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