compiler/rustc_resolve/src/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, LabelSuggestion, TypoSuggestion};
   2 use crate::late::{AliasPossibility, LateResolutionVisitor, RibKind};
   3 use crate::late::{LifetimeBinderKind, LifetimeRes, LifetimeRibKind, LifetimeUseSet};
   4 use crate::path_names_to_string;
   5 use crate::{Module, ModuleKind, ModuleOrUniformRoot};
   6 use crate::{PathResult, PathSource, Segment};
   7
   8 use rustc_ast::visit::{FnCtxt, FnKind, LifetimeCtxt};
   9 use rustc_ast::{
  10     self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
  11     NodeId, Path, Ty, TyKind, DUMMY_NODE_ID,
  12 };
  13 use rustc_ast_pretty::pprust::path_segment_to_string;
  14 use rustc_data_structures::fx::FxHashSet;
  15 use rustc_errors::{
  16     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
  17     MultiSpan,
  18 };
  19 use rustc_hir as hir;
  20 use rustc_hir::def::Namespace::{self, *};
  21 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind};
  22 use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
  23 use rustc_hir::PrimTy;
  24 use rustc_session::lint;
  25 use rustc_session::parse::feature_err;
  26 use rustc_session::Session;
  27 use rustc_span::edition::Edition;
  28 use rustc_span::hygiene::MacroKind;
  29 use rustc_span::lev_distance::find_best_match_for_name;
  30 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  31 use rustc_span::{BytePos, Span};
  32
  33 use std::iter;
  34 use std::ops::Deref;
  35
  36 use tracing::debug;
  37
  38 type Res = def::Res<ast::NodeId>;
  39
  40 /// A field or associated item from self type suggested in case of resolution failure.
  41 enum AssocSuggestion {
  42     Field,
  43     MethodWithSelf,
  44     AssocFn,
  45     AssocType,
  46     AssocConst,
  47 }
  48
  49 impl AssocSuggestion {
  50     fn action(&self) -> &'static str {
  51         match self {
  52             AssocSuggestion::Field => "use the available field",
  53             AssocSuggestion::MethodWithSelf => "call the method with the fully-qualified path",
  54             AssocSuggestion::AssocFn => "call the associated function",
  55             AssocSuggestion::AssocConst => "use the associated `const`",
  56             AssocSuggestion::AssocType => "use the associated type",
  57         }
  58     }
  59 }
  60
  61 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  62     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  63 }
  64
  65 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  66     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  67 }
  68
  69 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  70 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
  71     let variant_path = &suggestion.path;
  72     let variant_path_string = path_names_to_string(variant_path);
  73
  74     let path_len = suggestion.path.segments.len();
  75     let enum_path = ast::Path {
  76         span: suggestion.path.span,
  77         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
  78         tokens: None,
  79     };
  80     let enum_path_string = path_names_to_string(&enum_path);
  81
  82     (variant_path_string, enum_path_string)
  83 }
  84
  85 /// Description of an elided lifetime.
  86 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
  87 pub(super) struct MissingLifetime {
  88     /// Used to overwrite the resolution with the suggestion, to avoid cascasing errors.
  89     pub id: NodeId,
  90     /// Where to suggest adding the lifetime.
  91     pub span: Span,
  92     /// How the lifetime was introduced, to have the correct space and comma.
  93     pub kind: MissingLifetimeKind,
  94     /// Number of elided lifetimes, used for elision in path.
  95     pub count: usize,
  96 }
  97
  98 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
  99 pub(super) enum MissingLifetimeKind {
 100     /// An explicit `'_`.
 101     Underscore,
 102     /// An elided lifetime `&' ty`.
 103     Ampersand,
 104     /// An elided lifetime in brackets with written brackets.
 105     Comma,
 106     /// An elided lifetime with elided brackets.
 107     Brackets,
 108 }
 109
 110 /// Description of the lifetimes appearing in a function parameter.
 111 /// This is used to provide a literal explanation to the elision failure.
 112 #[derive(Clone, Debug)]
 113 pub(super) struct ElisionFnParameter {
 114     /// The index of the argument in the original definition.
 115     pub index: usize,
 116     /// The name of the argument if it's a simple ident.
 117     pub ident: Option<Ident>,
 118     /// The number of lifetimes in the parameter.
 119     pub lifetime_count: usize,
 120     /// The span of the parameter.
 121     pub span: Span,
 122 }
 123
 124 /// Description of lifetimes that appear as candidates for elision.
 125 /// This is used to suggest introducing an explicit lifetime.
 126 #[derive(Debug)]
 127 pub(super) enum LifetimeElisionCandidate {
 128     /// This is not a real lifetime.
 129     Ignore,
 130     /// There is a named lifetime, we won't suggest anything.
 131     Named,
 132     Missing(MissingLifetime),
 133 }
 134
 135 impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 136     fn def_span(&self, def_id: DefId) -> Option<Span> {
 137         match def_id.krate {
 138             LOCAL_CRATE => self.r.opt_span(def_id),
 139             _ => Some(self.r.cstore().get_span_untracked(def_id, self.r.session)),
 140         }
 141     }
 142
 143     /// Handles error reporting for `smart_resolve_path_fragment` function.
 144     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
 145     pub(crate) fn smart_resolve_report_errors(
 146         &mut self,
 147         path: &[Segment],
 148         span: Span,
 149         source: PathSource<'_>,
 150         res: Option<Res>,
 151     ) -> (DiagnosticBuilder<'a, ErrorGuaranteed>, Vec<ImportSuggestion>) {
 152         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
 153         let ns = source.namespace();
 154         let is_expected = &|res| source.is_expected(res);
 155         let is_enum_variant = &|res| matches!(res, Res::Def(DefKind::Variant, _));
 156
 157         debug!(?res, ?source);
 158
 159         // Make the base error.
 160         struct BaseError<'a> {
 161             msg: String,
 162             fallback_label: String,
 163             span: Span,
 164             could_be_expr: bool,
 165             suggestion: Option<(Span, &'a str, String)>,
 166         }
 167         let mut expected = source.descr_expected();
 168         let path_str = Segment::names_to_string(path);
 169         let item_str = path.last().unwrap().ident;
 170         let base_error = if let Some(res) = res {
 171             BaseError {
 172                 msg: format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
 173                 fallback_label: format!("not a {expected}"),
 174                 span,
 175                 could_be_expr: match res {
 176                     Res::Def(DefKind::Fn, _) => {
 177                         // Verify whether this is a fn call or an Fn used as a type.
 178                         self.r
 179                             .session
 180                             .source_map()
 181                             .span_to_snippet(span)
 182                             .map(|snippet| snippet.ends_with(')'))
 183                             .unwrap_or(false)
 184                     }
 185                     Res::Def(
 186                         DefKind::Ctor(..) | DefKind::AssocFn | DefKind::Const | DefKind::AssocConst,
 187                         _,
 188                     )
 189                     | Res::SelfCtor(_)
 190                     | Res::PrimTy(_)
 191                     | Res::Local(_) => true,
 192                     _ => false,
 193                 },
 194                 suggestion: None,
 195             }
 196         } else {
 197             let item_span = path.last().unwrap().ident.span;
 198             let (mod_prefix, mod_str, suggestion) = if path.len() == 1 {
 199                 debug!(?self.diagnostic_metadata.current_impl_items);
 200                 debug!(?self.diagnostic_metadata.current_function);
 201                 let suggestion = if let Some(items) = self.diagnostic_metadata.current_impl_items
 202                     && let Some((fn_kind, _)) = self.diagnostic_metadata.current_function
 203                     && self.current_trait_ref.is_none()
 204                     && let Some(FnCtxt::Assoc(_)) = fn_kind.ctxt()
 205                     && let Some(item) = items.iter().find(|i| {
 206                         if let AssocItemKind::Fn(fn_) = &i.kind
 207                             && !fn_.sig.decl.has_self()
 208                             && i.ident.name == item_str.name
 209                         {
 210                             debug!(?item_str.name);
 211                             debug!(?fn_.sig.decl.inputs);
 212                             return true
 213                         }
 214                         false
 215                     })
 216                 {
 217                     Some((
 218                         item_span,
 219                         "consider using the associated function",
 220                         format!("Self::{}", item.ident)
 221                     ))
 222                 } else {
 223                     None
 224                 };
 225                 (String::new(), "this scope".to_string(), suggestion)
 226             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 227                 if self.r.session.edition() > Edition::Edition2015 {
 228                     // In edition 2018 onwards, the `::foo` syntax may only pull from the extern prelude
 229                     // which overrides all other expectations of item type
 230                     expected = "crate";
 231                     (String::new(), "the list of imported crates".to_string(), None)
 232                 } else {
 233                     (String::new(), "the crate root".to_string(), None)
 234                 }
 235             } else if path.len() == 2 && path[0].ident.name == kw::Crate {
 236                 (String::new(), "the crate root".to_string(), None)
 237             } else {
 238                 let mod_path = &path[..path.len() - 1];
 239                 let mod_prefix = match self.resolve_path(mod_path, Some(TypeNS), None) {
 240                     PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 241                     _ => None,
 242                 }
 243                 .map_or_else(String::new, |res| format!("{} ", res.descr()));
 244                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)), None)
 245             };
 246             BaseError {
 247                 msg: format!("cannot find {expected} `{item_str}` in {mod_prefix}{mod_str}"),
 248                 fallback_label: if path_str == "async" && expected.starts_with("struct") {
 249                     "`async` blocks are only allowed in Rust 2018 or later".to_string()
 250                 } else {
 251                     format!("not found in {mod_str}")
 252                 },
 253                 span: item_span,
 254                 could_be_expr: false,
 255                 suggestion,
 256             }
 257         };
 258
 259         let code = source.error_code(res.is_some());
 260         let mut err =
 261             self.r.session.struct_span_err_with_code(base_error.span, &base_error.msg, code);
 262
 263         self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
 264
 265         if let Some(sugg) = base_error.suggestion {
 266             err.span_suggestion_verbose(sugg.0, sugg.1, sugg.2, Applicability::MaybeIncorrect);
 267         }
 268
 269         if let Some(span) = self.diagnostic_metadata.current_block_could_be_bare_struct_literal {
 270             err.multipart_suggestion(
 271                 "you might have meant to write a `struct` literal",
 272                 vec![
 273                     (span.shrink_to_lo(), "{ SomeStruct ".to_string()),
 274                     (span.shrink_to_hi(), "}".to_string()),
 275                 ],
 276                 Applicability::HasPlaceholders,
 277             );
 278         }
 279         match (source, self.diagnostic_metadata.in_if_condition) {
 280             (
 281                 PathSource::Expr(_),
 282                 Some(Expr { span: expr_span, kind: ExprKind::Assign(lhs, _, _), .. }),
 283             ) => {
 284                 // Icky heuristic so we don't suggest:
 285                 // `if (i + 2) = 2` => `if let (i + 2) = 2` (approximately pattern)
 286                 // `if 2 = i` => `if let 2 = i` (lhs needs to contain error span)
 287                 if lhs.is_approximately_pattern() && lhs.span.contains(span) {
 288                     err.span_suggestion_verbose(
 289                         expr_span.shrink_to_lo(),
 290                         "you might have meant to use pattern matching",
 291                         "let ",
 292                         Applicability::MaybeIncorrect,
 293                     );
 294                 }
 295             }
 296             _ => {}
 297         }
 298
 299         let is_assoc_fn = self.self_type_is_available();
 300         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 301         if ["this", "my"].contains(&item_str.as_str()) && is_assoc_fn {
 302             err.span_suggestion_short(
 303                 span,
 304                 "you might have meant to use `self` here instead",
 305                 "self",
 306                 Applicability::MaybeIncorrect,
 307             );
 308             if !self.self_value_is_available(path[0].ident.span) {
 309                 if let Some((FnKind::Fn(_, _, sig, ..), fn_span)) =
 310                     &self.diagnostic_metadata.current_function
 311                 {
 312                     let (span, sugg) = if let Some(param) = sig.decl.inputs.get(0) {
 313                         (param.span.shrink_to_lo(), "&self, ")
 314                     } else {
 315                         (
 316                             self.r
 317                                 .session
 318                                 .source_map()
 319                                 .span_through_char(*fn_span, '(')
 320                                 .shrink_to_hi(),
 321                             "&self",
 322                         )
 323                     };
 324                     err.span_suggestion_verbose(
 325                         span,
 326                         "if you meant to use `self`, you are also missing a `self` receiver \
 327                          argument",
 328                         sugg,
 329                         Applicability::MaybeIncorrect,
 330                     );
 331                 }
 332             }
 333         }
 334
 335         self.detect_assoct_type_constraint_meant_as_path(base_error.span, &mut err);
 336
 337         // Emit special messages for unresolved `Self` and `self`.
 338         if is_self_type(path, ns) {
 339             err.code(rustc_errors::error_code!(E0411));
 340             err.span_label(
 341                 span,
 342                 "`Self` is only available in impls, traits, and type definitions".to_string(),
 343             );
 344             if let Some(item_kind) = self.diagnostic_metadata.current_item {
 345                 err.span_label(
 346                     item_kind.ident.span,
 347                     format!(
 348                         "`Self` not allowed in {} {}",
 349                         item_kind.kind.article(),
 350                         item_kind.kind.descr()
 351                     ),
 352                 );
 353             }
 354             return (err, Vec::new());
 355         }
 356         if is_self_value(path, ns) {
 357             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 358
 359             err.code(rustc_errors::error_code!(E0424));
 360             err.span_label(span, match source {
 361                 PathSource::Pat => "`self` value is a keyword and may not be bound to variables or shadowed",
 362                 _ => "`self` value is a keyword only available in methods with a `self` parameter",
 363             });
 364             if let Some((fn_kind, span)) = &self.diagnostic_metadata.current_function {
 365                 // The current function has a `self' parameter, but we were unable to resolve
 366                 // a reference to `self`. This can only happen if the `self` identifier we
 367                 // are resolving came from a different hygiene context.
 368                 if fn_kind.decl().inputs.get(0).map_or(false, |p| p.is_self()) {
 369                     err.span_label(*span, "this function has a `self` parameter, but a macro invocation can only access identifiers it receives from parameters");
 370                 } else {
 371                     let doesnt = if is_assoc_fn {
 372                         let (span, sugg) = fn_kind
 373                             .decl()
 374                             .inputs
 375                             .get(0)
 376                             .map(|p| (p.span.shrink_to_lo(), "&self, "))
 377                             .unwrap_or_else(|| {
 378                                 // Try to look for the "(" after the function name, if possible.
 379                                 // This avoids placing the suggestion into the visibility specifier.
 380                                 let span = fn_kind
 381                                     .ident()
 382                                     .map_or(*span, |ident| span.with_lo(ident.span.hi()));
 383                                 (
 384                                     self.r
 385                                         .session
 386                                         .source_map()
 387                                         .span_through_char(span, '(')
 388                                         .shrink_to_hi(),
 389                                     "&self",
 390                                 )
 391                             });
 392                         err.span_suggestion_verbose(
 393                             span,
 394                             "add a `self` receiver parameter to make the associated `fn` a method",
 395                             sugg,
 396                             Applicability::MaybeIncorrect,
 397                         );
 398                         "doesn't"
 399                     } else {
 400                         "can't"
 401                     };
 402                     if let Some(ident) = fn_kind.ident() {
 403                         err.span_label(
 404                             ident.span,
 405                             &format!("this function {} have a `self` parameter", doesnt),
 406                         );
 407                     }
 408                 }
 409             } else if let Some(item_kind) = self.diagnostic_metadata.current_item {
 410                 err.span_label(
 411                     item_kind.ident.span,
 412                     format!(
 413                         "`self` not allowed in {} {}",
 414                         item_kind.kind.article(),
 415                         item_kind.kind.descr()
 416                     ),
 417                 );
 418             }
 419             return (err, Vec::new());
 420         }
 421
 422         // Try to lookup name in more relaxed fashion for better error reporting.
 423         let ident = path.last().unwrap().ident;
 424         let mut candidates = self
 425             .r
 426             .lookup_import_candidates(ident, ns, &self.parent_scope, is_expected)
 427             .into_iter()
 428             .filter(|ImportSuggestion { did, .. }| {
 429                 match (did, res.and_then(|res| res.opt_def_id())) {
 430                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 431                     _ => true,
 432                 }
 433             })
 434             .collect::<Vec<_>>();
 435         let crate_def_id = CRATE_DEF_ID.to_def_id();
 436         // Try to filter out intrinsics candidates, as long as we have
 437         // some other candidates to suggest.
 438         let intrinsic_candidates: Vec<_> = candidates
 439             .drain_filter(|sugg| {
 440                 let path = path_names_to_string(&sugg.path);
 441                 path.starts_with("core::intrinsics::") || path.starts_with("std::intrinsics::")
 442             })
 443             .collect();
 444         if candidates.is_empty() {
 445             // Put them back if we have no more candidates to suggest...
 446             candidates.extend(intrinsic_candidates);
 447         }
 448         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 449             let mut enum_candidates: Vec<_> = self
 450                 .r
 451                 .lookup_import_candidates(ident, ns, &self.parent_scope, is_enum_variant)
 452                 .into_iter()
 453                 .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 454                 .filter(|(_, enum_ty_path)| !enum_ty_path.starts_with("std::prelude::"))
 455                 .collect();
 456             if !enum_candidates.is_empty() {
 457                 if let (PathSource::Type, Some(span)) =
 458                     (source, self.diagnostic_metadata.current_type_ascription.last())
 459                 {
 460                     if self
 461                         .r
 462                         .session
 463                         .parse_sess
 464                         .type_ascription_path_suggestions
 465                         .borrow()
 466                         .contains(span)
 467                     {
 468                         // Already reported this issue on the lhs of the type ascription.
 469                         err.delay_as_bug();
 470                         return (err, candidates);
 471                     }
 472                 }
 473
 474                 enum_candidates.sort();
 475
 476                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 477                 // (that it's a variant) for E0573 "expected type, found variant".
 478                 let preamble = if res.is_none() {
 479                     let others = match enum_candidates.len() {
 480                         1 => String::new(),
 481                         2 => " and 1 other".to_owned(),
 482                         n => format!(" and {} others", n),
 483                     };
 484                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 485                 } else {
 486                     String::new()
 487                 };
 488                 let msg = format!("{}try using the variant's enum", preamble);
 489
 490                 err.span_suggestions(
 491                     span,
 492                     &msg,
 493                     enum_candidates.into_iter().map(|(_variant_path, enum_ty_path)| enum_ty_path),
 494                     Applicability::MachineApplicable,
 495                 );
 496             }
 497         }
 498         // Try Levenshtein algorithm.
 499         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected);
 500         if path.len() == 1 && self.self_type_is_available() {
 501             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 502                 let self_is_available = self.self_value_is_available(path[0].ident.span);
 503                 match candidate {
 504                     AssocSuggestion::Field => {
 505                         if self_is_available {
 506                             err.span_suggestion(
 507                                 span,
 508                                 "you might have meant to use the available field",
 509                                 format!("self.{path_str}"),
 510                                 Applicability::MachineApplicable,
 511                             );
 512                         } else {
 513                             err.span_label(span, "a field by this name exists in `Self`");
 514                         }
 515                     }
 516                     AssocSuggestion::MethodWithSelf if self_is_available => {
 517                         err.span_suggestion(
 518                             span,
 519                             "you might have meant to call the method",
 520                             format!("self.{path_str}"),
 521                             Applicability::MachineApplicable,
 522                         );
 523                     }
 524                     AssocSuggestion::MethodWithSelf
 525                     | AssocSuggestion::AssocFn
 526                     | AssocSuggestion::AssocConst
 527                     | AssocSuggestion::AssocType => {
 528                         err.span_suggestion(
 529                             span,
 530                             &format!("you might have meant to {}", candidate.action()),
 531                             format!("Self::{path_str}"),
 532                             Applicability::MachineApplicable,
 533                         );
 534                     }
 535                 }
 536                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 537                 return (err, candidates);
 538             }
 539
 540             // If the first argument in call is `self` suggest calling a method.
 541             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 542                 let mut args_snippet = String::new();
 543                 if let Some(args_span) = args_span {
 544                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 545                         args_snippet = snippet;
 546                     }
 547                 }
 548
 549                 err.span_suggestion(
 550                     call_span,
 551                     &format!("try calling `{ident}` as a method"),
 552                     format!("self.{path_str}({args_snippet})"),
 553                     Applicability::MachineApplicable,
 554                 );
 555                 return (err, candidates);
 556             }
 557         }
 558
 559         // Try context-dependent help if relaxed lookup didn't work.
 560         if let Some(res) = res {
 561             if self.smart_resolve_context_dependent_help(
 562                 &mut err,
 563                 span,
 564                 source,
 565                 res,
 566                 &path_str,
 567                 &base_error.fallback_label,
 568             ) {
 569                 // We do this to avoid losing a secondary span when we override the main error span.
 570                 self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 571                 return (err, candidates);
 572             }
 573         }
 574
 575         let is_macro =
 576             base_error.span.from_expansion() && base_error.span.desugaring_kind().is_none();
 577         if !self.type_ascription_suggestion(&mut err, base_error.span) {
 578             let mut fallback = false;
 579             if let (
 580                 PathSource::Trait(AliasPossibility::Maybe),
 581                 Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)),
 582                 false,
 583             ) = (source, res, is_macro)
 584             {
 585                 if let Some(bounds @ [_, .., _]) = self.diagnostic_metadata.current_trait_object {
 586                     fallback = true;
 587                     let spans: Vec<Span> = bounds
 588                         .iter()
 589                         .map(|bound| bound.span())
 590                         .filter(|&sp| sp != base_error.span)
 591                         .collect();
 592
 593                     let start_span = bounds.iter().map(|bound| bound.span()).next().unwrap();
 594                     // `end_span` is the end of the poly trait ref (Foo + 'baz + Bar><)
 595                     let end_span = bounds.iter().map(|bound| bound.span()).last().unwrap();
 596                     // `last_bound_span` is the last bound of the poly trait ref (Foo + >'baz< + Bar)
 597                     let last_bound_span = spans.last().cloned().unwrap();
 598                     let mut multi_span: MultiSpan = spans.clone().into();
 599                     for sp in spans {
 600                         let msg = if sp == last_bound_span {
 601                             format!(
 602                                 "...because of {these} bound{s}",
 603                                 these = pluralize!("this", bounds.len() - 1),
 604                                 s = pluralize!(bounds.len() - 1),
 605                             )
 606                         } else {
 607                             String::new()
 608                         };
 609                         multi_span.push_span_label(sp, msg);
 610                     }
 611                     multi_span
 612                         .push_span_label(base_error.span, "expected this type to be a trait...");
 613                     err.span_help(
 614                         multi_span,
 615                         "`+` is used to constrain a \"trait object\" type with lifetimes or \
 616                          auto-traits; structs and enums can't be bound in that way",
 617                     );
 618                     if bounds.iter().all(|bound| match bound {
 619                         ast::GenericBound::Outlives(_) => true,
 620                         ast::GenericBound::Trait(tr, _) => tr.span == base_error.span,
 621                     }) {
 622                         let mut sugg = vec![];
 623                         if base_error.span != start_span {
 624                             sugg.push((start_span.until(base_error.span), String::new()));
 625                         }
 626                         if base_error.span != end_span {
 627                             sugg.push((base_error.span.shrink_to_hi().to(end_span), String::new()));
 628                         }
 629
 630                         err.multipart_suggestion(
 631                             "if you meant to use a type and not a trait here, remove the bounds",
 632                             sugg,
 633                             Applicability::MaybeIncorrect,
 634                         );
 635                     }
 636                 }
 637             }
 638
 639             fallback |= self.restrict_assoc_type_in_where_clause(span, &mut err);
 640
 641             if !self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span) {
 642                 fallback = true;
 643                 match self.diagnostic_metadata.current_let_binding {
 644                     Some((pat_sp, Some(ty_sp), None))
 645                         if ty_sp.contains(base_error.span) && base_error.could_be_expr =>
 646                     {
 647                         err.span_suggestion_short(
 648                             pat_sp.between(ty_sp),
 649                             "use `=` if you meant to assign",
 650                             " = ",
 651                             Applicability::MaybeIncorrect,
 652                         );
 653                     }
 654                     _ => {}
 655                 }
 656
 657                 // If the trait has a single item (which wasn't matched by Levenshtein), suggest it
 658                 let suggestion = self.get_single_associated_item(&path, &source, is_expected);
 659                 self.r.add_typo_suggestion(&mut err, suggestion, ident_span);
 660             }
 661             if fallback {
 662                 // Fallback label.
 663                 err.span_label(base_error.span, base_error.fallback_label);
 664             }
 665         }
 666         if let Some(err_code) = &err.code {
 667             if err_code == &rustc_errors::error_code!(E0425) {
 668                 for label_rib in &self.label_ribs {
 669                     for (label_ident, node_id) in &label_rib.bindings {
 670                         if format!("'{}", ident) == label_ident.to_string() {
 671                             err.span_label(label_ident.span, "a label with a similar name exists");
 672                             if let PathSource::Expr(Some(Expr {
 673                                 kind: ExprKind::Break(None, Some(_)),
 674                                 ..
 675                             })) = source
 676                             {
 677                                 err.span_suggestion(
 678                                     span,
 679                                     "use the similarly named label",
 680                                     label_ident.name,
 681                                     Applicability::MaybeIncorrect,
 682                                 );
 683                                 // Do not lint against unused label when we suggest them.
 684                                 self.diagnostic_metadata.unused_labels.remove(node_id);
 685                             }
 686                         }
 687                     }
 688                 }
 689             } else if err_code == &rustc_errors::error_code!(E0412) {
 690                 if let Some(correct) = Self::likely_rust_type(path) {
 691                     err.span_suggestion(
 692                         span,
 693                         "perhaps you intended to use this type",
 694                         correct,
 695                         Applicability::MaybeIncorrect,
 696                     );
 697                 }
 698             }
 699         }
 700
 701         (err, candidates)
 702     }
 703
 704     fn detect_assoct_type_constraint_meant_as_path(&self, base_span: Span, err: &mut Diagnostic) {
 705         let Some(ty) = self.diagnostic_metadata.current_type_path else { return; };
 706         let TyKind::Path(_, path) = &ty.kind else { return; };
 707         for segment in &path.segments {
 708             let Some(params) = &segment.args else { continue; };
 709             let ast::GenericArgs::AngleBracketed(ref params) = params.deref() else { continue; };
 710             for param in &params.args {
 711                 let ast::AngleBracketedArg::Constraint(constraint) = param else { continue; };
 712                 let ast::AssocConstraintKind::Bound { bounds } = &constraint.kind else {
 713                     continue;
 714                 };
 715                 for bound in bounds {
 716                     let ast::GenericBound::Trait(trait_ref, ast::TraitBoundModifier::None)
 717                         = bound else
 718                     {
 719                         continue;
 720                     };
 721                     if base_span == trait_ref.span {
 722                         err.span_suggestion_verbose(
 723                             constraint.ident.span.between(trait_ref.span),
 724                             "you might have meant to write a path instead of an associated type bound",
 725                             "::",
 726                             Applicability::MachineApplicable,
 727                         );
 728                     }
 729                 }
 730             }
 731         }
 732     }
 733
 734     fn suggest_swapping_misplaced_self_ty_and_trait(
 735         &mut self,
 736         err: &mut Diagnostic,
 737         source: PathSource<'_>,
 738         res: Option<Res>,
 739         span: Span,
 740     ) {
 741         if let Some((trait_ref, self_ty)) =
 742             self.diagnostic_metadata.currently_processing_impl_trait.clone()
 743             && let TyKind::Path(_, self_ty_path) = &self_ty.kind
 744             && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 745                 self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
 746             && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
 747             && trait_ref.path.span == span
 748             && let PathSource::Trait(_) = source
 749             && let Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)) = res
 750             && let Ok(self_ty_str) =
 751                 self.r.session.source_map().span_to_snippet(self_ty.span)
 752             && let Ok(trait_ref_str) =
 753                 self.r.session.source_map().span_to_snippet(trait_ref.path.span)
 754         {
 755                 err.multipart_suggestion(
 756                     "`impl` items mention the trait being implemented first and the type it is being implemented for second",
 757                     vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
 758                     Applicability::MaybeIncorrect,
 759                 );
 760         }
 761     }
 762
 763     fn get_single_associated_item(
 764         &mut self,
 765         path: &[Segment],
 766         source: &PathSource<'_>,
 767         filter_fn: &impl Fn(Res) -> bool,
 768     ) -> Option<TypoSuggestion> {
 769         if let crate::PathSource::TraitItem(_) = source {
 770             let mod_path = &path[..path.len() - 1];
 771             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
 772                 self.resolve_path(mod_path, None, None)
 773             {
 774                 let resolutions = self.r.resolutions(module).borrow();
 775                 let targets: Vec<_> =
 776                     resolutions
 777                         .iter()
 778                         .filter_map(|(key, resolution)| {
 779                             resolution.borrow().binding.map(|binding| binding.res()).and_then(
 780                                 |res| if filter_fn(res) { Some((key, res)) } else { None },
 781                             )
 782                         })
 783                         .collect();
 784                 if targets.len() == 1 {
 785                     let target = targets[0];
 786                     return Some(TypoSuggestion::single_item_from_res(
 787                         target.0.ident.name,
 788                         target.1,
 789                     ));
 790                 }
 791             }
 792         }
 793         None
 794     }
 795
 796     /// Given `where <T as Bar>::Baz: String`, suggest `where T: Bar<Baz = String>`.
 797     fn restrict_assoc_type_in_where_clause(&mut self, span: Span, err: &mut Diagnostic) -> bool {
 798         // Detect that we are actually in a `where` predicate.
 799         let (bounded_ty, bounds, where_span) =
 800             if let Some(ast::WherePredicate::BoundPredicate(ast::WhereBoundPredicate {
 801                 bounded_ty,
 802                 bound_generic_params,
 803                 bounds,
 804                 span,
 805             })) = self.diagnostic_metadata.current_where_predicate
 806             {
 807                 if !bound_generic_params.is_empty() {
 808                     return false;
 809                 }
 810                 (bounded_ty, bounds, span)
 811             } else {
 812                 return false;
 813             };
 814
 815         // Confirm that the target is an associated type.
 816         let (ty, position, path) = if let ast::TyKind::Path(
 817             Some(ast::QSelf { ty, position, .. }),
 818             path,
 819         ) = &bounded_ty.kind
 820         {
 821             // use this to verify that ident is a type param.
 822             let Some(partial_res) = self.r.partial_res_map.get(&bounded_ty.id) else {
 823                 return false;
 824             };
 825             if !(matches!(
 826                 partial_res.base_res(),
 827                 hir::def::Res::Def(hir::def::DefKind::AssocTy, _)
 828             ) && partial_res.unresolved_segments() == 0)
 829             {
 830                 return false;
 831             }
 832             (ty, position, path)
 833         } else {
 834             return false;
 835         };
 836
 837         let peeled_ty = ty.peel_refs();
 838         if let ast::TyKind::Path(None, type_param_path) = &peeled_ty.kind {
 839             // Confirm that the `SelfTy` is a type parameter.
 840             let Some(partial_res) = self.r.partial_res_map.get(&peeled_ty.id) else {
 841                 return false;
 842             };
 843             if !(matches!(
 844                 partial_res.base_res(),
 845                 hir::def::Res::Def(hir::def::DefKind::TyParam, _)
 846             ) && partial_res.unresolved_segments() == 0)
 847             {
 848                 return false;
 849             }
 850             if let (
 851                 [ast::PathSegment { ident: constrain_ident, args: None, .. }],
 852                 [ast::GenericBound::Trait(poly_trait_ref, ast::TraitBoundModifier::None)],
 853             ) = (&type_param_path.segments[..], &bounds[..])
 854             {
 855                 if let [ast::PathSegment { ident, args: None, .. }] =
 856                     &poly_trait_ref.trait_ref.path.segments[..]
 857                 {
 858                     if ident.span == span {
 859                         err.span_suggestion_verbose(
 860                             *where_span,
 861                             &format!("constrain the associated type to `{}`", ident),
 862                             format!(
 863                                 "{}: {}<{} = {}>",
 864                                 self.r
 865                                     .session
 866                                     .source_map()
 867                                     .span_to_snippet(ty.span) // Account for `<&'a T as Foo>::Bar`.
 868                                     .unwrap_or_else(|_| constrain_ident.to_string()),
 869                                 path.segments[..*position]
 870                                     .iter()
 871                                     .map(|segment| path_segment_to_string(segment))
 872                                     .collect::<Vec<_>>()
 873                                     .join("::"),
 874                                 path.segments[*position..]
 875                                     .iter()
 876                                     .map(|segment| path_segment_to_string(segment))
 877                                     .collect::<Vec<_>>()
 878                                     .join("::"),
 879                                 ident,
 880                             ),
 881                             Applicability::MaybeIncorrect,
 882                         );
 883                     }
 884                     return true;
 885                 }
 886             }
 887         }
 888         false
 889     }
 890
 891     /// Check if the source is call expression and the first argument is `self`. If true,
 892     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 893     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 894         let mut has_self_arg = None;
 895         if let PathSource::Expr(Some(parent)) = source {
 896             match &parent.kind {
 897                 ExprKind::Call(_, args) if !args.is_empty() => {
 898                     let mut expr_kind = &args[0].kind;
 899                     loop {
 900                         match expr_kind {
 901                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 902                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 903                                     let call_span = parent.span;
 904                                     let tail_args_span = if args.len() > 1 {
 905                                         Some(Span::new(
 906                                             args[1].span.lo(),
 907                                             args.last().unwrap().span.hi(),
 908                                             call_span.ctxt(),
 909                                             None,
 910                                         ))
 911                                     } else {
 912                                         None
 913                                     };
 914                                     has_self_arg = Some((call_span, tail_args_span));
 915                                 }
 916                                 break;
 917                             }
 918                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 919                             _ => break,
 920                         }
 921                     }
 922                 }
 923                 _ => (),
 924             }
 925         };
 926         has_self_arg
 927     }
 928
 929     fn followed_by_brace(&self, span: Span) -> (bool, Option<Span>) {
 930         // HACK(estebank): find a better way to figure out that this was a
 931         // parser issue where a struct literal is being used on an expression
 932         // where a brace being opened means a block is being started. Look
 933         // ahead for the next text to see if `span` is followed by a `{`.
 934         let sm = self.r.session.source_map();
 935         let mut sp = span;
 936         loop {
 937             sp = sm.next_point(sp);
 938             match sm.span_to_snippet(sp) {
 939                 Ok(ref snippet) => {
 940                     if snippet.chars().any(|c| !c.is_whitespace()) {
 941                         break;
 942                     }
 943                 }
 944                 _ => break,
 945             }
 946         }
 947         let followed_by_brace = matches!(sm.span_to_snippet(sp), Ok(ref snippet) if snippet == "{");
 948         // In case this could be a struct literal that needs to be surrounded
 949         // by parentheses, find the appropriate span.
 950         let mut i = 0;
 951         let mut closing_brace = None;
 952         loop {
 953             sp = sm.next_point(sp);
 954             match sm.span_to_snippet(sp) {
 955                 Ok(ref snippet) => {
 956                     if snippet == "}" {
 957                         closing_brace = Some(span.to(sp));
 958                         break;
 959                     }
 960                 }
 961                 _ => break,
 962             }
 963             i += 1;
 964             // The bigger the span, the more likely we're incorrect --
 965             // bound it to 100 chars long.
 966             if i > 100 {
 967                 break;
 968             }
 969         }
 970         (followed_by_brace, closing_brace)
 971     }
 972
 973     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 974     /// function.
 975     /// Returns `true` if able to provide context-dependent help.
 976     fn smart_resolve_context_dependent_help(
 977         &mut self,
 978         err: &mut Diagnostic,
 979         span: Span,
 980         source: PathSource<'_>,
 981         res: Res,
 982         path_str: &str,
 983         fallback_label: &str,
 984     ) -> bool {
 985         let ns = source.namespace();
 986         let is_expected = &|res| source.is_expected(res);
 987
 988         let path_sep = |err: &mut Diagnostic, expr: &Expr| match expr.kind {
 989             ExprKind::Field(_, ident) => {
 990                 err.span_suggestion(
 991                     expr.span,
 992                     "use the path separator to refer to an item",
 993                     format!("{}::{}", path_str, ident),
 994                     Applicability::MaybeIncorrect,
 995                 );
 996                 true
 997             }
 998             ExprKind::MethodCall(ref segment, ..) => {
 999                 let span = expr.span.with_hi(segment.ident.span.hi());
1000                 err.span_suggestion(
1001                     span,
1002                     "use the path separator to refer to an item",
1003                     format!("{}::{}", path_str, segment.ident),
1004                     Applicability::MaybeIncorrect,
1005                 );
1006                 true
1007             }
1008             _ => false,
1009         };
1010
1011         let find_span = |source: &PathSource<'_>, err: &mut Diagnostic| {
1012             match source {
1013                 PathSource::Expr(Some(Expr { span, kind: ExprKind::Call(_, _), .. }))
1014                 | PathSource::TupleStruct(span, _) => {
1015                     // We want the main underline to cover the suggested code as well for
1016                     // cleaner output.
1017                     err.set_span(*span);
1018                     *span
1019                 }
1020                 _ => span,
1021             }
1022         };
1023
1024         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
1025             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
1026
1027             match source {
1028                 PathSource::Expr(Some(
1029                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
1030                 )) if path_sep(err, &parent) => {}
1031                 PathSource::Expr(
1032                     None
1033                     | Some(Expr {
1034                         kind:
1035                             ExprKind::Path(..)
1036                             | ExprKind::Binary(..)
1037                             | ExprKind::Unary(..)
1038                             | ExprKind::If(..)
1039                             | ExprKind::While(..)
1040                             | ExprKind::ForLoop(..)
1041                             | ExprKind::Match(..),
1042                         ..
1043                     }),
1044                 ) if followed_by_brace => {
1045                     if let Some(sp) = closing_brace {
1046                         err.span_label(span, fallback_label);
1047                         err.multipart_suggestion(
1048                             "surround the struct literal with parentheses",
1049                             vec![
1050                                 (sp.shrink_to_lo(), "(".to_string()),
1051                                 (sp.shrink_to_hi(), ")".to_string()),
1052                             ],
1053                             Applicability::MaybeIncorrect,
1054                         );
1055                     } else {
1056                         err.span_label(
1057                             span, // Note the parentheses surrounding the suggestion below
1058                             format!(
1059                                 "you might want to surround a struct literal with parentheses: \
1060                                  `({} {{ /* fields */ }})`?",
1061                                 path_str
1062                             ),
1063                         );
1064                     }
1065                 }
1066                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1067                     let span = find_span(&source, err);
1068                     if let Some(span) = self.def_span(def_id) {
1069                         err.span_label(span, &format!("`{}` defined here", path_str));
1070                     }
1071                     let (tail, descr, applicability) = match source {
1072                         PathSource::Pat | PathSource::TupleStruct(..) => {
1073                             ("", "pattern", Applicability::MachineApplicable)
1074                         }
1075                         _ => (": val", "literal", Applicability::HasPlaceholders),
1076                     };
1077                     let (fields, applicability) = match self.r.field_names.get(&def_id) {
1078                         Some(fields) => (
1079                             fields
1080                                 .iter()
1081                                 .map(|f| format!("{}{}", f.node, tail))
1082                                 .collect::<Vec<String>>()
1083                                 .join(", "),
1084                             applicability,
1085                         ),
1086                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
1087                     };
1088                     let pad = match self.r.field_names.get(&def_id) {
1089                         Some(fields) if fields.is_empty() => "",
1090                         _ => " ",
1091                     };
1092                     err.span_suggestion(
1093                         span,
1094                         &format!("use struct {} syntax instead", descr),
1095                         format!("{path_str} {{{pad}{fields}{pad}}}"),
1096                         applicability,
1097                     );
1098                 }
1099                 _ => {
1100                     err.span_label(span, fallback_label);
1101                 }
1102             }
1103         };
1104
1105         match (res, source) {
1106             (
1107                 Res::Def(DefKind::Macro(MacroKind::Bang), _),
1108                 PathSource::Expr(Some(Expr {
1109                     kind: ExprKind::Index(..) | ExprKind::Call(..), ..
1110                 }))
1111                 | PathSource::Struct,
1112             ) => {
1113                 err.span_label(span, fallback_label);
1114                 err.span_suggestion_verbose(
1115                     span.shrink_to_hi(),
1116                     "use `!` to invoke the macro",
1117                     "!",
1118                     Applicability::MaybeIncorrect,
1119                 );
1120                 if path_str == "try" && span.rust_2015() {
1121                     err.note("if you want the `try` keyword, you need Rust 2018 or later");
1122                 }
1123             }
1124             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
1125                 err.span_label(span, fallback_label);
1126             }
1127             (Res::Def(DefKind::TyAlias, def_id), PathSource::Trait(_)) => {
1128                 err.span_label(span, "type aliases cannot be used as traits");
1129                 if self.r.session.is_nightly_build() {
1130                     let msg = "you might have meant to use `#![feature(trait_alias)]` instead of a \
1131                                `type` alias";
1132                     if let Some(span) = self.def_span(def_id) {
1133                         if let Ok(snip) = self.r.session.source_map().span_to_snippet(span) {
1134                             // The span contains a type alias so we should be able to
1135                             // replace `type` with `trait`.
1136                             let snip = snip.replacen("type", "trait", 1);
1137                             err.span_suggestion(span, msg, snip, Applicability::MaybeIncorrect);
1138                         } else {
1139                             err.span_help(span, msg);
1140                         }
1141                     } else {
1142                         err.help(msg);
1143                     }
1144                 }
1145             }
1146             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
1147                 if !path_sep(err, &parent) {
1148                     return false;
1149                 }
1150             }
1151             (
1152                 Res::Def(DefKind::Enum, def_id),
1153                 PathSource::TupleStruct(..) | PathSource::Expr(..),
1154             ) => {
1155                 if self
1156                     .diagnostic_metadata
1157                     .current_type_ascription
1158                     .last()
1159                     .map(|sp| {
1160                         self.r
1161                             .session
1162                             .parse_sess
1163                             .type_ascription_path_suggestions
1164                             .borrow()
1165                             .contains(&sp)
1166                     })
1167                     .unwrap_or(false)
1168                 {
1169                     err.downgrade_to_delayed_bug();
1170                     // We already suggested changing `:` into `::` during parsing.
1171                     return false;
1172                 }
1173
1174                 self.suggest_using_enum_variant(err, source, def_id, span);
1175             }
1176             (Res::Def(DefKind::Struct, def_id), source) if ns == ValueNS => {
1177                 let (ctor_def, ctor_vis, fields) =
1178                     if let Some(struct_ctor) = self.r.struct_constructors.get(&def_id).cloned() {
1179                         if let PathSource::Expr(Some(parent)) = source {
1180                             if let ExprKind::Field(..) | ExprKind::MethodCall(..) = parent.kind {
1181                                 bad_struct_syntax_suggestion(def_id);
1182                                 return true;
1183                             }
1184                         }
1185                         struct_ctor
1186                     } else {
1187                         bad_struct_syntax_suggestion(def_id);
1188                         return true;
1189                     };
1190
1191                 let is_accessible = self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
1192                 if !is_expected(ctor_def) || is_accessible {
1193                     return true;
1194                 }
1195
1196                 let field_spans = match source {
1197                     // e.g. `if let Enum::TupleVariant(field1, field2) = _`
1198                     PathSource::TupleStruct(_, pattern_spans) => {
1199                         err.set_primary_message(
1200                             "cannot match against a tuple struct which contains private fields",
1201                         );
1202
1203                         // Use spans of the tuple struct pattern.
1204                         Some(Vec::from(pattern_spans))
1205                     }
1206                     // e.g. `let _ = Enum::TupleVariant(field1, field2);`
1207                     _ if source.is_call() => {
1208                         err.set_primary_message(
1209                             "cannot initialize a tuple struct which contains private fields",
1210                         );
1211
1212                         // Use spans of the tuple struct definition.
1213                         self.r
1214                             .field_names
1215                             .get(&def_id)
1216                             .map(|fields| fields.iter().map(|f| f.span).collect::<Vec<_>>())
1217                     }
1218                     _ => None,
1219                 };
1220
1221                 if let Some(spans) =
1222                     field_spans.filter(|spans| spans.len() > 0 && fields.len() == spans.len())
1223                 {
1224                     let non_visible_spans: Vec<Span> = iter::zip(&fields, &spans)
1225                         .filter(|(vis, _)| {
1226                             !self.r.is_accessible_from(**vis, self.parent_scope.module)
1227                         })
1228                         .map(|(_, span)| *span)
1229                         .collect();
1230
1231                     if non_visible_spans.len() > 0 {
1232                         let mut m: MultiSpan = non_visible_spans.clone().into();
1233                         non_visible_spans
1234                             .into_iter()
1235                             .for_each(|s| m.push_span_label(s, "private field"));
1236                         err.span_note(m, "constructor is not visible here due to private fields");
1237                     }
1238
1239                     return true;
1240                 }
1241
1242                 err.span_label(span, "constructor is not visible here due to private fields");
1243             }
1244             (
1245                 Res::Def(
1246                     DefKind::Union | DefKind::Variant | DefKind::Ctor(_, CtorKind::Fictive),
1247                     def_id,
1248                 ),
1249                 _,
1250             ) if ns == ValueNS => {
1251                 bad_struct_syntax_suggestion(def_id);
1252             }
1253             (Res::Def(DefKind::Ctor(_, CtorKind::Const), def_id), _) if ns == ValueNS => {
1254                 match source {
1255                     PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
1256                         let span = find_span(&source, err);
1257                         if let Some(span) = self.def_span(def_id) {
1258                             err.span_label(span, &format!("`{}` defined here", path_str));
1259                         }
1260                         err.span_suggestion(
1261                             span,
1262                             "use this syntax instead",
1263                             path_str,
1264                             Applicability::MaybeIncorrect,
1265                         );
1266                     }
1267                     _ => return false,
1268                 }
1269             }
1270             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
1271                 if let Some(span) = self.def_span(def_id) {
1272                     err.span_label(span, &format!("`{}` defined here", path_str));
1273                 }
1274                 let fields = self.r.field_names.get(&def_id).map_or_else(
1275                     || "/* fields */".to_string(),
1276                     |fields| vec!["_"; fields.len()].join(", "),
1277                 );
1278                 err.span_suggestion(
1279                     span,
1280                     "use the tuple variant pattern syntax instead",
1281                     format!("{}({})", path_str, fields),
1282                     Applicability::HasPlaceholders,
1283                 );
1284             }
1285             (Res::SelfTy { .. }, _) if ns == ValueNS => {
1286                 err.span_label(span, fallback_label);
1287                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
1288             }
1289             (Res::Def(DefKind::TyAlias | DefKind::AssocTy, _), _) if ns == ValueNS => {
1290                 err.note("can't use a type alias as a constructor");
1291             }
1292             _ => return false,
1293         }
1294         true
1295     }
1296
1297     /// Given the target `ident` and `kind`, search for the similarly named associated item
1298     /// in `self.current_trait_ref`.
1299     pub(crate) fn find_similarly_named_assoc_item(
1300         &mut self,
1301         ident: Symbol,
1302         kind: &AssocItemKind,
1303     ) -> Option<Symbol> {
1304         let (module, _) = self.current_trait_ref.as_ref()?;
1305         if ident == kw::Underscore {
1306             // We do nothing for `_`.
1307             return None;
1308         }
1309
1310         let resolutions = self.r.resolutions(module);
1311         let targets = resolutions
1312             .borrow()
1313             .iter()
1314             .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
1315             .filter(|(_, res)| match (kind, res) {
1316                 (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
1317                 (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
1318                 (AssocItemKind::TyAlias(..), Res::Def(DefKind::AssocTy, _)) => true,
1319                 _ => false,
1320             })
1321             .map(|(key, _)| key.ident.name)
1322             .collect::<Vec<_>>();
1323
1324         find_best_match_for_name(&targets, ident, None)
1325     }
1326
1327     fn lookup_assoc_candidate<FilterFn>(
1328         &mut self,
1329         ident: Ident,
1330         ns: Namespace,
1331         filter_fn: FilterFn,
1332     ) -> Option<AssocSuggestion>
1333     where
1334         FilterFn: Fn(Res) -> bool,
1335     {
1336         fn extract_node_id(t: &Ty) -> Option<NodeId> {
1337             match t.kind {
1338                 TyKind::Path(None, _) => Some(t.id),
1339                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
1340                 // This doesn't handle the remaining `Ty` variants as they are not
1341                 // that commonly the self_type, it might be interesting to provide
1342                 // support for those in future.
1343                 _ => None,
1344             }
1345         }
1346
1347         // Fields are generally expected in the same contexts as locals.
1348         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
1349             if let Some(node_id) =
1350                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
1351             {
1352                 // Look for a field with the same name in the current self_type.
1353                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
1354                     match resolution.base_res() {
1355                         Res::Def(DefKind::Struct | DefKind::Union, did)
1356                             if resolution.unresolved_segments() == 0 =>
1357                         {
1358                             if let Some(field_names) = self.r.field_names.get(&did) {
1359                                 if field_names
1360                                     .iter()
1361                                     .any(|&field_name| ident.name == field_name.node)
1362                                 {
1363                                     return Some(AssocSuggestion::Field);
1364                                 }
1365                             }
1366                         }
1367                         _ => {}
1368                     }
1369                 }
1370             }
1371         }
1372
1373         if let Some(items) = self.diagnostic_metadata.current_trait_assoc_items {
1374             for assoc_item in items {
1375                 if assoc_item.ident == ident {
1376                     return Some(match &assoc_item.kind {
1377                         ast::AssocItemKind::Const(..) => AssocSuggestion::AssocConst,
1378                         ast::AssocItemKind::Fn(box ast::Fn { sig, .. }) if sig.decl.has_self() => {
1379                             AssocSuggestion::MethodWithSelf
1380                         }
1381                         ast::AssocItemKind::Fn(..) => AssocSuggestion::AssocFn,
1382                         ast::AssocItemKind::TyAlias(..) => AssocSuggestion::AssocType,
1383                         ast::AssocItemKind::MacCall(_) => continue,
1384                     });
1385                 }
1386             }
1387         }
1388
1389         // Look for associated items in the current trait.
1390         if let Some((module, _)) = self.current_trait_ref {
1391             if let Ok(binding) = self.r.maybe_resolve_ident_in_module(
1392                 ModuleOrUniformRoot::Module(module),
1393                 ident,
1394                 ns,
1395                 &self.parent_scope,
1396             ) {
1397                 let res = binding.res();
1398                 if filter_fn(res) {
1399                     if self.r.has_self.contains(&res.def_id()) {
1400                         return Some(AssocSuggestion::MethodWithSelf);
1401                     } else {
1402                         match res {
1403                             Res::Def(DefKind::AssocFn, _) => return Some(AssocSuggestion::AssocFn),
1404                             Res::Def(DefKind::AssocConst, _) => {
1405                                 return Some(AssocSuggestion::AssocConst);
1406                             }
1407                             Res::Def(DefKind::AssocTy, _) => {
1408                                 return Some(AssocSuggestion::AssocType);
1409                             }
1410                             _ => {}
1411                         }
1412                     }
1413                 }
1414             }
1415         }
1416
1417         None
1418     }
1419
1420     fn lookup_typo_candidate(
1421         &mut self,
1422         path: &[Segment],
1423         ns: Namespace,
1424         filter_fn: &impl Fn(Res) -> bool,
1425     ) -> Option<TypoSuggestion> {
1426         let mut names = Vec::new();
1427         if path.len() == 1 {
1428             // Search in lexical scope.
1429             // Walk backwards up the ribs in scope and collect candidates.
1430             for rib in self.ribs[ns].iter().rev() {
1431                 // Locals and type parameters
1432                 for (ident, &res) in &rib.bindings {
1433                     if filter_fn(res) {
1434                         names.push(TypoSuggestion::typo_from_res(ident.name, res));
1435                     }
1436                 }
1437                 // Items in scope
1438                 if let RibKind::ModuleRibKind(module) = rib.kind {
1439                     // Items from this module
1440                     self.r.add_module_candidates(module, &mut names, &filter_fn);
1441
1442                     if let ModuleKind::Block = module.kind {
1443                         // We can see through blocks
1444                     } else {
1445                         // Items from the prelude
1446                         if !module.no_implicit_prelude {
1447                             let extern_prelude = self.r.extern_prelude.clone();
1448                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
1449                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(
1450                                     |crate_id| {
1451                                         let crate_mod =
1452                                             Res::Def(DefKind::Mod, crate_id.as_def_id());
1453
1454                                         if filter_fn(crate_mod) {
1455                                             Some(TypoSuggestion::typo_from_res(
1456                                                 ident.name, crate_mod,
1457                                             ))
1458                                         } else {
1459                                             None
1460                                         }
1461                                     },
1462                                 )
1463                             }));
1464
1465                             if let Some(prelude) = self.r.prelude {
1466                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
1467                             }
1468                         }
1469                         break;
1470                     }
1471                 }
1472             }
1473             // Add primitive types to the mix
1474             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
1475                 names.extend(PrimTy::ALL.iter().map(|prim_ty| {
1476                     TypoSuggestion::typo_from_res(prim_ty.name(), Res::PrimTy(*prim_ty))
1477                 }))
1478             }
1479         } else {
1480             // Search in module.
1481             let mod_path = &path[..path.len() - 1];
1482             if let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
1483                 self.resolve_path(mod_path, Some(TypeNS), None)
1484             {
1485                 self.r.add_module_candidates(module, &mut names, &filter_fn);
1486             }
1487         }
1488
1489         let name = path[path.len() - 1].ident.name;
1490         // Make sure error reporting is deterministic.
1491         names.sort_by(|a, b| a.candidate.as_str().partial_cmp(b.candidate.as_str()).unwrap());
1492
1493         match find_best_match_for_name(
1494             &names.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
1495             name,
1496             None,
1497         ) {
1498             Some(found) if found != name => {
1499                 names.into_iter().find(|suggestion| suggestion.candidate == found)
1500             }
1501             _ => None,
1502         }
1503     }
1504
1505     // Returns the name of the Rust type approximately corresponding to
1506     // a type name in another programming language.
1507     fn likely_rust_type(path: &[Segment]) -> Option<Symbol> {
1508         let name = path[path.len() - 1].ident.as_str();
1509         // Common Java types
1510         Some(match name {
1511             "byte" => sym::u8, // In Java, bytes are signed, but in practice one almost always wants unsigned bytes.
1512             "short" => sym::i16,
1513             "Bool" => sym::bool,
1514             "Boolean" => sym::bool,
1515             "boolean" => sym::bool,
1516             "int" => sym::i32,
1517             "long" => sym::i64,
1518             "float" => sym::f32,
1519             "double" => sym::f64,
1520             _ => return None,
1521         })
1522     }
1523
1524     /// Only used in a specific case of type ascription suggestions
1525     fn get_colon_suggestion_span(&self, start: Span) -> Span {
1526         let sm = self.r.session.source_map();
1527         start.to(sm.next_point(start))
1528     }
1529
1530     fn type_ascription_suggestion(&self, err: &mut Diagnostic, base_span: Span) -> bool {
1531         let sm = self.r.session.source_map();
1532         let base_snippet = sm.span_to_snippet(base_span);
1533         if let Some(&sp) = self.diagnostic_metadata.current_type_ascription.last() {
1534             if let Ok(snippet) = sm.span_to_snippet(sp) {
1535                 let len = snippet.trim_end().len() as u32;
1536                 if snippet.trim() == ":" {
1537                     let colon_sp =
1538                         sp.with_lo(sp.lo() + BytePos(len - 1)).with_hi(sp.lo() + BytePos(len));
1539                     let mut show_label = true;
1540                     if sm.is_multiline(sp) {
1541                         err.span_suggestion_short(
1542                             colon_sp,
1543                             "maybe you meant to write `;` here",
1544                             ";",
1545                             Applicability::MaybeIncorrect,
1546                         );
1547                     } else {
1548                         let after_colon_sp =
1549                             self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
1550                         if snippet.len() == 1 {
1551                             // `foo:bar`
1552                             err.span_suggestion(
1553                                 colon_sp,
1554                                 "maybe you meant to write a path separator here",
1555                                 "::",
1556                                 Applicability::MaybeIncorrect,
1557                             );
1558                             show_label = false;
1559                             if !self
1560                                 .r
1561                                 .session
1562                                 .parse_sess
1563                                 .type_ascription_path_suggestions
1564                                 .borrow_mut()
1565                                 .insert(colon_sp)
1566                             {
1567                                 err.downgrade_to_delayed_bug();
1568                             }
1569                         }
1570                         if let Ok(base_snippet) = base_snippet {
1571                             let mut sp = after_colon_sp;
1572                             for _ in 0..100 {
1573                                 // Try to find an assignment
1574                                 sp = sm.next_point(sp);
1575                                 let snippet = sm.span_to_snippet(sp.to(sm.next_point(sp)));
1576                                 match snippet {
1577                                     Ok(ref x) if x.as_str() == "=" => {
1578                                         err.span_suggestion(
1579                                             base_span,
1580                                             "maybe you meant to write an assignment here",
1581                                             format!("let {}", base_snippet),
1582                                             Applicability::MaybeIncorrect,
1583                                         );
1584                                         show_label = false;
1585                                         break;
1586                                     }
1587                                     Ok(ref x) if x.as_str() == "\n" => break,
1588                                     Err(_) => break,
1589                                     Ok(_) => {}
1590                                 }
1591                             }
1592                         }
1593                     }
1594                     if show_label {
1595                         err.span_label(
1596                             base_span,
1597                             "expecting a type here because of type ascription",
1598                         );
1599                     }
1600                     return show_label;
1601                 }
1602             }
1603         }
1604         false
1605     }
1606
1607     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
1608         let mut result = None;
1609         let mut seen_modules = FxHashSet::default();
1610         let mut worklist = vec![(self.r.graph_root, Vec::new())];
1611
1612         while let Some((in_module, path_segments)) = worklist.pop() {
1613             // abort if the module is already found
1614             if result.is_some() {
1615                 break;
1616             }
1617
1618             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
1619                 // abort if the module is already found or if name_binding is private external
1620                 if result.is_some() || !name_binding.vis.is_visible_locally() {
1621                     return;
1622                 }
1623                 if let Some(module) = name_binding.module() {
1624                     // form the path
1625                     let mut path_segments = path_segments.clone();
1626                     path_segments.push(ast::PathSegment::from_ident(ident));
1627                     let module_def_id = module.def_id();
1628                     if module_def_id == def_id {
1629                         let path =
1630                             Path { span: name_binding.span, segments: path_segments, tokens: None };
1631                         result = Some((
1632                             module,
1633                             ImportSuggestion {
1634                                 did: Some(def_id),
1635                                 descr: "module",
1636                                 path,
1637                                 accessible: true,
1638                                 note: None,
1639                             },
1640                         ));
1641                     } else {
1642                         // add the module to the lookup
1643                         if seen_modules.insert(module_def_id) {
1644                             worklist.push((module, path_segments));
1645                         }
1646                     }
1647                 }
1648             });
1649         }
1650
1651         result
1652     }
1653
1654     fn collect_enum_ctors(&mut self, def_id: DefId) -> Option<Vec<(Path, DefId, CtorKind)>> {
1655         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
1656             let mut variants = Vec::new();
1657             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
1658                 if let Res::Def(DefKind::Ctor(CtorOf::Variant, kind), def_id) = name_binding.res() {
1659                     let mut segms = enum_import_suggestion.path.segments.clone();
1660                     segms.push(ast::PathSegment::from_ident(ident));
1661                     let path = Path { span: name_binding.span, segments: segms, tokens: None };
1662                     variants.push((path, def_id, kind));
1663                 }
1664             });
1665             variants
1666         })
1667     }
1668
1669     /// Adds a suggestion for using an enum's variant when an enum is used instead.
1670     fn suggest_using_enum_variant(
1671         &mut self,
1672         err: &mut Diagnostic,
1673         source: PathSource<'_>,
1674         def_id: DefId,
1675         span: Span,
1676     ) {
1677         let Some(variants) = self.collect_enum_ctors(def_id) else {
1678             err.note("you might have meant to use one of the enum's variants");
1679             return;
1680         };
1681
1682         let suggest_only_tuple_variants =
1683             matches!(source, PathSource::TupleStruct(..)) || source.is_call();
1684         if suggest_only_tuple_variants {
1685             // Suggest only tuple variants regardless of whether they have fields and do not
1686             // suggest path with added parentheses.
1687             let suggestable_variants = variants
1688                 .iter()
1689                 .filter(|(.., kind)| *kind == CtorKind::Fn)
1690                 .map(|(variant, ..)| path_names_to_string(variant))
1691                 .collect::<Vec<_>>();
1692
1693             let non_suggestable_variant_count = variants.len() - suggestable_variants.len();
1694
1695             let source_msg = if source.is_call() {
1696                 "to construct"
1697             } else if matches!(source, PathSource::TupleStruct(..)) {
1698                 "to match against"
1699             } else {
1700                 unreachable!()
1701             };
1702
1703             if !suggestable_variants.is_empty() {
1704                 let msg = if non_suggestable_variant_count == 0 && suggestable_variants.len() == 1 {
1705                     format!("try {} the enum's variant", source_msg)
1706                 } else {
1707                     format!("try {} one of the enum's variants", source_msg)
1708                 };
1709
1710                 err.span_suggestions(
1711                     span,
1712                     &msg,
1713                     suggestable_variants.into_iter(),
1714                     Applicability::MaybeIncorrect,
1715                 );
1716             }
1717
1718             // If the enum has no tuple variants..
1719             if non_suggestable_variant_count == variants.len() {
1720                 err.help(&format!("the enum has no tuple variants {}", source_msg));
1721             }
1722
1723             // If there are also non-tuple variants..
1724             if non_suggestable_variant_count == 1 {
1725                 err.help(&format!(
1726                     "you might have meant {} the enum's non-tuple variant",
1727                     source_msg
1728                 ));
1729             } else if non_suggestable_variant_count >= 1 {
1730                 err.help(&format!(
1731                     "you might have meant {} one of the enum's non-tuple variants",
1732                     source_msg
1733                 ));
1734             }
1735         } else {
1736             let needs_placeholder = |def_id: DefId, kind: CtorKind| {
1737                 let has_no_fields = self.r.field_names.get(&def_id).map_or(false, |f| f.is_empty());
1738                 match kind {
1739                     CtorKind::Const => false,
1740                     CtorKind::Fn | CtorKind::Fictive if has_no_fields => false,
1741                     _ => true,
1742                 }
1743             };
1744
1745             let mut suggestable_variants = variants
1746                 .iter()
1747                 .filter(|(_, def_id, kind)| !needs_placeholder(*def_id, *kind))
1748                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1749                 .map(|(variant, kind)| match kind {
1750                     CtorKind::Const => variant,
1751                     CtorKind::Fn => format!("({}())", variant),
1752                     CtorKind::Fictive => format!("({} {{}})", variant),
1753                 })
1754                 .collect::<Vec<_>>();
1755
1756             if !suggestable_variants.is_empty() {
1757                 let msg = if suggestable_variants.len() == 1 {
1758                     "you might have meant to use the following enum variant"
1759                 } else {
1760                     "you might have meant to use one of the following enum variants"
1761                 };
1762
1763                 err.span_suggestions(
1764                     span,
1765                     msg,
1766                     suggestable_variants.drain(..),
1767                     Applicability::MaybeIncorrect,
1768                 );
1769             }
1770
1771             let suggestable_variants_with_placeholders = variants
1772                 .iter()
1773                 .filter(|(_, def_id, kind)| needs_placeholder(*def_id, *kind))
1774                 .map(|(variant, _, kind)| (path_names_to_string(variant), kind))
1775                 .filter_map(|(variant, kind)| match kind {
1776                     CtorKind::Fn => Some(format!("({}(/* fields */))", variant)),
1777                     CtorKind::Fictive => Some(format!("({} {{ /* fields */ }})", variant)),
1778                     _ => None,
1779                 })
1780                 .collect::<Vec<_>>();
1781
1782             if !suggestable_variants_with_placeholders.is_empty() {
1783                 let msg = match (
1784                     suggestable_variants.is_empty(),
1785                     suggestable_variants_with_placeholders.len(),
1786                 ) {
1787                     (true, 1) => "the following enum variant is available",
1788                     (true, _) => "the following enum variants are available",
1789                     (false, 1) => "alternatively, the following enum variant is available",
1790                     (false, _) => "alternatively, the following enum variants are also available",
1791                 };
1792
1793                 err.span_suggestions(
1794                     span,
1795                     msg,
1796                     suggestable_variants_with_placeholders.into_iter(),
1797                     Applicability::HasPlaceholders,
1798                 );
1799             }
1800         };
1801
1802         if def_id.is_local() {
1803             if let Some(span) = self.def_span(def_id) {
1804                 err.span_note(span, "the enum is defined here");
1805             }
1806         }
1807     }
1808
1809     pub(crate) fn report_missing_type_error(
1810         &self,
1811         path: &[Segment],
1812     ) -> Option<(Span, &'static str, String, Applicability)> {
1813         let (ident, span) = match path {
1814             [segment] if !segment.has_generic_args && segment.ident.name != kw::SelfUpper => {
1815                 (segment.ident.to_string(), segment.ident.span)
1816             }
1817             _ => return None,
1818         };
1819         let mut iter = ident.chars().map(|c| c.is_uppercase());
1820         let single_uppercase_char =
1821             matches!(iter.next(), Some(true)) && matches!(iter.next(), None);
1822         if !self.diagnostic_metadata.currently_processing_generics && !single_uppercase_char {
1823             return None;
1824         }
1825         match (self.diagnostic_metadata.current_item, single_uppercase_char, self.diagnostic_metadata.currently_processing_generics) {
1826             (Some(Item { kind: ItemKind::Fn(..), ident, .. }), _, _) if ident.name == sym::main => {
1827                 // Ignore `fn main()` as we don't want to suggest `fn main<T>()`
1828             }
1829             (
1830                 Some(Item {
1831                     kind:
1832                         kind @ ItemKind::Fn(..)
1833                         | kind @ ItemKind::Enum(..)
1834                         | kind @ ItemKind::Struct(..)
1835                         | kind @ ItemKind::Union(..),
1836                     ..
1837                 }),
1838                 true, _
1839             )
1840             // Without the 2nd `true`, we'd suggest `impl <T>` for `impl T` when a type `T` isn't found
1841             | (Some(Item { kind: kind @ ItemKind::Impl(..), .. }), true, true)
1842             | (Some(Item { kind, .. }), false, _) => {
1843                 // Likely missing type parameter.
1844                 if let Some(generics) = kind.generics() {
1845                     if span.overlaps(generics.span) {
1846                         // Avoid the following:
1847                         // error[E0405]: cannot find trait `A` in this scope
1848                         //  --> $DIR/typo-suggestion-named-underscore.rs:CC:LL
1849                         //   |
1850                         // L | fn foo<T: A>(x: T) {} // Shouldn't suggest underscore
1851                         //   |           ^- help: you might be missing a type parameter: `, A`
1852                         //   |           |
1853                         //   |           not found in this scope
1854                         return None;
1855                     }
1856                     let msg = "you might be missing a type parameter";
1857                     let (span, sugg) = if let [.., param] = &generics.params[..] {
1858                         let span = if let [.., bound] = &param.bounds[..] {
1859                             bound.span()
1860                         } else if let GenericParam {
1861                             kind: GenericParamKind::Const { ty, kw_span: _, default  }, ..
1862                         } = param {
1863                             default.as_ref().map(|def| def.value.span).unwrap_or(ty.span)
1864                         } else {
1865                             param.ident.span
1866                         };
1867                         (span, format!(", {}", ident))
1868                     } else {
1869                         (generics.span, format!("<{}>", ident))
1870                     };
1871                     // Do not suggest if this is coming from macro expansion.
1872                     if span.can_be_used_for_suggestions() {
1873                         return Some((
1874                             span.shrink_to_hi(),
1875                             msg,
1876                             sugg,
1877                             Applicability::MaybeIncorrect,
1878                         ));
1879                     }
1880                 }
1881             }
1882             _ => {}
1883         }
1884         None
1885     }
1886
1887     /// Given the target `label`, search the `rib_index`th label rib for similarly named labels,
1888     /// optionally returning the closest match and whether it is reachable.
1889     pub(crate) fn suggestion_for_label_in_rib(
1890         &self,
1891         rib_index: usize,
1892         label: Ident,
1893     ) -> Option<LabelSuggestion> {
1894         // Are ribs from this `rib_index` within scope?
1895         let within_scope = self.is_label_valid_from_rib(rib_index);
1896
1897         let rib = &self.label_ribs[rib_index];
1898         let names = rib
1899             .bindings
1900             .iter()
1901             .filter(|(id, _)| id.span.eq_ctxt(label.span))
1902             .map(|(id, _)| id.name)
1903             .collect::<Vec<Symbol>>();
1904
1905         find_best_match_for_name(&names, label.name, None).map(|symbol| {
1906             // Upon finding a similar name, get the ident that it was from - the span
1907             // contained within helps make a useful diagnostic. In addition, determine
1908             // whether this candidate is within scope.
1909             let (ident, _) = rib.bindings.iter().find(|(ident, _)| ident.name == symbol).unwrap();
1910             (*ident, within_scope)
1911         })
1912     }
1913
1914     pub(crate) fn maybe_report_lifetime_uses(
1915         &mut self,
1916         generics_span: Span,
1917         params: &[ast::GenericParam],
1918     ) {
1919         for (param_index, param) in params.iter().enumerate() {
1920             let GenericParamKind::Lifetime = param.kind else { continue };
1921
1922             let def_id = self.r.local_def_id(param.id);
1923
1924             let use_set = self.lifetime_uses.remove(&def_id);
1925             debug!(
1926                 "Use set for {:?}({:?} at {:?}) is {:?}",
1927                 def_id, param.ident, param.ident.span, use_set
1928             );
1929
1930             let deletion_span = || {
1931                 if params.len() == 1 {
1932                     // if sole lifetime, remove the entire `<>` brackets
1933                     generics_span
1934                 } else if param_index == 0 {
1935                     // if removing within `<>` brackets, we also want to
1936                     // delete a leading or trailing comma as appropriate
1937                     param.span().to(params[param_index + 1].span().shrink_to_lo())
1938                 } else {
1939                     // if removing within `<>` brackets, we also want to
1940                     // delete a leading or trailing comma as appropriate
1941                     params[param_index - 1].span().shrink_to_hi().to(param.span())
1942                 }
1943             };
1944             match use_set {
1945                 Some(LifetimeUseSet::Many) => {}
1946                 Some(LifetimeUseSet::One { use_span, use_ctxt }) => {
1947                     debug!(?param.ident, ?param.ident.span, ?use_span);
1948
1949                     let elidable = matches!(use_ctxt, LifetimeCtxt::Rptr);
1950
1951                     let deletion_span = deletion_span();
1952                     self.r.lint_buffer.buffer_lint_with_diagnostic(
1953                         lint::builtin::SINGLE_USE_LIFETIMES,
1954                         param.id,
1955                         param.ident.span,
1956                         &format!("lifetime parameter `{}` only used once", param.ident),
1957                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
1958                             param_span: param.ident.span,
1959                             use_span: Some((use_span, elidable)),
1960                             deletion_span,
1961                         },
1962                     );
1963                 }
1964                 None => {
1965                     debug!(?param.ident, ?param.ident.span);
1966
1967                     let deletion_span = deletion_span();
1968                     self.r.lint_buffer.buffer_lint_with_diagnostic(
1969                         lint::builtin::UNUSED_LIFETIMES,
1970                         param.id,
1971                         param.ident.span,
1972                         &format!("lifetime parameter `{}` never used", param.ident),
1973                         lint::BuiltinLintDiagnostics::SingleUseLifetime {
1974                             param_span: param.ident.span,
1975                             use_span: None,
1976                             deletion_span,
1977                         },
1978                     );
1979                 }
1980             }
1981         }
1982     }
1983
1984     pub(crate) fn emit_undeclared_lifetime_error(
1985         &self,
1986         lifetime_ref: &ast::Lifetime,
1987         outer_lifetime_ref: Option<Ident>,
1988     ) {
1989         debug_assert_ne!(lifetime_ref.ident.name, kw::UnderscoreLifetime);
1990         let mut err = if let Some(outer) = outer_lifetime_ref {
1991             let mut err = struct_span_err!(
1992                 self.r.session,
1993                 lifetime_ref.ident.span,
1994                 E0401,
1995                 "can't use generic parameters from outer item",
1996             );
1997             err.span_label(lifetime_ref.ident.span, "use of generic parameter from outer item");
1998             err.span_label(outer.span, "lifetime parameter from outer item");
1999             err
2000         } else {
2001             let mut err = struct_span_err!(
2002                 self.r.session,
2003                 lifetime_ref.ident.span,
2004                 E0261,
2005                 "use of undeclared lifetime name `{}`",
2006                 lifetime_ref.ident
2007             );
2008             err.span_label(lifetime_ref.ident.span, "undeclared lifetime");
2009             err
2010         };
2011         self.suggest_introducing_lifetime(
2012             &mut err,
2013             Some(lifetime_ref.ident.name.as_str()),
2014             |err, _, span, message, suggestion| {
2015                 err.span_suggestion(span, message, suggestion, Applicability::MaybeIncorrect);
2016                 true
2017             },
2018         );
2019         err.emit();
2020     }
2021
2022     fn suggest_introducing_lifetime(
2023         &self,
2024         err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
2025         name: Option<&str>,
2026         suggest: impl Fn(&mut DiagnosticBuilder<'_, ErrorGuaranteed>, bool, Span, &str, String) -> bool,
2027     ) {
2028         let mut suggest_note = true;
2029         for rib in self.lifetime_ribs.iter().rev() {
2030             let mut should_continue = true;
2031             match rib.kind {
2032                 LifetimeRibKind::Generics { binder: _, span, kind } => {
2033                     if !span.can_be_used_for_suggestions() && suggest_note && let Some(name) = name {
2034                         suggest_note = false; // Avoid displaying the same help multiple times.
2035                         err.span_label(
2036                             span,
2037                             &format!(
2038                                 "lifetime `{}` is missing in item created through this procedural macro",
2039                                 name,
2040                             ),
2041                         );
2042                         continue;
2043                     }
2044
2045                     let higher_ranked = matches!(
2046                         kind,
2047                         LifetimeBinderKind::BareFnType
2048                             | LifetimeBinderKind::PolyTrait
2049                             | LifetimeBinderKind::WhereBound
2050                     );
2051                     let (span, sugg) = if span.is_empty() {
2052                         let sugg = format!(
2053                             "{}<{}>{}",
2054                             if higher_ranked { "for" } else { "" },
2055                             name.unwrap_or("'a"),
2056                             if higher_ranked { " " } else { "" },
2057                         );
2058                         (span, sugg)
2059                     } else {
2060                         let span =
2061                             self.r.session.source_map().span_through_char(span, '<').shrink_to_hi();
2062                         let sugg = format!("{}, ", name.unwrap_or("'a"));
2063                         (span, sugg)
2064                     };
2065                     if higher_ranked {
2066                         let message = format!(
2067                             "consider making the {} lifetime-generic with a new `{}` lifetime",
2068                             kind.descr(),
2069                             name.unwrap_or("'a"),
2070                         );
2071                         should_continue = suggest(err, true, span, &message, sugg);
2072                         err.note_once(
2073                             "for more information on higher-ranked polymorphism, visit \
2074                              https://doc.rust-lang.org/nomicon/hrtb.html",
2075                         );
2076                     } else if let Some(name) = name {
2077                         let message = format!("consider introducing lifetime `{}` here", name);
2078                         should_continue = suggest(err, false, span, &message, sugg);
2079                     } else {
2080                         let message = format!("consider introducing a named lifetime parameter");
2081                         should_continue = suggest(err, false, span, &message, sugg);
2082                     }
2083                 }
2084                 LifetimeRibKind::Item => break,
2085                 _ => {}
2086             }
2087             if !should_continue {
2088                 break;
2089             }
2090         }
2091     }
2092
2093     pub(crate) fn emit_non_static_lt_in_const_generic_error(&self, lifetime_ref: &ast::Lifetime) {
2094         struct_span_err!(
2095             self.r.session,
2096             lifetime_ref.ident.span,
2097             E0771,
2098             "use of non-static lifetime `{}` in const generic",
2099             lifetime_ref.ident
2100         )
2101         .note(
2102             "for more information, see issue #74052 \
2103             <https://github.com/rust-lang/rust/issues/74052>",
2104         )
2105         .emit();
2106     }
2107
2108     /// Non-static lifetimes are prohibited in anonymous constants under `min_const_generics`.
2109     /// This function will emit an error if `generic_const_exprs` is not enabled, the body identified by
2110     /// `body_id` is an anonymous constant and `lifetime_ref` is non-static.
2111     pub(crate) fn maybe_emit_forbidden_non_static_lifetime_error(
2112         &self,
2113         lifetime_ref: &ast::Lifetime,
2114     ) {
2115         let feature_active = self.r.session.features_untracked().generic_const_exprs;
2116         if !feature_active {
2117             feature_err(
2118                 &self.r.session.parse_sess,
2119                 sym::generic_const_exprs,
2120                 lifetime_ref.ident.span,
2121                 "a non-static lifetime is not allowed in a `const`",
2122             )
2123             .emit();
2124         }
2125     }
2126
2127     pub(crate) fn report_missing_lifetime_specifiers(
2128         &mut self,
2129         lifetime_refs: Vec<MissingLifetime>,
2130         function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
2131     ) -> ErrorGuaranteed {
2132         let num_lifetimes: usize = lifetime_refs.iter().map(|lt| lt.count).sum();
2133         let spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();
2134
2135         let mut err = struct_span_err!(
2136             self.r.session,
2137             spans,
2138             E0106,
2139             "missing lifetime specifier{}",
2140             pluralize!(num_lifetimes)
2141         );
2142         self.add_missing_lifetime_specifiers_label(
2143             &mut err,
2144             lifetime_refs,
2145             function_param_lifetimes,
2146         );
2147         err.emit()
2148     }
2149
2150     pub(crate) fn add_missing_lifetime_specifiers_label(
2151         &mut self,
2152         err: &mut DiagnosticBuilder<'_, ErrorGuaranteed>,
2153         lifetime_refs: Vec<MissingLifetime>,
2154         function_param_lifetimes: Option<(Vec<MissingLifetime>, Vec<ElisionFnParameter>)>,
2155     ) {
2156         for &lt in &lifetime_refs {
2157             err.span_label(
2158                 lt.span,
2159                 format!(
2160                     "expected {} lifetime parameter{}",
2161                     if lt.count == 1 { "named".to_string() } else { lt.count.to_string() },
2162                     pluralize!(lt.count),
2163                 ),
2164             );
2165         }
2166
2167         let mut in_scope_lifetimes: Vec<_> = self
2168             .lifetime_ribs
2169             .iter()
2170             .rev()
2171             .take_while(|rib| !matches!(rib.kind, LifetimeRibKind::Item))
2172             .flat_map(|rib| rib.bindings.iter())
2173             .map(|(&ident, &res)| (ident, res))
2174             .filter(|(ident, _)| ident.name != kw::UnderscoreLifetime)
2175             .collect();
2176         debug!(?in_scope_lifetimes);
2177
2178         debug!(?function_param_lifetimes);
2179         if let Some((param_lifetimes, params)) = &function_param_lifetimes {
2180             let elided_len = param_lifetimes.len();
2181             let num_params = params.len();
2182
2183             let mut m = String::new();
2184
2185             for (i, info) in params.iter().enumerate() {
2186                 let ElisionFnParameter { ident, index, lifetime_count, span } = *info;
2187                 debug_assert_ne!(lifetime_count, 0);
2188
2189                 err.span_label(span, "");
2190
2191                 if i != 0 {
2192                     if i + 1 < num_params {
2193                         m.push_str(", ");
2194                     } else if num_params == 2 {
2195                         m.push_str(" or ");
2196                     } else {
2197                         m.push_str(", or ");
2198                     }
2199                 }
2200
2201                 let help_name = if let Some(ident) = ident {
2202                     format!("`{}`", ident)
2203                 } else {
2204                     format!("argument {}", index + 1)
2205                 };
2206
2207                 if lifetime_count == 1 {
2208                     m.push_str(&help_name[..])
2209                 } else {
2210                     m.push_str(&format!("one of {}'s {} lifetimes", help_name, lifetime_count)[..])
2211                 }
2212             }
2213
2214             if num_params == 0 {
2215                 err.help(
2216                     "this function's return type contains a borrowed value, \
2217                  but there is no value for it to be borrowed from",
2218                 );
2219                 if in_scope_lifetimes.is_empty() {
2220                     in_scope_lifetimes = vec![(
2221                         Ident::with_dummy_span(kw::StaticLifetime),
2222                         (DUMMY_NODE_ID, LifetimeRes::Static),
2223                     )];
2224                 }
2225             } else if elided_len == 0 {
2226                 err.help(
2227                     "this function's return type contains a borrowed value with \
2228                  an elided lifetime, but the lifetime cannot be derived from \
2229                  the arguments",
2230                 );
2231                 if in_scope_lifetimes.is_empty() {
2232                     in_scope_lifetimes = vec![(
2233                         Ident::with_dummy_span(kw::StaticLifetime),
2234                         (DUMMY_NODE_ID, LifetimeRes::Static),
2235                     )];
2236                 }
2237             } else if num_params == 1 {
2238                 err.help(&format!(
2239                     "this function's return type contains a borrowed value, \
2240                  but the signature does not say which {} it is borrowed from",
2241                     m
2242                 ));
2243             } else {
2244                 err.help(&format!(
2245                     "this function's return type contains a borrowed value, \
2246                  but the signature does not say whether it is borrowed from {}",
2247                     m
2248                 ));
2249             }
2250         }
2251
2252         let existing_name = match &in_scope_lifetimes[..] {
2253             [] => Symbol::intern("'a"),
2254             [(existing, _)] => existing.name,
2255             _ => Symbol::intern("'lifetime"),
2256         };
2257
2258         let mut spans_suggs: Vec<_> = Vec::new();
2259         let build_sugg = |lt: MissingLifetime| match lt.kind {
2260             MissingLifetimeKind::Underscore => {
2261                 debug_assert_eq!(lt.count, 1);
2262                 (lt.span, existing_name.to_string())
2263             }
2264             MissingLifetimeKind::Ampersand => {
2265                 debug_assert_eq!(lt.count, 1);
2266                 (lt.span.shrink_to_hi(), format!("{} ", existing_name))
2267             }
2268             MissingLifetimeKind::Comma => {
2269                 let sugg: String = std::iter::repeat([existing_name.as_str(), ", "])
2270                     .take(lt.count)
2271                     .flatten()
2272                     .collect();
2273                 (lt.span.shrink_to_hi(), sugg)
2274             }
2275             MissingLifetimeKind::Brackets => {
2276                 let sugg: String = std::iter::once("<")
2277                     .chain(
2278                         std::iter::repeat(existing_name.as_str()).take(lt.count).intersperse(", "),
2279                     )
2280                     .chain([">"])
2281                     .collect();
2282                 (lt.span.shrink_to_hi(), sugg)
2283             }
2284         };
2285         for &lt in &lifetime_refs {
2286             spans_suggs.push(build_sugg(lt));
2287         }
2288         debug!(?spans_suggs);
2289         match in_scope_lifetimes.len() {
2290             0 => {
2291                 if let Some((param_lifetimes, _)) = function_param_lifetimes {
2292                     for lt in param_lifetimes {
2293                         spans_suggs.push(build_sugg(lt))
2294                     }
2295                 }
2296                 self.suggest_introducing_lifetime(
2297                     err,
2298                     None,
2299                     |err, higher_ranked, span, message, intro_sugg| {
2300                         err.multipart_suggestion_verbose(
2301                             message,
2302                             std::iter::once((span, intro_sugg))
2303                                 .chain(spans_suggs.clone())
2304                                 .collect(),
2305                             Applicability::MaybeIncorrect,
2306                         );
2307                         higher_ranked
2308                     },
2309                 );
2310             }
2311             1 => {
2312                 err.multipart_suggestion_verbose(
2313                     &format!("consider using the `{}` lifetime", existing_name),
2314                     spans_suggs,
2315                     Applicability::MaybeIncorrect,
2316                 );
2317
2318                 // Record as using the suggested resolution.
2319                 let (_, (_, res)) = in_scope_lifetimes[0];
2320                 for &lt in &lifetime_refs {
2321                     self.r.lifetimes_res_map.insert(lt.id, res);
2322                 }
2323             }
2324             _ => {
2325                 let lifetime_spans: Vec<_> =
2326                     in_scope_lifetimes.iter().map(|(ident, _)| ident.span).collect();
2327                 err.span_note(lifetime_spans, "these named lifetimes are available to use");
2328
2329                 if spans_suggs.len() > 0 {
2330                     // This happens when we have `Foo<T>` where we point at the space before `T`,
2331                     // but this can be confusing so we give a suggestion with placeholders.
2332                     err.multipart_suggestion_verbose(
2333                         "consider using one of the available lifetimes here",
2334                         spans_suggs,
2335                         Applicability::HasPlaceholders,
2336                     );
2337                 }
2338             }
2339         }
2340     }
2341 }
2342
2343 /// Report lifetime/lifetime shadowing as an error.
2344 pub fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: Ident) {
2345     let mut err = struct_span_err!(
2346         sess,
2347         shadower.span,
2348         E0496,
2349         "lifetime name `{}` shadows a lifetime name that is already in scope",
2350         orig.name,
2351     );
2352     err.span_label(orig.span, "first declared here");
2353     err.span_label(shadower.span, format!("lifetime `{}` already in scope", orig.name));
2354     err.emit();
2355 }
2356
2357 /// Shadowing involving a label is only a warning for historical reasons.
2358 //FIXME: make this a proper lint.
2359 pub fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {
2360     let name = shadower.name;
2361     let shadower = shadower.span;
2362     let mut err = sess.struct_span_warn(
2363         shadower,
2364         &format!("label name `{}` shadows a label name that is already in scope", name),
2365     );
2366     err.span_label(orig, "first declared here");
2367     err.span_label(shadower, format!("label `{}` already in scope", name));
2368     err.emit();
2369 }