Test case illustrating some variants of the issue pointed out by ariel.

Expanded to cover partial-initialization ideas.

Author: pnkfelix

src/test/compile-fail/borrowck/borrowck-uninit-ref-chain.rs

@@ -0,0 +1,60 @@
+// Copyright 2017 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.
+
+// revisions: ast mir
+//[mir]compile-flags: -Z emit-end-regions -Z borrowck-mir
+
+struct S<X, Y> {
+    x: X,
+    y: Y,
+}
+
+fn main() {
+    let x: &&Box<i32>;
+    let _y = &**x; //[ast]~ ERROR use of possibly uninitialized variable: `**x` [E0381]
+                   //[mir]~^ (Ast) [E0381]
+                   //[mir]~| (Mir) [E0381]
+
+    let x: &&S<i32, i32>;
+    let _y = &**x; //[ast]~ ERROR use of possibly uninitialized variable: `**x` [E0381]
+                   //[mir]~^ (Ast) [E0381]
+                   //[mir]~| (Mir) [E0381]
+
+    let x: &&i32;
+    let _y = &**x; //[ast]~ ERROR use of possibly uninitialized variable: `**x` [E0381]
+                   //[mir]~^ (Ast) [E0381]
+                   //[mir]~| (Mir) [E0381]
+
+
+    let mut a: S<i32, i32>;
+    a.x = 0;
+    let _b = &a.x; //[ast]~ ERROR use of possibly uninitialized variable: `a.x` [E0381]
+                   //[mir]~^ ERROR (Ast) [E0381]
+                   // (deliberately *not* an error under MIR-borrowck)
+
+    let mut a: S<&&i32, &&i32>;
+    a.x = &&0;
+    let _b = &**a.x; //[ast]~ ERROR use of possibly uninitialized variable: `**a.x` [E0381]
+                     //[mir]~^ ERROR (Ast) [E0381]
+                     // (deliberately *not* an error under MIR-borrowck)
+
+
+    let mut a: S<i32, i32>;
+    a.x = 0;
+    let _b = &a.y; //[ast]~ ERROR use of possibly uninitialized variable: `a.y` [E0381]
+                   //[mir]~^ ERROR (Ast) [E0381]
+                   //[mir]~| ERROR (Mir) [E0381]
+
+    let mut a: S<&&i32, &&i32>;
+    a.x = &&0;
+    let _b = &**a.y; //[ast]~ ERROR use of possibly uninitialized variable: `**a.y` [E0381]
+                     //[mir]~^ ERROR (Ast) [E0381]
+                     //[mir]~| ERROR (Mir) [E0381]
+}