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

   1 //! Error Reporting for when the lifetime for a type doesn't match the `impl` selected for a predicate
   2 //! to hold.
   3
   4 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
   5 use crate::infer::error_reporting::note_and_explain_region;
   6 use crate::infer::lexical_region_resolve::RegionResolutionError;
   7 use crate::infer::{SubregionOrigin, TypeTrace};
   8 use crate::traits::ObligationCauseCode;
   9 use rustc_data_structures::stable_set::FxHashSet;
  10 use rustc_errors::{Applicability, ErrorReported};
  11 use rustc_hir as hir;
  12 use rustc_hir::intravisit::Visitor;
  13 use rustc_middle::ty::{self, TypeVisitor};
  14 use rustc_span::MultiSpan;
  15
  16 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  17     pub(super) fn try_report_mismatched_static_lifetime(&self) -> Option<ErrorReported> {
  18         let error = self.error.as_ref()?;
  19         debug!("try_report_mismatched_static_lifetime {:?}", error);
  20
  21         let (origin, sub, sup) = match error.clone() {
  22             RegionResolutionError::ConcreteFailure(origin, sub, sup) => (origin, sub, sup),
  23             _ => return None,
  24         };
  25         if *sub != ty::RegionKind::ReStatic {
  26             return None;
  27         }
  28         let cause = match origin {
  29             SubregionOrigin::Subtype(box TypeTrace { ref cause, .. }) => cause,
  30             _ => return None,
  31         };
  32         let (parent, impl_def_id) = match &cause.code {
  33             ObligationCauseCode::MatchImpl(parent, impl_def_id) => (parent, impl_def_id),
  34             _ => return None,
  35         };
  36         let binding_span = match **parent {
  37             ObligationCauseCode::BindingObligation(_def_id, binding_span) => binding_span,
  38             _ => return None,
  39         };
  40         let mut err = self.tcx().sess.struct_span_err(cause.span, "incompatible lifetime on type");
  41         // FIXME: we should point at the lifetime
  42         let mut multi_span: MultiSpan = vec![binding_span].into();
  43         multi_span
  44             .push_span_label(binding_span, "introduces a `'static` lifetime requirement".into());
  45         err.span_note(multi_span, "because this has an unmet lifetime requirement");
  46         note_and_explain_region(self.tcx(), &mut err, "", sup, "...", Some(binding_span));
  47         if let Some(impl_node) = self.tcx().hir().get_if_local(*impl_def_id) {
  48             // If an impl is local, then maybe this isn't what they want. Try to
  49             // be as helpful as possible with implicit lifetimes.
  50
  51             // First, let's get the hir self type of the impl
  52             let impl_self_ty = match impl_node {
  53                 hir::Node::Item(hir::Item {
  54                     kind: hir::ItemKind::Impl(hir::Impl { self_ty, .. }),
  55                     ..
  56                 }) => self_ty,
  57                 _ => bug!("Node not an impl."),
  58             };
  59
  60             // Next, let's figure out the set of trait objects with implict static bounds
  61             let ty = self.tcx().type_of(*impl_def_id);
  62             let mut v = super::static_impl_trait::TraitObjectVisitor(FxHashSet::default());
  63             v.visit_ty(ty);
  64             let mut traits = vec![];
  65             for matching_def_id in v.0 {
  66                 let mut hir_v =
  67                     super::static_impl_trait::HirTraitObjectVisitor(&mut traits, matching_def_id);
  68                 hir_v.visit_ty(&impl_self_ty);
  69             }
  70
  71             if traits.is_empty() {
  72                 // If there are no trait object traits to point at, either because
  73                 // there aren't trait objects or because none are implicit, then just
  74                 // write a single note on the impl itself.
  75
  76                 let impl_span = self.tcx().def_span(*impl_def_id);
  77                 err.span_note(impl_span, "...does not necessarily outlive the static lifetime introduced by the compatible `impl`");
  78             } else {
  79                 // Otherwise, point at all implicit static lifetimes
  80
  81                 err.note("...does not necessarily outlive the static lifetime introduced by the compatible `impl`");
  82                 for span in &traits {
  83                     err.span_note(*span, "this has an implicit `'static` lifetime requirement");
  84                     // It would be nice to put this immediately under the above note, but they get
  85                     // pushed to the end.
  86                     err.span_suggestion_verbose(
  87                         span.shrink_to_hi(),
  88                         "consider relaxing the implicit `'static` requirement",
  89                         " + '_".to_string(),
  90                         Applicability::MaybeIncorrect,
  91                     );
  92                 }
  93             }
  94         } else {
  95             // Otherwise just point out the impl.
  96
  97             let impl_span = self.tcx().def_span(*impl_def_id);
  98             err.span_note(impl_span, "...does not necessarily outlive the static lifetime introduced by the compatible `impl`");
  99         }
 100         err.emit();
 101         Some(ErrorReported)
 102     }
 103 }