src/librustc_typeck/check/method/suggest.rs

   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.
   4 //
   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.
  10
  11 //! Give useful errors and suggestions to users when an item can't be
  12 //! found or is otherwise invalid.
  13
  14 use CrateCtxt;
  15
  16 use astconv::AstConv;
  17 use check::{self, FnCtxt};
  18 use front::map as hir_map;
  19 use middle::ty::{self, Ty, ToPolyTraitRef, ToPredicate, HasTypeFlags};
  20 use middle::cstore::{self, CrateStore, DefLike};
  21 use middle::def;
  22 use middle::def_id::DefId;
  23 use middle::lang_items::FnOnceTraitLangItem;
  24 use middle::subst::Substs;
  25 use middle::traits::{Obligation, SelectionContext};
  26 use util::nodemap::{FnvHashSet};
  27
  28 use syntax::ast;
  29 use syntax::codemap::Span;
  30 use syntax::errors::DiagnosticBuilder;
  31 use rustc_front::print::pprust;
  32 use rustc_front::hir;
  33
  34 use std::cell;
  35 use std::cmp::Ordering;
  36
  37 use super::{MethodError, NoMatchData, CandidateSource, impl_item, trait_item};
  38 use super::probe::Mode;
  39
  40 pub fn report_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
  41                               span: Span,
  42                               rcvr_ty: Ty<'tcx>,
  43                               item_name: ast::Name,
  44                               rcvr_expr: Option<&hir::Expr>,
  45                               error: MethodError<'tcx>)
  46 {
  47     // avoid suggestions when we don't know what's going on.
  48     if rcvr_ty.references_error() {
  49         return
  50     }
  51
  52     match error {
  53         MethodError::NoMatch(NoMatchData { static_candidates: static_sources,
  54                                            unsatisfied_predicates,
  55                                            out_of_scope_traits,
  56                                            mode }) => {
  57             let cx = fcx.tcx();
  58
  59             let mut err = fcx.type_error_struct(
  60                 span,
  61                 |actual| {
  62                     format!("no {} named `{}` found for type `{}` \
  63                              in the current scope",
  64                             if mode == Mode::MethodCall { "method" }
  65                             else { "associated item" },
  66                             item_name,
  67                             actual)
  68                 },
  69                 rcvr_ty,
  70                 None);
  71
  72             // If the item has the name of a field, give a help note
  73             if let (&ty::TyStruct(def, substs), Some(expr)) = (&rcvr_ty.sty, rcvr_expr) {
  74                 if let Some(field) = def.struct_variant().find_field_named(item_name) {
  75                     let expr_string = match cx.sess.codemap().span_to_snippet(expr.span) {
  76                         Ok(expr_string) => expr_string,
  77                         _ => "s".into() // Default to a generic placeholder for the
  78                                         // expression when we can't generate a string
  79                                         // snippet
  80                     };
  81
  82                     macro_rules! span_stored_function {
  83                         () => {
  84                             err.span_note(span,
  85                                           &format!("use `({0}.{1})(...)` if you meant to call \
  86                                                     the function stored in the `{1}` field",
  87                                                    expr_string, item_name));
  88                         }
  89                     }
  90
  91                     macro_rules! span_did_you_mean {
  92                         () => {
  93                             err.span_note(span, &format!("did you mean to write `{0}.{1}`?",
  94                                                          expr_string, item_name));
  95                         }
  96                     }
  97
  98                     // Determine if the field can be used as a function in some way
  99                     let field_ty = field.ty(cx, substs);
 100
 101                     match field_ty.sty {
 102                         // Not all of these (e.g. unsafe fns) implement FnOnce
 103                         // so we look for these beforehand
 104                         ty::TyClosure(..) | ty::TyBareFn(..) => {
 105                             span_stored_function!();
 106                         }
 107                         // If it's not a simple function, look for things which implement FnOnce
 108                         _ => {
 109                             if let Ok(fn_once_trait_did) =
 110                                     cx.lang_items.require(FnOnceTraitLangItem) {
 111                                 let infcx = fcx.infcx();
 112                                 infcx.probe(|_| {
 113                                     let fn_once_substs =
 114                                         Substs::new_trait(vec![infcx.next_ty_var()],
 115                                                           Vec::new(),
 116                                                           field_ty);
 117                                     let trait_ref =
 118                                       ty::TraitRef::new(fn_once_trait_did,
 119                                                         cx.mk_substs(fn_once_substs));
 120                                     let poly_trait_ref = trait_ref.to_poly_trait_ref();
 121                                     let obligation = Obligation::misc(span,
 122                                                                       fcx.body_id,
 123                                                                       poly_trait_ref
 124                                                                          .to_predicate());
 125                                     let mut selcx = SelectionContext::new(infcx);
 126
 127                                     if selcx.evaluate_obligation(&obligation) {
 128                                         span_stored_function!();
 129                                     } else {
 130                                         span_did_you_mean!();
 131                                     }
 132                                 });
 133                             } else {
 134                                 span_did_you_mean!();
 135                             }
 136                         }
 137                     }
 138                 }
 139             }
 140
 141             if !static_sources.is_empty() {
 142                 err.fileline_note(
 143                     span,
 144                     "found defined static methods, maybe a `self` is missing?");
 145
 146                 report_candidates(fcx, &mut err, span, item_name, static_sources);
 147             }
 148
 149             if !unsatisfied_predicates.is_empty() {
 150                 let bound_list = unsatisfied_predicates.iter()
 151                     .map(|p| format!("`{} : {}`",
 152                                      p.self_ty(),
 153                                      p))
 154                     .collect::<Vec<_>>()
 155                     .join(", ");
 156                 err.fileline_note(
 157                     span,
 158                     &format!("the method `{}` exists but the \
 159                              following trait bounds were not satisfied: {}",
 160                              item_name,
 161                              bound_list));
 162             }
 163
 164             suggest_traits_to_import(fcx, &mut err, span, rcvr_ty, item_name,
 165                                      rcvr_expr, out_of_scope_traits);
 166             err.emit();
 167         }
 168
 169         MethodError::Ambiguity(sources) => {
 170             let mut err = struct_span_err!(fcx.sess(), span, E0034,
 171                                            "multiple applicable items in scope");
 172
 173             report_candidates(fcx, &mut err, span, item_name, sources);
 174             err.emit();
 175         }
 176
 177         MethodError::ClosureAmbiguity(trait_def_id) => {
 178             let msg = format!("the `{}` method from the `{}` trait cannot be explicitly \
 179                                invoked on this closure as we have not yet inferred what \
 180                                kind of closure it is",
 181                                item_name,
 182                                fcx.tcx().item_path_str(trait_def_id));
 183             let msg = if let Some(callee) = rcvr_expr {
 184                 format!("{}; use overloaded call notation instead (e.g., `{}()`)",
 185                         msg, pprust::expr_to_string(callee))
 186             } else {
 187                 msg
 188             };
 189             fcx.sess().span_err(span, &msg);
 190         }
 191     }
 192
 193     fn report_candidates(fcx: &FnCtxt,
 194                          err: &mut DiagnosticBuilder,
 195                          span: Span,
 196                          item_name: ast::Name,
 197                          mut sources: Vec<CandidateSource>) {
 198         sources.sort();
 199         sources.dedup();
 200
 201         for (idx, source) in sources.iter().enumerate() {
 202             match *source {
 203                 CandidateSource::ImplSource(impl_did) => {
 204                     // Provide the best span we can. Use the item, if local to crate, else
 205                     // the impl, if local to crate (item may be defaulted), else the call site.
 206                     let item = impl_item(fcx.tcx(), impl_did, item_name)
 207                         .or_else(|| {
 208                             trait_item(
 209                                 fcx.tcx(),
 210                                 fcx.tcx().impl_trait_ref(impl_did).unwrap().def_id,
 211                                 item_name
 212                             )
 213                         }).unwrap();
 214                     let impl_span = fcx.tcx().map.def_id_span(impl_did, span);
 215                     let item_span = fcx.tcx().map.def_id_span(item.def_id(), impl_span);
 216
 217                     let impl_ty = check::impl_self_ty(fcx, span, impl_did).ty;
 218
 219                     let insertion = match fcx.tcx().impl_trait_ref(impl_did) {
 220                         None => format!(""),
 221                         Some(trait_ref) => {
 222                             format!(" of the trait `{}`",
 223                                     fcx.tcx().item_path_str(trait_ref.def_id))
 224                         }
 225                     };
 226
 227                     span_note!(err, item_span,
 228                                "candidate #{} is defined in an impl{} for the type `{}`",
 229                                idx + 1,
 230                                insertion,
 231                                impl_ty);
 232                 }
 233                 CandidateSource::TraitSource(trait_did) => {
 234                     let item = trait_item(fcx.tcx(), trait_did, item_name).unwrap();
 235                     let item_span = fcx.tcx().map.def_id_span(item.def_id(), span);
 236                     span_note!(err, item_span,
 237                                "candidate #{} is defined in the trait `{}`",
 238                                idx + 1,
 239                                fcx.tcx().item_path_str(trait_did));
 240                 }
 241             }
 242         }
 243     }
 244 }
 245
 246
 247 pub type AllTraitsVec = Vec<TraitInfo>;
 248
 249 fn suggest_traits_to_import<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 250                                       err: &mut DiagnosticBuilder,
 251                                       span: Span,
 252                                       rcvr_ty: Ty<'tcx>,
 253                                       item_name: ast::Name,
 254                                       rcvr_expr: Option<&hir::Expr>,
 255                                       valid_out_of_scope_traits: Vec<DefId>)
 256 {
 257     let tcx = fcx.tcx();
 258
 259     if !valid_out_of_scope_traits.is_empty() {
 260         let mut candidates = valid_out_of_scope_traits;
 261         candidates.sort();
 262         candidates.dedup();
 263         let msg = format!(
 264             "items from traits can only be used if the trait is in scope; \
 265              the following {traits_are} implemented but not in scope, \
 266              perhaps add a `use` for {one_of_them}:",
 267             traits_are = if candidates.len() == 1 {"trait is"} else {"traits are"},
 268             one_of_them = if candidates.len() == 1 {"it"} else {"one of them"});
 269
 270         err.fileline_help(span, &msg[..]);
 271
 272         for (i, trait_did) in candidates.iter().enumerate() {
 273             err.fileline_help(span,
 274                               &*format!("candidate #{}: use `{}`",
 275                                         i + 1,
 276                                         fcx.tcx().item_path_str(*trait_did)));
 277         }
 278         return
 279     }
 280
 281     let type_is_local = type_derefs_to_local(fcx, span, rcvr_ty, rcvr_expr);
 282
 283     // there's no implemented traits, so lets suggest some traits to
 284     // implement, by finding ones that have the item name, and are
 285     // legal to implement.
 286     let mut candidates = all_traits(fcx.ccx)
 287         .filter(|info| {
 288             // we approximate the coherence rules to only suggest
 289             // traits that are legal to implement by requiring that
 290             // either the type or trait is local. Multidispatch means
 291             // this isn't perfect (that is, there are cases when
 292             // implementing a trait would be legal but is rejected
 293             // here).
 294             (type_is_local || info.def_id.is_local())
 295                 && trait_item(tcx, info.def_id, item_name).is_some()
 296         })
 297         .collect::<Vec<_>>();
 298
 299     if !candidates.is_empty() {
 300         // sort from most relevant to least relevant
 301         candidates.sort_by(|a, b| a.cmp(b).reverse());
 302         candidates.dedup();
 303
 304         // FIXME #21673 this help message could be tuned to the case
 305         // of a type parameter: suggest adding a trait bound rather
 306         // than implementing.
 307         let msg = format!(
 308             "items from traits can only be used if the trait is implemented and in scope; \
 309              the following {traits_define} an item `{name}`, \
 310              perhaps you need to implement {one_of_them}:",
 311             traits_define = if candidates.len() == 1 {"trait defines"} else {"traits define"},
 312             one_of_them = if candidates.len() == 1 {"it"} else {"one of them"},
 313             name = item_name);
 314
 315         err.fileline_help(span, &msg[..]);
 316
 317         for (i, trait_info) in candidates.iter().enumerate() {
 318             err.fileline_help(span,
 319                               &*format!("candidate #{}: `{}`",
 320                                         i + 1,
 321                                         fcx.tcx().item_path_str(trait_info.def_id)));
 322         }
 323     }
 324 }
 325
 326 /// Checks whether there is a local type somewhere in the chain of
 327 /// autoderefs of `rcvr_ty`.
 328 fn type_derefs_to_local<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
 329                                   span: Span,
 330                                   rcvr_ty: Ty<'tcx>,
 331                                   rcvr_expr: Option<&hir::Expr>) -> bool {
 332     fn is_local(ty: Ty) -> bool {
 333         match ty.sty {
 334             ty::TyEnum(def, _) | ty::TyStruct(def, _) => def.did.is_local(),
 335
 336             ty::TyTrait(ref tr) => tr.principal_def_id().is_local(),
 337
 338             ty::TyParam(_) => true,
 339
 340             // everything else (primitive types etc.) is effectively
 341             // non-local (there are "edge" cases, e.g. (LocalType,), but
 342             // the noise from these sort of types is usually just really
 343             // annoying, rather than any sort of help).
 344             _ => false
 345         }
 346     }
 347
 348     // This occurs for UFCS desugaring of `T::method`, where there is no
 349     // receiver expression for the method call, and thus no autoderef.
 350     if rcvr_expr.is_none() {
 351         return is_local(fcx.resolve_type_vars_if_possible(rcvr_ty));
 352     }
 353
 354     check::autoderef(fcx, span, rcvr_ty, None,
 355                      check::UnresolvedTypeAction::Ignore, ty::NoPreference,
 356                      |ty, _| {
 357         if is_local(ty) {
 358             Some(())
 359         } else {
 360             None
 361         }
 362     }).2.is_some()
 363 }
 364
 365 #[derive(Copy, Clone)]
 366 pub struct TraitInfo {
 367     pub def_id: DefId,
 368 }
 369
 370 impl TraitInfo {
 371     fn new(def_id: DefId) -> TraitInfo {
 372         TraitInfo {
 373             def_id: def_id,
 374         }
 375     }
 376 }
 377 impl PartialEq for TraitInfo {
 378     fn eq(&self, other: &TraitInfo) -> bool {
 379         self.cmp(other) == Ordering::Equal
 380     }
 381 }
 382 impl Eq for TraitInfo {}
 383 impl PartialOrd for TraitInfo {
 384     fn partial_cmp(&self, other: &TraitInfo) -> Option<Ordering> { Some(self.cmp(other)) }
 385 }
 386 impl Ord for TraitInfo {
 387     fn cmp(&self, other: &TraitInfo) -> Ordering {
 388         // local crates are more important than remote ones (local:
 389         // cnum == 0), and otherwise we throw in the defid for totality
 390
 391         let lhs = (other.def_id.krate, other.def_id);
 392         let rhs = (self.def_id.krate, self.def_id);
 393         lhs.cmp(&rhs)
 394     }
 395 }
 396
 397 /// Retrieve all traits in this crate and any dependent crates.
 398 pub fn all_traits<'a>(ccx: &'a CrateCtxt) -> AllTraits<'a> {
 399     if ccx.all_traits.borrow().is_none() {
 400         use rustc_front::intravisit;
 401
 402         let mut traits = vec![];
 403
 404         // Crate-local:
 405         //
 406         // meh.
 407         struct Visitor<'a, 'tcx:'a> {
 408             map: &'a hir_map::Map<'tcx>,
 409             traits: &'a mut AllTraitsVec,
 410         }
 411         impl<'v, 'a, 'tcx> intravisit::Visitor<'v> for Visitor<'a, 'tcx> {
 412             fn visit_item(&mut self, i: &'v hir::Item) {
 413                 match i.node {
 414                     hir::ItemTrait(..) => {
 415                         let def_id = self.map.local_def_id(i.id);
 416                         self.traits.push(TraitInfo::new(def_id));
 417                     }
 418                     _ => {}
 419                 }
 420             }
 421         }
 422         ccx.tcx.map.krate().visit_all_items(&mut Visitor {
 423             map: &ccx.tcx.map,
 424             traits: &mut traits
 425         });
 426
 427         // Cross-crate:
 428         let mut external_mods = FnvHashSet();
 429         fn handle_external_def(traits: &mut AllTraitsVec,
 430                                external_mods: &mut FnvHashSet<DefId>,
 431                                ccx: &CrateCtxt,
 432                                cstore: &for<'a> cstore::CrateStore<'a>,
 433                                dl: cstore::DefLike) {
 434             match dl {
 435                 cstore::DlDef(def::DefTrait(did)) => {
 436                     traits.push(TraitInfo::new(did));
 437                 }
 438                 cstore::DlDef(def::DefMod(did)) => {
 439                     if !external_mods.insert(did) {
 440                         return;
 441                     }
 442                     for child in cstore.item_children(did) {
 443                         handle_external_def(traits, external_mods,
 444                                             ccx, cstore, child.def)
 445                     }
 446                 }
 447                 _ => {}
 448             }
 449         }
 450         let cstore = &*ccx.tcx.sess.cstore;
 451
 452         for cnum in ccx.tcx.sess.cstore.crates() {
 453             for child in cstore.crate_top_level_items(cnum) {
 454                 handle_external_def(&mut traits, &mut external_mods,
 455                                     ccx, cstore, child.def)
 456             }
 457         }
 458
 459         *ccx.all_traits.borrow_mut() = Some(traits);
 460     }
 461
 462     let borrow = ccx.all_traits.borrow();
 463     assert!(borrow.is_some());
 464     AllTraits {
 465         borrow: borrow,
 466         idx: 0
 467     }
 468 }
 469
 470 pub struct AllTraits<'a> {
 471     borrow: cell::Ref<'a, Option<AllTraitsVec>>,
 472     idx: usize
 473 }
 474
 475 impl<'a> Iterator for AllTraits<'a> {
 476     type Item = TraitInfo;
 477
 478     fn next(&mut self) -> Option<TraitInfo> {
 479         let AllTraits { ref borrow, ref mut idx } = *self;
 480         // ugh.
 481         borrow.as_ref().unwrap().get(*idx).map(|info| {
 482             *idx += 1;
 483             *info
 484         })
 485     }
 486 }