Better diagnostics when mismatched types due to implict static lifetime

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1590,17 +1590,13 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             }
         };
         if let Some((expected, found)) = expected_found {
-            let expected_label = match exp_found {
-                Mismatch::Variable(ef) => ef.expected.prefix_string(self.tcx),
-                Mismatch::Fixed(s) => s.into(),
-            };
-            let found_label = match exp_found {
-                Mismatch::Variable(ef) => ef.found.prefix_string(self.tcx),
-                Mismatch::Fixed(s) => s.into(),
-            };
-            let exp_found = match exp_found {
-                Mismatch::Variable(exp_found) => Some(exp_found),
-                Mismatch::Fixed(_) => None,
+            let (expected_label, found_label, exp_found) = match exp_found {
+                Mismatch::Variable(ef) => (
+                    ef.expected.prefix_string(self.tcx),
+                    ef.found.prefix_string(self.tcx),
+                    Some(ef),
+                ),
+                Mismatch::Fixed(s) => (s.into(), s.into(), None),
             };
             match (&terr, expected == found) {
                 (TypeError::Sorts(values), extra) => {

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

@@ -0,0 +1,84 @@
+//! Error Reporting for when the lifetime for a type doesn't match the `impl` selected for a predicate
+//! to hold.
+
+use crate::infer::error_reporting::nice_region_error::NiceRegionError;
+use crate::infer::error_reporting::note_and_explain_region;
+use crate::infer::lexical_region_resolve::RegionResolutionError;
+use crate::infer::{SubregionOrigin, TypeTrace};
+use crate::traits::ObligationCauseCode;
+use rustc_errors::{Applicability, ErrorReported};
+use rustc_hir as hir;
+use rustc_hir::intravisit::Visitor;
+use rustc_middle::ty::{self, TypeVisitor};
+use rustc_span::MultiSpan;
+
+impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
+    pub(super) fn try_report_mismatched_static_lifetime(&self) -> Option<ErrorReported> {
+        let error = self.error.as_ref()?;
+        debug!("try_report_mismatched_static_lifetime {:?}", error);
+
+        let (origin, sub, sup) = match error.clone() {
+            RegionResolutionError::ConcreteFailure(origin, sub, sup) => (origin, sub, sup),
+            _ => return None,
+        };
+        if *sub != ty::RegionKind::ReStatic {
+            return None;
+        }
+        let cause = match origin {
+            SubregionOrigin::Subtype(box TypeTrace { ref cause, .. }) => cause,
+            _ => return None,
+        };
+        let (parent, impl_def_id) = match &cause.code {
+            ObligationCauseCode::MatchImpl(parent, impl_def_id) => (parent, impl_def_id),
+            _ => return None,
+        };
+        let binding_span = match **parent {
+            ObligationCauseCode::BindingObligation(_def_id, binding_span) => binding_span,
+            _ => return None,
+        };
+        let mut err = self.tcx().sess.struct_span_err(cause.span, "incompatible lifetime on type");
+        // FIXME: we should point at the lifetime
+        let mut multi_span: MultiSpan = vec![binding_span].into();
+        multi_span
+            .push_span_label(binding_span, "introduces a `'static` lifetime requirement".into());
+        err.span_note(multi_span, "because this has an unmet lifetime requirement");
+        note_and_explain_region(self.tcx(), &mut err, "...", sup, "...");
+        if let Some(impl_node) = self.tcx().hir().get_if_local(*impl_def_id) {
+            let ty = self.tcx().type_of(*impl_def_id);
+            let mut v = super::static_impl_trait::TraitObjectVisitor(vec![]);
+            v.visit_ty(ty);
+            let matching_def_ids = v.0;
+
+            let impl_self_ty = match impl_node {
+                hir::Node::Item(hir::Item {
+                    kind: hir::ItemKind::Impl(hir::Impl { self_ty, .. }),
+                    ..
+                }) => self_ty,
+                _ => bug!("Node not an impl."),
+            };
+
+            for matching_def_id in matching_def_ids {
+                let mut hir_v =
+                    super::static_impl_trait::HirTraitObjectVisitor(vec![], matching_def_id);
+                hir_v.visit_ty(&impl_self_ty);
+
+                let mut multi_span: MultiSpan = hir_v.0.clone().into();
+                for span in &hir_v.0 {
+                    multi_span.push_span_label(
+                        *span,
+                        "this has an implicit `'static` lifetime requirement".to_string(),
+                    );
+                    err.span_suggestion_verbose(
+                        span.shrink_to_hi(),
+                        "consider relaxing the implicit `'static` requirement",
+                        " + '_".to_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+                err.span_note(multi_span, "...does not necessarily outlive the static lifetime introduced by the compatible `impl`");
+            }
+        }
+        err.emit();
+        Some(ErrorReported)
+    }
+}

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

@@ -7,6 +7,7 @@ use rustc_span::source_map::Span;
 
 mod different_lifetimes;
 pub mod find_anon_type;
+mod mismatched_static_lifetime;
 mod named_anon_conflict;
 mod placeholder_error;
 mod static_impl_trait;
@@ -58,6 +59,7 @@ impl<'cx, 'tcx> NiceRegionError<'cx, 'tcx> {
             .or_else(|| self.try_report_impl_not_conforming_to_trait())
             .or_else(|| self.try_report_anon_anon_conflict())
             .or_else(|| self.try_report_static_impl_trait())
+            .or_else(|| self.try_report_mismatched_static_lifetime())
     }
 
     pub fn regions(&self) -> Option<(Span, ty::Region<'tcx>, ty::Region<'tcx>)> {

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

@@ -185,7 +185,11 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
             }
         }
         if let SubregionOrigin::Subtype(box TypeTrace { cause, .. }) = &sub_origin {
-            if let ObligationCauseCode::ItemObligation(item_def_id) = cause.code {
+            let code = match &cause.code {
+                ObligationCauseCode::MatchImpl(parent, ..) => &**parent,
+                _ => &cause.code,
+            };
+            if let ObligationCauseCode::ItemObligation(item_def_id) = *code {
                 // Same case of `impl Foo for dyn Bar { fn qux(&self) {} }` introducing a `'static`
                 // lifetime as above, but called using a fully-qualified path to the method:
                 // `Foo::qux(bar)`.
@@ -468,7 +472,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 }
 
 /// Collect all the trait objects in a type that could have received an implicit `'static` lifetime.
-struct TraitObjectVisitor(Vec<DefId>);
+pub(super) struct TraitObjectVisitor(pub(super) Vec<DefId>);
 
 impl TypeVisitor<'_> for TraitObjectVisitor {
     fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<Self::BreakTy> {
@@ -485,7 +489,7 @@ impl TypeVisitor<'_> for TraitObjectVisitor {
 }
 
 /// Collect all `hir::Ty<'_>` `Span`s for trait objects with an implicit lifetime.
-struct HirTraitObjectVisitor(Vec<Span>, DefId);
+pub(super) struct HirTraitObjectVisitor(pub(super) Vec<Span>, pub(super) DefId);
 
 impl<'tcx> Visitor<'tcx> for HirTraitObjectVisitor {
     type Map = ErasedMap<'tcx>;