improve the suggestion of generic_bound_failure

Author: aliemjay

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

@@ -1057,24 +1057,29 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Returns the `DefId` and the `BoundRegionKind` corresponding to the given region.
-    pub fn is_suitable_region(self, region: Region<'tcx>) -> Option<FreeRegionInfo> {
-        let (suitable_region_binding_scope, bound_region) = match *region {
-            ty::ReFree(ref free_region) => {
-                (free_region.scope.expect_local(), free_region.bound_region)
+    pub fn is_suitable_region(self, mut region: Region<'tcx>) -> Option<FreeRegionInfo> {
+        let (suitable_region_binding_scope, bound_region) = loop {
+            let def_id = match region.kind() {
+                ty::ReFree(fr) => fr.bound_region.get_id()?.as_local()?,
+                ty::ReEarlyBound(ebr) => ebr.def_id.expect_local(),
+                _ => return None, // not a free region
+            };
+            let scope = self.local_parent(def_id);
+            if self.def_kind(scope) == DefKind::OpaqueTy {
+                // Lifetime params of opaque types are synthetic and thus irrelevant to
+                // diagnostics. Map them back to their origin!
+                region = self.map_rpit_lifetime_to_fn_lifetime(def_id);
+                continue;
             }
-            ty::ReEarlyBound(ref ebr) => (
-                self.local_parent(ebr.def_id.expect_local()),
-                ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name),
-            ),
-            _ => return None, // not a free region
+            break (scope, ty::BrNamed(def_id.into(), self.item_name(def_id.into())));
         };
 
         let is_impl_item = match self.hir().find_by_def_id(suitable_region_binding_scope) {
             Some(Node::Item(..) | Node::TraitItem(..)) => false,
             Some(Node::ImplItem(..)) => {
                 self.is_bound_region_in_impl_item(suitable_region_binding_scope)
             }
-            _ => return None,
+            _ => false,
         };
 
         Some(FreeRegionInfo {

compiler/rustc_middle/src/ty/context.rs

@@ -2,9 +2,12 @@ error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/regionck-1.rs:9:30
    |
 LL |     type NoTyOutliv<'a, T> = &'a T;
-   |                              ^^^^^- help: consider adding a where clause: `where T: 'a`
-   |                              |
-   |                              ...so that the reference type `&'a T` does not outlive the data it points at
+   |                              ^^^^^ ...so that the reference type `&'a T` does not outlive the data it points at
+   |
+help: consider adding an explicit lifetime bound...
+   |
+LL |     type NoTyOutliv<'a, T: 'a> = &'a T;
+   |                          ++++
 
 error[E0491]: in type `&'a &'b ()`, reference has a longer lifetime than the data it references
   --> $DIR/regionck-1.rs:10:31

tests/ui/associated-inherent-types/regionck-1.stderr

@@ -14,6 +14,10 @@ note: ...so that the reference type `&(T, U)` does not outlive the data it point
    |
 LL |     async fn foo(&self) -> &(T, U) where T: Debug + Sized, U: Hash;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider adding an explicit lifetime bound...
+   |
+LL |     async fn foo<'a>(&'a self) -> &'a (T, U) where T: Debug + Sized, U: Hash, U: 'a;
+   |                 ++++  ++           ++                                       +++++++
 
 error[E0311]: the parameter type `T` may not live long enough
   --> $DIR/async-generics-and-bounds.rs:12:5
@@ -31,6 +35,10 @@ note: ...so that the reference type `&(T, U)` does not outlive the data it point
    |
 LL |     async fn foo(&self) -> &(T, U) where T: Debug + Sized, U: Hash;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider adding an explicit lifetime bound...
+   |
+LL |     async fn foo<'a>(&'a self) -> &'a (T, U) where T: Debug + Sized, U: Hash, T: 'a;
+   |                 ++++  ++           ++                                       +++++++
 
 error: aborting due to 2 previous errors
 

tests/ui/async-await/in-trait/async-generics-and-bounds.stderr

@@ -14,6 +14,10 @@ note: ...so that the reference type `&(T, U)` does not outlive the data it point
    |
 LL |     async fn foo(&self) -> &(T, U);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider adding an explicit lifetime bound...
+   |
+LL |     async fn foo<'a>(&'a self) -> &'a (T, U) where U: 'a;
+   |                 ++++  ++           ++        +++++++++++
 
 error[E0311]: the parameter type `T` may not live long enough
   --> $DIR/async-generics.rs:9:5
@@ -31,6 +35,10 @@ note: ...so that the reference type `&(T, U)` does not outlive the data it point
    |
 LL |     async fn foo(&self) -> &(T, U);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: consider adding an explicit lifetime bound...
+   |
+LL |     async fn foo<'a>(&'a self) -> &'a (T, U) where T: 'a;
+   |                 ++++  ++           ++        +++++++++++
 
 error: aborting due to 2 previous errors
 

tests/ui/async-await/in-trait/async-generics.stderr

@@ -2,7 +2,7 @@
 
 #![allow(warnings)]
 
-fn no_restriction<'a, T: 'a>(x: &'a ()) -> &() {
+fn no_restriction<'a, T: 'a>(x: &'a ()) -> &'a () {
     with_restriction::<T>(x) //~ ERROR E0311
 }
 

tests/ui/error-codes/E0311.fixed

@@ -16,8 +16,8 @@ LL |     with_restriction::<T>(x)
    |     ^^^^^^^^^^^^^^^^^^^^^
 help: consider adding an explicit lifetime bound...
    |
-LL | fn no_restriction<'a, T: 'a>(x: &'a ()) -> &() {
-   |                   +++  ++++      ++
+LL | fn no_restriction<'a, T: 'a>(x: &'a ()) -> &'a () {
+   |                   +++  ++++      ++         ++
 
 error: aborting due to previous error
 

tests/ui/error-codes/E0311.stderr

@@ -2,9 +2,12 @@ error[E0309]: the parameter type `T` may not live long enough
   --> $DIR/issue-84931.rs:14:21
    |
 LL |     type Item<'a> = &'a mut T;
-   |                     ^^^^^^^^^- help: consider adding a where clause: `where T: 'a`
-   |                     |
-   |                     ...so that the reference type `&'a mut T` does not outlive the data it points at
+   |                     ^^^^^^^^^ ...so that the reference type `&'a mut T` does not outlive the data it points at
+   |
+help: consider adding an explicit lifetime bound...
+   |
+LL |     type Item<'a> = &'a mut T where T: 'a;
+   |                               +++++++++++
 
 error: aborting due to previous error
 

tests/ui/generic-associated-types/issue-84931.stderr

@@ -17,8 +17,8 @@ LL |     fn generic_in_parent<'a, L: X<&'a Nested<K>>>() {
    |
 help: consider adding an explicit lifetime bound...
    |
-LL | impl<K: 'a> Nested<K> {
-   |       ++++
+LL |     fn generic_in_parent<'a, L: X<&'a Nested<K>>>() where K: 'a {
+   |                                                     +++++++++++
 
 error[E0309]: the parameter type `M` may not live long enough
   --> $DIR/lifetime-doesnt-live-long-enough.rs:44:36
@@ -39,17 +39,19 @@ LL |     fn foo<'a, L: X<&'a Nested<K>>>();
    |
 help: consider adding an explicit lifetime bound...
    |
-LL | trait X<K: 'a>: Sized {
-   |          ++++
+LL |     fn foo<'a, L: X<&'a Nested<K>>>() where K: 'a;
+   |                                       +++++++++++
 
 error[E0309]: the parameter type `Self` may not live long enough
   --> $DIR/lifetime-doesnt-live-long-enough.rs:28:19
    |
 LL |     fn bar<'a, L: X<&'a Nested<Self>>>();
-   |                   ^^^^^^^^^^^^^^^^^^^
+   |                   ^^^^^^^^^^^^^^^^^^^ ...so that the reference type `&'a Nested<Self>` does not outlive the data it points at
    |
-   = help: consider adding an explicit lifetime bound `Self: 'a`...
-   = note: ...so that the reference type `&'a Nested<Self>` does not outlive the data it points at
+help: consider adding an explicit lifetime bound...
+   |
+LL |     fn bar<'a, L: X<&'a Nested<Self>>>() where Self: 'a;
+   |                                          ++++++++++++++
 
 error[E0309]: the parameter type `L` may not live long enough
   --> $DIR/lifetime-doesnt-live-long-enough.rs:32:22

tests/ui/lifetimes/lifetime-doesnt-live-long-enough.stderr

@@ -2,7 +2,7 @@
 
 #![allow(warnings)]
 
-fn no_restriction<'a, T: 'a>(x: &'a ()) -> &() {
+fn no_restriction<'a, T: 'a>(x: &'a ()) -> &'a () {
     with_restriction::<T>(x) //~ ERROR the parameter type `T` may not live long enough
 }