add some more tests

src/test/ui/sized/recursive-type-1.rs

@@ -0,0 +1,10 @@
+// check-pass
+trait A { type Assoc; }
+
+impl A for () {
+    // FIXME: it would be nice for this to at least cause a warning.
+    type Assoc = Foo<()>;
+}
+struct Foo<T: A>(T::Assoc);
+
+fn main() {}

src/test/ui/sized/recursive-type-2.rs

@@ -0,0 +1,13 @@
+// build-fail
+//~^ ERROR cycle detected when computing layout of `Foo<()>`
+
+trait A { type Assoc: ?Sized; }
+
+impl A for () {
+    type Assoc = Foo<()>;
+}
+struct Foo<T: A>(T::Assoc);
+
+fn main() {
+    let x: Foo<()>;
+}

src/test/ui/sized/recursive-type-2.stderr

@@ -0,0 +1,12 @@
+error[E0391]: cycle detected when computing layout of `Foo<()>`
+   |
+   = note: ...which again requires computing layout of `Foo<()>`, completing the cycle
+note: cycle used when optimizing MIR for `main`
+  --> $DIR/recursive-type-2.rs:11:1
+   |
+LL | fn main() {
+   | ^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0391`.