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::{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};
  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         if let Some(ref error) = self.error {
  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)) =
  31                     (&sup_origin, &sub_origin)
  32                 {
  33                     if let (
  34                         ValuePairs::Types(sub_expected_found),
  35                         ValuePairs::Types(sup_expected_found),
  36                         CompareImplMethodObligation { trait_item_def_id, .. },
  37                     ) = (&sub_trace.values, &sup_trace.values, &sub_trace.cause.code)
  38                     {
  39                         if sup_expected_found == sub_expected_found {
  40                             self.emit_err(
  41                                 var_origin.span(),
  42                                 sub_expected_found.expected,
  43                                 sub_expected_found.found,
  44                                 *trait_item_def_id,
  45                             );
  46                             return Some(ErrorReported);
  47                         }
  48                     }
  49                 }
  50             }
  51         }
  52         None
  53     }
  54
  55     fn emit_err(&self, sp: Span, expected: Ty<'tcx>, found: Ty<'tcx>, trait_def_id: DefId) {
  56         let trait_sp = self.tcx().def_span(trait_def_id);
  57         let mut err = self
  58             .tcx()
  59             .sess
  60             .struct_span_err(sp, "`impl` item signature doesn't match `trait` item signature");
  61         err.span_label(sp, &format!("found `{}`", found));
  62         err.span_label(trait_sp, &format!("expected `{}`", expected));
  63
  64         // Get the span of all the used type parameters in the method.
  65         let assoc_item = self.tcx().associated_item(trait_def_id);
  66         let mut visitor = TypeParamSpanVisitor { tcx: self.tcx(), types: vec![] };
  67         match assoc_item.kind {
  68             ty::AssocKind::Fn => {
  69                 let hir = self.tcx().hir();
  70                 if let Some(hir_id) =
  71                     assoc_item.def_id.as_local().map(|id| hir.local_def_id_to_hir_id(id))
  72                 {
  73                     if let Some(decl) = hir.fn_decl_by_hir_id(hir_id) {
  74                         visitor.visit_fn_decl(decl);
  75                     }
  76                 }
  77             }
  78             _ => {}
  79         }
  80         let mut type_param_span: MultiSpan = visitor.types.to_vec().into();
  81         for &span in &visitor.types {
  82             type_param_span.push_span_label(
  83                 span,
  84                 "consider borrowing this type parameter in the trait".to_string(),
  85             );
  86         }
  87
  88         if let Some((expected, found)) =
  89             self.infcx.expected_found_str_ty(&ExpectedFound { expected, found })
  90         {
  91             // Highlighted the differences when showing the "expected/found" note.
  92             err.note_expected_found(&"", expected, &"", found);
  93         } else {
  94             // This fallback shouldn't be necessary, but let's keep it in just in case.
  95             err.note(&format!("expected `{}`\n   found `{}`", expected, found));
  96         }
  97         err.span_help(
  98             type_param_span,
  99             "the lifetime requirements from the `impl` do not correspond to the requirements in \
 100              the `trait`",
 101         );
 102         if visitor.types.is_empty() {
 103             err.help(
 104                 "verify the lifetime relationships in the `trait` and `impl` between the `self` \
 105                  argument, the other inputs and its output",
 106             );
 107         }
 108         err.emit();
 109     }
 110 }
 111
 112 struct TypeParamSpanVisitor<'tcx> {
 113     tcx: TyCtxt<'tcx>,
 114     types: Vec<Span>,
 115 }
 116
 117 impl Visitor<'tcx> for TypeParamSpanVisitor<'tcx> {
 118     type Map = rustc_middle::hir::map::Map<'tcx>;
 119
 120     fn nested_visit_map(&mut self) -> hir::intravisit::NestedVisitorMap<Self::Map> {
 121         hir::intravisit::NestedVisitorMap::OnlyBodies(self.tcx.hir())
 122     }
 123
 124     fn visit_ty(&mut self, arg: &'tcx hir::Ty<'tcx>) {
 125         match arg.kind {
 126             hir::TyKind::Rptr(_, ref mut_ty) => {
 127                 // We don't want to suggest looking into borrowing `&T` or `&Self`.
 128                 hir::intravisit::walk_ty(self, mut_ty.ty);
 129                 return;
 130             }
 131             hir::TyKind::Path(hir::QPath::Resolved(None, path)) => match &path.segments {
 132                 [segment]
 133                     if segment
 134                         .res
 135                         .map(|res| match res {
 136                             Res::SelfTy(_, _) | Res::Def(hir::def::DefKind::TyParam, _) => true,
 137                             _ => false,
 138                         })
 139                         .unwrap_or(false) =>
 140                 {
 141                     self.types.push(path.span);
 142                 }
 143                 _ => {}
 144             },
 145             _ => {}
 146         }
 147         hir::intravisit::walk_ty(self, arg);
 148     }
 149 }