Point out region bound mismatches in check_region_bounds_on_impl_item

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1137,7 +1137,10 @@ fn check_region_bounds_on_impl_item<'tcx>(
     // but found 0" it's confusing, because it looks like there
     // are zero. Since I don't quite know how to phrase things at
     // the moment, give a kind of vague error message.
-    if trait_params != impl_params {
+    if trait_params == impl_params {
+        return Ok(());
+    }
+
     let span = tcx
         .hir_get_generics(impl_m.def_id.expect_local())
         .expect("expected impl item to have generics or else we can't compare them")
@@ -1146,6 +1149,7 @@ fn check_region_bounds_on_impl_item<'tcx>(
     let mut generics_span = None;
     let mut bounds_span = vec![];
     let mut where_span = None;
+
     if let Some(trait_node) = tcx.hir_get_if_local(trait_m.def_id)
         && let Some(trait_generics) = trait_node.generics()
     {
@@ -1153,26 +1157,46 @@ fn check_region_bounds_on_impl_item<'tcx>(
         // FIXME: we could potentially look at the impl's bounds to not point at bounds that
         // *are* present in the impl.
         for p in trait_generics.predicates {
-                if let hir::WherePredicateKind::BoundPredicate(pred) = p.kind {
-                    for b in pred.bounds {
+            match p.kind {
+                hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate {
+                    bounds,
+                    ..
+                })
+                | hir::WherePredicateKind::RegionPredicate(hir::WhereRegionPredicate {
+                    bounds,
+                    ..
+                }) => {
+                    for b in *bounds {
                         if let hir::GenericBound::Outlives(lt) = b {
                             bounds_span.push(lt.ident.span);
                         }
                     }
                 }
+                _ => {}
+            }
         }
         if let Some(impl_node) = tcx.hir_get_if_local(impl_m.def_id)
             && let Some(impl_generics) = impl_node.generics()
         {
             let mut impl_bounds = 0;
             for p in impl_generics.predicates {
-                    if let hir::WherePredicateKind::BoundPredicate(pred) = p.kind {
-                        for b in pred.bounds {
+                match p.kind {
+                    hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate {
+                        bounds,
+                        ..
+                    })
+                    | hir::WherePredicateKind::RegionPredicate(hir::WhereRegionPredicate {
+                        bounds,
+                        ..
+                    }) => {
+                        for b in *bounds {
                             if let hir::GenericBound::Outlives(_) = b {
                                 impl_bounds += 1;
                             }
                         }
                     }
+                    _ => {}
+                }
             }
             if impl_bounds == bounds_span.len() {
                 bounds_span = vec![];
@@ -1181,6 +1205,7 @@ fn check_region_bounds_on_impl_item<'tcx>(
             }
         }
     }
+
     let reported = tcx
         .dcx()
         .create_err(LifetimesOrBoundsMismatchOnTrait {
@@ -1192,10 +1217,8 @@ fn check_region_bounds_on_impl_item<'tcx>(
             where_span,
         })
         .emit_unless(delay);
-        return Err(reported);
-    }
 
-    Ok(())
+    Err(reported)
 }
 
 #[instrument(level = "debug", skip(infcx))]

tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr

@@ -11,7 +11,10 @@ error[E0195]: lifetime parameters or bounds on method `has_bound` do not match t
   --> $DIR/regions-bound-missing-bound-in-impl.rs:23:17
    |
 LL |     fn has_bound<'b:'a>(self, b: Inv<'b>);
-   |                 ------- lifetimes in impl do not match this method in trait
+   |                 -------
+   |                 |   |
+   |                 |   this bound might be missing in the impl
+   |                 lifetimes in impl do not match this method in trait
 ...
 LL |     fn has_bound<'b>(self, b: Inv<'b>) {
    |                 ^^^^ lifetimes do not match method in trait
@@ -58,7 +61,11 @@ error[E0195]: lifetime parameters or bounds on method `wrong_bound2` do not matc
   --> $DIR/regions-bound-missing-bound-in-impl.rs:42:20
    |
 LL |     fn wrong_bound2<'b,'c,'d:'a+'b>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>);
-   |                    ---------------- lifetimes in impl do not match this method in trait
+   |                    ----------------
+   |                    |         |  |
+   |                    |         |  this bound might be missing in the impl
+   |                    |         this bound might be missing in the impl
+   |                    lifetimes in impl do not match this method in trait
 ...
 LL |     fn wrong_bound2(self, b: Inv, c: Inv, d: Inv) {
    |                    ^ lifetimes do not match method in trait

tests/ui/error-codes/E0195.rs

@@ -8,6 +8,7 @@ struct Foo;
 impl Trait for Foo {
     fn bar<'a,'b>(x: &'a str, y: &'b str) { //~ ERROR E0195
     //~^ NOTE lifetimes do not match associated function in trait
+    //~| NOTE this bound might be missing in the impl
     }
 }
 

tests/ui/error-codes/E0195.stderr

@@ -2,7 +2,10 @@ error[E0195]: lifetime parameters or bounds on associated function `bar` do not
   --> $DIR/E0195.rs:9:11
    |
 LL |     fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
-   |           ---------- lifetimes in impl do not match this associated function in trait
+   |           ----------
+   |           |      |
+   |           |      this bound might be missing in the impl
+   |           lifetimes in impl do not match this associated function in trait
 ...
 LL |     fn bar<'a,'b>(x: &'a str, y: &'b str) {
    |           ^^^^^^^ lifetimes do not match associated function in trait