src/librustc_resolve/late/diagnostics.rs

   1 use crate::diagnostics::{ImportSuggestion, TypoSuggestion};
   2 use crate::late::{LateResolutionVisitor, RibKind};
   3 use crate::path_names_to_string;
   4 use crate::{CrateLint, Module, ModuleKind, ModuleOrUniformRoot};
   5 use crate::{PathResult, PathSource, Segment};
   6
   7 use rustc::session::config::nightly_options;
   8 use rustc_data_structures::fx::FxHashSet;
   9 use rustc_errors::{Applicability, DiagnosticBuilder};
  10 use rustc_hir::def::Namespace::{self, *};
  11 use rustc_hir::def::{self, CtorKind, DefKind};
  12 use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
  13 use rustc_hir::PrimTy;
  14 use rustc_span::hygiene::MacroKind;
  15 use rustc_span::symbol::kw;
  16 use rustc_span::Span;
  17 use syntax::ast::{self, Expr, ExprKind, Ident, NodeId, Path, Ty, TyKind};
  18 use syntax::util::lev_distance::find_best_match_for_name;
  19
  20 use log::debug;
  21
  22 type Res = def::Res<ast::NodeId>;
  23
  24 /// A field or associated item from self type suggested in case of resolution failure.
  25 enum AssocSuggestion {
  26     Field,
  27     MethodWithSelf,
  28     AssocItem,
  29 }
  30
  31 fn is_self_type(path: &[Segment], namespace: Namespace) -> bool {
  32     namespace == TypeNS && path.len() == 1 && path[0].ident.name == kw::SelfUpper
  33 }
  34
  35 fn is_self_value(path: &[Segment], namespace: Namespace) -> bool {
  36     namespace == ValueNS && path.len() == 1 && path[0].ident.name == kw::SelfLower
  37 }
  38
  39 /// Gets the stringified path for an enum from an `ImportSuggestion` for an enum variant.
  40 fn import_candidate_to_enum_paths(suggestion: &ImportSuggestion) -> (String, String) {
  41     let variant_path = &suggestion.path;
  42     let variant_path_string = path_names_to_string(variant_path);
  43
  44     let path_len = suggestion.path.segments.len();
  45     let enum_path = ast::Path {
  46         span: suggestion.path.span,
  47         segments: suggestion.path.segments[0..path_len - 1].to_vec(),
  48     };
  49     let enum_path_string = path_names_to_string(&enum_path);
  50
  51     (variant_path_string, enum_path_string)
  52 }
  53
  54 impl<'a> LateResolutionVisitor<'a, '_> {
  55     /// Handles error reporting for `smart_resolve_path_fragment` function.
  56     /// Creates base error and amends it with one short label and possibly some longer helps/notes.
  57     pub(crate) fn smart_resolve_report_errors(
  58         &mut self,
  59         path: &[Segment],
  60         span: Span,
  61         source: PathSource<'_>,
  62         res: Option<Res>,
  63     ) -> (DiagnosticBuilder<'a>, Vec<ImportSuggestion>) {
  64         let ident_span = path.last().map_or(span, |ident| ident.ident.span);
  65         let ns = source.namespace();
  66         let is_expected = &|res| source.is_expected(res);
  67         let is_enum_variant = &|res| {
  68             if let Res::Def(DefKind::Variant, _) = res { true } else { false }
  69         };
  70
  71         // Make the base error.
  72         let expected = source.descr_expected();
  73         let path_str = Segment::names_to_string(path);
  74         let item_str = path.last().unwrap().ident;
  75         let (base_msg, fallback_label, base_span, could_be_expr) = if let Some(res) = res {
  76             (
  77                 format!("expected {}, found {} `{}`", expected, res.descr(), path_str),
  78                 format!("not a {}", expected),
  79                 span,
  80                 match res {
  81                     Res::Def(DefKind::Fn, _) => {
  82                         // Verify whether this is a fn call or an Fn used as a type.
  83                         self.r
  84                             .session
  85                             .source_map()
  86                             .span_to_snippet(span)
  87                             .map(|snippet| snippet.ends_with(')'))
  88                             .unwrap_or(false)
  89                     }
  90                     Res::Def(DefKind::Ctor(..), _)
  91                     | Res::Def(DefKind::Method, _)
  92                     | Res::Def(DefKind::Const, _)
  93                     | Res::Def(DefKind::AssocConst, _)
  94                     | Res::SelfCtor(_)
  95                     | Res::PrimTy(_)
  96                     | Res::Local(_) => true,
  97                     _ => false,
  98                 },
  99             )
 100         } else {
 101             let item_span = path.last().unwrap().ident.span;
 102             let (mod_prefix, mod_str) = if path.len() == 1 {
 103                 (String::new(), "this scope".to_string())
 104             } else if path.len() == 2 && path[0].ident.name == kw::PathRoot {
 105                 (String::new(), "the crate root".to_string())
 106             } else {
 107                 let mod_path = &path[..path.len() - 1];
 108                 let mod_prefix =
 109                     match self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No) {
 110                         PathResult::Module(ModuleOrUniformRoot::Module(module)) => module.res(),
 111                         _ => None,
 112                     }
 113                     .map_or(String::new(), |res| format!("{} ", res.descr()));
 114                 (mod_prefix, format!("`{}`", Segment::names_to_string(mod_path)))
 115             };
 116             (
 117                 format!("cannot find {} `{}` in {}{}", expected, item_str, mod_prefix, mod_str),
 118                 format!("not found in {}", mod_str),
 119                 item_span,
 120                 false,
 121             )
 122         };
 123
 124         let code = source.error_code(res.is_some());
 125         let mut err = self.r.session.struct_span_err_with_code(base_span, &base_msg, code);
 126
 127         // Emit help message for fake-self from other languages (e.g., `this` in Javascript).
 128         if ["this", "my"].contains(&&*item_str.as_str())
 129             && self.self_value_is_available(path[0].ident.span, span)
 130         {
 131             err.span_suggestion(
 132                 span,
 133                 "did you mean",
 134                 "self".to_string(),
 135                 Applicability::MaybeIncorrect,
 136             );
 137         }
 138
 139         // Emit special messages for unresolved `Self` and `self`.
 140         if is_self_type(path, ns) {
 141             err.code(rustc_errors::error_code!(E0411));
 142             err.span_label(
 143                 span,
 144                 format!("`Self` is only available in impls, traits, and type definitions"),
 145             );
 146             return (err, Vec::new());
 147         }
 148         if is_self_value(path, ns) {
 149             debug!("smart_resolve_path_fragment: E0424, source={:?}", source);
 150
 151             err.code(rustc_errors::error_code!(E0424));
 152             err.span_label(span, match source {
 153                 PathSource::Pat => format!(
 154                     "`self` value is a keyword and may not be bound to variables or shadowed",
 155                 ),
 156                 _ => format!(
 157                     "`self` value is a keyword only available in methods with a `self` parameter",
 158                 ),
 159             });
 160             if let Some(span) = &self.diagnostic_metadata.current_function {
 161                 err.span_label(*span, "this function doesn't have a `self` parameter");
 162             }
 163             return (err, Vec::new());
 164         }
 165
 166         // Try to lookup name in more relaxed fashion for better error reporting.
 167         let ident = path.last().unwrap().ident;
 168         let candidates = self
 169             .r
 170             .lookup_import_candidates(ident, ns, is_expected)
 171             .drain(..)
 172             .filter(|ImportSuggestion { did, .. }| {
 173                 match (did, res.and_then(|res| res.opt_def_id())) {
 174                     (Some(suggestion_did), Some(actual_did)) => *suggestion_did != actual_did,
 175                     _ => true,
 176                 }
 177             })
 178             .collect::<Vec<_>>();
 179         let crate_def_id = DefId::local(CRATE_DEF_INDEX);
 180         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {
 181             let enum_candidates = self.r.lookup_import_candidates(ident, ns, is_enum_variant);
 182             let mut enum_candidates = enum_candidates
 183                 .iter()
 184                 .map(|suggestion| import_candidate_to_enum_paths(&suggestion))
 185                 .collect::<Vec<_>>();
 186             enum_candidates.sort();
 187
 188             if !enum_candidates.is_empty() {
 189                 // Contextualize for E0412 "cannot find type", but don't belabor the point
 190                 // (that it's a variant) for E0573 "expected type, found variant".
 191                 let preamble = if res.is_none() {
 192                     let others = match enum_candidates.len() {
 193                         1 => String::new(),
 194                         2 => " and 1 other".to_owned(),
 195                         n => format!(" and {} others", n),
 196                     };
 197                     format!("there is an enum variant `{}`{}; ", enum_candidates[0].0, others)
 198                 } else {
 199                     String::new()
 200                 };
 201                 let msg = format!("{}try using the variant's enum", preamble);
 202
 203                 err.span_suggestions(
 204                     span,
 205                     &msg,
 206                     enum_candidates
 207                         .into_iter()
 208                         .map(|(_variant_path, enum_ty_path)| enum_ty_path)
 209                         // Variants re-exported in prelude doesn't mean `prelude::v1` is the
 210                         // type name!
 211                         // FIXME: is there a more principled way to do this that
 212                         // would work for other re-exports?
 213                         .filter(|enum_ty_path| enum_ty_path != "std::prelude::v1")
 214                         // Also write `Option` rather than `std::prelude::v1::Option`.
 215                         .map(|enum_ty_path| {
 216                             // FIXME #56861: DRY-er prelude filtering.
 217                             enum_ty_path.trim_start_matches("std::prelude::v1::").to_owned()
 218                         }),
 219                     Applicability::MachineApplicable,
 220                 );
 221             }
 222         }
 223         if path.len() == 1 && self.self_type_is_available(span) {
 224             if let Some(candidate) = self.lookup_assoc_candidate(ident, ns, is_expected) {
 225                 let self_is_available = self.self_value_is_available(path[0].ident.span, span);
 226                 match candidate {
 227                     AssocSuggestion::Field => {
 228                         if self_is_available {
 229                             err.span_suggestion(
 230                                 span,
 231                                 "you might have meant to use the available field",
 232                                 format!("self.{}", path_str),
 233                                 Applicability::MachineApplicable,
 234                             );
 235                         } else {
 236                             err.span_label(span, "a field by this name exists in `Self`");
 237                         }
 238                     }
 239                     AssocSuggestion::MethodWithSelf if self_is_available => {
 240                         err.span_suggestion(
 241                             span,
 242                             "try",
 243                             format!("self.{}", path_str),
 244                             Applicability::MachineApplicable,
 245                         );
 246                     }
 247                     AssocSuggestion::MethodWithSelf | AssocSuggestion::AssocItem => {
 248                         err.span_suggestion(
 249                             span,
 250                             "try",
 251                             format!("Self::{}", path_str),
 252                             Applicability::MachineApplicable,
 253                         );
 254                     }
 255                 }
 256                 return (err, candidates);
 257             }
 258
 259             // If the first argument in call is `self` suggest calling a method.
 260             if let Some((call_span, args_span)) = self.call_has_self_arg(source) {
 261                 let mut args_snippet = String::new();
 262                 if let Some(args_span) = args_span {
 263                     if let Ok(snippet) = self.r.session.source_map().span_to_snippet(args_span) {
 264                         args_snippet = snippet;
 265                     }
 266                 }
 267
 268                 err.span_suggestion(
 269                     call_span,
 270                     &format!("try calling `{}` as a method", ident),
 271                     format!("self.{}({})", path_str, args_snippet),
 272                     Applicability::MachineApplicable,
 273                 );
 274                 return (err, candidates);
 275             }
 276         }
 277
 278         // Try Levenshtein algorithm.
 279         let typo_sugg = self.lookup_typo_candidate(path, ns, is_expected, span);
 280         let levenshtein_worked = self.r.add_typo_suggestion(&mut err, typo_sugg, ident_span);
 281
 282         // Try context-dependent help if relaxed lookup didn't work.
 283         if let Some(res) = res {
 284             if self.smart_resolve_context_dependent_help(
 285                 &mut err,
 286                 span,
 287                 source,
 288                 res,
 289                 &path_str,
 290                 &fallback_label,
 291             ) {
 292                 return (err, candidates);
 293             }
 294         }
 295
 296         // Fallback label.
 297         if !levenshtein_worked {
 298             err.span_label(base_span, fallback_label);
 299             self.type_ascription_suggestion(&mut err, base_span);
 300             match self.diagnostic_metadata.current_let_binding {
 301                 Some((pat_sp, Some(ty_sp), None)) if ty_sp.contains(base_span) && could_be_expr => {
 302                     err.span_suggestion_short(
 303                         pat_sp.between(ty_sp),
 304                         "use `=` if you meant to assign",
 305                         " = ".to_string(),
 306                         Applicability::MaybeIncorrect,
 307                     );
 308                 }
 309                 _ => {}
 310             }
 311         }
 312         (err, candidates)
 313     }
 314
 315     /// Check if the source is call expression and the first argument is `self`. If true,
 316     /// return the span of whole call and the span for all arguments expect the first one (`self`).
 317     fn call_has_self_arg(&self, source: PathSource<'_>) -> Option<(Span, Option<Span>)> {
 318         let mut has_self_arg = None;
 319         if let PathSource::Expr(parent) = source {
 320             match &parent?.kind {
 321                 ExprKind::Call(_, args) if args.len() > 0 => {
 322                     let mut expr_kind = &args[0].kind;
 323                     loop {
 324                         match expr_kind {
 325                             ExprKind::Path(_, arg_name) if arg_name.segments.len() == 1 => {
 326                                 if arg_name.segments[0].ident.name == kw::SelfLower {
 327                                     let call_span = parent.unwrap().span;
 328                                     let tail_args_span = if args.len() > 1 {
 329                                         Some(Span::new(
 330                                             args[1].span.lo(),
 331                                             args.last().unwrap().span.hi(),
 332                                             call_span.ctxt(),
 333                                         ))
 334                                     } else {
 335                                         None
 336                                     };
 337                                     has_self_arg = Some((call_span, tail_args_span));
 338                                 }
 339                                 break;
 340                             }
 341                             ExprKind::AddrOf(_, _, expr) => expr_kind = &expr.kind,
 342                             _ => break,
 343                         }
 344                     }
 345                 }
 346                 _ => (),
 347             }
 348         };
 349         return has_self_arg;
 350     }
 351
 352     fn followed_by_brace(&self, span: Span) -> (bool, Option<(Span, String)>) {
 353         // HACK(estebank): find a better way to figure out that this was a
 354         // parser issue where a struct literal is being used on an expression
 355         // where a brace being opened means a block is being started. Look
 356         // ahead for the next text to see if `span` is followed by a `{`.
 357         let sm = self.r.session.source_map();
 358         let mut sp = span;
 359         loop {
 360             sp = sm.next_point(sp);
 361             match sm.span_to_snippet(sp) {
 362                 Ok(ref snippet) => {
 363                     if snippet.chars().any(|c| !c.is_whitespace()) {
 364                         break;
 365                     }
 366                 }
 367                 _ => break,
 368             }
 369         }
 370         let followed_by_brace = match sm.span_to_snippet(sp) {
 371             Ok(ref snippet) if snippet == "{" => true,
 372             _ => false,
 373         };
 374         // In case this could be a struct literal that needs to be surrounded
 375         // by parenthesis, find the appropriate span.
 376         let mut i = 0;
 377         let mut closing_brace = None;
 378         loop {
 379             sp = sm.next_point(sp);
 380             match sm.span_to_snippet(sp) {
 381                 Ok(ref snippet) => {
 382                     if snippet == "}" {
 383                         let sp = span.to(sp);
 384                         if let Ok(snippet) = sm.span_to_snippet(sp) {
 385                             closing_brace = Some((sp, snippet));
 386                         }
 387                         break;
 388                     }
 389                 }
 390                 _ => break,
 391             }
 392             i += 1;
 393             // The bigger the span, the more likely we're incorrect --
 394             // bound it to 100 chars long.
 395             if i > 100 {
 396                 break;
 397             }
 398         }
 399         return (followed_by_brace, closing_brace);
 400     }
 401
 402     /// Provides context-dependent help for errors reported by the `smart_resolve_path_fragment`
 403     /// function.
 404     /// Returns `true` if able to provide context-dependent help.
 405     fn smart_resolve_context_dependent_help(
 406         &mut self,
 407         err: &mut DiagnosticBuilder<'a>,
 408         span: Span,
 409         source: PathSource<'_>,
 410         res: Res,
 411         path_str: &str,
 412         fallback_label: &str,
 413     ) -> bool {
 414         let ns = source.namespace();
 415         let is_expected = &|res| source.is_expected(res);
 416
 417         let path_sep = |err: &mut DiagnosticBuilder<'_>, expr: &Expr| match expr.kind {
 418             ExprKind::Field(_, ident) => {
 419                 err.span_suggestion(
 420                     expr.span,
 421                     "use the path separator to refer to an item",
 422                     format!("{}::{}", path_str, ident),
 423                     Applicability::MaybeIncorrect,
 424                 );
 425                 true
 426             }
 427             ExprKind::MethodCall(ref segment, ..) => {
 428                 let span = expr.span.with_hi(segment.ident.span.hi());
 429                 err.span_suggestion(
 430                     span,
 431                     "use the path separator to refer to an item",
 432                     format!("{}::{}", path_str, segment.ident),
 433                     Applicability::MaybeIncorrect,
 434                 );
 435                 true
 436             }
 437             _ => false,
 438         };
 439
 440         let mut bad_struct_syntax_suggestion = |def_id: DefId| {
 441             let (followed_by_brace, closing_brace) = self.followed_by_brace(span);
 442             let mut suggested = false;
 443             match source {
 444                 PathSource::Expr(Some(parent)) => {
 445                     suggested = path_sep(err, &parent);
 446                 }
 447                 PathSource::Expr(None) if followed_by_brace == true => {
 448                     if let Some((sp, snippet)) = closing_brace {
 449                         err.span_suggestion(
 450                             sp,
 451                             "surround the struct literal with parenthesis",
 452                             format!("({})", snippet),
 453                             Applicability::MaybeIncorrect,
 454                         );
 455                     } else {
 456                         err.span_label(
 457                             span, // Note the parenthesis surrounding the suggestion below
 458                             format!("did you mean `({} {{ /* fields */ }})`?", path_str),
 459                         );
 460                     }
 461                     suggested = true;
 462                 }
 463                 _ => {}
 464             }
 465             if !suggested {
 466                 if let Some(span) = self.r.definitions.opt_span(def_id) {
 467                     err.span_label(span, &format!("`{}` defined here", path_str));
 468                 }
 469                 err.span_label(span, format!("did you mean `{} {{ /* fields */ }}`?", path_str));
 470             }
 471         };
 472
 473         match (res, source) {
 474             (Res::Def(DefKind::Macro(MacroKind::Bang), _), _) => {
 475                 err.span_suggestion(
 476                     span,
 477                     "use `!` to invoke the macro",
 478                     format!("{}!", path_str),
 479                     Applicability::MaybeIncorrect,
 480                 );
 481                 if path_str == "try" && span.rust_2015() {
 482                     err.note("if you want the `try` keyword, you need to be in the 2018 edition");
 483                 }
 484             }
 485             (Res::Def(DefKind::TyAlias, _), PathSource::Trait(_)) => {
 486                 err.span_label(span, "type aliases cannot be used as traits");
 487                 if nightly_options::is_nightly_build() {
 488                     err.note("did you mean to use a trait alias?");
 489                 }
 490             }
 491             (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
 492                 if !path_sep(err, &parent) {
 493                     return false;
 494                 }
 495             }
 496             (Res::Def(DefKind::Enum, def_id), PathSource::TupleStruct)
 497             | (Res::Def(DefKind::Enum, def_id), PathSource::Expr(..)) => {
 498                 if let Some(variants) = self.collect_enum_variants(def_id) {
 499                     if !variants.is_empty() {
 500                         let msg = if variants.len() == 1 {
 501                             "try using the enum's variant"
 502                         } else {
 503                             "try using one of the enum's variants"
 504                         };
 505
 506                         err.span_suggestions(
 507                             span,
 508                             msg,
 509                             variants.iter().map(path_names_to_string),
 510                             Applicability::MaybeIncorrect,
 511                         );
 512                     }
 513                 } else {
 514                     err.note("did you mean to use one of the enum's variants?");
 515                 }
 516             }
 517             (Res::Def(DefKind::Struct, def_id), _) if ns == ValueNS => {
 518                 if let Some((ctor_def, ctor_vis)) = self.r.struct_constructors.get(&def_id).cloned()
 519                 {
 520                     let accessible_ctor =
 521                         self.r.is_accessible_from(ctor_vis, self.parent_scope.module);
 522                     if is_expected(ctor_def) && !accessible_ctor {
 523                         err.span_label(
 524                             span,
 525                             format!("constructor is not visible here due to private fields"),
 526                         );
 527                     }
 528                 } else {
 529                     bad_struct_syntax_suggestion(def_id);
 530                 }
 531             }
 532             (Res::Def(DefKind::Union, def_id), _)
 533             | (Res::Def(DefKind::Variant, def_id), _)
 534             | (Res::Def(DefKind::Ctor(_, CtorKind::Fictive), def_id), _)
 535                 if ns == ValueNS =>
 536             {
 537                 bad_struct_syntax_suggestion(def_id);
 538             }
 539             (Res::Def(DefKind::Ctor(_, CtorKind::Fn), def_id), _) if ns == ValueNS => {
 540                 if let Some(span) = self.r.definitions.opt_span(def_id) {
 541                     err.span_label(span, &format!("`{}` defined here", path_str));
 542                 }
 543                 err.span_label(span, format!("did you mean `{}( /* fields */ )`?", path_str));
 544             }
 545             (Res::SelfTy(..), _) if ns == ValueNS => {
 546                 err.span_label(span, fallback_label);
 547                 err.note("can't use `Self` as a constructor, you must use the implemented struct");
 548             }
 549             (Res::Def(DefKind::TyAlias, _), _) | (Res::Def(DefKind::AssocTy, _), _)
 550                 if ns == ValueNS =>
 551             {
 552                 err.note("can't use a type alias as a constructor");
 553             }
 554             _ => return false,
 555         }
 556         true
 557     }
 558
 559     fn lookup_assoc_candidate<FilterFn>(
 560         &mut self,
 561         ident: Ident,
 562         ns: Namespace,
 563         filter_fn: FilterFn,
 564     ) -> Option<AssocSuggestion>
 565     where
 566         FilterFn: Fn(Res) -> bool,
 567     {
 568         fn extract_node_id(t: &Ty) -> Option<NodeId> {
 569             match t.kind {
 570                 TyKind::Path(None, _) => Some(t.id),
 571                 TyKind::Rptr(_, ref mut_ty) => extract_node_id(&mut_ty.ty),
 572                 // This doesn't handle the remaining `Ty` variants as they are not
 573                 // that commonly the self_type, it might be interesting to provide
 574                 // support for those in future.
 575                 _ => None,
 576             }
 577         }
 578
 579         // Fields are generally expected in the same contexts as locals.
 580         if filter_fn(Res::Local(ast::DUMMY_NODE_ID)) {
 581             if let Some(node_id) =
 582                 self.diagnostic_metadata.current_self_type.as_ref().and_then(extract_node_id)
 583             {
 584                 // Look for a field with the same name in the current self_type.
 585                 if let Some(resolution) = self.r.partial_res_map.get(&node_id) {
 586                     match resolution.base_res() {
 587                         Res::Def(DefKind::Struct, did) | Res::Def(DefKind::Union, did)
 588                             if resolution.unresolved_segments() == 0 =>
 589                         {
 590                             if let Some(field_names) = self.r.field_names.get(&did) {
 591                                 if field_names
 592                                     .iter()
 593                                     .any(|&field_name| ident.name == field_name.node)
 594                                 {
 595                                     return Some(AssocSuggestion::Field);
 596                                 }
 597                             }
 598                         }
 599                         _ => {}
 600                     }
 601                 }
 602             }
 603         }
 604
 605         for assoc_type_ident in &self.diagnostic_metadata.current_trait_assoc_types {
 606             if *assoc_type_ident == ident {
 607                 return Some(AssocSuggestion::AssocItem);
 608             }
 609         }
 610
 611         // Look for associated items in the current trait.
 612         if let Some((module, _)) = self.current_trait_ref {
 613             if let Ok(binding) = self.r.resolve_ident_in_module(
 614                 ModuleOrUniformRoot::Module(module),
 615                 ident,
 616                 ns,
 617                 &self.parent_scope,
 618                 false,
 619                 module.span,
 620             ) {
 621                 let res = binding.res();
 622                 if filter_fn(res) {
 623                     return Some(if self.r.has_self.contains(&res.def_id()) {
 624                         AssocSuggestion::MethodWithSelf
 625                     } else {
 626                         AssocSuggestion::AssocItem
 627                     });
 628                 }
 629             }
 630         }
 631
 632         None
 633     }
 634
 635     fn lookup_typo_candidate(
 636         &mut self,
 637         path: &[Segment],
 638         ns: Namespace,
 639         filter_fn: &impl Fn(Res) -> bool,
 640         span: Span,
 641     ) -> Option<TypoSuggestion> {
 642         let mut names = Vec::new();
 643         if path.len() == 1 {
 644             // Search in lexical scope.
 645             // Walk backwards up the ribs in scope and collect candidates.
 646             for rib in self.ribs[ns].iter().rev() {
 647                 // Locals and type parameters
 648                 for (ident, &res) in &rib.bindings {
 649                     if filter_fn(res) {
 650                         names.push(TypoSuggestion::from_res(ident.name, res));
 651                     }
 652                 }
 653                 // Items in scope
 654                 if let RibKind::ModuleRibKind(module) = rib.kind {
 655                     // Items from this module
 656                     self.r.add_module_candidates(module, &mut names, &filter_fn);
 657
 658                     if let ModuleKind::Block(..) = module.kind {
 659                         // We can see through blocks
 660                     } else {
 661                         // Items from the prelude
 662                         if !module.no_implicit_prelude {
 663                             let extern_prelude = self.r.extern_prelude.clone();
 664                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
 665                                 self.r
 666                                     .crate_loader
 667                                     .maybe_process_path_extern(ident.name, ident.span)
 668                                     .and_then(|crate_id| {
 669                                         let crate_mod = Res::Def(
 670                                             DefKind::Mod,
 671                                             DefId { krate: crate_id, index: CRATE_DEF_INDEX },
 672                                         );
 673
 674                                         if filter_fn(crate_mod) {
 675                                             Some(TypoSuggestion::from_res(ident.name, crate_mod))
 676                                         } else {
 677                                             None
 678                                         }
 679                                     })
 680                             }));
 681
 682                             if let Some(prelude) = self.r.prelude {
 683                                 self.r.add_module_candidates(prelude, &mut names, &filter_fn);
 684                             }
 685                         }
 686                         break;
 687                     }
 688                 }
 689             }
 690             // Add primitive types to the mix
 691             if filter_fn(Res::PrimTy(PrimTy::Bool)) {
 692                 names.extend(
 693                     self.r.primitive_type_table.primitive_types.iter().map(|(name, prim_ty)| {
 694                         TypoSuggestion::from_res(*name, Res::PrimTy(*prim_ty))
 695                     }),
 696                 )
 697             }
 698         } else {
 699             // Search in module.
 700             let mod_path = &path[..path.len() - 1];
 701             if let PathResult::Module(module) =
 702                 self.resolve_path(mod_path, Some(TypeNS), false, span, CrateLint::No)
 703             {
 704                 if let ModuleOrUniformRoot::Module(module) = module {
 705                     self.r.add_module_candidates(module, &mut names, &filter_fn);
 706                 }
 707             }
 708         }
 709
 710         let name = path[path.len() - 1].ident.name;
 711         // Make sure error reporting is deterministic.
 712         names.sort_by_cached_key(|suggestion| suggestion.candidate.as_str());
 713
 714         match find_best_match_for_name(
 715             names.iter().map(|suggestion| &suggestion.candidate),
 716             &name.as_str(),
 717             None,
 718         ) {
 719             Some(found) if found != name => {
 720                 names.into_iter().find(|suggestion| suggestion.candidate == found)
 721             }
 722             _ => None,
 723         }
 724     }
 725
 726     /// Only used in a specific case of type ascription suggestions
 727     fn get_colon_suggestion_span(&self, start: Span) -> Span {
 728         let cm = self.r.session.source_map();
 729         start.to(cm.next_point(start))
 730     }
 731
 732     fn type_ascription_suggestion(&self, err: &mut DiagnosticBuilder<'_>, base_span: Span) {
 733         let cm = self.r.session.source_map();
 734         let base_snippet = cm.span_to_snippet(base_span);
 735         if let Some(sp) = self.diagnostic_metadata.current_type_ascription.last() {
 736             let mut sp = *sp;
 737             loop {
 738                 // Try to find the `:`; bail on first non-':' / non-whitespace.
 739                 sp = cm.next_point(sp);
 740                 if let Ok(snippet) = cm.span_to_snippet(sp.to(cm.next_point(sp))) {
 741                     let line_sp = cm.lookup_char_pos(sp.hi()).line;
 742                     let line_base_sp = cm.lookup_char_pos(base_span.lo()).line;
 743                     if snippet == ":" {
 744                         let mut show_label = true;
 745                         if line_sp != line_base_sp {
 746                             err.span_suggestion_short(
 747                                 sp,
 748                                 "did you mean to use `;` here instead?",
 749                                 ";".to_string(),
 750                                 Applicability::MaybeIncorrect,
 751                             );
 752                         } else {
 753                             let colon_sp = self.get_colon_suggestion_span(sp);
 754                             let after_colon_sp =
 755                                 self.get_colon_suggestion_span(colon_sp.shrink_to_hi());
 756                             if !cm
 757                                 .span_to_snippet(after_colon_sp)
 758                                 .map(|s| s == " ")
 759                                 .unwrap_or(false)
 760                             {
 761                                 err.span_suggestion(
 762                                     colon_sp,
 763                                     "maybe you meant to write a path separator here",
 764                                     "::".to_string(),
 765                                     Applicability::MaybeIncorrect,
 766                                 );
 767                                 show_label = false;
 768                             }
 769                             if let Ok(base_snippet) = base_snippet {
 770                                 let mut sp = after_colon_sp;
 771                                 for _ in 0..100 {
 772                                     // Try to find an assignment
 773                                     sp = cm.next_point(sp);
 774                                     let snippet = cm.span_to_snippet(sp.to(cm.next_point(sp)));
 775                                     match snippet {
 776                                         Ok(ref x) if x.as_str() == "=" => {
 777                                             err.span_suggestion(
 778                                                 base_span,
 779                                                 "maybe you meant to write an assignment here",
 780                                                 format!("let {}", base_snippet),
 781                                                 Applicability::MaybeIncorrect,
 782                                             );
 783                                             show_label = false;
 784                                             break;
 785                                         }
 786                                         Ok(ref x) if x.as_str() == "\n" => break,
 787                                         Err(_) => break,
 788                                         Ok(_) => {}
 789                                     }
 790                                 }
 791                             }
 792                         }
 793                         if show_label {
 794                             err.span_label(
 795                                 base_span,
 796                                 "expecting a type here because of type ascription",
 797                             );
 798                         }
 799                         break;
 800                     } else if !snippet.trim().is_empty() {
 801                         debug!("tried to find type ascription `:` token, couldn't find it");
 802                         break;
 803                     }
 804                 } else {
 805                     break;
 806                 }
 807             }
 808         }
 809     }
 810
 811     fn find_module(&mut self, def_id: DefId) -> Option<(Module<'a>, ImportSuggestion)> {
 812         let mut result = None;
 813         let mut seen_modules = FxHashSet::default();
 814         let mut worklist = vec![(self.r.graph_root, Vec::new())];
 815
 816         while let Some((in_module, path_segments)) = worklist.pop() {
 817             // abort if the module is already found
 818             if result.is_some() {
 819                 break;
 820             }
 821
 822             in_module.for_each_child(self.r, |_, ident, _, name_binding| {
 823                 // abort if the module is already found or if name_binding is private external
 824                 if result.is_some() || !name_binding.vis.is_visible_locally() {
 825                     return;
 826                 }
 827                 if let Some(module) = name_binding.module() {
 828                     // form the path
 829                     let mut path_segments = path_segments.clone();
 830                     path_segments.push(ast::PathSegment::from_ident(ident));
 831                     let module_def_id = module.def_id().unwrap();
 832                     if module_def_id == def_id {
 833                         let path = Path { span: name_binding.span, segments: path_segments };
 834                         result = Some((module, ImportSuggestion { did: Some(def_id), path }));
 835                     } else {
 836                         // add the module to the lookup
 837                         if seen_modules.insert(module_def_id) {
 838                             worklist.push((module, path_segments));
 839                         }
 840                     }
 841                 }
 842             });
 843         }
 844
 845         result
 846     }
 847
 848     fn collect_enum_variants(&mut self, def_id: DefId) -> Option<Vec<Path>> {
 849         self.find_module(def_id).map(|(enum_module, enum_import_suggestion)| {
 850             let mut variants = Vec::new();
 851             enum_module.for_each_child(self.r, |_, ident, _, name_binding| {
 852                 if let Res::Def(DefKind::Variant, _) = name_binding.res() {
 853                     let mut segms = enum_import_suggestion.path.segments.clone();
 854                     segms.push(ast::PathSegment::from_ident(ident));
 855                     variants.push(Path { span: name_binding.span, segments: segms });
 856                 }
 857             });
 858             variants
 859         })
 860     }
 861 }