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;
295 let mut err = struct_span_err!(
299 "no {} named `{}` found for type `{}` in the current scope",
304 if let Some(span) = tcx.sess.confused_type_with_std_module.borrow()
307 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*span) {
310 "you are looking for the module in `std`, \
311 not the primitive type",
312 format!("std::{}", snippet),
313 Applicability::MachineApplicable,
320 tcx.sess.diagnostic().struct_dummy()
323 if let Some(def) = actual.ty_adt_def() {
324 if let Some(full_sp) = tcx.hir().span_if_local(def.did) {
325 let def_sp = tcx.sess.source_map().def_span(full_sp);
326 err.span_label(def_sp, format!("{} `{}` not found {}",
329 if def.is_enum() && !is_method {
337 // If the method name is the name of a field with a function or closure type,
338 // give a helping note that it has to be called as `(x.f)(...)`.
339 if let SelfSource::MethodCall(expr) = source {
340 let field_receiver = self
341 .autoderef(span, rcvr_ty)
342 .find_map(|(ty, _)| match ty.sty {
343 ty::Adt(def, substs) if !def.is_enum() => {
344 let variant = &def.non_enum_variant();
345 self.tcx.find_field_index(item_name, variant).map(|index| {
346 let field = &variant.fields[index];
347 let field_ty = field.ty(tcx, substs);
354 if let Some((field, field_ty)) = field_receiver {
355 let scope = self.tcx.hir().get_module_parent_by_hir_id(self.body_id);
356 let is_accessible = field.vis.is_accessible_from(scope, self.tcx);
359 if self.is_fn_ty(&field_ty, span) {
360 let expr_span = expr.span.to(item_name.span);
361 err.multipart_suggestion(
363 "to call the function stored in `{}`, \
364 surround the field access with parentheses",
368 (expr_span.shrink_to_lo(), '('.to_string()),
369 (expr_span.shrink_to_hi(), ')'.to_string()),
371 Applicability::MachineApplicable,
374 let call_expr = self.tcx.hir().expect_expr_by_hir_id(
375 self.tcx.hir().get_parent_node_by_hir_id(expr.hir_id),
378 let span = call_expr.span.trim_start(item_name.span).unwrap();
382 "remove the arguments",
384 Applicability::MaybeIncorrect,
389 let field_kind = if is_accessible {
394 err.span_label(item_name.span, format!("{}, not a method", field_kind));
397 err.span_label(span, format!("{} not found in `{}`", item_kind, ty_str));
398 self.tcx.sess.trait_methods_not_found.borrow_mut().insert(orig_span);
401 if self.is_fn_ty(&rcvr_ty, span) {
402 macro_rules! report_function {
403 ($span:expr, $name:expr) => {
404 err.note(&format!("{} is a function, perhaps you wish to call it",
409 if let SelfSource::MethodCall(expr) = source {
410 if let Ok(expr_string) = tcx.sess.source_map().span_to_snippet(expr.span) {
411 report_function!(expr.span, expr_string);
412 } else if let ExprKind::Path(QPath::Resolved(_, ref path)) =
415 if let Some(segment) = path.segments.last() {
416 report_function!(expr.span, segment.ident);
422 if !static_sources.is_empty() {
423 err.note("found the following associated functions; to be used as methods, \
424 functions must have a `self` parameter");
425 err.span_label(span, "this is an associated function, not a method");
427 if static_sources.len() == 1 {
428 if let SelfSource::MethodCall(expr) = source {
429 err.span_suggestion(expr.span.to(span),
430 "use associated function syntax instead",
432 self.ty_to_string(actual),
434 Applicability::MachineApplicable);
436 err.help(&format!("try with `{}::{}`",
437 self.ty_to_string(actual), item_name));
440 report_candidates(span, &mut err, static_sources);
441 } else if static_sources.len() > 1 {
442 report_candidates(span, &mut err, static_sources);
445 if !unsatisfied_predicates.is_empty() {
446 let mut bound_list = unsatisfied_predicates.iter()
447 .map(|p| format!("`{} : {}`", p.self_ty(), p))
448 .collect::<Vec<_>>();
450 bound_list.dedup(); // #35677
451 let bound_list = bound_list.join("\n");
452 err.note(&format!("the method `{}` exists but the following trait bounds \
453 were not satisfied:\n{}",
458 if actual.is_numeric() && actual.is_fresh() {
461 self.suggest_traits_to_import(&mut err,
466 out_of_scope_traits);
469 if actual.is_enum() {
470 let adt_def = actual.ty_adt_def().expect("enum is not an ADT");
471 if let Some(suggestion) = lev_distance::find_best_match_for_name(
472 adt_def.variants.iter().map(|s| &s.ident.name),
478 "there is a variant with a similar name",
479 suggestion.to_string(),
480 Applicability::MaybeIncorrect,
485 if let Some(lev_candidate) = lev_candidate {
486 let def = lev_candidate.def();
490 "there is {} {} with a similar name",
494 lev_candidate.ident.to_string(),
495 Applicability::MaybeIncorrect,
502 MethodError::Ambiguity(sources) => {
503 let mut err = struct_span_err!(self.sess(),
506 "multiple applicable items in scope");
507 err.span_label(span, format!("multiple `{}` found", item_name));
509 report_candidates(span, &mut err, sources);
513 MethodError::PrivateMatch(def, out_of_scope_traits) => {
514 let mut err = struct_span_err!(self.tcx.sess, span, E0624,
515 "{} `{}` is private", def.kind_name(), item_name);
516 self.suggest_valid_traits(&mut err, out_of_scope_traits);
520 MethodError::IllegalSizedBound(candidates) => {
521 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
522 let mut err = self.sess().struct_span_err(span, &msg);
523 if !candidates.is_empty() {
524 let help = format!("{an}other candidate{s} {were} found in the following \
525 trait{s}, perhaps add a `use` for {one_of_them}:",
526 an = if candidates.len() == 1 {"an" } else { "" },
527 s = if candidates.len() == 1 { "" } else { "s" },
528 were = if candidates.len() == 1 { "was" } else { "were" },
529 one_of_them = if candidates.len() == 1 {
534 self.suggest_use_candidates(&mut err, help, candidates);
539 MethodError::BadReturnType => {
540 bug!("no return type expectations but got BadReturnType")
545 fn suggest_use_candidates(&self,
546 err: &mut DiagnosticBuilder<'_>,
548 candidates: Vec<DefId>) {
549 let module_did = self.tcx.hir().get_module_parent_by_hir_id(self.body_id);
550 let module_id = self.tcx.hir().as_local_hir_id(module_did).unwrap();
551 let krate = self.tcx.hir().krate();
552 let (span, found_use) = UsePlacementFinder::check(self.tcx, krate, module_id);
553 if let Some(span) = span {
554 let path_strings = candidates.iter().map(|did| {
555 // Produce an additional newline to separate the new use statement
556 // from the directly following item.
557 let additional_newline = if found_use {
564 with_crate_prefix(|| self.tcx.def_path_str(*did)),
569 err.span_suggestions(span, &msg, path_strings, Applicability::MaybeIncorrect);
571 let limit = if candidates.len() == 5 { 5 } else { 4 };
572 for (i, trait_did) in candidates.iter().take(limit).enumerate() {
573 if candidates.len() > 1 {
576 "\ncandidate #{}: `use {};`",
578 with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
585 with_crate_prefix(|| self.tcx.def_path_str(*trait_did))
590 if candidates.len() > limit {
591 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
597 fn suggest_valid_traits(&self,
598 err: &mut DiagnosticBuilder<'_>,
599 valid_out_of_scope_traits: Vec<DefId>) -> bool {
600 if !valid_out_of_scope_traits.is_empty() {
601 let mut candidates = valid_out_of_scope_traits;
604 err.help("items from traits can only be used if the trait is in scope");
605 let msg = format!("the following {traits_are} implemented but not in scope, \
606 perhaps add a `use` for {one_of_them}:",
607 traits_are = if candidates.len() == 1 {
612 one_of_them = if candidates.len() == 1 {
618 self.suggest_use_candidates(err, msg, candidates);
625 fn suggest_traits_to_import<'b>(&self,
626 err: &mut DiagnosticBuilder<'_>,
629 item_name: ast::Ident,
630 source: SelfSource<'b>,
631 valid_out_of_scope_traits: Vec<DefId>) {
632 if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
636 let type_is_local = self.type_derefs_to_local(span, rcvr_ty, source);
638 // There are no traits implemented, so lets suggest some traits to
639 // implement, by finding ones that have the item name, and are
640 // legal to implement.
641 let mut candidates = all_traits(self.tcx)
644 // We approximate the coherence rules to only suggest
645 // traits that are legal to implement by requiring that
646 // either the type or trait is local. Multi-dispatch means
647 // this isn't perfect (that is, there are cases when
648 // implementing a trait would be legal but is rejected
650 (type_is_local || info.def_id.is_local()) &&
651 self.associated_item(info.def_id, item_name, Namespace::Value)
653 // We only want to suggest public or local traits (#45781).
654 item.vis == ty::Visibility::Public || info.def_id.is_local()
658 .collect::<Vec<_>>();
660 if !candidates.is_empty() {
661 // Sort from most relevant to least relevant.
662 candidates.sort_by(|a, b| a.cmp(b).reverse());
665 // FIXME #21673: this help message could be tuned to the case
666 // of a type parameter: suggest adding a trait bound rather
667 // than implementing.
668 err.help("items from traits can only be used if the trait is implemented and in scope");
669 let mut msg = format!("the following {traits_define} an item `{name}`, \
670 perhaps you need to implement {one_of_them}:",
671 traits_define = if candidates.len() == 1 {
676 one_of_them = if candidates.len() == 1 {
683 for (i, trait_info) in candidates.iter().enumerate() {
684 msg.push_str(&format!("\ncandidate #{}: `{}`",
686 self.tcx.def_path_str(trait_info.def_id)));
692 /// Checks whether there is a local type somewhere in the chain of
693 /// autoderefs of `rcvr_ty`.
694 fn type_derefs_to_local(&self,
697 source: SelfSource<'_>) -> bool {
698 fn is_local(ty: Ty<'_>) -> bool {
700 ty::Adt(def, _) => def.did.is_local(),
701 ty::Foreign(did) => did.is_local(),
703 ty::Dynamic(ref tr, ..) =>
704 tr.principal().map(|d| d.def_id().is_local()).unwrap_or(false),
706 ty::Param(_) => true,
708 // Everything else (primitive types, etc.) is effectively
709 // non-local (there are "edge" cases, e.g., `(LocalType,)`, but
710 // the noise from these sort of types is usually just really
711 // annoying, rather than any sort of help).
716 // This occurs for UFCS desugaring of `T::method`, where there is no
717 // receiver expression for the method call, and thus no autoderef.
718 if let SelfSource::QPath(_) = source {
719 return is_local(self.resolve_type_vars_with_obligations(rcvr_ty));
722 self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
726 #[derive(Copy, Clone)]
727 pub enum SelfSource<'a> {
729 MethodCall(&'a hir::Expr /* rcvr */),
732 #[derive(Copy, Clone)]
733 pub struct TraitInfo {
737 impl PartialEq for TraitInfo {
738 fn eq(&self, other: &TraitInfo) -> bool {
739 self.cmp(other) == Ordering::Equal
742 impl Eq for TraitInfo {}
743 impl PartialOrd for TraitInfo {
744 fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
745 Some(self.cmp(other))
748 impl Ord for TraitInfo {
749 fn cmp(&self, other: &TraitInfo) -> Ordering {
750 // Local crates are more important than remote ones (local:
751 // `cnum == 0`), and otherwise we throw in the defid for totality.
753 let lhs = (other.def_id.krate, other.def_id);
754 let rhs = (self.def_id.krate, self.def_id);
759 /// Retrieves all traits in this crate and any dependent crates.
760 pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<TraitInfo> {
761 tcx.all_traits(LOCAL_CRATE).iter().map(|&def_id| TraitInfo { def_id }).collect()
764 /// Computes all traits in this crate and any dependent crates.
765 fn compute_all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Vec<DefId> {
766 use hir::itemlikevisit;
768 let mut traits = vec![];
772 struct Visitor<'a, 'tcx: 'a> {
773 map: &'a hir_map::Map<'tcx>,
774 traits: &'a mut Vec<DefId>,
777 impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
778 fn visit_item(&mut self, i: &'v hir::Item) {
780 hir::ItemKind::Trait(..) |
781 hir::ItemKind::TraitAlias(..) => {
782 let def_id = self.map.local_def_id_from_hir_id(i.hir_id);
783 self.traits.push(def_id);
789 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {}
791 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {}
794 tcx.hir().krate().visit_all_item_likes(&mut Visitor {
801 let mut external_mods = FxHashSet::default();
802 fn handle_external_def(tcx: TyCtxt<'_, '_, '_>,
803 traits: &mut Vec<DefId>,
804 external_mods: &mut FxHashSet<DefId>,
808 Def::TraitAlias(def_id) => {
811 Def::Mod(def_id) => {
812 if !external_mods.insert(def_id) {
815 for child in tcx.item_children(def_id).iter() {
816 handle_external_def(tcx, traits, external_mods, child.def)
822 for &cnum in tcx.crates().iter() {
825 index: CRATE_DEF_INDEX,
827 handle_external_def(tcx, &mut traits, &mut external_mods, Def::Mod(def_id));
833 pub fn provide(providers: &mut ty::query::Providers<'_>) {
834 providers.all_traits = |tcx, cnum| {
835 assert_eq!(cnum, LOCAL_CRATE);
836 Lrc::new(compute_all_traits(tcx))
840 struct UsePlacementFinder<'a, 'tcx: 'a, 'gcx: 'tcx> {
841 target_module: hir::HirId,
844 tcx: TyCtxt<'a, 'gcx, 'tcx>
847 impl<'a, 'tcx, 'gcx> UsePlacementFinder<'a, 'tcx, 'gcx> {
849 tcx: TyCtxt<'a, 'gcx, 'tcx>,
850 krate: &'tcx hir::Crate,
851 target_module: hir::HirId,
852 ) -> (Option<Span>, bool) {
853 let mut finder = UsePlacementFinder {
859 hir::intravisit::walk_crate(&mut finder, krate);
860 (finder.span, finder.found_use)
864 impl<'a, 'tcx, 'gcx> hir::intravisit::Visitor<'tcx> for UsePlacementFinder<'a, 'tcx, 'gcx> {
867 module: &'tcx hir::Mod,
871 if self.span.is_some() {
874 if hir_id != self.target_module {
875 hir::intravisit::walk_mod(self, module, hir_id);
878 // Find a `use` statement.
879 for item_id in &module.item_ids {
880 let item = self.tcx.hir().expect_item_by_hir_id(item_id.id);
882 hir::ItemKind::Use(..) => {
883 // Don't suggest placing a `use` before the prelude
884 // import or other generated ones.
885 if item.span.ctxt().outer().expn_info().is_none() {
886 self.span = Some(item.span.shrink_to_lo());
887 self.found_use = true;
891 // Don't place `use` before `extern crate`...
892 hir::ItemKind::ExternCrate(_) => {}
893 // ...but do place them before the first other item.
894 _ => if self.span.map_or(true, |span| item.span < span ) {
895 if item.span.ctxt().outer().expn_info().is_none() {
896 // Don't insert between attributes and an item.
897 if item.attrs.is_empty() {
898 self.span = Some(item.span.shrink_to_lo());
900 // Find the first attribute on the item.
901 for attr in &item.attrs {
902 if self.span.map_or(true, |span| attr.span < span) {
903 self.span = Some(attr.span.shrink_to_lo());
913 fn nested_visit_map<'this>(
915 ) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
916 hir::intravisit::NestedVisitorMap::None