Add tests for two random issues that seem to be fixed on this branch.

Fixes #20346.
Fixes #20371.

src/test/compile-fail/associated-types-issue-20346.rs

@@ -0,0 +1,46 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test that we reliably check the value of the associated type.
+
+#![crate_type = "lib"]
+#![feature(associated_types)]
+#![no_implicit_prelude]
+
+use std::option::Option::{None, Some, mod};
+use std::vec::Vec;
+
+trait Iterator {
+    type Item;
+
+    fn next(&mut self) -> Option<Self::Item>;
+}
+
+fn is_iterator_of<A, I: Iterator<Item=A>>(_: &I) {}
+
+struct Adapter<I> {
+    iter: I,
+    found_none: bool,
+}
+
+impl<T, I> Iterator for Adapter<I> where I: Iterator<Item=Option<T>> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        loop {}
+    }
+}
+
+fn test_adapter<T, I: Iterator<Item=Option<T>>>(it: I) {
+    is_iterator_of::<Option<T>, _>(&it);  // Sanity check
+    let adapter = Adapter { iter: it, found_none: false };
+    is_iterator_of::<T, _>(&adapter); // OK
+    is_iterator_of::<Option<T>, _>(&adapter); //~ ERROR type mismatch
+}

src/test/run-pass/associated-types-issue-20371.rs

@@ -0,0 +1,17 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test that we are able to have an impl that defines an associated type
+// before the actual trait.
+
+#![feature(associated_types)]
+impl X for f64 { type Y = int; }
+trait X {type Y; }
+fn main() {}