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, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
  11     NodeId, Path, Ty, 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};
  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             .into_iter()
 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                                             None,
 772                                         ))
 773                                     } else {
 774                                         None
 775                                     };
 776                                     has_self_arg = Some((call_span, tail_args_span));
 777                                 }
 778                                 break;
 779                             }
 780                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 781                             _ => break,
 782                         }
 783                     }
 784                 }
 785                 _ => (),
 786             }
 787         };
 788         has_self_arg
 789     }
 790
 791     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 792         // HACK(estebank): find a better way to figure out that this was a
 793         // parser issue where a struct literal is being used on an expression
 794         // where a brace being opened means a block is being started. Look
 795         // ahead for the next text to see if `span` is followed by a `{`.
 796         let sm = self.r.session.source_map();
 797         let mut sp = span;
 798         loop {
 799             sp = sm.next_point(sp);
 800             match sm.span_to_snippet(sp) {
 801                 Ok(ref snippet) => {
 802                     if snippet.chars().any(|c| !c.is_whitespace()) {
 803                         break;
 804                     }
 805                 }
 806                 _ => break,
 807             }
 808         }
 809         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
 810         // In case this could be a struct literal that needs to be surrounded
 811         // by parentheses, find the appropriate span.
 812         let mut i = 0;
 813         let mut closing_brace = None;
 814         loop {
 815             sp = sm.next_point(sp);
 816             match sm.span_to_snippet(sp) {
 817                 Ok(ref snippet) => {
 818                     if snippet == "}" {
 819                         closing_brace = Some(span.to(sp));
 820                         break;
 821                     }
 822                 }
 823                 _ => break,
 824             }
 825             i += 1;
 826             // The bigger the span, the more likely we're incorrect --
 827             // bound it to 100 chars long.
 828             if i > 100 {
 829                 break;
 830             }
 831         }
 832         (followed_by_brace, closing_brace)
 833     }
 834
 835     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 836     /// function.
 837     /// Returns `true` if able to provide context-dependent help.
 838     fn smart_resolve_context_dependent_help(
 839         &mut self,
 840         err: &mut DiagnosticBuilder<'a>,
 841         span: Span,
 842         source: PathSource<'_>,
 843         res: Res,
 844         path_str: &str,
 845         fallback_label: &str,
 846     ) -> bool {
 847         let ns = source.namespace();
 848         let is_expected = &|res| source.is_expected(res);
 849
 850         let path_sep = |err: &mut DiagnosticBuilder<'_>, expr: &Expr| match expr.kind {
 851             ExprKind::Field(_, ident) => {
 852                 err.span_suggestion(
 853                     expr.span,
 854                     "use the path separator to refer to an item",
 855                     format!("{}::{}", path_str, ident),
 856                     Applicability::MaybeIncorrect,
 857                 );
 858                 true
 859             }
 860             ExprKind::MethodCall(ref segment, ..) => {
 861                 let span = expr.span.with_hi(segment.ident.span.hi());
 862                 err.span_suggestion(
 863                     span,
 864                     "use the path separator to refer to an item",
 865                     format!("{}::{}", path_str, segment.ident),
 866                     Applicability::MaybeIncorrect,
 867                 );
 868                 true
 869             }
 870             _ => false,
 871         };
 872
 873         let find_span = |source: &PathSource<'_>, err: &mut DiagnosticBuilder<'_>| {
 874             match source {
 875                 PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
 876                 | PathSource::TupleStruct(span, _) => {
 877                     // We want the main underline to cover the suggested code as well for
 878                     // cleaner output.
 879                     err.set_span(*span);
 880                     *span
 881                 }
 882                 _ => span,
 883             }
 884         };
 885
 886         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 887             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 888
 889             match source {
 890                 PathSource::Expr(Some(
 891                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
 892                 )) if path_sep(err, &parent) => {}
 893                 PathSource::Expr(
 894                     None
 895                     | Some(Expr {
 896                         kind:
 897                             ExprKind::Path(..)
 898                             | ExprKind::Binary(..)
 899                             | ExprKind::Unary(..)
 900                             | ExprKind::If(..)
 901                             | ExprKind::While(..)
 902                             | ExprKind::ForLoop(..)
 903                             | ExprKind::Match(..),
 904                         ..
 905                     }),
 906                 ) if followed_by_brace => {
 907                     if let Some(sp) = closing_brace {
 908                         err.span_label(span, fallback_label);
 909                         err.multipart_suggestion(
 910                             "surround the struct literal with parentheses",
 911                             vec![
 912                                 (sp.shrink_to_lo(), "(".to_string()),
 913                                 (sp.shrink_to_hi(), ")".to_string()),
 914                             ],
 915                             Applicability::MaybeIncorrect,
 916                         );
 917                     } else {
 918                         err.span_label(
 919                             span, // Note the parentheses surrounding the suggestion below
 920                             format!(
 921                                 "you might want to surround a struct literal with parentheses: \
 922                                  `({} {{ /* fields */ }})`?",
 923                                 path_str
 924                             ),
 925                         );
 926                     }
 927                 }
 928                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
 929                     let span = find_span(&source, err);
 930                     if let Some(span) = self.def_span(def_id) {
 931                         err.span_label(span, &format!("`{}` defined here", path_str));
 932                     }
 933                     let (tail, descr, applicability) = match source {
 934                         PathSource::Pat | PathSource::TupleStruct(..) => {
 935                             ("", "pattern", Applicability::MachineApplicable)
 936                         }
 937                         _ => (": val", "literal", Applicability::HasPlaceholders),
 938                     };
 939                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
 940                         Some(fields) => (
 941                             fields
 942                                 .iter()
 943                                 .map(|f| format!("{}{}", f.node, tail))
 944                                 .collect::<Vec<String>>()
 945                                 .join(", "),
 946                             applicability,
 947                         ),
 948                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
 949                     };
 950                     let pad = match self.r.field_names.get(&def_id) {
 951                         Some(fields) if fields.is_empty() => "",
 952                         _ => " ",
 953                     };
 954                     err.span_suggestion(
 955                         span,
 956                         &format!("use struct {} syntax instead", descr),
 957                         format!("{path_str} {{{pad}{fields}{pad}}}"),
 958                         applicability,
 959                     );
 960                 }
 961                 _ => {
 962                     err.span_label(span, fallback_label);
 963                 }
 964             }
 965         };
 966
 967         match (res, source) {
 968             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
 969                 err.span_label(span, fallback_label);
 970                 err.span_suggestion_verbose(
 971                     span.shrink_to_hi(),
 972                     "use `!` to invoke the macro",
 973                     "!".to_string(),
 974                     Applicability::MaybeIncorrect,
 975                 );
 976                 if path_str == "try" && span.rust_2015() {
 977                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
 978                 }
 979             }
 980             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
 981                 err.span_label(span, "type aliases cannot be used as traits");
 982                 if self.r.session.is_nightly_build() {
 983                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
 984                                `type` alias";
 985                     if let Some(span) = self.def_span(def_id) {
 986                         if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
 987                             // The span contains a type alias so we should be able to
 988                             // replace `type` with `trait`.
 989                             let snip = snip.replacen("type", "trait", 1);
 990                             err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
 991                         } else {
 992                             err.span_help(span, msg);
 993                         }
 994                     } else {
 995                         err.help(msg);
 996                     }
 997                 }
 998             }
 999             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
1000                 if !path_sep(err, &parent) {
1001                     return false;
1002                 }
1003             }
1004             (
1005                 Res::Def(DefKind::Enum, def_id),
1006                 PathSource::TupleStruct(..) | PathSource::Expr(..),
1007             ) => {
1008                 if self
1009                     .diagnostic_metadata
1010                     .current_type_ascription
1011                     .last()
1012                     .map(|sp| {
1013                         self.r
1014                             .session
1015                             .parse_sess
1016                             .type_ascription_path_suggestions
1017                             .borrow()
1018                             .contains(&sp)
1019                     })
1020                     .unwrap_or(false)
1021                 {
1022                     err.delay_as_bug();
1023                     // We already suggested changing `:` into `::` during parsing.
1024                     return false;
1025                 }
1026
1027                 self.suggest_using_enum_variant(err, source, def_id, span);
1028             }
1029             (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
1030                 let (ctor_def, ctor_vis, fields) =
1031                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
1032                         if let PathSource::Expr(Some(parent)) = source {
1033                             if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
1034                                 bad_struct_syntax_suggestion(def_id);
1035                                 return true;
1036                             }
1037                         }
1038                         struct_ctor
1039                     } else {
1040                         bad_struct_syntax_suggestion(def_id);
1041                         return true;
1042                     };
1043
1044                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
1045                 if !is_expected(ctor_def) || is_accessible {
1046                     return true;
1047                 }
1048
1049                 let field_spans = match source {
1050                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
1051                     PathSource::TupleStruct(_, pattern_spans) => {
1052                         err.set_primary_message(
1053                             "cannot match against a tuple struct which contains private fields",
1054                         );
1055
1056                         // Use spans of the tuple struct pattern.
1057                         Some(Vec::from(pattern_spans))
1058                     }
1059                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
1060                     _ if source.is_call() => {
1061                         err.set_primary_message(
1062                             "cannot initialize a tuple struct which contains private fields",
1063                         );
1064
1065                         // Use spans of the tuple struct definition.
1066                         self.r
1067                             .field_names
1068                             .get(&def_id)
1069                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
1070                     }
1071                     _ => None,
1072                 };
1073
1074                 if let Some(spans) =
1075                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
1076                 {
1077                     let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
1078                         .filter(|(vis, _)| {
1079                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
1080                         })
1081                         .map(|(_, span)| *span)
1082                         .collect();
1083
1084                     if non_visible_spans.len() > 0 {
1085                         let mut m: rustc_span::MultiSpan = non_visible_spans.clone().into();
1086                         non_visible_spans
1087                             .into_iter()
1088                             .for_each(|s| m.push_span_label(s, "private field".to_string()));
1089                         err.span_note(m, "constructor is not visible here due to private fields");
1090                     }
1091
1092                     return true;
1093                 }
1094
1095                 err.span_label(
1096                     span,
1097                     "constructor is not visible here due to private fields".to_string(),
1098                 );
1099             }
1100             (
1101                 Res::Def(
1102                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
1103                     def_id,
1104                 ),
1105                 _,
1106             ) if ns == ValueNS => {
1107                 bad_struct_syntax_suggestion(def_id);
1108             }
1109             (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
1110                 match source {
1111                     PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1112                         let span = find_span(&source, err);
1113                         if let Some(span) = self.def_span(def_id) {
1114                             err.span_label(span, &format!("`{}` defined here", path_str));
1115                         }
1116                         err.span_suggestion(
1117                             span,
1118                             &"use this syntax instead",
1119                             format!("{path_str}"),
1120                             Applicability::MaybeIncorrect,
1121                         );
1122                     }
1123                     _ => return false,
1124                 }
1125             }
1126             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
1127                 if let Some(span) = self.def_span(def_id) {
1128                     err.span_label(span, &format!("`{}` defined here", path_str));
1129                 }
1130                 let fields = self.r.field_names.get(&def_id).map_or_else(
1131                     || "/* fields */".to_string(),
1132                     |fields| vec!["_"; fields.len()].join(", "),
1133                 );
1134                 err.span_suggestion(
1135                     span,
1136                     "use the tuple variant pattern syntax instead",
1137                     format!("{}({})", path_str, fields),
1138                     Applicability::HasPlaceholders,
1139                 );
1140             }
1141             (Res::SelfTy(..), _) if ns == ValueNS => {
1142                 err.span_label(span, fallback_label);
1143                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1144             }
1145             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1146                 err.note("can't use a type alias as a constructor");
1147             }
1148             _ => return false,
1149         }
1150         true
1151     }
1152
1153     /// Given the target `ident` and `kind`, search for the similarly named associated item
1154     /// in `self.current_trait_ref`.
1155     crate fn find_similarly_named_assoc_item(
1156         &mut self,
1157         ident: Symbol,
1158         kind: &AssocItemKind,
1159     ) -> Option<Symbol> {
1160         let module = if let Some((module, _)) = self.current_trait_ref {
1161             module
1162         } else {
1163             return None;
1164         };
1165         if ident == kw::Underscore {
1166             // We do nothing for `_`.
1167             return None;
1168         }
1169
1170         let resolutions = self.r.resolutions(module);
1171         let targets = resolutions
1172             .borrow()
1173             .iter()
1174             .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
1175             .filter(|(_, res)| match (kind, res) {
1176                 (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
1177                 (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
1178                 (AssocItemKind::TyAlias(..), Res::Def(DefKind::AssocTy, _)) => true,
1179                 _ => false,
1180             })
1181             .map(|(key, _)| key.ident.name)
1182             .collect::<Vec<_>>();
1183
1184         find_best_match_for_name(&targets, ident, None)
1185     }
1186
1187     fn lookup_assoc_candidate<FilterFn>(
1188         &mut self,
1189         ident: Ident,
1190         ns: Namespace,
1191         filter_fn: FilterFn,
1192     ) -> Option<AssocSuggestion>
1193     where
1194         FilterFn: Fn(Res) -> bool,
1195     {
1196         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1197             match t.kind {
1198                 TyKind::Path(None, _) => Some(t.id),
1199                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1200                 // This doesn't handle the remaining `Ty` variants as they are not
1201                 // that commonly the self_type, it might be interesting to provide
1202                 // support for those in future.
1203                 _ => None,
1204             }
1205         }
1206
1207         // Fields are generally expected in the same contexts as locals.
1208         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1209             if let Some(node_id) =
1210                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1211             {
1212                 // Look for a field with the same name in the current self_type.
1213                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1214                     match resolution.base_res() {
1215                         Res::Def(DefKind::Struct | DefKind::Union, did)
1216                             if resolution.unresolved_segments() == 0 =>
1217                         {
1218                             if let Some(field_names) = self.r.field_names.get(&did) {
1219                                 if field_names
1220                                     .iter()
1221                                     .any(|&field_name| ident.name == field_name.node)
1222                                 {
1223                                     return Some(AssocSuggestion::Field);
1224                                 }
1225                             }
1226                         }
1227                         _ => {}
1228                     }
1229                 }
1230             }
1231         }
1232
1233         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1234             for assoc_item in items {
1235                 if assoc_item.ident == ident {
1236                     return Some(match &assoc_item.kind {
1237                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1238                         ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
1239                             AssocSuggestion::MethodWithSelf
1240                         }
1241                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn,
1242                         ast::AssocItemKind::TyAlias(..) => AssocSuggestion::AssocType,
1243                         ast::AssocItemKind::MacCall(_) => continue,
1244                     });
1245                 }
1246             }
1247         }
1248
1249         // Look for associated items in the current trait.
1250         if let Some((module, _)) = self.current_trait_ref {
1251             if let Ok(binding) = self.r.resolve_ident_in_module(
1252                 ModuleOrUniformRoot::Module(module),
1253                 ident,
1254                 ns,
1255                 &self.parent_scope,
1256                 false,
1257                 module.span,
1258             ) {
1259                 let res = binding.res();
1260                 if filter_fn(res) {
1261                     if self.r.has_self.contains(&res.def_id()) {
1262                         return Some(AssocSuggestion::MethodWithSelf);
1263                     } else {
1264                         match res {
1265                             Res::Def(DefKind::AssocFn, _) => return Some(AssocSuggestion::AssocFn),
1266                             Res::Def(DefKind::AssocConst, _) => {
1267                                 return Some(AssocSuggestion::AssocConst);
1268                             }
1269                             Res::Def(DefKind::AssocTy, _) => {
1270                                 return Some(AssocSuggestion::AssocType);
1271                             }
1272                             _ => {}
1273                         }
1274                     }
1275                 }
1276             }
1277         }
1278
1279         None
1280     }
1281
1282     fn lookup_typo_candidate(
1283         &mut self,
1284         path: &[Segment],
1285         ns: Namespace,
1286         filter_fn: &impl Fn(Res) -> bool,
1287         span: Span,
1288     ) -> Option<TypoSuggestion> {
1289         let mut names = Vec::new();
1290         if path.len() == 1 {
1291             // Search in lexical scope.
1292             // Walk backwards up the ribs in scope and collect candidates.
1293             for rib in self.ribs[ns].iter().rev() {
1294                 // Locals and type parameters
1295                 for (ident, &res) in &rib.bindings {
1296                     if filter_fn(res) {
1297                         names.push(TypoSuggestion::typo_from_res(ident.name, res));
1298                     }
1299                 }
1300                 // Items in scope
1301                 if let RibKind::ModuleRibKind(module) = rib.kind {
1302                     // Items from this module
1303                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1304
1305                     if let ModuleKind::Block(..) = module.kind {
1306                         // We can see through blocks
1307                     } else {
1308                         // Items from the prelude
1309                         if !module.no_implicit_prelude {
1310                             let extern_prelude = self.r.extern_prelude.clone();
1311                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1312                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
1313                                     |crate_id| {
1314                                         let crate_mod = Res::Def(
1315                                             DefKind::Mod,
1316                                             DefId { krate: crate_id, index: CRATE_DEF_INDEX },
1317                                         );
1318
1319                                         if filter_fn(crate_mod) {
1320                                             Some(TypoSuggestion::typo_from_res(
1321                                                 ident.name, crate_mod,
1322                                             ))
1323                                         } else {
1324                                             None
1325                                         }
1326                                     },
1327                                 )
1328                             }));
1329
1330                             if let Some(prelude) = self.r.prelude {
1331                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
1332                             }
1333                         }
1334                         break;
1335                     }
1336                 }
1337             }
1338             // Add primitive types to the mix
1339             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1340                 names.extend(PrimTy::ALL.iter().map(|prim_ty| {
1341                     TypoSuggestion::typo_from_res(prim_ty.name(), Res::PrimTy(*prim_ty))
1342                 }))
1343             }
1344         } else {
1345             // Search in module.
1346             let mod_path = &path[..path.len() - 1];
1347             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1348                 self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No)
1349             {
1350                 self.r.add_module_candidates(module, &mut names, &filter_fn);
1351             }
1352         }
1353
1354         let name = path[path.len() - 1].ident.name;
1355         // Make sure error reporting is deterministic.
1356         names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
1357
1358         match find_best_match_for_name(
1359             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1360             name,
1361             None,
1362         ) {
1363             Some(found) if found != name => {
1364                 names.into_iter().find(|suggestion| suggestion.candidate == found)
1365             }
1366             _ => None,
1367         }
1368     }
1369
1370     // Returns the name of the Rust type approximately corresponding to
1371     // a type name in another programming language.
1372     fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
1373         let name = path[path.len() - 1].ident.as_str();
1374         // Common Java types
1375         Some(match &*name {
1376             "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
1377             "short" => sym::i16,
1378             "boolean" => sym::bool,
1379             "int" => sym::i32,
1380             "long" => sym::i64,
1381             "float" => sym::f32,
1382             "double" => sym::f64,
1383             _ => return None,
1384         })
1385     }
1386
1387     /// Only used in a specific case of type ascription suggestions
1388     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1389         let sm = self.r.session.source_map();
1390         start.to(sm.next_point(start))
1391     }
1392
1393     fn type_ascription_suggestion(&self, err: &mut DiagnosticBuilder<'_>, base_span: Span) -> bool {
1394         let sm = self.r.session.source_map();
1395         let base_snippet = sm.span_to_snippet(base_span);
1396         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1397             if let Ok(snippet) = sm.span_to_snippet(sp) {
1398                 let len = snippet.trim_end().len() as u32;
1399                 if snippet.trim() == ":" {
1400                     let colon_sp =
1401                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1402                     let mut show_label = true;
1403                     if sm.is_multiline(sp) {
1404                         err.span_suggestion_short(
1405                             colon_sp,
1406                             "maybe you meant to write `;` here",
1407                             ";".to_string(),
1408                             Applicability::MaybeIncorrect,
1409                         );
1410                     } else {
1411                         let after_colon_sp =
1412                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1413                         if snippet.len() == 1 {
1414                             // `foo:bar`
1415                             err.span_suggestion(
1416                                 colon_sp,
1417                                 "maybe you meant to write a path separator here",
1418                                 "::".to_string(),
1419                                 Applicability::MaybeIncorrect,
1420                             );
1421                             show_label = false;
1422                             if !self
1423                                 .r
1424                                 .session
1425                                 .parse_sess
1426                                 .type_ascription_path_suggestions
1427                                 .borrow_mut()
1428                                 .insert(colon_sp)
1429                             {
1430                                 err.delay_as_bug();
1431                             }
1432                         }
1433                         if let Ok(base_snippet) = base_snippet {
1434                             let mut sp = after_colon_sp;
1435                             for _ in 0..100 {
1436                                 // Try to find an assignment
1437                                 sp = sm.next_point(sp);
1438                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
1439                                 match snippet {
1440                                     Ok(ref x) if x.as_str() == "=" => {
1441                                         err.span_suggestion(
1442                                             base_span,
1443                                             "maybe you meant to write an assignment here",
1444                                             format!("let {}", base_snippet),
1445                                             Applicability::MaybeIncorrect,
1446                                         );
1447                                         show_label = false;
1448                                         break;
1449                                     }
1450                                     Ok(ref x) if x.as_str() == "\n" => break,
1451                                     Err(_) => break,
1452                                     Ok(_) => {}
1453                                 }
1454                             }
1455                         }
1456                     }
1457                     if show_label {
1458                         err.span_label(
1459                             base_span,
1460                             "expecting a type here because of type ascription",
1461                         );
1462                     }
1463                     return show_label;
1464                 }
1465             }
1466         }
1467         false
1468     }
1469
1470     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1471         let mut result = None;
1472         let mut seen_modules = FxHashSet::default();
1473         let mut worklist = vec![(self.r.graph_root, Vec::new())];
1474
1475         while let Some((in_module, path_segments)) = worklist.pop() {
1476             // abort if the module is already found
1477             if result.is_some() {
1478                 break;
1479             }
1480
1481             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1482                 // abort if the module is already found or if name_binding is private external
1483                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1484                     return;
1485                 }
1486                 if let Some(module) = name_binding.module() {
1487                     // form the path
1488                     let mut path_segments = path_segments.clone();
1489                     path_segments.push(ast::PathSegment::from_ident(ident));
1490                     let module_def_id = module.def_id();
1491                     if module_def_id == def_id {
1492                         let path =
1493                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1494                         result = Some((
1495                             module,
1496                             ImportSuggestion {
1497                                 did: Some(def_id),
1498                                 descr: "module",
1499                                 path,
1500                                 accessible: true,
1501                                 note: None,
1502                             },
1503                         ));
1504                     } else {
1505                         // add the module to the lookup
1506                         if seen_modules.insert(module_def_id) {
1507                             worklist.push((module, path_segments));
1508                         }
1509                     }
1510                 }
1511             });
1512         }
1513
1514         result
1515     }
1516
1517     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1518         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1519             let mut variants = Vec::new();
1520             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1521                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1522                     let mut segms = enum_import_suggestion.path.segments.clone();
1523                     segms.push(ast::PathSegment::from_ident(ident));
1524                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1525                     variants.push((path, def_id, kind));
1526                 }
1527             });
1528             variants
1529         })
1530     }
1531
1532     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1533     fn suggest_using_enum_variant(
1534         &mut self,
1535         err: &mut DiagnosticBuilder<'a>,
1536         source: PathSource<'_>,
1537         def_id: DefId,
1538         span: Span,
1539     ) {
1540         let variants = match self.collect_enum_ctors(def_id) {
1541             Some(variants) => variants,
1542             None => {
1543                 err.note("you might have meant to use one of the enum's variants");
1544                 return;
1545             }
1546         };
1547
1548         let suggest_only_tuple_variants =
1549             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1550         if suggest_only_tuple_variants {
1551             // Suggest only tuple variants regardless of whether they have fields and do not
1552             // suggest path with added parentheses.
1553             let suggestable_variants = variants
1554                 .iter()
1555                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1556                 .map(|(variant, ..)| path_names_to_string(variant))
1557                 .collect::<Vec<_>>();
1558
1559             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1560
1561             let source_msg = if source.is_call() {
1562                 "to construct"
1563             } else if matches!(source, PathSource::TupleStruct(..)) {
1564                 "to match against"
1565             } else {
1566                 unreachable!()
1567             };
1568
1569             if !suggestable_variants.is_empty() {
1570                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1571                     format!("try {} the enum's variant", source_msg)
1572                 } else {
1573                     format!("try {} one of the enum's variants", source_msg)
1574                 };
1575
1576                 err.span_suggestions(
1577                     span,
1578                     &msg,
1579                     suggestable_variants.into_iter(),
1580                     Applicability::MaybeIncorrect,
1581                 );
1582             }
1583
1584             // If the enum has no tuple variants..
1585             if non_suggestable_variant_count == variants.len() {
1586                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1587             }
1588
1589             // If there are also non-tuple variants..
1590             if non_suggestable_variant_count == 1 {
1591                 err.help(&format!(
1592                     "you might have meant {} the enum's non-tuple variant",
1593                     source_msg
1594                 ));
1595             } else if non_suggestable_variant_count >= 1 {
1596                 err.help(&format!(
1597                     "you might have meant {} one of the enum's non-tuple variants",
1598                     source_msg
1599                 ));
1600             }
1601         } else {
1602             let needs_placeholder = |def_id: DefId, kind: CtorKind| {
1603                 let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
1604                 match kind {
1605                     CtorKind::Const => false,
1606                     CtorKind::Fn | CtorKind::Fictive if has_no_fields => false,
1607                     _ => true,
1608                 }
1609             };
1610
1611             let mut suggestable_variants = variants
1612                 .iter()
1613                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1614                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1615                 .map(|(variant, kind)| match kind {
1616                     CtorKind::Const => variant,
1617                     CtorKind::Fn => format!("({}())", variant),
1618                     CtorKind::Fictive => format!("({} {{}})", variant),
1619                 })
1620                 .collect::<Vec<_>>();
1621
1622             if !suggestable_variants.is_empty() {
1623                 let msg = if suggestable_variants.len() == 1 {
1624                     "you might have meant to use the following enum variant"
1625                 } else {
1626                     "you might have meant to use one of the following enum variants"
1627                 };
1628
1629                 err.span_suggestions(
1630                     span,
1631                     msg,
1632                     suggestable_variants.drain(..),
1633                     Applicability::MaybeIncorrect,
1634                 );
1635             }
1636
1637             let suggestable_variants_with_placeholders = variants
1638                 .iter()
1639                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
1640                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1641                 .filter_map(|(variant, kind)| match kind {
1642                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
1643                     CtorKind::Fictive => Some(format!("({} {{ /* fields */ }})", variant)),
1644                     _ => None,
1645                 })
1646                 .collect::<Vec<_>>();
1647
1648             if !suggestable_variants_with_placeholders.is_empty() {
1649                 let msg = match (
1650                     suggestable_variants.is_empty(),
1651                     suggestable_variants_with_placeholders.len(),
1652                 ) {
1653                     (true, 1) => "the following enum variant is available",
1654                     (true, _) => "the following enum variants are available",
1655                     (false, 1) => "alternatively, the following enum variant is available",
1656                     (false, _) => "alternatively, the following enum variants are also available",
1657                 };
1658
1659                 err.span_suggestions(
1660                     span,
1661                     msg,
1662                     suggestable_variants_with_placeholders.into_iter(),
1663                     Applicability::HasPlaceholders,
1664                 );
1665             }
1666         };
1667
1668         if def_id.is_local() {
1669             if let Some(span) = self.def_span(def_id) {
1670                 err.span_note(span, "the enum is defined here");
1671             }
1672         }
1673     }
1674
1675     crate fn report_missing_type_error(
1676         &self,
1677         path: &[Segment],
1678     ) -> Option<(Span, &'static str, String, Applicability)> {
1679         let (ident, span) = match path {
1680             [segment] if !segment.has_generic_args => {
1681                 (segment.ident.to_string(), segment.ident.span)
1682             }
1683             _ => return None,
1684         };
1685         let mut iter = ident.chars().map(|c| c.is_uppercase());
1686         let single_uppercase_char =
1687             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1688         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1689             return None;
1690         }
1691         match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
1692             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
1693                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1694             }
1695             (
1696                 Some(Item {
1697                     kind:
1698                         kind @ ItemKind::Fn(..)
1699                         | kind @ ItemKind::Enum(..)
1700                         | kind @ ItemKind::Struct(..)
1701                         | kind @ ItemKind::Union(..),
1702                     ..
1703                 }),
1704                 true, _
1705             )
1706             // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
1707             | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
1708             | (Some(Item { kind, .. }), false, _) => {
1709                 // Likely missing type parameter.
1710                 if let Some(generics) = kind.generics() {
1711                     if span.overlaps(generics.span) {
1712                         // Avoid the following:
1713                         // error[E0405]: cannot find trait `A` in this scope
1714                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1715                         //   |
1716                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1717                         //   |           ^- help: you might be missing a type parameter: `, A`
1718                         //   |           |
1719                         //   |           not found in this scope
1720                         return None;
1721                     }
1722                     let msg = "you might be missing a type parameter";
1723                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1724                         let span = if let [.., bound] = &param.bounds[..] {
1725                             bound.span()
1726                         } else if let GenericParam {
1727                             kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
1728                         } = param {
1729                             default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
1730                         } else {
1731                             param.ident.span
1732                         };
1733                         (span, format!(", {}", ident))
1734                     } else {
1735                         (generics.span, format!("<{}>", ident))
1736                     };
1737                     // Do not suggest if this is coming from macro expansion.
1738                     if !span.from_expansion() {
1739                         return Some((
1740                             span.shrink_to_hi(),
1741                             msg,
1742                             sugg,
1743                             Applicability::MaybeIncorrect,
1744                         ));
1745                     }
1746                 }
1747             }
1748             _ => {}
1749         }
1750         None
1751     }
1752
1753     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1754     /// optionally returning the closest match and whether it is reachable.
1755     crate fn suggestion_for_label_in_rib(
1756         &self,
1757         rib_index: usize,
1758         label: Ident,
1759     ) -> Option<LabelSuggestion> {
1760         // Are ribs from this `rib_index` within scope?
1761         let within_scope = self.is_label_valid_from_rib(rib_index);
1762
1763         let rib = &self.label_ribs[rib_index];
1764         let names = rib
1765             .bindings
1766             .iter()
1767             .filter(|(id, _)| id.span.ctxt() == label.span.ctxt())
1768             .map(|(id, _)| id.name)
1769             .collect::<Vec<Symbol>>();
1770
1771         find_best_match_for_name(&names, label.name, None).map(|symbol| {
1772             // Upon finding a similar name, get the ident that it was from - the span
1773             // contained within helps make a useful diagnostic. In addition, determine
1774             // whether this candidate is within scope.
1775             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1776             (*ident, within_scope)
1777         })
1778     }
1779 }
1780
1781 impl<'tcx> LifetimeContext<'_, 'tcx> {
1782     crate fn report_missing_lifetime_specifiers(
1783         &self,
1784         spans: Vec<Span>,
1785         count: usize,
1786     ) -> DiagnosticBuilder<'tcx> {
1787         struct_span_err!(
1788             self.tcx.sess,
1789             spans,
1790             E0106,
1791             "missing lifetime specifier{}",
1792             pluralize!(count)
1793         )
1794     }
1795
1796     crate fn emit_undeclared_lifetime_error(&self, lifetime_ref: &hir::Lifetime) {
1797         let mut err = struct_span_err!(
1798             self.tcx.sess,
1799             lifetime_ref.span,
1800             E0261,
1801             "use of undeclared lifetime name `{}`",
1802             lifetime_ref
1803         );
1804         err.span_label(lifetime_ref.span, "undeclared lifetime");
1805         let mut suggests_in_band = false;
1806         let mut suggest_note = true;
1807         for missing in &self.missing_named_lifetime_spots {
1808             match missing {
1809                 MissingLifetimeSpot::Generics(generics) => {
1810                     let (span, sugg) = if let Some(param) = generics.params.iter().find(|p| {
1811                         !matches!(
1812                             p.kind,
1813                             hir::GenericParamKind::Type {
1814                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1815                                 ..
1816                             } | hir::GenericParamKind::Lifetime {
1817                                 kind: hir::LifetimeParamKind::Elided,
1818                             }
1819                         )
1820                     }) {
1821                         (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref))
1822                     } else {
1823                         suggests_in_band = true;
1824                         (generics.span, format!("<{}>", lifetime_ref))
1825                     };
1826                     if !span.from_expansion() {
1827                         err.span_suggestion(
1828                             span,
1829                             &format!("consider introducing lifetime `{}` here", lifetime_ref),
1830                             sugg,
1831                             Applicability::MaybeIncorrect,
1832                         );
1833                     } else if suggest_note {
1834                         suggest_note = false; // Avoid displaying the same help multiple times.
1835                         err.span_label(
1836                             span,
1837                             &format!(
1838                                 "lifetime `{}` is missing in item created through this procedural \
1839                                  macro",
1840                                 lifetime_ref,
1841                             ),
1842                         );
1843                     }
1844                 }
1845                 MissingLifetimeSpot::HigherRanked { span, span_type } => {
1846                     err.span_suggestion(
1847                         *span,
1848                         &format!(
1849                             "consider making the {} lifetime-generic with a new `{}` lifetime",
1850                             span_type.descr(),
1851                             lifetime_ref
1852                         ),
1853                         span_type.suggestion(&lifetime_ref.to_string()),
1854                         Applicability::MaybeIncorrect,
1855                     );
1856                     err.note(
1857                         "for more information on higher-ranked polymorphism, visit \
1858                          https://doc.rust-lang.org/nomicon/hrtb.html",
1859                     );
1860                 }
1861                 _ => {}
1862             }
1863         }
1864         if self.tcx.sess.is_nightly_build()
1865             && !self.tcx.features().in_band_lifetimes
1866             && suggests_in_band
1867         {
1868             err.help(
1869                 "if you want to experiment with in-band lifetime bindings, \
1870                  add `#![feature(in_band_lifetimes)]` to the crate attributes",
1871             );
1872         }
1873         err.emit();
1874     }
1875
1876     // FIXME(const_generics): This patches over an ICE caused by non-'static lifetimes in const
1877     // generics. We are disallowing this until we can decide on how we want to handle non-'static
1878     // lifetimes in const generics. See issue #74052 for discussion.
1879     crate fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &hir::Lifetime) {
1880         let mut err = struct_span_err!(
1881             self.tcx.sess,
1882             lifetime_ref.span,
1883             E0771,
1884             "use of non-static lifetime `{}` in const generic",
1885             lifetime_ref
1886         );
1887         err.note(
1888             "for more information, see issue #74052 \
1889             <https://github.com/rust-lang/rust/issues/74052>",
1890         );
1891         err.emit();
1892     }
1893
1894     crate fn is_trait_ref_fn_scope(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) -> bool {
1895         if let def::Res::Def(_, did) = trait_ref.trait_ref.path.res {
1896             if [
1897                 self.tcx.lang_items().fn_once_trait(),
1898                 self.tcx.lang_items().fn_trait(),
1899                 self.tcx.lang_items().fn_mut_trait(),
1900             ]
1901             .contains(&Some(did))
1902             {
1903                 let (span, span_type) = match &trait_ref.bound_generic_params {
1904                     [] => (trait_ref.span.shrink_to_lo(), ForLifetimeSpanType::BoundEmpty),
1905                     [.., bound] => (bound.span.shrink_to_hi(), ForLifetimeSpanType::BoundTail),
1906                 };
1907                 self.missing_named_lifetime_spots
1908                     .push(MissingLifetimeSpot::HigherRanked { span, span_type });
1909                 return true;
1910             }
1911         };
1912         false
1913     }
1914
1915     crate fn add_missing_lifetime_specifiers_label(
1916         &self,
1917         err: &mut DiagnosticBuilder<'_>,
1918         mut spans_with_counts: Vec<(Span, usize)>,
1919         lifetime_names: &FxHashSet<Symbol>,
1920         lifetime_spans: Vec<Span>,
1921         params: &[ElisionFailureInfo],
1922     ) {
1923         let snippets: Vec<Option<String>> = spans_with_counts
1924             .iter()
1925             .map(|(span, _)| self.tcx.sess.source_map().span_to_snippet(*span).ok())
1926             .collect();
1927
1928         // Empty generics are marked with a span of "<", but since from now on
1929         // that information is in the snippets it can be removed from the spans.
1930         for ((span, _), snippet) in spans_with_counts.iter_mut().zip(&snippets) {
1931             if snippet.as_deref() == Some("<") {
1932                 *span = span.shrink_to_hi();
1933             }
1934         }
1935
1936         for &(span, count) in &spans_with_counts {
1937             err.span_label(
1938                 span,
1939                 format!(
1940                     "expected {} lifetime parameter{}",
1941                     if count == 1 { "named".to_string() } else { count.to_string() },
1942                     pluralize!(count),
1943                 ),
1944             );
1945         }
1946
1947         let suggest_existing =
1948             |err: &mut DiagnosticBuilder<'_>,
1949              name: &str,
1950              formatters: Vec<Option<Box<dyn Fn(&str) -> String>>>| {
1951                 if let Some(MissingLifetimeSpot::HigherRanked { span: for_span, span_type }) =
1952                     self.missing_named_lifetime_spots.iter().rev().next()
1953                 {
1954                     // When we have `struct S<'a>(&'a dyn Fn(&X) -> &X);` we want to not only suggest
1955                     // using `'a`, but also introduce the concept of HRLTs by suggesting
1956                     // `struct S<'a>(&'a dyn for<'b> Fn(&X) -> &'b X);`. (#72404)
1957                     let mut introduce_suggestion = vec![];
1958
1959                     let a_to_z_repeat_n = |n| {
1960                         (b'a'..=b'z').map(move |c| {
1961                             let mut s = '\''.to_string();
1962                             s.extend(std::iter::repeat(char::from(c)).take(n));
1963                             s
1964                         })
1965                     };
1966
1967                     // If all single char lifetime names are present, we wrap around and double the chars.
1968                     let lt_name = (1..)
1969                         .flat_map(a_to_z_repeat_n)
1970                         .find(|lt| !lifetime_names.contains(&Symbol::intern(&lt)))
1971                         .unwrap();
1972                     let msg = format!(
1973                         "consider making the {} lifetime-generic with a new `{}` lifetime",
1974                         span_type.descr(),
1975                         lt_name,
1976                     );
1977                     err.note(
1978                         "for more information on higher-ranked polymorphism, visit \
1979                     https://doc.rust-lang.org/nomicon/hrtb.html",
1980                     );
1981                     let for_sugg = span_type.suggestion(&lt_name);
1982                     for param in params {
1983                         if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span)
1984                         {
1985                             if snippet.starts_with('&') && !snippet.starts_with("&'") {
1986                                 introduce_suggestion
1987                                     .push((param.span, format!("&{} {}", lt_name, &snippet[1..])));
1988                             } else if let Some(stripped) = snippet.strip_prefix("&'_ ") {
1989                                 introduce_suggestion
1990                                     .push((param.span, format!("&{} {}", lt_name, stripped)));
1991                             }
1992                         }
1993                     }
1994                     introduce_suggestion.push((*for_span, for_sugg));
1995                     for ((span, _), formatter) in spans_with_counts.iter().zip(formatters.iter()) {
1996                         if let Some(formatter) = formatter {
1997                             introduce_suggestion.push((*span, formatter(&lt_name)));
1998                         }
1999                     }
2000                     err.multipart_suggestion_verbose(
2001                         &msg,
2002                         introduce_suggestion,
2003                         Applicability::MaybeIncorrect,
2004                     );
2005                 }
2006
2007                 let spans_suggs: Vec<_> = formatters
2008                     .into_iter()
2009                     .zip(spans_with_counts.iter())
2010                     .filter_map(|(fmt, (span, _))| {
2011                         if let Some(formatter) = fmt { Some((formatter, span)) } else { None }
2012                     })
2013                     .map(|(formatter, span)| (*span, formatter(name)))
2014                     .collect();
2015                 err.multipart_suggestion_verbose(
2016                     &format!(
2017                         "consider using the `{}` lifetime",
2018                         lifetime_names.iter().next().unwrap()
2019                     ),
2020                     spans_suggs,
2021                     Applicability::MaybeIncorrect,
2022                 );
2023             };
2024         let suggest_new = |err: &mut DiagnosticBuilder<'_>, suggs: Vec<Option<String>>| {
2025             for missing in self.missing_named_lifetime_spots.iter().rev() {
2026                 let mut introduce_suggestion = vec![];
2027                 let msg;
2028                 let should_break;
2029                 introduce_suggestion.push(match missing {
2030                     MissingLifetimeSpot::Generics(generics) => {
2031                         if generics.span == DUMMY_SP {
2032                             // Account for malformed generics in the HIR. This shouldn't happen,
2033                             // but if we make a mistake elsewhere, mainly by keeping something in
2034                             // `missing_named_lifetime_spots` that we shouldn't, like associated
2035                             // `const`s or making a mistake in the AST lowering we would provide
2036                             // non-sensical suggestions. Guard against that by skipping these.
2037                             // (#74264)
2038                             continue;
2039                         }
2040                         msg = "consider introducing a named lifetime parameter".to_string();
2041                         should_break = true;
2042                         if let Some(param) = generics.params.iter().find(|p| {
2043                             !matches!(
2044                                 p.kind,
2045                                 hir::GenericParamKind::Type {
2046                                     synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
2047                                     ..
2048                                 } | hir::GenericParamKind::Lifetime {
2049                                     kind: hir::LifetimeParamKind::Elided
2050                                 }
2051                             )
2052                         }) {
2053                             (param.span.shrink_to_lo(), "'a, ".to_string())
2054                         } else {
2055                             (generics.span, "<'a>".to_string())
2056                         }
2057                     }
2058                     MissingLifetimeSpot::HigherRanked { span, span_type } => {
2059                         msg = format!(
2060                             "consider making the {} lifetime-generic with a new `'a` lifetime",
2061                             span_type.descr(),
2062                         );
2063                         should_break = false;
2064                         err.note(
2065                             "for more information on higher-ranked polymorphism, visit \
2066                             https://doc.rust-lang.org/nomicon/hrtb.html",
2067                         );
2068                         (*span, span_type.suggestion("'a"))
2069                     }
2070                     MissingLifetimeSpot::Static => {
2071                         let mut spans_suggs = Vec::new();
2072                         for ((span, count), snippet) in
2073                             spans_with_counts.iter().copied().zip(snippets.iter())
2074                         {
2075                             let (span, sugg) = match snippet.as_deref() {
2076                                 Some("&") => (span.shrink_to_hi(), "'static ".to_owned()),
2077                                 Some("'_") => (span, "'static".to_owned()),
2078                                 Some(snippet) if !snippet.ends_with('>') => {
2079                                     if snippet == "" {
2080                                         (
2081                                             span,
2082                                             std::iter::repeat("'static")
2083                                                 .take(count)
2084                                                 .collect::<Vec<_>>()
2085                                                 .join(", "),
2086                                         )
2087                                     } else if snippet == "<" || snippet == "(" {
2088                                         (
2089                                             span.shrink_to_hi(),
2090                                             std::iter::repeat("'static")
2091                                                 .take(count)
2092                                                 .collect::<Vec<_>>()
2093                                                 .join(", "),
2094                                         )
2095                                     } else {
2096                                         (
2097                                             span.shrink_to_hi(),
2098                                             format!(
2099                                                 "<{}>",
2100                                                 std::iter::repeat("'static")
2101                                                     .take(count)
2102                                                     .collect::<Vec<_>>()
2103                                                     .join(", "),
2104                                             ),
2105                                         )
2106                                     }
2107                                 }
2108                                 _ => continue,
2109                             };
2110                             spans_suggs.push((span, sugg.to_string()));
2111                         }
2112                         err.multipart_suggestion_verbose(
2113                             "consider using the `'static` lifetime",
2114                             spans_suggs,
2115                             Applicability::MaybeIncorrect,
2116                         );
2117                         continue;
2118                     }
2119                 });
2120
2121                 struct Lifetime(Span, String);
2122                 impl Lifetime {
2123                     fn is_unnamed(&self) -> bool {
2124                         self.1.starts_with('&') && !self.1.starts_with("&'")
2125                     }
2126                     fn is_underscore(&self) -> bool {
2127                         self.1.starts_with("&'_ ")
2128                     }
2129                     fn is_named(&self) -> bool {
2130                         self.1.starts_with("&'")
2131                     }
2132                     fn suggestion(&self, sugg: String) -> Option<(Span, String)> {
2133                         Some(
2134                             match (
2135                                 self.is_unnamed(),
2136                                 self.is_underscore(),
2137                                 self.is_named(),
2138                                 sugg.starts_with('&'),
2139                             ) {
2140                                 (true, _, _, false) => (self.span_unnamed_borrow(), sugg),
2141                                 (true, _, _, true) => {
2142                                     (self.span_unnamed_borrow(), sugg[1..].to_string())
2143                                 }
2144                                 (_, true, _, false) => {
2145                                     (self.span_underscore_borrow(), sugg.trim().to_string())
2146                                 }
2147                                 (_, true, _, true) => {
2148                                     (self.span_underscore_borrow(), sugg[1..].trim().to_string())
2149                                 }
2150                                 (_, _, true, false) => {
2151                                     (self.span_named_borrow(), sugg.trim().to_string())
2152                                 }
2153                                 (_, _, true, true) => {
2154                                     (self.span_named_borrow(), sugg[1..].trim().to_string())
2155                                 }
2156                                 _ => return None,
2157                             },
2158                         )
2159                     }
2160                     fn span_unnamed_borrow(&self) -> Span {
2161                         let lo = self.0.lo() + BytePos(1);
2162                         self.0.with_lo(lo).with_hi(lo)
2163                     }
2164                     fn span_named_borrow(&self) -> Span {
2165                         let lo = self.0.lo() + BytePos(1);
2166                         self.0.with_lo(lo)
2167                     }
2168                     fn span_underscore_borrow(&self) -> Span {
2169                         let lo = self.0.lo() + BytePos(1);
2170                         let hi = lo + BytePos(2);
2171                         self.0.with_lo(lo).with_hi(hi)
2172                     }
2173                 }
2174
2175                 for param in params {
2176                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
2177                         if let Some((span, sugg)) =
2178                             Lifetime(param.span, snippet).suggestion("'a ".to_string())
2179                         {
2180                             introduce_suggestion.push((span, sugg));
2181                         }
2182                     }
2183                 }
2184                 for (span, sugg) in spans_with_counts.iter().copied().zip(suggs.iter()).filter_map(
2185                     |((span, _), sugg)| match &sugg {
2186                         Some(sugg) => Some((span, sugg.to_string())),
2187                         _ => None,
2188                     },
2189                 ) {
2190                     let (span, sugg) = self
2191                         .tcx
2192                         .sess
2193                         .source_map()
2194                         .span_to_snippet(span)
2195                         .ok()
2196                         .and_then(|snippet| Lifetime(span, snippet).suggestion(sugg.clone()))
2197                         .unwrap_or((span, sugg));
2198                     introduce_suggestion.push((span, sugg.to_string()));
2199                 }
2200                 err.multipart_suggestion_verbose(
2201                     &msg,
2202                     introduce_suggestion,
2203                     Applicability::MaybeIncorrect,
2204                 );
2205                 if should_break {
2206                     break;
2207                 }
2208             }
2209         };
2210
2211         let lifetime_names: Vec<_> = lifetime_names.iter().collect();
2212         match &lifetime_names[..] {
2213             [name] => {
2214                 let mut suggs: Vec<Option<Box<dyn Fn(&str) -> String>>> = Vec::new();
2215                 for (snippet, (_, count)) in snippets.iter().zip(spans_with_counts.iter().copied())
2216                 {
2217                     suggs.push(match snippet.as_deref() {
2218                         Some("&") => Some(Box::new(|name| format!("&{} ", name))),
2219                         Some("'_") => Some(Box::new(|n| n.to_string())),
2220                         Some("") => Some(Box::new(move |n| format!("{}, ", n).repeat(count))),
2221                         Some("<") => Some(Box::new(move |n| {
2222                             std::iter::repeat(n).take(count).collect::<Vec<_>>().join(", ")
2223                         })),
2224                         Some(snippet) if !snippet.ends_with('>') => Some(Box::new(move |name| {
2225                             format!(
2226                                 "{}<{}>",
2227                                 snippet,
2228                                 std::iter::repeat(name.to_string())
2229                                     .take(count)
2230                                     .collect::<Vec<_>>()
2231                                     .join(", ")
2232                             )
2233                         })),
2234                         _ => None,
2235                     });
2236                 }
2237                 suggest_existing(err, &name.as_str()[..], suggs);
2238             }
2239             [] => {
2240                 let mut suggs = Vec::new();
2241                 for (snippet, (_, count)) in
2242                     snippets.iter().cloned().zip(spans_with_counts.iter().copied())
2243                 {
2244                     suggs.push(match snippet.as_deref() {
2245                         Some("&") => Some("&'a ".to_string()),
2246                         Some("'_") => Some("'a".to_string()),
2247                         Some("") => {
2248                             Some(std::iter::repeat("'a, ").take(count).collect::<Vec<_>>().join(""))
2249                         }
2250                         Some("<") => {
2251                             Some(std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", "))
2252                         }
2253                         Some(snippet) => Some(format!(
2254                             "{}<{}>",
2255                             snippet,
2256                             std::iter::repeat("'a").take(count).collect::<Vec<_>>().join(", "),
2257                         )),
2258                         None => None,
2259                     });
2260                 }
2261                 suggest_new(err, suggs);
2262             }
2263             lts if lts.len() > 1 => {
2264                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
2265
2266                 let mut spans_suggs: Vec<_> = Vec::new();
2267                 for ((span, _), snippet) in spans_with_counts.iter().copied().zip(snippets.iter()) {
2268                     match snippet.as_deref() {
2269                         Some("") => spans_suggs.push((span, "'lifetime, ".to_string())),
2270                         Some("&") => spans_suggs
2271                             .push((span.with_lo(span.lo() + BytePos(1)), "'lifetime ".to_string())),
2272                         _ => {}
2273                     }
2274                 }
2275
2276                 if spans_suggs.len() > 0 {
2277                     // This happens when we have `Foo<T>` where we point at the space before `T`,
2278                     // but this can be confusing so we give a suggestion with placeholders.
2279                     err.multipart_suggestion_verbose(
2280                         "consider using one of the available lifetimes here",
2281                         spans_suggs,
2282                         Applicability::HasPlaceholders,
2283                     );
2284                 }
2285             }
2286             _ => unreachable!(),
2287         }
2288     }
2289
2290     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
2291     /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
2292     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
2293     crate fn maybe_emit_forbidden_non_static_lifetime_error(
2294         &self,
2295         body_id: hir::BodyId,
2296         lifetime_ref: &'tcx hir::Lifetime,
2297     ) {
2298         let is_anon_const = matches!(
2299             self.tcx.def_kind(self.tcx.hir().body_owner_def_id(body_id)),
2300             hir::def::DefKind::AnonConst
2301         );
2302         let is_allowed_lifetime = matches!(
2303             lifetime_ref.name,
2304             hir::LifetimeName::Implicit | hir::LifetimeName::Static | hir::LifetimeName::Underscore
2305         );
2306
2307         if !self.tcx.lazy_normalization() && is_anon_const && !is_allowed_lifetime {
2308             feature_err(
2309                 &self.tcx.sess.parse_sess,
2310                 sym::generic_const_exprs,
2311                 lifetime_ref.span,
2312                 "a non-static lifetime is not allowed in a `const`",
2313             )
2314             .emit();
2315         }
2316     }
2317 }