docs/test: add UI test and long-form error docs for `E0377`

2 files changed, 23 insertions, 0 deletions

diff --git a/src/test/ui/error-codes/E0377.rs b/src/test/ui/error-codes/E0377.rs
new file mode 100644
index 00000000000..6da2c20956a
--- /dev/null
+++ b/src/test/ui/error-codes/E0377.rs
@@ -0,0 +1,14 @@
+#![feature(coerce_unsized)]
+use std::ops::CoerceUnsized;
+
+pub struct Foo<T: ?Sized> {
+    field_with_unsized_type: T,
+}
+
+pub struct Bar<T: ?Sized> {
+    field_with_unsized_type: T,
+}
+
+impl<T, U> CoerceUnsized<Bar<U>> for Foo<T> where T: CoerceUnsized<U> {} //~ ERROR E0377
+
+fn main() {}
diff --git a/src/test/ui/error-codes/E0377.stderr b/src/test/ui/error-codes/E0377.stderr
new file mode 100644
index 00000000000..bf7d8c8d39d
--- /dev/null
+++ b/src/test/ui/error-codes/E0377.stderr
@@ -0,0 +1,9 @@
+error[E0377]: the trait `CoerceUnsized` may only be implemented for a coercion between structures with the same definition; expected `Foo`, found `Bar`
+  --> $DIR/E0377.rs:12:1
+   |
+LL | impl<T, U> CoerceUnsized<Bar<U>> for Foo<T> where T: CoerceUnsized<U> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0377`.