compiler/rustc_infer/src/infer/error_reporting/nice_region_error/trait_impl_difference.rs

   1 //! Error Reporting for `impl` items that do not match the obligations from their `trait`.
   2
   3 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
   4 use crate::infer::lexical_region_resolve::RegionResolutionError;
   5 use crate::infer::{SubregionOrigin, Subtype, ValuePairs};
   6 use crate::traits::ObligationCauseCode::CompareImplMethodObligation;
   7 use rustc_errors::ErrorReported;
   8 use rustc_hir as hir;
   9 use rustc_hir::def::Res;
  10 use rustc_hir::def_id::DefId;
  11 use rustc_hir::intravisit::Visitor;
  12 use rustc_middle::ty::print::RegionHighlightMode;
  13 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeVisitor};
  14
  15 use rustc_span::{MultiSpan, Span, Symbol};
  16
  17 use std::ops::ControlFlow;
  18
  19 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  20     /// Print the error message for lifetime errors when the `impl` doesn't conform to the `trait`.
  21     pub(super) fn try_report_impl_not_conforming_to_trait(&self) -> Option<ErrorReported> {
  22         let error = self.error.as_ref()?;
  23         debug!("try_report_impl_not_conforming_to_trait {:?}", error);
  24         if let RegionResolutionError::SubSupConflict(
  25             _,
  26             var_origin,
  27             sub_origin,
  28             _sub,
  29             sup_origin,
  30             _sup,
  31         ) = error.clone()
  32         {
  33             if let (&Subtype(ref sup_trace), &Subtype(ref sub_trace)) = (&sup_origin, &sub_origin) {
  34                 if let (
  35                     ValuePairs::Types(sub_expected_found),
  36                     ValuePairs::Types(sup_expected_found),
  37                     CompareImplMethodObligation { trait_item_def_id, .. },
  38                 ) = (&sub_trace.values, &sup_trace.values, &sub_trace.cause.code)
  39                 {
  40                     if sup_expected_found == sub_expected_found {
  41                         self.emit_err(
  42                             var_origin.span(),
  43                             sub_expected_found.expected,
  44                             sub_expected_found.found,
  45                             *trait_item_def_id,
  46                         );
  47                         return Some(ErrorReported);
  48                     }
  49                 }
  50             }
  51         }
  52         if let RegionResolutionError::ConcreteFailure(origin, _, _)
  53         | RegionResolutionError::GenericBoundFailure(origin, _, _) = error.clone()
  54         {
  55             if let SubregionOrigin::CompareImplTypeObligation {
  56                 span,
  57                 impl_item_def_id,
  58                 trait_item_def_id,
  59             } = origin
  60             {
  61                 self.emit_associated_type_err(
  62                     span,
  63                     self.infcx.tcx.item_name(impl_item_def_id),
  64                     impl_item_def_id,
  65                     trait_item_def_id,
  66                 );
  67                 return Some(ErrorReported);
  68             }
  69         }
  70         None
  71     }
  72
  73     fn emit_err(&self, sp: Span, expected: Ty<'tcx>, found: Ty<'tcx>, trait_def_id: DefId) {
  74         let trait_sp = self.tcx().def_span(trait_def_id);
  75         let mut err = self
  76             .tcx()
  77             .sess
  78             .struct_span_err(sp, "`impl` item signature doesn't match `trait` item signature");
  79
  80         // Mark all unnamed regions in the type with a number.
  81         // This diagnostic is called in response to lifetime errors, so be informative.
  82         struct HighlightBuilder<'tcx> {
  83             highlight: RegionHighlightMode,
  84             tcx: TyCtxt<'tcx>,
  85             counter: usize,
  86         }
  87
  88         impl HighlightBuilder<'tcx> {
  89             fn build(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> RegionHighlightMode {
  90                 let mut builder =
  91                     HighlightBuilder { highlight: RegionHighlightMode::default(), counter: 1, tcx };
  92                 builder.visit_ty(ty);
  93                 builder.highlight
  94             }
  95         }
  96
  97         impl<'tcx> ty::fold::TypeVisitor<'tcx> for HighlightBuilder<'tcx> {
  98             fn tcx_for_anon_const_substs(&self) -> Option<TyCtxt<'tcx>> {
  99                 Some(self.tcx)
 100             }
 101
 102             fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
 103                 if !r.has_name() && self.counter <= 3 {
 104                     self.highlight.highlighting_region(r, self.counter);
 105                     self.counter += 1;
 106                 }
 107                 r.super_visit_with(self)
 108             }
 109         }
 110
 111         let expected_highlight = HighlightBuilder::build(self.tcx(), expected);
 112         let expected = self
 113             .infcx
 114             .extract_inference_diagnostics_data(expected.into(), Some(expected_highlight))
 115             .name;
 116         let found_highlight = HighlightBuilder::build(self.tcx(), found);
 117         let found =
 118             self.infcx.extract_inference_diagnostics_data(found.into(), Some(found_highlight)).name;
 119
 120         err.span_label(sp, &format!("found `{}`", found));
 121         err.span_label(trait_sp, &format!("expected `{}`", expected));
 122
 123         // Get the span of all the used type parameters in the method.
 124         let assoc_item = self.tcx().associated_item(trait_def_id);
 125         let mut visitor = TypeParamSpanVisitor { tcx: self.tcx(), types: vec![] };
 126         match assoc_item.kind {
 127             ty::AssocKind::Fn => {
 128                 let hir = self.tcx().hir();
 129                 if let Some(hir_id) =
 130                     assoc_item.def_id.as_local().map(|id| hir.local_def_id_to_hir_id(id))
 131                 {
 132                     if let Some(decl) = hir.fn_decl_by_hir_id(hir_id) {
 133                         visitor.visit_fn_decl(decl);
 134                     }
 135                 }
 136             }
 137             _ => {}
 138         }
 139         let mut type_param_span: MultiSpan = visitor.types.to_vec().into();
 140         for &span in &visitor.types {
 141             type_param_span.push_span_label(
 142                 span,
 143                 "consider borrowing this type parameter in the trait".to_string(),
 144             );
 145         }
 146
 147         err.note(&format!("expected `{}`\n   found `{}`", expected, found));
 148
 149         err.span_help(
 150             type_param_span,
 151             "the lifetime requirements from the `impl` do not correspond to the requirements in \
 152              the `trait`",
 153         );
 154         if visitor.types.is_empty() {
 155             err.help(
 156                 "verify the lifetime relationships in the `trait` and `impl` between the `self` \
 157                  argument, the other inputs and its output",
 158             );
 159         }
 160         err.emit();
 161     }
 162
 163     fn emit_associated_type_err(
 164         &self,
 165         span: Span,
 166         item_name: Symbol,
 167         impl_item_def_id: DefId,
 168         trait_item_def_id: DefId,
 169     ) {
 170         let impl_sp = self.tcx().def_span(impl_item_def_id);
 171         let trait_sp = self.tcx().def_span(trait_item_def_id);
 172         let mut err = self
 173             .tcx()
 174             .sess
 175             .struct_span_err(span, &format!("`impl` associated type signature for `{}` doesn't match `trait` associated type signature", item_name));
 176         err.span_label(impl_sp, "found");
 177         err.span_label(trait_sp, "expected");
 178
 179         err.emit();
 180     }
 181 }
 182
 183 struct TypeParamSpanVisitor<'tcx> {
 184     tcx: TyCtxt<'tcx>,
 185     types: Vec<Span>,
 186 }
 187
 188 impl Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
 189     type Map = rustc_middle::hir::map::Map<'tcx>;
 190
 191     fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
 192         hir::intravisit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
 193     }
 194
 195     fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
 196         match arg.kind {
 197             hir::TyKind::Rptr(_, ref mut_ty) => {
 198                 // We don't want to suggest looking into borrowing `&T` or `&Self`.
 199                 hir::intravisit::walk_ty(self, mut_ty.ty);
 200                 return;
 201             }
 202             hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
 203                 [segment]
 204                     if segment
 205                         .res
 206                         .map(|res| {
 207                             matches!(
 208                                 res,
 209                                 Res::SelfTy(_, _) | Res::Def(hir::def::DefKind::TyParam, _)
 210                             )
 211                         })
 212                         .unwrap_or(false) =>
 213                 {
 214                     self.types.push(path.span);
 215                 }
 216                 _ => {}
 217             },
 218             _ => {}
 219         }
 220         hir::intravisit::walk_ty(self, arg);
 221     }
 222 }