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