compiler/rustc_resolve/src/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::lifetimes::{ElisionFailureInfo, LifetimeContext};
   3 use crate::late::{AliasPossibility, LateResolutionVisitor, RibKind};
   4 use crate::path_names_to_string;
   5 use crate::{CrateLint, Module, ModuleKind, ModuleOrUniformRoot};
   6 use crate::{PathResult, PathSource, Segment};
   7
   8 use rustc_ast::visit::FnKind;
   9 use rustc_ast::{
  10     self as ast, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind, NodeId, Path, Ty,
  11     TyKind,
  12 };
  13 use rustc_ast_pretty::pprust::path_segment_to_string;
  14 use rustc_data_structures::fx::FxHashSet;
  15 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, SuggestionStyle};
  16 use rustc_hir as hir;
  17 use rustc_hir::def::Namespace::{self, *};
  18 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
  19 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  20 use rustc_hir::PrimTy;
  21 use rustc_session::parse::feature_err;
  22 use rustc_span::edition::Edition;
  23 use rustc_span::hygiene::MacroKind;
  24 use rustc_span::lev_distance::find_best_match_for_name;
  25 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  26 use rustc_span::{BytePos, MultiSpan, Span, DUMMY_SP};
  27
  28 use std::iter;
  29
  30 use tracing::debug;
  31
  32 type Res = def::Res<ast::NodeId>;
  33
  34 /// A field or associated item from self type suggested in case of resolution failure.
  35 enum AssocSuggestion {
  36     Field,
  37     MethodWithSelf,
  38     AssocFn,
  39     AssocType,
  40     AssocConst,
  41 }
  42
  43 impl AssocSuggestion {
  44     fn action(&self) -> &'static str {
  45         match self {
  46             AssocSuggestion::Field => "use the available field",
  47             AssocSuggestion::MethodWithSelf => "call the method with the fully-qualified path",
  48             AssocSuggestion::AssocFn => "call the associated function",
  49             AssocSuggestion::AssocConst => "use the associated `const`",
  50             AssocSuggestion::AssocType => "use the associated type",
  51         }
  52     }
  53 }
  54
  55 crate enum MissingLifetimeSpot<'tcx> {
  56     Generics(&'tcx hir::Generics<'tcx>),
  57     HigherRanked { span: Span, span_type: ForLifetimeSpanType },
  58     Static,
  59 }
  60
  61 crate enum ForLifetimeSpanType {
  62     BoundEmpty,
  63     BoundTail,
  64     TypeEmpty,
  65     TypeTail,
  66 }
  67
  68 impl ForLifetimeSpanType {
  69     crate fn descr(&self) -> &'static str {
  70         match self {
  71             Self::BoundEmpty | Self::BoundTail => "bound",
  72             Self::TypeEmpty | Self::TypeTail => "type",
  73         }
  74     }
  75
  76     crate fn suggestion(&self, sugg: &str) -> String {
  77         match self {
  78             Self::BoundEmpty | Self::TypeEmpty => format!("for<{}> ", sugg),
  79             Self::BoundTail | Self::TypeTail => format!(", {}", sugg),
  80         }
  81     }
  82 }
  83
  84 impl<'tcx> Into<MissingLifetimeSpot<'tcx>> for &'tcx hir::Generics<'tcx> {
  85     fn into(self) -> MissingLifetimeSpot<'tcx> {
  86         MissingLifetimeSpot::Generics(self)
  87     }
  88 }
  89
  90 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  91     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  92 }
  93
  94 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  95     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  96 }
  97
  98 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  99 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
 100     let variant_path = &suggestion.path;
 101     let variant_path_string = path_names_to_string(variant_path);
 102
 103     let path_len = suggestion.path.segments.len();
 104     let enum_path = ast::Path {
 105         span: suggestion.path.span,
 106         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
 107         tokens: None,
 108     };
 109     let enum_path_string = path_names_to_string(&enum_path);
 110
 111     (variant_path_string, enum_path_string)
 112 }
 113
 114 impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 115     fn def_span(&self, def_id: DefId) -> Option<Span> {
 116         match def_id.krate {
 117             LOCAL_CRATE => self.r.opt_span(def_id),
 118             _ => Some(
 119                 self.r
 120                     .session
 121                     .source_map()
 122                     .guess_head_span(self.r.cstore().get_span_untracked(def_id, self.r.session)),
 123             ),
 124         }
 125     }
 126
 127     /// Handles error reporting for `smart_resolve_path_fragment` function.
 128     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 129     pub(crate) fn smart_resolve_report_errors(
 130         &mut self,
 131         path: &[Segment],
 132         span: Span,
 133         source: PathSource<'_>,
 134         res: Option<Res>,
 135     ) -> (DiagnosticBuilder<'a>, Vec<ImportSuggestion>) {
 136         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 137         let ns = source.namespace();
 138         let is_expected = &|res| source.is_expected(res);
 139         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 140
 141         // Make the base error.
 142         let mut expected = source.descr_expected();
 143         let path_str = Segment::names_to_string(path);
 144         let item_str = path.last().unwrap().ident;
 145         let (base_msg, fallback_label, base_span, could_be_expr) = if let Some(res) = res {
 146             (
 147                 format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 148                 format!("not a {}", expected),
 149                 span,
 150                 match res {
 151                     Res::Def(DefKind::Fn, _) => {
 152                         // Verify whether this is a fn call or an Fn used as a type.
 153                         self.r
 154                             .session
 155                             .source_map()
 156                             .span_to_snippet(span)
 157                             .map(|snippet| snippet.ends_with(')'))
 158                             .unwrap_or(false)
 159                     }
 160                     Res::Def(
 161                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 162                         _,
 163                     )
 164                     | Res::SelfCtor(_)
 165                     | Res::PrimTy(_)
 166                     | Res::Local(_) => true,
 167                     _ => false,
 168                 },
 169             )
 170         } else {
 171             let item_span = path.last().unwrap().ident.span;
 172             let (mod_prefix, mod_str) = if path.len() == 1 {
 173                 (String::new(), "this scope".to_string())
 174             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 175                 if self.r.session.edition() > Edition::Edition2015 {
 176                     // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
 177                     // which overrides all other expectations of item type
 178                     expected = "crate";
 179                     (String::new(), "the list of imported crates".to_string())
 180                 } else {
 181                     (String::new(), "the crate root".to_string())
 182                 }
 183             } else if path.len() == 2 && path[0].ident.name == kw::Crate {
 184                 (String::new(), "the crate root".to_string())
 185             } else {
 186                 let mod_path = &path[..path.len() - 1];
 187                 let mod_prefix =
 188                     match self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No) {
 189                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 190                         _ => None,
 191                     }
 192                     .map_or_else(String::new, |res| format!("{} ", res.descr()));
 193                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)))
 194             };
 195             (
 196                 format!("cannot find {} `{}` in {}{}", expected, item_str, mod_prefix, mod_str),
 197                 if path_str == "async" && expected.starts_with("struct") {
 198                     "`async` blocks are only allowed in Rust 2018 or later".to_string()
 199                 } else {
 200                     format!("not found in {}", mod_str)
 201                 },
 202                 item_span,
 203                 false,
 204             )
 205         };
 206
 207         let code = source.error_code(res.is_some());
 208         let mut err = self.r.session.struct_span_err_with_code(base_span, &base_msg, code);
 209
 210         if let Some(span) = self.diagnostic_metadata.current_block_could_be_bare_struct_literal {
 211             err.multipart_suggestion(
 212                 "you might have meant to write a `struct` literal",
 213                 vec![
 214                     (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
 215                     (span.shrink_to_hi(), "}".to_string()),
 216                 ],
 217                 Applicability::HasPlaceholders,
 218             );
 219         }
 220         match (source, self.diagnostic_metadata.in_if_condition) {
 221             (PathSource::Expr(_), Some(Expr { span, kind: ExprKind::Assign(..), .. })) => {
 222                 err.span_suggestion_verbose(
 223                     span.shrink_to_lo(),
 224                     "you might have meant to use pattern matching",
 225                     "let ".to_string(),
 226                     Applicability::MaybeIncorrect,
 227                 );
 228             }
 229             _ => {}
 230         }
 231
 232         let is_assoc_fn = self.self_type_is_available(span);
 233         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 234         if ["this", "my"].contains(&&*item_str.as_str()) && is_assoc_fn {
 235             err.span_suggestion_short(
 236                 span,
 237                 "you might have meant to use `self` here instead",
 238                 "self".to_string(),
 239                 Applicability::MaybeIncorrect,
 240             );
 241             if !self.self_value_is_available(path[0].ident.span, span) {
 242                 if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
 243                     &self.diagnostic_metadata.current_function
 244                 {
 245                     let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
 246                         (param.span.shrink_to_lo(), "&self, ")
 247                     } else {
 248                         (
 249                             self.r
 250                                 .session
 251                                 .source_map()
 252                                 .span_through_char(*fn_span, '(')
 253                                 .shrink_to_hi(),
 254                             "&self",
 255                         )
 256                     };
 257                     err.span_suggestion_verbose(
 258                         span,
 259                         "if you meant to use `self`, you are also missing a `self` receiver \
 260                          argument",
 261                         sugg.to_string(),
 262                         Applicability::MaybeIncorrect,
 263                     );
 264                 }
 265             }
 266         }
 267
 268         // Emit special messages for unresolved `Self` and `self`.
 269         if is_self_type(path, ns) {
 270             err.code(rustc_errors::error_code!(E0411));
 271             err.span_label(
 272                 span,
 273                 "`Self` is only available in impls, traits, and type definitions".to_string(),
 274             );
 275             return (err, Vec::new());
 276         }
 277         if is_self_value(path, ns) {
 278             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 279
 280             err.code(rustc_errors::error_code!(E0424));
 281             err.span_label(span, match source {
 282                 PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed"
 283                                    .to_string(),
 284                 _ => "`self` value is a keyword only available in methods with a `self` parameter"
 285                      .to_string(),
 286             });
 287             if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 288                 // The current function has a `self' parameter, but we were unable to resolve
 289                 // a reference to `self`. This can only happen if the `self` identifier we
 290                 // are resolving came from a different hygiene context.
 291                 if fn_kind.decl().inputs.get(0).map_or(false, |p| p.is_self()) {
 292                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 293                 } else {
 294                     let doesnt = if is_assoc_fn {
 295                         let (span, sugg) = fn_kind
 296                             .decl()
 297                             .inputs
 298                             .get(0)
 299                             .map(|p| (p.span.shrink_to_lo(), "&self, "))
 300                             .unwrap_or_else(|| {
 301                                 (
 302                                     self.r
 303                                         .session
 304                                         .source_map()
 305                                         .span_through_char(*span, '(')
 306                                         .shrink_to_hi(),
 307                                     "&self",
 308                                 )
 309                             });
 310                         err.span_suggestion_verbose(
 311                             span,
 312                             "add a `self` receiver parameter to make the associated `fn` a method",
 313                             sugg.to_string(),
 314                             Applicability::MaybeIncorrect,
 315                         );
 316                         "doesn't"
 317                     } else {
 318                         "can't"
 319                     };
 320                     if let Some(ident) = fn_kind.ident() {
 321                         err.span_label(
 322                             ident.span,
 323                             &format!("this function {} have a `self` parameter", doesnt),
 324                         );
 325                     }
 326                 }
 327             }
 328             return (err, Vec::new());
 329         }
 330
 331         // Try to lookup name in more relaxed fashion for better error reporting.
 332         let ident = path.last().unwrap().ident;
 333         let candidates = self
 334             .r
 335             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 336             .drain(..)
 337             .filter(|ImportSuggestion { did, .. }| {
 338                 match (did, res.and_then(|res| res.opt_def_id())) {
 339                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 340                     _ => true,
 341                 }
 342             })
 343             .collect::<Vec<_>>();
 344         let crate_def_id = DefId::local(CRATE_DEF_INDEX);
 345         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 346             let mut enum_candidates: Vec<_> = self
 347                 .r
 348                 .lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant)
 349                 .into_iter()
 350                 .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 351                 .filter(|(_, enum_ty_path)| !enum_ty_path.starts_with("std::prelude::"))
 352                 .collect();
 353             if !enum_candidates.is_empty() {
 354                 if let (PathSource::Type, Some(span)) =
 355                     (source, self.diagnostic_metadata.current_type_ascription.last())
 356                 {
 357                     if self
 358                         .r
 359                         .session
 360                         .parse_sess
 361                         .type_ascription_path_suggestions
 362                         .borrow()
 363                         .contains(span)
 364                     {
 365                         // Already reported this issue on the lhs of the type ascription.
 366                         err.delay_as_bug();
 367                         return (err, candidates);
 368                     }
 369                 }
 370
 371                 enum_candidates.sort();
 372
 373                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 374                 // (that it's a variant) for E0573 "expected type, found variant".
 375                 let preamble = if res.is_none() {
 376                     let others = match enum_candidates.len() {
 377                         1 => String::new(),
 378                         2 => " and 1 other".to_owned(),
 379                         n => format!(" and {} others", n),
 380                     };
 381                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 382                 } else {
 383                     String::new()
 384                 };
 385                 let msg = format!("{}try using the variant's enum", preamble);
 386
 387                 err.span_suggestions(
 388                     span,
 389                     &msg,
 390                     enum_candidates.into_iter().map(|(_variant_path, enum_ty_path)| enum_ty_path),
 391                     Applicability::MachineApplicable,
 392                 );
 393             }
 394         }
 395         if path.len() == 1 && self.self_type_is_available(span) {
 396             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 397                 let self_is_available = self.self_value_is_available(path[0].ident.span, span);
 398                 match candidate {
 399                     AssocSuggestion::Field => {
 400                         if self_is_available {
 401                             err.span_suggestion(
 402                                 span,
 403                                 "you might have meant to use the available field",
 404                                 format!("self.{}", path_str),
 405                                 Applicability::MachineApplicable,
 406                             );
 407                         } else {
 408                             err.span_label(span, "a field by this name exists in `Self`");
 409                         }
 410                     }
 411                     AssocSuggestion::MethodWithSelf if self_is_available => {
 412                         err.span_suggestion(
 413                             span,
 414                             "you might have meant to call the method",
 415                             format!("self.{}", path_str),
 416                             Applicability::MachineApplicable,
 417                         );
 418                     }
 419                     AssocSuggestion::MethodWithSelf
 420                     | AssocSuggestion::AssocFn
 421                     | AssocSuggestion::AssocConst
 422                     | AssocSuggestion::AssocType => {
 423                         err.span_suggestion(
 424                             span,
 425                             &format!("you might have meant to {}", candidate.action()),
 426                             format!("Self::{}", path_str),
 427                             Applicability::MachineApplicable,
 428                         );
 429                     }
 430                 }
 431                 return (err, candidates);
 432             }
 433
 434             // If the first argument in call is `self` suggest calling a method.
 435             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 436                 let mut args_snippet = String::new();
 437                 if let Some(args_span) = args_span {
 438                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 439                         args_snippet = snippet;
 440                     }
 441                 }
 442
 443                 err.span_suggestion(
 444                     call_span,
 445                     &format!("try calling `{}` as a method", ident),
 446                     format!("self.{}({})", path_str, args_snippet),
 447                     Applicability::MachineApplicable,
 448                 );
 449                 return (err, candidates);
 450             }
 451         }
 452
 453         // Try Levenshtein algorithm.
 454         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected, span);
 455         // Try context-dependent help if relaxed lookup didn't work.
 456         if let Some(res) = res {
 457             if self.smart_resolve_context_dependent_help(
 458                 &mut err,
 459                 span,
 460                 source,
 461                 res,
 462                 &path_str,
 463                 &fallback_label,
 464             ) {
 465                 // We do this to avoid losing a secondary span when we override the main error span.
 466                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 467                 return (err, candidates);
 468             }
 469         }
 470
 471         let is_macro = base_span.from_expansion() && base_span.desugaring_kind().is_none();
 472         if !self.type_ascription_suggestion(&mut err, base_span) {
 473             let mut fallback = false;
 474             if let (
 475                 PathSource::Trait(AliasPossibility::Maybe),
 476                 Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
 477                 false,
 478             ) = (source, res, is_macro)
 479             {
 480                 if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
 481                     fallback = true;
 482                     let spans: Vec<Span> = bounds
 483                         .iter()
 484                         .map(|bound| bound.span())
 485                         .filter(|&sp| sp != base_span)
 486                         .collect();
 487
 488                     let start_span = bounds.iter().map(|bound| bound.span()).next().unwrap();
 489                     // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
 490                     let end_span = bounds.iter().map(|bound| bound.span()).last().unwrap();
 491                     // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
 492                     let last_bound_span = spans.last().cloned().unwrap();
 493                     let mut multi_span: MultiSpan = spans.clone().into();
 494                     for sp in spans {
 495                         let msg = if sp == last_bound_span {
 496                             format!(
 497                                 "...because of {} bound{}",
 498                                 if bounds.len() <= 2 { "this" } else { "these" },
 499                                 if bounds.len() <= 2 { "" } else { "s" },
 500                             )
 501                         } else {
 502                             String::new()
 503                         };
 504                         multi_span.push_span_label(sp, msg);
 505                     }
 506                     multi_span.push_span_label(
 507                         base_span,
 508                         "expected this type to be a trait...".to_string(),
 509                     );
 510                     err.span_help(
 511                         multi_span,
 512                         "`+` is used to constrain a \"trait object\" type with lifetimes or \
 513                          auto-traits; structs and enums can't be bound in that way",
 514                     );
 515                     if bounds.iter().all(|bound| match bound {
 516                         ast::GenericBound::Outlives(_) => true,
 517                         ast::GenericBound::Trait(tr, _) => tr.span == base_span,
 518                     }) {
 519                         let mut sugg = vec![];
 520                         if base_span != start_span {
 521                             sugg.push((start_span.until(base_span), String::new()));
 522                         }
 523                         if base_span != end_span {
 524                             sugg.push((base_span.shrink_to_hi().to(end_span), String::new()));
 525                         }
 526
 527                         err.multipart_suggestion(
 528                             "if you meant to use a type and not a trait here, remove the bounds",
 529                             sugg,
 530                             Applicability::MaybeIncorrect,
 531                         );
 532                     }
 533                 }
 534             }
 535
 536             fallback |= self.restrict_assoc_type_in_where_clause(span, &mut err);
 537
 538             if !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span) {
 539                 fallback = true;
 540                 match self.diagnostic_metadata.current_let_binding {
 541                     Some((pat_sp, Some(ty_sp), None))
 542                         if ty_sp.contains(base_span) && could_be_expr =>
 543                     {
 544                         err.span_suggestion_short(
 545                             pat_sp.between(ty_sp),
 546                             "use `=` if you meant to assign",
 547                             " = ".to_string(),
 548                             Applicability::MaybeIncorrect,
 549                         );
 550                     }
 551                     _ => {}
 552                 }
 553
 554                 // If the trait has a single item (which wasn't matched by Levenshtein), suggest it
 555                 let suggestion = self.get_single_associated_item(&path, span, &source, is_expected);
 556                 self.r.add_typo_suggestion(&mut err, suggestion, ident_span);
 557             }
 558             if fallback {
 559                 // Fallback label.
 560                 err.span_label(base_span, fallback_label);
 561             }
 562         }
 563         if let Some(err_code) = &err.code {
 564             if err_code == &rustc_errors::error_code!(E0425) {
 565                 for label_rib in &self.label_ribs {
 566                     for (label_ident, node_id) in &label_rib.bindings {
 567                         if format!("'{}", ident) == label_ident.to_string() {
 568                             err.span_label(label_ident.span, "a label with a similar name exists");
 569                             if let PathSource::Expr(Some(Expr {
 570                                 kind: ExprKind::Break(None, Some(_)),
 571                                 ..
 572                             })) = source
 573                             {
 574                                 err.span_suggestion(
 575                                     span,
 576                                     "use the similarly named label",
 577                                     label_ident.name.to_string(),
 578                                     Applicability::MaybeIncorrect,
 579                                 );
 580                                 // Do not lint against unused label when we suggest them.
 581                                 self.diagnostic_metadata.unused_labels.remove(node_id);
 582                             }
 583                         }
 584                     }
 585                 }
 586             } else if err_code == &rustc_errors::error_code!(E0412) {
 587                 if let Some(correct) = Self::likely_rust_type(path) {
 588                     err.span_suggestion(
 589                         span,
 590                         "perhaps you intended to use this type",
 591                         correct.to_string(),
 592                         Applicability::MaybeIncorrect,
 593                     );
 594                 }
 595             }
 596         }
 597
 598         (err, candidates)
 599     }
 600
 601     fn get_single_associated_item(
 602         &mut self,
 603         path: &[Segment],
 604         span: Span,
 605         source: &PathSource<'_>,
 606         filter_fn: &impl Fn(Res) -> bool,
 607     ) -> Option<TypoSuggestion> {
 608         if let crate::PathSource::TraitItem(_) = source {
 609             let mod_path = &path[..path.len() - 1];
 610             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 611                 self.resolve_path(mod_path, None, false, span, CrateLint::No)
 612             {
 613                 let resolutions = self.r.resolutions(module).borrow();
 614                 let targets: Vec<_> =
 615                     resolutions
 616                         .iter()
 617                         .filter_map(|(key, resolution)| {
 618                             resolution.borrow().binding.map(|binding| binding.res()).and_then(
 619                                 |res| if filter_fn(res) { Some((key, res)) } else { None },
 620                             )
 621                         })
 622                         .collect();
 623                 if targets.len() == 1 {
 624                     let target = targets[0];
 625                     return Some(TypoSuggestion::single_item_from_res(
 626                         target.0.ident.name,
 627                         target.1,
 628                     ));
 629                 }
 630             }
 631         }
 632         None
 633     }
 634
 635     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
 636     fn restrict_assoc_type_in_where_clause(
 637         &mut self,
 638         span: Span,
 639         err: &mut DiagnosticBuilder<'_>,
 640     ) -> bool {
 641         // Detect that we are actually in a `where` predicate.
 642         let (bounded_ty, bounds, where_span) =
 643             if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 644                 bounded_ty,
 645                 bound_generic_params,
 646                 bounds,
 647                 span,
 648             })) = self.diagnostic_metadata.current_where_predicate
 649             {
 650                 if !bound_generic_params.is_empty() {
 651                     return false;
 652                 }
 653                 (bounded_ty, bounds, span)
 654             } else {
 655                 return false;
 656             };
 657
 658         // Confirm that the target is an associated type.
 659         let (ty, position, path) = if let ast::TyKind::Path(
 660             Some(ast::QSelf { ty, position, .. }),
 661             path,
 662         ) = &bounded_ty.kind
 663         {
 664             // use this to verify that ident is a type param.
 665             let partial_res = if let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
 666                 bounded_ty.id,
 667                 None,
 668                 &Segment::from_path(path),
 669                 Namespace::TypeNS,
 670                 span,
 671                 true,
 672                 CrateLint::No,
 673             ) {
 674                 partial_res
 675             } else {
 676                 return false;
 677             };
 678             if !(matches!(
 679                 partial_res.base_res(),
 680                 hir::def::Res::Def(hir::def::DefKind::AssocTy, _)
 681             ) && partial_res.unresolved_segments() == 0)
 682             {
 683                 return false;
 684             }
 685             (ty, position, path)
 686         } else {
 687             return false;
 688         };
 689
 690         if let ast::TyKind::Path(None, type_param_path) = &ty.peel_refs().kind {
 691             // Confirm that the `SelfTy` is a type parameter.
 692             let partial_res = if let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
 693                 bounded_ty.id,
 694                 None,
 695                 &Segment::from_path(type_param_path),
 696                 Namespace::TypeNS,
 697                 span,
 698                 true,
 699                 CrateLint::No,
 700             ) {
 701                 partial_res
 702             } else {
 703                 return false;
 704             };
 705             if !(matches!(
 706                 partial_res.base_res(),
 707                 hir::def::Res::Def(hir::def::DefKind::TyParam, _)
 708             ) && partial_res.unresolved_segments() == 0)
 709             {
 710                 return false;
 711             }
 712             if let (
 713                 [ast::PathSegment { ident: constrain_ident, args: None, .. }],
 714                 [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
 715             ) = (&type_param_path.segments[..], &bounds[..])
 716             {
 717                 if let [ast::PathSegment { ident, args: None, .. }] =
 718                     &poly_trait_ref.trait_ref.path.segments[..]
 719                 {
 720                     if ident.span == span {
 721                         err.span_suggestion_verbose(
 722                             *where_span,
 723                             &format!("constrain the associated type to `{}`", ident),
 724                             format!(
 725                                 "{}: {}<{} = {}>",
 726                                 self.r
 727                                     .session
 728                                     .source_map()
 729                                     .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
 730                                     .unwrap_or_else(|_| constrain_ident.to_string()),
 731                                 path.segments[..*position]
 732                                     .iter()
 733                                     .map(|segment| path_segment_to_string(segment))
 734                                     .collect::<Vec<_>>()
 735                                     .join("::"),
 736                                 path.segments[*position..]
 737                                     .iter()
 738                                     .map(|segment| path_segment_to_string(segment))
 739                                     .collect::<Vec<_>>()
 740                                     .join("::"),
 741                                 ident,
 742                             ),
 743                             Applicability::MaybeIncorrect,
 744                         );
 745                     }
 746                     return true;
 747                 }
 748             }
 749         }
 750         false
 751     }
 752
 753     /// Check if the source is call expression and the first argument is `self`. If true,
 754     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 755     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 756         let mut has_self_arg = None;
 757         if let PathSource::Expr(Some(parent)) = source {
 758             match &parent.kind {
 759                 ExprKind::Call(_, args) if !args.is_empty() => {
 760                     let mut expr_kind = &args[0].kind;
 761                     loop {
 762                         match expr_kind {
 763                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 764                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 765                                     let call_span = parent.span;
 766                                     let tail_args_span = if args.len() > 1 {
 767                                         Some(Span::new(
 768                                             args[1].span.lo(),
 769                                             args.last().unwrap().span.hi(),
 770                                             call_span.ctxt(),
 771                                         ))
 772                                     } else {
 773                                         None
 774                                     };
 775                                     has_self_arg = Some((call_span, tail_args_span));
 776                                 }
 777                                 break;
 778                             }
 779                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 780                             _ => break,
 781                         }
 782                     }
 783                 }
 784                 _ => (),
 785             }
 786         };
 787         has_self_arg
 788     }
 789
 790     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 791         // HACK(estebank): find a better way to figure out that this was a
 792         // parser issue where a struct literal is being used on an expression
 793         // where a brace being opened means a block is being started. Look
 794         // ahead for the next text to see if `span` is followed by a `{`.
 795         let sm = self.r.session.source_map();
 796         let mut sp = span;
 797         loop {
 798             sp = sm.next_point(sp);
 799             match sm.span_to_snippet(sp) {
 800                 Ok(ref snippet) => {
 801                     if snippet.chars().any(|c| !c.is_whitespace()) {
 802                         break;
 803                     }
 804                 }
 805                 _ => break,
 806             }
 807         }
 808         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
 809         // In case this could be a struct literal that needs to be surrounded
 810         // by parentheses, find the appropriate span.
 811         let mut i = 0;
 812         let mut closing_brace = None;
 813         loop {
 814             sp = sm.next_point(sp);
 815             match sm.span_to_snippet(sp) {
 816                 Ok(ref snippet) => {
 817                     if snippet == "}" {
 818                         closing_brace = Some(span.to(sp));
 819                         break;
 820                     }
 821                 }
 822                 _ => break,
 823             }
 824             i += 1;
 825             // The bigger the span, the more likely we're incorrect --
 826             // bound it to 100 chars long.
 827             if i > 100 {
 828                 break;
 829             }
 830         }
 831         (followed_by_brace, closing_brace)
 832     }
 833
 834     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 835     /// function.
 836     /// Returns `true` if able to provide context-dependent help.
 837     fn smart_resolve_context_dependent_help(
 838         &mut self,
 839         err: &mut DiagnosticBuilder<'a>,
 840         span: Span,
 841         source: PathSource<'_>,
 842         res: Res,
 843         path_str: &str,
 844         fallback_label: &str,
 845     ) -> bool {
 846         let ns = source.namespace();
 847         let is_expected = &|res| source.is_expected(res);
 848
 849         let path_sep = |err: &mut DiagnosticBuilder<'_>, expr: &Expr| match expr.kind {
 850             ExprKind::Field(_, ident) => {
 851                 err.span_suggestion(
 852                     expr.span,
 853                     "use the path separator to refer to an item",
 854                     format!("{}::{}", path_str, ident),
 855                     Applicability::MaybeIncorrect,
 856                 );
 857                 true
 858             }
 859             ExprKind::MethodCall(ref segment, ..) => {
 860                 let span = expr.span.with_hi(segment.ident.span.hi());
 861                 err.span_suggestion(
 862                     span,
 863                     "use the path separator to refer to an item",
 864                     format!("{}::{}", path_str, segment.ident),
 865                     Applicability::MaybeIncorrect,
 866                 );
 867                 true
 868             }
 869             _ => false,
 870         };
 871
 872         let find_span = |source: &PathSource<'_>, err: &mut DiagnosticBuilder<'_>| {
 873             match source {
 874                 PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
 875                 | PathSource::TupleStruct(span, _) => {
 876                     // We want the main underline to cover the suggested code as well for
 877                     // cleaner output.
 878                     err.set_span(*span);
 879                     *span
 880                 }
 881                 _ => span,
 882             }
 883         };
 884
 885         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 886             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 887
 888             match source {
 889                 PathSource::Expr(Some(
 890                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
 891                 )) if path_sep(err, &parent) => {}
 892                 PathSource::Expr(
 893                     None
 894                     | Some(Expr {
 895                         kind:
 896                             ExprKind::Path(..)
 897                             | ExprKind::Binary(..)
 898                             | ExprKind::Unary(..)
 899                             | ExprKind::If(..)
 900                             | ExprKind::While(..)
 901                             | ExprKind::ForLoop(..)
 902                             | ExprKind::Match(..),
 903                         ..
 904                     }),
 905                 ) if followed_by_brace => {
 906                     if let Some(sp) = closing_brace {
 907                         err.span_label(span, fallback_label);
 908                         err.multipart_suggestion(
 909                             "surround the struct literal with parentheses",
 910                             vec![
 911                                 (sp.shrink_to_lo(), "(".to_string()),
 912                                 (sp.shrink_to_hi(), ")".to_string()),
 913                             ],
 914                             Applicability::MaybeIncorrect,
 915                         );
 916                     } else {
 917                         err.span_label(
 918                             span, // Note the parentheses surrounding the suggestion below
 919                             format!(
 920                                 "you might want to surround a struct literal with parentheses: \
 921                                  `({} {{ /* fields */ }})`?",
 922                                 path_str
 923                             ),
 924                         );
 925                     }
 926                 }
 927                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
 928                     let span = find_span(&source, err);
 929                     if let Some(span) = self.def_span(def_id) {
 930                         err.span_label(span, &format!("`{}` defined here", path_str));
 931                     }
 932                     let (tail, descr, applicability) = match source {
 933                         PathSource::Pat | PathSource::TupleStruct(..) => {
 934                             ("", "pattern", Applicability::MachineApplicable)
 935                         }
 936                         _ => (": val", "literal", Applicability::HasPlaceholders),
 937                     };
 938                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
 939                         Some(fields) => (
 940                             fields
 941                                 .iter()
 942                                 .map(|f| format!("{}{}", f.node, tail))
 943                                 .collect::<Vec<String>>()
 944                                 .join(", "),
 945                             applicability,
 946                         ),
 947                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
 948                     };
 949                     let pad = match self.r.field_names.get(&def_id) {
 950                         Some(fields) if fields.is_empty() => "",
 951                         _ => " ",
 952                     };
 953                     err.span_suggestion(
 954                         span,
 955                         &format!("use struct {} syntax instead", descr),
 956                         format!("{path_str} {{{pad}{fields}{pad}}}"),
 957                         applicability,
 958                     );
 959                 }
 960                 _ => {
 961                     err.span_label(span, fallback_label);
 962                 }
 963             }
 964         };
 965
 966         match (res, source) {
 967             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
 968                 err.span_label(span, fallback_label);
 969                 err.span_suggestion_verbose(
 970                     span.shrink_to_hi(),
 971                     "use `!` to invoke the macro",
 972                     "!".to_string(),
 973                     Applicability::MaybeIncorrect,
 974                 );
 975                 if path_str == "try" && span.rust_2015() {
 976                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
 977                 }
 978             }
 979             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
 980                 err.span_label(span, "type aliases cannot be used as traits");
 981                 if self.r.session.is_nightly_build() {
 982                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
 983                                `type` alias";
 984                     if let Some(span) = self.def_span(def_id) {
 985                         if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
 986                             // The span contains a type alias so we should be able to
 987                             // replace `type` with `trait`.
 988                             let snip = snip.replacen("type", "trait", 1);
 989                             err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
 990                         } else {
 991                             err.span_help(span, msg);
 992                         }
 993                     } else {
 994                         err.help(msg);
 995                     }
 996                 }
 997             }
 998             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
 999                 if !path_sep(err, &parent) {
1000                     return false;
1001                 }
1002             }
1003             (
1004                 Res::Def(DefKind::Enum, def_id),
1005                 PathSource::TupleStruct(..) | PathSource::Expr(..),
1006             ) => {
1007                 if self
1008                     .diagnostic_metadata
1009                     .current_type_ascription
1010                     .last()
1011                     .map(|sp| {
1012                         self.r
1013                             .session
1014                             .parse_sess
1015                             .type_ascription_path_suggestions
1016                             .borrow()
1017                             .contains(&sp)
1018                     })
1019                     .unwrap_or(false)
1020                 {
1021                     err.delay_as_bug();
1022                     // We already suggested changing `:` into `::` during parsing.
1023                     return false;
1024                 }
1025
1026                 self.suggest_using_enum_variant(err, source, def_id, span);
1027             }
1028             (Res::Def(DefKind::Struct, def_id), _) if ns == ValueNS => {
1029                 let (ctor_def, ctor_vis, fields) =
1030                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
1031                         struct_ctor
1032                     } else {
1033                         bad_struct_syntax_suggestion(def_id);
1034                         return true;
1035                     };
1036
1037                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
1038                 if !is_expected(ctor_def) || is_accessible {
1039                     return true;
1040                 }
1041
1042                 let field_spans = match source {
1043                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
1044                     PathSource::TupleStruct(_, pattern_spans) => {
1045                         err.set_primary_message(
1046                             "cannot match against a tuple struct which contains private fields",
1047                         );
1048
1049                         // Use spans of the tuple struct pattern.
1050                         Some(Vec::from(pattern_spans))
1051                     }
1052                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
1053                     _ if source.is_call() => {
1054                         err.set_primary_message(
1055                             "cannot initialize a tuple struct which contains private fields",
1056                         );
1057
1058                         // Use spans of the tuple struct definition.
1059                         self.r
1060                             .field_names
1061                             .get(&def_id)
1062                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
1063                     }
1064                     _ => None,
1065                 };
1066
1067                 if let Some(spans) =
1068                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
1069                 {
1070                     let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
1071                         .filter(|(vis, _)| {
1072                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
1073                         })
1074                         .map(|(_, span)| *span)
1075                         .collect();
1076
1077                     if non_visible_spans.len() > 0 {
1078                         let mut m: rustc_span::MultiSpan = non_visible_spans.clone().into();
1079                         non_visible_spans
1080                             .into_iter()
1081                             .for_each(|s| m.push_span_label(s, "private field".to_string()));
1082                         err.span_note(m, "constructor is not visible here due to private fields");
1083                     }
1084
1085                     return true;
1086                 }
1087
1088                 err.span_label(
1089                     span,
1090                     "constructor is not visible here due to private fields".to_string(),
1091                 );
1092             }
1093             (
1094                 Res::Def(
1095                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
1096                     def_id,
1097                 ),
1098                 _,
1099             ) if ns == ValueNS => {
1100                 bad_struct_syntax_suggestion(def_id);
1101             }
1102             (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
1103                 match source {
1104                     PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1105                         let span = find_span(&source, err);
1106                         if let Some(span) = self.def_span(def_id) {
1107                             err.span_label(span, &format!("`{}` defined here", path_str));
1108                         }
1109                         err.span_suggestion(
1110                             span,
1111                             &"use this syntax instead",
1112                             format!("{path_str}"),
1113                             Applicability::MaybeIncorrect,
1114                         );
1115                     }
1116                     _ => return false,
1117                 }
1118             }
1119             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
1120                 if let Some(span) = self.def_span(def_id) {
1121                     err.span_label(span, &format!("`{}` defined here", path_str));
1122                 }
1123                 let fields = self.r.field_names.get(&def_id).map_or_else(
1124                     || "/* fields */".to_string(),
1125                     |fields| vec!["_"; fields.len()].join(", "),
1126                 );
1127                 err.span_suggestion(
1128                     span,
1129                     "use the tuple variant pattern syntax instead",
1130                     format!("{}({})", path_str, fields),
1131                     Applicability::HasPlaceholders,
1132                 );
1133             }
1134             (Res::SelfTy(..), _) if ns == ValueNS => {
1135                 err.span_label(span, fallback_label);
1136                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1137             }
1138             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1139                 err.note("can't use a type alias as a constructor");
1140             }
1141             _ => return false,
1142         }
1143         true
1144     }
1145
1146     fn lookup_assoc_candidate<FilterFn>(
1147         &mut self,
1148         ident: Ident,
1149         ns: Namespace,
1150         filter_fn: FilterFn,
1151     ) -> Option<AssocSuggestion>
1152     where
1153         FilterFn: Fn(Res) -> bool,
1154     {
1155         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1156             match t.kind {
1157                 TyKind::Path(None, _) => Some(t.id),
1158                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1159                 // This doesn't handle the remaining `Ty` variants as they are not
1160                 // that commonly the self_type, it might be interesting to provide
1161                 // support for those in future.
1162                 _ => None,
1163             }
1164         }
1165
1166         // Fields are generally expected in the same contexts as locals.
1167         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1168             if let Some(node_id) =
1169                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1170             {
1171                 // Look for a field with the same name in the current self_type.
1172                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1173                     match resolution.base_res() {
1174                         Res::Def(DefKind::Struct | DefKind::Union, did)
1175                             if resolution.unresolved_segments() == 0 =>
1176                         {
1177                             if let Some(field_names) = self.r.field_names.get(&did) {
1178                                 if field_names
1179                                     .iter()
1180                                     .any(|&field_name| ident.name == field_name.node)
1181                                 {
1182                                     return Some(AssocSuggestion::Field);
1183                                 }
1184                             }
1185                         }
1186                         _ => {}
1187                     }
1188                 }
1189             }
1190         }
1191
1192         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1193             for assoc_item in items {
1194                 if assoc_item.ident == ident {
1195                     return Some(match &assoc_item.kind {
1196                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1197                         ast::AssocItemKind::Fn(box ast::FnKind(_, sig, ..))
1198                             if sig.decl.has_self() =>
1199                         {
1200                             AssocSuggestion::MethodWithSelf
1201                         }
1202                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn,
1203                         ast::AssocItemKind::TyAlias(..) => AssocSuggestion::AssocType,
1204                         ast::AssocItemKind::MacCall(_) => continue,
1205                     });
1206                 }
1207             }
1208         }
1209
1210         // Look for associated items in the current trait.
1211         if let Some((module, _)) = self.current_trait_ref {
1212             if let Ok(binding) = self.r.resolve_ident_in_module(
1213                 ModuleOrUniformRoot::Module(module),
1214                 ident,
1215                 ns,
1216                 &self.parent_scope,
1217                 false,
1218                 module.span,
1219             ) {
1220                 let res = binding.res();
1221                 if filter_fn(res) {
1222                     if self.r.has_self.contains(&res.def_id()) {
1223                         return Some(AssocSuggestion::MethodWithSelf);
1224                     } else {
1225                         match res {
1226                             Res::Def(DefKind::AssocFn, _) => return Some(AssocSuggestion::AssocFn),
1227                             Res::Def(DefKind::AssocConst, _) => {
1228                                 return Some(AssocSuggestion::AssocConst);
1229                             }
1230                             Res::Def(DefKind::AssocTy, _) => {
1231                                 return Some(AssocSuggestion::AssocType);
1232                             }
1233                             _ => {}
1234                         }
1235                     }
1236                 }
1237             }
1238         }
1239
1240         None
1241     }
1242
1243     fn lookup_typo_candidate(
1244         &mut self,
1245         path: &[Segment],
1246         ns: Namespace,
1247         filter_fn: &impl Fn(Res) -> bool,
1248         span: Span,
1249     ) -> Option<TypoSuggestion> {
1250         let mut names = Vec::new();
1251         if path.len() == 1 {
1252             // Search in lexical scope.
1253             // Walk backwards up the ribs in scope and collect candidates.
1254             for rib in self.ribs[ns].iter().rev() {
1255                 // Locals and type parameters
1256                 for (ident, &res) in &rib.bindings {
1257                     if filter_fn(res) {
1258                         names.push(TypoSuggestion::typo_from_res(ident.name, res));
1259                     }
1260                 }
1261                 // Items in scope
1262                 if let RibKind::ModuleRibKind(module) = rib.kind {
1263                     // Items from this module
1264                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1265
1266                     if let ModuleKind::Block(..) = module.kind {
1267                         // We can see through blocks
1268                     } else {
1269                         // Items from the prelude
1270                         if !module.no_implicit_prelude {
1271                             let extern_prelude = self.r.extern_prelude.clone();
1272                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1273                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
1274                                     |crate_id| {
1275                                         let crate_mod = Res::Def(
1276                                             DefKind::Mod,
1277                                             DefId { krate: crate_id, index: CRATE_DEF_INDEX },
1278                                         );
1279
1280                                         if filter_fn(crate_mod) {
1281                                             Some(TypoSuggestion::typo_from_res(
1282                                                 ident.name, crate_mod,
1283                                             ))
1284                                         } else {
1285                                             None
1286                                         }
1287                                     },
1288                                 )
1289                             }));
1290
1291                             if let Some(prelude) = self.r.prelude {
1292                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
1293                             }
1294                         }
1295                         break;
1296                     }
1297                 }
1298             }
1299             // Add primitive types to the mix
1300             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1301                 names.extend(PrimTy::ALL.iter().map(|prim_ty| {
1302                     TypoSuggestion::typo_from_res(prim_ty.name(), Res::PrimTy(*prim_ty))
1303                 }))
1304             }
1305         } else {
1306             // Search in module.
1307             let mod_path = &path[..path.len() - 1];
1308             if let PathResult::Module(module) =
1309                 self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No)
1310             {
1311                 if let ModuleOrUniformRoot::Module(module) = module {
1312                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1313                 }
1314             }
1315         }
1316
1317         let name = path[path.len() - 1].ident.name;
1318         // Make sure error reporting is deterministic.
1319         names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
1320
1321         match find_best_match_for_name(
1322             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1323             name,
1324             None,
1325         ) {
1326             Some(found) if found != name => {
1327                 names.into_iter().find(|suggestion| suggestion.candidate == found)
1328             }
1329             _ => None,
1330         }
1331     }
1332
1333     // Returns the name of the Rust type approximately corresponding to
1334     // a type name in another programming language.
1335     fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
1336         let name = path[path.len() - 1].ident.as_str();
1337         // Common Java types
1338         Some(match &*name {
1339             "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
1340             "short" => sym::i16,
1341             "boolean" => sym::bool,
1342             "int" => sym::i32,
1343             "long" => sym::i64,
1344             "float" => sym::f32,
1345             "double" => sym::f64,
1346             _ => return None,
1347         })
1348     }
1349
1350     /// Only used in a specific case of type ascription suggestions
1351     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1352         let sm = self.r.session.source_map();
1353         start.to(sm.next_point(start))
1354     }
1355
1356     fn type_ascription_suggestion(&self, err: &mut DiagnosticBuilder<'_>, base_span: Span) -> bool {
1357         let sm = self.r.session.source_map();
1358         let base_snippet = sm.span_to_snippet(base_span);
1359         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1360             if let Ok(snippet) = sm.span_to_snippet(sp) {
1361                 let len = snippet.trim_end().len() as u32;
1362                 if snippet.trim() == ":" {
1363                     let colon_sp =
1364                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1365                     let mut show_label = true;
1366                     if sm.is_multiline(sp) {
1367                         err.span_suggestion_short(
1368                             colon_sp,
1369                             "maybe you meant to write `;` here",
1370                             ";".to_string(),
1371                             Applicability::MaybeIncorrect,
1372                         );
1373                     } else {
1374                         let after_colon_sp =
1375                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1376                         if snippet.len() == 1 {
1377                             // `foo:bar`
1378                             err.span_suggestion(
1379                                 colon_sp,
1380                                 "maybe you meant to write a path separator here",
1381                                 "::".to_string(),
1382                                 Applicability::MaybeIncorrect,
1383                             );
1384                             show_label = false;
1385                             if !self
1386                                 .r
1387                                 .session
1388                                 .parse_sess
1389                                 .type_ascription_path_suggestions
1390                                 .borrow_mut()
1391                                 .insert(colon_sp)
1392                             {
1393                                 err.delay_as_bug();
1394                             }
1395                         }
1396                         if let Ok(base_snippet) = base_snippet {
1397                             let mut sp = after_colon_sp;
1398                             for _ in 0..100 {
1399                                 // Try to find an assignment
1400                                 sp = sm.next_point(sp);
1401                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
1402                                 match snippet {
1403                                     Ok(ref x) if x.as_str() == "=" => {
1404                                         err.span_suggestion(
1405                                             base_span,
1406                                             "maybe you meant to write an assignment here",
1407                                             format!("let {}", base_snippet),
1408                                             Applicability::MaybeIncorrect,
1409                                         );
1410                                         show_label = false;
1411                                         break;
1412                                     }
1413                                     Ok(ref x) if x.as_str() == "\n" => break,
1414                                     Err(_) => break,
1415                                     Ok(_) => {}
1416                                 }
1417                             }
1418                         }
1419                     }
1420                     if show_label {
1421                         err.span_label(
1422                             base_span,
1423                             "expecting a type here because of type ascription",
1424                         );
1425                     }
1426                     return show_label;
1427                 }
1428             }
1429         }
1430         false
1431     }
1432
1433     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1434         let mut result = None;
1435         let mut seen_modules = FxHashSet::default();
1436         let mut worklist = vec![(self.r.graph_root, Vec::new())];
1437
1438         while let Some((in_module, path_segments)) = worklist.pop() {
1439             // abort if the module is already found
1440             if result.is_some() {
1441                 break;
1442             }
1443
1444             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1445                 // abort if the module is already found or if name_binding is private external
1446                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1447                     return;
1448                 }
1449                 if let Some(module) = name_binding.module() {
1450                     // form the path
1451                     let mut path_segments = path_segments.clone();
1452                     path_segments.push(ast::PathSegment::from_ident(ident));
1453                     let module_def_id = module.def_id().unwrap();
1454                     if module_def_id == def_id {
1455                         let path =
1456                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1457                         result = Some((
1458                             module,
1459                             ImportSuggestion {
1460                                 did: Some(def_id),
1461                                 descr: "module",
1462                                 path,
1463                                 accessible: true,
1464                             },
1465                         ));
1466                     } else {
1467                         // add the module to the lookup
1468                         if seen_modules.insert(module_def_id) {
1469                             worklist.push((module, path_segments));
1470                         }
1471                     }
1472                 }
1473             });
1474         }
1475
1476         result
1477     }
1478
1479     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1480         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1481             let mut variants = Vec::new();
1482             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1483                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1484                     let mut segms = enum_import_suggestion.path.segments.clone();
1485                     segms.push(ast::PathSegment::from_ident(ident));
1486                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1487                     variants.push((path, def_id, kind));
1488                 }
1489             });
1490             variants
1491         })
1492     }
1493
1494     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1495     fn suggest_using_enum_variant(
1496         &mut self,
1497         err: &mut DiagnosticBuilder<'a>,
1498         source: PathSource<'_>,
1499         def_id: DefId,
1500         span: Span,
1501     ) {
1502         let variants = match self.collect_enum_ctors(def_id) {
1503             Some(variants) => variants,
1504             None => {
1505                 err.note("you might have meant to use one of the enum's variants");
1506                 return;
1507             }
1508         };
1509
1510         let suggest_only_tuple_variants =
1511             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1512         if suggest_only_tuple_variants {
1513             // Suggest only tuple variants regardless of whether they have fields and do not
1514             // suggest path with added parenthesis.
1515             let mut suggestable_variants = variants
1516                 .iter()
1517                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1518                 .map(|(variant, ..)| path_names_to_string(variant))
1519                 .collect::<Vec<_>>();
1520
1521             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1522
1523             let source_msg = if source.is_call() {
1524                 "to construct"
1525             } else if matches!(source, PathSource::TupleStruct(..)) {
1526                 "to match against"
1527             } else {
1528                 unreachable!()
1529             };
1530
1531             if !suggestable_variants.is_empty() {
1532                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1533                     format!("try {} the enum's variant", source_msg)
1534                 } else {
1535                     format!("try {} one of the enum's variants", source_msg)
1536                 };
1537
1538                 err.span_suggestions(
1539                     span,
1540                     &msg,
1541                     suggestable_variants.drain(..),
1542                     Applicability::MaybeIncorrect,
1543                 );
1544             }
1545
1546             // If the enum has no tuple variants..
1547             if non_suggestable_variant_count == variants.len() {
1548                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1549             }
1550
1551             // If there are also non-tuple variants..
1552             if non_suggestable_variant_count == 1 {
1553                 err.help(&format!(
1554                     "you might have meant {} the enum's non-tuple variant",
1555                     source_msg
1556                 ));
1557             } else if non_suggestable_variant_count >= 1 {
1558                 err.help(&format!(
1559                     "you might have meant {} one of the enum's non-tuple variants",
1560                     source_msg
1561                 ));
1562             }
1563         } else {
1564             let needs_placeholder = |def_id: DefId, kind: CtorKind| {
1565                 let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
1566                 match kind {
1567                     CtorKind::Const => false,
1568                     CtorKind::Fn | CtorKind::Fictive if has_no_fields => false,
1569                     _ => true,
1570                 }
1571             };
1572
1573             let mut suggestable_variants = variants
1574                 .iter()
1575                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1576                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1577                 .map(|(variant, kind)| match kind {
1578                     CtorKind::Const => variant,
1579                     CtorKind::Fn => format!("({}())", variant),
1580                     CtorKind::Fictive => format!("({} {{}})", variant),
1581                 })
1582                 .collect::<Vec<_>>();
1583
1584             if !suggestable_variants.is_empty() {
1585                 let msg = if suggestable_variants.len() == 1 {
1586                     "you might have meant to use the following enum variant"
1587                 } else {
1588                     "you might have meant to use one of the following enum variants"
1589                 };
1590
1591                 err.span_suggestions(
1592                     span,
1593                     msg,
1594                     suggestable_variants.drain(..),
1595                     Applicability::MaybeIncorrect,
1596                 );
1597             }
1598
1599             let mut suggestable_variants_with_placeholders = variants
1600                 .iter()
1601                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
1602                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1603                 .filter_map(|(variant, kind)| match kind {
1604                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
1605                     CtorKind::Fictive => Some(format!("({} {{ /* fields */ }})", variant)),
1606                     _ => None,
1607                 })
1608                 .collect::<Vec<_>>();
1609
1610             if !suggestable_variants_with_placeholders.is_empty() {
1611                 let msg = match (
1612                     suggestable_variants.is_empty(),
1613                     suggestable_variants_with_placeholders.len(),
1614                 ) {
1615                     (true, 1) => "the following enum variant is available",
1616                     (true, _) => "the following enum variants are available",
1617                     (false, 1) => "alternatively, the following enum variant is available",
1618                     (false, _) => "alternatively, the following enum variants are also available",
1619                 };
1620
1621                 err.span_suggestions(
1622                     span,
1623                     msg,
1624                     suggestable_variants_with_placeholders.drain(..),
1625                     Applicability::HasPlaceholders,
1626                 );
1627             }
1628         };
1629
1630         if def_id.is_local() {
1631             if let Some(span) = self.def_span(def_id) {
1632                 err.span_note(span, "the enum is defined here");
1633             }
1634         }
1635     }
1636
1637     crate fn report_missing_type_error(
1638         &self,
1639         path: &[Segment],
1640     ) -> Option<(Span, &'static str, String, Applicability)> {
1641         let (ident, span) = match path {
1642             [segment] if !segment.has_generic_args => {
1643                 (segment.ident.to_string(), segment.ident.span)
1644             }
1645             _ => return None,
1646         };
1647         let mut iter = ident.chars().map(|c| c.is_uppercase());
1648         let single_uppercase_char =
1649             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1650         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1651             return None;
1652         }
1653         match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
1654             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
1655                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1656             }
1657             (
1658                 Some(Item {
1659                     kind:
1660                         kind @ ItemKind::Fn(..)
1661                         | kind @ ItemKind::Enum(..)
1662                         | kind @ ItemKind::Struct(..)
1663                         | kind @ ItemKind::Union(..),
1664                     ..
1665                 }),
1666                 true, _
1667             )
1668             // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
1669             | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
1670             | (Some(Item { kind, .. }), false, _) => {
1671                 // Likely missing type parameter.
1672                 if let Some(generics) = kind.generics() {
1673                     if span.overlaps(generics.span) {
1674                         // Avoid the following:
1675                         // error[E0405]: cannot find trait `A` in this scope
1676                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1677                         //   |
1678                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1679                         //   |           ^- help: you might be missing a type parameter: `, A`
1680                         //   |           |
1681                         //   |           not found in this scope
1682                         return None;
1683                     }
1684                     let msg = "you might be missing a type parameter";
1685                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1686                         let span = if let [.., bound] = &param.bounds[..] {
1687                             bound.span()
1688                         } else if let GenericParam {
1689                             kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
1690                         } = param {
1691                             default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
1692                         } else {
1693                             param.ident.span
1694                         };
1695                         (span, format!(", {}", ident))
1696                     } else {
1697                         (generics.span, format!("<{}>", ident))
1698                     };
1699                     // Do not suggest if this is coming from macro expansion.
1700                     if !span.from_expansion() {
1701                         return Some((
1702                             span.shrink_to_hi(),
1703                             msg,
1704                             sugg,
1705                             Applicability::MaybeIncorrect,
1706                         ));
1707                     }
1708                 }
1709             }
1710             _ => {}
1711         }
1712         None
1713     }
1714
1715     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1716     /// optionally returning the closest match and whether it is reachable.
1717     crate fn suggestion_for_label_in_rib(
1718         &self,
1719         rib_index: usize,
1720         label: Ident,
1721     ) -> Option<LabelSuggestion> {
1722         // Are ribs from this `rib_index` within scope?
1723         let within_scope = self.is_label_valid_from_rib(rib_index);
1724
1725         let rib = &self.label_ribs[rib_index];
1726         let names = rib
1727             .bindings
1728             .iter()
1729             .filter(|(id, _)| id.span.ctxt() == label.span.ctxt())
1730             .map(|(id, _)| id.name)
1731             .collect::<Vec<Symbol>>();
1732
1733         find_best_match_for_name(&names, label.name, None).map(|symbol| {
1734             // Upon finding a similar name, get the ident that it was from - the span
1735             // contained within helps make a useful diagnostic. In addition, determine
1736             // whether this candidate is within scope.
1737             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1738             (*ident, within_scope)
1739         })
1740     }
1741 }
1742
1743 impl<'tcx> LifetimeContext<'_, 'tcx> {
1744     crate fn report_missing_lifetime_specifiers(
1745         &self,
1746         spans: Vec<Span>,
1747         count: usize,
1748     ) -> DiagnosticBuilder<'tcx> {
1749         struct_span_err!(
1750             self.tcx.sess,
1751             spans,
1752             E0106,
1753             "missing lifetime specifier{}",
1754             pluralize!(count)
1755         )
1756     }
1757
1758     crate fn emit_undeclared_lifetime_error(&self, lifetime_ref: &hir::Lifetime) {
1759         let mut err = struct_span_err!(
1760             self.tcx.sess,
1761             lifetime_ref.span,
1762             E0261,
1763             "use of undeclared lifetime name `{}`",
1764             lifetime_ref
1765         );
1766         err.span_label(lifetime_ref.span, "undeclared lifetime");
1767         let mut suggests_in_band = false;
1768         let mut suggest_note = true;
1769         for missing in &self.missing_named_lifetime_spots {
1770             match missing {
1771                 MissingLifetimeSpot::Generics(generics) => {
1772                     let (span, sugg) = if let Some(param) = generics.params.iter().find(|p| {
1773                         !matches!(
1774                             p.kind,
1775                             hir::GenericParamKind::Type {
1776                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1777                                 ..
1778                             } | hir::GenericParamKind::Lifetime {
1779                                 kind: hir::LifetimeParamKind::Elided,
1780                             }
1781                         )
1782                     }) {
1783                         (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref))
1784                     } else {
1785                         suggests_in_band = true;
1786                         (generics.span, format!("<{}>", lifetime_ref))
1787                     };
1788                     if !span.from_expansion() {
1789                         err.span_suggestion(
1790                             span,
1791                             &format!("consider introducing lifetime `{}` here", lifetime_ref),
1792                             sugg,
1793                             Applicability::MaybeIncorrect,
1794                         );
1795                     } else if suggest_note {
1796                         suggest_note = false; // Avoid displaying the same help multiple times.
1797                         err.span_label(
1798                             span,
1799                             &format!(
1800                                 "lifetime `{}` is missing in item created through this procedural \
1801                                  macro",
1802                                 lifetime_ref,
1803                             ),
1804                         );
1805                     }
1806                 }
1807                 MissingLifetimeSpot::HigherRanked { span, span_type } => {
1808                     err.span_suggestion(
1809                         *span,
1810                         &format!(
1811                             "consider making the {} lifetime-generic with a new `{}` lifetime",
1812                             span_type.descr(),
1813                             lifetime_ref
1814                         ),
1815                         span_type.suggestion(&lifetime_ref.to_string()),
1816                         Applicability::MaybeIncorrect,
1817                     );
1818                     err.note(
1819                         "for more information on higher-ranked polymorphism, visit \
1820                          https://doc.rust-lang.org/nomicon/hrtb.html",
1821                     );
1822                 }
1823                 _ => {}
1824             }
1825         }
1826         if self.tcx.sess.is_nightly_build()
1827             && !self.tcx.features().in_band_lifetimes
1828             && suggests_in_band
1829         {
1830             err.help(
1831                 "if you want to experiment with in-band lifetime bindings, \
1832                  add `#![feature(in_band_lifetimes)]` to the crate attributes",
1833             );
1834         }
1835         err.emit();
1836     }
1837
1838     // FIXME(const_generics): This patches over an ICE caused by non-'static lifetimes in const
1839     // generics. We are disallowing this until we can decide on how we want to handle non-'static
1840     // lifetimes in const generics. See issue #74052 for discussion.
1841     crate fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &hir::Lifetime) {
1842         let mut err = struct_span_err!(
1843             self.tcx.sess,
1844             lifetime_ref.span,
1845             E0771,
1846             "use of non-static lifetime `{}` in const generic",
1847             lifetime_ref
1848         );
1849         err.note(
1850             "for more information, see issue #74052 \
1851             <https://github.com/rust-lang/rust/issues/74052>",
1852         );
1853         err.emit();
1854     }
1855
1856     crate fn is_trait_ref_fn_scope(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) -> bool {
1857         if let def::Res::Def(_, did) = trait_ref.trait_ref.path.res {
1858             if [
1859                 self.tcx.lang_items().fn_once_trait(),
1860                 self.tcx.lang_items().fn_trait(),
1861                 self.tcx.lang_items().fn_mut_trait(),
1862             ]
1863             .contains(&Some(did))
1864             {
1865                 let (span, span_type) = match &trait_ref.bound_generic_params {
1866                     [] => (trait_ref.span.shrink_to_lo(), ForLifetimeSpanType::BoundEmpty),
1867                     [.., bound] => (bound.span.shrink_to_hi(), ForLifetimeSpanType::BoundTail),
1868                 };
1869                 self.missing_named_lifetime_spots
1870                     .push(MissingLifetimeSpot::HigherRanked { span, span_type });
1871                 return true;
1872             }
1873         };
1874         false
1875     }
1876
1877     crate fn add_missing_lifetime_specifiers_label(
1878         &self,
1879         err: &mut DiagnosticBuilder<'_>,
1880         mut spans_with_counts: Vec<(Span, usize)>,
1881         lifetime_names: &FxHashSet<Symbol>,
1882         lifetime_spans: Vec<Span>,
1883         params: &[ElisionFailureInfo],
1884     ) {
1885         let snippets: Vec<Option<String>> = spans_with_counts
1886             .iter()
1887             .map(|(span, _)| self.tcx.sess.source_map().span_to_snippet(*span).ok())
1888             .collect();
1889
1890         // Empty generics are marked with a span of "<", but since from now on
1891         // that information is in the snippets it can be removed from the spans.
1892         for ((span, _), snippet) in spans_with_counts.iter_mut().zip(&snippets) {
1893             if snippet.as_deref() == Some("<") {
1894                 *span = span.shrink_to_hi();
1895             }
1896         }
1897
1898         for &(span, count) in &spans_with_counts {
1899             err.span_label(
1900                 span,
1901                 format!(
1902                     "expected {} lifetime parameter{}",
1903                     if count == 1 { "named".to_string() } else { count.to_string() },
1904                     pluralize!(count),
1905                 ),
1906             );
1907         }
1908
1909         let suggest_existing =
1910             |err: &mut DiagnosticBuilder<'_>,
1911              name: &str,
1912              formatters: Vec<Option<Box<dyn Fn(&str) -> String>>>| {
1913                 if let Some(MissingLifetimeSpot::HigherRanked { span: for_span, span_type }) =
1914                     self.missing_named_lifetime_spots.iter().rev().next()
1915                 {
1916                     // When we have `struct S<'a>(&'a dyn Fn(&X) -> &X);` we want to not only suggest
1917                     // using `'a`, but also introduce the concept of HRLTs by suggesting
1918                     // `struct S<'a>(&'a dyn for<'b> Fn(&X) -> &'b X);`. (#72404)
1919                     let mut introduce_suggestion = vec![];
1920
1921                     let a_to_z_repeat_n = |n| {
1922                         (b'a'..=b'z').map(move |c| {
1923                             let mut s = '\''.to_string();
1924                             s.extend(std::iter::repeat(char::from(c)).take(n));
1925                             s
1926                         })
1927                     };
1928
1929                     // If all single char lifetime names are present, we wrap around and double the chars.
1930                     let lt_name = (1..)
1931                         .flat_map(a_to_z_repeat_n)
1932                         .find(|lt| !lifetime_names.contains(&Symbol::intern(&lt)))
1933                         .unwrap();
1934                     let msg = format!(
1935                         "consider making the {} lifetime-generic with a new `{}` lifetime",
1936                         span_type.descr(),
1937                         lt_name,
1938                     );
1939                     err.note(
1940                         "for more information on higher-ranked polymorphism, visit \
1941                     https://doc.rust-lang.org/nomicon/hrtb.html",
1942                     );
1943                     let for_sugg = span_type.suggestion(&lt_name);
1944                     for param in params {
1945                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span)
1946                         {
1947                             if snippet.starts_with('&') && !snippet.starts_with("&'") {
1948                                 introduce_suggestion
1949                                     .push((param.span, format!("&{} {}", lt_name, &snippet[1..])));
1950                             } else if let Some(stripped) = snippet.strip_prefix("&'_ ") {
1951                                 introduce_suggestion
1952                                     .push((param.span, format!("&{} {}", lt_name, stripped)));
1953                             }
1954                         }
1955                     }
1956                     introduce_suggestion.push((*for_span, for_sugg));
1957                     for ((span, _), formatter) in spans_with_counts.iter().zip(formatters.iter()) {
1958                         if let Some(formatter) = formatter {
1959                             introduce_suggestion.push((*span, formatter(&lt_name)));
1960                         }
1961                     }
1962                     err.multipart_suggestion_with_style(
1963                         &msg,
1964                         introduce_suggestion,
1965                         Applicability::MaybeIncorrect,
1966                         SuggestionStyle::ShowAlways,
1967                     );
1968                 }
1969
1970                 let spans_suggs: Vec<_> = formatters
1971                     .into_iter()
1972                     .zip(spans_with_counts.iter())
1973                     .filter_map(|(fmt, (span, _))| {
1974                         if let Some(formatter) = fmt { Some((formatter, span)) } else { None }
1975                     })
1976                     .map(|(formatter, span)| (*span, formatter(name)))
1977                     .collect();
1978                 err.multipart_suggestion_with_style(
1979                     &format!(
1980                         "consider using the `{}` lifetime",
1981                         lifetime_names.iter().next().unwrap()
1982                     ),
1983                     spans_suggs,
1984                     Applicability::MaybeIncorrect,
1985                     SuggestionStyle::ShowAlways,
1986                 );
1987             };
1988         let suggest_new = |err: &mut DiagnosticBuilder<'_>, suggs: Vec<Option<String>>| {
1989             for missing in self.missing_named_lifetime_spots.iter().rev() {
1990                 let mut introduce_suggestion = vec![];
1991                 let msg;
1992                 let should_break;
1993                 introduce_suggestion.push(match missing {
1994                     MissingLifetimeSpot::Generics(generics) => {
1995                         if generics.span == DUMMY_SP {
1996                             // Account for malformed generics in the HIR. This shouldn't happen,
1997                             // but if we make a mistake elsewhere, mainly by keeping something in
1998                             // `missing_named_lifetime_spots` that we shouldn't, like associated
1999                             // `const`s or making a mistake in the AST lowering we would provide
2000                             // non-sensical suggestions. Guard against that by skipping these.
2001                             // (#74264)
2002                             continue;
2003                         }
2004                         msg = "consider introducing a named lifetime parameter".to_string();
2005                         should_break = true;
2006                         if let Some(param) = generics.params.iter().find(|p| {
2007                             !matches!(
2008                                 p.kind,
2009                                 hir::GenericParamKind::Type {
2010                                     synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
2011                                     ..
2012                                 } | hir::GenericParamKind::Lifetime {
2013                                     kind: hir::LifetimeParamKind::Elided
2014                                 }
2015                             )
2016                         }) {
2017                             (param.span.shrink_to_lo(), "'a, ".to_string())
2018                         } else {
2019                             (generics.span, "<'a>".to_string())
2020                         }
2021                     }
2022                     MissingLifetimeSpot::HigherRanked { span, span_type } => {
2023                         msg = format!(
2024                             "consider making the {} lifetime-generic with a new `'a` lifetime",
2025                             span_type.descr(),
2026                         );
2027                         should_break = false;
2028                         err.note(
2029                             "for more information on higher-ranked polymorphism, visit \
2030                             https://doc.rust-lang.org/nomicon/hrtb.html",
2031                         );
2032                         (*span, span_type.suggestion("'a"))
2033                     }
2034                     MissingLifetimeSpot::Static => {
2035                         let mut spans_suggs = Vec::new();
2036                         for ((span, count), snippet) in
2037                             spans_with_counts.iter().copied().zip(snippets.iter())
2038                         {
2039                             let (span, sugg) = match snippet.as_deref() {
2040                                 Some("&") => (span.shrink_to_hi(), "'static ".to_owned()),
2041                                 Some("'_") => (span, "'static".to_owned()),
2042                                 Some(snippet) if !snippet.ends_with('>') => {
2043                                     if snippet == "" {
2044                                         (
2045                                             span,
2046                                             std::iter::repeat("'static")
2047                                                 .take(count)
2048                                                 .collect::<Vec<_>>()
2049                                                 .join(", "),
2050                                         )
2051                                     } else if snippet == "<" || snippet == "(" {
2052                                         (
2053                                             span.shrink_to_hi(),
2054                                             std::iter::repeat("'static")
2055                                                 .take(count)
2056                                                 .collect::<Vec<_>>()
2057                                                 .join(", "),
2058                                         )
2059                                     } else {
2060                                         (
2061                                             span.shrink_to_hi(),
2062                                             format!(
2063                                                 "<{}>",
2064                                                 std::iter::repeat("'static")
2065                                                     .take(count)
2066                                                     .collect::<Vec<_>>()
2067                                                     .join(", "),
2068                                             ),
2069                                         )
2070                                     }
2071                                 }
2072                                 _ => continue,
2073                             };
2074                             spans_suggs.push((span, sugg.to_string()));
2075                         }
2076                         err.multipart_suggestion_with_style(
2077                             "consider using the `'static` lifetime",
2078                             spans_suggs,
2079                             Applicability::MaybeIncorrect,
2080                             SuggestionStyle::ShowAlways,
2081                         );
2082                         continue;
2083                     }
2084                 });
2085
2086                 struct Lifetime(Span, String);
2087                 impl Lifetime {
2088                     fn is_unnamed(&self) -> bool {
2089                         self.1.starts_with('&') && !self.1.starts_with("&'")
2090                     }
2091                     fn is_underscore(&self) -> bool {
2092                         self.1.starts_with("&'_ ")
2093                     }
2094                     fn is_named(&self) -> bool {
2095                         self.1.starts_with("&'")
2096                     }
2097                     fn suggestion(&self, sugg: String) -> Option<(Span, String)> {
2098                         Some(
2099                             match (
2100                                 self.is_unnamed(),
2101                                 self.is_underscore(),
2102                                 self.is_named(),
2103                                 sugg.starts_with('&'),
2104                             ) {
2105                                 (true, _, _, false) => (self.span_unnamed_borrow(), sugg),
2106                                 (true, _, _, true) => {
2107                                     (self.span_unnamed_borrow(), sugg[1..].to_string())
2108                                 }
2109                                 (_, true, _, false) => {
2110                                     (self.span_underscore_borrow(), sugg.trim().to_string())
2111                                 }
2112                                 (_, true, _, true) => {
2113                                     (self.span_underscore_borrow(), sugg[1..].trim().to_string())
2114                                 }
2115                                 (_, _, true, false) => {
2116                                     (self.span_named_borrow(), sugg.trim().to_string())
2117                                 }
2118                                 (_, _, true, true) => {
2119                                     (self.span_named_borrow(), sugg[1..].trim().to_string())
2120                                 }
2121                                 _ => return None,
2122                             },
2123                         )
2124                     }
2125                     fn span_unnamed_borrow(&self) -> Span {
2126                         let lo = self.0.lo() + BytePos(1);
2127                         self.0.with_lo(lo).with_hi(lo)
2128                     }
2129                     fn span_named_borrow(&self) -> Span {
2130                         let lo = self.0.lo() + BytePos(1);
2131                         self.0.with_lo(lo)
2132                     }
2133                     fn span_underscore_borrow(&self) -> Span {
2134                         let lo = self.0.lo() + BytePos(1);
2135                         let hi = lo + BytePos(2);
2136                         self.0.with_lo(lo).with_hi(hi)
2137                     }
2138                 }
2139
2140                 for param in params {
2141                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
2142                         if let Some((span, sugg)) =
2143                             Lifetime(param.span, snippet).suggestion("'a ".to_string())
2144                         {
2145                             introduce_suggestion.push((span, sugg));
2146                         }
2147                     }
2148                 }
2149                 for (span, sugg) in spans_with_counts.iter().copied().zip(suggs.iter()).filter_map(
2150                     |((span, _), sugg)| match &sugg {
2151                         Some(sugg) => Some((span, sugg.to_string())),
2152                         _ => None,
2153                     },
2154                 ) {
2155                     let (span, sugg) = self
2156                         .tcx
2157                         .sess
2158                         .source_map()
2159                         .span_to_snippet(span)
2160                         .ok()
2161                         .and_then(|snippet| Lifetime(span, snippet).suggestion(sugg.clone()))
2162                         .unwrap_or((span, sugg));
2163                     introduce_suggestion.push((span, sugg.to_string()));
2164                 }
2165                 err.multipart_suggestion_with_style(
2166                     &msg,
2167                     introduce_suggestion,
2168                     Applicability::MaybeIncorrect,
2169                     SuggestionStyle::ShowAlways,
2170                 );
2171                 if should_break {
2172                     break;
2173                 }
2174             }
2175         };
2176
2177         let lifetime_names: Vec<_> = lifetime_names.iter().collect();
2178         match &lifetime_names[..] {
2179             [name] => {
2180                 let mut suggs: Vec<Option<Box<dyn Fn(&str) -> String>>> = Vec::new();
2181                 for (snippet, (_, count)) in snippets.iter().zip(spans_with_counts.iter().copied())
2182                 {
2183                     suggs.push(match snippet.as_deref() {
2184                         Some("&") => Some(Box::new(|name| format!("&{} ", name))),
2185                         Some("'_") => Some(Box::new(|n| n.to_string())),
2186                         Some("") => Some(Box::new(move |n| format!("{}, ", n).repeat(count))),
2187                         Some("<") => Some(Box::new(move |n| {
2188                             std::iter::repeat(n).take(count).collect::<Vec<_>>().join(", ")
2189                         })),
2190                         Some(snippet) if !snippet.ends_with('>') => Some(Box::new(move |name| {
2191                             format!(
2192                                 "{}<{}>",
2193                                 snippet,
2194                                 std::iter::repeat(name.to_string())
2195                                     .take(count)
2196                                     .collect::<Vec<_>>()
2197                                     .join(", ")
2198                             )
2199                         })),
2200                         _ => None,
2201                     });
2202                 }
2203                 suggest_existing(err, &name.as_str()[..], suggs);
2204             }
2205             [] => {
2206                 let mut suggs = Vec::new();
2207                 for (snippet, (_, count)) in
2208                     snippets.iter().cloned().zip(spans_with_counts.iter().copied())
2209                 {
2210                     suggs.push(match snippet.as_deref() {
2211                         Some("&") => Some("&'a ".to_string()),
2212                         Some("'_") => Some("'a".to_string()),
2213                         Some("") => {
2214                             Some(std::iter::repeat("'a, ").take(count).collect::<Vec<_>>().join(""))
2215                         }
2216                         Some("<") => {
2217                             Some(std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", "))
2218                         }
2219                         Some(snippet) => Some(format!(
2220                             "{}<{}>",
2221                             snippet,
2222                             std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", "),
2223                         )),
2224                         None => None,
2225                     });
2226                 }
2227                 suggest_new(err, suggs);
2228             }
2229             lts if lts.len() > 1 => {
2230                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
2231
2232                 let mut spans_suggs: Vec<_> = Vec::new();
2233                 for ((span, _), snippet) in spans_with_counts.iter().copied().zip(snippets.iter()) {
2234                     match snippet.as_deref() {
2235                         Some("") => spans_suggs.push((span, "'lifetime, ".to_string())),
2236                         Some("&") => spans_suggs
2237                             .push((span.with_lo(span.lo() + BytePos(1)), "'lifetime ".to_string())),
2238                         _ => {}
2239                     }
2240                 }
2241
2242                 if spans_suggs.len() > 0 {
2243                     // This happens when we have `Foo<T>` where we point at the space before `T`,
2244                     // but this can be confusing so we give a suggestion with placeholders.
2245                     err.multipart_suggestion_with_style(
2246                         "consider using one of the available lifetimes here",
2247                         spans_suggs,
2248                         Applicability::HasPlaceholders,
2249                         SuggestionStyle::ShowAlways,
2250                     );
2251                 }
2252             }
2253             _ => unreachable!(),
2254         }
2255     }
2256
2257     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
2258     /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
2259     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
2260     crate fn maybe_emit_forbidden_non_static_lifetime_error(
2261         &self,
2262         body_id: hir::BodyId,
2263         lifetime_ref: &'tcx hir::Lifetime,
2264     ) {
2265         let is_anon_const = matches!(
2266             self.tcx.def_kind(self.tcx.hir().body_owner_def_id(body_id)),
2267             hir::def::DefKind::AnonConst
2268         );
2269         let is_allowed_lifetime = matches!(
2270             lifetime_ref.name,
2271             hir::LifetimeName::Implicit | hir::LifetimeName::Static | hir::LifetimeName::Underscore
2272         );
2273
2274         if !self.tcx.lazy_normalization() && is_anon_const && !is_allowed_lifetime {
2275             feature_err(
2276                 &self.tcx.sess.parse_sess,
2277                 sym::generic_const_exprs,
2278                 lifetime_ref.span,
2279                 "a non-static lifetime is not allowed in a `const`",
2280             )
2281             .emit();
2282         }
2283     }
2284 }