Rollup merge of rust-lang#129070 - estebank:static-trait, r=davidtwco

Point at explicit `'static` obligations on a trait

Given `trait Any: 'static` and a `struct` with a `Box<dyn Any + 'a>` field, point at the `'static` bound in `Any` to explain why `'a: 'static`.

```
error[E0478]: lifetime bound not satisfied
   --> f202.rs:2:12
    |
2   |     value: Box<dyn std::any::Any + 'a>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
note: lifetime parameter instantiated with the lifetime `'a` as defined here
   --> f202.rs:1:14
    |
1   | struct Hello<'a> {
    |              ^^
note: but lifetime parameter must outlive the static lifetime
   --> /home/gh-estebank/rust/library/core/src/any.rs:113:16
    |
113 | pub trait Any: 'static {
    |                ^^^^^^^
```

Partially address rust-lang#33652.

Author: jieyouxu

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -747,7 +747,7 @@ fn region_known_to_outlive<'tcx>(
     region_b: ty::Region<'tcx>,
 ) -> bool {
     test_region_obligations(tcx, id, param_env, wf_tys, |infcx| {
-        infcx.sub_regions(infer::RelateRegionParamBound(DUMMY_SP), region_b, region_a);
+        infcx.sub_regions(infer::RelateRegionParamBound(DUMMY_SP, None), region_b, region_a);
     })
 }
 

compiler/rustc_infer/src/infer/context.rs

@@ -167,7 +167,7 @@ impl<'tcx> InferCtxtLike for InferCtxt<'tcx> {
     }
 
     fn sub_regions(&self, sub: ty::Region<'tcx>, sup: ty::Region<'tcx>) {
-        self.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), sub, sup)
+        self.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP, None), sub, sup)
     }
 
     fn register_ty_outlives(&self, ty: Ty<'tcx>, r: ty::Region<'tcx>) {

compiler/rustc_infer/src/infer/mod.rs

@@ -390,7 +390,7 @@ pub enum SubregionOrigin<'tcx> {
 
     /// The given region parameter was instantiated with a region
     /// that must outlive some other region.
-    RelateRegionParamBound(Span),
+    RelateRegionParamBound(Span, Option<Ty<'tcx>>),
 
     /// Creating a pointer `b` to contents of another reference.
     Reborrow(Span),
@@ -859,7 +859,7 @@ impl<'tcx> InferCtxt<'tcx> {
     ) {
         self.enter_forall(predicate, |ty::OutlivesPredicate(r_a, r_b)| {
             let origin = SubregionOrigin::from_obligation_cause(cause, || {
-                RelateRegionParamBound(cause.span)
+                RelateRegionParamBound(cause.span, None)
             });
             self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
         })
@@ -1685,7 +1685,7 @@ impl<'tcx> SubregionOrigin<'tcx> {
             Subtype(ref a) => a.span(),
             RelateObjectBound(a) => a,
             RelateParamBound(a, ..) => a,
-            RelateRegionParamBound(a) => a,
+            RelateRegionParamBound(a, _) => a,
             Reborrow(a) => a,
             ReferenceOutlivesReferent(_, a) => a,
             CompareImplItemObligation { span, .. } => span,
@@ -1726,6 +1726,10 @@ impl<'tcx> SubregionOrigin<'tcx> {
                 SubregionOrigin::AscribeUserTypeProvePredicate(span)
             }
 
+            traits::ObligationCauseCode::ObjectTypeBound(ty, _reg) => {
+                SubregionOrigin::RelateRegionParamBound(cause.span, Some(ty))
+            }
+
             _ => default(),
         }
     }

compiler/rustc_trait_selection/src/error_reporting/infer/nice_region_error/placeholder_relation.rs

@@ -11,7 +11,7 @@ impl<'tcx> NiceRegionError<'_, 'tcx> {
     pub(super) fn try_report_placeholder_relation(&self) -> Option<Diag<'tcx>> {
         match &self.error {
             Some(RegionResolutionError::ConcreteFailure(
-                SubregionOrigin::RelateRegionParamBound(span),
+                SubregionOrigin::RelateRegionParamBound(span, _),
                 Region(Interned(
                     RePlaceholder(ty::Placeholder {
                         bound: ty::BoundRegion { kind: sub_name, .. },

compiler/rustc_trait_selection/src/error_reporting/infer/note.rs

@@ -52,7 +52,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         .add_to_diag(err);
                 }
             }
-            infer::RelateRegionParamBound(span) => {
+            infer::RelateRegionParamBound(span, _) => {
                 RegionOriginNote::Plain { span, msg: fluent::infer_relate_region_param_bound }
                     .add_to_diag(err);
             }
@@ -199,7 +199,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     note,
                 })
             }
-            infer::RelateRegionParamBound(span) => {
+            infer::RelateRegionParamBound(span, _) => {
                 let param_instantiated = note_and_explain::RegionExplanation::new(
                     self.tcx,
                     generic_param_scope,

compiler/rustc_trait_selection/src/error_reporting/infer/region.rs

@@ -257,7 +257,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     .add_to_diag(err);
                 }
             }
-            infer::RelateRegionParamBound(span) => {
+            infer::RelateRegionParamBound(span, _) => {
                 RegionOriginNote::Plain {
                     span,
                     msg: fluent::trait_selection_relate_region_param_bound,
@@ -410,7 +410,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     note,
                 })
             }
-            infer::RelateRegionParamBound(span) => {
+            infer::RelateRegionParamBound(span, ty) => {
                 let param_instantiated = note_and_explain::RegionExplanation::new(
                     self.tcx,
                     generic_param_scope,
@@ -419,11 +419,31 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     note_and_explain::PrefixKind::LfParamInstantiatedWith,
                     note_and_explain::SuffixKind::Empty,
                 );
+                let mut alt_span = None;
+                if let Some(ty) = ty
+                    && sub.is_static()
+                    && let ty::Dynamic(preds, _, ty::DynKind::Dyn) = ty.kind()
+                    && let Some(def_id) = preds.principal_def_id()
+                {
+                    for (clause, span) in
+                        self.tcx.predicates_of(def_id).instantiate_identity(self.tcx)
+                    {
+                        if let ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) =
+                            clause.kind().skip_binder()
+                            && let ty::Param(param) = a.kind()
+                            && param.name == kw::SelfUpper
+                            && b.is_static()
+                        {
+                            // Point at explicit `'static` bound on the trait (`trait T: 'static`).
+                            alt_span = Some(span);
+                        }
+                    }
+                }
                 let param_must_outlive = note_and_explain::RegionExplanation::new(
                     self.tcx,
                     generic_param_scope,
                     sub,
-                    None,
+                    alt_span,
                     note_and_explain::PrefixKind::LfParamMustOutlive,
                     note_and_explain::SuffixKind::Empty,
                 );

tests/ui/regions/explicit-static-bound-on-trait.rs

@@ -0,0 +1,13 @@
+struct Hello<'a> {
+    value: Box<dyn std::any::Any + 'a>,
+    //~^ ERROR lifetime bound not satisfied
+}
+
+impl<'a> Hello<'a> {
+    fn new<T: 'a>(value: T) -> Self {
+        Self { value: Box::new(value) }
+        //~^ ERROR the parameter type `T` may not live long enough
+    }
+}
+
+fn main() {}

tests/ui/regions/explicit-static-bound-on-trait.stderr

@@ -0,0 +1,32 @@
+error[E0478]: lifetime bound not satisfied
+  --> $DIR/explicit-static-bound-on-trait.rs:2:12
+   |
+LL |     value: Box<dyn std::any::Any + 'a>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: lifetime parameter instantiated with the lifetime `'a` as defined here
+  --> $DIR/explicit-static-bound-on-trait.rs:1:14
+   |
+LL | struct Hello<'a> {
+   |              ^^
+note: but lifetime parameter must outlive the static lifetime
+  --> $SRC_DIR/core/src/any.rs:LL:COL
+
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/explicit-static-bound-on-trait.rs:8:23
+   |
+LL |         Self { value: Box::new(value) }
+   |                       ^^^^^^^^^^^^^^^
+   |                       |
+   |                       the parameter type `T` must be valid for the static lifetime...
+   |                       ...so that the type `T` will meet its required lifetime bounds
+   |
+help: consider adding an explicit lifetime bound
+   |
+LL |     fn new<T: 'a + 'static>(value: T) -> Self {
+   |                  +++++++++
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0310, E0478.
+For more information about an error, try `rustc --explain E0310`.