Allow the elaborator to only filter to real supertraits

2 files changed, 34 insertions, 0 deletions

diff --git a/tests/ui/traits/alias/dont-elaborate-non-self.stderr b/tests/ui/traits/alias/dont-elaborate-non-self.stderr
new file mode 100644
index 00000000000..247a4f81280
--- /dev/null
+++ b/tests/ui/traits/alias/dont-elaborate-non-self.stderr
@@ -0,0 +1,20 @@
+error[E0277]: the size for values of type `(dyn Fn() -> Fut + 'static)` cannot be known at compilation time
+  --> $DIR/dont-elaborate-non-self.rs:7:11
+   |
+LL | fn f<Fut>(a: dyn F<Fut>) {}
+   |           ^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `(dyn Fn() -> Fut + 'static)`
+   = help: unsized fn params are gated as an unstable feature
+help: you can use `impl Trait` as the argument type
+   |
+LL | fn f<Fut>(a: impl F<Fut>) {}
+   |              ~~~~
+help: function arguments must have a statically known size, borrowed types always have a known size
+   |
+LL | fn f<Fut>(a: &dyn F<Fut>) {}
+   |              +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/traits/trait-upcasting/alias-where-clause-isnt-supertrait.stderr b/tests/ui/traits/trait-upcasting/alias-where-clause-isnt-supertrait.stderr
new file mode 100644
index 00000000000..5574a032089
--- /dev/null
+++ b/tests/ui/traits/trait-upcasting/alias-where-clause-isnt-supertrait.stderr
@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/alias-where-clause-isnt-supertrait.rs:27:5
+   |
+LL | fn test(x: &dyn C) -> &dyn B {
+   |                       ------ expected `&dyn B` because of return type
+LL |     x
+   |     ^ expected trait `B`, found trait `C`
+   |
+   = note: expected reference `&dyn B`
+              found reference `&dyn C`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.