                         }
2501                         Some(snippet) => Some(format!(
2502                             "{}<{}>",
2503                             snippet,
2504                             std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", "),
2505                         )),
2506                         None => None,
2507                     });
2508                 }
2509                 suggest_new(err, suggs);
2510             }
2511             lts if lts.len() > 1 => {
2512                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
2513
2514                 let mut spans_suggs: Vec<_> = Vec::new();
2515                 for ((span, _), snippet) in spans_with_counts.iter().copied().zip(snippets.iter()) {
2516                     match snippet.as_deref() {
2517                         Some("") => spans_suggs.push((span, "'lifetime, ".to_string())),
2518                         Some("&") => spans_suggs
2519                             .push((span.with_lo(span.lo() + BytePos(1)), "'lifetime ".to_string())),
2520                         _ => {}
2521                     }
2522                 }
2523
2524                 if spans_suggs.len() > 0 {
2525                     // This happens when we have `Foo<T>` where we point at the space before `T`,
2526                     // but this can be confusing so we give a suggestion with placeholders.
2527                     err.multipart_suggestion_verbose(
2528                         "consider using one of the available lifetimes here",
2529                         spans_suggs,
2530                         Applicability::HasPlaceholders,
2531                     );
2532                 }
2533             }
2534             _ => unreachable!(),
2535         }
2536     }
2537 }