apply the same logic to ConcreteFailure errors

src/librustc/infer/error_reporting/nice_region_error/placeholder_error.rs

@@ -89,6 +89,56 @@ impl NiceRegionError<'me, 'gcx, 'tcx> {
                 // I actually can't see why this would be the case ever.
             },
 
+            Some(RegionResolutionError::ConcreteFailure(
+                SubregionOrigin::Subtype(TypeTrace { .. }),
+                ty::RePlaceholder(_),
+                ty::RePlaceholder(_),
+            )) => {
+                // I actually can't see why this would be the case ever.
+            },
+
+            Some(RegionResolutionError::ConcreteFailure(
+                SubregionOrigin::Subtype(TypeTrace {
+                    cause,
+                    values: ValuePairs::TraitRefs(ExpectedFound { expected, found }),
+                }),
+                sub_region,
+                sup_region @ ty::RePlaceholder(_),
+            )) => if expected.def_id == found.def_id {
+                return Some(self.try_report_placeholders_trait(
+                    Some(sub_region),
+                    cause,
+                    None,
+                    Some(*sup_region),
+                    expected.def_id,
+                    expected.substs,
+                    found.substs,
+                ));
+            } else {
+                // I actually can't see why this would be the case ever.
+            },
+
+            Some(RegionResolutionError::ConcreteFailure(
+                SubregionOrigin::Subtype(TypeTrace {
+                    cause,
+                    values: ValuePairs::TraitRefs(ExpectedFound { expected, found }),
+                }),
+                sub_region @ ty::RePlaceholder(_),
+                sup_region,
+            )) => if expected.def_id == found.def_id {
+                return Some(self.try_report_placeholders_trait(
+                    Some(sup_region),
+                    cause,
+                    None,
+                    Some(*sub_region),
+                    expected.def_id,
+                    expected.substs,
+                    found.substs,
+                ));
+            } else {
+                // I actually can't see why this would be the case ever.
+            },
+
             _ => {}
         }
 

src/test/ui/generator/auto-trait-regions.rs

@@ -28,8 +28,7 @@ fn main() {
         assert_foo(x);
     };
     assert_foo(gen);
-    //~^ ERROR mismatched types
-    //~| ERROR mismatched types
+    //~^ ERROR implementation of `Foo` is not general enough
 
     // Allow impls which matches any lifetime
     let x = &OnlyFooIfRef(No);

src/test/ui/generator/auto-trait-regions.stderr

@@ -1,34 +1,20 @@
-error[E0308]: mismatched types
-  --> $DIR/auto-trait-regions.rs:30:5
-   |
-LL |     assert_foo(gen);
-   |     ^^^^^^^^^^ lifetime mismatch
-   |
-   = note: expected type `Foo`
-              found type `Foo`
-   = note: lifetime RePlaceholder(Placeholder { universe: U31, name: BrAnon(1) })...
-   = note: ...does not necessarily outlive the static lifetime
-
-error[E0308]: mismatched types
+error: implementation of `Foo` is not general enough
   --> $DIR/auto-trait-regions.rs:30:5
    |
 LL |     assert_foo(gen);
-   |     ^^^^^^^^^^ lifetime mismatch
+   |     ^^^^^^^^^^
    |
-   = note: expected type `Foo`
-              found type `Foo`
-   = note: lifetime RePlaceholder(Placeholder { universe: U35, name: BrAnon(1) })...
-   = note: ...does not necessarily outlive the static lifetime
+   = note: `&'0 OnlyFooIfStaticRef` must implement `Foo` for any lifetime `'0`
+   = note: but `&'1 OnlyFooIfStaticRef` only implements `Foo` for some lifetime `'1`
 
 error: implementation of `Foo` is not general enough
-  --> $DIR/auto-trait-regions.rs:49:5
+  --> $DIR/auto-trait-regions.rs:48:5
    |
 LL |     assert_foo(gen);
    |     ^^^^^^^^^^
    |
    = note: `A<'0, '1>` must implement `Foo` for any two lifetimes `'0` and `'1`
    = note: but `A<'_, '2>` only implements `Foo` for some lifetime `'2`
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0308`.

src/test/ui/hrtb/hrtb-just-for-static.stderr

@@ -1,13 +1,12 @@
-error[E0308]: mismatched types
+error: implementation of `Foo` is not general enough
   --> $DIR/hrtb-just-for-static.rs:24:5
    |
 LL |     want_hrtb::<StaticInt>() //~ ERROR
-   |     ^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |     ^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: expected type `Foo<&'a isize>`
-              found type `Foo<&'static isize>`
-   = note: lifetime RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:11), 'a) })...
-   = note: ...does not necessarily outlive the static lifetime
+   = note: Due to a where-clause on `want_hrtb`,
+   = note: `StaticInt` must implement `Foo<&'0 isize>` for any lifetime `'0`
+   = note: but `StaticInt` only implements `Foo<&'1 isize>` for some lifetime `'1`
 
 error: implementation of `Foo` is not general enough
   --> $DIR/hrtb-just-for-static.rs:30:5
@@ -21,4 +20,3 @@ LL |     want_hrtb::<&'a u32>() //~ ERROR
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0308`.

src/test/ui/where-clauses/where-for-self-2.rs

@@ -18,5 +18,5 @@ fn foo<T>(x: &T)
 {}
 
 fn main() {
-    foo(&X); //~ ERROR E0308
+    foo(&X); //~ ERROR implementation of `Bar` is not general enough
 }

src/test/ui/where-clauses/where-for-self-2.stderr

@@ -1,14 +1,12 @@
-error[E0308]: mismatched types
+error: implementation of `Bar` is not general enough
   --> $DIR/where-for-self-2.rs:21:5
    |
-LL |     foo(&X); //~ ERROR E0308
-   |     ^^^ lifetime mismatch
+LL |     foo(&X); //~ ERROR implementation of `Bar` is not general enough
+   |     ^^^
    |
-   = note: expected type `Bar`
-              found type `Bar`
-   = note: lifetime RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:10), 'a) })...
-   = note: ...does not necessarily outlive the static lifetime
+   = note: Due to a where-clause on `foo`,
+   = note: `&'0 _` must implement `Bar` for any lifetime `'0`
+   = note: but `&'1 u32` only implements `Bar` for some lifetime `'1`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.