1 //! Give useful errors and suggestions to users when an item can't be
2 //! found or is otherwise invalid.
4 use crate::check::FnCtxt;
5 use crate::middle::lang_items::FnOnceTraitLangItem;
6 use crate::namespace::Namespace;
7 use crate::util::nodemap::FxHashSet;
8 use errors::{Applicability, DiagnosticBuilder};
9 use rustc_data_structures::sync::Lrc;
10 use rustc::hir::{self, ExprKind, Node, QPath};
11 use rustc::hir::def::Def;
12 use rustc::hir::def_id::{CRATE_DEF_INDEX, LOCAL_CRATE, DefId};
13 use rustc::hir::map as hir_map;
14 use rustc::hir::print;
15 use rustc::infer::type_variable::TypeVariableOrigin;
16 use rustc::traits::Obligation;
17 use rustc::ty::{self, Ty, TyCtxt, ToPolyTraitRef, ToPredicate, TypeFoldable};
18 use rustc::ty::print::with_crate_prefix;
19 use syntax_pos::{Span, FileName};
21 use syntax::util::lev_distance;
23 use std::cmp::Ordering;
25 use super::{MethodError, NoMatchData, CandidateSource};
26 use super::probe::Mode;
28 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
29 fn is_fn_ty(&self, ty: &Ty<'tcx>, span: Span) -> bool {
32 // Not all of these (e.g., unsafe fns) implement `FnOnce`,
33 // so we look for these beforehand.
37 // If it's not a simple function, look for things which implement `FnOnce`.
39 let fn_once = match tcx.lang_items().require(FnOnceTraitLangItem) {
40 Ok(fn_once) => fn_once,
41 Err(..) => return false,
44 self.autoderef(span, ty).any(|(ty, _)| {
46 let fn_once_substs = tcx.mk_substs_trait(ty, &[
47 self.next_ty_var(TypeVariableOrigin::MiscVariable(span)).into()
49 let trait_ref = ty::TraitRef::new(fn_once, fn_once_substs);
50 let poly_trait_ref = trait_ref.to_poly_trait_ref();
52 Obligation::misc(span,
55 poly_trait_ref.to_predicate());
56 self.predicate_may_hold(&obligation)
63 pub fn report_method_error<'b>(
67 item_name: ast::Ident,
68 source: SelfSource<'b>,
69 error: MethodError<'tcx>,
70 args: Option<&'gcx [hir::Expr]>,
74 // Avoid suggestions when we don't know what's going on.
75 if rcvr_ty.references_error() {
79 let report_candidates = |
81 err: &mut DiagnosticBuilder<'_>,
82 mut sources: Vec<CandidateSource>,
86 // Dynamic limit to avoid hiding just one candidate, which is silly.
87 let limit = if sources.len() == 5 { 5 } else { 4 };
89 for (idx, source) in sources.iter().take(limit).enumerate() {
91 CandidateSource::ImplSource(impl_did) => {
92 // Provide the best span we can. Use the item, if local to crate, else
93 // the impl, if local to crate (item may be defaulted), else nothing.
94 let item = self.associated_item(impl_did, item_name, Namespace::Value)
97 self.tcx.impl_trait_ref(impl_did).unwrap().def_id,
102 let note_span = self.tcx.hir().span_if_local(item.def_id).or_else(|| {
103 self.tcx.hir().span_if_local(impl_did)
106 let impl_ty = self.impl_self_ty(span, impl_did).ty;
108 let insertion = match self.tcx.impl_trait_ref(impl_did) {
109 None => String::new(),
111 format!(" of the trait `{}`",
112 self.tcx.def_path_str(trait_ref.def_id))
116 let note_str = if sources.len() > 1 {
117 format!("candidate #{} is defined in an impl{} for the type `{}`",
122 format!("the candidate is defined in an impl{} for the type `{}`",
126 if let Some(note_span) = note_span {
127 // We have a span pointing to the method. Show note with snippet.
128 err.span_note(self.tcx.sess.source_map().def_span(note_span),
134 CandidateSource::TraitSource(trait_did) => {
136 .associated_item(trait_did, item_name, Namespace::Value)
138 let item_span = self.tcx.sess.source_map()
139 .def_span(self.tcx.def_span(item.def_id));
140 if sources.len() > 1 {
143 "candidate #{} is defined in the trait `{}`",
145 self.tcx.def_path_str(trait_did));
149 "the candidate is defined in the trait `{}`",
150 self.tcx.def_path_str(trait_did));
152 err.help(&format!("to disambiguate the method call, write `{}::{}({}{})` \
154 self.tcx.def_path_str(trait_did),
156 if rcvr_ty.is_region_ptr() && args.is_some() {
157 if rcvr_ty.is_mutable_pointer() {
165 args.map(|arg| arg.iter()
166 .map(|arg| print::to_string(print::NO_ANN,
167 |s| s.print_expr(arg)))
169 .join(", ")).unwrap_or_else(|| "...".to_owned())));
173 if sources.len() > limit {
174 err.note(&format!("and {} others", sources.len() - limit));
179 MethodError::NoMatch(NoMatchData {
180 static_candidates: static_sources,
181 unsatisfied_predicates,
188 let actual = self.resolve_type_vars_if_possible(&rcvr_ty);
189 let ty_str = self.ty_to_string(actual);
190 let is_method = mode == Mode::MethodCall;
191 let item_kind = if is_method {
193 } else if actual.is_enum() {
194 "variant or associated item"
196 match (item_name.as_str().chars().next(), actual.is_fresh_ty()) {
197 (Some(name), false) if name.is_lowercase() => {
198 "function or associated item"
200 (Some(_), false) => "associated item",
201 (Some(_), true) | (None, false) => {
202 "variant or associated item"
204 (None, true) => "variant",
207 let mut err = if !actual.references_error() {
208 // Suggest clamping down the type if the method that is being attempted to
209 // be used exists at all, and the type is an ambiuous numeric type
210 // ({integer}/{float}).
211 let mut candidates = all_traits(self.tcx)
214 self.associated_item(info.def_id, item_name, Namespace::Value)
216 if let (true, false, SelfSource::MethodCall(expr), Some(_)) =
217 (actual.is_numeric(),
218 actual.has_concrete_skeleton(),
221 let mut err = struct_span_err!(
225 "can't call {} `{}` on ambiguous numeric type `{}`",
230 let concrete_type = if actual.is_integral() {
236 ExprKind::Lit(ref lit) => {
238 let snippet = tcx.sess.source_map().span_to_snippet(lit.span)
239 .unwrap_or_else(|_| "<numeric literal>".to_owned());
243 &format!("you must specify a concrete type for \
244 this numeric value, like `{}`", concrete_type),
245 format!("{}_{}", snippet, concrete_type),
246 Applicability::MaybeIncorrect,
249 ExprKind::Path(ref qpath) => {
251 if let &QPath::Resolved(_, ref path) = &qpath {
252 if let hir::def::Def::Local(hir_id) = path.def {
253 let span = tcx.hir().span_by_hir_id(hir_id);
254 let snippet = tcx.sess.source_map().span_to_snippet(span)
256 let filename = tcx.sess.source_map().span_to_filename(span);
258 let parent_node = self.tcx.hir().get_by_hir_id(
259 self.tcx.hir().get_parent_node_by_hir_id(hir_id),
262 "you must specify a type for this binding, like `{}`",
266 match (filename, parent_node) {
267 (FileName::Real(_), Node::Local(hir::Local {
268 source: hir::LocalSource::Normal,
273 // account for `let x: _ = 42;`
275 span.to(ty.as_ref().map(|ty| ty.span)
278 format!("{}: {}", snippet, concrete_type),
279 Applicability::MaybeIncorrect,
283 err.span_label(span, msg);
294 span = item_name.span;
299 "no {} named `{}` found for type `{}` in the current scope",
306 tcx.sess.diagnostic().struct_dummy()
309 if let Some(def) = actual.ty_adt_def() {
310 if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
311 let def_sp = tcx.sess.source_map().def_span(full_sp);
312 err.span_label(def_sp, format!("{} `{}` not found {}",
315 if def.is_enum() && !is_method {
323 // If the method name is the name of a field with a function or closure type,
324 // give a helping note that it has to be called as `(x.f)(...)`.
325 if let SelfSource::MethodCall(expr) = source {
326 let field_receiver = self
327 .autoderef(span, rcvr_ty)
328 .find_map(|(ty, _)| match ty.sty {
329 ty::Adt(def, substs) if !def.is_enum() => {
330 let variant = &def.non_enum_variant();
331 self.tcx.find_field_index(item_name, variant).map(|index| {
332 let field = &variant.fields[index];
333 let field_ty = field.ty(tcx, substs);
340 if let Some((field, field_ty)) = field_receiver {
341 let scope = self.tcx.hir().get_module_parent_by_hir_id(self.body_id);
342 let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
345 if self.is_fn_ty(&field_ty, span) {
346 let expr_span = expr.span.to(item_name.span);
347 err.multipart_suggestion(
349 "to call the function stored in `{}`, \
350 surround the field access with parentheses",
354 (expr_span.shrink_to_lo(), '('.to_string()),
355 (expr_span.shrink_to_hi(), ')'.to_string()),
357 Applicability::MachineApplicable,
360 let call_expr = self.tcx.hir().expect_expr_by_hir_id(
361 self.tcx.hir().get_parent_node_by_hir_id(expr.hir_id),
364 let span = call_expr.span.trim_start(item_name.span).unwrap();
368 "remove the arguments",
370 Applicability::MaybeIncorrect,
375 let field_kind = if is_accessible {
380 err.span_label(item_name.span, format!("{}, not a method", field_kind));
383 err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
384 self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
387 if self.is_fn_ty(&rcvr_ty, span) {
388 macro_rules! report_function {
389 ($span:expr, $name:expr) => {
390 err.note(&format!("{} is a function, perhaps you wish to call it",
395 if let SelfSource::MethodCall(expr) = source {
396 if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
397 report_function!(expr.span, expr_string);
398 } else if let ExprKind::Path(QPath::Resolved(_, ref path)) =
401 if let Some(segment) = path.segments.last() {
402 report_function!(expr.span, segment.ident);
408 if !static_sources.is_empty() {
409 err.note("found the following associated functions; to be used as methods, \
410 functions must have a `self` parameter");
411 err.span_label(span, "this is an associated function, not a method");
413 if static_sources.len() == 1 {
414 if let SelfSource::MethodCall(expr) = source {
415 err.span_suggestion(expr.span.to(span),
416 "use associated function syntax instead",
418 self.ty_to_string(actual),
420 Applicability::MachineApplicable);
422 err.help(&format!("try with `{}::{}`",
423 self.ty_to_string(actual), item_name));
426 report_candidates(span, &mut err, static_sources);
427 } else if static_sources.len() > 1 {
428 report_candidates(span, &mut err, static_sources);
431 if !unsatisfied_predicates.is_empty() {
432 let mut bound_list = unsatisfied_predicates.iter()
433 .map(|p| format!("`{} : {}`", p.self_ty(), p))
434 .collect::<Vec<_>>();
436 bound_list.dedup(); // #35677
437 let bound_list = bound_list.join("\n");
438 err.note(&format!("the method `{}` exists but the following trait bounds \
439 were not satisfied:\n{}",
444 if actual.is_numeric() && actual.is_fresh() {
447 self.suggest_traits_to_import(&mut err,
452 out_of_scope_traits);
455 if actual.is_enum() {
456 let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
457 if let Some(suggestion) = lev_distance::find_best_match_for_name(
458 adt_def.variants.iter().map(|s| &s.ident.name),
464 "there is a variant with a similar name",
465 suggestion.to_string(),
466 Applicability::MaybeIncorrect,
471 if let Some(lev_candidate) = lev_candidate {
472 let def = lev_candidate.def();
476 "there is {} {} with a similar name",
480 lev_candidate.ident.to_string(),
481 Applicability::MaybeIncorrect,
488 MethodError::Ambiguity(sources) => {
489 let mut err = struct_span_err!(self.sess(),
492 "multiple applicable items in scope");
493 err.span_label(span, format!("multiple `{}` found", item_name));
495 report_candidates(span, &mut err, sources);
499 MethodError::PrivateMatch(def, out_of_scope_traits) => {
500 let mut err = struct_span_err!(self.tcx.sess, span, E0624,
501 "{} `{}` is private", def.kind_name(), item_name);
502 self.suggest_valid_traits(&mut err, out_of_scope_traits);
506 MethodError::IllegalSizedBound(candidates) => {
507 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
508 let mut err = self.sess().struct_span_err(span, &msg);
509 if !candidates.is_empty() {
510 let help = format!("{an}other candidate{s} {were} found in the following \
511 trait{s}, perhaps add a `use` for {one_of_them}:",
512 an = if candidates.len() == 1 {"an" } else { "" },
513 s = if candidates.len() == 1 { "" } else { "s" },
514 were = if candidates.len() == 1 { "was" } else { "were" },
515 one_of_them = if candidates.len() == 1 {
520 self.suggest_use_candidates(&mut err, help, candidates);
525 MethodError::BadReturnType => {
526 bug!("no return type expectations but got BadReturnType")
531 fn suggest_use_candidates(&self,
532 err: &mut DiagnosticBuilder<'_>,
534 candidates: Vec<DefId>) {
535 let module_did = self.tcx.hir().get_module_parent_by_hir_id(self.body_id);
536 let module_id = self.tcx.hir().as_local_hir_id(module_did).unwrap();
537 let krate = self.tcx.hir().krate();
538 let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
539 if let Some(span) = span {
540 let path_strings = candidates.iter().map(|did| {
541 // Produce an additional newline to separate the new use statement
542 // from the directly following item.
543 let additional_newline = if found_use {
550 with_crate_prefix(|| self.tcx.def_path_str(*did)),
555 err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
557 let limit = if candidates.len() == 5 { 5 } else { 4 };
558 for (i, trait_did) in candidates.iter().take(limit).enumerate() {
559 if candidates.len() > 1 {
562 "\ncandidate #{}: `use {};`",
564 with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
571 with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
576 if candidates.len() > limit {
577 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
583 fn suggest_valid_traits(&self,
584 err: &mut DiagnosticBuilder<'_>,
585 valid_out_of_scope_traits: Vec<DefId>) -> bool {
586 if !valid_out_of_scope_traits.is_empty() {
587 let mut candidates = valid_out_of_scope_traits;
590 err.help("items from traits can only be used if the trait is in scope");
591 let msg = format!("the following {traits_are} implemented but not in scope, \
592 perhaps add a `use` for {one_of_them}:",
593 traits_are = if candidates.len() == 1 {
598 one_of_them = if candidates.len() == 1 {
604 self.suggest_use_candidates(err, msg, candidates);
611 fn suggest_traits_to_import<'b>(&self,
612 err: &mut DiagnosticBuilder<'_>,
615 item_name: ast::Ident,
616 source: SelfSource<'b>,
617 valid_out_of_scope_traits: Vec<DefId>) {
618 if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
622 let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
624 // There are no traits implemented, so lets suggest some traits to
625 // implement, by finding ones that have the item name, and are
626 // legal to implement.
627 let mut candidates = all_traits(self.tcx)
630 // We approximate the coherence rules to only suggest
631 // traits that are legal to implement by requiring that
632 // either the type or trait is local. Multi-dispatch means
633 // this isn't perfect (that is, there are cases when
634 // implementing a trait would be legal but is rejected
636 (type_is_local || info.def_id.is_local()) &&
637 self.associated_item(info.def_id, item_name, Namespace::Value)
639 // We only want to suggest public or local traits (#45781).
640 item.vis == ty::Visibility::Public || info.def_id.is_local()
644 .collect::<Vec<_>>();
646 if !candidates.is_empty() {
647 // Sort from most relevant to least relevant.
648 candidates.sort_by(|a, b| a.cmp(b).reverse());
651 // FIXME #21673: this help message could be tuned to the case
652 // of a type parameter: suggest adding a trait bound rather
653 // than implementing.
654 err.help("items from traits can only be used if the trait is implemented and in scope");
655 let mut msg = format!("the following {traits_define} an item `{name}`, \
656 perhaps you need to implement {one_of_them}:",
657 traits_define = if candidates.len() == 1 {
662 one_of_them = if candidates.len() == 1 {
669 for (i, trait_info) in candidates.iter().enumerate() {
670 msg.push_str(&format!("\ncandidate #{}: `{}`",
672 self.tcx.def_path_str(trait_info.def_id)));
678 /// Checks whether there is a local type somewhere in the chain of
679 /// autoderefs of `rcvr_ty`.
680 fn type_derefs_to_local(&self,
683 source: SelfSource<'_>) -> bool {
684 fn is_local(ty: Ty<'_>) -> bool {
686 ty::Adt(def, _) => def.did.is_local(),
687 ty::Foreign(did) => did.is_local(),
689 ty::Dynamic(ref tr, ..) =>
690 tr.principal().map(|d| d.def_id().is_local()).unwrap_or(false),
692 ty::Param(_) => true,
694 // Everything else (primitive types, etc.) is effectively
695 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
696 // the noise from these sort of types is usually just really
697 // annoying, rather than any sort of help).
702 // This occurs for UFCS desugaring of `T::method`, where there is no
703 // receiver expression for the method call, and thus no autoderef.
704 if let SelfSource::QPath(_) = source {
705 return is_local(self.resolve_type_vars_with_obligations(rcvr_ty));
708 self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
712 #[derive(Copy, Clone)]
713 pub enum SelfSource<'a> {
715 MethodCall(&'a hir::Expr /* rcvr */),
718 #[derive(Copy, Clone)]
719 pub struct TraitInfo {
723 impl PartialEq for TraitInfo {
724 fn eq(&self, other: &TraitInfo) -> bool {
725 self.cmp(other) == Ordering::Equal
728 impl Eq for TraitInfo {}
729 impl PartialOrd for TraitInfo {
730 fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
731 Some(self.cmp(other))
734 impl Ord for TraitInfo {
735 fn cmp(&self, other: &TraitInfo) -> Ordering {
736 // Local crates are more important than remote ones (local:
737 // `cnum == 0`), and otherwise we throw in the defid for totality.
739 let lhs = (other.def_id.krate, other.def_id);
740 let rhs = (self.def_id.krate, self.def_id);
745 /// Retrieves all traits in this crate and any dependent crates.
746 pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<TraitInfo> {
747 tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
750 /// Computes all traits in this crate and any dependent crates.
751 fn compute_all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<DefId> {
752 use hir::itemlikevisit;
754 let mut traits = vec![];
758 struct Visitor<'a, 'tcx: 'a> {
759 map: &'a hir_map::Map<'tcx>,
760 traits: &'a mut Vec<DefId>,
763 impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
764 fn visit_item(&mut self, i: &'v hir::Item) {
766 hir::ItemKind::Trait(..) |
767 hir::ItemKind::TraitAlias(..) => {
768 let def_id = self.map.local_def_id_from_hir_id(i.hir_id);
769 self.traits.push(def_id);
775 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {}
777 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {}
780 tcx.hir().krate().visit_all_item_likes(&mut Visitor {
787 let mut external_mods = FxHashSet::default();
788 fn handle_external_def(tcx: TyCtxt<'_, '_, '_>,
789 traits: &mut Vec<DefId>,
790 external_mods: &mut FxHashSet<DefId>,
794 Def::TraitAlias(def_id) => {
797 Def::Mod(def_id) => {
798 if !external_mods.insert(def_id) {
801 for child in tcx.item_children(def_id).iter() {
802 handle_external_def(tcx, traits, external_mods, child.def)
808 for &cnum in tcx.crates().iter() {
811 index: CRATE_DEF_INDEX,
813 handle_external_def(tcx, &mut traits, &mut external_mods, Def::Mod(def_id));
819 pub fn provide(providers: &mut ty::query::Providers<'_>) {
820 providers.all_traits = |tcx, cnum| {
821 assert_eq!(cnum, LOCAL_CRATE);
822 Lrc::new(compute_all_traits(tcx))
826 struct UsePlacementFinder<'a, 'tcx: 'a, 'gcx: 'tcx> {
827 target_module: hir::HirId,
830 tcx: TyCtxt<'a, 'gcx, 'tcx>
833 impl<'a, 'tcx, 'gcx> UsePlacementFinder<'a, 'tcx, 'gcx> {
835 tcx: TyCtxt<'a, 'gcx, 'tcx>,
836 krate: &'tcx hir::Crate,
837 target_module: hir::HirId,
838 ) -> (Option<Span>, bool) {
839 let mut finder = UsePlacementFinder {
845 hir::intravisit::walk_crate(&mut finder, krate);
846 (finder.span, finder.found_use)
850 impl<'a, 'tcx, 'gcx> hir::intravisit::Visitor<'tcx> for UsePlacementFinder<'a, 'tcx, 'gcx> {
853 module: &'tcx hir::Mod,
857 if self.span.is_some() {
860 if hir_id != self.target_module {
861 hir::intravisit::walk_mod(self, module, hir_id);
864 // Find a `use` statement.
865 for item_id in &module.item_ids {
866 let item = self.tcx.hir().expect_item_by_hir_id(item_id.id);
868 hir::ItemKind::Use(..) => {
869 // Don't suggest placing a `use` before the prelude
870 // import or other generated ones.
871 if item.span.ctxt().outer().expn_info().is_none() {
872 self.span = Some(item.span.shrink_to_lo());
873 self.found_use = true;
877 // Don't place `use` before `extern crate`...
878 hir::ItemKind::ExternCrate(_) => {}
879 // ...but do place them before the first other item.
880 _ => if self.span.map_or(true, |span| item.span < span ) {
881 if item.span.ctxt().outer().expn_info().is_none() {
882 // Don't insert between attributes and an item.
883 if item.attrs.is_empty() {
884 self.span = Some(item.span.shrink_to_lo());
886 // Find the first attribute on the item.
887 for attr in &item.attrs {
888 if self.span.map_or(true, |span| attr.span < span) {
889 self.span = Some(attr.span.shrink_to_lo());
899 fn nested_visit_map<'this>(
901 ) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
902 hir::intravisit::NestedVisitorMap::None