Improve span for consider adding an explicit lifetime bound suggestions under NLL

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -4,6 +4,7 @@ use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed
 use rustc_infer::infer::{
     error_reporting::nice_region_error::NiceRegionError,
     error_reporting::unexpected_hidden_region_diagnostic, NllRegionVariableOrigin,
+    RelateParamBound,
 };
 use rustc_middle::hir::place::PlaceBase;
 use rustc_middle::mir::{ConstraintCategory, ReturnConstraint};
@@ -166,11 +167,14 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     let type_test_span = type_test.locations.span(&self.body);
 
                     if let Some(lower_bound_region) = lower_bound_region {
+                        let generic_ty = type_test.generic_kind.to_ty(self.infcx.tcx);
+                        let origin = RelateParamBound(type_test_span, generic_ty, None);
                         self.buffer_error(self.infcx.construct_generic_bound_failure(
                             type_test_span,
-                            None,
+                            Some(origin),
                             type_test.generic_kind,
                             lower_bound_region,
+                            self.body.source.def_id().as_local(),
                         ));
                     } else {
                         // FIXME. We should handle this case better. It

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

@@ -61,7 +61,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Diagnostic, ErrorGuaranteed};
 use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString, MultiSpan};
 use rustc_hir as hir;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{Item, ItemKind, Node};
 use rustc_middle::dep_graph::DepContext;
@@ -2285,7 +2285,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         bound_kind: GenericKind<'tcx>,
         sub: Region<'tcx>,
     ) {
-        self.construct_generic_bound_failure(span, origin, bound_kind, sub).emit();
+        let owner =
+            self.in_progress_typeck_results.map(|typeck_results| typeck_results.borrow().hir_owner);
+        self.construct_generic_bound_failure(span, origin, bound_kind, sub, owner).emit();
     }
 
     pub fn construct_generic_bound_failure(
@@ -2294,31 +2296,29 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         origin: Option<SubregionOrigin<'tcx>>,
         bound_kind: GenericKind<'tcx>,
         sub: Region<'tcx>,
+        owner: Option<LocalDefId>,
     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         let hir = self.tcx.hir();
         // Attempt to obtain the span of the parameter so we can
         // suggest adding an explicit lifetime bound to it.
-        let generics = self
-            .in_progress_typeck_results
-            .map(|typeck_results| typeck_results.borrow().hir_owner)
-            .map(|owner| {
-                let hir_id = hir.local_def_id_to_hir_id(owner);
-                let parent_id = hir.get_parent_item(hir_id);
-                (
-                    // Parent item could be a `mod`, so we check the HIR before calling:
-                    if let Some(Node::Item(Item {
-                        kind: ItemKind::Trait(..) | ItemKind::Impl { .. },
-                        ..
-                    })) = hir.find_by_def_id(parent_id)
-                    {
-                        Some(self.tcx.generics_of(parent_id))
-                    } else {
-                        None
-                    },
-                    self.tcx.generics_of(owner.to_def_id()),
-                    hir.span(hir_id),
-                )
-            });
+        let generics = owner.map(|owner| {
+            let hir_id = hir.local_def_id_to_hir_id(owner);
+            let parent_id = hir.get_parent_item(hir_id);
+            (
+                // Parent item could be a `mod`, so we check the HIR before calling:
+                if let Some(Node::Item(Item {
+                    kind: ItemKind::Trait(..) | ItemKind::Impl { .. },
+                    ..
+                })) = hir.find_by_def_id(parent_id)
+                {
+                    Some(self.tcx.generics_of(parent_id))
+                } else {
+                    None
+                },
+                self.tcx.generics_of(owner.to_def_id()),
+                hir.span(hir_id),
+            )
+        });
 
         let span = match generics {
             // This is to get around the trait identity obligation, that has a `DUMMY_SP` as signal
@@ -2606,11 +2606,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     None,
                 );
                 if let Some(infer::RelateParamBound(_, t, _)) = origin {
-                    let return_impl_trait = self
-                        .in_progress_typeck_results
-                        .map(|typeck_results| typeck_results.borrow().hir_owner)
-                        .and_then(|owner| self.tcx.return_type_impl_trait(owner))
-                        .is_some();
+                    let return_impl_trait =
+                        owner.and_then(|owner| self.tcx.return_type_impl_trait(owner)).is_some();
                     let t = self.resolve_vars_if_possible(t);
                     match t.kind() {
                         // We've got:

src/test/ui/impl-trait/must_outlive_least_region_or_bound.nll.stderr

@@ -82,10 +82,11 @@ LL | fn move_lifetime_into_fn<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Fn(&'a u32
 error[E0310]: the parameter type `T` may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:41:5
    |
+LL | fn ty_param_wont_outlive_static<T:Debug>(x: T) -> impl Debug + 'static {
+   |                                 -- help: consider adding an explicit lifetime bound...: `T: 'static +`
+...
 LL |     x
-   |     ^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'static`...
+   |     ^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to 9 previous errors
 

src/test/ui/impl-trait/type_parameters_captured.nll.stderr

@@ -1,10 +1,11 @@
 error[E0310]: the parameter type `T` may not live long enough
   --> $DIR/type_parameters_captured.rs:10:5
    |
+LL | fn foo<T>(x: T) -> impl Any + 'static {
+   |        - help: consider adding an explicit lifetime bound...: `T: 'static`
+...
 LL |     x
-   |     ^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'static`...
+   |     ^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/lifetimes/lifetime-errors/issue_74400.nll.stderr

@@ -1,10 +1,10 @@
 error[E0310]: the parameter type `T` may not live long enough
   --> $DIR/issue_74400.rs:12:5
    |
+LL | fn g<T>(data: &[T]) {
+   |      - help: consider adding an explicit lifetime bound...: `T: 'static`
 LL |     f(data, identity)
-   |     ^^^^^^^^^^^^^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'static`...
+   |     ^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error[E0308]: mismatched types
   --> $DIR/issue_74400.rs:12:5

src/test/ui/nll/closure-requirements/propagate-from-trait-match.stderr

@@ -36,6 +36,9 @@ LL | | }
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/propagate-from-trait-match.rs:32:36
    |
+LL |   fn supply<'a, T>(value: T)
+   |                 - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |       establish_relationships(value, |value| {
    |  ____________________________________^
 LL | |
@@ -44,9 +47,7 @@ LL | |         // This function call requires that
 ...  |
 LL | |         require(value);
 LL | |     });
-   | |_____^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   | |_____^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/nll/ty-outlives/impl-trait-outlives.stderr

@@ -1,18 +1,20 @@
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/impl-trait-outlives.rs:11:5
    |
+LL | fn no_region<'a, T>(x: Box<T>) -> impl Debug + 'a
+   |                  - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     x
-   |     ^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |     ^ ...so that the type `T` will meet its required lifetime bounds
 
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/impl-trait-outlives.rs:26:5
    |
+LL | fn wrong_region<'a, 'b, T>(x: Box<T>) -> impl Debug + 'a
+   |                         - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     x
-   |     ^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |     ^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to 2 previous errors
 

src/test/ui/nll/ty-outlives/projection-implied-bounds.stderr

@@ -1,10 +1,10 @@
 error[E0310]: the parameter type `T` may not live long enough
   --> $DIR/projection-implied-bounds.rs:30:18
    |
+LL | fn generic2<T: Iterator>(value: T) {
+   |             -- help: consider adding an explicit lifetime bound...: `T: 'static +`
 LL |     twice(value, |value_ref, item| invoke2(value_ref, item));
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'static`...
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/nll/ty-outlives/projection-no-regions-closure.stderr

@@ -33,6 +33,7 @@ LL |     with_signature(x, |mut y| Box::new(y.next()))
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as Iterator>::Item: 'a`...
+   = note: ...so that the type `<T as Iterator>::Item` will meet its required lifetime bounds
 
 note: external requirements
   --> $DIR/projection-no-regions-closure.rs:34:23
@@ -96,6 +97,7 @@ LL |     with_signature(x, |mut y| Box::new(y.next()))
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as Iterator>::Item: 'a`...
+   = note: ...so that the type `<T as Iterator>::Item` will meet its required lifetime bounds
 
 note: external requirements
   --> $DIR/projection-no-regions-closure.rs:52:23

src/test/ui/nll/ty-outlives/projection-no-regions-fn.stderr

@@ -5,6 +5,7 @@ LL |     Box::new(x.next())
    |     ^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as Iterator>::Item: 'a`...
+   = note: ...so that the type `<T as Iterator>::Item` will meet its required lifetime bounds
 
 error[E0309]: the associated type `<T as Iterator>::Item` may not live long enough
   --> $DIR/projection-no-regions-fn.rs:28:5
@@ -13,6 +14,7 @@ LL |     Box::new(x.next())
    |     ^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as Iterator>::Item: 'a`...
+   = note: ...so that the type `<T as Iterator>::Item` will meet its required lifetime bounds
 
 error: aborting due to 2 previous errors
 

src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr

@@ -31,10 +31,11 @@ LL | | }
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/projection-one-region-closure.rs:45:29
    |
+LL | fn no_relationships_late<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                                  - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error: lifetime may not live long enough
   --> $DIR/projection-one-region-closure.rs:45:39
@@ -81,10 +82,11 @@ LL | | }
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/projection-one-region-closure.rs:56:29
    |
+LL | fn no_relationships_early<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                                   - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
-   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error: lifetime may not live long enough
   --> $DIR/projection-one-region-closure.rs:56:39

src/test/ui/nll/ty-outlives/projection-two-region-trait-bound-closure.stderr

@@ -34,6 +34,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as Anything<ReEarlyBound(0, 'b), ReEarlyBound(1, 'c)>>::AssocType: 'a`...
+   = note: ...so that the type `<T as Anything<ReEarlyBound(0, 'b), ReEarlyBound(1, 'c)>>::AssocType` will meet its required lifetime bounds
 
 note: external requirements
   --> $DIR/projection-two-region-trait-bound-closure.rs:48:29
@@ -70,6 +71,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as Anything<ReEarlyBound(1, 'b), ReEarlyBound(2, 'c)>>::AssocType: 'a`...
+   = note: ...so that the type `<T as Anything<ReEarlyBound(1, 'b), ReEarlyBound(2, 'c)>>::AssocType` will meet its required lifetime bounds
 
 note: external requirements
   --> $DIR/projection-two-region-trait-bound-closure.rs:61:29

src/test/ui/nll/ty-outlives/projection-where-clause-env-wrong-bound.nll.stderr

@@ -5,6 +5,7 @@ LL |     bar::<T::Output>()
    |     ^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as MyTrait<'_>>::Output: 'a`...
+   = note: ...so that the type `<T as MyTrait<'_>>::Output` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/nll/ty-outlives/projection-where-clause-env-wrong-lifetime.nll.stderr

@@ -5,6 +5,7 @@ LL |     bar::<<T as MyTrait<'a>>::Output>()
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: consider adding an explicit lifetime bound `<T as MyTrait<'_>>::Output: 'a`...
+   = note: ...so that the type `<T as MyTrait<'_>>::Output` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/nll/ty-outlives/projection-where-clause-none.stderr

@@ -1,10 +1,11 @@
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/projection-where-clause-none.rs:16:5
    |
+LL | fn foo<'a, T>() -> &'a ()
+   |            - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     bar::<T::Output>()
-   |     ^^^^^^^^^^^^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |     ^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/nll/ty-outlives/ty-param-closure-approximate-lower-bound.stderr

@@ -52,10 +52,10 @@ LL | | }
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/ty-param-closure-approximate-lower-bound.rs:29:24
    |
+LL | fn generic_fail<'a, T>(cell: Cell<&'a ()>, value: T) {
+   |                     - help: consider adding an explicit lifetime bound...: `T: 'a`
 LL |     twice(cell, value, |a, b| invoke(a, b));
-   |                        ^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |                        ^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to previous error
 

src/test/ui/nll/ty-outlives/ty-param-closure-outlives-from-return-type.stderr

@@ -29,18 +29,20 @@ LL | | }
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/ty-param-closure-outlives-from-return-type.rs:26:23
    |
+LL | fn no_region<'a, T>(x: Box<T>) -> Box<dyn Debug + 'a>
+   |                  - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     with_signature(x, |y| y)
-   |                       ^^^^^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |                       ^^^^^ ...so that the type `T` will meet its required lifetime bounds
 
 error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/ty-param-closure-outlives-from-return-type.rs:41:5
    |
+LL | fn wrong_region<'a, 'b, T>(x: Box<T>) -> Box<Debug + 'a>
+   |                         - help: consider adding an explicit lifetime bound...: `T: 'a`
+...
 LL |     x
-   |     ^
-   |
-   = help: consider adding an explicit lifetime bound `T: 'a`...
+   |     ^ ...so that the type `T` will meet its required lifetime bounds
 
 error: aborting due to 2 previous errors