1 files changed, 46 insertions, 0 deletions
diff --git a/src/test/ui/methods/method-two-trait-defer-resolution-2.rs b/src/test/ui/methods/method-two-trait-defer-resolution-2.rs
new file mode 100644
index 000000000..fc5766da9
--- /dev/null
+++ b/src/test/ui/methods/method-two-trait-defer-resolution-2.rs
@@ -0,0 +1,46 @@
+// run-pass
+// Test that when we write `x.foo()`, we do not have to know the
+// complete type of `x` in order to type-check the method call. In
+// this case, we know that `x: Vec<_1>`, but we don't know what type
+// `_1` is (because the call to `push` comes later). To pick between
+// the impls, we would have to know `_1`, since we have to know
+// whether `_1: MyCopy` or `_1 == Box<i32>`.  However (and this is the
+// point of the test), we don't have to pick between the two impls --
+// it is enough to know that `foo` comes from the `Foo` trait. We can
+// codegen the call as `Foo::foo(&x)` and let the specific impl get
+// chosen later.
+
+trait Foo {
+    fn foo(&self) -> isize;
+}
+
+trait MyCopy { fn foo(&self) { } }
+impl MyCopy for i32 { }
+
+impl<T:MyCopy> Foo for Vec<T> {
+    fn foo(&self) -> isize {1}
+}
+
+impl Foo for Vec<Box<i32>> {
+    fn foo(&self) -> isize {2}
+}
+
+fn call_foo_copy() -> isize {
+    let mut x = Vec::new();
+    let y = x.foo();
+    x.push(0_i32);
+    y
+}
+
+fn call_foo_other() -> isize {
+    let mut x: Vec<_> = Vec::new();
+    let y = x.foo();
+    let z: Box<i32> = Box::new(0);
+    x.push(z);
+    y
+}
+
+fn main() {
+    assert_eq!(call_foo_copy(), 1);
+    assert_eq!(call_foo_other(), 2);
+}