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::error::ExpectedFound;
  13 use rustc_middle::ty::{self, Ty, TyCtxt};
  14 use rustc_span::{MultiSpan, Span, Symbol};
  15
  16 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  17     /// Print the error message for lifetime errors when the `impl` doesn't conform to the `trait`.
  18     pub(super) fn try_report_impl_not_conforming_to_trait(&self) -> Option<ErrorReported> {
  19         let error = self.error.as_ref()?;
  20         debug!("try_report_impl_not_conforming_to_trait {:?}", error);
  21         if let RegionResolutionError::SubSupConflict(
  22             _,
  23             var_origin,
  24             sub_origin,
  25             _sub,
  26             sup_origin,
  27             _sup,
  28         ) = error.clone()
  29         {
  30             if let (&Subtype(ref sup_trace), &Subtype(ref sub_trace)) = (&sup_origin, &sub_origin) {
  31                 if let (
  32                     ValuePairs::Types(sub_expected_found),
  33                     ValuePairs::Types(sup_expected_found),
  34                     CompareImplMethodObligation { trait_item_def_id, .. },
  35                 ) = (&sub_trace.values, &sup_trace.values, &sub_trace.cause.code)
  36                 {
  37                     if sup_expected_found == sub_expected_found {
  38                         self.emit_err(
  39                             var_origin.span(),
  40                             sub_expected_found.expected,
  41                             sub_expected_found.found,
  42                             *trait_item_def_id,
  43                         );
  44                         return Some(ErrorReported);
  45                     }
  46                 }
  47             }
  48         }
  49         if let RegionResolutionError::ConcreteFailure(origin, _, _) = error.clone() {
  50             if let SubregionOrigin::CompareImplTypeObligation {
  51                 span,
  52                 item_name,
  53                 impl_item_def_id,
  54                 trait_item_def_id,
  55             } = origin
  56             {
  57                 self.emit_associated_type_err(span, item_name, impl_item_def_id, trait_item_def_id);
  58                 return Some(ErrorReported);
  59             }
  60         }
  61         None
  62     }
  63
  64     fn emit_err(&self, sp: Span, expected: Ty<'tcx>, found: Ty<'tcx>, trait_def_id: DefId) {
  65         let trait_sp = self.tcx().def_span(trait_def_id);
  66         let mut err = self
  67             .tcx()
  68             .sess
  69             .struct_span_err(sp, "`impl` item signature doesn't match `trait` item signature");
  70         err.span_label(sp, &format!("found `{}`", found));
  71         err.span_label(trait_sp, &format!("expected `{}`", expected));
  72
  73         // Get the span of all the used type parameters in the method.
  74         let assoc_item = self.tcx().associated_item(trait_def_id);
  75         let mut visitor = TypeParamSpanVisitor { tcx: self.tcx(), types: vec![] };
  76         match assoc_item.kind {
  77             ty::AssocKind::Fn => {
  78                 let hir = self.tcx().hir();
  79                 if let Some(hir_id) =
  80                     assoc_item.def_id.as_local().map(|id| hir.local_def_id_to_hir_id(id))
  81                 {
  82                     if let Some(decl) = hir.fn_decl_by_hir_id(hir_id) {
  83                         visitor.visit_fn_decl(decl);
  84                     }
  85                 }
  86             }
  87             _ => {}
  88         }
  89         let mut type_param_span: MultiSpan = visitor.types.to_vec().into();
  90         for &span in &visitor.types {
  91             type_param_span.push_span_label(
  92                 span,
  93                 "consider borrowing this type parameter in the trait".to_string(),
  94             );
  95         }
  96
  97         if let Some((expected, found)) =
  98             self.infcx.expected_found_str_ty(ExpectedFound { expected, found })
  99         {
 100             // Highlighted the differences when showing the "expected/found" note.
 101             err.note_expected_found(&"", expected, &"", found);
 102         } else {
 103             // This fallback shouldn't be necessary, but let's keep it in just in case.
 104             err.note(&format!("expected `{}`\n   found `{}`", expected, found));
 105         }
 106         err.span_help(
 107             type_param_span,
 108             "the lifetime requirements from the `impl` do not correspond to the requirements in \
 109              the `trait`",
 110         );
 111         if visitor.types.is_empty() {
 112             err.help(
 113                 "verify the lifetime relationships in the `trait` and `impl` between the `self` \
 114                  argument, the other inputs and its output",
 115             );
 116         }
 117         err.emit();
 118     }
 119
 120     fn emit_associated_type_err(
 121         &self,
 122         span: Span,
 123         item_name: Symbol,
 124         impl_item_def_id: DefId,
 125         trait_item_def_id: DefId,
 126     ) {
 127         let impl_sp = self.tcx().def_span(impl_item_def_id);
 128         let trait_sp = self.tcx().def_span(trait_item_def_id);
 129         let mut err = self
 130             .tcx()
 131             .sess
 132             .struct_span_err(span, &format!("`impl` associated type signature for `{}` doesn't match `trait` associated type signature", item_name));
 133         err.span_label(impl_sp, &format!("found"));
 134         err.span_label(trait_sp, &format!("expected"));
 135
 136         err.emit();
 137     }
 138 }
 139
 140 struct TypeParamSpanVisitor<'tcx> {
 141     tcx: TyCtxt<'tcx>,
 142     types: Vec<Span>,
 143 }
 144
 145 impl Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
 146     type Map = rustc_middle::hir::map::Map<'tcx>;
 147
 148     fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
 149         hir::intravisit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
 150     }
 151
 152     fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
 153         match arg.kind {
 154             hir::TyKind::Rptr(_, ref mut_ty) => {
 155                 // We don't want to suggest looking into borrowing `&T` or `&Self`.
 156                 hir::intravisit::walk_ty(self, mut_ty.ty);
 157                 return;
 158             }
 159             hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
 160                 [segment]
 161                     if segment
 162                         .res
 163                         .map(|res| {
 164                             matches!(
 165                                 res,
 166                                 Res::SelfTy(_, _) | Res::Def(hir::def::DefKind::TyParam, _)
 167                             )
 168                         })
 169                         .unwrap_or(false) =>
 170                 {
 171                     self.types.push(path.span);
 172                 }
 173                 _ => {}
 174             },
 175             _ => {}
 176         }
 177         hir::intravisit::walk_ty(self, arg);
 178     }
 179 }