src/librustc_resolve/diagnostics.rs

   1 use std::cmp::Reverse;
   2
   3 use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
   4 use log::debug;
   5 use rustc::bug;
   6 use rustc::hir::def::{self, DefKind, NonMacroAttrKind};
   7 use rustc::hir::def::Namespace::{self, *};
   8 use rustc::hir::def_id::{CRATE_DEF_INDEX, DefId};
   9 use rustc::session::Session;
  10 use rustc::ty::{self, DefIdTree};
  11 use rustc::util::nodemap::FxHashSet;
  12 use syntax::ast::{self, Ident, Path};
  13 use syntax::feature_gate::BUILTIN_ATTRIBUTES;
  14 use syntax::source_map::SourceMap;
  15 use syntax::struct_span_err;
  16 use syntax::symbol::{Symbol, kw};
  17 use syntax::util::lev_distance::find_best_match_for_name;
  18 use syntax_pos::hygiene::MacroKind;
  19 use syntax_pos::{BytePos, Span, MultiSpan};
  20
  21 use crate::resolve_imports::{ImportDirective, ImportDirectiveSubclass, ImportResolver};
  22 use crate::{path_names_to_string, KNOWN_TOOLS};
  23 use crate::{BindingError, CrateLint, HasGenericParams, LegacyScope, Module, ModuleOrUniformRoot};
  24 use crate::{PathResult, ParentScope, ResolutionError, Resolver, Scope, ScopeSet, Segment};
  25
  26 type Res = def::Res<ast::NodeId>;
  27
  28 /// A vector of spans and replacements, a message and applicability.
  29 crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
  30
  31 crate struct TypoSuggestion {
  32     pub candidate: Symbol,
  33     pub res: Res,
  34 }
  35
  36 impl TypoSuggestion {
  37     crate fn from_res(candidate: Symbol, res: Res) -> TypoSuggestion {
  38         TypoSuggestion { candidate, res }
  39     }
  40 }
  41
  42 /// A free importable items suggested in case of resolution failure.
  43 crate struct ImportSuggestion {
  44     pub did: Option<DefId>,
  45     pub path: Path,
  46 }
  47
  48 /// Adjust the impl span so that just the `impl` keyword is taken by removing
  49 /// everything after `<` (`"impl<T> Iterator for A<T> {}" -> "impl"`) and
  50 /// everything after the first whitespace (`"impl Iterator for A" -> "impl"`).
  51 ///
  52 /// *Attention*: the method used is very fragile since it essentially duplicates the work of the
  53 /// parser. If you need to use this function or something similar, please consider updating the
  54 /// `source_map` functions and this function to something more robust.
  55 fn reduce_impl_span_to_impl_keyword(cm: &SourceMap, impl_span: Span) -> Span {
  56     let impl_span = cm.span_until_char(impl_span, '<');
  57     let impl_span = cm.span_until_whitespace(impl_span);
  58     impl_span
  59 }
  60
  61 impl<'a> Resolver<'a> {
  62     crate fn add_module_candidates(
  63         &mut self,
  64         module: Module<'a>,
  65         names: &mut Vec<TypoSuggestion>,
  66         filter_fn: &impl Fn(Res) -> bool,
  67     ) {
  68         for (key, resolution) in self.resolutions(module).borrow().iter() {
  69             if let Some(binding) = resolution.borrow().binding {
  70                 let res = binding.res();
  71                 if filter_fn(res) {
  72                     names.push(TypoSuggestion::from_res(key.ident.name, res));
  73                 }
  74             }
  75         }
  76     }
  77
  78     /// Combines an error with provided span and emits it.
  79     ///
  80     /// This takes the error provided, combines it with the span and any additional spans inside the
  81     /// error and emits it.
  82     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  83         self.into_struct_error(span, resolution_error).emit();
  84     }
  85
  86     crate fn into_struct_error(
  87         &self, span: Span, resolution_error: ResolutionError<'_>
  88     ) -> DiagnosticBuilder<'_> {
  89         match resolution_error {
  90             ResolutionError::GenericParamsFromOuterFunction(outer_res, has_generic_params) => {
  91                 let mut err = struct_span_err!(self.session,
  92                     span,
  93                     E0401,
  94                     "can't use generic parameters from outer function",
  95                 );
  96                 err.span_label(span, format!("use of generic parameter from outer function"));
  97
  98                 let cm = self.session.source_map();
  99                 match outer_res {
 100                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 101                         if let Some(impl_span) = maybe_impl_defid.and_then(|def_id| {
 102                             self.definitions.opt_span(def_id)
 103                         }) {
 104                             err.span_label(
 105                                 reduce_impl_span_to_impl_keyword(cm, impl_span),
 106                                 "`Self` type implicitly declared here, by this `impl`",
 107                             );
 108                         }
 109                         match (maybe_trait_defid, maybe_impl_defid) {
 110                             (Some(_), None) => {
 111                                 err.span_label(span, "can't use `Self` here");
 112                             }
 113                             (_, Some(_)) => {
 114                                 err.span_label(span, "use a type here instead");
 115                             }
 116                             (None, None) => bug!("`impl` without trait nor type?"),
 117                         }
 118                         return err;
 119                     },
 120                     Res::Def(DefKind::TyParam, def_id) => {
 121                         if let Some(span) = self.definitions.opt_span(def_id) {
 122                             err.span_label(span, "type parameter from outer function");
 123                         }
 124                     }
 125                     Res::Def(DefKind::ConstParam, def_id) => {
 126                         if let Some(span) = self.definitions.opt_span(def_id) {
 127                             err.span_label(span, "const parameter from outer function");
 128                         }
 129                     }
 130                     _ => {
 131                         bug!("GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 132                             DefKind::TyParam");
 133                     }
 134                 }
 135
 136                 if has_generic_params == HasGenericParams::Yes {
 137                     // Try to retrieve the span of the function signature and generate a new
 138                     // message with a local type or const parameter.
 139                     let sugg_msg = &format!("try using a local generic parameter instead");
 140                     if let Some((sugg_span, snippet)) = cm.generate_local_type_param_snippet(span) {
 141                         // Suggest the modification to the user
 142                         err.span_suggestion(
 143                             sugg_span,
 144                             sugg_msg,
 145                             snippet,
 146                             Applicability::MachineApplicable,
 147                         );
 148                     } else if let Some(sp) = cm.generate_fn_name_span(span) {
 149                         err.span_label(sp,
 150                             format!("try adding a local generic parameter in this method instead"));
 151                     } else {
 152                         err.help(&format!("try using a local generic parameter instead"));
 153                     }
 154                 }
 155
 156                 err
 157             }
 158             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 159                 let mut err = struct_span_err!(
 160                     self.session,
 161                     span,
 162                     E0403,
 163                     "the name `{}` is already used for a generic \
 164                      parameter in this item's generic parameters",
 165                     name,
 166                 );
 167                 err.span_label(span, "already used");
 168                 err.span_label(first_use_span, format!("first use of `{}`", name));
 169                 err
 170             }
 171             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 172                 let mut err = struct_span_err!(self.session,
 173                                             span,
 174                                             E0407,
 175                                             "method `{}` is not a member of trait `{}`",
 176                                             method,
 177                                             trait_);
 178                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 179                 err
 180             }
 181             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 182                 let mut err = struct_span_err!(self.session,
 183                                 span,
 184                                 E0437,
 185                                 "type `{}` is not a member of trait `{}`",
 186                                 type_,
 187                                 trait_);
 188                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 189                 err
 190             }
 191             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 192                 let mut err = struct_span_err!(self.session,
 193                                 span,
 194                                 E0438,
 195                                 "const `{}` is not a member of trait `{}`",
 196                                 const_,
 197                                 trait_);
 198                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 199                 err
 200             }
 201             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 202                 let BindingError { name, target, origin, could_be_path } = binding_error;
 203
 204                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 205                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 206
 207                 let msp = MultiSpan::from_spans(target_sp.clone());
 208                 let msg = format!("variable `{}` is not bound in all patterns", name);
 209                 let mut err = self.session.struct_span_err_with_code(
 210                     msp,
 211                     &msg,
 212                     DiagnosticId::Error("E0408".into()),
 213                 );
 214                 for sp in target_sp {
 215                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 216                 }
 217                 for sp in origin_sp {
 218                     err.span_label(sp, "variable not in all patterns");
 219                 }
 220                 if *could_be_path {
 221                     let help_msg = format!(
 222                         "if you meant to match on a variant or a `const` item, consider \
 223                          making the path in the pattern qualified: `?::{}`",
 224                          name,
 225                      );
 226                     err.span_help(span, &help_msg);
 227                 }
 228                 err
 229             }
 230             ResolutionError::VariableBoundWithDifferentMode(variable_name,
 231                                                             first_binding_span) => {
 232                 let mut err = struct_span_err!(self.session,
 233                                 span,
 234                                 E0409,
 235                                 "variable `{}` is bound in inconsistent \
 236                                 ways within the same match arm",
 237                                 variable_name);
 238                 err.span_label(span, "bound in different ways");
 239                 err.span_label(first_binding_span, "first binding");
 240                 err
 241             }
 242             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 243                 let mut err = struct_span_err!(self.session,
 244                                 span,
 245                                 E0415,
 246                                 "identifier `{}` is bound more than once in this parameter list",
 247                                 identifier);
 248                 err.span_label(span, "used as parameter more than once");
 249                 err
 250             }
 251             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 252                 let mut err = struct_span_err!(self.session,
 253                                 span,
 254                                 E0416,
 255                                 "identifier `{}` is bound more than once in the same pattern",
 256                                 identifier);
 257                 err.span_label(span, "used in a pattern more than once");
 258                 err
 259             }
 260             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 261                 let mut err = struct_span_err!(self.session,
 262                                             span,
 263                                             E0426,
 264                                             "use of undeclared label `{}`",
 265                                             name);
 266                 if let Some(lev_candidate) = lev_candidate {
 267                     err.span_suggestion(
 268                         span,
 269                         "a label with a similar name exists in this scope",
 270                         lev_candidate.to_string(),
 271                         Applicability::MaybeIncorrect,
 272                     );
 273                 } else {
 274                     err.span_label(span, format!("undeclared label `{}`", name));
 275                 }
 276                 err
 277             }
 278             ResolutionError::SelfImportsOnlyAllowedWithin => {
 279                 struct_span_err!(self.session,
 280                                 span,
 281                                 E0429,
 282                                 "{}",
 283                                 "`self` imports are only allowed within a { } list")
 284             }
 285             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 286                 let mut err = struct_span_err!(self.session, span, E0430,
 287                                             "`self` import can only appear once in an import list");
 288                 err.span_label(span, "can only appear once in an import list");
 289                 err
 290             }
 291             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 292                 let mut err = struct_span_err!(self.session, span, E0431,
 293                                             "`self` import can only appear in an import list with \
 294                                                 a non-empty prefix");
 295                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 296                 err
 297             }
 298             ResolutionError::FailedToResolve { label, suggestion } => {
 299                 let mut err = struct_span_err!(self.session, span, E0433,
 300                                             "failed to resolve: {}", &label);
 301                 err.span_label(span, label);
 302
 303                 if let Some((suggestions, msg, applicability)) = suggestion {
 304                     err.multipart_suggestion(&msg, suggestions, applicability);
 305                 }
 306
 307                 err
 308             }
 309             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 310                 let mut err = struct_span_err!(self.session,
 311                                             span,
 312                                             E0434,
 313                                             "{}",
 314                                             "can't capture dynamic environment in a fn item");
 315                 err.help("use the `|| { ... }` closure form instead");
 316                 err
 317             }
 318             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 319                 let mut err = struct_span_err!(self.session, span, E0435,
 320                                             "attempt to use a non-constant value in a constant");
 321                 err.span_label(span, "non-constant value");
 322                 err
 323             }
 324             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 325                 let res = binding.res();
 326                 let shadows_what = res.descr();
 327                 let mut err = struct_span_err!(self.session, span, E0530, "{}s cannot shadow {}s",
 328                                             what_binding, shadows_what);
 329                 err.span_label(span, format!("cannot be named the same as {} {}",
 330                                             res.article(), shadows_what));
 331                 let participle = if binding.is_import() { "imported" } else { "defined" };
 332                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 333                 err.span_label(binding.span, msg);
 334                 err
 335             }
 336             ResolutionError::ForwardDeclaredTyParam => {
 337                 let mut err = struct_span_err!(self.session, span, E0128,
 338                                             "type parameters with a default cannot use \
 339                                                 forward declared identifiers");
 340                 err.span_label(
 341                     span, "defaulted type parameters cannot be forward declared".to_string());
 342                 err
 343             }
 344             ResolutionError::SelfInTyParamDefault => {
 345                 let mut err = struct_span_err!(
 346                     self.session,
 347                     span,
 348                     E0735,
 349                     "type parameters cannot use `Self` in their defaults"
 350                 );
 351                 err.span_label(
 352                     span, "`Self` in type parameter default".to_string());
 353                 err
 354             }
 355         }
 356     }
 357
 358     /// Lookup typo candidate in scope for a macro or import.
 359     fn early_lookup_typo_candidate(
 360         &mut self,
 361         scope_set: ScopeSet,
 362         parent_scope: &ParentScope<'a>,
 363         ident: Ident,
 364         filter_fn: &impl Fn(Res) -> bool,
 365     ) -> Option<TypoSuggestion> {
 366         let mut suggestions = Vec::new();
 367         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 368             match scope {
 369                 Scope::DeriveHelpers => {
 370                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 371                     if filter_fn(res) {
 372                         for derive in parent_scope.derives {
 373                             let parent_scope =
 374                                 &ParentScope { derives: &[], ..*parent_scope };
 375                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 376                                 derive, Some(MacroKind::Derive), parent_scope, false, false
 377                             ) {
 378                                 suggestions.extend(ext.helper_attrs.iter().map(|name| {
 379                                     TypoSuggestion::from_res(*name, res)
 380                                 }));
 381                             }
 382                         }
 383                     }
 384                 }
 385                 Scope::MacroRules(legacy_scope) => {
 386                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 387                         let res = legacy_binding.binding.res();
 388                         if filter_fn(res) {
 389                             suggestions.push(
 390                                 TypoSuggestion::from_res(legacy_binding.ident.name, res)
 391                             )
 392                         }
 393                     }
 394                 }
 395                 Scope::CrateRoot => {
 396                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 397                     let root_module = this.resolve_crate_root(root_ident);
 398                     this.add_module_candidates(root_module, &mut suggestions, filter_fn);
 399                 }
 400                 Scope::Module(module) => {
 401                     this.add_module_candidates(module, &mut suggestions, filter_fn);
 402                 }
 403                 Scope::MacroUsePrelude => {
 404                     suggestions.extend(this.macro_use_prelude.iter().filter_map(|(name, binding)| {
 405                         let res = binding.res();
 406                         if filter_fn(res) {
 407                             Some(TypoSuggestion::from_res(*name, res))
 408                         } else {
 409                             None
 410                         }
 411                     }));
 412                 }
 413                 Scope::BuiltinAttrs => {
 414                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 415                     if filter_fn(res) {
 416                         suggestions.extend(BUILTIN_ATTRIBUTES.iter().map(|(name, ..)| {
 417                             TypoSuggestion::from_res(*name, res)
 418                         }));
 419                     }
 420                 }
 421                 Scope::LegacyPluginHelpers => {
 422                     let res = Res::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper);
 423                     if filter_fn(res) {
 424                         let plugin_attributes = this.session.plugin_attributes.borrow();
 425                         suggestions.extend(plugin_attributes.iter().map(|(name, _)| {
 426                             TypoSuggestion::from_res(*name, res)
 427                         }));
 428                     }
 429                 }
 430                 Scope::ExternPrelude => {
 431                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 432                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 433                         if filter_fn(res) {
 434                             Some(TypoSuggestion::from_res(ident.name, res))
 435                         } else {
 436                             None
 437                         }
 438                     }));
 439                 }
 440                 Scope::ToolPrelude => {
 441                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 442                     suggestions.extend(KNOWN_TOOLS.iter().map(|name| {
 443                         TypoSuggestion::from_res(*name, res)
 444                     }));
 445                 }
 446                 Scope::StdLibPrelude => {
 447                     if let Some(prelude) = this.prelude {
 448                         let mut tmp_suggestions = Vec::new();
 449                         this.add_module_candidates(prelude, &mut tmp_suggestions, filter_fn);
 450                         suggestions.extend(tmp_suggestions.into_iter().filter(|s| {
 451                             use_prelude || this.is_builtin_macro(s.res)
 452                         }));
 453                     }
 454                 }
 455                 Scope::BuiltinTypes => {
 456                     let primitive_types = &this.primitive_type_table.primitive_types;
 457                     suggestions.extend(
 458                         primitive_types.iter().flat_map(|(name, prim_ty)| {
 459                             let res = Res::PrimTy(*prim_ty);
 460                             if filter_fn(res) {
 461                                 Some(TypoSuggestion::from_res(*name, res))
 462                             } else {
 463                                 None
 464                             }
 465                         })
 466                     )
 467                 }
 468             }
 469
 470             None::<()>
 471         });
 472
 473         // Make sure error reporting is deterministic.
 474         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 475
 476         match find_best_match_for_name(
 477             suggestions.iter().map(|suggestion| &suggestion.candidate),
 478             &ident.as_str(),
 479             None,
 480         ) {
 481             Some(found) if found != ident.name => suggestions
 482                 .into_iter()
 483                 .find(|suggestion| suggestion.candidate == found),
 484             _ => None,
 485         }
 486     }
 487
 488     fn lookup_import_candidates_from_module<FilterFn>(&mut self,
 489                                           lookup_ident: Ident,
 490                                           namespace: Namespace,
 491                                           start_module: Module<'a>,
 492                                           crate_name: Ident,
 493                                           filter_fn: FilterFn)
 494                                           -> Vec<ImportSuggestion>
 495         where FilterFn: Fn(Res) -> bool
 496     {
 497         let mut candidates = Vec::new();
 498         let mut seen_modules = FxHashSet::default();
 499         let not_local_module = crate_name.name != kw::Crate;
 500         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 501
 502         while let Some((in_module,
 503                         path_segments,
 504                         in_module_is_extern)) = worklist.pop() {
 505             // We have to visit module children in deterministic order to avoid
 506             // instabilities in reported imports (#43552).
 507             in_module.for_each_child(self, |this, ident, ns, name_binding| {
 508                 // avoid imports entirely
 509                 if name_binding.is_import() && !name_binding.is_extern_crate() { return; }
 510                 // avoid non-importable candidates as well
 511                 if !name_binding.is_importable() { return; }
 512
 513                 // collect results based on the filter function
 514                 if ident.name == lookup_ident.name && ns == namespace {
 515                     let res = name_binding.res();
 516                     if filter_fn(res) {
 517                         // create the path
 518                         let mut segms = path_segments.clone();
 519                         if lookup_ident.span.rust_2018() {
 520                             // crate-local absolute paths start with `crate::` in edition 2018
 521                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 522                             segms.insert(
 523                                 0, ast::PathSegment::from_ident(crate_name)
 524                             );
 525                         }
 526
 527                         segms.push(ast::PathSegment::from_ident(ident));
 528                         let path = Path {
 529                             span: name_binding.span,
 530                             segments: segms,
 531                         };
 532                         // the entity is accessible in the following cases:
 533                         // 1. if it's defined in the same crate, it's always
 534                         // accessible (since private entities can be made public)
 535                         // 2. if it's defined in another crate, it's accessible
 536                         // only if both the module is public and the entity is
 537                         // declared as public (due to pruning, we don't explore
 538                         // outside crate private modules => no need to check this)
 539                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 540                             let did = match res {
 541                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 542                                 _ => res.opt_def_id(),
 543                             };
 544                             candidates.push(ImportSuggestion { did, path });
 545                         }
 546                     }
 547                 }
 548
 549                 // collect submodules to explore
 550                 if let Some(module) = name_binding.module() {
 551                     // form the path
 552                     let mut path_segments = path_segments.clone();
 553                     path_segments.push(ast::PathSegment::from_ident(ident));
 554
 555                     let is_extern_crate_that_also_appears_in_prelude =
 556                         name_binding.is_extern_crate() &&
 557                         lookup_ident.span.rust_2018();
 558
 559                     let is_visible_to_user =
 560                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 561
 562                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 563                         // add the module to the lookup
 564                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 565                         if seen_modules.insert(module.def_id().unwrap()) {
 566                             worklist.push((module, path_segments, is_extern));
 567                         }
 568                     }
 569                 }
 570             })
 571         }
 572
 573         candidates
 574     }
 575
 576     /// When name resolution fails, this method can be used to look up candidate
 577     /// entities with the expected name. It allows filtering them using the
 578     /// supplied predicate (which should be used to only accept the types of
 579     /// definitions expected, e.g., traits). The lookup spans across all crates.
 580     ///
 581     /// N.B., the method does not look into imports, but this is not a problem,
 582     /// since we report the definitions (thus, the de-aliased imports).
 583     crate fn lookup_import_candidates<FilterFn>(
 584         &mut self, lookup_ident: Ident, namespace: Namespace, filter_fn: FilterFn
 585     ) -> Vec<ImportSuggestion>
 586         where FilterFn: Fn(Res) -> bool
 587     {
 588         let mut suggestions = self.lookup_import_candidates_from_module(
 589             lookup_ident, namespace, self.graph_root, Ident::with_dummy_span(kw::Crate), &filter_fn
 590         );
 591
 592         if lookup_ident.span.rust_2018() {
 593             let extern_prelude_names = self.extern_prelude.clone();
 594             for (ident, _) in extern_prelude_names.into_iter() {
 595                 if ident.span.from_expansion() {
 596                     // Idents are adjusted to the root context before being
 597                     // resolved in the extern prelude, so reporting this to the
 598                     // user is no help. This skips the injected
 599                     // `extern crate std` in the 2018 edition, which would
 600                     // otherwise cause duplicate suggestions.
 601                     continue;
 602                 }
 603                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name,
 604                                                                                     ident.span) {
 605                     let crate_root = self.get_module(DefId {
 606                         krate: crate_id,
 607                         index: CRATE_DEF_INDEX,
 608                     });
 609                     suggestions.extend(self.lookup_import_candidates_from_module(
 610                         lookup_ident, namespace, crate_root, ident, &filter_fn));
 611                 }
 612             }
 613         }
 614
 615         suggestions
 616     }
 617
 618     crate fn unresolved_macro_suggestions(
 619         &mut self,
 620         err: &mut DiagnosticBuilder<'a>,
 621         macro_kind: MacroKind,
 622         parent_scope: &ParentScope<'a>,
 623         ident: Ident,
 624     ) {
 625         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 626         let suggestion = self.early_lookup_typo_candidate(
 627             ScopeSet::Macro(macro_kind), parent_scope, ident, is_expected
 628         );
 629         self.add_typo_suggestion(err, suggestion, ident.span);
 630
 631         if macro_kind == MacroKind::Derive &&
 632            (ident.as_str() == "Send" || ident.as_str() == "Sync") {
 633             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 634             err.span_note(ident.span, &msg);
 635         }
 636         if self.macro_names.contains(&ident.modern()) {
 637             err.help("have you added the `#[macro_use]` on the module/import?");
 638         }
 639     }
 640
 641     crate fn add_typo_suggestion(
 642         &self,
 643         err: &mut DiagnosticBuilder<'_>,
 644         suggestion: Option<TypoSuggestion>,
 645         span: Span,
 646     ) -> bool {
 647         if let Some(suggestion) = suggestion {
 648             let msg = format!(
 649                 "{} {} with a similar name exists", suggestion.res.article(), suggestion.res.descr()
 650             );
 651             err.span_suggestion(
 652                 span, &msg, suggestion.candidate.to_string(), Applicability::MaybeIncorrect
 653             );
 654             let def_span = suggestion.res.opt_def_id()
 655                 .and_then(|def_id| self.definitions.opt_span(def_id));
 656             if let Some(span) = def_span {
 657                 err.span_label(span, &format!(
 658                     "similarly named {} `{}` defined here",
 659                     suggestion.res.descr(),
 660                     suggestion.candidate.as_str(),
 661                 ));
 662             }
 663             return true;
 664         }
 665         false
 666     }
 667 }
 668
 669 impl<'a, 'b> ImportResolver<'a, 'b> {
 670     /// Adds suggestions for a path that cannot be resolved.
 671     pub(crate) fn make_path_suggestion(
 672         &mut self,
 673         span: Span,
 674         mut path: Vec<Segment>,
 675         parent_scope: &ParentScope<'b>,
 676     ) -> Option<(Vec<Segment>, Vec<String>)> {
 677         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 678
 679         match (path.get(0), path.get(1)) {
 680             // `{{root}}::ident::...` on both editions.
 681             // On 2015 `{{root}}` is usually added implicitly.
 682             (Some(fst), Some(snd)) if fst.ident.name == kw::PathRoot &&
 683                                       !snd.ident.is_path_segment_keyword() => {}
 684             // `ident::...` on 2018.
 685             (Some(fst), _) if fst.ident.span.rust_2018() &&
 686                               !fst.ident.is_path_segment_keyword() => {
 687                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 688                 path.insert(0, Segment::from_ident(Ident::invalid()));
 689             }
 690             _ => return None,
 691         }
 692
 693         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 694             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 695             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 696             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 697     }
 698
 699     /// Suggest a missing `self::` if that resolves to an correct module.
 700     ///
 701     /// ```
 702     ///    |
 703     /// LL | use foo::Bar;
 704     ///    |     ^^^ did you mean `self::foo`?
 705     /// ```
 706     fn make_missing_self_suggestion(
 707         &mut self,
 708         span: Span,
 709         mut path: Vec<Segment>,
 710         parent_scope: &ParentScope<'b>,
 711     ) -> Option<(Vec<Segment>, Vec<String>)> {
 712         // Replace first ident with `self` and check if that is valid.
 713         path[0].ident.name = kw::SelfLower;
 714         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 715         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
 716         if let PathResult::Module(..) = result {
 717             Some((path, Vec::new()))
 718         } else {
 719             None
 720         }
 721     }
 722
 723     /// Suggests a missing `crate::` if that resolves to an correct module.
 724     ///
 725     /// ```
 726     ///    |
 727     /// LL | use foo::Bar;
 728     ///    |     ^^^ did you mean `crate::foo`?
 729     /// ```
 730     fn make_missing_crate_suggestion(
 731         &mut self,
 732         span: Span,
 733         mut path: Vec<Segment>,
 734         parent_scope: &ParentScope<'b>,
 735     ) -> Option<(Vec<Segment>, Vec<String>)> {
 736         // Replace first ident with `crate` and check if that is valid.
 737         path[0].ident.name = kw::Crate;
 738         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 739         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
 740         if let PathResult::Module(..) = result {
 741             Some((
 742                 path,
 743                 vec![
 744                     "`use` statements changed in Rust 2018; read more at \
 745                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
 746                      clarity.html>".to_string()
 747                 ],
 748             ))
 749         } else {
 750             None
 751         }
 752     }
 753
 754     /// Suggests a missing `super::` if that resolves to an correct module.
 755     ///
 756     /// ```
 757     ///    |
 758     /// LL | use foo::Bar;
 759     ///    |     ^^^ did you mean `super::foo`?
 760     /// ```
 761     fn make_missing_super_suggestion(
 762         &mut self,
 763         span: Span,
 764         mut path: Vec<Segment>,
 765         parent_scope: &ParentScope<'b>,
 766     ) -> Option<(Vec<Segment>, Vec<String>)> {
 767         // Replace first ident with `crate` and check if that is valid.
 768         path[0].ident.name = kw::Super;
 769         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 770         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
 771         if let PathResult::Module(..) = result {
 772             Some((path, Vec::new()))
 773         } else {
 774             None
 775         }
 776     }
 777
 778     /// Suggests a missing external crate name if that resolves to an correct module.
 779     ///
 780     /// ```
 781     ///    |
 782     /// LL | use foobar::Baz;
 783     ///    |     ^^^^^^ did you mean `baz::foobar`?
 784     /// ```
 785     ///
 786     /// Used when importing a submodule of an external crate but missing that crate's
 787     /// name as the first part of path.
 788     fn make_external_crate_suggestion(
 789         &mut self,
 790         span: Span,
 791         mut path: Vec<Segment>,
 792         parent_scope: &ParentScope<'b>,
 793     ) -> Option<(Vec<Segment>, Vec<String>)> {
 794         if path[1].ident.span.rust_2015() {
 795             return None;
 796         }
 797
 798         // Sort extern crate names in reverse order to get
 799         // 1) some consistent ordering for emitted dignostics, and
 800         // 2) `std` suggestions before `core` suggestions.
 801         let mut extern_crate_names =
 802             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
 803         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
 804
 805         for name in extern_crate_names.into_iter() {
 806             // Replace first ident with a crate name and check if that is valid.
 807             path[0].ident.name = name;
 808             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 809             debug!("make_external_crate_suggestion: name={:?} path={:?} result={:?}",
 810                     name, path, result);
 811             if let PathResult::Module(..) = result {
 812                 return Some((path, Vec::new()));
 813             }
 814         }
 815
 816         None
 817     }
 818
 819     /// Suggests importing a macro from the root of the crate rather than a module within
 820     /// the crate.
 821     ///
 822     /// ```
 823     /// help: a macro with this name exists at the root of the crate
 824     ///    |
 825     /// LL | use issue_59764::makro;
 826     ///    |     ^^^^^^^^^^^^^^^^^^
 827     ///    |
 828     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
 829     ///            at the root of the crate instead of the module where it is defined
 830     /// ```
 831     pub(crate) fn check_for_module_export_macro(
 832         &mut self,
 833         directive: &'b ImportDirective<'b>,
 834         module: ModuleOrUniformRoot<'b>,
 835         ident: Ident,
 836     ) -> Option<(Option<Suggestion>, Vec<String>)> {
 837         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
 838             module
 839         } else {
 840             return None;
 841         };
 842
 843         while let Some(parent) = crate_module.parent {
 844             crate_module = parent;
 845         }
 846
 847         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
 848             // Don't make a suggestion if the import was already from the root of the
 849             // crate.
 850             return None;
 851         }
 852
 853         let resolutions = self.r.resolutions(crate_module).borrow();
 854         let resolution = resolutions.get(&self.r.new_key(ident, MacroNS))?;
 855         let binding = resolution.borrow().binding()?;
 856         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
 857             let module_name = crate_module.kind.name().unwrap();
 858             let import = match directive.subclass {
 859                 ImportDirectiveSubclass::SingleImport { source, target, .. } if source != target =>
 860                     format!("{} as {}", source, target),
 861                 _ => format!("{}", ident),
 862             };
 863
 864             let mut corrections: Vec<(Span, String)> = Vec::new();
 865             if !directive.is_nested() {
 866                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
 867                 // intermediate segments.
 868                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
 869             } else {
 870                 // Find the binding span (and any trailing commas and spaces).
 871                 //   ie. `use a::b::{c, d, e};`
 872                 //                      ^^^
 873                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
 874                     self.r.session, directive.span, directive.use_span,
 875                 );
 876                 debug!("check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
 877                        found_closing_brace, binding_span);
 878
 879                 let mut removal_span = binding_span;
 880                 if found_closing_brace {
 881                     // If the binding span ended with a closing brace, as in the below example:
 882                     //   ie. `use a::b::{c, d};`
 883                     //                      ^
 884                     // Then expand the span of characters to remove to include the previous
 885                     // binding's trailing comma.
 886                     //   ie. `use a::b::{c, d};`
 887                     //                    ^^^
 888                     if let Some(previous_span) = extend_span_to_previous_binding(
 889                         self.r.session, binding_span,
 890                     ) {
 891                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
 892                         removal_span = removal_span.with_lo(previous_span.lo());
 893                     }
 894                 }
 895                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
 896
 897                 // Remove the `removal_span`.
 898                 corrections.push((removal_span, "".to_string()));
 899
 900                 // Find the span after the crate name and if it has nested imports immediatately
 901                 // after the crate name already.
 902                 //   ie. `use a::b::{c, d};`
 903                 //               ^^^^^^^^^
 904                 //   or  `use a::{b, c, d}};`
 905                 //               ^^^^^^^^^^^
 906                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
 907                     self.r.session, module_name, directive.use_span,
 908                 );
 909                 debug!("check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
 910                        has_nested, after_crate_name);
 911
 912                 let source_map = self.r.session.source_map();
 913
 914                 // Add the import to the start, with a `{` if required.
 915                 let start_point = source_map.start_point(after_crate_name);
 916                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
 917                     corrections.push((
 918                         start_point,
 919                         if has_nested {
 920                             // In this case, `start_snippet` must equal '{'.
 921                             format!("{}{}, ", start_snippet, import)
 922                         } else {
 923                             // In this case, add a `{`, then the moved import, then whatever
 924                             // was there before.
 925                             format!("{{{}, {}", import, start_snippet)
 926                         }
 927                     ));
 928                 }
 929
 930                 // Add a `};` to the end if nested, matching the `{` added at the start.
 931                 if !has_nested {
 932                     corrections.push((source_map.end_point(after_crate_name),
 933                                      "};".to_string()));
 934                 }
 935             }
 936
 937             let suggestion = Some((
 938                 corrections,
 939                 String::from("a macro with this name exists at the root of the crate"),
 940                 Applicability::MaybeIncorrect,
 941             ));
 942             let note = vec![
 943                 "this could be because a macro annotated with `#[macro_export]` will be exported \
 944                  at the root of the crate instead of the module where it is defined".to_string(),
 945             ];
 946             Some((suggestion, note))
 947         } else {
 948             None
 949         }
 950     }
 951 }
 952
 953 /// Given a `binding_span` of a binding within a use statement:
 954 ///
 955 /// ```
 956 /// use foo::{a, b, c};
 957 ///              ^
 958 /// ```
 959 ///
 960 /// then return the span until the next binding or the end of the statement:
 961 ///
 962 /// ```
 963 /// use foo::{a, b, c};
 964 ///              ^^^
 965 /// ```
 966 pub(crate) fn find_span_of_binding_until_next_binding(
 967     sess: &Session,
 968     binding_span: Span,
 969     use_span: Span,
 970 ) -> (bool, Span) {
 971     let source_map = sess.source_map();
 972
 973     // Find the span of everything after the binding.
 974     //   ie. `a, e};` or `a};`
 975     let binding_until_end = binding_span.with_hi(use_span.hi());
 976
 977     // Find everything after the binding but not including the binding.
 978     //   ie. `, e};` or `};`
 979     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
 980
 981     // Keep characters in the span until we encounter something that isn't a comma or
 982     // whitespace.
 983     //   ie. `, ` or ``.
 984     //
 985     // Also note whether a closing brace character was encountered. If there
 986     // was, then later go backwards to remove any trailing commas that are left.
 987     let mut found_closing_brace = false;
 988     let after_binding_until_next_binding = source_map.span_take_while(
 989         after_binding_until_end,
 990         |&ch| {
 991             if ch == '}' { found_closing_brace = true; }
 992             ch == ' ' || ch == ','
 993         }
 994     );
 995
 996     // Combine the two spans.
 997     //   ie. `a, ` or `a`.
 998     //
 999     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
1000     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
1001
1002     (found_closing_brace, span)
1003 }
1004
1005 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
1006 /// binding.
1007 ///
1008 /// ```
1009 /// use foo::a::{a, b, c};
1010 ///               ^^--- binding span
1011 ///               |
1012 ///               returned span
1013 ///
1014 /// use foo::{a, b, c};
1015 ///           --- binding span
1016 /// ```
1017 pub(crate) fn extend_span_to_previous_binding(
1018     sess: &Session,
1019     binding_span: Span,
1020 ) -> Option<Span> {
1021     let source_map = sess.source_map();
1022
1023     // `prev_source` will contain all of the source that came before the span.
1024     // Then split based on a command and take the first (ie. closest to our span)
1025     // snippet. In the example, this is a space.
1026     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1027
1028     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1029     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1030     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1031         return None;
1032     }
1033
1034     let prev_comma = prev_comma.first().unwrap();
1035     let prev_starting_brace = prev_starting_brace.first().unwrap();
1036
1037     // If the amount of source code before the comma is greater than
1038     // the amount of source code before the starting brace then we've only
1039     // got one item in the nested item (eg. `issue_52891::{self}`).
1040     if prev_comma.len() > prev_starting_brace.len() {
1041         return None;
1042     }
1043
1044     Some(binding_span.with_lo(BytePos(
1045         // Take away the number of bytes for the characters we've found and an
1046         // extra for the comma.
1047         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1
1048     )))
1049 }
1050
1051 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1052 /// it is a nested use tree.
1053 ///
1054 /// ```
1055 /// use foo::a::{b, c};
1056 ///          ^^^^^^^^^^ // false
1057 ///
1058 /// use foo::{a, b, c};
1059 ///          ^^^^^^^^^^ // true
1060 ///
1061 /// use foo::{a, b::{c, d}};
1062 ///          ^^^^^^^^^^^^^^^ // true
1063 /// ```
1064 fn find_span_immediately_after_crate_name(
1065     sess: &Session,
1066     module_name: Symbol,
1067     use_span: Span,
1068 ) -> (bool, Span) {
1069     debug!("find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1070            module_name, use_span);
1071     let source_map = sess.source_map();
1072
1073     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1074     let mut num_colons = 0;
1075     // Find second colon.. `use issue_59764:`
1076     let until_second_colon = source_map.span_take_while(use_span, |c| {
1077         if *c == ':' { num_colons += 1; }
1078         match c {
1079             ':' if num_colons == 2 => false,
1080             _ => true,
1081         }
1082     });
1083     // Find everything after the second colon.. `foo::{baz, makro};`
1084     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1085
1086     let mut found_a_non_whitespace_character = false;
1087     // Find the first non-whitespace character in `from_second_colon`.. `f`
1088     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1089         if found_a_non_whitespace_character { return false; }
1090         if !c.is_whitespace() { found_a_non_whitespace_character = true; }
1091         true
1092     });
1093
1094     // Find the first `{` in from_second_colon.. `foo::{`
1095     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1096
1097     (next_left_bracket == after_second_colon, from_second_colon)
1098 }
1099
1100 /// When an entity with a given name is not available in scope, we search for
1101 /// entities with that name in all crates. This method allows outputting the
1102 /// results of this search in a programmer-friendly way
1103 crate fn show_candidates(
1104     err: &mut DiagnosticBuilder<'_>,
1105     // This is `None` if all placement locations are inside expansions
1106     span: Option<Span>,
1107     candidates: &[ImportSuggestion],
1108     better: bool,
1109     found_use: bool,
1110 ) {
1111     // we want consistent results across executions, but candidates are produced
1112     // by iterating through a hash map, so make sure they are ordered:
1113     let mut path_strings: Vec<_> =
1114         candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
1115     path_strings.sort();
1116
1117     let better = if better { "better " } else { "" };
1118     let msg_diff = match path_strings.len() {
1119         1 => " is found in another module, you can import it",
1120         _ => "s are found in other modules, you can import them",
1121     };
1122     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1123
1124     if let Some(span) = span {
1125         for candidate in &mut path_strings {
1126             // produce an additional newline to separate the new use statement
1127             // from the directly following item.
1128             let additional_newline = if found_use {
1129                 ""
1130             } else {
1131                 "\n"
1132             };
1133             *candidate = format!("use {};\n{}", candidate, additional_newline);
1134         }
1135
1136         err.span_suggestions(
1137             span,
1138             &msg,
1139             path_strings.into_iter(),
1140             Applicability::Unspecified,
1141         );
1142     } else {
1143         let mut msg = msg;
1144         msg.push(':');
1145         for candidate in path_strings {
1146             msg.push('\n');
1147             msg.push_str(&candidate);
1148         }
1149     }
1150 }