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 middle::infer::InferCtxt;
  22 use middle::ty::{self, AsPredicate, ReferencesError, ToPolyTraitRef};
  23 use syntax::codemap::Span;
  24 use util::ppaux::{Repr, UserString};
  25
  26 pub fn report_fulfillment_errors<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  27                                            errors: &Vec<FulfillmentError<'tcx>>) {
  28     for error in errors.iter() {
  29         report_fulfillment_error(infcx, error);
  30     }
  31 }
  32
  33 fn report_fulfillment_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  34                                       error: &FulfillmentError<'tcx>) {
  35     match error.code {
  36         FulfillmentErrorCode::CodeSelectionError(ref e) => {
  37             report_selection_error(infcx, &error.obligation, e);
  38         }
  39         FulfillmentErrorCode::CodeProjectionError(ref e) => {
  40             report_projection_error(infcx, &error.obligation, e);
  41         }
  42         FulfillmentErrorCode::CodeAmbiguity => {
  43             maybe_report_ambiguity(infcx, &error.obligation);
  44         }
  45     }
  46 }
  47
  48 pub fn report_projection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  49                                          obligation: &PredicateObligation<'tcx>,
  50                                          error: &MismatchedProjectionTypes<'tcx>)
  51 {
  52     let predicate =
  53         infcx.resolve_type_vars_if_possible(&obligation.predicate);
  54     if !predicate.references_error() {
  55         infcx.tcx.sess.span_err(
  56             obligation.cause.span,
  57             format!(
  58                 "type mismatch resolving `{}`: {}",
  59                 predicate.user_string(infcx.tcx),
  60                 ty::type_err_to_str(infcx.tcx, &error.err)).as_slice());
  61         note_obligation_cause(infcx, obligation);
  62     }
  63 }
  64
  65 pub fn report_selection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
  66                                         obligation: &PredicateObligation<'tcx>,
  67                                         error: &SelectionError<'tcx>)
  68 {
  69     match *error {
  70         SelectionError::Overflow => {
  71             // We could track the stack here more precisely if we wanted, I imagine.
  72             let predicate =
  73                 infcx.resolve_type_vars_if_possible(&obligation.predicate);
  74             infcx.tcx.sess.span_err(
  75                 obligation.cause.span,
  76                 format!(
  77                     "overflow evaluating the requirement `{}`",
  78                     predicate.user_string(infcx.tcx)).as_slice());
  79
  80             suggest_new_overflow_limit(infcx.tcx, obligation.cause.span);
  81
  82             note_obligation_cause(infcx, obligation);
  83         }
  84         SelectionError::Unimplemented => {
  85             match obligation.predicate {
  86                 ty::Predicate::Trait(ref trait_predicate) => {
  87                     let trait_predicate =
  88                         infcx.resolve_type_vars_if_possible(trait_predicate);
  89                     if !trait_predicate.references_error() {
  90                         let trait_ref = trait_predicate.to_poly_trait_ref();
  91                         infcx.tcx.sess.span_err(
  92                             obligation.cause.span,
  93                             format!(
  94                                 "the trait `{}` is not implemented for the type `{}`",
  95                                 trait_ref.user_string(infcx.tcx),
  96                                 trait_ref.self_ty().user_string(infcx.tcx)).as_slice());
  97                     }
  98                 }
  99
 100                 ty::Predicate::Equate(ref predicate) => {
 101                     let predicate = infcx.resolve_type_vars_if_possible(predicate);
 102                     let err = infcx.equality_predicate(obligation.cause.span,
 103                                                              &predicate).unwrap_err();
 104                     infcx.tcx.sess.span_err(
 105                         obligation.cause.span,
 106                         format!(
 107                             "the requirement `{}` is not satisfied (`{}`)",
 108                             predicate.user_string(infcx.tcx),
 109                             ty::type_err_to_str(infcx.tcx, &err)).as_slice());
 110                 }
 111
 112                 ty::Predicate::RegionOutlives(ref predicate) => {
 113                     let predicate = infcx.resolve_type_vars_if_possible(predicate);
 114                     let err = infcx.region_outlives_predicate(obligation.cause.span,
 115                                                               &predicate).unwrap_err();
 116                     infcx.tcx.sess.span_err(
 117                         obligation.cause.span,
 118                         format!(
 119                             "the requirement `{}` is not satisfied (`{}`)",
 120                             predicate.user_string(infcx.tcx),
 121                             ty::type_err_to_str(infcx.tcx, &err)).as_slice());
 122                 }
 123
 124                 ty::Predicate::Projection(..) |
 125                 ty::Predicate::TypeOutlives(..) => {
 126                     let predicate =
 127                         infcx.resolve_type_vars_if_possible(&obligation.predicate);
 128                     infcx.tcx.sess.span_err(
 129                         obligation.cause.span,
 130                         format!(
 131                             "the requirement `{}` is not satisfied",
 132                             predicate.user_string(infcx.tcx)).as_slice());
 133                 }
 134             }
 135         }
 136         OutputTypeParameterMismatch(ref expected_trait_ref, ref actual_trait_ref, ref e) => {
 137             let expected_trait_ref = infcx.resolve_type_vars_if_possible(&*expected_trait_ref);
 138             let actual_trait_ref = infcx.resolve_type_vars_if_possible(&*actual_trait_ref);
 139             if !ty::type_is_error(actual_trait_ref.self_ty()) {
 140                 infcx.tcx.sess.span_err(
 141                     obligation.cause.span,
 142                     format!(
 143                         "type mismatch: the type `{}` implements the trait `{}`, \
 144                          but the trait `{}` is required ({})",
 145                         expected_trait_ref.self_ty().user_string(infcx.tcx),
 146                         expected_trait_ref.user_string(infcx.tcx),
 147                         actual_trait_ref.user_string(infcx.tcx),
 148                         ty::type_err_to_str(infcx.tcx, e)).as_slice());
 149                 note_obligation_cause(infcx, obligation);
 150             }
 151         }
 152     }
 153 }
 154
 155 pub fn maybe_report_ambiguity<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 156                                         obligation: &PredicateObligation<'tcx>) {
 157     // Unable to successfully determine, probably means
 158     // insufficient type information, but could mean
 159     // ambiguous impls. The latter *ought* to be a
 160     // coherence violation, so we don't report it here.
 161
 162     let predicate = infcx.resolve_type_vars_if_possible(&obligation.predicate);
 163
 164     debug!("maybe_report_ambiguity(predicate={}, obligation={})",
 165            predicate.repr(infcx.tcx),
 166            obligation.repr(infcx.tcx));
 167
 168     match predicate {
 169         ty::Predicate::Trait(ref data) => {
 170             let trait_ref = data.to_poly_trait_ref();
 171             let self_ty = trait_ref.self_ty();
 172             let all_types = &trait_ref.substs().types;
 173             if all_types.iter().any(|&t| ty::type_is_error(t)) {
 174             } else if all_types.iter().any(|&t| ty::type_needs_infer(t)) {
 175                 // This is kind of a hack: it frequently happens that some earlier
 176                 // error prevents types from being fully inferred, and then we get
 177                 // a bunch of uninteresting errors saying something like "<generic
 178                 // #0> doesn't implement Sized".  It may even be true that we
 179                 // could just skip over all checks where the self-ty is an
 180                 // inference variable, but I was afraid that there might be an
 181                 // inference variable created, registered as an obligation, and
 182                 // then never forced by writeback, and hence by skipping here we'd
 183                 // be ignoring the fact that we don't KNOW the type works
 184                 // out. Though even that would probably be harmless, given that
 185                 // we're only talking about builtin traits, which are known to be
 186                 // inhabited. But in any case I just threw in this check for
 187                 // has_errors() to be sure that compilation isn't happening
 188                 // anyway. In that case, why inundate the user.
 189                 if !infcx.tcx.sess.has_errors() {
 190                     if
 191                         infcx.tcx.lang_items.sized_trait()
 192                         .map_or(false, |sized_id| sized_id == trait_ref.def_id())
 193                     {
 194                         infcx.tcx.sess.span_err(
 195                             obligation.cause.span,
 196                             format!(
 197                                 "unable to infer enough type information about `{}`; \
 198                                  type annotations required",
 199                                 self_ty.user_string(infcx.tcx)).as_slice());
 200                     } else {
 201                         infcx.tcx.sess.span_err(
 202                             obligation.cause.span,
 203                             format!(
 204                                 "type annotations required: cannot resolve `{}`",
 205                                 predicate.user_string(infcx.tcx)).as_slice());
 206                         note_obligation_cause(infcx, obligation);
 207                     }
 208                 }
 209             } else if !infcx.tcx.sess.has_errors() {
 210                 // Ambiguity. Coherence should have reported an error.
 211                 infcx.tcx.sess.span_bug(
 212                     obligation.cause.span,
 213                     format!(
 214                         "coherence failed to report ambiguity: \
 215                          cannot locate the impl of the trait `{}` for \
 216                          the type `{}`",
 217                         trait_ref.user_string(infcx.tcx),
 218                         self_ty.user_string(infcx.tcx)).as_slice());
 219             }
 220         }
 221
 222         _ => {
 223             if !infcx.tcx.sess.has_errors() {
 224                 infcx.tcx.sess.span_err(
 225                     obligation.cause.span,
 226                     format!(
 227                         "type annotations required: cannot resolve `{}`",
 228                         predicate.user_string(infcx.tcx)).as_slice());
 229                 note_obligation_cause(infcx, obligation);
 230             }
 231         }
 232     }
 233 }
 234
 235 fn note_obligation_cause<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 236                                    obligation: &PredicateObligation<'tcx>)
 237 {
 238     note_obligation_cause_code(infcx,
 239                                &obligation.predicate,
 240                                obligation.cause.span,
 241                                &obligation.cause.code);
 242 }
 243
 244 fn note_obligation_cause_code<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
 245                                         _predicate: &ty::Predicate<'tcx>,
 246                                         cause_span: Span,
 247                                         cause_code: &ObligationCauseCode<'tcx>)
 248 {
 249     let tcx = infcx.tcx;
 250     match *cause_code {
 251         ObligationCauseCode::MiscObligation => { }
 252         ObligationCauseCode::ItemObligation(item_def_id) => {
 253             let item_name = ty::item_path_str(tcx, item_def_id);
 254             tcx.sess.span_note(
 255                 cause_span,
 256                 format!("required by `{}`", item_name).as_slice());
 257         }
 258         ObligationCauseCode::ObjectCastObligation(object_ty) => {
 259             tcx.sess.span_note(
 260                 cause_span,
 261                 format!(
 262                     "required for the cast to the object type `{}`",
 263                     infcx.ty_to_string(object_ty)).as_slice());
 264         }
 265         ObligationCauseCode::RepeatVec => {
 266             tcx.sess.span_note(
 267                 cause_span,
 268                 "the `Copy` trait is required because the \
 269                  repeated element will be copied");
 270         }
 271         ObligationCauseCode::VariableType(_) => {
 272             tcx.sess.span_note(
 273                 cause_span,
 274                 "all local variables must have a statically known size");
 275         }
 276         ObligationCauseCode::ReturnType => {
 277             tcx.sess.span_note(
 278                 cause_span,
 279                 "the return type of a function must have a \
 280                  statically known size");
 281         }
 282         ObligationCauseCode::AssignmentLhsSized => {
 283             tcx.sess.span_note(
 284                 cause_span,
 285                 "the left-hand-side of an assignment must have a statically known size");
 286         }
 287         ObligationCauseCode::StructInitializerSized => {
 288             tcx.sess.span_note(
 289                 cause_span,
 290                 "structs must have a statically known size to be initialized");
 291         }
 292         ObligationCauseCode::ClosureCapture(var_id, closure_span, builtin_bound) => {
 293             let def_id = tcx.lang_items.from_builtin_kind(builtin_bound).unwrap();
 294             let trait_name = ty::item_path_str(tcx, def_id);
 295             let name = ty::local_var_name_str(tcx, var_id);
 296             span_note!(tcx.sess, closure_span,
 297                        "the closure that captures `{}` requires that all captured variables \
 298                        implement the trait `{}`",
 299                        name,
 300                        trait_name);
 301         }
 302         ObligationCauseCode::FieldSized => {
 303             span_note!(tcx.sess, cause_span,
 304                        "only the last field of a struct or enum variant \
 305                        may have a dynamically sized type")
 306         }
 307         ObligationCauseCode::ObjectSized => {
 308             span_note!(tcx.sess, cause_span,
 309                        "only sized types can be made into objects");
 310         }
 311         ObligationCauseCode::SharedStatic => {
 312             span_note!(tcx.sess, cause_span,
 313                        "shared static variables must have a type that implements `Sync`");
 314         }
 315         ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
 316             let parent_trait_ref = infcx.resolve_type_vars_if_possible(&data.parent_trait_ref);
 317             span_note!(tcx.sess, cause_span,
 318                        "required because it appears within the type `{}`",
 319                        parent_trait_ref.0.self_ty().user_string(infcx.tcx));
 320             let parent_predicate = parent_trait_ref.as_predicate();
 321             note_obligation_cause_code(infcx, &parent_predicate, cause_span, &*data.parent_code);
 322         }
 323         ObligationCauseCode::ImplDerivedObligation(ref data) => {
 324             let parent_trait_ref = infcx.resolve_type_vars_if_possible(&data.parent_trait_ref);
 325             span_note!(tcx.sess, cause_span,
 326                        "required because of the requirements on the impl of `{}` for `{}`",
 327                        parent_trait_ref.user_string(infcx.tcx),
 328                        parent_trait_ref.0.self_ty().user_string(infcx.tcx));
 329             let parent_predicate = parent_trait_ref.as_predicate();
 330             note_obligation_cause_code(infcx, &parent_predicate, cause_span, &*data.parent_code);
 331         }
 332     }
 333 }
 334
 335 pub fn suggest_new_overflow_limit(tcx: &ty::ctxt, span: Span) {
 336     let current_limit = tcx.sess.recursion_limit.get();
 337     let suggested_limit = current_limit * 2;
 338     tcx.sess.span_note(
 339         span,
 340         format!(
 341             "consider adding a `#![recursion_limit=\"{}\"]` attribute to your crate",
 342             suggested_limit)[]);
 343 }