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, self.body_id, poly_trait_ref.to_predicate());
61 SelectionContext::new(self).evaluate_obligation(&obligation)
68 pub fn report_method_error(&self,
72 rcvr_expr: Option<&hir::Expr>,
73 error: MethodError<'tcx>,
74 args: Option<&'gcx [hir::Expr]>) {
75 // avoid suggestions when we don't know what's going on.
76 if rcvr_ty.references_error() {
80 let report_candidates = |err: &mut DiagnosticBuilder, mut sources: Vec<CandidateSource>| {
84 // Dynamic limit to avoid hiding just one candidate, which is silly.
85 let limit = if sources.len() == 5 { 5 } else { 4 };
87 for (idx, source) in sources.iter().take(limit).enumerate() {
89 CandidateSource::ImplSource(impl_did) => {
90 // Provide the best span we can. Use the item, if local to crate, else
91 // the impl, if local to crate (item may be defaulted), else nothing.
92 let item = self.associated_item(impl_did, item_name)
95 self.tcx.impl_trait_ref(impl_did).unwrap().def_id,
100 let note_span = self.tcx.hir.span_if_local(item.def_id).or_else(|| {
101 self.tcx.hir.span_if_local(impl_did)
104 let impl_ty = self.impl_self_ty(span, impl_did).ty;
106 let insertion = match self.tcx.impl_trait_ref(impl_did) {
109 format!(" of the trait `{}`",
110 self.tcx.item_path_str(trait_ref.def_id))
114 let note_str = format!("candidate #{} is defined in an impl{} \
119 if let Some(note_span) = note_span {
120 // We have a span pointing to the method. Show note with snippet.
121 err.span_note(note_span, ¬e_str);
126 CandidateSource::TraitSource(trait_did) => {
127 let item = self.associated_item(trait_did, item_name).unwrap();
128 let item_span = self.tcx.def_span(item.def_id);
131 "candidate #{} is defined in the trait `{}`",
133 self.tcx.item_path_str(trait_did));
134 err.help(&format!("to disambiguate the method call, write `{}::{}({}{})` \
136 self.tcx.item_path_str(trait_did),
138 if rcvr_ty.is_region_ptr() && args.is_some() {
139 if rcvr_ty.is_mutable_pointer() {
147 args.map(|arg| arg.iter()
148 .map(|arg| print::to_string(print::NO_ANN,
149 |s| s.print_expr(arg)))
151 .join(", ")).unwrap_or("...".to_owned())));
155 if sources.len() > limit {
156 err.note(&format!("and {} others", sources.len() - limit));
161 MethodError::NoMatch(NoMatchData { static_candidates: static_sources,
162 unsatisfied_predicates,
168 let mut err = self.type_error_struct(span,
170 format!("no {} named `{}` found for type `{}` in the current scope",
171 if mode == Mode::MethodCall {
181 // If the method name is the name of a field with a function or closure type,
182 // give a helping note that it has to be called as (x.f)(...).
183 if let Some(expr) = rcvr_expr {
184 for (ty, _) in self.autoderef(span, rcvr_ty) {
186 ty::TyAdt(def, substs) if !def.is_enum() => {
187 if let Some(field) = def.struct_variant()
188 .find_field_named(item_name) {
189 let snippet = tcx.sess.codemap().span_to_snippet(expr.span);
190 let expr_string = match snippet {
191 Ok(expr_string) => expr_string,
192 _ => "s".into(), // Default to a generic placeholder for the
193 // expression when we can't generate a
197 let field_ty = field.ty(tcx, substs);
199 if tcx.vis_is_accessible_from(field.vis, self.body_id) {
200 if self.is_fn_ty(&field_ty, span) {
201 err.help(&format!("use `({0}.{1})(...)` if you \
202 meant to call the function \
203 stored in the `{1}` field",
207 err.help(&format!("did you mean to write `{0}.{1}` \
208 instead of `{0}.{1}(...)`?",
212 err.span_label(span, "field, not a method");
214 err.span_label(span, "private field, not a method");
224 if self.is_fn_ty(&rcvr_ty, span) {
225 macro_rules! report_function {
226 ($span:expr, $name:expr) => {
227 err.note(&format!("{} is a function, perhaps you wish to call it",
232 if let Some(expr) = rcvr_expr {
233 if let Ok(expr_string) = tcx.sess.codemap().span_to_snippet(expr.span) {
234 report_function!(expr.span, expr_string);
235 } else if let hir::ExprPath(hir::QPath::Resolved(_, ref path)) = expr.node {
236 if let Some(segment) = path.segments.last() {
237 report_function!(expr.span, segment.name);
243 if !static_sources.is_empty() {
244 err.note("found the following associated functions; to be used as methods, \
245 functions must have a `self` parameter");
247 report_candidates(&mut err, static_sources);
250 if !unsatisfied_predicates.is_empty() {
251 let bound_list = unsatisfied_predicates.iter()
252 .map(|p| format!("`{} : {}`", p.self_ty(), p))
255 err.note(&format!("the method `{}` exists but the following trait bounds \
256 were not satisfied: {}",
261 self.suggest_traits_to_import(&mut err,
266 out_of_scope_traits);
270 MethodError::Ambiguity(sources) => {
271 let mut err = struct_span_err!(self.sess(),
274 "multiple applicable items in scope");
275 err.span_label(span, format!("multiple `{}` found", item_name));
277 report_candidates(&mut err, sources);
281 MethodError::ClosureAmbiguity(trait_def_id) => {
282 let msg = format!("the `{}` method from the `{}` trait cannot be explicitly \
283 invoked on this closure as we have not yet inferred what \
284 kind of closure it is",
286 self.tcx.item_path_str(trait_def_id));
287 let msg = if let Some(callee) = rcvr_expr {
288 format!("{}; use overloaded call notation instead (e.g., `{}()`)",
290 self.tcx.hir.node_to_pretty_string(callee.id))
294 self.sess().span_err(span, &msg);
297 MethodError::PrivateMatch(def) => {
298 let msg = format!("{} `{}` is private", def.kind_name(), item_name);
299 self.tcx.sess.span_err(span, &msg);
304 fn suggest_traits_to_import(&self,
305 err: &mut DiagnosticBuilder,
308 item_name: ast::Name,
309 rcvr_expr: Option<&hir::Expr>,
310 valid_out_of_scope_traits: Vec<DefId>) {
311 if !valid_out_of_scope_traits.is_empty() {
312 let mut candidates = valid_out_of_scope_traits;
315 let msg = format!("items from traits can only be used if the trait is in scope; the \
316 following {traits_are} implemented but not in scope, perhaps add \
317 a `use` for {one_of_them}:",
318 traits_are = if candidates.len() == 1 {
323 one_of_them = if candidates.len() == 1 {
331 let limit = if candidates.len() == 5 { 5 } else { 4 };
332 for (i, trait_did) in candidates.iter().take(limit).enumerate() {
333 err.help(&format!("candidate #{}: `use {};`",
335 self.tcx.item_path_str(*trait_did)));
337 if candidates.len() > limit {
338 err.note(&format!("and {} others", candidates.len() - limit));
343 let type_is_local = self.type_derefs_to_local(span, rcvr_ty, rcvr_expr);
345 // there's no implemented traits, so lets suggest some traits to
346 // implement, by finding ones that have the item name, and are
347 // legal to implement.
348 let mut candidates = all_traits(self.tcx)
350 // we approximate the coherence rules to only suggest
351 // traits that are legal to implement by requiring that
352 // either the type or trait is local. Multidispatch means
353 // this isn't perfect (that is, there are cases when
354 // implementing a trait would be legal but is rejected
356 (type_is_local || info.def_id.is_local())
357 && self.associated_item(info.def_id, item_name).is_some()
359 .collect::<Vec<_>>();
361 if !candidates.is_empty() {
362 // sort from most relevant to least relevant
363 candidates.sort_by(|a, b| a.cmp(b).reverse());
366 // FIXME #21673 this help message could be tuned to the case
367 // of a type parameter: suggest adding a trait bound rather
368 // than implementing.
369 let msg = format!("items from traits can only be used if the trait is implemented \
370 and in scope; the following {traits_define} an item `{name}`, \
371 perhaps you need to implement {one_of_them}:",
372 traits_define = if candidates.len() == 1 {
377 one_of_them = if candidates.len() == 1 {
386 for (i, trait_info) in candidates.iter().enumerate() {
387 err.help(&format!("candidate #{}: `{}`",
389 self.tcx.item_path_str(trait_info.def_id)));
394 /// Checks whether there is a local type somewhere in the chain of
395 /// autoderefs of `rcvr_ty`.
396 fn type_derefs_to_local(&self,
399 rcvr_expr: Option<&hir::Expr>)
401 fn is_local(ty: Ty) -> bool {
403 ty::TyAdt(def, _) => def.did.is_local(),
405 ty::TyDynamic(ref tr, ..) => tr.principal()
406 .map_or(false, |p| p.def_id().is_local()),
408 ty::TyParam(_) => true,
410 // everything else (primitive types etc.) is effectively
411 // non-local (there are "edge" cases, e.g. (LocalType,), but
412 // the noise from these sort of types is usually just really
413 // annoying, rather than any sort of help).
418 // This occurs for UFCS desugaring of `T::method`, where there is no
419 // receiver expression for the method call, and thus no autoderef.
420 if rcvr_expr.is_none() {
421 return is_local(self.resolve_type_vars_with_obligations(rcvr_ty));
424 self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))
428 pub type AllTraitsVec = Vec<DefId>;
430 #[derive(Copy, Clone)]
431 pub struct TraitInfo {
436 fn new(def_id: DefId) -> TraitInfo {
437 TraitInfo { def_id: def_id }
440 impl PartialEq for TraitInfo {
441 fn eq(&self, other: &TraitInfo) -> bool {
442 self.cmp(other) == Ordering::Equal
445 impl Eq for TraitInfo {}
446 impl PartialOrd for TraitInfo {
447 fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> {
448 Some(self.cmp(other))
451 impl Ord for TraitInfo {
452 fn cmp(&self, other: &TraitInfo) -> Ordering {
453 // local crates are more important than remote ones (local:
454 // cnum == 0), and otherwise we throw in the defid for totality
456 let lhs = (other.def_id.krate, other.def_id);
457 let rhs = (self.def_id.krate, self.def_id);
462 /// Retrieve all traits in this crate and any dependent crates.
463 pub fn all_traits<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> AllTraits<'a> {
464 if tcx.all_traits.borrow().is_none() {
465 use rustc::hir::itemlikevisit;
467 let mut traits = vec![];
472 struct Visitor<'a, 'tcx: 'a> {
473 map: &'a hir_map::Map<'tcx>,
474 traits: &'a mut AllTraitsVec,
476 impl<'v, 'a, 'tcx> itemlikevisit::ItemLikeVisitor<'v> for Visitor<'a, 'tcx> {
477 fn visit_item(&mut self, i: &'v hir::Item) {
479 hir::ItemTrait(..) => {
480 let def_id = self.map.local_def_id(i.id);
481 self.traits.push(def_id);
487 fn visit_trait_item(&mut self, _trait_item: &hir::TraitItem) {
490 fn visit_impl_item(&mut self, _impl_item: &hir::ImplItem) {
493 tcx.hir.krate().visit_all_item_likes(&mut Visitor {
499 let mut external_mods = FxHashSet();
500 fn handle_external_def(tcx: TyCtxt,
501 traits: &mut AllTraitsVec,
502 external_mods: &mut FxHashSet<DefId>,
504 let def_id = def.def_id();
510 if !external_mods.insert(def_id) {
513 for child in tcx.sess.cstore.item_children(def_id) {
514 handle_external_def(tcx, traits, external_mods, child.def)
520 for cnum in tcx.sess.cstore.crates() {
523 index: CRATE_DEF_INDEX,
525 handle_external_def(tcx, &mut traits, &mut external_mods, Def::Mod(def_id));
528 *tcx.all_traits.borrow_mut() = Some(traits);
531 let borrow = tcx.all_traits.borrow();
532 assert!(borrow.is_some());
539 pub struct AllTraits<'a> {
540 borrow: cell::Ref<'a, Option<AllTraitsVec>>,
544 impl<'a> Iterator for AllTraits<'a> {
545 type Item = TraitInfo;
547 fn next(&mut self) -> Option<TraitInfo> {
548 let AllTraits { ref borrow, ref mut idx } = *self;
550 borrow.as_ref().unwrap().get(*idx).map(|info| {
552 TraitInfo::new(*info)