LTA: Diag: Detect bivariant ty params that are only used recursively

2 files changed, 13 insertions, 14 deletions

diff --git a/tests/ui/lazy-type-alias/inherent-impls-overflow.next.stderr b/tests/ui/lazy-type-alias/inherent-impls-overflow.next.stderr
index 48e7da96612..192b5eebdaa 100644
--- a/tests/ui/lazy-type-alias/inherent-impls-overflow.next.stderr
+++ b/tests/ui/lazy-type-alias/inherent-impls-overflow.next.stderr
@@ -4,27 +4,27 @@ error[E0275]: overflow evaluating the requirement `Loop == _`
 LL | impl Loop {}
    |      ^^^^
 
-error[E0392]: type parameter `T` is never used
-  --> $DIR/inherent-impls-overflow.rs:14:12
+error: type parameter `T` is only used recursively
+  --> $DIR/inherent-impls-overflow.rs:14:24
    |
 LL | type Poly0<T> = Poly1<(T,)>;
-   |            ^           - `T` is named here, but is likely unused in the containing type
+   |            -           ^
    |            |
-   |            unused type parameter
+   |            type parameter must be used non-recursively in the definition
    |
    = help: consider removing `T` or referring to it in the body of the type alias
-   = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
+   = note: all type parameters must be used in a non-recursive way in order to constrain their variance
 
-error[E0392]: type parameter `T` is never used
-  --> $DIR/inherent-impls-overflow.rs:17:12
+error: type parameter `T` is only used recursively
+  --> $DIR/inherent-impls-overflow.rs:17:24
    |
 LL | type Poly1<T> = Poly0<(T,)>;
-   |            ^           - `T` is named here, but is likely unused in the containing type
+   |            -           ^
    |            |
-   |            unused type parameter
+   |            type parameter must be used non-recursively in the definition
    |
    = help: consider removing `T` or referring to it in the body of the type alias
-   = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
+   = note: all type parameters must be used in a non-recursive way in order to constrain their variance
 
 error[E0275]: overflow evaluating the requirement `Poly0<()> == _`
   --> $DIR/inherent-impls-overflow.rs:21:6
@@ -36,5 +36,4 @@ LL | impl Poly0<()> {}
 
 error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0275, E0392.
-For more information about an error, try `rustc --explain E0275`.
+For more information about this error, try `rustc --explain E0275`.
diff --git a/tests/ui/lazy-type-alias/inherent-impls-overflow.rs b/tests/ui/lazy-type-alias/inherent-impls-overflow.rs
index 98f0d811a47..1397695a3fe 100644
--- a/tests/ui/lazy-type-alias/inherent-impls-overflow.rs
+++ b/tests/ui/lazy-type-alias/inherent-impls-overflow.rs
@@ -13,10 +13,10 @@ impl Loop {}
 
 type Poly0<T> = Poly1<(T,)>;
 //[current]~^ ERROR overflow normalizing the type alias `Poly0<(((((((...,),),),),),),)>`
-//[next]~^^ ERROR type parameter `T` is never used
+//[next]~^^ ERROR type parameter `T` is only used recursively
 type Poly1<T> = Poly0<(T,)>;
 //[current]~^ ERROR  overflow normalizing the type alias `Poly1<(((((((...,),),),),),),)>`
-//[next]~^^ ERROR type parameter `T` is never used
+//[next]~^^ ERROR type parameter `T` is only used recursively
 
 impl Poly0<()> {}
 //[current]~^ ERROR overflow normalizing the type alias `Poly1<(((((((...,),),),),),),)>`