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::ext::base::MacroKind;
  14 use syntax::feature_gate::BUILTIN_ATTRIBUTES;
  15 use syntax::source_map::SourceMap;
  16 use syntax::struct_span_err;
  17 use syntax::symbol::{Symbol, kw};
  18 use syntax::util::lev_distance::find_best_match_for_name;
  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, 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 crate fn add_typo_suggestion(
  62     err: &mut DiagnosticBuilder<'_>, suggestion: Option<TypoSuggestion>, span: Span
  63 ) -> bool {
  64     if let Some(suggestion) = suggestion {
  65         let msg = format!(
  66             "{} {} with a similar name exists", suggestion.res.article(), suggestion.res.descr()
  67         );
  68         err.span_suggestion(
  69             span, &msg, suggestion.candidate.to_string(), Applicability::MaybeIncorrect
  70         );
  71         return true;
  72     }
  73     false
  74 }
  75
  76 crate fn add_module_candidates<'a>(
  77     resolver: &mut Resolver<'a>,
  78     module: Module<'a>,
  79     names: &mut Vec<TypoSuggestion>,
  80     filter_fn: &impl Fn(Res) -> bool,
  81 ) {
  82     for (&(ident, _), resolution) in resolver.resolutions(module).borrow().iter() {
  83         if let Some(binding) = resolution.borrow().binding {
  84             let res = binding.res();
  85             if filter_fn(res) {
  86                 names.push(TypoSuggestion::from_res(ident.name, res));
  87             }
  88         }
  89     }
  90 }
  91
  92 impl<'a> Resolver<'a> {
  93     /// Combines an error with provided span and emits it.
  94     ///
  95     /// This takes the error provided, combines it with the span and any additional spans inside the
  96     /// error and emits it.
  97     crate fn report_error(&self, span: Span, resolution_error: ResolutionError<'_>) {
  98         self.into_struct_error(span, resolution_error).emit();
  99     }
 100
 101     crate fn into_struct_error(
 102         &self, span: Span, resolution_error: ResolutionError<'_>
 103     ) -> DiagnosticBuilder<'_> {
 104         match resolution_error {
 105             ResolutionError::GenericParamsFromOuterFunction(outer_res) => {
 106                 let mut err = struct_span_err!(self.session,
 107                     span,
 108                     E0401,
 109                     "can't use generic parameters from outer function",
 110                 );
 111                 err.span_label(span, format!("use of generic parameter from outer function"));
 112
 113                 let cm = self.session.source_map();
 114                 match outer_res {
 115                     Res::SelfTy(maybe_trait_defid, maybe_impl_defid) => {
 116                         if let Some(impl_span) = maybe_impl_defid.and_then(|def_id| {
 117                             self.definitions.opt_span(def_id)
 118                         }) {
 119                             err.span_label(
 120                                 reduce_impl_span_to_impl_keyword(cm, impl_span),
 121                                 "`Self` type implicitly declared here, by this `impl`",
 122                             );
 123                         }
 124                         match (maybe_trait_defid, maybe_impl_defid) {
 125                             (Some(_), None) => {
 126                                 err.span_label(span, "can't use `Self` here");
 127                             }
 128                             (_, Some(_)) => {
 129                                 err.span_label(span, "use a type here instead");
 130                             }
 131                             (None, None) => bug!("`impl` without trait nor type?"),
 132                         }
 133                         return err;
 134                     },
 135                     Res::Def(DefKind::TyParam, def_id) => {
 136                         if let Some(span) = self.definitions.opt_span(def_id) {
 137                             err.span_label(span, "type parameter from outer function");
 138                         }
 139                     }
 140                     Res::Def(DefKind::ConstParam, def_id) => {
 141                         if let Some(span) = self.definitions.opt_span(def_id) {
 142                             err.span_label(span, "const parameter from outer function");
 143                         }
 144                     }
 145                     _ => {
 146                         bug!("GenericParamsFromOuterFunction should only be used with Res::SelfTy, \
 147                             DefKind::TyParam");
 148                     }
 149                 }
 150
 151                 // Try to retrieve the span of the function signature and generate a new message
 152                 // with a local type or const parameter.
 153                 let sugg_msg = &format!("try using a local generic parameter instead");
 154                 if let Some((sugg_span, new_snippet)) = cm.generate_local_type_param_snippet(span) {
 155                     // Suggest the modification to the user
 156                     err.span_suggestion(
 157                         sugg_span,
 158                         sugg_msg,
 159                         new_snippet,
 160                         Applicability::MachineApplicable,
 161                     );
 162                 } else if let Some(sp) = cm.generate_fn_name_span(span) {
 163                     err.span_label(sp,
 164                         format!("try adding a local generic parameter in this method instead"));
 165                 } else {
 166                     err.help(&format!("try using a local generic parameter instead"));
 167                 }
 168
 169                 err
 170             }
 171             ResolutionError::NameAlreadyUsedInParameterList(name, first_use_span) => {
 172                 let mut err = struct_span_err!(self.session,
 173                                                 span,
 174                                                 E0403,
 175                                                 "the name `{}` is already used for a generic \
 176                                                 parameter in this list of generic parameters",
 177                                                 name);
 178                 err.span_label(span, "already used");
 179                 err.span_label(first_use_span, format!("first use of `{}`", name));
 180                 err
 181             }
 182             ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
 183                 let mut err = struct_span_err!(self.session,
 184                                             span,
 185                                             E0407,
 186                                             "method `{}` is not a member of trait `{}`",
 187                                             method,
 188                                             trait_);
 189                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 190                 err
 191             }
 192             ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
 193                 let mut err = struct_span_err!(self.session,
 194                                 span,
 195                                 E0437,
 196                                 "type `{}` is not a member of trait `{}`",
 197                                 type_,
 198                                 trait_);
 199                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 200                 err
 201             }
 202             ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
 203                 let mut err = struct_span_err!(self.session,
 204                                 span,
 205                                 E0438,
 206                                 "const `{}` is not a member of trait `{}`",
 207                                 const_,
 208                                 trait_);
 209                 err.span_label(span, format!("not a member of trait `{}`", trait_));
 210                 err
 211             }
 212             ResolutionError::VariableNotBoundInPattern(binding_error) => {
 213                 let BindingError { name, target, origin, could_be_path } = binding_error;
 214
 215                 let target_sp = target.iter().copied().collect::<Vec<_>>();
 216                 let origin_sp = origin.iter().copied().collect::<Vec<_>>();
 217
 218                 let msp = MultiSpan::from_spans(target_sp.clone());
 219                 let msg = format!("variable `{}` is not bound in all patterns", name);
 220                 let mut err = self.session.struct_span_err_with_code(
 221                     msp,
 222                     &msg,
 223                     DiagnosticId::Error("E0408".into()),
 224                 );
 225                 for sp in target_sp {
 226                     err.span_label(sp, format!("pattern doesn't bind `{}`", name));
 227                 }
 228                 for sp in origin_sp {
 229                     err.span_label(sp, "variable not in all patterns");
 230                 }
 231                 if *could_be_path {
 232                     let help_msg = format!(
 233                         "if you meant to match on a variant or a `const` item, consider \
 234                          making the path in the pattern qualified: `?::{}`",
 235                          name,
 236                      );
 237                     err.span_help(span, &help_msg);
 238                 }
 239                 err
 240             }
 241             ResolutionError::VariableBoundWithDifferentMode(variable_name,
 242                                                             first_binding_span) => {
 243                 let mut err = struct_span_err!(self.session,
 244                                 span,
 245                                 E0409,
 246                                 "variable `{}` is bound in inconsistent \
 247                                 ways within the same match arm",
 248                                 variable_name);
 249                 err.span_label(span, "bound in different ways");
 250                 err.span_label(first_binding_span, "first binding");
 251                 err
 252             }
 253             ResolutionError::IdentifierBoundMoreThanOnceInParameterList(identifier) => {
 254                 let mut err = struct_span_err!(self.session,
 255                                 span,
 256                                 E0415,
 257                                 "identifier `{}` is bound more than once in this parameter list",
 258                                 identifier);
 259                 err.span_label(span, "used as parameter more than once");
 260                 err
 261             }
 262             ResolutionError::IdentifierBoundMoreThanOnceInSamePattern(identifier) => {
 263                 let mut err = struct_span_err!(self.session,
 264                                 span,
 265                                 E0416,
 266                                 "identifier `{}` is bound more than once in the same pattern",
 267                                 identifier);
 268                 err.span_label(span, "used in a pattern more than once");
 269                 err
 270             }
 271             ResolutionError::UndeclaredLabel(name, lev_candidate) => {
 272                 let mut err = struct_span_err!(self.session,
 273                                             span,
 274                                             E0426,
 275                                             "use of undeclared label `{}`",
 276                                             name);
 277                 if let Some(lev_candidate) = lev_candidate {
 278                     err.span_suggestion(
 279                         span,
 280                         "a label with a similar name exists in this scope",
 281                         lev_candidate.to_string(),
 282                         Applicability::MaybeIncorrect,
 283                     );
 284                 } else {
 285                     err.span_label(span, format!("undeclared label `{}`", name));
 286                 }
 287                 err
 288             }
 289             ResolutionError::SelfImportsOnlyAllowedWithin => {
 290                 struct_span_err!(self.session,
 291                                 span,
 292                                 E0429,
 293                                 "{}",
 294                                 "`self` imports are only allowed within a { } list")
 295             }
 296             ResolutionError::SelfImportCanOnlyAppearOnceInTheList => {
 297                 let mut err = struct_span_err!(self.session, span, E0430,
 298                                             "`self` import can only appear once in an import list");
 299                 err.span_label(span, "can only appear once in an import list");
 300                 err
 301             }
 302             ResolutionError::SelfImportOnlyInImportListWithNonEmptyPrefix => {
 303                 let mut err = struct_span_err!(self.session, span, E0431,
 304                                             "`self` import can only appear in an import list with \
 305                                                 a non-empty prefix");
 306                 err.span_label(span, "can only appear in an import list with a non-empty prefix");
 307                 err
 308             }
 309             ResolutionError::FailedToResolve { label, suggestion } => {
 310                 let mut err = struct_span_err!(self.session, span, E0433,
 311                                             "failed to resolve: {}", &label);
 312                 err.span_label(span, label);
 313
 314                 if let Some((suggestions, msg, applicability)) = suggestion {
 315                     err.multipart_suggestion(&msg, suggestions, applicability);
 316                 }
 317
 318                 err
 319             }
 320             ResolutionError::CannotCaptureDynamicEnvironmentInFnItem => {
 321                 let mut err = struct_span_err!(self.session,
 322                                             span,
 323                                             E0434,
 324                                             "{}",
 325                                             "can't capture dynamic environment in a fn item");
 326                 err.help("use the `|| { ... }` closure form instead");
 327                 err
 328             }
 329             ResolutionError::AttemptToUseNonConstantValueInConstant => {
 330                 let mut err = struct_span_err!(self.session, span, E0435,
 331                                             "attempt to use a non-constant value in a constant");
 332                 err.span_label(span, "non-constant value");
 333                 err
 334             }
 335             ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
 336                 let res = binding.res();
 337                 let shadows_what = res.descr();
 338                 let mut err = struct_span_err!(self.session, span, E0530, "{}s cannot shadow {}s",
 339                                             what_binding, shadows_what);
 340                 err.span_label(span, format!("cannot be named the same as {} {}",
 341                                             res.article(), shadows_what));
 342                 let participle = if binding.is_import() { "imported" } else { "defined" };
 343                 let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
 344                 err.span_label(binding.span, msg);
 345                 err
 346             }
 347             ResolutionError::ForwardDeclaredTyParam => {
 348                 let mut err = struct_span_err!(self.session, span, E0128,
 349                                             "type parameters with a default cannot use \
 350                                                 forward declared identifiers");
 351                 err.span_label(
 352                     span, "defaulted type parameters cannot be forward declared".to_string());
 353                 err
 354             }
 355             ResolutionError::ConstParamDependentOnTypeParam => {
 356                 let mut err = struct_span_err!(
 357                     self.session,
 358                     span,
 359                     E0671,
 360                     "const parameters cannot depend on type parameters"
 361                 );
 362                 err.span_label(span, format!("const parameter depends on type parameter"));
 363                 err
 364             }
 365         }
 366     }
 367
 368     /// Lookup typo candidate in scope for a macro or import.
 369     fn early_lookup_typo_candidate(
 370         &mut self,
 371         scope_set: ScopeSet,
 372         parent_scope: &ParentScope<'a>,
 373         ident: Ident,
 374         filter_fn: &impl Fn(Res) -> bool,
 375     ) -> Option<TypoSuggestion> {
 376         let mut suggestions = Vec::new();
 377         self.visit_scopes(scope_set, parent_scope, ident, |this, scope, use_prelude, _| {
 378             match scope {
 379                 Scope::DeriveHelpers => {
 380                     let res = Res::NonMacroAttr(NonMacroAttrKind::DeriveHelper);
 381                     if filter_fn(res) {
 382                         for derive in parent_scope.derives {
 383                             let parent_scope =
 384                                 &ParentScope { derives: &[], ..*parent_scope };
 385                             if let Ok((Some(ext), _)) = this.resolve_macro_path(
 386                                 derive, Some(MacroKind::Derive), parent_scope, false, false
 387                             ) {
 388                                 suggestions.extend(ext.helper_attrs.iter().map(|name| {
 389                                     TypoSuggestion::from_res(*name, res)
 390                                 }));
 391                             }
 392                         }
 393                     }
 394                 }
 395                 Scope::MacroRules(legacy_scope) => {
 396                     if let LegacyScope::Binding(legacy_binding) = legacy_scope {
 397                         let res = legacy_binding.binding.res();
 398                         if filter_fn(res) {
 399                             suggestions.push(
 400                                 TypoSuggestion::from_res(legacy_binding.ident.name, res)
 401                             )
 402                         }
 403                     }
 404                 }
 405                 Scope::CrateRoot => {
 406                     let root_ident = Ident::new(kw::PathRoot, ident.span);
 407                     let root_module = this.resolve_crate_root(root_ident);
 408                     add_module_candidates(this, root_module, &mut suggestions, filter_fn);
 409                 }
 410                 Scope::Module(module) => {
 411                     add_module_candidates(this, module, &mut suggestions, filter_fn);
 412                 }
 413                 Scope::MacroUsePrelude => {
 414                     suggestions.extend(this.macro_use_prelude.iter().filter_map(|(name, binding)| {
 415                         let res = binding.res();
 416                         if filter_fn(res) {
 417                             Some(TypoSuggestion::from_res(*name, res))
 418                         } else {
 419                             None
 420                         }
 421                     }));
 422                 }
 423                 Scope::BuiltinAttrs => {
 424                     let res = Res::NonMacroAttr(NonMacroAttrKind::Builtin);
 425                     if filter_fn(res) {
 426                         suggestions.extend(BUILTIN_ATTRIBUTES.iter().map(|(name, ..)| {
 427                             TypoSuggestion::from_res(*name, res)
 428                         }));
 429                     }
 430                 }
 431                 Scope::LegacyPluginHelpers => {
 432                     let res = Res::NonMacroAttr(NonMacroAttrKind::LegacyPluginHelper);
 433                     if filter_fn(res) {
 434                         let plugin_attributes = this.session.plugin_attributes.borrow();
 435                         suggestions.extend(plugin_attributes.iter().map(|(name, _)| {
 436                             TypoSuggestion::from_res(*name, res)
 437                         }));
 438                     }
 439                 }
 440                 Scope::ExternPrelude => {
 441                     suggestions.extend(this.extern_prelude.iter().filter_map(|(ident, _)| {
 442                         let res = Res::Def(DefKind::Mod, DefId::local(CRATE_DEF_INDEX));
 443                         if filter_fn(res) {
 444                             Some(TypoSuggestion::from_res(ident.name, res))
 445                         } else {
 446                             None
 447                         }
 448                     }));
 449                 }
 450                 Scope::ToolPrelude => {
 451                     let res = Res::NonMacroAttr(NonMacroAttrKind::Tool);
 452                     suggestions.extend(KNOWN_TOOLS.iter().map(|name| {
 453                         TypoSuggestion::from_res(*name, res)
 454                     }));
 455                 }
 456                 Scope::StdLibPrelude => {
 457                     if let Some(prelude) = this.prelude {
 458                         let mut tmp_suggestions = Vec::new();
 459                         add_module_candidates(this, prelude, &mut tmp_suggestions, filter_fn);
 460                         suggestions.extend(tmp_suggestions.into_iter().filter(|s| {
 461                             use_prelude || this.is_builtin_macro(s.res)
 462                         }));
 463                     }
 464                 }
 465                 Scope::BuiltinTypes => {
 466                     let primitive_types = &this.primitive_type_table.primitive_types;
 467                     suggestions.extend(
 468                         primitive_types.iter().flat_map(|(name, prim_ty)| {
 469                             let res = Res::PrimTy(*prim_ty);
 470                             if filter_fn(res) {
 471                                 Some(TypoSuggestion::from_res(*name, res))
 472                             } else {
 473                                 None
 474                             }
 475                         })
 476                     )
 477                 }
 478             }
 479
 480             None::<()>
 481         });
 482
 483         // Make sure error reporting is deterministic.
 484         suggestions.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 485
 486         match find_best_match_for_name(
 487             suggestions.iter().map(|suggestion| &suggestion.candidate),
 488             &ident.as_str(),
 489             None,
 490         ) {
 491             Some(found) if found != ident.name => suggestions
 492                 .into_iter()
 493                 .find(|suggestion| suggestion.candidate == found),
 494             _ => None,
 495         }
 496     }
 497
 498     fn lookup_import_candidates_from_module<FilterFn>(&mut self,
 499                                           lookup_ident: Ident,
 500                                           namespace: Namespace,
 501                                           start_module: Module<'a>,
 502                                           crate_name: Ident,
 503                                           filter_fn: FilterFn)
 504                                           -> Vec<ImportSuggestion>
 505         where FilterFn: Fn(Res) -> bool
 506     {
 507         let mut candidates = Vec::new();
 508         let mut seen_modules = FxHashSet::default();
 509         let not_local_module = crate_name.name != kw::Crate;
 510         let mut worklist = vec![(start_module, Vec::<ast::PathSegment>::new(), not_local_module)];
 511
 512         while let Some((in_module,
 513                         path_segments,
 514                         in_module_is_extern)) = worklist.pop() {
 515             // We have to visit module children in deterministic order to avoid
 516             // instabilities in reported imports (#43552).
 517             in_module.for_each_child_stable(self, |this, ident, ns, name_binding| {
 518                 // avoid imports entirely
 519                 if name_binding.is_import() && !name_binding.is_extern_crate() { return; }
 520                 // avoid non-importable candidates as well
 521                 if !name_binding.is_importable() { return; }
 522
 523                 // collect results based on the filter function
 524                 if ident.name == lookup_ident.name && ns == namespace {
 525                     let res = name_binding.res();
 526                     if filter_fn(res) {
 527                         // create the path
 528                         let mut segms = path_segments.clone();
 529                         if lookup_ident.span.rust_2018() {
 530                             // crate-local absolute paths start with `crate::` in edition 2018
 531                             // FIXME: may also be stabilized for Rust 2015 (Issues #45477, #44660)
 532                             segms.insert(
 533                                 0, ast::PathSegment::from_ident(crate_name)
 534                             );
 535                         }
 536
 537                         segms.push(ast::PathSegment::from_ident(ident));
 538                         let path = Path {
 539                             span: name_binding.span,
 540                             segments: segms,
 541                         };
 542                         // the entity is accessible in the following cases:
 543                         // 1. if it's defined in the same crate, it's always
 544                         // accessible (since private entities can be made public)
 545                         // 2. if it's defined in another crate, it's accessible
 546                         // only if both the module is public and the entity is
 547                         // declared as public (due to pruning, we don't explore
 548                         // outside crate private modules => no need to check this)
 549                         if !in_module_is_extern || name_binding.vis == ty::Visibility::Public {
 550                             let did = match res {
 551                                 Res::Def(DefKind::Ctor(..), did) => this.parent(did),
 552                                 _ => res.opt_def_id(),
 553                             };
 554                             candidates.push(ImportSuggestion { did, path });
 555                         }
 556                     }
 557                 }
 558
 559                 // collect submodules to explore
 560                 if let Some(module) = name_binding.module() {
 561                     // form the path
 562                     let mut path_segments = path_segments.clone();
 563                     path_segments.push(ast::PathSegment::from_ident(ident));
 564
 565                     let is_extern_crate_that_also_appears_in_prelude =
 566                         name_binding.is_extern_crate() &&
 567                         lookup_ident.span.rust_2018();
 568
 569                     let is_visible_to_user =
 570                         !in_module_is_extern || name_binding.vis == ty::Visibility::Public;
 571
 572                     if !is_extern_crate_that_also_appears_in_prelude && is_visible_to_user {
 573                         // add the module to the lookup
 574                         let is_extern = in_module_is_extern || name_binding.is_extern_crate();
 575                         if seen_modules.insert(module.def_id().unwrap()) {
 576                             worklist.push((module, path_segments, is_extern));
 577                         }
 578                     }
 579                 }
 580             })
 581         }
 582
 583         candidates
 584     }
 585
 586     /// When name resolution fails, this method can be used to look up candidate
 587     /// entities with the expected name. It allows filtering them using the
 588     /// supplied predicate (which should be used to only accept the types of
 589     /// definitions expected, e.g., traits). The lookup spans across all crates.
 590     ///
 591     /// N.B., the method does not look into imports, but this is not a problem,
 592     /// since we report the definitions (thus, the de-aliased imports).
 593     crate fn lookup_import_candidates<FilterFn>(
 594         &mut self, lookup_ident: Ident, namespace: Namespace, filter_fn: FilterFn
 595     ) -> Vec<ImportSuggestion>
 596         where FilterFn: Fn(Res) -> bool
 597     {
 598         let mut suggestions = self.lookup_import_candidates_from_module(
 599             lookup_ident, namespace, self.graph_root, Ident::with_dummy_span(kw::Crate), &filter_fn
 600         );
 601
 602         if lookup_ident.span.rust_2018() {
 603             let extern_prelude_names = self.extern_prelude.clone();
 604             for (ident, _) in extern_prelude_names.into_iter() {
 605                 if let Some(crate_id) = self.crate_loader.maybe_process_path_extern(ident.name,
 606                                                                                     ident.span) {
 607                     let crate_root = self.get_module(DefId {
 608                         krate: crate_id,
 609                         index: CRATE_DEF_INDEX,
 610                     });
 611                     suggestions.extend(self.lookup_import_candidates_from_module(
 612                         lookup_ident, namespace, crate_root, ident, &filter_fn));
 613                 }
 614             }
 615         }
 616
 617         suggestions
 618     }
 619
 620     crate fn unresolved_macro_suggestions(
 621         &mut self,
 622         err: &mut DiagnosticBuilder<'a>,
 623         macro_kind: MacroKind,
 624         parent_scope: &ParentScope<'a>,
 625         ident: Ident,
 626     ) {
 627         let is_expected = &|res: Res| res.macro_kind() == Some(macro_kind);
 628         let suggestion = self.early_lookup_typo_candidate(
 629             ScopeSet::Macro(macro_kind), parent_scope, ident, is_expected
 630         );
 631         add_typo_suggestion(err, suggestion, ident.span);
 632
 633         if macro_kind == MacroKind::Derive &&
 634            (ident.as_str() == "Send" || ident.as_str() == "Sync") {
 635             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
 636             err.span_note(ident.span, &msg);
 637         }
 638         if self.macro_names.contains(&ident.modern()) {
 639             err.help("have you added the `#[macro_use]` on the module/import?");
 640         }
 641     }
 642 }
 643
 644 impl<'a, 'b> ImportResolver<'a, 'b> {
 645     /// Adds suggestions for a path that cannot be resolved.
 646     pub(crate) fn make_path_suggestion(
 647         &mut self,
 648         span: Span,
 649         mut path: Vec<Segment>,
 650         parent_scope: &ParentScope<'b>,
 651     ) -> Option<(Vec<Segment>, Vec<String>)> {
 652         debug!("make_path_suggestion: span={:?} path={:?}", span, path);
 653
 654         match (path.get(0), path.get(1)) {
 655             // `{{root}}::ident::...` on both editions.
 656             // On 2015 `{{root}}` is usually added implicitly.
 657             (Some(fst), Some(snd)) if fst.ident.name == kw::PathRoot &&
 658                                       !snd.ident.is_path_segment_keyword() => {}
 659             // `ident::...` on 2018.
 660             (Some(fst), _) if fst.ident.span.rust_2018() &&
 661                               !fst.ident.is_path_segment_keyword() => {
 662                 // Insert a placeholder that's later replaced by `self`/`super`/etc.
 663                 path.insert(0, Segment::from_ident(Ident::invalid()));
 664             }
 665             _ => return None,
 666         }
 667
 668         self.make_missing_self_suggestion(span, path.clone(), parent_scope)
 669             .or_else(|| self.make_missing_crate_suggestion(span, path.clone(), parent_scope))
 670             .or_else(|| self.make_missing_super_suggestion(span, path.clone(), parent_scope))
 671             .or_else(|| self.make_external_crate_suggestion(span, path, parent_scope))
 672     }
 673
 674     /// Suggest a missing `self::` if that resolves to an correct module.
 675     ///
 676     /// ```
 677     ///    |
 678     /// LL | use foo::Bar;
 679     ///    |     ^^^ did you mean `self::foo`?
 680     /// ```
 681     fn make_missing_self_suggestion(
 682         &mut self,
 683         span: Span,
 684         mut path: Vec<Segment>,
 685         parent_scope: &ParentScope<'b>,
 686     ) -> Option<(Vec<Segment>, Vec<String>)> {
 687         // Replace first ident with `self` and check if that is valid.
 688         path[0].ident.name = kw::SelfLower;
 689         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 690         debug!("make_missing_self_suggestion: path={:?} result={:?}", path, result);
 691         if let PathResult::Module(..) = result {
 692             Some((path, Vec::new()))
 693         } else {
 694             None
 695         }
 696     }
 697
 698     /// Suggests a missing `crate::` if that resolves to an correct module.
 699     ///
 700     /// ```
 701     ///    |
 702     /// LL | use foo::Bar;
 703     ///    |     ^^^ did you mean `crate::foo`?
 704     /// ```
 705     fn make_missing_crate_suggestion(
 706         &mut self,
 707         span: Span,
 708         mut path: Vec<Segment>,
 709         parent_scope: &ParentScope<'b>,
 710     ) -> Option<(Vec<Segment>, Vec<String>)> {
 711         // Replace first ident with `crate` and check if that is valid.
 712         path[0].ident.name = kw::Crate;
 713         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 714         debug!("make_missing_crate_suggestion:  path={:?} result={:?}", path, result);
 715         if let PathResult::Module(..) = result {
 716             Some((
 717                 path,
 718                 vec![
 719                     "`use` statements changed in Rust 2018; read more at \
 720                      <https://doc.rust-lang.org/edition-guide/rust-2018/module-system/path-\
 721                      clarity.html>".to_string()
 722                 ],
 723             ))
 724         } else {
 725             None
 726         }
 727     }
 728
 729     /// Suggests a missing `super::` if that resolves to an correct module.
 730     ///
 731     /// ```
 732     ///    |
 733     /// LL | use foo::Bar;
 734     ///    |     ^^^ did you mean `super::foo`?
 735     /// ```
 736     fn make_missing_super_suggestion(
 737         &mut self,
 738         span: Span,
 739         mut path: Vec<Segment>,
 740         parent_scope: &ParentScope<'b>,
 741     ) -> Option<(Vec<Segment>, Vec<String>)> {
 742         // Replace first ident with `crate` and check if that is valid.
 743         path[0].ident.name = kw::Super;
 744         let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 745         debug!("make_missing_super_suggestion:  path={:?} result={:?}", path, result);
 746         if let PathResult::Module(..) = result {
 747             Some((path, Vec::new()))
 748         } else {
 749             None
 750         }
 751     }
 752
 753     /// Suggests a missing external crate name if that resolves to an correct module.
 754     ///
 755     /// ```
 756     ///    |
 757     /// LL | use foobar::Baz;
 758     ///    |     ^^^^^^ did you mean `baz::foobar`?
 759     /// ```
 760     ///
 761     /// Used when importing a submodule of an external crate but missing that crate's
 762     /// name as the first part of path.
 763     fn make_external_crate_suggestion(
 764         &mut self,
 765         span: Span,
 766         mut path: Vec<Segment>,
 767         parent_scope: &ParentScope<'b>,
 768     ) -> Option<(Vec<Segment>, Vec<String>)> {
 769         if path[1].ident.span.rust_2015() {
 770             return None;
 771         }
 772
 773         // Sort extern crate names in reverse order to get
 774         // 1) some consistent ordering for emitted dignostics, and
 775         // 2) `std` suggestions before `core` suggestions.
 776         let mut extern_crate_names =
 777             self.r.extern_prelude.iter().map(|(ident, _)| ident.name).collect::<Vec<_>>();
 778         extern_crate_names.sort_by_key(|name| Reverse(name.as_str()));
 779
 780         for name in extern_crate_names.into_iter() {
 781             // Replace first ident with a crate name and check if that is valid.
 782             path[0].ident.name = name;
 783             let result = self.r.resolve_path(&path, None, parent_scope, false, span, CrateLint::No);
 784             debug!("make_external_crate_suggestion: name={:?} path={:?} result={:?}",
 785                     name, path, result);
 786             if let PathResult::Module(..) = result {
 787                 return Some((path, Vec::new()));
 788             }
 789         }
 790
 791         None
 792     }
 793
 794     /// Suggests importing a macro from the root of the crate rather than a module within
 795     /// the crate.
 796     ///
 797     /// ```
 798     /// help: a macro with this name exists at the root of the crate
 799     ///    |
 800     /// LL | use issue_59764::makro;
 801     ///    |     ^^^^^^^^^^^^^^^^^^
 802     ///    |
 803     ///    = note: this could be because a macro annotated with `#[macro_export]` will be exported
 804     ///            at the root of the crate instead of the module where it is defined
 805     /// ```
 806     pub(crate) fn check_for_module_export_macro(
 807         &mut self,
 808         directive: &'b ImportDirective<'b>,
 809         module: ModuleOrUniformRoot<'b>,
 810         ident: Ident,
 811     ) -> Option<(Option<Suggestion>, Vec<String>)> {
 812         let mut crate_module = if let ModuleOrUniformRoot::Module(module) = module {
 813             module
 814         } else {
 815             return None;
 816         };
 817
 818         while let Some(parent) = crate_module.parent {
 819             crate_module = parent;
 820         }
 821
 822         if ModuleOrUniformRoot::same_def(ModuleOrUniformRoot::Module(crate_module), module) {
 823             // Don't make a suggestion if the import was already from the root of the
 824             // crate.
 825             return None;
 826         }
 827
 828         let resolutions = self.r.resolutions(crate_module).borrow();
 829         let resolution = resolutions.get(&(ident, MacroNS))?;
 830         let binding = resolution.borrow().binding()?;
 831         if let Res::Def(DefKind::Macro(MacroKind::Bang), _) = binding.res() {
 832             let module_name = crate_module.kind.name().unwrap();
 833             let import = match directive.subclass {
 834                 ImportDirectiveSubclass::SingleImport { source, target, .. } if source != target =>
 835                     format!("{} as {}", source, target),
 836                 _ => format!("{}", ident),
 837             };
 838
 839             let mut corrections: Vec<(Span, String)> = Vec::new();
 840             if !directive.is_nested() {
 841                 // Assume this is the easy case of `use issue_59764::foo::makro;` and just remove
 842                 // intermediate segments.
 843                 corrections.push((directive.span, format!("{}::{}", module_name, import)));
 844             } else {
 845                 // Find the binding span (and any trailing commas and spaces).
 846                 //   ie. `use a::b::{c, d, e};`
 847                 //                      ^^^
 848                 let (found_closing_brace, binding_span) = find_span_of_binding_until_next_binding(
 849                     self.r.session, directive.span, directive.use_span,
 850                 );
 851                 debug!("check_for_module_export_macro: found_closing_brace={:?} binding_span={:?}",
 852                        found_closing_brace, binding_span);
 853
 854                 let mut removal_span = binding_span;
 855                 if found_closing_brace {
 856                     // If the binding span ended with a closing brace, as in the below example:
 857                     //   ie. `use a::b::{c, d};`
 858                     //                      ^
 859                     // Then expand the span of characters to remove to include the previous
 860                     // binding's trailing comma.
 861                     //   ie. `use a::b::{c, d};`
 862                     //                    ^^^
 863                     if let Some(previous_span) = extend_span_to_previous_binding(
 864                         self.r.session, binding_span,
 865                     ) {
 866                         debug!("check_for_module_export_macro: previous_span={:?}", previous_span);
 867                         removal_span = removal_span.with_lo(previous_span.lo());
 868                     }
 869                 }
 870                 debug!("check_for_module_export_macro: removal_span={:?}", removal_span);
 871
 872                 // Remove the `removal_span`.
 873                 corrections.push((removal_span, "".to_string()));
 874
 875                 // Find the span after the crate name and if it has nested imports immediatately
 876                 // after the crate name already.
 877                 //   ie. `use a::b::{c, d};`
 878                 //               ^^^^^^^^^
 879                 //   or  `use a::{b, c, d}};`
 880                 //               ^^^^^^^^^^^
 881                 let (has_nested, after_crate_name) = find_span_immediately_after_crate_name(
 882                     self.r.session, module_name, directive.use_span,
 883                 );
 884                 debug!("check_for_module_export_macro: has_nested={:?} after_crate_name={:?}",
 885                        has_nested, after_crate_name);
 886
 887                 let source_map = self.r.session.source_map();
 888
 889                 // Add the import to the start, with a `{` if required.
 890                 let start_point = source_map.start_point(after_crate_name);
 891                 if let Ok(start_snippet) = source_map.span_to_snippet(start_point) {
 892                     corrections.push((
 893                         start_point,
 894                         if has_nested {
 895                             // In this case, `start_snippet` must equal '{'.
 896                             format!("{}{}, ", start_snippet, import)
 897                         } else {
 898                             // In this case, add a `{`, then the moved import, then whatever
 899                             // was there before.
 900                             format!("{{{}, {}", import, start_snippet)
 901                         }
 902                     ));
 903                 }
 904
 905                 // Add a `};` to the end if nested, matching the `{` added at the start.
 906                 if !has_nested {
 907                     corrections.push((source_map.end_point(after_crate_name),
 908                                      "};".to_string()));
 909                 }
 910             }
 911
 912             let suggestion = Some((
 913                 corrections,
 914                 String::from("a macro with this name exists at the root of the crate"),
 915                 Applicability::MaybeIncorrect,
 916             ));
 917             let note = vec![
 918                 "this could be because a macro annotated with `#[macro_export]` will be exported \
 919                  at the root of the crate instead of the module where it is defined".to_string(),
 920             ];
 921             Some((suggestion, note))
 922         } else {
 923             None
 924         }
 925     }
 926 }
 927
 928 /// Given a `binding_span` of a binding within a use statement:
 929 ///
 930 /// ```
 931 /// use foo::{a, b, c};
 932 ///              ^
 933 /// ```
 934 ///
 935 /// then return the span until the next binding or the end of the statement:
 936 ///
 937 /// ```
 938 /// use foo::{a, b, c};
 939 ///              ^^^
 940 /// ```
 941 pub(crate) fn find_span_of_binding_until_next_binding(
 942     sess: &Session,
 943     binding_span: Span,
 944     use_span: Span,
 945 ) -> (bool, Span) {
 946     let source_map = sess.source_map();
 947
 948     // Find the span of everything after the binding.
 949     //   ie. `a, e};` or `a};`
 950     let binding_until_end = binding_span.with_hi(use_span.hi());
 951
 952     // Find everything after the binding but not including the binding.
 953     //   ie. `, e};` or `};`
 954     let after_binding_until_end = binding_until_end.with_lo(binding_span.hi());
 955
 956     // Keep characters in the span until we encounter something that isn't a comma or
 957     // whitespace.
 958     //   ie. `, ` or ``.
 959     //
 960     // Also note whether a closing brace character was encountered. If there
 961     // was, then later go backwards to remove any trailing commas that are left.
 962     let mut found_closing_brace = false;
 963     let after_binding_until_next_binding = source_map.span_take_while(
 964         after_binding_until_end,
 965         |&ch| {
 966             if ch == '}' { found_closing_brace = true; }
 967             ch == ' ' || ch == ','
 968         }
 969     );
 970
 971     // Combine the two spans.
 972     //   ie. `a, ` or `a`.
 973     //
 974     // Removing these would leave `issue_52891::{d, e};` or `issue_52891::{d, e, };`
 975     let span = binding_span.with_hi(after_binding_until_next_binding.hi());
 976
 977     (found_closing_brace, span)
 978 }
 979
 980 /// Given a `binding_span`, return the span through to the comma or opening brace of the previous
 981 /// binding.
 982 ///
 983 /// ```
 984 /// use foo::a::{a, b, c};
 985 ///               ^^--- binding span
 986 ///               |
 987 ///               returned span
 988 ///
 989 /// use foo::{a, b, c};
 990 ///           --- binding span
 991 /// ```
 992 pub(crate) fn extend_span_to_previous_binding(
 993     sess: &Session,
 994     binding_span: Span,
 995 ) -> Option<Span> {
 996     let source_map = sess.source_map();
 997
 998     // `prev_source` will contain all of the source that came before the span.
 999     // Then split based on a command and take the first (ie. closest to our span)
1000     // snippet. In the example, this is a space.
1001     let prev_source = source_map.span_to_prev_source(binding_span).ok()?;
1002
1003     let prev_comma = prev_source.rsplit(',').collect::<Vec<_>>();
1004     let prev_starting_brace = prev_source.rsplit('{').collect::<Vec<_>>();
1005     if prev_comma.len() <= 1 || prev_starting_brace.len() <= 1 {
1006         return None;
1007     }
1008
1009     let prev_comma = prev_comma.first().unwrap();
1010     let prev_starting_brace = prev_starting_brace.first().unwrap();
1011
1012     // If the amount of source code before the comma is greater than
1013     // the amount of source code before the starting brace then we've only
1014     // got one item in the nested item (eg. `issue_52891::{self}`).
1015     if prev_comma.len() > prev_starting_brace.len() {
1016         return None;
1017     }
1018
1019     Some(binding_span.with_lo(BytePos(
1020         // Take away the number of bytes for the characters we've found and an
1021         // extra for the comma.
1022         binding_span.lo().0 - (prev_comma.as_bytes().len() as u32) - 1
1023     )))
1024 }
1025
1026 /// Given a `use_span` of a binding within a use statement, returns the highlighted span and if
1027 /// it is a nested use tree.
1028 ///
1029 /// ```
1030 /// use foo::a::{b, c};
1031 ///          ^^^^^^^^^^ // false
1032 ///
1033 /// use foo::{a, b, c};
1034 ///          ^^^^^^^^^^ // true
1035 ///
1036 /// use foo::{a, b::{c, d}};
1037 ///          ^^^^^^^^^^^^^^^ // true
1038 /// ```
1039 fn find_span_immediately_after_crate_name(
1040     sess: &Session,
1041     module_name: Symbol,
1042     use_span: Span,
1043 ) -> (bool, Span) {
1044     debug!("find_span_immediately_after_crate_name: module_name={:?} use_span={:?}",
1045            module_name, use_span);
1046     let source_map = sess.source_map();
1047
1048     // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
1049     let mut num_colons = 0;
1050     // Find second colon.. `use issue_59764:`
1051     let until_second_colon = source_map.span_take_while(use_span, |c| {
1052         if *c == ':' { num_colons += 1; }
1053         match c {
1054             ':' if num_colons == 2 => false,
1055             _ => true,
1056         }
1057     });
1058     // Find everything after the second colon.. `foo::{baz, makro};`
1059     let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
1060
1061     let mut found_a_non_whitespace_character = false;
1062     // Find the first non-whitespace character in `from_second_colon`.. `f`
1063     let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
1064         if found_a_non_whitespace_character { return false; }
1065         if !c.is_whitespace() { found_a_non_whitespace_character = true; }
1066         true
1067     });
1068
1069     // Find the first `{` in from_second_colon.. `foo::{`
1070     let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
1071
1072     (next_left_bracket == after_second_colon, from_second_colon)
1073 }
1074
1075 /// When an entity with a given name is not available in scope, we search for
1076 /// entities with that name in all crates. This method allows outputting the
1077 /// results of this search in a programmer-friendly way
1078 crate fn show_candidates(
1079     err: &mut DiagnosticBuilder<'_>,
1080     // This is `None` if all placement locations are inside expansions
1081     span: Option<Span>,
1082     candidates: &[ImportSuggestion],
1083     better: bool,
1084     found_use: bool,
1085 ) {
1086     // we want consistent results across executions, but candidates are produced
1087     // by iterating through a hash map, so make sure they are ordered:
1088     let mut path_strings: Vec<_> =
1089         candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
1090     path_strings.sort();
1091
1092     let better = if better { "better " } else { "" };
1093     let msg_diff = match path_strings.len() {
1094         1 => " is found in another module, you can import it",
1095         _ => "s are found in other modules, you can import them",
1096     };
1097     let msg = format!("possible {}candidate{} into scope", better, msg_diff);
1098
1099     if let Some(span) = span {
1100         for candidate in &mut path_strings {
1101             // produce an additional newline to separate the new use statement
1102             // from the directly following item.
1103             let additional_newline = if found_use {
1104                 ""
1105             } else {
1106                 "\n"
1107             };
1108             *candidate = format!("use {};\n{}", candidate, additional_newline);
1109         }
1110
1111         err.span_suggestions(
1112             span,
1113             &msg,
1114             path_strings.into_iter(),
1115             Applicability::Unspecified,
1116         );
1117     } else {
1118         let mut msg = msg;
1119         msg.push(':');
1120         for candidate in path_strings {
1121             msg.push('\n');
1122             msg.push_str(&candidate);
1123         }
1124     }
1125 }