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             }
  59         }
  60         None
  61     }
  62
  63     fn emit_err(&self, sp: Span, expected: Ty<'tcx>, found: Ty<'tcx>, trait_def_id: DefId) {
  64         let trait_sp = self.tcx().def_span(trait_def_id);
  65         let mut err = self
  66             .tcx()
  67             .sess
  68             .struct_span_err(sp, "`impl` item signature doesn't match `trait` item signature");
  69         err.span_label(sp, &format!("found `{}`", found));
  70         err.span_label(trait_sp, &format!("expected `{}`", expected));
  71
  72         // Get the span of all the used type parameters in the method.
  73         let assoc_item = self.tcx().associated_item(trait_def_id);
  74         let mut visitor = TypeParamSpanVisitor { tcx: self.tcx(), types: vec![] };
  75         match assoc_item.kind {
  76             ty::AssocKind::Fn => {
  77                 let hir = self.tcx().hir();
  78                 if let Some(hir_id) =
  79                     assoc_item.def_id.as_local().map(|id| hir.local_def_id_to_hir_id(id))
  80                 {
  81                     if let Some(decl) = hir.fn_decl_by_hir_id(hir_id) {
  82                         visitor.visit_fn_decl(decl);
  83                     }
  84                 }
  85             }
  86             _ => {}
  87         }
  88         let mut type_param_span: MultiSpan = visitor.types.to_vec().into();
  89         for &span in &visitor.types {
  90             type_param_span.push_span_label(
  91                 span,
  92                 "consider borrowing this type parameter in the trait".to_string(),
  93             );
  94         }
  95
  96         if let Some((expected, found)) =
  97             self.infcx.expected_found_str_ty(ExpectedFound { expected, found })
  98         {
  99             // Highlighted the differences when showing the "expected/found" note.
 100             err.note_expected_found(&"", expected, &"", found);
 101         } else {
 102             // This fallback shouldn't be necessary, but let's keep it in just in case.
 103             err.note(&format!("expected `{}`\n   found `{}`", expected, found));
 104         }
 105         err.span_help(
 106             type_param_span,
 107             "the lifetime requirements from the `impl` do not correspond to the requirements in \
 108              the `trait`",
 109         );
 110         if visitor.types.is_empty() {
 111             err.help(
 112                 "verify the lifetime relationships in the `trait` and `impl` between the `self` \
 113                  argument, the other inputs and its output",
 114             );
 115         }
 116         err.emit();
 117     }
 118
 119     fn emit_associated_type_err(
 120         &self,
 121         span: Span,
 122         item_name: Symbol,
 123         impl_item_def_id: DefId,
 124         trait_item_def_id: DefId,
 125     ) {
 126         let impl_sp = self.tcx().def_span(impl_item_def_id);
 127         let trait_sp = self.tcx().def_span(trait_item_def_id);
 128         let mut err = self
 129             .tcx()
 130             .sess
 131             .struct_span_err(span, &format!("`impl` associated type signature for `{}` doesn't match `trait` associated type signature", item_name));
 132         err.span_label(impl_sp, &format!("found"));
 133         err.span_label(trait_sp, &format!("expected"));
 134
 135         err.emit();
 136     }
 137 }
 138
 139 struct TypeParamSpanVisitor<'tcx> {
 140     tcx: TyCtxt<'tcx>,
 141     types: Vec<Span>,
 142 }
 143
 144 impl Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
 145     type Map = rustc_middle::hir::map::Map<'tcx>;
 146
 147     fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
 148         hir::intravisit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
 149     }
 150
 151     fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
 152         match arg.kind {
 153             hir::TyKind::Rptr(_, ref mut_ty) => {
 154                 // We don't want to suggest looking into borrowing `&T` or `&Self`.
 155                 hir::intravisit::walk_ty(self, mut_ty.ty);
 156                 return;
 157             }
 158             hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
 159                 [segment]
 160                     if segment
 161                         .res
 162                         .map(|res| {
 163                             matches!(
 164                                 res,
 165                                 Res::SelfTy(_, _) | Res::Def(hir::def::DefKind::TyParam, _)
 166                             )
 167                         })
 168                         .unwrap_or(false) =>
 169                 {
 170                     self.types.push(path.span);
 171                 }
 172                 _ => {}
 173             },
 174             _ => {}
 175         }
 176         hir::intravisit::walk_ty(self, arg);
 177     }
 178 }