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         infcx.tcx.sess.span_err(
  59             obligation.cause.span,
  60             format!(
  61                 "type mismatch resolving `{}`: {}",
  62                 predicate.user_string(infcx.tcx),
  63                 ty::type_err_to_str(infcx.tcx, &error.err)).as_slice());
  64         note_obligation_cause(infcx, obligation);
  65     }
  66 }
  67
  68 fn report_on_unimplemented<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  69                                      trait_ref: &TraitRef<'tcx>,
  70                                      span: Span) -> Option<String> {
  71     let def_id = trait_ref.def_id;
  72     let mut report = None;
  73     for item in ty::get_attrs(infcx.tcx, def_id).iter() {
  74         if item.check_name("rustc_on_unimplemented") {
  75             let err_sp = if item.meta().span == DUMMY_SP {
  76                 span
  77             } else {
  78                 item.meta().span
  79             };
  80             let def = ty::lookup_trait_def(infcx.tcx, def_id);
  81             let trait_str = def.trait_ref.user_string(infcx.tcx);
  82             if let Some(ref istring) = item.value_str() {
  83                 let mut generic_map = def.generics.types.iter_enumerated()
  84                                          .map(|(param, i, gen)| {
  85                                                (gen.name.as_str().to_string(),
  86                                                 trait_ref.substs.types.get(param, i)
  87                                                          .user_string(infcx.tcx))
  88                                               }).collect::<HashMap<String, String>>();
  89                 generic_map.insert("Self".to_string(),
  90                                    trait_ref.self_ty().user_string(infcx.tcx));
  91                 let parser = Parser::new(istring.get());
  92                 let mut errored = false;
  93                 let err: String = parser.filter_map(|p| {
  94                     match p {
  95                         Piece::String(s) => Some(s),
  96                         Piece::NextArgument(a) => match a.position {
  97                             Position::ArgumentNamed(s) => match generic_map.get(s) {
  98                                 Some(val) => Some(val.as_slice()),
  99                                 None => {
 100                                     infcx.tcx.sess
 101                                          .span_err(err_sp,
 102                                                    format!("the #[rustc_on_unimplemented] \
 103                                                             attribute on \
 104                                                             trait definition for {} refers to \
 105                                                             non-existent type parameter {}",
 106                                                            trait_str, s)
 107                                                    .as_slice());
 108                                     errored = true;
 109                                     None
 110                                 }
 111                             },
 112                             _ => {
 113                                 infcx.tcx.sess
 114                                      .span_err(err_sp,
 115                                                format!("the #[rustc_on_unimplemented] \
 116                                                         attribute on \
 117                                                         trait definition for {} must have named \
 118                                                         format arguments, \
 119                                                         eg `#[rustc_on_unimplemented = \
 120                                                         \"foo {{T}}\"]`",
 121                                                        trait_str).as_slice());
 122                                 errored = true;
 123                                 None
 124                             }
 125                         }
 126                     }
 127                 }).collect();
 128                 // Report only if the format string checks out
 129                 if !errored {
 130                     report = Some(err);
 131                 }
 132             } else {
 133                 infcx.tcx.sess.span_err(err_sp,
 134                                         format!("the #[rustc_on_unimplemented] attribute on \
 135                                                  trait definition for {} must have a value, \
 136                                                  eg `#[rustc_on_unimplemented = \"foo\"]`",
 137                                                  trait_str).as_slice());
 138             }
 139             break;
 140         }
 141     }
 142     report
 143 }
 144
 145 pub fn report_selection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 146                                         obligation: &PredicateObligation<'tcx>,
 147                                         error: &SelectionError<'tcx>)
 148 {
 149     match *error {
 150         SelectionError::Overflow => {
 151             // We could track the stack here more precisely if we wanted, I imagine.
 152             let predicate =
 153                 infcx.resolve_type_vars_if_possible(&obligation.predicate);
 154             infcx.tcx.sess.span_err(
 155                 obligation.cause.span,
 156                 format!(
 157                     "overflow evaluating the requirement `{}`",
 158                     predicate.user_string(infcx.tcx)).as_slice());
 159
 160             suggest_new_overflow_limit(infcx.tcx, obligation.cause.span);
 161
 162             note_obligation_cause(infcx, obligation);
 163         }
 164
 165         SelectionError::Unimplemented => {
 166             match &obligation.cause.code {
 167                 &ObligationCauseCode::CompareImplMethodObligation => {
 168                     infcx.tcx.sess.span_err(
 169                         obligation.cause.span,
 170                         format!(
 171                             "the requirement `{}` appears on the impl \
 172                             method but not on the corresponding trait method",
 173                             obligation.predicate.user_string(infcx.tcx)).as_slice());
 174                 }
 175                 _ => {
 176                     match obligation.predicate {
 177                         ty::Predicate::Trait(ref trait_predicate) => {
 178                             let trait_predicate =
 179                                 infcx.resolve_type_vars_if_possible(trait_predicate);
 180
 181                             if !trait_predicate.references_error() {
 182                                 let trait_ref = trait_predicate.to_poly_trait_ref();
 183                                 infcx.tcx.sess.span_err(
 184                                     obligation.cause.span,
 185                                     format!(
 186                                         "the trait `{}` is not implemented for the type `{}`",
 187                                         trait_ref.user_string(infcx.tcx),
 188                                         trait_ref.self_ty().user_string(infcx.tcx)).as_slice());
 189                                 // Check if it has a custom "#[rustc_on_unimplemented]"
 190                                 // error message, report with that message if it does
 191                                 let custom_note = report_on_unimplemented(infcx, &*trait_ref.0,
 192                                                                           obligation.cause.span);
 193                                 if let Some(s) = custom_note {
 194                                     infcx.tcx.sess.span_note(obligation.cause.span,
 195                                                              s.as_slice());
 196                                 }
 197                             }
 198                         }
 199
 200                         ty::Predicate::Equate(ref predicate) => {
 201                             let predicate = infcx.resolve_type_vars_if_possible(predicate);
 202                             let err = infcx.equality_predicate(obligation.cause.span,
 203                                                                &predicate).unwrap_err();
 204                             infcx.tcx.sess.span_err(
 205                                 obligation.cause.span,
 206                                 format!(
 207                                     "the requirement `{}` is not satisfied (`{}`)",
 208                                     predicate.user_string(infcx.tcx),
 209                                     ty::type_err_to_str(infcx.tcx, &err)).as_slice());
 210                         }
 211
 212                         ty::Predicate::RegionOutlives(ref predicate) => {
 213                             let predicate = infcx.resolve_type_vars_if_possible(predicate);
 214                             let err = infcx.region_outlives_predicate(obligation.cause.span,
 215                                                                       &predicate).unwrap_err();
 216                             infcx.tcx.sess.span_err(
 217                                 obligation.cause.span,
 218                                 format!(
 219                                     "the requirement `{}` is not satisfied (`{}`)",
 220                                     predicate.user_string(infcx.tcx),
 221                                     ty::type_err_to_str(infcx.tcx, &err)).as_slice());
 222                         }
 223
 224                         ty::Predicate::Projection(..) | ty::Predicate::TypeOutlives(..) => {
 225                                 let predicate =
 226                                     infcx.resolve_type_vars_if_possible(&obligation.predicate);
 227                                 infcx.tcx.sess.span_err(
 228                                     obligation.cause.span,
 229                                     format!(
 230                                         "the requirement `{}` is not satisfied",
 231                                         predicate.user_string(infcx.tcx)).as_slice());
 232                         }
 233                     }
 234                 }
 235             }
 236         }
 237
 238         OutputTypeParameterMismatch(ref expected_trait_ref, ref actual_trait_ref, ref e) => {
 239             let expected_trait_ref = infcx.resolve_type_vars_if_possible(&*expected_trait_ref);
 240             let actual_trait_ref = infcx.resolve_type_vars_if_possible(&*actual_trait_ref);
 241             if !ty::type_is_error(actual_trait_ref.self_ty()) {
 242                 infcx.tcx.sess.span_err(
 243                     obligation.cause.span,
 244                     format!(
 245                         "type mismatch: the type `{}` implements the trait `{}`, \
 246                         but the trait `{}` is required ({})",
 247                         expected_trait_ref.self_ty().user_string(infcx.tcx),
 248                         expected_trait_ref.user_string(infcx.tcx),
 249                         actual_trait_ref.user_string(infcx.tcx),
 250                         ty::type_err_to_str(infcx.tcx, e)).as_slice());
 251                     note_obligation_cause(infcx, obligation);
 252             }
 253         }
 254     }
 255 }
 256
 257 pub fn maybe_report_ambiguity<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 258                                         obligation: &PredicateObligation<'tcx>) {
 259     // Unable to successfully determine, probably means
 260     // insufficient type information, but could mean
 261     // ambiguous impls. The latter *ought* to be a
 262     // coherence violation, so we don't report it here.
 263
 264     let predicate = infcx.resolve_type_vars_if_possible(&obligation.predicate);
 265
 266     debug!("maybe_report_ambiguity(predicate={}, obligation={})",
 267            predicate.repr(infcx.tcx),
 268            obligation.repr(infcx.tcx));
 269
 270     match predicate {
 271         ty::Predicate::Trait(ref data) => {
 272             let trait_ref = data.to_poly_trait_ref();
 273             let self_ty = trait_ref.self_ty();
 274             let all_types = &trait_ref.substs().types;
 275             if all_types.iter().any(|&t| ty::type_is_error(t)) {
 276             } else if all_types.iter().any(|&t| ty::type_needs_infer(t)) {
 277                 // This is kind of a hack: it frequently happens that some earlier
 278                 // error prevents types from being fully inferred, and then we get
 279                 // a bunch of uninteresting errors saying something like "<generic
 280                 // #0> doesn't implement Sized".  It may even be true that we
 281                 // could just skip over all checks where the self-ty is an
 282                 // inference variable, but I was afraid that there might be an
 283                 // inference variable created, registered as an obligation, and
 284                 // then never forced by writeback, and hence by skipping here we'd
 285                 // be ignoring the fact that we don't KNOW the type works
 286                 // out. Though even that would probably be harmless, given that
 287                 // we're only talking about builtin traits, which are known to be
 288                 // inhabited. But in any case I just threw in this check for
 289                 // has_errors() to be sure that compilation isn't happening
 290                 // anyway. In that case, why inundate the user.
 291                 if !infcx.tcx.sess.has_errors() {
 292                     if
 293                         infcx.tcx.lang_items.sized_trait()
 294                         .map_or(false, |sized_id| sized_id == trait_ref.def_id())
 295                     {
 296                         infcx.tcx.sess.span_err(
 297                             obligation.cause.span,
 298                             format!(
 299                                 "unable to infer enough type information about `{}`; \
 300                                  type annotations required",
 301                                 self_ty.user_string(infcx.tcx)).as_slice());
 302                     } else {
 303                         infcx.tcx.sess.span_err(
 304                             obligation.cause.span,
 305                             format!(
 306                                 "type annotations required: cannot resolve `{}`",
 307                                 predicate.user_string(infcx.tcx)).as_slice());
 308                         note_obligation_cause(infcx, obligation);
 309                     }
 310                 }
 311             } else if !infcx.tcx.sess.has_errors() {
 312                 // Ambiguity. Coherence should have reported an error.
 313                 infcx.tcx.sess.span_bug(
 314                     obligation.cause.span,
 315                     format!(
 316                         "coherence failed to report ambiguity: \
 317                          cannot locate the impl of the trait `{}` for \
 318                          the type `{}`",
 319                         trait_ref.user_string(infcx.tcx),
 320                         self_ty.user_string(infcx.tcx)).as_slice());
 321             }
 322         }
 323
 324         _ => {
 325             if !infcx.tcx.sess.has_errors() {
 326                 infcx.tcx.sess.span_err(
 327                     obligation.cause.span,
 328                     format!(
 329                         "type annotations required: cannot resolve `{}`",
 330                         predicate.user_string(infcx.tcx)).as_slice());
 331                 note_obligation_cause(infcx, obligation);
 332             }
 333         }
 334     }
 335 }
 336
 337 fn note_obligation_cause<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 338                                    obligation: &PredicateObligation<'tcx>)
 339 {
 340     note_obligation_cause_code(infcx,
 341                                &obligation.predicate,
 342                                obligation.cause.span,
 343                                &obligation.cause.code);
 344 }
 345
 346 fn note_obligation_cause_code<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 347                                         predicate: &ty::Predicate<'tcx>,
 348                                         cause_span: Span,
 349                                         cause_code: &ObligationCauseCode<'tcx>)
 350 {
 351     let tcx = infcx.tcx;
 352     match *cause_code {
 353         ObligationCauseCode::MiscObligation => { }
 354         ObligationCauseCode::ItemObligation(item_def_id) => {
 355             let item_name = ty::item_path_str(tcx, item_def_id);
 356             tcx.sess.span_note(
 357                 cause_span,
 358                 format!("required by `{}`", item_name).as_slice());
 359         }
 360         ObligationCauseCode::ObjectCastObligation(object_ty) => {
 361             tcx.sess.span_note(
 362                 cause_span,
 363                 format!(
 364                     "required for the cast to the object type `{}`",
 365                     infcx.ty_to_string(object_ty)).as_slice());
 366         }
 367         ObligationCauseCode::RepeatVec => {
 368             tcx.sess.span_note(
 369                 cause_span,
 370                 "the `Copy` trait is required because the \
 371                  repeated element will be copied");
 372         }
 373         ObligationCauseCode::VariableType(_) => {
 374             tcx.sess.span_note(
 375                 cause_span,
 376                 "all local variables must have a statically known size");
 377         }
 378         ObligationCauseCode::ReturnType => {
 379             tcx.sess.span_note(
 380                 cause_span,
 381                 "the return type of a function must have a \
 382                  statically known size");
 383         }
 384         ObligationCauseCode::AssignmentLhsSized => {
 385             tcx.sess.span_note(
 386                 cause_span,
 387                 "the left-hand-side of an assignment must have a statically known size");
 388         }
 389         ObligationCauseCode::StructInitializerSized => {
 390             tcx.sess.span_note(
 391                 cause_span,
 392                 "structs must have a statically known size to be initialized");
 393         }
 394         ObligationCauseCode::ClosureCapture(var_id, closure_span, builtin_bound) => {
 395             let def_id = tcx.lang_items.from_builtin_kind(builtin_bound).unwrap();
 396             let trait_name = ty::item_path_str(tcx, def_id);
 397             let name = ty::local_var_name_str(tcx, var_id);
 398             span_note!(tcx.sess, closure_span,
 399                        "the closure that captures `{}` requires that all captured variables \
 400                        implement the trait `{}`",
 401                        name,
 402                        trait_name);
 403         }
 404         ObligationCauseCode::FieldSized => {
 405             span_note!(tcx.sess, cause_span,
 406                        "only the last field of a struct or enum variant \
 407                        may have a dynamically sized type")
 408         }
 409         ObligationCauseCode::ObjectSized => {
 410             span_note!(tcx.sess, cause_span,
 411                        "only sized types can be made into objects");
 412         }
 413         ObligationCauseCode::SharedStatic => {
 414             span_note!(tcx.sess, cause_span,
 415                        "shared static variables must have a type that implements `Sync`");
 416         }
 417         ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
 418             let parent_trait_ref = infcx.resolve_type_vars_if_possible(&data.parent_trait_ref);
 419             span_note!(tcx.sess, cause_span,
 420                        "required because it appears within the type `{}`",
 421                        parent_trait_ref.0.self_ty().user_string(infcx.tcx));
 422             let parent_predicate = parent_trait_ref.as_predicate();
 423             note_obligation_cause_code(infcx, &parent_predicate, cause_span, &*data.parent_code);
 424         }
 425         ObligationCauseCode::ImplDerivedObligation(ref data) => {
 426             let parent_trait_ref = infcx.resolve_type_vars_if_possible(&data.parent_trait_ref);
 427             span_note!(tcx.sess, cause_span,
 428                        "required because of the requirements on the impl of `{}` for `{}`",
 429                        parent_trait_ref.user_string(infcx.tcx),
 430                        parent_trait_ref.0.self_ty().user_string(infcx.tcx));
 431             let parent_predicate = parent_trait_ref.as_predicate();
 432             note_obligation_cause_code(infcx, &parent_predicate, cause_span, &*data.parent_code);
 433         }
 434         ObligationCauseCode::CompareImplMethodObligation => {
 435             span_note!(tcx.sess, cause_span,
 436                       "the requirement `{}` appears on the impl method\
 437                       but not on the corresponding trait method",
 438                       predicate.user_string(infcx.tcx));
 439         }
 440     }
 441 }
 442
 443 pub fn suggest_new_overflow_limit(tcx: &ty::ctxt, span: Span) {
 444     let current_limit = tcx.sess.recursion_limit.get();
 445     let suggested_limit = current_limit * 2;
 446     tcx.sess.span_note(
 447         span,
 448         &format!(
 449             "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
 450             suggested_limit)[]);
 451 }