1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Give useful errors and suggestions to users when an item can't be
12 //! found or is otherwise invalid.
15 use rustc::hir::map as hir_map;
16 use rustc::ty::{self, Ty, TyCtxt, ToPolyTraitRef, ToPredicate, TypeFoldable};
18 use hir::def_id::{CRATE_DEF_INDEX, DefId};
19 use middle::lang_items::FnOnceTraitLangItem;
20 use rustc::traits::{Obligation, SelectionContext};
21 use util::nodemap::FxHashSet;
24 use errors::DiagnosticBuilder;
28 use rustc::hir::print;
29 use rustc::infer::type_variable::TypeVariableOrigin;
32 use std::cmp::Ordering;
34 use super::{MethodError, NoMatchData, CandidateSource};
35 use super::probe::Mode;
37 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
38 fn is_fn_ty(&self, ty: &Ty<'tcx>, span: Span) -> bool {
41 // Not all of these (e.g. unsafe fns) implement FnOnce
42 // so we look for these beforehand
45 ty::TyFnPtr(_) => true,
46 // If it's not a simple function, look for things which implement FnOnce
48 let fn_once = match tcx.lang_items.require(FnOnceTraitLangItem) {
49 Ok(fn_once) => fn_once,
50 Err(..) => return false,
53 self.autoderef(span, ty).any(|(ty, _)| {
55 let fn_once_substs = tcx.mk_substs_trait(ty,
56 &[self.next_ty_var(TypeVariableOrigin::MiscVariable(span))]);
57 let trait_ref = ty::TraitRef::new(fn_once, fn_once_substs);
58 let poly_trait_ref = trait_ref.to_poly_trait_ref();
60 Obligation::misc(span,
63 poly_trait_ref.to_predicate());
64 SelectionContext::new(self).evaluate_obligation(&obligation)
71 pub fn report_method_error(&self,
75 rcvr_expr: Option<&hir::Expr>,
76 error: MethodError<'tcx>,
77 args: Option<&'gcx [hir::Expr]>) {
78 // avoid suggestions when we don't know what's going on.
79 if rcvr_ty.references_error() {
83 let report_candidates = |err: &mut DiagnosticBuilder, mut sources: Vec<CandidateSource>| {
87 // Dynamic limit to avoid hiding just one candidate, which is silly.
88 let limit = if sources.len() == 5 { 5 } else { 4 };
90 for (idx, source) in sources.iter().take(limit).enumerate() {
92 CandidateSource::ImplSource(impl_did) => {
93 // Provide the best span we can. Use the item, if local to crate, else
94 // the impl, if local to crate (item may be defaulted), else nothing.
95 let item = self.associated_item(impl_did, item_name)
98 self.tcx.impl_trait_ref(impl_did).unwrap().def_id,
103 let note_span = self.tcx.hir.span_if_local(item.def_id).or_else(|| {
104 self.tcx.hir.span_if_local(impl_did)
107 let impl_ty = self.impl_self_ty(span, impl_did).ty;
109 let insertion = match self.tcx.impl_trait_ref(impl_did) {
112 format!(" of the trait `{}`",
113 self.tcx.item_path_str(trait_ref.def_id))
117 let note_str = format!("candidate #{} is defined in an impl{} \
122 if let Some(note_span) = note_span {
123 // We have a span pointing to the method. Show note with snippet.
124 err.span_note(note_span, ¬e_str);
129 CandidateSource::TraitSource(trait_did) => {
130 let item = self.associated_item(trait_did, item_name).unwrap();
131 let item_span = self.tcx.def_span(item.def_id);
134 "candidate #{} is defined in the trait `{}`",
136 self.tcx.item_path_str(trait_did));
137 err.help(&format!("to disambiguate the method call, write `{}::{}({}{})` \
139 self.tcx.item_path_str(trait_did),
141 if rcvr_ty.is_region_ptr() && args.is_some() {
142 if rcvr_ty.is_mutable_pointer() {
150 args.map(|arg| arg.iter()
151 .map(|arg| print::to_string(print::NO_ANN,
152 |s| s.print_expr(arg)))
154 .join(", ")).unwrap_or("...".to_owned())));
158 if sources.len() > limit {
159 err.note(&format!("and {} others", sources.len() - limit));
164 MethodError::NoMatch(NoMatchData { static_candidates: static_sources,
165 unsatisfied_predicates,
171 let actual = self.resolve_type_vars_if_possible(&rcvr_ty);
172 let mut err = if !actual.references_error() {
173 struct_span_err!(tcx.sess, span, E0599,
174 "no {} named `{}` found for type `{}` in the \
176 if mode == Mode::MethodCall {
179 match item_name.as_str().chars().next() {
181 if name.is_lowercase() {
182 "function or associated item"
193 self.ty_to_string(actual))
195 self.tcx.sess.diagnostic().struct_dummy()
198 // If the method name is the name of a field with a function or closure type,
199 // give a helping note that it has to be called as (x.f)(...).
200 if let Some(expr) = rcvr_expr {
201 for (ty, _) in self.autoderef(span, rcvr_ty) {
203 ty::TyAdt(def, substs) if !def.is_enum() => {
204 if let Some(field) = def.struct_variant()
205 .find_field_named(item_name) {
206 let snippet = tcx.sess.codemap().span_to_snippet(expr.span);
207 let expr_string = match snippet {
208 Ok(expr_string) => expr_string,
209 _ => "s".into(), // Default to a generic placeholder for the
210 // expression when we can't generate a
214 let field_ty = field.ty(tcx, substs);
215 let scope = self.tcx.hir.get_module_parent(self.body_id);
216 if field.vis.is_accessible_from(scope, self.tcx) {
217 if self.is_fn_ty(&field_ty, span) {
218 err.help(&format!("use `({0}.{1})(...)` if you \
219 meant to call the function \
220 stored in the `{1}` field",
224 err.help(&format!("did you mean to write `{0}.{1}` \
225 instead of `{0}.{1}(...)`?",
229 err.span_label(span, "field, not a method");
231 err.span_label(span, "private field, not a method");
241 if self.is_fn_ty(&rcvr_ty, span) {
242 macro_rules! report_function {
243 ($span:expr, $name:expr) => {
244 err.note(&format!("{} is a function, perhaps you wish to call it",
249 if let Some(expr) = rcvr_expr {
250 if let Ok(expr_string) = tcx.sess.codemap().span_to_snippet(expr.span) {
251 report_function!(expr.span, expr_string);
252 } else if let hir::ExprPath(hir::QPath::Resolved(_, ref path)) = expr.node {
253 if let Some(segment) = path.segments.last() {
254 report_function!(expr.span, segment.name);
260 if !static_sources.is_empty() {
261 err.note("found the following associated functions; to be used as methods, \
262 functions must have a `self` parameter");
264 report_candidates(&mut err, static_sources);
267 if !unsatisfied_predicates.is_empty() {
268 let bound_list = unsatisfied_predicates.iter()
269 .map(|p| format!("`{} : {}`", p.self_ty(), p))
272 err.note(&format!("the method `{}` exists but the following trait bounds \
273 were not satisfied:\n{}",
278 self.suggest_traits_to_import(&mut err,
283 out_of_scope_traits);
287 MethodError::Ambiguity(sources) => {
288 let mut err = struct_span_err!(self.sess(),
291 "multiple applicable items in scope");
292 err.span_label(span, format!("multiple `{}` found", item_name));
294 report_candidates(&mut err, sources);
298 MethodError::ClosureAmbiguity(trait_def_id) => {
299 let msg = format!("the `{}` method from the `{}` trait cannot be explicitly \
300 invoked on this closure as we have not yet inferred what \
301 kind of closure it is",
303 self.tcx.item_path_str(trait_def_id));
304 let msg = if let Some(callee) = rcvr_expr {
305 format!("{}; use overloaded call notation instead (e.g., `{}()`)",
307 self.tcx.hir.node_to_pretty_string(callee.id))
311 self.sess().span_err(span, &msg);
314 MethodError::PrivateMatch(def, out_of_scope_traits) => {
315 let mut err = struct_span_err!(self.tcx.sess, span, E0624,
316 "{} `{}` is private", def.kind_name(), item_name);
317 self.suggest_valid_traits(&mut err, out_of_scope_traits);
321 MethodError::IllegalSizedBound(candidates) => {
322 let msg = format!("the `{}` method cannot be invoked on a trait object", item_name);
323 let mut err = self.sess().struct_span_err(span, &msg);
324 if !candidates.is_empty() {
325 let help = format!("{an}other candidate{s} {were} found in the following \
326 trait{s}, perhaps add a `use` for {one_of_them}:",
327 an = if candidates.len() == 1 {"an" } else { "" },
328 s = if candidates.len() == 1 { "" } else { "s" },
329 were = if candidates.len() == 1 { "was" } else { "were" },
330 one_of_them = if candidates.len() == 1 {
335 self.suggest_use_candidates(&mut err, help, candidates);
342 fn suggest_use_candidates(&self,
343 err: &mut DiagnosticBuilder,
345 candidates: Vec<DefId>) {
346 let limit = if candidates.len() == 5 { 5 } else { 4 };
347 for (i, trait_did) in candidates.iter().take(limit).enumerate() {
348 msg.push_str(&format!("\ncandidate #{}: `use {};`",
350 self.tcx.item_path_str(*trait_did)));
352 if candidates.len() > limit {
353 msg.push_str(&format!("\nand {} others", candidates.len() - limit));
358 fn suggest_valid_traits(&self,
359 err: &mut DiagnosticBuilder,
360 valid_out_of_scope_traits: Vec<DefId>) -> bool {
361 if !valid_out_of_scope_traits.is_empty() {
362 let mut candidates = valid_out_of_scope_traits;
365 err.help("items from traits can only be used if the trait is in scope");
366 let msg = format!("the following {traits_are} implemented but not in scope, \
367 perhaps add a `use` for {one_of_them}:",
368 traits_are = if candidates.len() == 1 {
373 one_of_them = if candidates.len() == 1 {
379 self.suggest_use_candidates(err, msg, candidates);
386 fn suggest_traits_to_import(&self,
387 err: &mut DiagnosticBuilder,
390 item_name: ast::Name,
391 rcvr_expr: Option<&hir::Expr>,
392 valid_out_of_scope_traits: Vec<DefId>) {
393 if self.suggest_valid_traits(err, valid_out_of_scope_traits) {
397 let type_is_local = self.type_derefs_to_local(span, rcvr_ty, rcvr_expr);
399 // there's no implemented traits, so lets suggest some traits to
400 // implement, by finding ones that have the item name, and are
401 // legal to implement.
402 let mut candidates = all_traits(self.tcx)
404 // we approximate the coherence rules to only suggest
405 // traits that are legal to implement by requiring that
406 // either the type or trait is local. Multidispatch means
407 // this isn't perfect (that is, there are cases when
408 // implementing a trait would be legal but is rejected
410 (type_is_local || info.def_id.is_local())
411 && self.associated_item(info.def_id, item_name).is_some()
413 .collect::<Vec<_>>();
415 if !candidates.is_empty() {
416 // sort from most relevant to least relevant
417 candidates.sort_by(|a, b| a.cmp(b).reverse());
420 // FIXME #21673 this help message could be tuned to the case
421 // of a type parameter: suggest adding a trait bound rather
422 // than implementing.
423 err.help("items from traits can only be used if the trait is implemented and in scope");
424 let mut msg = format!("the following {traits_define} an item `{name}`, \
425 perhaps you need to implement {one_of_them}:",
426 traits_define = if candidates.len() == 1 {
431 one_of_them = if candidates.len() == 1 {
438 for (i, trait_info) in candidates.iter().enumerate() {
439 msg.push_str(&format!("\ncandidate #{}: `{}`",
441 self.tcx.item_path_str(trait_info.def_id)));
447 /// Checks whether there is a local type somewhere in the chain of
448 /// autoderefs of `rcvr_ty`.
449 fn type_derefs_to_local(&self,
452 rcvr_expr: Option<&hir::Expr>)
454 fn is_local(ty: Ty) -> bool {
456 ty::TyAdt(def, _) => def.did.is_local(),
458 ty::TyDynamic(ref tr, ..) => tr.principal()
459 .map_or(false, |p| p.def_id().is_local()),
461 ty::TyParam(_) => true,
463 // everything else (primitive types etc.) is effectively
464 // non-local (there are "edge" cases, e.g. (LocalType,), but
465 // the noise from these sort of types is usually just really
466 // annoying, rather than any sort of help).
471 // This occurs for UFCS desugaring of `T::method`, where there is no
472 // receiver expression for the method call, and thus no autoderef.
473 if rcvr_expr.is_none() {
474 return is_local(self.resolve_type_vars_with_obligations(rcvr_ty));
477 self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
481 pub type AllTraitsVec = Vec<DefId>;
483 #[derive(Copy, Clone)]
484 pub struct TraitInfo {
489 fn new(def_id: DefId) -> TraitInfo {
490 TraitInfo { def_id: def_id }
493 impl PartialEq for TraitInfo {
494 fn eq(&self, other: &TraitInfo) -> bool {
495 self.cmp(other) == Ordering::Equal
498 impl Eq for TraitInfo {}
499 impl PartialOrd for TraitInfo {
500 fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
501 Some(self.cmp(other))
504 impl Ord for TraitInfo {
505 fn cmp(&self, other: &TraitInfo) -> Ordering {
506 // local crates are more important than remote ones (local:
507 // cnum == 0), and otherwise we throw in the defid for totality
509 let lhs = (other.def_id.krate, other.def_id);
510 let rhs = (self.def_id.krate, self.def_id);
515 /// Retrieve all traits in this crate and any dependent crates.
516 pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> AllTraits<'a> {
517 if tcx.all_traits.borrow().is_none() {
518 use rustc::hir::itemlikevisit;
520 let mut traits = vec![];
525 struct Visitor<'a, 'tcx: 'a> {
526 map: &'a hir_map::Map<'tcx>,
527 traits: &'a mut AllTraitsVec,
529 impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
530 fn visit_item(&mut self, i: &'v hir::Item) {
532 hir::ItemTrait(..) => {
533 let def_id = self.map.local_def_id(i.id);
534 self.traits.push(def_id);
540 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {
543 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {
546 tcx.hir.krate().visit_all_item_likes(&mut Visitor {
552 let mut external_mods = FxHashSet();
553 fn handle_external_def(tcx: TyCtxt,
554 traits: &mut AllTraitsVec,
555 external_mods: &mut FxHashSet<DefId>,
557 let def_id = def.def_id();
563 if !external_mods.insert(def_id) {
566 for child in tcx.sess.cstore.item_children(def_id, tcx.sess) {
567 handle_external_def(tcx, traits, external_mods, child.def)
573 for cnum in tcx.sess.cstore.crates() {
576 index: CRATE_DEF_INDEX,
578 handle_external_def(tcx, &mut traits, &mut external_mods, Def::Mod(def_id));
581 *tcx.all_traits.borrow_mut() = Some(traits);
584 let borrow = tcx.all_traits.borrow();
585 assert!(borrow.is_some());
592 pub struct AllTraits<'a> {
593 borrow: cell::Ref<'a, Option<AllTraitsVec>>,
597 impl<'a> Iterator for AllTraits<'a> {
598 type Item = TraitInfo;
600 fn next(&mut self) -> Option<TraitInfo> {
601 let AllTraits { ref borrow, ref mut idx } = *self;
603 borrow.as_ref().unwrap().get(*idx).map(|info| {
605 TraitInfo::new(*info)