look for the note on the guarantor, not the root cmt

This was causing upvar inference to fail for all cases where the move
was from a projection, not the root variable.

src/test/ui/unboxed-closures-infer-fn-once-move-from-projection.rs

@@ -0,0 +1,26 @@
+// 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.
+
+#![allow(unused)]
+
+fn foo<F>(f: F)
+    where F: Fn()
+{
+}
+
+fn main() {
+    // Test that this closure is inferred to `FnOnce` because it moves
+    // from `y.0`. This affects the error output (the error is that
+    // the closure implements `FnOnce`, not that it moves from inside
+    // a `Fn` closure.)
+    let y = (vec![1, 2, 3], 0);
+    let c = || drop(y.0);
+    foo(c);
+}

src/test/ui/unboxed-closures-infer-fn-once-move-from-projection.stderr

@@ -0,0 +1,16 @@
+error[E0525]: expected a closure that implements the `Fn` trait, but this closure only implements `FnOnce`
+  --> $DIR/unboxed-closures-infer-fn-once-move-from-projection.rs:24:13
+   |
+24 |     let c = || drop(y.0);
+   |             ^^^^^^^^^^^^
+25 |     foo(c);
+   |     --- the requirement to implement `Fn` derives from here
+   |
+note: closure is `FnOnce` because it moves the variable `y` out of its environment
+  --> $DIR/unboxed-closures-infer-fn-once-move-from-projection.rs:24:21
+   |
+24 |     let c = || drop(y.0);
+   |                     ^
+
+error: aborting due to previous error
+