src/librustc/middle/traits/error_reporting.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 use super::{
  12     FulfillmentError,
  13     FulfillmentErrorCode,
  14     MismatchedProjectionTypes,
  15     ObligationCauseCode,
  16     OutputTypeParameterMismatch,
  17     PredicateObligation,
  18     SelectionError,
  19 };
  20
  21 use fmt_macros::{Parser, Piece, Position};
  22 use middle::infer::InferCtxt;
  23 use middle::ty::{self, AsPredicate, ReferencesError, ToPolyTraitRef, TraitRef};
  24 use std::collections::HashMap;
  25 use syntax::codemap::{DUMMY_SP, Span};
  26 use syntax::attr::{AttributeMethods, AttrMetaMethods};
  27 use util::ppaux::{Repr, UserString};
  28
  29 pub fn report_fulfillment_errors<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  30                                            errors: &Vec<FulfillmentError<'tcx>>) {
  31     for error in errors.iter() {
  32         report_fulfillment_error(infcx, error);
  33     }
  34 }
  35
  36 fn report_fulfillment_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  37                                       error: &FulfillmentError<'tcx>) {
  38     match error.code {
  39         FulfillmentErrorCode::CodeSelectionError(ref e) => {
  40             report_selection_error(infcx, &error.obligation, e);
  41         }
  42         FulfillmentErrorCode::CodeProjectionError(ref e) => {
  43             report_projection_error(infcx, &error.obligation, e);
  44         }
  45         FulfillmentErrorCode::CodeAmbiguity => {
  46             maybe_report_ambiguity(infcx, &error.obligation);
  47         }
  48     }
  49 }
  50
  51 pub fn report_projection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  52                                          obligation: &PredicateObligation<'tcx>,
  53                                          error: &MismatchedProjectionTypes<'tcx>)
  54 {
  55     let predicate =
  56         infcx.resolve_type_vars_if_possible(&obligation.predicate);
  57     if !predicate.references_error() {
  58         span_err!(infcx.tcx.sess, obligation.cause.span, E0271,
  59                 "type mismatch resolving `{}`: {}",
  60                 predicate.user_string(infcx.tcx),
  61                 ty::type_err_to_str(infcx.tcx, &error.err));
  62         note_obligation_cause(infcx, obligation);
  63     }
  64 }
  65
  66 fn report_on_unimplemented<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  67                                      trait_ref: &TraitRef<'tcx>,
  68                                      span: Span) -> Option<String> {
  69     let def_id = trait_ref.def_id;
  70     let mut report = None;
  71     for item in ty::get_attrs(infcx.tcx, def_id).iter() {
  72         if item.check_name("rustc_on_unimplemented") {
  73             let err_sp = if item.meta().span == DUMMY_SP {
  74                 span
  75             } else {
  76                 item.meta().span
  77             };
  78             let def = ty::lookup_trait_def(infcx.tcx, def_id);
  79             let trait_str = def.trait_ref.user_string(infcx.tcx);
  80             if let Some(ref istring) = item.value_str() {
  81                 let mut generic_map = def.generics.types.iter_enumerated()
  82                                          .map(|(param, i, gen)| {
  83                                                (gen.name.as_str().to_string(),
  84                                                 trait_ref.substs.types.get(param, i)
  85                                                          .user_string(infcx.tcx))
  86                                               }).collect::<HashMap<String, String>>();
  87                 generic_map.insert("Self".to_string(),
  88                                    trait_ref.self_ty().user_string(infcx.tcx));
  89                 let parser = Parser::new(istring.get());
  90                 let mut errored = false;
  91                 let err: String = parser.filter_map(|p| {
  92                     match p {
  93                         Piece::String(s) => Some(s),
  94                         Piece::NextArgument(a) => match a.position {
  95                             Position::ArgumentNamed(s) => match generic_map.get(s) {
  96                                 Some(val) => Some(val.as_slice()),
  97                                 None => {
  98                                     span_err!(infcx.tcx.sess, err_sp, E0272,
  99                                                    "the #[rustc_on_unimplemented] \
 100                                                             attribute on \
 101                                                             trait definition for {} refers to \
 102                                                             non-existent type parameter {}",
 103                                                            trait_str, s);
 104                                     errored = true;
 105                                     None
 106                                 }
 107                             },
 108                             _ => {
 109                                      span_err!(infcx.tcx.sess, err_sp, E0273,
 110                                                "the #[rustc_on_unimplemented] \
 111                                                         attribute on \
 112                                                         trait definition for {} must have named \
 113                                                         format arguments, \
 114                                                         eg `#[rustc_on_unimplemented = \
 115                                                         \"foo {{T}}\"]`",
 116                                                        trait_str);
 117                                 errored = true;
 118                                 None
 119                             }
 120                         }
 121                     }
 122                 }).collect();
 123                 // Report only if the format string checks out
 124                 if !errored {
 125                     report = Some(err);
 126                 }
 127             } else {
 128                 span_err!(infcx.tcx.sess, err_sp, E0274,
 129                                         "the #[rustc_on_unimplemented] attribute on \
 130                                                  trait definition for {} must have a value, \
 131                                                  eg `#[rustc_on_unimplemented = \"foo\"]`",
 132                                                  trait_str);
 133             }
 134             break;
 135         }
 136     }
 137     report
 138 }
 139
 140 pub fn report_selection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 141                                         obligation: &PredicateObligation<'tcx>,
 142                                         error: &SelectionError<'tcx>)
 143 {
 144     match *error {
 145         SelectionError::Overflow => {
 146             // We could track the stack here more precisely if we wanted, I imagine.
 147             let predicate =
 148                 infcx.resolve_type_vars_if_possible(&obligation.predicate);
 149             span_err!(infcx.tcx.sess, obligation.cause.span, E0275,
 150                     "overflow evaluating the requirement `{}`",
 151                     predicate.user_string(infcx.tcx));
 152
 153             suggest_new_overflow_limit(infcx.tcx, obligation.cause.span);
 154
 155             note_obligation_cause(infcx, obligation);
 156         }
 157
 158         SelectionError::Unimplemented => {
 159             match &obligation.cause.code {
 160                 &ObligationCauseCode::CompareImplMethodObligation => {
 161                     span_err!(infcx.tcx.sess, obligation.cause.span, E0276,
 162                             "the requirement `{}` appears on the impl \
 163                             method but not on the corresponding trait method",
 164                             obligation.predicate.user_string(infcx.tcx));;
 165                 }
 166                 _ => {
 167                     match obligation.predicate {
 168                         ty::Predicate::Trait(ref trait_predicate) => {
 169                             let trait_predicate =
 170                                 infcx.resolve_type_vars_if_possible(trait_predicate);
 171
 172                             if !trait_predicate.references_error() {
 173                                 let trait_ref = trait_predicate.to_poly_trait_ref();
 174                                 span_err!(infcx.tcx.sess, obligation.cause.span, E0277,
 175                                         "the trait `{}` is not implemented for the type `{}`",
 176                                         trait_ref.user_string(infcx.tcx),
 177                                         trait_ref.self_ty().user_string(infcx.tcx));
 178                                 // Check if it has a custom "#[rustc_on_unimplemented]"
 179                                 // error message, report with that message if it does
 180                                 let custom_note = report_on_unimplemented(infcx, &*trait_ref.0,
 181                                                                           obligation.cause.span);
 182                                 if let Some(s) = custom_note {
 183                                     infcx.tcx.sess.span_note(obligation.cause.span,
 184                                                              s.as_slice());
 185                                 }
 186                             }
 187                         }
 188
 189                         ty::Predicate::Equate(ref predicate) => {
 190                             let predicate = infcx.resolve_type_vars_if_possible(predicate);
 191                             let err = infcx.equality_predicate(obligation.cause.span,
 192                                                                &predicate).err().unwrap();
 193                             span_err!(infcx.tcx.sess, obligation.cause.span, E0278,
 194                                     "the requirement `{}` is not satisfied (`{}`)",
 195                                     predicate.user_string(infcx.tcx),
 196                                     ty::type_err_to_str(infcx.tcx, &err));
 197                         }
 198
 199                         ty::Predicate::RegionOutlives(ref predicate) => {
 200                             let predicate = infcx.resolve_type_vars_if_possible(predicate);
 201                             let err = infcx.region_outlives_predicate(obligation.cause.span,
 202                                                                       &predicate).err().unwrap();
 203                             span_err!(infcx.tcx.sess, obligation.cause.span, E0279,
 204                                     "the requirement `{}` is not satisfied (`{}`)",
 205                                     predicate.user_string(infcx.tcx),
 206                                     ty::type_err_to_str(infcx.tcx, &err));
 207                         }
 208
 209                         ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
 210                                 let predicate =
 211                                     infcx.resolve_type_vars_if_possible(&obligation.predicate);
 212                                 span_err!(infcx.tcx.sess, obligation.cause.span, E0280,
 213                                         "the requirement `{}` is not satisfied",
 214                                         predicate.user_string(infcx.tcx));
 215                         }
 216                     }
 217                 }
 218             }
 219         }
 220
 221         OutputTypeParameterMismatch(ref expected_trait_ref, ref actual_trait_ref, ref e) => {
 222             let expected_trait_ref = infcx.resolve_type_vars_if_possible(&*expected_trait_ref);
 223             let actual_trait_ref = infcx.resolve_type_vars_if_possible(&*actual_trait_ref);
 224             if !ty::type_is_error(actual_trait_ref.self_ty()) {
 225                 span_err!(infcx.tcx.sess, obligation.cause.span, E0281,
 226                         "type mismatch: the type `{}` implements the trait `{}`, \
 227                         but the trait `{}` is required ({})",
 228                         expected_trait_ref.self_ty().user_string(infcx.tcx),
 229                         expected_trait_ref.user_string(infcx.tcx),
 230                         actual_trait_ref.user_string(infcx.tcx),
 231                         ty::type_err_to_str(infcx.tcx, e));
 232                     note_obligation_cause(infcx, obligation);
 233             }
 234         }
 235     }
 236 }
 237
 238 pub fn maybe_report_ambiguity<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 239                                         obligation: &PredicateObligation<'tcx>) {
 240     // Unable to successfully determine, probably means
 241     // insufficient type information, but could mean
 242     // ambiguous impls. The latter *ought* to be a
 243     // coherence violation, so we don't report it here.
 244
 245     let predicate = infcx.resolve_type_vars_if_possible(&obligation.predicate);
 246
 247     debug!("maybe_report_ambiguity(predicate={}, obligation={})",
 248            predicate.repr(infcx.tcx),
 249            obligation.repr(infcx.tcx));
 250
 251     match predicate {
 252         ty::Predicate::Trait(ref data) => {
 253             let trait_ref = data.to_poly_trait_ref();
 254             let self_ty = trait_ref.self_ty();
 255             let all_types = &trait_ref.substs().types;
 256             if all_types.iter().any(|&t| ty::type_is_error(t)) {
 257             } else if all_types.iter().any(|&t| ty::type_needs_infer(t)) {
 258                 // This is kind of a hack: it frequently happens that some earlier
 259                 // error prevents types from being fully inferred, and then we get
 260                 // a bunch of uninteresting errors saying something like "<generic
 261                 // #0> doesn't implement Sized".  It may even be true that we
 262                 // could just skip over all checks where the self-ty is an
 263                 // inference variable, but I was afraid that there might be an
 264                 // inference variable created, registered as an obligation, and
 265                 // then never forced by writeback, and hence by skipping here we'd
 266                 // be ignoring the fact that we don't KNOW the type works
 267                 // out. Though even that would probably be harmless, given that
 268                 // we're only talking about builtin traits, which are known to be
 269                 // inhabited. But in any case I just threw in this check for
 270                 // has_errors() to be sure that compilation isn't happening
 271                 // anyway. In that case, why inundate the user.
 272                 if !infcx.tcx.sess.has_errors() {
 273                     if
 274                         infcx.tcx.lang_items.sized_trait()
 275                         .map_or(false, |sized_id| sized_id == trait_ref.def_id())
 276                     {
 277                         span_err!(infcx.tcx.sess, obligation.cause.span, E0282,
 278                                 "unable to infer enough type information about `{}`; \
 279                                  type annotations required",
 280                                 self_ty.user_string(infcx.tcx));
 281                     } else {
 282                         span_err!(infcx.tcx.sess, obligation.cause.span, E0283,
 283                                 "type annotations required: cannot resolve `{}`",
 284                                 predicate.user_string(infcx.tcx));;
 285                         note_obligation_cause(infcx, obligation);
 286                     }
 287                 }
 288             } else if !infcx.tcx.sess.has_errors() {
 289                 // Ambiguity. Coherence should have reported an error.
 290                 infcx.tcx.sess.span_bug(
 291                     obligation.cause.span,
 292                     format!(
 293                         "coherence failed to report ambiguity: \
 294                          cannot locate the impl of the trait `{}` for \
 295                          the type `{}`",
 296                         trait_ref.user_string(infcx.tcx),
 297                         self_ty.user_string(infcx.tcx)).as_slice());
 298             }
 299         }
 300
 301         _ => {
 302             if !infcx.tcx.sess.has_errors() {
 303                 span_err!(infcx.tcx.sess, obligation.cause.span, E0284,
 304                         "type annotations required: cannot resolve `{}`",
 305                         predicate.user_string(infcx.tcx));;
 306                 note_obligation_cause(infcx, obligation);
 307             }
 308         }
 309     }
 310 }
 311
 312 fn note_obligation_cause<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 313                                    obligation: &PredicateObligation<'tcx>)
 314 {
 315     note_obligation_cause_code(infcx,
 316                                &obligation.predicate,
 317                                obligation.cause.span,
 318                                &obligation.cause.code);
 319 }
 320
 321 fn note_obligation_cause_code<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 322                                         predicate: &ty::Predicate<'tcx>,
 323                                         cause_span: Span,
 324                                         cause_code: &ObligationCauseCode<'tcx>)
 325 {
 326     let tcx = infcx.tcx;
 327     match *cause_code {
 328         ObligationCauseCode::MiscObligation => { }
 329         ObligationCauseCode::ItemObligation(item_def_id) => {
 330             let item_name = ty::item_path_str(tcx, item_def_id);
 331             tcx.sess.span_note(
 332                 cause_span,
 333                 format!("required by `{}`", item_name).as_slice());
 334         }
 335         ObligationCauseCode::ObjectCastObligation(object_ty) => {
 336             tcx.sess.span_note(
 337                 cause_span,
 338                 format!(
 339                     "required for the cast to the object type `{}`",
 340                     infcx.ty_to_string(object_ty)).as_slice());
 341         }
 342         ObligationCauseCode::RepeatVec => {
 343             tcx.sess.span_note(
 344                 cause_span,
 345                 "the `Copy` trait is required because the \
 346                  repeated element will be copied");
 347         }
 348         ObligationCauseCode::VariableType(_) => {
 349             tcx.sess.span_note(
 350                 cause_span,
 351                 "all local variables must have a statically known size");
 352         }
 353         ObligationCauseCode::ReturnType => {
 354             tcx.sess.span_note(
 355                 cause_span,
 356                 "the return type of a function must have a \
 357                  statically known size");
 358         }
 359         ObligationCauseCode::AssignmentLhsSized => {
 360             tcx.sess.span_note(
 361                 cause_span,
 362                 "the left-hand-side of an assignment must have a statically known size");
 363         }
 364         ObligationCauseCode::StructInitializerSized => {
 365             tcx.sess.span_note(
 366                 cause_span,
 367                 "structs must have a statically known size to be initialized");
 368         }
 369         ObligationCauseCode::ClosureCapture(var_id, closure_span, builtin_bound) => {
 370             let def_id = tcx.lang_items.from_builtin_kind(builtin_bound).unwrap();
 371             let trait_name = ty::item_path_str(tcx, def_id);
 372             let name = ty::local_var_name_str(tcx, var_id);
 373             span_note!(tcx.sess, closure_span,
 374                        "the closure that captures `{}` requires that all captured variables \
 375                        implement the trait `{}`",
 376                        name,
 377                        trait_name);
 378         }
 379         ObligationCauseCode::FieldSized => {
 380             span_note!(tcx.sess, cause_span,
 381                        "only the last field of a struct or enum variant \
 382                        may have a dynamically sized type")
 383         }
 384         ObligationCauseCode::ObjectSized => {
 385             span_note!(tcx.sess, cause_span,
 386                        "only sized types can be made into objects");
 387         }
 388         ObligationCauseCode::SharedStatic => {
 389             span_note!(tcx.sess, cause_span,
 390                        "shared static variables must have a type that implements `Sync`");
 391         }
 392         ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
 393             let parent_trait_ref = infcx.resolve_type_vars_if_possible(&data.parent_trait_ref);
 394             span_note!(tcx.sess, cause_span,
 395                        "required because it appears within the type `{}`",
 396                        parent_trait_ref.0.self_ty().user_string(infcx.tcx));
 397             let parent_predicate = parent_trait_ref.as_predicate();
 398             note_obligation_cause_code(infcx, &parent_predicate, cause_span, &*data.parent_code);
 399         }
 400         ObligationCauseCode::ImplDerivedObligation(ref data) => {
 401             let parent_trait_ref = infcx.resolve_type_vars_if_possible(&data.parent_trait_ref);
 402             span_note!(tcx.sess, cause_span,
 403                        "required because of the requirements on the impl of `{}` for `{}`",
 404                        parent_trait_ref.user_string(infcx.tcx),
 405                        parent_trait_ref.0.self_ty().user_string(infcx.tcx));
 406             let parent_predicate = parent_trait_ref.as_predicate();
 407             note_obligation_cause_code(infcx, &parent_predicate, cause_span, &*data.parent_code);
 408         }
 409         ObligationCauseCode::CompareImplMethodObligation => {
 410             span_note!(tcx.sess, cause_span,
 411                       "the requirement `{}` appears on the impl method\
 412                       but not on the corresponding trait method",
 413                       predicate.user_string(infcx.tcx));
 414         }
 415     }
 416 }
 417
 418 pub fn suggest_new_overflow_limit(tcx: &ty::ctxt, span: Span) {
 419     let current_limit = tcx.sess.recursion_limit.get();
 420     let suggested_limit = current_limit * 2;
 421     tcx.sess.span_note(
 422         span,
 423         &format!(
 424             "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
 425             suggested_limit)[]);
 426 }