RFC 2027: "first draft" of implementation

These are a squashed series of commits.

2 files changed, 30 insertions, 0 deletions

diff --git a/src/test/ui/coherence/coherence-unsafe-trait-object-impl.rs b/src/test/ui/coherence/coherence-unsafe-trait-object-impl.rs
new file mode 100644
index 00000000000..9859a226efd
--- /dev/null
+++ b/src/test/ui/coherence/coherence-unsafe-trait-object-impl.rs
@@ -0,0 +1,18 @@
+// Check that unsafe trait object do not implement themselves
+// automatically
+
+#![feature(object_safe_for_dispatch)]
+
+trait Trait: Sized {
+    fn call(&self);
+}
+
+fn takes_t<S: Trait>(s: S) {
+    s.call();
+}
+
+fn takes_t_obj(t: &dyn Trait) {
+    takes_t(t); //~ ERROR E0277
+}
+
+fn main() {}
diff --git a/src/test/ui/coherence/coherence-unsafe-trait-object-impl.stderr b/src/test/ui/coherence/coherence-unsafe-trait-object-impl.stderr
new file mode 100644
index 00000000000..b5a86acfb97
--- /dev/null
+++ b/src/test/ui/coherence/coherence-unsafe-trait-object-impl.stderr
@@ -0,0 +1,12 @@
+error[E0277]: the trait bound `&dyn Trait: Trait` is not satisfied
+  --> $DIR/coherence-unsafe-trait-object-impl.rs:15:13
+   |
+LL | fn takes_t<S: Trait>(s: S) {
+   |    -------    ----- required by this bound in `takes_t`
+...
+LL |     takes_t(t);
+   |             ^ the trait `Trait` is not implemented for `&dyn Trait`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.