compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

   1 use rustc_errors::DiagnosticBuilder;
   2 use rustc_infer::infer::canonical::Canonical;
   3 use rustc_infer::infer::error_reporting::nice_region_error::NiceRegionError;
   4 use rustc_infer::infer::region_constraints::Constraint;
   5 use rustc_infer::infer::{InferCtxt, RegionResolutionError, SubregionOrigin, TyCtxtInferExt as _};
   6 use rustc_infer::traits::{Normalized, ObligationCause, TraitEngine, TraitEngineExt};
   7 use rustc_middle::ty::error::TypeError;
   8 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
   9 use rustc_span::Span;
  10 use rustc_trait_selection::traits::query::type_op;
  11 use rustc_trait_selection::traits::{SelectionContext, TraitEngineExt as _};
  12 use rustc_traits::{type_op_ascribe_user_type_with_span, type_op_prove_predicate_with_cause};
  13
  14 use std::fmt;
  15 use std::rc::Rc;
  16
  17 use crate::region_infer::values::RegionElement;
  18 use crate::MirBorrowckCtxt;
  19
  20 #[derive(Clone)]
  21 crate struct UniverseInfo<'tcx>(UniverseInfoInner<'tcx>);
  22
  23 /// What operation a universe was created for.
  24 #[derive(Clone)]
  25 enum UniverseInfoInner<'tcx> {
  26     /// Relating two types which have binders.
  27     RelateTys { expected: Ty<'tcx>, found: Ty<'tcx> },
  28     /// Created from performing a `TypeOp`.
  29     TypeOp(Rc<dyn TypeOpInfo<'tcx> + 'tcx>),
  30     /// Any other reason.
  31     Other,
  32 }
  33
  34 impl<'tcx> UniverseInfo<'tcx> {
  35     crate fn other() -> UniverseInfo<'tcx> {
  36         UniverseInfo(UniverseInfoInner::Other)
  37     }
  38
  39     crate fn relate(expected: Ty<'tcx>, found: Ty<'tcx>) -> UniverseInfo<'tcx> {
  40         UniverseInfo(UniverseInfoInner::RelateTys { expected, found })
  41     }
  42
  43     crate fn report_error(
  44         &self,
  45         mbcx: &mut MirBorrowckCtxt<'_, 'tcx>,
  46         placeholder: ty::PlaceholderRegion,
  47         error_element: RegionElement,
  48         cause: ObligationCause<'tcx>,
  49     ) {
  50         match self.0 {
  51             UniverseInfoInner::RelateTys { expected, found } => {
  52                 let err = mbcx.infcx.report_mismatched_types(
  53                     &cause,
  54                     expected,
  55                     found,
  56                     TypeError::RegionsPlaceholderMismatch,
  57                 );
  58                 mbcx.buffer_error(err);
  59             }
  60             UniverseInfoInner::TypeOp(ref type_op_info) => {
  61                 type_op_info.report_error(mbcx, placeholder, error_element, cause);
  62             }
  63             UniverseInfoInner::Other => {
  64                 // FIXME: This error message isn't great, but it doesn't show
  65                 // up in the existing UI tests. Consider investigating this
  66                 // some more.
  67                 mbcx.buffer_error(
  68                     mbcx.infcx.tcx.sess.struct_span_err(cause.span, "higher-ranked subtype error"),
  69                 );
  70             }
  71         }
  72     }
  73 }
  74
  75 crate trait ToUniverseInfo<'tcx> {
  76     fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx>;
  77 }
  78
  79 impl<'tcx> ToUniverseInfo<'tcx>
  80     for Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::prove_predicate::ProvePredicate<'tcx>>>
  81 {
  82     fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
  83         UniverseInfo(UniverseInfoInner::TypeOp(Rc::new(PredicateQuery {
  84             canonical_query: self,
  85             base_universe,
  86         })))
  87     }
  88 }
  89
  90 impl<'tcx, T: Copy + fmt::Display + TypeFoldable<'tcx> + 'tcx> ToUniverseInfo<'tcx>
  91     for Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::Normalize<T>>>
  92 {
  93     fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
  94         UniverseInfo(UniverseInfoInner::TypeOp(Rc::new(NormalizeQuery {
  95             canonical_query: self,
  96             base_universe,
  97         })))
  98     }
  99 }
 100
 101 impl<'tcx> ToUniverseInfo<'tcx>
 102     for Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::AscribeUserType<'tcx>>>
 103 {
 104     fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
 105         UniverseInfo(UniverseInfoInner::TypeOp(Rc::new(AscribeUserTypeQuery {
 106             canonical_query: self,
 107             base_universe,
 108         })))
 109     }
 110 }
 111
 112 impl<'tcx, F, G> ToUniverseInfo<'tcx> for Canonical<'tcx, type_op::custom::CustomTypeOp<F, G>> {
 113     fn to_universe_info(self, _base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
 114         // We can't rerun custom type ops.
 115         UniverseInfo::other()
 116     }
 117 }
 118
 119 #[allow(unused_lifetimes)]
 120 trait TypeOpInfo<'tcx> {
 121     /// Returns an error to be reported if rerunning the type op fails to
 122     /// recover the error's cause.
 123     fn fallback_error(&self, tcx: TyCtxt<'tcx>, span: Span) -> DiagnosticBuilder<'tcx>;
 124
 125     fn base_universe(&self) -> ty::UniverseIndex;
 126
 127     fn nice_error(
 128         &self,
 129         tcx: TyCtxt<'tcx>,
 130         cause: ObligationCause<'tcx>,
 131         placeholder_region: ty::Region<'tcx>,
 132         error_region: Option<ty::Region<'tcx>>,
 133     ) -> Option<DiagnosticBuilder<'tcx>>;
 134
 135     fn report_error(
 136         &self,
 137         mbcx: &mut MirBorrowckCtxt<'_, 'tcx>,
 138         placeholder: ty::PlaceholderRegion,
 139         error_element: RegionElement,
 140         cause: ObligationCause<'tcx>,
 141     ) {
 142         let tcx = mbcx.infcx.tcx;
 143         let base_universe = self.base_universe();
 144
 145         let Some(adjusted_universe) =
 146             placeholder.universe.as_u32().checked_sub(base_universe.as_u32())
 147         else {
 148             mbcx.buffer_error(self.fallback_error(tcx, cause.span));
 149             return;
 150         };
 151
 152         let placeholder_region = tcx.mk_region(ty::RePlaceholder(ty::Placeholder {
 153             name: placeholder.name,
 154             universe: adjusted_universe.into(),
 155         }));
 156
 157         let error_region =
 158             if let RegionElement::PlaceholderRegion(error_placeholder) = error_element {
 159                 let adjusted_universe =
 160                     error_placeholder.universe.as_u32().checked_sub(base_universe.as_u32());
 161                 adjusted_universe.map(|adjusted| {
 162                     tcx.mk_region(ty::RePlaceholder(ty::Placeholder {
 163                         name: error_placeholder.name,
 164                         universe: adjusted.into(),
 165                     }))
 166                 })
 167             } else {
 168                 None
 169             };
 170
 171         debug!(?placeholder_region);
 172
 173         let span = cause.span;
 174         let nice_error = self.nice_error(tcx, cause, placeholder_region, error_region);
 175
 176         if let Some(nice_error) = nice_error {
 177             mbcx.buffer_error(nice_error);
 178         } else {
 179             mbcx.buffer_error(self.fallback_error(tcx, span));
 180         }
 181     }
 182 }
 183
 184 struct PredicateQuery<'tcx> {
 185     canonical_query:
 186         Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::prove_predicate::ProvePredicate<'tcx>>>,
 187     base_universe: ty::UniverseIndex,
 188 }
 189
 190 impl<'tcx> TypeOpInfo<'tcx> for PredicateQuery<'tcx> {
 191     fn fallback_error(&self, tcx: TyCtxt<'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
 192         let mut err = tcx.sess.struct_span_err(span, "higher-ranked lifetime error");
 193         err.note(&format!("could not prove {}", self.canonical_query.value.value.predicate));
 194         err
 195     }
 196
 197     fn base_universe(&self) -> ty::UniverseIndex {
 198         self.base_universe
 199     }
 200
 201     fn nice_error(
 202         &self,
 203         tcx: TyCtxt<'tcx>,
 204         cause: ObligationCause<'tcx>,
 205         placeholder_region: ty::Region<'tcx>,
 206         error_region: Option<ty::Region<'tcx>>,
 207     ) -> Option<DiagnosticBuilder<'tcx>> {
 208         tcx.infer_ctxt().enter_with_canonical(
 209             cause.span,
 210             &self.canonical_query,
 211             |ref infcx, key, _| {
 212                 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(tcx);
 213                 type_op_prove_predicate_with_cause(infcx, &mut *fulfill_cx, key, cause);
 214                 try_extract_error_from_fulfill_cx(
 215                     fulfill_cx,
 216                     infcx,
 217                     placeholder_region,
 218                     error_region,
 219                 )
 220             },
 221         )
 222     }
 223 }
 224
 225 struct NormalizeQuery<'tcx, T> {
 226     canonical_query: Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::Normalize<T>>>,
 227     base_universe: ty::UniverseIndex,
 228 }
 229
 230 impl<'tcx, T> TypeOpInfo<'tcx> for NormalizeQuery<'tcx, T>
 231 where
 232     T: Copy + fmt::Display + TypeFoldable<'tcx> + 'tcx,
 233 {
 234     fn fallback_error(&self, tcx: TyCtxt<'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
 235         let mut err = tcx.sess.struct_span_err(span, "higher-ranked lifetime error");
 236         err.note(&format!("could not normalize `{}`", self.canonical_query.value.value.value));
 237         err
 238     }
 239
 240     fn base_universe(&self) -> ty::UniverseIndex {
 241         self.base_universe
 242     }
 243
 244     fn nice_error(
 245         &self,
 246         tcx: TyCtxt<'tcx>,
 247         cause: ObligationCause<'tcx>,
 248         placeholder_region: ty::Region<'tcx>,
 249         error_region: Option<ty::Region<'tcx>>,
 250     ) -> Option<DiagnosticBuilder<'tcx>> {
 251         tcx.infer_ctxt().enter_with_canonical(
 252             cause.span,
 253             &self.canonical_query,
 254             |ref infcx, key, _| {
 255                 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(tcx);
 256
 257                 let mut selcx = SelectionContext::new(infcx);
 258
 259                 // FIXME(lqd): Unify and de-duplicate the following with the actual
 260                 // `rustc_traits::type_op::type_op_normalize` query to allow the span we need in the
 261                 // `ObligationCause`. The normalization results are currently different between
 262                 // `AtExt::normalize` used in the query and `normalize` called below: the former fails
 263                 // to normalize the `nll/relate_tys/impl-fn-ignore-binder-via-bottom.rs` test. Check
 264                 // after #85499 lands to see if its fixes have erased this difference.
 265                 let (param_env, value) = key.into_parts();
 266                 let Normalized { value: _, obligations } = rustc_trait_selection::traits::normalize(
 267                     &mut selcx,
 268                     param_env,
 269                     cause,
 270                     value.value,
 271                 );
 272                 fulfill_cx.register_predicate_obligations(infcx, obligations);
 273
 274                 try_extract_error_from_fulfill_cx(
 275                     fulfill_cx,
 276                     infcx,
 277                     placeholder_region,
 278                     error_region,
 279                 )
 280             },
 281         )
 282     }
 283 }
 284
 285 struct AscribeUserTypeQuery<'tcx> {
 286     canonical_query: Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::AscribeUserType<'tcx>>>,
 287     base_universe: ty::UniverseIndex,
 288 }
 289
 290 impl<'tcx> TypeOpInfo<'tcx> for AscribeUserTypeQuery<'tcx> {
 291     fn fallback_error(&self, tcx: TyCtxt<'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
 292         // FIXME: This error message isn't great, but it doesn't show up in the existing UI tests,
 293         // and is only the fallback when the nice error fails. Consider improving this some more.
 294         tcx.sess.struct_span_err(span, "higher-ranked lifetime error")
 295     }
 296
 297     fn base_universe(&self) -> ty::UniverseIndex {
 298         self.base_universe
 299     }
 300
 301     fn nice_error(
 302         &self,
 303         tcx: TyCtxt<'tcx>,
 304         cause: ObligationCause<'tcx>,
 305         placeholder_region: ty::Region<'tcx>,
 306         error_region: Option<ty::Region<'tcx>>,
 307     ) -> Option<DiagnosticBuilder<'tcx>> {
 308         tcx.infer_ctxt().enter_with_canonical(
 309             cause.span,
 310             &self.canonical_query,
 311             |ref infcx, key, _| {
 312                 let mut fulfill_cx = <dyn TraitEngine<'_>>::new(tcx);
 313                 type_op_ascribe_user_type_with_span(infcx, &mut *fulfill_cx, key, Some(cause.span))
 314                     .ok()?;
 315                 try_extract_error_from_fulfill_cx(
 316                     fulfill_cx,
 317                     infcx,
 318                     placeholder_region,
 319                     error_region,
 320                 )
 321             },
 322         )
 323     }
 324 }
 325
 326 #[instrument(skip(fulfill_cx, infcx), level = "debug")]
 327 fn try_extract_error_from_fulfill_cx<'tcx>(
 328     mut fulfill_cx: Box<dyn TraitEngine<'tcx> + 'tcx>,
 329     infcx: &InferCtxt<'_, 'tcx>,
 330     placeholder_region: ty::Region<'tcx>,
 331     error_region: Option<ty::Region<'tcx>>,
 332 ) -> Option<DiagnosticBuilder<'tcx>> {
 333     let tcx = infcx.tcx;
 334
 335     // We generally shouldn't have errors here because the query was
 336     // already run, but there's no point using `delay_span_bug`
 337     // when we're going to emit an error here anyway.
 338     let _errors = fulfill_cx.select_all_or_error(infcx);
 339
 340     let (sub_region, cause) = infcx.with_region_constraints(|region_constraints| {
 341         debug!("{:#?}", region_constraints);
 342         region_constraints.constraints.iter().find_map(|(constraint, cause)| {
 343             match *constraint {
 344                 Constraint::RegSubReg(sub, sup) if sup == placeholder_region && sup != sub => {
 345                     Some((sub, cause.clone()))
 346                 }
 347                 // FIXME: Should this check the universe of the var?
 348                 Constraint::VarSubReg(vid, sup) if sup == placeholder_region => {
 349                     Some((tcx.mk_region(ty::ReVar(vid)), cause.clone()))
 350                 }
 351                 _ => None,
 352             }
 353         })
 354     })?;
 355
 356     debug!(?sub_region, "cause = {:#?}", cause);
 357     let nice_error = match (error_region, *sub_region) {
 358         (Some(error_region), ty::ReVar(vid)) => NiceRegionError::new(
 359             infcx,
 360             RegionResolutionError::SubSupConflict(
 361                 vid,
 362                 infcx.region_var_origin(vid),
 363                 cause.clone(),
 364                 error_region,
 365                 cause.clone(),
 366                 placeholder_region,
 367                 vec![],
 368             ),
 369         ),
 370         (Some(error_region), _) => NiceRegionError::new(
 371             infcx,
 372             RegionResolutionError::ConcreteFailure(cause.clone(), error_region, placeholder_region),
 373         ),
 374         // Note universe here is wrong...
 375         (None, ty::ReVar(vid)) => NiceRegionError::new(
 376             infcx,
 377             RegionResolutionError::UpperBoundUniverseConflict(
 378                 vid,
 379                 infcx.region_var_origin(vid),
 380                 infcx.universe_of_region(sub_region),
 381                 cause.clone(),
 382                 placeholder_region,
 383             ),
 384         ),
 385         (None, _) => NiceRegionError::new(
 386             infcx,
 387             RegionResolutionError::ConcreteFailure(cause.clone(), sub_region, placeholder_region),
 388         ),
 389     };
 390     nice_error.try_report_from_nll().or_else(|| {
 391         if let SubregionOrigin::Subtype(trace) = cause {
 392             Some(
 393                 infcx.report_and_explain_type_error(*trace, &TypeError::RegionsPlaceholderMismatch),
 394             )
 395         } else {
 396             None
 397         }
 398     })
 399 }