src/librustc_resolve/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::lifetimes::{ElisionFailureInfo, LifetimeContext};
   3 use crate::late::{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::ast::{self, Expr, ExprKind, Item, ItemKind, NodeId, Path, Ty, TyKind};
   9 use rustc_ast::util::lev_distance::find_best_match_for_name;
  10 use rustc_data_structures::fx::FxHashSet;
  11 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
  12 use rustc_hir as hir;
  13 use rustc_hir::def::Namespace::{self, *};
  14 use rustc_hir::def::{self, CtorKind, DefKind};
  15 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  16 use rustc_hir::PrimTy;
  17 use rustc_session::config::nightly_options;
  18 use rustc_span::hygiene::MacroKind;
  19 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  20 use rustc_span::{BytePos, Span, DUMMY_SP};
  21
  22 use log::debug;
  23
  24 type Res = def::Res<ast::NodeId>;
  25
  26 /// A field or associated item from self type suggested in case of resolution failure.
  27 enum AssocSuggestion {
  28     Field,
  29     MethodWithSelf,
  30     AssocItem,
  31 }
  32
  33 crate enum MissingLifetimeSpot<'tcx> {
  34     Generics(&'tcx hir::Generics<'tcx>),
  35     HigherRanked { span: Span, span_type: ForLifetimeSpanType },
  36 }
  37
  38 crate enum ForLifetimeSpanType {
  39     BoundEmpty,
  40     BoundTail,
  41     TypeEmpty,
  42     TypeTail,
  43 }
  44
  45 impl ForLifetimeSpanType {
  46     crate fn descr(&self) -> &'static str {
  47         match self {
  48             Self::BoundEmpty | Self::BoundTail => "bound",
  49             Self::TypeEmpty | Self::TypeTail => "type",
  50         }
  51     }
  52
  53     crate fn suggestion(&self, sugg: &str) -> String {
  54         match self {
  55             Self::BoundEmpty | Self::TypeEmpty => format!("for<{}> ", sugg),
  56             Self::BoundTail | Self::TypeTail => format!(", {}", sugg),
  57         }
  58     }
  59 }
  60
  61 impl<'tcx> Into<MissingLifetimeSpot<'tcx>> for &'tcx hir::Generics<'tcx> {
  62     fn into(self) -> MissingLifetimeSpot<'tcx> {
  63         MissingLifetimeSpot::Generics(self)
  64     }
  65 }
  66
  67 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  68     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  69 }
  70
  71 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  72     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  73 }
  74
  75 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  76 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
  77     let variant_path = &suggestion.path;
  78     let variant_path_string = path_names_to_string(variant_path);
  79
  80     let path_len = suggestion.path.segments.len();
  81     let enum_path = ast::Path {
  82         span: suggestion.path.span,
  83         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
  84     };
  85     let enum_path_string = path_names_to_string(&enum_path);
  86
  87     (variant_path_string, enum_path_string)
  88 }
  89
  90 impl<'a> LateResolutionVisitor<'a, '_, '_> {
  91     fn def_span(&self, def_id: DefId) -> Option<Span> {
  92         match def_id.krate {
  93             LOCAL_CRATE => self.r.opt_span(def_id),
  94             _ => Some(
  95                 self.r
  96                     .session
  97                     .source_map()
  98                     .guess_head_span(self.r.cstore().get_span_untracked(def_id, self.r.session)),
  99             ),
 100         }
 101     }
 102
 103     /// Handles error reporting for `smart_resolve_path_fragment` function.
 104     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 105     pub(crate) fn smart_resolve_report_errors(
 106         &mut self,
 107         path: &[Segment],
 108         span: Span,
 109         source: PathSource<'_>,
 110         res: Option<Res>,
 111     ) -> (DiagnosticBuilder<'a>, Vec<ImportSuggestion>) {
 112         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 113         let ns = source.namespace();
 114         let is_expected = &|res| source.is_expected(res);
 115         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 116
 117         // Make the base error.
 118         let expected = source.descr_expected();
 119         let path_str = Segment::names_to_string(path);
 120         let item_str = path.last().unwrap().ident;
 121         let (base_msg, fallback_label, base_span, could_be_expr) = if let Some(res) = res {
 122             (
 123                 format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 124                 format!("not a {}", expected),
 125                 span,
 126                 match res {
 127                     Res::Def(DefKind::Fn, _) => {
 128                         // Verify whether this is a fn call or an Fn used as a type.
 129                         self.r
 130                             .session
 131                             .source_map()
 132                             .span_to_snippet(span)
 133                             .map(|snippet| snippet.ends_with(')'))
 134                             .unwrap_or(false)
 135                     }
 136                     Res::Def(
 137                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 138                         _,
 139                     )
 140                     | Res::SelfCtor(_)
 141                     | Res::PrimTy(_)
 142                     | Res::Local(_) => true,
 143                     _ => false,
 144                 },
 145             )
 146         } else {
 147             let item_span = path.last().unwrap().ident.span;
 148             let (mod_prefix, mod_str) = if path.len() == 1 {
 149                 (String::new(), "this scope".to_string())
 150             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 151                 (String::new(), "the crate root".to_string())
 152             } else {
 153                 let mod_path = &path[..path.len() - 1];
 154                 let mod_prefix =
 155                     match self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No) {
 156                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 157                         _ => None,
 158                     }
 159                     .map_or(String::new(), |res| format!("{} ", res.descr()));
 160                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)))
 161             };
 162             (
 163                 format!("cannot find {} `{}` in {}{}", expected, item_str, mod_prefix, mod_str),
 164                 if path_str == "async" && expected.starts_with("struct") {
 165                     "`async` blocks are only allowed in the 2018 edition".to_string()
 166                 } else {
 167                     format!("not found in {}", mod_str)
 168                 },
 169                 item_span,
 170                 false,
 171             )
 172         };
 173
 174         let code = source.error_code(res.is_some());
 175         let mut err = self.r.session.struct_span_err_with_code(base_span, &base_msg, code);
 176
 177         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 178         if ["this", "my"].contains(&&*item_str.as_str())
 179             && self.self_value_is_available(path[0].ident.span, span)
 180         {
 181             err.span_suggestion_short(
 182                 span,
 183                 "you might have meant to use `self` here instead",
 184                 "self".to_string(),
 185                 Applicability::MaybeIncorrect,
 186             );
 187         }
 188
 189         // Emit special messages for unresolved `Self` and `self`.
 190         if is_self_type(path, ns) {
 191             err.code(rustc_errors::error_code!(E0411));
 192             err.span_label(
 193                 span,
 194                 "`Self` is only available in impls, traits, and type definitions".to_string(),
 195             );
 196             return (err, Vec::new());
 197         }
 198         if is_self_value(path, ns) {
 199             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 200
 201             err.code(rustc_errors::error_code!(E0424));
 202             err.span_label(span, match source {
 203                 PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed"
 204                                    .to_string(),
 205                 _ => "`self` value is a keyword only available in methods with a `self` parameter"
 206                      .to_string(),
 207             });
 208             if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 209                 // The current function has a `self' parameter, but we were unable to resolve
 210                 // a reference to `self`. This can only happen if the `self` identifier we
 211                 // are resolving came from a different hygiene context.
 212                 if fn_kind.decl().inputs.get(0).map(|p| p.is_self()).unwrap_or(false) {
 213                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 214                 } else {
 215                     err.span_label(*span, "this function doesn't have a `self` parameter");
 216                 }
 217             }
 218             return (err, Vec::new());
 219         }
 220
 221         // Try to lookup name in more relaxed fashion for better error reporting.
 222         let ident = path.last().unwrap().ident;
 223         let candidates = self
 224             .r
 225             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 226             .drain(..)
 227             .filter(|ImportSuggestion { did, .. }| {
 228                 match (did, res.and_then(|res| res.opt_def_id())) {
 229                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 230                     _ => true,
 231                 }
 232             })
 233             .collect::<Vec<_>>();
 234         let crate_def_id = DefId::local(CRATE_DEF_INDEX);
 235         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 236             let enum_candidates =
 237                 self.r.lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant);
 238
 239             if !enum_candidates.is_empty() {
 240                 if let (PathSource::Type, Some(span)) =
 241                     (source, self.diagnostic_metadata.current_type_ascription.last())
 242                 {
 243                     if self
 244                         .r
 245                         .session
 246                         .parse_sess
 247                         .type_ascription_path_suggestions
 248                         .borrow()
 249                         .contains(span)
 250                     {
 251                         // Already reported this issue on the lhs of the type ascription.
 252                         err.delay_as_bug();
 253                         return (err, candidates);
 254                     }
 255                 }
 256
 257                 let mut enum_candidates = enum_candidates
 258                     .iter()
 259                     .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 260                     .collect::<Vec<_>>();
 261                 enum_candidates.sort();
 262
 263                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 264                 // (that it's a variant) for E0573 "expected type, found variant".
 265                 let preamble = if res.is_none() {
 266                     let others = match enum_candidates.len() {
 267                         1 => String::new(),
 268                         2 => " and 1 other".to_owned(),
 269                         n => format!(" and {} others", n),
 270                     };
 271                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 272                 } else {
 273                     String::new()
 274                 };
 275                 let msg = format!("{}try using the variant's enum", preamble);
 276
 277                 err.span_suggestions(
 278                     span,
 279                     &msg,
 280                     enum_candidates
 281                         .into_iter()
 282                         .map(|(_variant_path, enum_ty_path)| enum_ty_path)
 283                         // Variants re-exported in prelude doesn't mean `prelude::v1` is the
 284                         // type name!
 285                         // FIXME: is there a more principled way to do this that
 286                         // would work for other re-exports?
 287                         .filter(|enum_ty_path| enum_ty_path != "std::prelude::v1")
 288                         // Also write `Option` rather than `std::prelude::v1::Option`.
 289                         .map(|enum_ty_path| {
 290                             // FIXME #56861: DRY-er prelude filtering.
 291                             enum_ty_path.trim_start_matches("std::prelude::v1::").to_owned()
 292                         }),
 293                     Applicability::MachineApplicable,
 294                 );
 295             }
 296         }
 297         if path.len() == 1 && self.self_type_is_available(span) {
 298             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 299                 let self_is_available = self.self_value_is_available(path[0].ident.span, span);
 300                 match candidate {
 301                     AssocSuggestion::Field => {
 302                         if self_is_available {
 303                             err.span_suggestion(
 304                                 span,
 305                                 "you might have meant to use the available field",
 306                                 format!("self.{}", path_str),
 307                                 Applicability::MachineApplicable,
 308                             );
 309                         } else {
 310                             err.span_label(span, "a field by this name exists in `Self`");
 311                         }
 312                     }
 313                     AssocSuggestion::MethodWithSelf if self_is_available => {
 314                         err.span_suggestion(
 315                             span,
 316                             "try",
 317                             format!("self.{}", path_str),
 318                             Applicability::MachineApplicable,
 319                         );
 320                     }
 321                     AssocSuggestion::MethodWithSelf | AssocSuggestion::AssocItem => {
 322                         err.span_suggestion(
 323                             span,
 324                             "try",
 325                             format!("Self::{}", path_str),
 326                             Applicability::MachineApplicable,
 327                         );
 328                     }
 329                 }
 330                 return (err, candidates);
 331             }
 332
 333             // If the first argument in call is `self` suggest calling a method.
 334             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 335                 let mut args_snippet = String::new();
 336                 if let Some(args_span) = args_span {
 337                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 338                         args_snippet = snippet;
 339                     }
 340                 }
 341
 342                 err.span_suggestion(
 343                     call_span,
 344                     &format!("try calling `{}` as a method", ident),
 345                     format!("self.{}({})", path_str, args_snippet),
 346                     Applicability::MachineApplicable,
 347                 );
 348                 return (err, candidates);
 349             }
 350         }
 351
 352         // Try Levenshtein algorithm.
 353         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected, span);
 354         // Try context-dependent help if relaxed lookup didn't work.
 355         if let Some(res) = res {
 356             if self.smart_resolve_context_dependent_help(
 357                 &mut err,
 358                 span,
 359                 source,
 360                 res,
 361                 &path_str,
 362                 &fallback_label,
 363             ) {
 364                 // We do this to avoid losing a secondary span when we override the main error span.
 365                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 366                 return (err, candidates);
 367             }
 368         }
 369
 370         if !self.type_ascription_suggestion(&mut err, base_span)
 371             && !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span)
 372         {
 373             // Fallback label.
 374             err.span_label(base_span, fallback_label);
 375
 376             match self.diagnostic_metadata.current_let_binding {
 377                 Some((pat_sp, Some(ty_sp), None)) if ty_sp.contains(base_span) && could_be_expr => {
 378                     err.span_suggestion_short(
 379                         pat_sp.between(ty_sp),
 380                         "use `=` if you meant to assign",
 381                         " = ".to_string(),
 382                         Applicability::MaybeIncorrect,
 383                     );
 384                 }
 385                 _ => {}
 386             }
 387         }
 388         (err, candidates)
 389     }
 390
 391     /// Check if the source is call expression and the first argument is `self`. If true,
 392     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 393     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 394         let mut has_self_arg = None;
 395         if let PathSource::Expr(Some(parent)) = source {
 396             match &parent.kind {
 397                 ExprKind::Call(_, args) if !args.is_empty() => {
 398                     let mut expr_kind = &args[0].kind;
 399                     loop {
 400                         match expr_kind {
 401                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 402                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 403                                     let call_span = parent.span;
 404                                     let tail_args_span = if args.len() > 1 {
 405                                         Some(Span::new(
 406                                             args[1].span.lo(),
 407                                             args.last().unwrap().span.hi(),
 408                                             call_span.ctxt(),
 409                                         ))
 410                                     } else {
 411                                         None
 412                                     };
 413                                     has_self_arg = Some((call_span, tail_args_span));
 414                                 }
 415                                 break;
 416                             }
 417                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 418                             _ => break,
 419                         }
 420                     }
 421                 }
 422                 _ => (),
 423             }
 424         };
 425         has_self_arg
 426     }
 427
 428     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 429         // HACK(estebank): find a better way to figure out that this was a
 430         // parser issue where a struct literal is being used on an expression
 431         // where a brace being opened means a block is being started. Look
 432         // ahead for the next text to see if `span` is followed by a `{`.
 433         let sm = self.r.session.source_map();
 434         let mut sp = span;
 435         loop {
 436             sp = sm.next_point(sp);
 437             match sm.span_to_snippet(sp) {
 438                 Ok(ref snippet) => {
 439                     if snippet.chars().any(|c| !c.is_whitespace()) {
 440                         break;
 441                     }
 442                 }
 443                 _ => break,
 444             }
 445         }
 446         let followed_by_brace = match sm.span_to_snippet(sp) {
 447             Ok(ref snippet) if snippet == "{" => true,
 448             _ => false,
 449         };
 450         // In case this could be a struct literal that needs to be surrounded
 451         // by parentheses, find the appropriate span.
 452         let mut i = 0;
 453         let mut closing_brace = None;
 454         loop {
 455             sp = sm.next_point(sp);
 456             match sm.span_to_snippet(sp) {
 457                 Ok(ref snippet) => {
 458                     if snippet == "}" {
 459                         closing_brace = Some(span.to(sp));
 460                         break;
 461                     }
 462                 }
 463                 _ => break,
 464             }
 465             i += 1;
 466             // The bigger the span, the more likely we're incorrect --
 467             // bound it to 100 chars long.
 468             if i > 100 {
 469                 break;
 470             }
 471         }
 472         (followed_by_brace, closing_brace)
 473     }
 474
 475     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 476     /// function.
 477     /// Returns `true` if able to provide context-dependent help.
 478     fn smart_resolve_context_dependent_help(
 479         &mut self,
 480         err: &mut DiagnosticBuilder<'a>,
 481         span: Span,
 482         source: PathSource<'_>,
 483         res: Res,
 484         path_str: &str,
 485         fallback_label: &str,
 486     ) -> bool {
 487         let ns = source.namespace();
 488         let is_expected = &|res| source.is_expected(res);
 489
 490         let path_sep = |err: &mut DiagnosticBuilder<'_>, expr: &Expr| match expr.kind {
 491             ExprKind::Field(_, ident) => {
 492                 err.span_suggestion(
 493                     expr.span,
 494                     "use the path separator to refer to an item",
 495                     format!("{}::{}", path_str, ident),
 496                     Applicability::MaybeIncorrect,
 497                 );
 498                 true
 499             }
 500             ExprKind::MethodCall(ref segment, ..) => {
 501                 let span = expr.span.with_hi(segment.ident.span.hi());
 502                 err.span_suggestion(
 503                     span,
 504                     "use the path separator to refer to an item",
 505                     format!("{}::{}", path_str, segment.ident),
 506                     Applicability::MaybeIncorrect,
 507                 );
 508                 true
 509             }
 510             _ => false,
 511         };
 512
 513         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 514             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 515
 516             match source {
 517                 PathSource::Expr(Some(
 518                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
 519                 )) if path_sep(err, &parent) => {}
 520                 PathSource::Expr(
 521                     None
 522                     | Some(Expr {
 523                         kind:
 524                             ExprKind::Path(..)
 525                             | ExprKind::Binary(..)
 526                             | ExprKind::Unary(..)
 527                             | ExprKind::If(..)
 528                             | ExprKind::While(..)
 529                             | ExprKind::ForLoop(..)
 530                             | ExprKind::Match(..),
 531                         ..
 532                     }),
 533                 ) if followed_by_brace => {
 534                     if let Some(sp) = closing_brace {
 535                         err.span_label(span, fallback_label);
 536                         err.multipart_suggestion(
 537                             "surround the struct literal with parentheses",
 538                             vec![
 539                                 (sp.shrink_to_lo(), "(".to_string()),
 540                                 (sp.shrink_to_hi(), ")".to_string()),
 541                             ],
 542                             Applicability::MaybeIncorrect,
 543                         );
 544                     } else {
 545                         err.span_label(
 546                             span, // Note the parentheses surrounding the suggestion below
 547                             format!(
 548                                 "you might want to surround a struct literal with parentheses: \
 549                                  `({} {{ /* fields */ }})`?",
 550                                 path_str
 551                             ),
 552                         );
 553                     }
 554                 }
 555                 PathSource::Expr(_) | PathSource::TupleStruct(_) | PathSource::Pat => {
 556                     let span = match &source {
 557                         PathSource::Expr(Some(Expr {
 558                             span, kind: ExprKind::Call(_, _), ..
 559                         }))
 560                         | PathSource::TupleStruct(span) => {
 561                             // We want the main underline to cover the suggested code as well for
 562                             // cleaner output.
 563                             err.set_span(*span);
 564                             *span
 565                         }
 566                         _ => span,
 567                     };
 568                     if let Some(span) = self.def_span(def_id) {
 569                         err.span_label(span, &format!("`{}` defined here", path_str));
 570                     }
 571                     let (tail, descr, applicability) = match source {
 572                         PathSource::Pat | PathSource::TupleStruct(_) => {
 573                             ("", "pattern", Applicability::MachineApplicable)
 574                         }
 575                         _ => (": val", "literal", Applicability::HasPlaceholders),
 576                     };
 577                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
 578                         Some(fields) => (
 579                             fields
 580                                 .iter()
 581                                 .map(|f| format!("{}{}", f.node, tail))
 582                                 .collect::<Vec<String>>()
 583                                 .join(", "),
 584                             applicability,
 585                         ),
 586                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
 587                     };
 588                     let pad = match self.r.field_names.get(&def_id) {
 589                         Some(fields) if fields.is_empty() => "",
 590                         _ => " ",
 591                     };
 592                     err.span_suggestion(
 593                         span,
 594                         &format!("use struct {} syntax instead", descr),
 595                         format!("{} {{{pad}{}{pad}}}", path_str, fields, pad = pad),
 596                         applicability,
 597                     );
 598                 }
 599                 _ => {
 600                     err.span_label(span, fallback_label);
 601                 }
 602             }
 603         };
 604
 605         match (res, source) {
 606             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
 607                 err.span_label(span, fallback_label);
 608                 err.span_suggestion_verbose(
 609                     span.shrink_to_hi(),
 610                     "use `!` to invoke the macro",
 611                     "!".to_string(),
 612                     Applicability::MaybeIncorrect,
 613                 );
 614                 if path_str == "try" && span.rust_2015() {
 615                     err.note("if you want the `try` keyword, you need to be in the 2018 edition");
 616                 }
 617             }
 618             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
 619                 err.span_label(span, "type aliases cannot be used as traits");
 620                 if nightly_options::is_nightly_build() {
 621                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
 622                                `type` alias";
 623                     if let Some(span) = self.def_span(def_id) {
 624                         err.span_help(span, msg);
 625                     } else {
 626                         err.help(msg);
 627                     }
 628                 }
 629             }
 630             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
 631                 if !path_sep(err, &parent) {
 632                     return false;
 633                 }
 634             }
 635             (
 636                 Res::Def(DefKind::Enum, def_id),
 637                 PathSource::TupleStruct(_) | PathSource::Expr(..),
 638             ) => {
 639                 if self
 640                     .diagnostic_metadata
 641                     .current_type_ascription
 642                     .last()
 643                     .map(|sp| {
 644                         self.r
 645                             .session
 646                             .parse_sess
 647                             .type_ascription_path_suggestions
 648                             .borrow()
 649                             .contains(&sp)
 650                     })
 651                     .unwrap_or(false)
 652                 {
 653                     err.delay_as_bug();
 654                     // We already suggested changing `:` into `::` during parsing.
 655                     return false;
 656                 }
 657                 if let Some(variants) = self.collect_enum_variants(def_id) {
 658                     if !variants.is_empty() {
 659                         let msg = if variants.len() == 1 {
 660                             "try using the enum's variant"
 661                         } else {
 662                             "try using one of the enum's variants"
 663                         };
 664
 665                         err.span_suggestions(
 666                             span,
 667                             msg,
 668                             variants.iter().map(path_names_to_string),
 669                             Applicability::MaybeIncorrect,
 670                         );
 671                     }
 672                 } else {
 673                     err.note("you might have meant to use one of the enum's variants");
 674                 }
 675             }
 676             (Res::Def(DefKind::Struct, def_id), _) if ns == ValueNS => {
 677                 if let Some((ctor_def, ctor_vis)) = self.r.struct_constructors.get(&def_id).cloned()
 678                 {
 679                     let accessible_ctor =
 680                         self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
 681                     if is_expected(ctor_def) && !accessible_ctor {
 682                         err.span_label(
 683                             span,
 684                             "constructor is not visible here due to private fields".to_string(),
 685                         );
 686                     }
 687                 } else {
 688                     bad_struct_syntax_suggestion(def_id);
 689                 }
 690             }
 691             (
 692                 Res::Def(
 693                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
 694                     def_id,
 695                 ),
 696                 _,
 697             ) if ns == ValueNS => {
 698                 bad_struct_syntax_suggestion(def_id);
 699             }
 700             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
 701                 if let Some(span) = self.def_span(def_id) {
 702                     err.span_label(span, &format!("`{}` defined here", path_str));
 703                 }
 704                 err.span_label(span, format!("did you mean `{}( /* fields */ )`?", path_str));
 705             }
 706             (Res::SelfTy(..), _) if ns == ValueNS => {
 707                 err.span_label(span, fallback_label);
 708                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
 709             }
 710             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
 711                 err.note("can't use a type alias as a constructor");
 712             }
 713             _ => return false,
 714         }
 715         true
 716     }
 717
 718     fn lookup_assoc_candidate<FilterFn>(
 719         &mut self,
 720         ident: Ident,
 721         ns: Namespace,
 722         filter_fn: FilterFn,
 723     ) -> Option<AssocSuggestion>
 724     where
 725         FilterFn: Fn(Res) -> bool,
 726     {
 727         fn extract_node_id(t: &Ty) -> Option<NodeId> {
 728             match t.kind {
 729                 TyKind::Path(None, _) => Some(t.id),
 730                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
 731                 // This doesn't handle the remaining `Ty` variants as they are not
 732                 // that commonly the self_type, it might be interesting to provide
 733                 // support for those in future.
 734                 _ => None,
 735             }
 736         }
 737
 738         // Fields are generally expected in the same contexts as locals.
 739         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
 740             if let Some(node_id) =
 741                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
 742             {
 743                 // Look for a field with the same name in the current self_type.
 744                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
 745                     match resolution.base_res() {
 746                         Res::Def(DefKind::Struct | DefKind::Union, did)
 747                             if resolution.unresolved_segments() == 0 =>
 748                         {
 749                             if let Some(field_names) = self.r.field_names.get(&did) {
 750                                 if field_names
 751                                     .iter()
 752                                     .any(|&field_name| ident.name == field_name.node)
 753                                 {
 754                                     return Some(AssocSuggestion::Field);
 755                                 }
 756                             }
 757                         }
 758                         _ => {}
 759                     }
 760                 }
 761             }
 762         }
 763
 764         for assoc_type_ident in &self.diagnostic_metadata.current_trait_assoc_types {
 765             if *assoc_type_ident == ident {
 766                 return Some(AssocSuggestion::AssocItem);
 767             }
 768         }
 769
 770         // Look for associated items in the current trait.
 771         if let Some((module, _)) = self.current_trait_ref {
 772             if let Ok(binding) = self.r.resolve_ident_in_module(
 773                 ModuleOrUniformRoot::Module(module),
 774                 ident,
 775                 ns,
 776                 &self.parent_scope,
 777                 false,
 778                 module.span,
 779             ) {
 780                 let res = binding.res();
 781                 if filter_fn(res) {
 782                     return Some(if self.r.has_self.contains(&res.def_id()) {
 783                         AssocSuggestion::MethodWithSelf
 784                     } else {
 785                         AssocSuggestion::AssocItem
 786                     });
 787                 }
 788             }
 789         }
 790
 791         None
 792     }
 793
 794     fn lookup_typo_candidate(
 795         &mut self,
 796         path: &[Segment],
 797         ns: Namespace,
 798         filter_fn: &impl Fn(Res) -> bool,
 799         span: Span,
 800     ) -> Option<TypoSuggestion> {
 801         let mut names = Vec::new();
 802         if path.len() == 1 {
 803             // Search in lexical scope.
 804             // Walk backwards up the ribs in scope and collect candidates.
 805             for rib in self.ribs[ns].iter().rev() {
 806                 // Locals and type parameters
 807                 for (ident, &res) in &rib.bindings {
 808                     if filter_fn(res) {
 809                         names.push(TypoSuggestion::from_res(ident.name, res));
 810                     }
 811                 }
 812                 // Items in scope
 813                 if let RibKind::ModuleRibKind(module) = rib.kind {
 814                     // Items from this module
 815                     self.r.add_module_candidates(module, &mut names, &filter_fn);
 816
 817                     if let ModuleKind::Block(..) = module.kind {
 818                         // We can see through blocks
 819                     } else {
 820                         // Items from the prelude
 821                         if !module.no_implicit_prelude {
 822                             let extern_prelude = self.r.extern_prelude.clone();
 823                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
 824                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
 825                                     |crate_id| {
 826                                         let crate_mod = Res::Def(
 827                                             DefKind::Mod,
 828                                             DefId { krate: crate_id, index: CRATE_DEF_INDEX },
 829                                         );
 830
 831                                         if filter_fn(crate_mod) {
 832                                             Some(TypoSuggestion::from_res(ident.name, crate_mod))
 833                                         } else {
 834                                             None
 835                                         }
 836                                     },
 837                                 )
 838                             }));
 839
 840                             if let Some(prelude) = self.r.prelude {
 841                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
 842                             }
 843                         }
 844                         break;
 845                     }
 846                 }
 847             }
 848             // Add primitive types to the mix
 849             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
 850                 names.extend(
 851                     self.r.primitive_type_table.primitive_types.iter().map(|(name, prim_ty)| {
 852                         TypoSuggestion::from_res(*name, Res::PrimTy(*prim_ty))
 853                     }),
 854                 )
 855             }
 856         } else {
 857             // Search in module.
 858             let mod_path = &path[..path.len() - 1];
 859             if let PathResult::Module(module) =
 860                 self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No)
 861             {
 862                 if let ModuleOrUniformRoot::Module(module) = module {
 863                     self.r.add_module_candidates(module, &mut names, &filter_fn);
 864                 }
 865             }
 866         }
 867
 868         let name = path[path.len() - 1].ident.name;
 869         // Make sure error reporting is deterministic.
 870         names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 871
 872         match find_best_match_for_name(
 873             names.iter().map(|suggestion| &suggestion.candidate),
 874             name,
 875             None,
 876         ) {
 877             Some(found) if found != name => {
 878                 names.into_iter().find(|suggestion| suggestion.candidate == found)
 879             }
 880             _ => None,
 881         }
 882     }
 883
 884     /// Only used in a specific case of type ascription suggestions
 885     fn get_colon_suggestion_span(&self, start: Span) -> Span {
 886         let sm = self.r.session.source_map();
 887         start.to(sm.next_point(start))
 888     }
 889
 890     fn type_ascription_suggestion(&self, err: &mut DiagnosticBuilder<'_>, base_span: Span) -> bool {
 891         let sm = self.r.session.source_map();
 892         let base_snippet = sm.span_to_snippet(base_span);
 893         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
 894             if let Ok(snippet) = sm.span_to_snippet(sp) {
 895                 let len = snippet.trim_end().len() as u32;
 896                 if snippet.trim() == ":" {
 897                     let colon_sp =
 898                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
 899                     let mut show_label = true;
 900                     if sm.is_multiline(sp) {
 901                         err.span_suggestion_short(
 902                             colon_sp,
 903                             "maybe you meant to write `;` here",
 904                             ";".to_string(),
 905                             Applicability::MaybeIncorrect,
 906                         );
 907                     } else {
 908                         let after_colon_sp =
 909                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
 910                         if snippet.len() == 1 {
 911                             // `foo:bar`
 912                             err.span_suggestion(
 913                                 colon_sp,
 914                                 "maybe you meant to write a path separator here",
 915                                 "::".to_string(),
 916                                 Applicability::MaybeIncorrect,
 917                             );
 918                             show_label = false;
 919                             if !self
 920                                 .r
 921                                 .session
 922                                 .parse_sess
 923                                 .type_ascription_path_suggestions
 924                                 .borrow_mut()
 925                                 .insert(colon_sp)
 926                             {
 927                                 err.delay_as_bug();
 928                             }
 929                         }
 930                         if let Ok(base_snippet) = base_snippet {
 931                             let mut sp = after_colon_sp;
 932                             for _ in 0..100 {
 933                                 // Try to find an assignment
 934                                 sp = sm.next_point(sp);
 935                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
 936                                 match snippet {
 937                                     Ok(ref x) if x.as_str() == "=" => {
 938                                         err.span_suggestion(
 939                                             base_span,
 940                                             "maybe you meant to write an assignment here",
 941                                             format!("let {}", base_snippet),
 942                                             Applicability::MaybeIncorrect,
 943                                         );
 944                                         show_label = false;
 945                                         break;
 946                                     }
 947                                     Ok(ref x) if x.as_str() == "\n" => break,
 948                                     Err(_) => break,
 949                                     Ok(_) => {}
 950                                 }
 951                             }
 952                         }
 953                     }
 954                     if show_label {
 955                         err.span_label(
 956                             base_span,
 957                             "expecting a type here because of type ascription",
 958                         );
 959                     }
 960                     return show_label;
 961                 }
 962             }
 963         }
 964         false
 965     }
 966
 967     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
 968         let mut result = None;
 969         let mut seen_modules = FxHashSet::default();
 970         let mut worklist = vec![(self.r.graph_root, Vec::new())];
 971
 972         while let Some((in_module, path_segments)) = worklist.pop() {
 973             // abort if the module is already found
 974             if result.is_some() {
 975                 break;
 976             }
 977
 978             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
 979                 // abort if the module is already found or if name_binding is private external
 980                 if result.is_some() || !name_binding.vis.is_visible_locally() {
 981                     return;
 982                 }
 983                 if let Some(module) = name_binding.module() {
 984                     // form the path
 985                     let mut path_segments = path_segments.clone();
 986                     path_segments.push(ast::PathSegment::from_ident(ident));
 987                     let module_def_id = module.def_id().unwrap();
 988                     if module_def_id == def_id {
 989                         let path = Path { span: name_binding.span, segments: path_segments };
 990                         result = Some((
 991                             module,
 992                             ImportSuggestion {
 993                                 did: Some(def_id),
 994                                 descr: "module",
 995                                 path,
 996                                 accessible: true,
 997                             },
 998                         ));
 999                     } else {
1000                         // add the module to the lookup
1001                         if seen_modules.insert(module_def_id) {
1002                             worklist.push((module, path_segments));
1003                         }
1004                     }
1005                 }
1006             });
1007         }
1008
1009         result
1010     }
1011
1012     fn collect_enum_variants(&mut self, def_id: DefId) -> Option<Vec<Path>> {
1013         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1014             let mut variants = Vec::new();
1015             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1016                 if let Res::Def(DefKind::Variant, _) = name_binding.res() {
1017                     let mut segms = enum_import_suggestion.path.segments.clone();
1018                     segms.push(ast::PathSegment::from_ident(ident));
1019                     variants.push(Path { span: name_binding.span, segments: segms });
1020                 }
1021             });
1022             variants
1023         })
1024     }
1025
1026     crate fn report_missing_type_error(
1027         &self,
1028         path: &[Segment],
1029     ) -> Option<(Span, &'static str, String, Applicability)> {
1030         let (ident, span) = match path {
1031             [segment] if !segment.has_generic_args => {
1032                 (segment.ident.to_string(), segment.ident.span)
1033             }
1034             _ => return None,
1035         };
1036         let mut iter = ident.chars().map(|c| c.is_uppercase());
1037         let single_uppercase_char =
1038             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1039         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1040             return None;
1041         }
1042         match (self.diagnostic_metadata.current_item, single_uppercase_char) {
1043             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _) if ident.name == sym::main => {
1044                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1045             }
1046             (
1047                 Some(Item {
1048                     kind:
1049                         kind @ ItemKind::Fn(..)
1050                         | kind @ ItemKind::Enum(..)
1051                         | kind @ ItemKind::Struct(..)
1052                         | kind @ ItemKind::Union(..),
1053                     ..
1054                 }),
1055                 true,
1056             )
1057             | (Some(Item { kind, .. }), false) => {
1058                 // Likely missing type parameter.
1059                 if let Some(generics) = kind.generics() {
1060                     if span.overlaps(generics.span) {
1061                         // Avoid the following:
1062                         // error[E0405]: cannot find trait `A` in this scope
1063                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1064                         //   |
1065                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1066                         //   |           ^- help: you might be missing a type parameter: `, A`
1067                         //   |           |
1068                         //   |           not found in this scope
1069                         return None;
1070                     }
1071                     let msg = "you might be missing a type parameter";
1072                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1073                         let span = if let [.., bound] = &param.bounds[..] {
1074                             bound.span()
1075                         } else {
1076                             param.ident.span
1077                         };
1078                         (span, format!(", {}", ident))
1079                     } else {
1080                         (generics.span, format!("<{}>", ident))
1081                     };
1082                     // Do not suggest if this is coming from macro expansion.
1083                     if !span.from_expansion() {
1084                         return Some((
1085                             span.shrink_to_hi(),
1086                             msg,
1087                             sugg,
1088                             Applicability::MaybeIncorrect,
1089                         ));
1090                     }
1091                 }
1092             }
1093             _ => {}
1094         }
1095         None
1096     }
1097
1098     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1099     /// optionally returning the closest match and whether it is reachable.
1100     crate fn suggestion_for_label_in_rib(
1101         &self,
1102         rib_index: usize,
1103         label: Ident,
1104     ) -> Option<LabelSuggestion> {
1105         // Are ribs from this `rib_index` within scope?
1106         let within_scope = self.is_label_valid_from_rib(rib_index);
1107
1108         let rib = &self.label_ribs[rib_index];
1109         let names = rib
1110             .bindings
1111             .iter()
1112             .filter(|(id, _)| id.span.ctxt() == label.span.ctxt())
1113             .map(|(id, _)| &id.name);
1114
1115         find_best_match_for_name(names, label.name, None).map(|symbol| {
1116             // Upon finding a similar name, get the ident that it was from - the span
1117             // contained within helps make a useful diagnostic. In addition, determine
1118             // whether this candidate is within scope.
1119             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1120             (*ident, within_scope)
1121         })
1122     }
1123 }
1124
1125 impl<'tcx> LifetimeContext<'_, 'tcx> {
1126     crate fn report_missing_lifetime_specifiers(
1127         &self,
1128         span: Span,
1129         count: usize,
1130     ) -> DiagnosticBuilder<'tcx> {
1131         struct_span_err!(
1132             self.tcx.sess,
1133             span,
1134             E0106,
1135             "missing lifetime specifier{}",
1136             pluralize!(count)
1137         )
1138     }
1139
1140     crate fn emit_undeclared_lifetime_error(&self, lifetime_ref: &hir::Lifetime) {
1141         let mut err = struct_span_err!(
1142             self.tcx.sess,
1143             lifetime_ref.span,
1144             E0261,
1145             "use of undeclared lifetime name `{}`",
1146             lifetime_ref
1147         );
1148         err.span_label(lifetime_ref.span, "undeclared lifetime");
1149         let mut suggests_in_band = false;
1150         for missing in &self.missing_named_lifetime_spots {
1151             match missing {
1152                 MissingLifetimeSpot::Generics(generics) => {
1153                     let (span, sugg) = if let Some(param) =
1154                         generics.params.iter().find(|p| match p.kind {
1155                             hir::GenericParamKind::Type {
1156                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1157                                 ..
1158                             } => false,
1159                             _ => true,
1160                         }) {
1161                         (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref))
1162                     } else {
1163                         suggests_in_band = true;
1164                         (generics.span, format!("<{}>", lifetime_ref))
1165                     };
1166                     err.span_suggestion(
1167                         span,
1168                         &format!("consider introducing lifetime `{}` here", lifetime_ref),
1169                         sugg,
1170                         Applicability::MaybeIncorrect,
1171                     );
1172                 }
1173                 MissingLifetimeSpot::HigherRanked { span, span_type } => {
1174                     err.span_suggestion(
1175                         *span,
1176                         &format!(
1177                             "consider making the {} lifetime-generic with a new `{}` lifetime",
1178                             span_type.descr(),
1179                             lifetime_ref
1180                         ),
1181                         span_type.suggestion(&lifetime_ref.to_string()),
1182                         Applicability::MaybeIncorrect,
1183                     );
1184                     err.note(
1185                         "for more information on higher-ranked polymorphism, visit \
1186                             https://doc.rust-lang.org/nomicon/hrtb.html",
1187                     );
1188                 }
1189             }
1190         }
1191         if nightly_options::is_nightly_build()
1192             && !self.tcx.features().in_band_lifetimes
1193             && suggests_in_band
1194         {
1195             err.help(
1196                 "if you want to experiment with in-band lifetime bindings, \
1197                     add `#![feature(in_band_lifetimes)]` to the crate attributes",
1198             );
1199         }
1200         err.emit();
1201     }
1202
1203     // FIXME(const_generics): This patches over a ICE caused by non-'static lifetimes in const
1204     // generics. We are disallowing this until we can decide on how we want to handle non-'static
1205     // lifetimes in const generics. See issue #74052 for discussion.
1206     crate fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &hir::Lifetime) {
1207         let mut err = struct_span_err!(
1208             self.tcx.sess,
1209             lifetime_ref.span,
1210             E0771,
1211             "use of non-static lifetime `{}` in const generic",
1212             lifetime_ref
1213         );
1214         err.note(
1215             "for more information, see issue #74052 \
1216             <https://github.com/rust-lang/rust/issues/74052>",
1217         );
1218         err.emit();
1219     }
1220
1221     crate fn is_trait_ref_fn_scope(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) -> bool {
1222         if let def::Res::Def(_, did) = trait_ref.trait_ref.path.res {
1223             if [
1224                 self.tcx.lang_items().fn_once_trait(),
1225                 self.tcx.lang_items().fn_trait(),
1226                 self.tcx.lang_items().fn_mut_trait(),
1227             ]
1228             .contains(&Some(did))
1229             {
1230                 let (span, span_type) = match &trait_ref.bound_generic_params {
1231                     [] => (trait_ref.span.shrink_to_lo(), ForLifetimeSpanType::BoundEmpty),
1232                     [.., bound] => (bound.span.shrink_to_hi(), ForLifetimeSpanType::BoundTail),
1233                 };
1234                 self.missing_named_lifetime_spots
1235                     .push(MissingLifetimeSpot::HigherRanked { span, span_type });
1236                 return true;
1237             }
1238         };
1239         false
1240     }
1241
1242     crate fn add_missing_lifetime_specifiers_label(
1243         &self,
1244         err: &mut DiagnosticBuilder<'_>,
1245         span: Span,
1246         count: usize,
1247         lifetime_names: &FxHashSet<Symbol>,
1248         lifetime_spans: Vec<Span>,
1249         params: &[ElisionFailureInfo],
1250     ) {
1251         let snippet = self.tcx.sess.source_map().span_to_snippet(span).ok();
1252
1253         err.span_label(
1254             span,
1255             &format!(
1256                 "expected {} lifetime parameter{}",
1257                 if count == 1 { "named".to_string() } else { count.to_string() },
1258                 pluralize!(count)
1259             ),
1260         );
1261
1262         let suggest_existing = |err: &mut DiagnosticBuilder<'_>,
1263                                 name: &str,
1264                                 formatter: &dyn Fn(&str) -> String| {
1265             if let Some(MissingLifetimeSpot::HigherRanked { span: for_span, span_type }) =
1266                 self.missing_named_lifetime_spots.iter().rev().next()
1267             {
1268                 // When we have `struct S<'a>(&'a dyn Fn(&X) -> &X);` we want to not only suggest
1269                 // using `'a`, but also introduce the concept of HRLTs by suggesting
1270                 // `struct S<'a>(&'a dyn for<'b> Fn(&X) -> &'b X);`. (#72404)
1271                 let mut introduce_suggestion = vec![];
1272
1273                 let a_to_z_repeat_n = |n| {
1274                     (b'a'..=b'z').map(move |c| {
1275                         let mut s = '\''.to_string();
1276                         s.extend(std::iter::repeat(char::from(c)).take(n));
1277                         s
1278                     })
1279                 };
1280
1281                 // If all single char lifetime names are present, we wrap around and double the chars.
1282                 let lt_name = (1..)
1283                     .flat_map(a_to_z_repeat_n)
1284                     .find(|lt| !lifetime_names.contains(&Symbol::intern(&lt)))
1285                     .unwrap();
1286                 let msg = format!(
1287                     "consider making the {} lifetime-generic with a new `{}` lifetime",
1288                     span_type.descr(),
1289                     lt_name,
1290                 );
1291                 err.note(
1292                     "for more information on higher-ranked polymorphism, visit \
1293                     https://doc.rust-lang.org/nomicon/hrtb.html",
1294                 );
1295                 let for_sugg = span_type.suggestion(&lt_name);
1296                 for param in params {
1297                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
1298                         if snippet.starts_with('&') && !snippet.starts_with("&'") {
1299                             introduce_suggestion
1300                                 .push((param.span, format!("&{} {}", lt_name, &snippet[1..])));
1301                         } else if snippet.starts_with("&'_ ") {
1302                             introduce_suggestion
1303                                 .push((param.span, format!("&{} {}", lt_name, &snippet[4..])));
1304                         }
1305                     }
1306                 }
1307                 introduce_suggestion.push((*for_span, for_sugg.to_string()));
1308                 introduce_suggestion.push((span, formatter(&lt_name)));
1309                 err.multipart_suggestion(&msg, introduce_suggestion, Applicability::MaybeIncorrect);
1310             }
1311
1312             err.span_suggestion_verbose(
1313                 span,
1314                 &format!("consider using the `{}` lifetime", lifetime_names.iter().next().unwrap()),
1315                 formatter(name),
1316                 Applicability::MaybeIncorrect,
1317             );
1318         };
1319         let suggest_new = |err: &mut DiagnosticBuilder<'_>, sugg: &str| {
1320             for missing in self.missing_named_lifetime_spots.iter().rev() {
1321                 let mut introduce_suggestion = vec![];
1322                 let msg;
1323                 let should_break;
1324                 introduce_suggestion.push(match missing {
1325                     MissingLifetimeSpot::Generics(generics) => {
1326                         if generics.span == DUMMY_SP {
1327                             // Account for malformed generics in the HIR. This shouldn't happen,
1328                             // but if we make a mistake elsewhere, mainly by keeping something in
1329                             // `missing_named_lifetime_spots` that we shouldn't, like associated
1330                             // `const`s or making a mistake in the AST lowering we would provide
1331                             // non-sensical suggestions. Guard against that by skipping these.
1332                             // (#74264)
1333                             continue;
1334                         }
1335                         msg = "consider introducing a named lifetime parameter".to_string();
1336                         should_break = true;
1337                         if let Some(param) = generics.params.iter().find(|p| match p.kind {
1338                             hir::GenericParamKind::Type {
1339                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1340                                 ..
1341                             } => false,
1342                             _ => true,
1343                         }) {
1344                             (param.span.shrink_to_lo(), "'a, ".to_string())
1345                         } else {
1346                             (generics.span, "<'a>".to_string())
1347                         }
1348                     }
1349                     MissingLifetimeSpot::HigherRanked { span, span_type } => {
1350                         msg = format!(
1351                             "consider making the {} lifetime-generic with a new `'a` lifetime",
1352                             span_type.descr(),
1353                         );
1354                         should_break = false;
1355                         err.note(
1356                             "for more information on higher-ranked polymorphism, visit \
1357                             https://doc.rust-lang.org/nomicon/hrtb.html",
1358                         );
1359                         (*span, span_type.suggestion("'a"))
1360                     }
1361                 });
1362                 for param in params {
1363                     if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(param.span) {
1364                         if snippet.starts_with('&') && !snippet.starts_with("&'") {
1365                             introduce_suggestion
1366                                 .push((param.span, format!("&'a {}", &snippet[1..])));
1367                         } else if snippet.starts_with("&'_ ") {
1368                             introduce_suggestion
1369                                 .push((param.span, format!("&'a {}", &snippet[4..])));
1370                         }
1371                     }
1372                 }
1373                 introduce_suggestion.push((span, sugg.to_string()));
1374                 err.multipart_suggestion(&msg, introduce_suggestion, Applicability::MaybeIncorrect);
1375                 if should_break {
1376                     break;
1377                 }
1378             }
1379         };
1380
1381         let lifetime_names: Vec<_> = lifetime_names.into_iter().collect();
1382         match (&lifetime_names[..], snippet.as_deref()) {
1383             ([name], Some("&")) => {
1384                 suggest_existing(err, &name.as_str()[..], &|name| format!("&{} ", name));
1385             }
1386             ([name], Some("'_")) => {
1387                 suggest_existing(err, &name.as_str()[..], &|n| n.to_string());
1388             }
1389             ([name], Some("")) => {
1390                 suggest_existing(err, &name.as_str()[..], &|n| format!("{}, ", n).repeat(count));
1391             }
1392             ([name], Some(snippet)) if !snippet.ends_with('>') => {
1393                 let f = |name: &str| {
1394                     format!(
1395                         "{}<{}>",
1396                         snippet,
1397                         std::iter::repeat(name.to_string())
1398                             .take(count)
1399                             .collect::<Vec<_>>()
1400                             .join(", ")
1401                     )
1402                 };
1403                 suggest_existing(err, &name.as_str()[..], &f);
1404             }
1405             ([], Some("&")) if count == 1 => {
1406                 suggest_new(err, "&'a ");
1407             }
1408             ([], Some("'_")) if count == 1 => {
1409                 suggest_new(err, "'a");
1410             }
1411             ([], Some(snippet)) if !snippet.ends_with('>') && count == 1 => {
1412                 if snippet == "" {
1413                     // This happens when we have `type Bar<'a> = Foo<T>` where we point at the space
1414                     // before `T`. We will suggest `type Bar<'a> = Foo<'a, T>`.
1415                     suggest_new(err, "'a, ");
1416                 } else {
1417                     suggest_new(err, &format!("{}<'a>", snippet));
1418                 }
1419             }
1420             (lts, ..) if lts.len() > 1 => {
1421                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
1422                 if Some("") == snippet.as_deref() {
1423                     // This happens when we have `Foo<T>` where we point at the space before `T`,
1424                     // but this can be confusing so we give a suggestion with placeholders.
1425                     err.span_suggestion_verbose(
1426                         span,
1427                         "consider using one of the available lifetimes here",
1428                         "'lifetime, ".repeat(count),
1429                         Applicability::HasPlaceholders,
1430                     );
1431                 }
1432             }
1433             _ => {}
1434         }
1435     }
1436 }