compiler/rustc_resolve/src/diagnostics.rs

   1 use std::cmp::Reverse;
   2 use std::ptr;
   3
   4 use rustc_ast::{self as ast, Path};
   5 use rustc_ast_pretty::pprust;
   6 use rustc_data_structures::fx::FxHashSet;
   7 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
   8 use rustc_feature::BUILTIN_ATTRIBUTES;
   9 use rustc_hir::def::Namespace::{self, *};
  10 use rustc_hir::def::{self, CtorKind, CtorOf, DefKind, NonMacroAttrKind};
  11 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
  12 use rustc_middle::bug;
  13 use rustc_middle::ty::{self, DefIdTree};
  14 use rustc_session::Session;
  15 use rustc_span::hygiene::MacroKind;
  16 use rustc_span::lev_distance::find_best_match_for_name;
  17 use rustc_span::source_map::SourceMap;
  18 use rustc_span::symbol::{kw, sym, Ident, Symbol};
  19 use rustc_span::{BytePos, MultiSpan, Span};
  20 use tracing::debug;
  21
  22 use crate::imports::{Import, ImportKind, ImportResolver};
  23 use crate::path_names_to_string;
  24 use crate::{AmbiguityError, AmbiguityErrorMisc, AmbiguityKind};
  25 use crate::{
  26     BindingError, CrateLint, HasGenericParams, MacroRulesScope, Module, ModuleOrUniformRoot,
  27 };
  28 use crate::{NameBinding, NameBindingKind, PrivacyError, VisResolutionError};
  29 use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet, Segment};
  30
  31 type Res = def::Res<ast::NodeId>;
  32
  33 /// A vector of spans and replacements, a message and applicability.
  34 crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
  35
  36 /// Potential candidate for an undeclared or out-of-scope label - contains the ident of a
  37 /// similarly named label and whether or not it is reachable.
  38 crate type LabelSuggestion = (Ident, bool);
  39
  40 crate struct TypoSuggestion {
  41     pub candidate: Symbol,
  42     pub res: Res,
  43 }
  44
  45 impl TypoSuggestion {
  46     crate fn from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  47         TypoSuggestion { candidate, res }
  48     }
  49 }
  50
  51 /// A free importable items suggested in case of resolution failure.
  52 crate struct ImportSuggestion {
  53     pub did: Option<DefId>,
  54     pub descr: &'static str,
  55     pub path: Path,
  56     pub accessible: bool,
  57 }
  58
  59 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  60 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  61 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  62 ///
  63 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  64 /// parser. If you need to use this function or something similar, please consider updating the
  65 /// `source_map` functions and this function to something more robust.
  66 fn reduce_impl_span_to_impl_keyword(sm: &SourceMap, impl_span: Span) -> Span {
  67     let impl_span = sm.span_until_char(impl_span, '<');
  68     sm.span_until_whitespace(impl_span)
  69 }
  70
  71 impl<'a> Resolver<'a> {
  72     crate fn add_module_candidates(
  73         &mut self,
  74         module: Module<'a>,
  75         names: &mut Vec<TypoSuggestion>,
  76         filter_fn: &impl Fn(Res) -> bool,
  77     ) {
  78         for (key, resolution) in self.resolutions(module).borrow().iter() {
  79             if let Some(binding) = resolution.borrow().binding {
  80                 let res = binding.res();
  81                 if filter_fn(res) {
  82                     names.push(TypoSuggestion::from_res(key.ident.name, res));
  83                 }
  84             }
  85         }
  86     }
  87
  88     /// Combines an error with provided span and emits it.
  89     ///
  90     /// This takes the error provided, combines it with the span and any additional spans inside the
  91     /// error and emits it.
  92     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  93         self.into_struct_error(span, resolution_error).emit();
  94     }
  95
  96     crate fn into_struct_error(
  97         &self,
  98         span: Span,
  99         resolution_error: ResolutionError<'_>,
 100     ) -> DiagnosticBuilder<'_> {
 101         match resolution_error {
 102             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
 103                 let mut err = struct_span_err!(
 104                     self.session,
 105                     span,
 106                     E0401,
 107                     "can't use generic parameters from outer function",
 108                 );
 109                 err.span_label(span, "use of generic parameter from outer function".to_string());
 110
 111                 let sm = self.session.source_map();
 112                 match outer_res {
 113                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 114                         if let Some(impl_span) =
 115                             maybe_impl_defid.and_then(|(def_id, _)| self.opt_span(def_id))
 116                         {
 117                             err.span_label(
 118                                 reduce_impl_span_to_impl_keyword(sm, impl_span),
 119                                 "`Self` type implicitly declared here, by this `impl`",
 120                             );
 121                         }
 122                         match (maybe_trait_defid, maybe_impl_defid) {
 123                             (Some(_), None) => {
 124                                 err.span_label(span, "can't use `Self` here");
 125                             }
 126                             (_, Some(_)) => {
 127                                 err.span_label(span, "use a type here instead");
 128                             }
 129                             (None, None) => bug!("`impl` without trait nor type?"),
 130                         }
 131                         return err;
 132                     }
 133                     Res::Def(DefKind::TyParam, def_id) => {
 134                         if let Some(span) = self.opt_span(def_id) {
 135                             err.span_label(span, "type parameter from outer function");
 136                         }
 137                     }
 138                     Res::Def(DefKind::ConstParam, def_id) => {
 139                         if let Some(span) = self.opt_span(def_id) {
 140                             err.span_label(span, "const parameter from outer function");
 141                         }
 142                     }
 143                     _ => {
 144                         bug!(
 145                             "GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 146                             DefKind::TyParam or DefKind::ConstParam"
 147                         );
 148                     }
 149                 }
 150
 151                 if has_generic_params == HasGenericParams::Yes {
 152                     // Try to retrieve the span of the function signature and generate a new
 153                     // message with a local type or const parameter.
 154                     let sugg_msg = "try using a local generic parameter instead";
 155                     if let Some((sugg_span, snippet)) = sm.generate_local_type_param_snippet(span) {
 156                         // Suggest the modification to the user
 157                         err.span_suggestion(
 158                             sugg_span,
 159                             sugg_msg,
 160                             snippet,
 161                             Applicability::MachineApplicable,
 162                         );
 163                     } else if let Some(sp) = sm.generate_fn_name_span(span) {
 164                         err.span_label(
 165                             sp,
 166                             "try adding a local generic parameter in this method instead"
 167                                 .to_string(),
 168                         );
 169                     } else {
 170                         err.help("try using a local generic parameter instead");
 171                     }
 172                 }
 173
 174                 err
 175             }
 176             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 177                 let mut err = struct_span_err!(
 178                     self.session,
 179                     span,
 180                     E0403,
 181                     "the name `{}` is already used for a generic \
 182                      parameter in this item's generic parameters",
 183                     name,
 184                 );
 185                 err.span_label(span, "already used");
 186                 err.span_label(first_use_span, format!("first use of `{}`", name));
 187                 err
 188             }
 189             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 190                 let mut err = struct_span_err!(
 191                     self.session,
 192                     span,
 193                     E0407,
 194                     "method `{}` is not a member of trait `{}`",
 195                     method,
 196                     trait_
 197                 );
 198                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 199                 err
 200             }
 201             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 202                 let mut err = struct_span_err!(
 203                     self.session,
 204                     span,
 205                     E0437,
 206                     "type `{}` is not a member of trait `{}`",
 207                     type_,
 208                     trait_
 209                 );
 210                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 211                 err
 212             }
 213             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 214                 let mut err = struct_span_err!(
 215                     self.session,
 216                     span,
 217                     E0438,
 218                     "const `{}` is not a member of trait `{}`",
 219                     const_,
 220                     trait_
 221                 );
 222                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 223                 err
 224             }
 225             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 226                 let BindingError { name, target, origin, could_be_path } = binding_error;
 227
 228                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 229                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 230
 231                 let msp = MultiSpan::from_spans(target_sp.clone());
 232                 let mut err = struct_span_err!(
 233                     self.session,
 234                     msp,
 235                     E0408,
 236                     "variable `{}` is not bound in all patterns",
 237                     name,
 238                 );
 239                 for sp in target_sp {
 240                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 241                 }
 242                 for sp in origin_sp {
 243                     err.span_label(sp, "variable not in all patterns");
 244                 }
 245                 if *could_be_path {
 246                     let help_msg = format!(
 247                         "if you meant to match on a variant or a `const` item, consider \
 248                          making the path in the pattern qualified: `?::{}`",
 249                         name,
 250                     );
 251                     err.span_help(span, &help_msg);
 252                 }
 253                 err
 254             }
 255             ResolutionError::VariableBoundWithDifferentMode(variable_name, first_binding_span) => {
 256                 let mut err = struct_span_err!(
 257                     self.session,
 258                     span,
 259                     E0409,
 260                     "variable `{}` is bound inconsistently across alternatives separated by `|`",
 261                     variable_name
 262                 );
 263                 err.span_label(span, "bound in different ways");
 264                 err.span_label(first_binding_span, "first binding");
 265                 err
 266             }
 267             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 268                 let mut err = struct_span_err!(
 269                     self.session,
 270                     span,
 271                     E0415,
 272                     "identifier `{}` is bound more than once in this parameter list",
 273                     identifier
 274                 );
 275                 err.span_label(span, "used as parameter more than once");
 276                 err
 277             }
 278             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 279                 let mut err = struct_span_err!(
 280                     self.session,
 281                     span,
 282                     E0416,
 283                     "identifier `{}` is bound more than once in the same pattern",
 284                     identifier
 285                 );
 286                 err.span_label(span, "used in a pattern more than once");
 287                 err
 288             }
 289             ResolutionError::UndeclaredLabel { name, suggestion } => {
 290                 let mut err = struct_span_err!(
 291                     self.session,
 292                     span,
 293                     E0426,
 294                     "use of undeclared label `{}`",
 295                     name
 296                 );
 297
 298                 err.span_label(span, format!("undeclared label `{}`", name));
 299
 300                 match suggestion {
 301                     // A reachable label with a similar name exists.
 302                     Some((ident, true)) => {
 303                         err.span_label(ident.span, "a label with a similar name is reachable");
 304                         err.span_suggestion(
 305                             span,
 306                             "try using similarly named label",
 307                             ident.name.to_string(),
 308                             Applicability::MaybeIncorrect,
 309                         );
 310                     }
 311                     // An unreachable label with a similar name exists.
 312                     Some((ident, false)) => {
 313                         err.span_label(
 314                             ident.span,
 315                             "a label with a similar name exists but is unreachable",
 316                         );
 317                     }
 318                     // No similarly-named labels exist.
 319                     None => (),
 320                 }
 321
 322                 err
 323             }
 324             ResolutionError::SelfImportsOnlyAllowedWithin { root, span_with_rename } => {
 325                 let mut err = struct_span_err!(
 326                     self.session,
 327                     span,
 328                     E0429,
 329                     "{}",
 330                     "`self` imports are only allowed within a { } list"
 331                 );
 332
 333                 // None of the suggestions below would help with a case like `use self`.
 334                 if !root {
 335                     // use foo::bar::self        -> foo::bar
 336                     // use foo::bar::self as abc -> foo::bar as abc
 337                     err.span_suggestion(
 338                         span,
 339                         "consider importing the module directly",
 340                         "".to_string(),
 341                         Applicability::MachineApplicable,
 342                     );
 343
 344                     // use foo::bar::self        -> foo::bar::{self}
 345                     // use foo::bar::self as abc -> foo::bar::{self as abc}
 346                     let braces = vec![
 347                         (span_with_rename.shrink_to_lo(), "{".to_string()),
 348                         (span_with_rename.shrink_to_hi(), "}".to_string()),
 349                     ];
 350                     err.multipart_suggestion(
 351                         "alternatively, use the multi-path `use` syntax to import `self`",
 352                         braces,
 353                         Applicability::MachineApplicable,
 354                     );
 355                 }
 356                 err
 357             }
 358             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 359                 let mut err = struct_span_err!(
 360                     self.session,
 361                     span,
 362                     E0430,
 363                     "`self` import can only appear once in an import list"
 364                 );
 365                 err.span_label(span, "can only appear once in an import list");
 366                 err
 367             }
 368             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 369                 let mut err = struct_span_err!(
 370                     self.session,
 371                     span,
 372                     E0431,
 373                     "`self` import can only appear in an import list with \
 374                                                 a non-empty prefix"
 375                 );
 376                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 377                 err
 378             }
 379             ResolutionError::FailedToResolve { label, suggestion } => {
 380                 let mut err =
 381                     struct_span_err!(self.session, span, E0433, "failed to resolve: {}", &label);
 382                 err.span_label(span, label);
 383
 384                 if let Some((suggestions, msg, applicability)) = suggestion {
 385                     err.multipart_suggestion(&msg, suggestions, applicability);
 386                 }
 387
 388                 err
 389             }
 390             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 391                 let mut err = struct_span_err!(
 392                     self.session,
 393                     span,
 394                     E0434,
 395                     "{}",
 396                     "can't capture dynamic environment in a fn item"
 397                 );
 398                 err.help("use the `|| { ... }` closure form instead");
 399                 err
 400             }
 401             ResolutionError::AttemptToUseNonConstantValueInConstant(ident, sugg, current) => {
 402                 let mut err = struct_span_err!(
 403                     self.session,
 404                     span,
 405                     E0435,
 406                     "attempt to use a non-constant value in a constant"
 407                 );
 408                 // let foo =...
 409                 //     ^^^ given this Span
 410                 // ------- get this Span to have an applicable suggestion
 411                 let sp =
 412                     self.session.source_map().span_extend_to_prev_str(ident.span, current, true);
 413                 if sp.lo().0 == 0 {
 414                     err.span_label(ident.span, &format!("this would need to be a `{}`", sugg));
 415                 } else {
 416                     let sp = sp.with_lo(BytePos(sp.lo().0 - current.len() as u32));
 417                     err.span_suggestion(
 418                         sp,
 419                         &format!("consider using `{}` instead of `{}`", sugg, current),
 420                         format!("{} {}", sugg, ident),
 421                         Applicability::MaybeIncorrect,
 422                     );
 423                     err.span_label(span, "non-constant value");
 424                 }
 425                 err
 426             }
 427             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 428                 let res = binding.res();
 429                 let shadows_what = res.descr();
 430                 let mut err = struct_span_err!(
 431                     self.session,
 432                     span,
 433                     E0530,
 434                     "{}s cannot shadow {}s",
 435                     what_binding,
 436                     shadows_what
 437                 );
 438                 err.span_label(
 439                     span,
 440                     format!("cannot be named the same as {} {}", res.article(), shadows_what),
 441                 );
 442                 let participle = if binding.is_import() { "imported" } else { "defined" };
 443                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 444                 err.span_label(binding.span, msg);
 445                 err
 446             }
 447             ResolutionError::ForwardDeclaredTyParam => {
 448                 let mut err = struct_span_err!(
 449                     self.session,
 450                     span,
 451                     E0128,
 452                     "type parameters with a default cannot use \
 453                                                 forward declared identifiers"
 454                 );
 455                 err.span_label(
 456                     span,
 457                     "defaulted type parameters cannot be forward declared".to_string(),
 458                 );
 459                 err
 460             }
 461             ResolutionError::ParamInTyOfConstParam(name) => {
 462                 let mut err = struct_span_err!(
 463                     self.session,
 464                     span,
 465                     E0770,
 466                     "the type of const parameters must not depend on other generic parameters"
 467                 );
 468                 err.span_label(
 469                     span,
 470                     format!("the type must not depend on the parameter `{}`", name),
 471                 );
 472                 err
 473             }
 474             ResolutionError::ParamInAnonConstInTyDefault(name) => {
 475                 let mut err = self.session.struct_span_err(
 476                     span,
 477                     "constant values inside of type parameter defaults must not depend on generic parameters",
 478                 );
 479                 err.span_label(
 480                     span,
 481                     format!("the anonymous constant must not depend on the parameter `{}`", name),
 482                 );
 483                 err
 484             }
 485             ResolutionError::ParamInNonTrivialAnonConst { name, is_type } => {
 486                 let mut err = self.session.struct_span_err(
 487                     span,
 488                     "generic parameters may not be used in const operations",
 489                 );
 490                 err.span_label(span, &format!("cannot perform const operation using `{}`", name));
 491
 492                 if is_type {
 493                     err.note("type parameters may not be used in const expressions");
 494                 } else {
 495                     err.help(&format!(
 496                         "const parameters may only be used as standalone arguments, i.e. `{}`",
 497                         name
 498                     ));
 499                 }
 500                 err.help("use `#![feature(const_generics)]` and `#![feature(const_evaluatable_checked)]` to allow generic const expressions");
 501
 502                 err
 503             }
 504             ResolutionError::SelfInTyParamDefault => {
 505                 let mut err = struct_span_err!(
 506                     self.session,
 507                     span,
 508                     E0735,
 509                     "type parameters cannot use `Self` in their defaults"
 510                 );
 511                 err.span_label(span, "`Self` in type parameter default".to_string());
 512                 err
 513             }
 514             ResolutionError::UnreachableLabel { name, definition_span, suggestion } => {
 515                 let mut err = struct_span_err!(
 516                     self.session,
 517                     span,
 518                     E0767,
 519                     "use of unreachable label `{}`",
 520                     name,
 521                 );
 522
 523                 err.span_label(definition_span, "unreachable label defined here");
 524                 err.span_label(span, format!("unreachable label `{}`", name));
 525                 err.note(
 526                     "labels are unreachable through functions, closures, async blocks and modules",
 527                 );
 528
 529                 match suggestion {
 530                     // A reachable label with a similar name exists.
 531                     Some((ident, true)) => {
 532                         err.span_label(ident.span, "a label with a similar name is reachable");
 533                         err.span_suggestion(
 534                             span,
 535                             "try using similarly named label",
 536                             ident.name.to_string(),
 537                             Applicability::MaybeIncorrect,
 538                         );
 539                     }
 540                     // An unreachable label with a similar name exists.
 541                     Some((ident, false)) => {
 542                         err.span_label(
 543                             ident.span,
 544                             "a label with a similar name exists but is also unreachable",
 545                         );
 546                     }
 547                     // No similarly-named labels exist.
 548                     None => (),
 549                 }
 550
 551                 err
 552             }
 553         }
 554     }
 555
 556     crate fn report_vis_error(&self, vis_resolution_error: VisResolutionError<'_>) {
 557         match vis_resolution_error {
 558             VisResolutionError::Relative2018(span, path) => {
 559                 let mut err = self.session.struct_span_err(
 560                     span,
 561                     "relative paths are not supported in visibilities on 2018 edition",
 562                 );
 563                 err.span_suggestion(
 564                     path.span,
 565                     "try",
 566                     format!("crate::{}", pprust::path_to_string(&path)),
 567                     Applicability::MaybeIncorrect,
 568                 );
 569                 err
 570             }
 571             VisResolutionError::AncestorOnly(span) => struct_span_err!(
 572                 self.session,
 573                 span,
 574                 E0742,
 575                 "visibilities can only be restricted to ancestor modules"
 576             ),
 577             VisResolutionError::FailedToResolve(span, label, suggestion) => {
 578                 self.into_struct_error(span, ResolutionError::FailedToResolve { label, suggestion })
 579             }
 580             VisResolutionError::ExpectedFound(span, path_str, res) => {
 581                 let mut err = struct_span_err!(
 582                     self.session,
 583                     span,
 584                     E0577,
 585                     "expected module, found {} `{}`",
 586                     res.descr(),
 587                     path_str
 588                 );
 589                 err.span_label(span, "not a module");
 590                 err
 591             }
 592             VisResolutionError::Indeterminate(span) => struct_span_err!(
 593                 self.session,
 594                 span,
 595                 E0578,
 596                 "cannot determine resolution for the visibility"
 597             ),
 598             VisResolutionError::ModuleOnly(span) => {
 599                 self.session.struct_span_err(span, "visibility must resolve to a module")
 600             }
 601         }
 602         .emit()
 603     }
 604
 605     /// Lookup typo candidate in scope for a macro or import.
 606     fn early_lookup_typo_candidate(
 607         &mut self,
 608         scope_set: ScopeSet,
 609         parent_scope: &ParentScope<'a>,
 610         ident: Ident,
 611         filter_fn: &impl Fn(Res) -> bool,
 612     ) -> Option<TypoSuggestion> {
 613         let mut suggestions = Vec::new();
 614         let ctxt = ident.span.ctxt();
 615         self.visit_scopes(scope_set, parent_scope, ctxt, |this, scope, use_prelude, _| {
 616             match scope {
 617                 Scope::DeriveHelpers(expn_id) => {
 618                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 619                     if filter_fn(res) {
 620                         suggestions.extend(
 621                             this.helper_attrs
 622                                 .get(&expn_id)
 623                                 .into_iter()
 624                                 .flatten()
 625                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 626                         );
 627                     }
 628                 }
 629                 Scope::DeriveHelpersCompat => {
 630                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelperCompat);
 631                     if filter_fn(res) {
 632                         for derive in parent_scope.derives {
 633                             let parent_scope = &ParentScope { derives: &[], ..*parent_scope };
 634                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 635                                 derive,
 636                                 Some(MacroKind::Derive),
 637                                 parent_scope,
 638                                 false,
 639                                 false,
 640                             ) {
 641                                 suggestions.extend(
 642                                     ext.helper_attrs
 643                                         .iter()
 644                                         .map(|name| TypoSuggestion::from_res(*name, res)),
 645                                 );
 646                             }
 647                         }
 648                     }
 649                 }
 650                 Scope::MacroRules(macro_rules_scope) => {
 651                     if let MacroRulesScope::Binding(macro_rules_binding) = macro_rules_scope.get() {
 652                         let res = macro_rules_binding.binding.res();
 653                         if filter_fn(res) {
 654                             suggestions
 655                                 .push(TypoSuggestion::from_res(macro_rules_binding.ident.name, res))
 656                         }
 657                     }
 658                 }
 659                 Scope::CrateRoot => {
 660                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 661                     let root_module = this.resolve_crate_root(root_ident);
 662                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 663                 }
 664                 Scope::Module(module) => {
 665                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 666                 }
 667                 Scope::RegisteredAttrs => {
 668                     let res = Res::NonMacroAttr(NonMacroAttrKind::Registered);
 669                     if filter_fn(res) {
 670                         suggestions.extend(
 671                             this.registered_attrs
 672                                 .iter()
 673                                 .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 674                         );
 675                     }
 676                 }
 677                 Scope::MacroUsePrelude => {
 678                     suggestions.extend(this.macro_use_prelude.iter().filter_map(
 679                         |(name, binding)| {
 680                             let res = binding.res();
 681                             filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 682                         },
 683                     ));
 684                 }
 685                 Scope::BuiltinAttrs => {
 686                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin(kw::Empty));
 687                     if filter_fn(res) {
 688                         suggestions.extend(
 689                             BUILTIN_ATTRIBUTES
 690                                 .iter()
 691                                 .map(|(name, ..)| TypoSuggestion::from_res(*name, res)),
 692                         );
 693                     }
 694                 }
 695                 Scope::ExternPrelude => {
 696                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 697                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 698                         filter_fn(res).then_some(TypoSuggestion::from_res(ident.name, res))
 699                     }));
 700                 }
 701                 Scope::ToolPrelude => {
 702                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 703                     suggestions.extend(
 704                         this.registered_tools
 705                             .iter()
 706                             .map(|ident| TypoSuggestion::from_res(ident.name, res)),
 707                     );
 708                 }
 709                 Scope::StdLibPrelude => {
 710                     if let Some(prelude) = this.prelude {
 711                         let mut tmp_suggestions = Vec::new();
 712                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 713                         suggestions.extend(
 714                             tmp_suggestions
 715                                 .into_iter()
 716                                 .filter(|s| use_prelude || this.is_builtin_macro(s.res)),
 717                         );
 718                     }
 719                 }
 720                 Scope::BuiltinTypes => {
 721                     let primitive_types = &this.primitive_type_table.primitive_types;
 722                     suggestions.extend(primitive_types.iter().flat_map(|(name, prim_ty)| {
 723                         let res = Res::PrimTy(*prim_ty);
 724                         filter_fn(res).then_some(TypoSuggestion::from_res(*name, res))
 725                     }))
 726                 }
 727             }
 728
 729             None::<()>
 730         });
 731
 732         // Make sure error reporting is deterministic.
 733         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 734
 735         match find_best_match_for_name(
 736             &suggestions.iter().map(|suggestion| suggestion.candidate).collect::<Vec<Symbol>>(),
 737             ident.name,
 738             None,
 739         ) {
 740             Some(found) if found != ident.name => {
 741                 suggestions.into_iter().find(|suggestion| suggestion.candidate == found)
 742             }
 743             _ => None,
 744         }
 745     }
 746
 747     fn lookup_import_candidates_from_module<FilterFn>(
 748         &mut self,
 749         lookup_ident: Ident,
 750         namespace: Namespace,
 751         parent_scope: &ParentScope<'a>,
 752         start_module: Module<'a>,
 753         crate_name: Ident,
 754         filter_fn: FilterFn,
 755     ) -> Vec<ImportSuggestion>
 756     where
 757         FilterFn: Fn(Res) -> bool,
 758     {
 759         let mut candidates = Vec::new();
 760         let mut seen_modules = FxHashSet::default();
 761         let not_local_module = crate_name.name != kw::Crate;
 762         let mut worklist =
 763             vec![(start_module, Vec::<ast::PathSegment>::new(), true, not_local_module)];
 764         let mut worklist_via_import = vec![];
 765
 766         while let Some((in_module, path_segments, accessible, in_module_is_extern)) =
 767             match worklist.pop() {
 768                 None => worklist_via_import.pop(),
 769                 Some(x) => Some(x),
 770             }
 771         {
 772             // We have to visit module children in deterministic order to avoid
 773             // instabilities in reported imports (#43552).
 774             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 775                 // avoid non-importable candidates
 776                 if !name_binding.is_importable() {
 777                     return;
 778                 }
 779
 780                 let child_accessible =
 781                     accessible && this.is_accessible_from(name_binding.vis, parent_scope.module);
 782
 783                 // do not venture inside inaccessible items of other crates
 784                 if in_module_is_extern && !child_accessible {
 785                     return;
 786                 }
 787
 788                 let via_import = name_binding.is_import() && !name_binding.is_extern_crate();
 789
 790                 // There is an assumption elsewhere that paths of variants are in the enum's
 791                 // declaration and not imported. With this assumption, the variant component is
 792                 // chopped and the rest of the path is assumed to be the enum's own path. For
 793                 // errors where a variant is used as the type instead of the enum, this causes
 794                 // funny looking invalid suggestions, i.e `foo` instead of `foo::MyEnum`.
 795                 if via_import && name_binding.is_possibly_imported_variant() {
 796                     return;
 797                 }
 798
 799                 // collect results based on the filter function
 800                 // avoid suggesting anything from the same module in which we are resolving
 801                 if ident.name == lookup_ident.name
 802                     && ns == namespace
 803                     && !ptr::eq(in_module, parent_scope.module)
 804                 {
 805                     let res = name_binding.res();
 806                     if filter_fn(res) {
 807                         // create the path
 808                         let mut segms = path_segments.clone();
 809                         if lookup_ident.span.rust_2018() {
 810                             // crate-local absolute paths start with `crate::` in edition 2018
 811                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 812                             segms.insert(0, ast::PathSegment::from_ident(crate_name));
 813                         }
 814
 815                         segms.push(ast::PathSegment::from_ident(ident));
 816                         let path = Path { span: name_binding.span, segments: segms, tokens: None };
 817                         let did = match res {
 818                             Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 819                             _ => res.opt_def_id(),
 820                         };
 821
 822                         if child_accessible {
 823                             // Remove invisible match if exists
 824                             if let Some(idx) = candidates
 825                                 .iter()
 826                                 .position(|v: &ImportSuggestion| v.did == did && !v.accessible)
 827                             {
 828                                 candidates.remove(idx);
 829                             }
 830                         }
 831
 832                         if candidates.iter().all(|v: &ImportSuggestion| v.did != did) {
 833                             candidates.push(ImportSuggestion {
 834                                 did,
 835                                 descr: res.descr(),
 836                                 path,
 837                                 accessible: child_accessible,
 838                             });
 839                         }
 840                     }
 841                 }
 842
 843                 // collect submodules to explore
 844                 if let Some(module) = name_binding.module() {
 845                     // form the path
 846                     let mut path_segments = path_segments.clone();
 847                     path_segments.push(ast::PathSegment::from_ident(ident));
 848
 849                     let is_extern_crate_that_also_appears_in_prelude =
 850                         name_binding.is_extern_crate() && lookup_ident.span.rust_2018();
 851
 852                     if !is_extern_crate_that_also_appears_in_prelude {
 853                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 854                         // add the module to the lookup
 855                         if seen_modules.insert(module.def_id().unwrap()) {
 856                             if via_import { &mut worklist_via_import } else { &mut worklist }
 857                                 .push((module, path_segments, child_accessible, is_extern));
 858                         }
 859                     }
 860                 }
 861             })
 862         }
 863
 864         // If only some candidates are accessible, take just them
 865         if !candidates.iter().all(|v: &ImportSuggestion| !v.accessible) {
 866             candidates = candidates.into_iter().filter(|x| x.accessible).collect();
 867         }
 868
 869         candidates
 870     }
 871
 872     /// When name resolution fails, this method can be used to look up candidate
 873     /// entities with the expected name. It allows filtering them using the
 874     /// supplied predicate (which should be used to only accept the types of
 875     /// definitions expected, e.g., traits). The lookup spans across all crates.
 876     ///
 877     /// N.B., the method does not look into imports, but this is not a problem,
 878     /// since we report the definitions (thus, the de-aliased imports).
 879     crate fn lookup_import_candidates<FilterFn>(
 880         &mut self,
 881         lookup_ident: Ident,
 882         namespace: Namespace,
 883         parent_scope: &ParentScope<'a>,
 884         filter_fn: FilterFn,
 885     ) -> Vec<ImportSuggestion>
 886     where
 887         FilterFn: Fn(Res) -> bool,
 888     {
 889         let mut suggestions = self.lookup_import_candidates_from_module(
 890             lookup_ident,
 891             namespace,
 892             parent_scope,
 893             self.graph_root,
 894             Ident::with_dummy_span(kw::Crate),
 895             &filter_fn,
 896         );
 897
 898         if lookup_ident.span.rust_2018() {
 899             let extern_prelude_names = self.extern_prelude.clone();
 900             for (ident, _) in extern_prelude_names.into_iter() {
 901                 if ident.span.from_expansion() {
 902                     // Idents are adjusted to the root context before being
 903                     // resolved in the extern prelude, so reporting this to the
 904                     // user is no help. This skips the injected
 905                     // `extern crate std` in the 2018 edition, which would
 906                     // otherwise cause duplicate suggestions.
 907                     continue;
 908                 }
 909                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name) {
 910                     let crate_root =
 911                         self.get_module(DefId { krate: crate_id, index: CRATE_DEF_INDEX });
 912                     suggestions.extend(self.lookup_import_candidates_from_module(
 913                         lookup_ident,
 914                         namespace,
 915                         parent_scope,
 916                         crate_root,
 917                         ident,
 918                         &filter_fn,
 919                     ));
 920                 }
 921             }
 922         }
 923
 924         suggestions
 925     }
 926
 927     crate fn unresolved_macro_suggestions(
 928         &mut self,
 929         err: &mut DiagnosticBuilder<'a>,
 930         macro_kind: MacroKind,
 931         parent_scope: &ParentScope<'a>,
 932         ident: Ident,
 933     ) {
 934         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 935         let suggestion = self.early_lookup_typo_candidate(
 936             ScopeSet::Macro(macro_kind),
 937             parent_scope,
 938             ident,
 939             is_expected,
 940         );
 941         self.add_typo_suggestion(err, suggestion, ident.span);
 942
 943         let import_suggestions =
 944             self.lookup_import_candidates(ident, Namespace::MacroNS, parent_scope, |res| {
 945                 matches!(res, Res::Def(DefKind::Macro(MacroKind::Bang), _))
 946             });
 947         show_candidates(err, None, &import_suggestions, false, true);
 948
 949         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
 950             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 951             err.span_note(ident.span, &msg);
 952         }
 953         if self.macro_names.contains(&ident.normalize_to_macros_2_0()) {
 954             err.help("have you added the `#[macro_use]` on the module/import?");
 955         }
 956     }
 957
 958     crate fn add_typo_suggestion(
 959         &self,
 960         err: &mut DiagnosticBuilder<'_>,
 961         suggestion: Option<TypoSuggestion>,
 962         span: Span,
 963     ) -> bool {
 964         let suggestion = match suggestion {
 965             None => return false,
 966             // We shouldn't suggest underscore.
 967             Some(suggestion) if suggestion.candidate == kw::Underscore => return false,
 968             Some(suggestion) => suggestion,
 969         };
 970         let def_span = suggestion.res.opt_def_id().and_then(|def_id| match def_id.krate {
 971             LOCAL_CRATE => self.opt_span(def_id),
 972             _ => Some(
 973                 self.session
 974                     .source_map()
 975                     .guess_head_span(self.cstore().get_span_untracked(def_id, self.session)),
 976             ),
 977         });
 978         if let Some(def_span) = def_span {
 979             if span.overlaps(def_span) {
 980                 // Don't suggest typo suggestion for itself like in the following:
 981                 // error[E0423]: expected function, tuple struct or tuple variant, found struct `X`
 982                 //   --> $DIR/issue-64792-bad-unicode-ctor.rs:3:14
 983                 //    |
 984                 // LL | struct X {}
 985                 //    | ----------- `X` defined here
 986                 // LL |
 987                 // LL | const Y: X = X("ö");
 988                 //    | -------------^^^^^^- similarly named constant `Y` defined here
 989                 //    |
 990                 // help: use struct literal syntax instead
 991                 //    |
 992                 // LL | const Y: X = X {};
 993                 //    |              ^^^^
 994                 // help: a constant with a similar name exists
 995                 //    |
 996                 // LL | const Y: X = Y("ö");
 997                 //    |              ^
 998                 return false;
 999             }
1000             err.span_label(
1001                 self.session.source_map().guess_head_span(def_span),
1002                 &format!(
1003                     "similarly named {} `{}` defined here",
1004                     suggestion.res.descr(),
1005                     suggestion.candidate.as_str(),
1006                 ),
1007             );
1008         }
1009         let msg = format!(
1010             "{} {} with a similar name exists",
1011             suggestion.res.article(),
1012             suggestion.res.descr()
1013         );
1014         err.span_suggestion(
1015             span,
1016             &msg,
1017             suggestion.candidate.to_string(),
1018             Applicability::MaybeIncorrect,
1019         );
1020         true
1021     }
1022
1023     fn binding_description(&self, b: &NameBinding<'_>, ident: Ident, from_prelude: bool) -> String {
1024         let res = b.res();
1025         if b.span.is_dummy() {
1026             // These already contain the "built-in" prefix or look bad with it.
1027             let add_built_in =
1028                 !matches!(b.res(), Res::NonMacroAttr(..) | Res::PrimTy(..) | Res::ToolMod);
1029             let (built_in, from) = if from_prelude {
1030                 ("", " from prelude")
1031             } else if b.is_extern_crate()
1032                 && !b.is_import()
1033                 && self.session.opts.externs.get(&ident.as_str()).is_some()
1034             {
1035                 ("", " passed with `--extern`")
1036             } else if add_built_in {
1037                 (" built-in", "")
1038             } else {
1039                 ("", "")
1040             };
1041
1042             let a = if built_in.is_empty() { res.article() } else { "a" };
1043             format!("{a}{built_in} {thing}{from}", thing = res.descr())
1044         } else {
1045             let introduced = if b.is_import() { "imported" } else { "defined" };
1046             format!("the {thing} {introduced} here", thing = res.descr())
1047         }
1048     }
1049
1050     crate fn report_ambiguity_error(&self, ambiguity_error: &AmbiguityError<'_>) {
1051         let AmbiguityError { kind, ident, b1, b2, misc1, misc2 } = *ambiguity_error;
1052         let (b1, b2, misc1, misc2, swapped) = if b2.span.is_dummy() && !b1.span.is_dummy() {
1053             // We have to print the span-less alternative first, otherwise formatting looks bad.
1054             (b2, b1, misc2, misc1, true)
1055         } else {
1056             (b1, b2, misc1, misc2, false)
1057         };
1058
1059         let mut err = struct_span_err!(
1060             self.session,
1061             ident.span,
1062             E0659,
1063             "`{ident}` is ambiguous ({why})",
1064             why = kind.descr()
1065         );
1066         err.span_label(ident.span, "ambiguous name");
1067
1068         let mut could_refer_to = |b: &NameBinding<'_>, misc: AmbiguityErrorMisc, also: &str| {
1069             let what = self.binding_description(b, ident, misc == AmbiguityErrorMisc::FromPrelude);
1070             let note_msg = format!("`{ident}` could{also} refer to {what}");
1071
1072             let thing = b.res().descr();
1073             let mut help_msgs = Vec::new();
1074             if b.is_glob_import()
1075                 && (kind == AmbiguityKind::GlobVsGlob
1076                     || kind == AmbiguityKind::GlobVsExpanded
1077                     || kind == AmbiguityKind::GlobVsOuter && swapped != also.is_empty())
1078             {
1079                 help_msgs.push(format!(
1080                     "consider adding an explicit import of `{ident}` to disambiguate"
1081                 ))
1082             }
1083             if b.is_extern_crate() && ident.span.rust_2018() {
1084                 help_msgs.push(format!("use `::{ident}` to refer to this {thing} unambiguously"))
1085             }
1086             if misc == AmbiguityErrorMisc::SuggestCrate {
1087                 help_msgs
1088                     .push(format!("use `crate::{ident}` to refer to this {thing} unambiguously"))
1089             } else if misc == AmbiguityErrorMisc::SuggestSelf {
1090                 help_msgs
1091                     .push(format!("use `self::{ident}` to refer to this {thing} unambiguously"))
1092             }
1093
1094             err.span_note(b.span, &note_msg);
1095             for (i, help_msg) in help_msgs.iter().enumerate() {
1096                 let or = if i == 0 { "" } else { "or " };
1097                 err.help(&format!("{}{}", or, help_msg));
1098             }
1099         };
1100
1101         could_refer_to(b1, misc1, "");
1102         could_refer_to(b2, misc2, " also");
1103         err.emit();
1104     }
1105
1106     /// If the binding refers to a tuple struct constructor with fields,
1107     /// returns the span of its fields.
1108     fn ctor_fields_span(&self, binding: &NameBinding<'_>) -> Option<Span> {
1109         if let NameBindingKind::Res(
1110             Res::Def(DefKind::Ctor(CtorOf::Struct, CtorKind::Fn), ctor_def_id),
1111             _,
1112         ) = binding.kind
1113         {
1114             let def_id = self.parent(ctor_def_id).expect("no parent for a constructor");
1115             let fields = self.field_names.get(&def_id)?;
1116             return fields.iter().map(|name| name.span).reduce(Span::to); // None for `struct Foo()`
1117         }
1118         None
1119     }
1120
1121     crate fn report_privacy_error(&self, privacy_error: &PrivacyError<'_>) {
1122         let PrivacyError { ident, binding, .. } = *privacy_error;
1123
1124         let res = binding.res();
1125         let ctor_fields_span = self.ctor_fields_span(binding);
1126         let plain_descr = res.descr().to_string();
1127         let nonimport_descr =
1128             if ctor_fields_span.is_some() { plain_descr + " constructor" } else { plain_descr };
1129         let import_descr = nonimport_descr.clone() + " import";
1130         let get_descr =
1131             |b: &NameBinding<'_>| if b.is_import() { &import_descr } else { &nonimport_descr };
1132
1133         // Print the primary message.
1134         let descr = get_descr(binding);
1135         let mut err =
1136             struct_span_err!(self.session, ident.span, E0603, "{} `{}` is private", descr, ident);
1137         err.span_label(ident.span, &format!("private {}", descr));
1138         if let Some(span) = ctor_fields_span {
1139             err.span_label(span, "a constructor is private if any of the fields is private");
1140         }
1141
1142         // Print the whole import chain to make it easier to see what happens.
1143         let first_binding = binding;
1144         let mut next_binding = Some(binding);
1145         let mut next_ident = ident;
1146         while let Some(binding) = next_binding {
1147             let name = next_ident;
1148             next_binding = match binding.kind {
1149                 _ if res == Res::Err => None,
1150                 NameBindingKind::Import { binding, import, .. } => match import.kind {
1151                     _ if binding.span.is_dummy() => None,
1152                     ImportKind::Single { source, .. } => {
1153                         next_ident = source;
1154                         Some(binding)
1155                     }
1156                     ImportKind::Glob { .. } | ImportKind::MacroUse => Some(binding),
1157                     ImportKind::ExternCrate { .. } => None,
1158                 },
1159                 _ => None,
1160             };
1161
1162             let first = ptr::eq(binding, first_binding);
1163             let msg = format!(
1164                 "{and_refers_to}the {item} `{name}`{which} is defined here{dots}",
1165                 and_refers_to = if first { "" } else { "...and refers to " },
1166                 item = get_descr(binding),
1167                 which = if first { "" } else { " which" },
1168                 dots = if next_binding.is_some() { "..." } else { "" },
1169             );
1170             let def_span = self.session.source_map().guess_head_span(binding.span);
1171             let mut note_span = MultiSpan::from_span(def_span);
1172             if !first && binding.vis == ty::Visibility::Public {
1173                 note_span.push_span_label(def_span, "consider importing it directly".into());
1174             }
1175             err.span_note(note_span, &msg);
1176         }
1177
1178         err.emit();
1179     }
1180 }
1181
1182 impl<'a, 'b> ImportResolver<'a, 'b> {
1183     /// Adds suggestions for a path that cannot be resolved.
1184     pub(crate) fn make_path_suggestion(
1185         &mut self,
1186         span: Span,
1187         mut path: Vec<Segment>,
1188         parent_scope: &ParentScope<'b>,
1189     ) -> Option<(Vec<Segment>, Vec<String>)> {
1190         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
1191
1192         match (path.get(0), path.get(1)) {
1193             // `{{root}}::ident::...` on both editions.
1194             // On 2015 `{{root}}` is usually added implicitly.
1195             (Some(fst), Some(snd))
1196                 if fst.ident.name == kw::PathRoot && !snd.ident.is_path_segment_keyword() => {}
1197             // `ident::...` on 2018.
1198             (Some(fst), _)
1199                 if fst.ident.span.rust_2018() && !fst.ident.is_path_segment_keyword() =>
1200             {
1201                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
1202                 path.insert(0, Segment::from_ident(Ident::invalid()));
1203             }
1204             _ => return None,
1205         }
1206
1207         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
1208             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
1209             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
1210             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
1211     }
1212
1213     /// Suggest a missing `self::` if that resolves to an correct module.
1214     ///
1215     /// ```text
1216     ///    |
1217     /// LL | use foo::Bar;
1218     ///    |     ^^^ did you mean `self::foo`?
1219     /// ```
1220     fn make_missing_self_suggestion(
1221         &mut self,
1222         span: Span,
1223         mut path: Vec<Segment>,
1224         parent_scope: &ParentScope<'b>,
1225     ) -> Option<(Vec<Segment>, Vec<String>)> {
1226         // Replace first ident with `self` and check if that is valid.
1227         path[0].ident.name = kw::SelfLower;
1228         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1229         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
1230         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1231     }
1232
1233     /// Suggests a missing `crate::` if that resolves to an correct module.
1234     ///
1235     /// ```text
1236     ///    |
1237     /// LL | use foo::Bar;
1238     ///    |     ^^^ did you mean `crate::foo`?
1239     /// ```
1240     fn make_missing_crate_suggestion(
1241         &mut self,
1242         span: Span,
1243         mut path: Vec<Segment>,
1244         parent_scope: &ParentScope<'b>,
1245     ) -> Option<(Vec<Segment>, Vec<String>)> {
1246         // Replace first ident with `crate` and check if that is valid.
1247         path[0].ident.name = kw::Crate;
1248         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1249         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
1250         if let PathResult::Module(..) = result {
1251             Some((
1252                 path,
1253                 vec![
1254                     "`use` statements changed in Rust 2018; read more at \
1255                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
1256                      clarity.html>"
1257                         .to_string(),
1258                 ],
1259             ))
1260         } else {
1261             None
1262         }
1263     }
1264
1265     /// Suggests a missing `super::` if that resolves to an correct module.
1266     ///
1267     /// ```text
1268     ///    |
1269     /// LL | use foo::Bar;
1270     ///    |     ^^^ did you mean `super::foo`?
1271     /// ```
1272     fn make_missing_super_suggestion(
1273         &mut self,
1274         span: Span,
1275         mut path: Vec<Segment>,
1276         parent_scope: &ParentScope<'b>,
1277     ) -> Option<(Vec<Segment>, Vec<String>)> {
1278         // Replace first ident with `crate` and check if that is valid.
1279         path[0].ident.name = kw::Super;
1280         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1281         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
1282         if let PathResult::Module(..) = result { Some((path, Vec::new())) } else { None }
1283     }
1284
1285     /// Suggests a missing external crate name if that resolves to an correct module.
1286     ///
1287     /// ```text
1288     ///    |
1289     /// LL | use foobar::Baz;
1290     ///    |     ^^^^^^ did you mean `baz::foobar`?
1291     /// ```
1292     ///
1293     /// Used when importing a submodule of an external crate but missing that crate's
1294     /// name as the first part of path.
1295     fn make_external_crate_suggestion(
1296         &mut self,
1297         span: Span,
1298         mut path: Vec<Segment>,
1299         parent_scope: &ParentScope<'b>,
1300     ) -> Option<(Vec<Segment>, Vec<String>)> {
1301         if path[1].ident.span.rust_2015() {
1302             return None;
1303         }
1304
1305         // Sort extern crate names in reverse order to get
1306         // 1) some consistent ordering for emitted diagnostics, and
1307         // 2) `std` suggestions before `core` suggestions.
1308         let mut extern_crate_names =
1309             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
1310         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
1311
1312         for name in extern_crate_names.into_iter() {
1313             // Replace first ident with a crate name and check if that is valid.
1314             path[0].ident.name = name;
1315             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
1316             debug!(
1317                 "make_external_crate_suggestion: name={:?} path={:?} result={:?}",
1318                 name, path, result
1319             );
1320             if let PathResult::Module(..) = result {
1321                 return Some((path, Vec::new()));
1322             }
1323         }
1324
1325         None
1326     }
1327
1328     /// Suggests importing a macro from the root of the crate rather than a module within
1329     /// the crate.
1330     ///
1331     /// ```text
1332     /// help: a macro with this name exists at the root of the crate
1333     ///    |
1334     /// LL | use issue_59764::makro;
1335     ///    |     ^^^^^^^^^^^^^^^^^^
1336     ///    |
1337     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
1338     ///            at the root of the crate instead of the module where it is defined
1339     /// ```
1340     pub(crate) fn check_for_module_export_macro(
1341         &mut self,
1342         import: &'b Import<'b>,
1343         module: ModuleOrUniformRoot<'b>,
1344         ident: Ident,
1345     ) -> Option<(Option<Suggestion>, Vec<String>)> {
1346         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
1347             module
1348         } else {
1349             return None;
1350         };
1351
1352         while let Some(parent) = crate_module.parent {
1353             crate_module = parent;
1354         }
1355
1356         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
1357             // Don't make a suggestion if the import was already from the root of the
1358             // crate.
1359             return None;
1360         }
1361
1362         let resolutions = self.r.resolutions(crate_module).borrow();
1363         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
1364         let binding = resolution.borrow().binding()?;
1365         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
1366             let module_name = crate_module.kind.name().unwrap();
1367             let import_snippet = match import.kind {
1368                 ImportKind::Single { source, target, .. } if source != target => {
1369                     format!("{} as {}", source, target)
1370                 }
1371                 _ => format!("{}", ident),
1372             };
1373
1374             let mut corrections: Vec<(Span, String)> = Vec::new();
1375             if !import.is_nested() {
1376                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
1377                 // intermediate segments.
1378                 corrections.push((import.span, format!("{}::{}", module_name, import_snippet)));
1379             } else {
1380                 // Find the binding span (and any trailing commas and spaces).
1381                 //   ie. `use a::b::{c, d, e};`
1382                 //                      ^^^
1383                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
1384                     self.r.session,
1385                     import.span,
1386                     import.use_span,
1387                 );
1388                 debug!(
1389                     "check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
1390                     found_closing_brace, binding_span
1391                 );
1392
1393                 let mut removal_span = binding_span;
1394                 if found_closing_brace {
1395                     // If the binding span ended with a closing brace, as in the below example:
1396                     //   ie. `use a::b::{c, d};`
1397                     //                      ^
1398                     // Then expand the span of characters to remove to include the previous
1399                     // binding's trailing comma.
1400                     //   ie. `use a::b::{c, d};`
1401                     //                    ^^^
1402                     if let Some(previous_span) =
1403                         extend_span_to_previous_binding(self.r.session, binding_span)
1404                     {
1405                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
1406                         removal_span = removal_span.with_lo(previous_span.lo());
1407                     }
1408                 }
1409                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
1410
1411                 // Remove the `removal_span`.
1412                 corrections.push((removal_span, "".to_string()));
1413
1414                 // Find the span after the crate name and if it has nested imports immediatately
1415                 // after the crate name already.
1416                 //   ie. `use a::b::{c, d};`
1417                 //               ^^^^^^^^^
1418                 //   or  `use a::{b, c, d}};`
1419                 //               ^^^^^^^^^^^
1420                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
1421                     self.r.session,
1422                     module_name,
1423                     import.use_span,
1424                 );
1425                 debug!(
1426                     "check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
1427                     has_nested, after_crate_name
1428                 );
1429
1430                 let source_map = self.r.session.source_map();
1431
1432                 // Add the import to the start, with a `{` if required.
1433                 let start_point = source_map.start_point(after_crate_name);
1434                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
1435                     corrections.push((
1436                         start_point,
1437                         if has_nested {
1438                             // In this case, `start_snippet` must equal '{'.
1439                             format!("{}{}, ", start_snippet, import_snippet)
1440                         } else {
1441                             // In this case, add a `{`, then the moved import, then whatever
1442                             // was there before.
1443                             format!("{{{}, {}", import_snippet, start_snippet)
1444                         },
1445                     ));
1446                 }
1447
1448                 // Add a `};` to the end if nested, matching the `{` added at the start.
1449                 if !has_nested {
1450                     corrections.push((source_map.end_point(after_crate_name), "};".to_string()));
1451                 }
1452             }
1453
1454             let suggestion = Some((
1455                 corrections,
1456                 String::from("a macro with this name exists at the root of the crate"),
1457                 Applicability::MaybeIncorrect,
1458             ));
1459             let note = vec![
1460                 "this could be because a macro annotated with `#[macro_export]` will be exported \
1461                  at the root of the crate instead of the module where it is defined"
1462                     .to_string(),
1463             ];
1464             Some((suggestion, note))
1465         } else {
1466             None
1467         }
1468     }
1469 }
1470
1471 /// Given a `binding_span` of a binding within a use statement:
1472 ///
1473 /// ```
1474 /// use foo::{a, b, c};
1475 ///              ^
1476 /// ```
1477 ///
1478 /// then return the span until the next binding or the end of the statement:
1479 ///
1480 /// ```
1481 /// use foo::{a, b, c};
1482 ///              ^^^
1483 /// ```
1484 pub(crate) fn find_span_of_binding_until_next_binding(
1485     sess: &Session,
1486     binding_span: Span,
1487     use_span: Span,
1488 ) -> (bool, Span) {
1489     let source_map = sess.source_map();
1490
1491     // Find the span of everything after the binding.
1492     //   ie. `a, e};` or `a};`
1493     let binding_until_end = binding_span.with_hi(use_span.hi());
1494
1495     // Find everything after the binding but not including the binding.
1496     //   ie. `, e};` or `};`
1497     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
1498
1499     // Keep characters in the span until we encounter something that isn't a comma or
1500     // whitespace.
1501     //   ie. `, ` or ``.
1502     //
1503     // Also note whether a closing brace character was encountered. If there
1504     // was, then later go backwards to remove any trailing commas that are left.
1505     let mut found_closing_brace = false;
1506     let after_binding_until_next_binding =
1507         source_map.span_take_while(after_binding_until_end, |&ch| {
1508             if ch == '}' {
1509                 found_closing_brace = true;
1510             }
1511             ch == ' ' || ch == ','
1512         });
1513
1514     // Combine the two spans.
1515     //   ie. `a, ` or `a`.
1516     //
1517     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1518     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1519
1520     (found_closing_brace, span)
1521 }
1522
1523 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1524 /// binding.
1525 ///
1526 /// ```
1527 /// use foo::a::{a, b, c};
1528 ///               ^^--- binding span
1529 ///               |
1530 ///               returned span
1531 ///
1532 /// use foo::{a, b, c};
1533 ///           --- binding span
1534 /// ```
1535 pub(crate) fn extend_span_to_previous_binding(sess: &Session, binding_span: Span) -> Option<Span> {
1536     let source_map = sess.source_map();
1537
1538     // `prev_source` will contain all of the source that came before the span.
1539     // Then split based on a command and take the first (ie. closest to our span)
1540     // snippet. In the example, this is a space.
1541     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1542
1543     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1544     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1545     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1546         return None;
1547     }
1548
1549     let prev_comma = prev_comma.first().unwrap();
1550     let prev_starting_brace = prev_starting_brace.first().unwrap();
1551
1552     // If the amount of source code before the comma is greater than
1553     // the amount of source code before the starting brace then we've only
1554     // got one item in the nested item (eg. `issue_52891::{self}`).
1555     if prev_comma.len() > prev_starting_brace.len() {
1556         return None;
1557     }
1558
1559     Some(binding_span.with_lo(BytePos(
1560         // Take away the number of bytes for the characters we've found and an
1561         // extra for the comma.
1562         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1,
1563     )))
1564 }
1565
1566 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1567 /// it is a nested use tree.
1568 ///
1569 /// ```
1570 /// use foo::a::{b, c};
1571 ///          ^^^^^^^^^^ // false
1572 ///
1573 /// use foo::{a, b, c};
1574 ///          ^^^^^^^^^^ // true
1575 ///
1576 /// use foo::{a, b::{c, d}};
1577 ///          ^^^^^^^^^^^^^^^ // true
1578 /// ```
1579 fn find_span_immediately_after_crate_name(
1580     sess: &Session,
1581     module_name: Symbol,
1582     use_span: Span,
1583 ) -> (bool, Span) {
1584     debug!(
1585         "find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1586         module_name, use_span
1587     );
1588     let source_map = sess.source_map();
1589
1590     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1591     let mut num_colons = 0;
1592     // Find second colon.. `use issue_59764:`
1593     let until_second_colon = source_map.span_take_while(use_span, |c| {
1594         if *c == ':' {
1595             num_colons += 1;
1596         }
1597         !matches!(c, ':' if num_colons == 2)
1598     });
1599     // Find everything after the second colon.. `foo::{baz, makro};`
1600     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1601
1602     let mut found_a_non_whitespace_character = false;
1603     // Find the first non-whitespace character in `from_second_colon`.. `f`
1604     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1605         if found_a_non_whitespace_character {
1606             return false;
1607         }
1608         if !c.is_whitespace() {
1609             found_a_non_whitespace_character = true;
1610         }
1611         true
1612     });
1613
1614     // Find the first `{` in from_second_colon.. `foo::{`
1615     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1616
1617     (next_left_bracket == after_second_colon, from_second_colon)
1618 }
1619
1620 /// When an entity with a given name is not available in scope, we search for
1621 /// entities with that name in all crates. This method allows outputting the
1622 /// results of this search in a programmer-friendly way
1623 crate fn show_candidates(
1624     err: &mut DiagnosticBuilder<'_>,
1625     // This is `None` if all placement locations are inside expansions
1626     use_placement_span: Option<Span>,
1627     candidates: &[ImportSuggestion],
1628     instead: bool,
1629     found_use: bool,
1630 ) {
1631     if candidates.is_empty() {
1632         return;
1633     }
1634
1635     // we want consistent results across executions, but candidates are produced
1636     // by iterating through a hash map, so make sure they are ordered:
1637     let mut path_strings: Vec<_> =
1638         candidates.iter().map(|c| path_names_to_string(&c.path)).collect();
1639
1640     path_strings.sort();
1641     path_strings.dedup();
1642
1643     let (determiner, kind) = if candidates.len() == 1 {
1644         ("this", candidates[0].descr)
1645     } else {
1646         ("one of these", "items")
1647     };
1648
1649     let instead = if instead { " instead" } else { "" };
1650     let mut msg = format!("consider importing {} {}{}", determiner, kind, instead);
1651
1652     if let Some(span) = use_placement_span {
1653         for candidate in &mut path_strings {
1654             // produce an additional newline to separate the new use statement
1655             // from the directly following item.
1656             let additional_newline = if found_use { "" } else { "\n" };
1657             *candidate = format!("use {};\n{}", candidate, additional_newline);
1658         }
1659
1660         err.span_suggestions(span, &msg, path_strings.into_iter(), Applicability::Unspecified);
1661     } else {
1662         msg.push(':');
1663
1664         for candidate in path_strings {
1665             msg.push('\n');
1666             msg.push_str(&candidate);
1667         }
1668
1669         err.note(&msg);
1670     }
1671 }